To realize the low-resistance shape optimization design of amphibious robots,an efficient optimization design framework is proposed to improve the geometric deformation flexibility and optimization efficiency.In the p...To realize the low-resistance shape optimization design of amphibious robots,an efficient optimization design framework is proposed to improve the geometric deformation flexibility and optimization efficiency.In the proposed framework,the free-form deformation parametric model of the flat slender body is established and an analytical calculation method for the height constraints is derived.CFD method is introduced to carry out the high-precision resistance calculation and a constrained Kriging-based optimization method is built to improve the optimization efficiency by circularly infilling the new sample points which satisfying the constraints.Finally,the shape of an amphibious robot example is optimized to get the low-resistance shape and the results demonstrate that the presented optimization design framework has the advantages of simplicity,flexibility and high efficiency.展开更多
The boundary condition is a crucial factor affecting the permeability variation due to suffusion.An experimental investigation on the permeability of gap-graded soil due to horizontal suffusion considering the boundar...The boundary condition is a crucial factor affecting the permeability variation due to suffusion.An experimental investigation on the permeability of gap-graded soil due to horizontal suffusion considering the boundary effect is conducted,where the hydraulic head difference(DH)varies,and the boundary includes non-loss and soil-loss conditions.Soil samples are filled into seven soil storerooms connected in turn.After evaluation,the variation in content of fine sand(ΔR_(f))and the hydraulic conductivity of soils in each storeroom(C_(i))are analyzed.In the non-loss test,the soil sample filling area is divided into runoff,transited,and accumulated areas according to the negative or positive ΔR_(f) values.ΔR_(f) increases from negative to positive along the seepage path,and Ci decreases from runoff area to transited area and then rebounds in accumulated area.In the soil-loss test,all soil sample filling areas belong to the runoff area,where the gentle-loss,strengthened-loss,and alleviated-loss parts are further divided.ΔR_(f) decreases from the gentle-loss part to the strengthened-loss part and then rebounds in the alleviated-loss part,and C_(i) increases and then decreases along the seepage path.The relationship between ΔR_(f) and Ci is different with the boundary condition.Ci exponentially decreases with ΔR_(f) in the non-loss test and increases with ΔR_(f) generally in the soil-loss test.展开更多
Water jet technology is widely used in submerged buried pipes as a non-traditional trenching process,often invol-ving a complex sediment response.An important adjustable and influential engineering variable in this tec...Water jet technology is widely used in submerged buried pipes as a non-traditional trenching process,often invol-ving a complex sediment response.An important adjustable and influential engineering variable in this technol-ogy is represented by the impinging distance.In this study,the FLOW-3D software was used to simulate the jet scouring of sand beds in a submerged environment.In particular,four sets of experimental conditions were con-sidered to discern the relationship between the maximum scour depth and mass and the impinging distance.As shown by the results,a critical impinging distance h0 exists by which the static scour depth can be maximized;the scour mass ratio between dynamic and static conditions decreases as the impinging distance increases.Moreover,the profile contours are similar when the erosion parameter Ec is in the range 0.35<Ec<2.Empirical equations applicable for predicting the jet trenching contour under both dynamic and static scour modes are also provided in this study.展开更多
Deepsea mining has been proposed since the 1960s to alleviate the lack of resources on land.Vertical hydraulic transport of collected ores from the seabed to the sea surface is considered the most promising method for...Deepsea mining has been proposed since the 1960s to alleviate the lack of resources on land.Vertical hydraulic transport of collected ores from the seabed to the sea surface is considered the most promising method for industrial applications.In the present study,an indoor model test of the vertical hydraulic transport of particles was conducted.A noncontact optical method has been proposed to measure the local characteristics of the particles inside a vertical pipe,including the local concentration and particle velocity.The hydraulic gradient of ore transport was evaluated with various particle size distributions,particle densities,feeding concentrations and mixture flow velocities.During transport,the local concentration is larger than the feeding concentration,whereas the particle velocity is less than the mixture velocity.The qualitative effects of the local concentration and local fluid velocity on the particle velocity and slip velocity were investigated.The local fluid velocity contributes significantly to particle velocity and slip velocity,whereas the effect of the local concentration is marginal.A higher feeding concentration and mixture flow velocity result in an increased hydraulic gradient.The effect of the particle size gradation is slight,whereas the particle density plays a crucial role in the transport.展开更多
The scattering of normally incident water waves by two surface-piercing inclined perforated barriers in water with a uniform finite depth is investigated within the framework of linear water wave theory.Considering th...The scattering of normally incident water waves by two surface-piercing inclined perforated barriers in water with a uniform finite depth is investigated within the framework of linear water wave theory.Considering that thin barriers are zero-thickness,a novel numerical method involving the the coupling of the dual boundary element method(DBEM)with damping layers is applied.In order to effectively damp out the reflected waves,two damping layers,instead of pseudoboundaries are implemented near the two side boundaries of the computational domain.Thus,the modified linearized free surface boundary conditions are formulated and used for solving both the ordinary boundary integral equation as well as the hypersingular boundary integral equation for degenerate boundaries.The newly developed numerical method is validated against analytical methods using the matched eigenfunction expansion method for the special case of two vertical barriers or the inclined angle to the vertical being zero.The influence of the length of the two damping layers has been discussed.Moreover,these findings are also validated against previous results for several cases.After validation,the numerical results for the reflection coefficient,transmission coefficient and dissipation coefficient are obtained by varying the inclination angle and porosity-effect parameter.The effects of both the inclination angle and the porosity on the amplitudes of wave forces acting on both the front and rear barriers are also investigated.It is found that the effect of the inclination angle mainly shifts the location of the extremal values of the reflection and the transmission coefficients.Additionally,a moderate value of the porosity-parameter is quite effective at dissipating wave energy and mitigating the wave loads on dual barriers.展开更多
Structural Health Monitoring(SHM)systems have become a crucial tool for the operational management of long tunnels.For immersed tunnels exposed to both traffic loads and the effects of the marine environment,efficient...Structural Health Monitoring(SHM)systems have become a crucial tool for the operational management of long tunnels.For immersed tunnels exposed to both traffic loads and the effects of the marine environment,efficiently identifying abnormal conditions from the extensive unannotated SHM data presents a significant challenge.This study proposed amodel-based approach for anomaly detection and conducted validation and comparative analysis of two distinct temporal predictive models using SHM data from a real immersed tunnel.Firstly,a dynamic predictive model-based anomaly detectionmethod is proposed,which utilizes a rolling time window for modeling to achieve dynamic prediction.Leveraging the assumption of temporal data similarity,an interval prediction value deviation was employed to determine the abnormality of the data.Subsequently,dynamic predictive models were constructed based on the Autoregressive Integrated Moving Average(ARIMA)and Long Short-Term Memory(LSTM)models.The hyperparameters of these models were optimized and selected using monitoring data from the immersed tunnel,yielding viable static and dynamic predictive models.Finally,the models were applied within the same segment of SHM data,to validate the effectiveness of the anomaly detection approach based on dynamic predictive modeling.A detailed comparative analysis discusses the discrepancies in temporal anomaly detection between the ARIMA-and LSTM-based models.The results demonstrated that the dynamic predictive modelbased anomaly detection approach was effective for dealing with unannotated SHM data.In a comparison between ARIMA and LSTM,it was found that ARIMA demonstrated higher modeling efficiency,rendering it suitable for short-term predictions.In contrast,the LSTM model exhibited greater capacity to capture long-term performance trends and enhanced early warning capabilities,thereby resulting in superior overall performance.展开更多
In this study,the frequency characteristics of the turbulent wind and the effects of wind-wave coupling on the low-and high-frequency responses of semi-submersible floating offshore wind turbines(FOWT)are investigated...In this study,the frequency characteristics of the turbulent wind and the effects of wind-wave coupling on the low-and high-frequency responses of semi-submersible floating offshore wind turbines(FOWT)are investigated.Various wave load components,such as first-order wave loads,combined first-and second-order difference-frequency wave loads,combined first-and second-order sum-frequency wave loads,and first-and complete second-order wave loads are taken into consideration,while different turbulent environments are considered in aerodynamic loads.The com-parison is based on time histories and frequency spectra of platform motions and structural load responses and statistical values.The findings indicate that the second-order difference-frequency wave loads will significantly increase the natural frequency of low-frequency motion in the responses of the platform motion and structure load of the semi-submersible platform,which will cause structural fatigue damage.Under the action of turbulent wind,the influences of second-order wave loads on the platform motion and structural load response cannot be ignored,especially under extreme sea conditions.Therefore,in order to evaluate the dynamic responses of semi-submersible FOWT more accurately,the actual environment should be simulated more realistically.展开更多
The current study investigates the hydrodynamic characteristics of gap resonance within a narrow gap formed by two adjacent boxes subjected to incident focused transient wave groups.A two-dimensional(2D)numerical wave...The current study investigates the hydrodynamic characteristics of gap resonance within a narrow gap formed by two adjacent boxes subjected to incident focused transient wave groups.A two-dimensional(2D)numerical wave tank based on the OpenFOAM package is utilized for this purpose.The weather-side box is fixed while the lee-side box is allowed to heave freely under wave actions.The effects of the focused wave amplitude and spectral peak period on the wave amplification within the gap,motion of the lee-side box,and wave forces(including horizontal and vertical wave forces)acting on each box are systematically examined.For comparison,another structural layout consisting of two fixed boxes is also considered.The results reveal that the release of the heave degree of freedom(DoF)of the lee-side box results in remarkably distinct resonance features.In the heave-box system,both its fluid resonant period and the period corresponding to the maximum heave displacement of the lee-side box are significantly larger(i.e.,1.6-1.7 times)than the fluid resonant period of the fixed-box system.However,the wave amplification factor inside the gap in the heave-box system is significantly lower than that in the fixed-box one.Both the variations of the maximum horizontal and vertical wave forces with the spectral peak period and their magnitudes are also significantly different between the two structural systems.展开更多
Fluid resonance in moonpool formed by twin boxes under wave actions is investigated by using a viscous numerical wave flume with ReNormalization Group(RNG)turbulent model.The accuracy of the numerical model is validat...Fluid resonance in moonpool formed by twin boxes under wave actions is investigated by using a viscous numerical wave flume with ReNormalization Group(RNG)turbulent model.The accuracy of the numerical model is validated by available experimental data.Three types of edge profiles,the sharp edge,concave edge and convex edge are con-sidered.Numerical simulations show that the normalized resonant amplitude in moonpool decreases with the decrease of moonpool opening or increase of incident wave amplitude.The increased reflection coefficients are the major reason for the phenomena,implying less wave energy is able to support the wave resonance in moonpool.With the increase of incident wave height,the energy coefficients increase for convex edges around resonant fre-quency,which are oppositely with those of sharp and concave edges.Various flow patterns of the wave resonance in the vicinity of the moonpool entrance are also identified,which are mainly dependent on the edge profiles.展开更多
This paper describes the quasi-static testing and analytical modelling of the hysteretic behavior of aluminum alloy rigid bus-flexible connectors of 220 kV electrical substations.The main objective of the study is to ...This paper describes the quasi-static testing and analytical modelling of the hysteretic behavior of aluminum alloy rigid bus-flexible connectors of 220 kV electrical substations.The main objective of the study is to experimentally investigate the hysteretic behavior of six different types of rigid bus-flexible connectors 220 kV electrical substations when subjected to cyclic loading.Another objective is to theoretically study the flexibility and effectiveness of a previously proposed analytical model in fitting the experimental hysteresis loops of the tested rigid bus-flexible connectors.The experimental investigation indicates that the tested rigid bus-flexible connectors exhibit highly asymmetric hysteresis behavior along with tension stiffening effect.The theoretical study demonstrates that the generalized Bouc-Wen model has high flexibility and is effective in fitting the experimental hysteresis resisting force-displacement curves of the six tested rigid bus-flexible connectors.展开更多
The estimation of ship speed in ice ridge fields is important for both route planning and prediction of emergency response time.An analytical method for estimating ship motion in first-year ice ridge is developed base...The estimation of ship speed in ice ridge fields is important for both route planning and prediction of emergency response time.An analytical method for estimating ship motion in first-year ice ridge is developed based on ice resistance models and ship motion equations,in which the effect of ship speed on ridge resistance is taken into account.Two model tests in level ice and one model test in ice ridge for an icebreaking multipurpose vessel are used to validate and benchmark the presented method.The predicted results including level ice resistances,net thrust and ship motion in the ice ridge field are compared with the model test data.The comparisons show that the presented method can generate reasonable results.The effects of input parameters on ship speed,penetration depth and number of necessary rams to transit ridge have been studied.Based on the calibrated model,insights into the ice resistance and the ship motion are obtained.It is found that the energy consumption of the keel obtained by integral calculation of the keel resistance at the penetration distance is with the same magnitude as the result of the maximum keel resistance multiplied by the ridge length.In addition,the effect of ridge width and keel depth on keel resistance and average transit speed is investigated.展开更多
A higher order boundary element method(HOBEM)is presented for inviscid flow passing cylinders in bounded or unbounded domain.The traditional boundary integral equation is established with respect to the velocity poten...A higher order boundary element method(HOBEM)is presented for inviscid flow passing cylinders in bounded or unbounded domain.The traditional boundary integral equation is established with respect to the velocity potential and its normal derivative.In present work,a new integral equation is derived for the tangential velocity.The boundary is discretized into higher order elements to ensure the continuity of slope at the element nodes.The velocity potential is also expanded with higher order shape functions,in which the unknown coefficients involve the tangential velocity.The expansion then ensures the continuities of the velocity and the slope of the boundary at element nodes.Through extensive comparison of the results for the analytical solution of cylinders,it is shown that the present HOBEM is much more accurate than the conventional BEM.展开更多
Unsteady wash waves generated by a ship with constant speed moving across an uneven bottom topography are investigated by numerical simulations based on a Mixed Euler–Lagrange(MEL) method. The transition is accomplis...Unsteady wash waves generated by a ship with constant speed moving across an uneven bottom topography are investigated by numerical simulations based on a Mixed Euler–Lagrange(MEL) method. The transition is accomplished by the ship traveling from the depth h1 into the depth h2 via a step bottom. A small tsunami would be created after this transition. However, the unsteady wave-making resistance induced by this new phenomenon has not been well documented by literature. Therefore, the main purpose of the present study is to quantify the effects of an uneven bottom on the unsteady wash waves and wave-making resistance acting on the ship. An upwind differential scheme is commonly used in the Euler method to deal with the convection terms under free-surface condition to prevent waves in the upstream. Evidently, it cannot be applied to the present problem due to upstream waves generated by the ship would be dampened by the upwind scheme. The central differential scheme provides more accurate results,but it is not unconditionally stable. An MEL method is therefore employed to investigate the upstream wave generated by the ship moving over the uneven bottom. Simulation results show that the hydrodynamic interaction between the ship and the uneven bottom could initiate an upstream tsunami, as well as unsteady wave-making resistance on ships.The unsteady wave-making resistance oscillates periodically, and the amplitude and period of the oscillations are highly dependent on speed and water depth.展开更多
Experiments were conducted to investigate the dynamics of an oscillating bubble generated by a spark in the presence of an inclined attached air bubble.The study primarily focused on the influence of the inclination a...Experiments were conducted to investigate the dynamics of an oscillating bubble generated by a spark in the presence of an inclined attached air bubble.The study primarily focused on the influence of the inclination angle on the behavior of bubble jetting orientation,air bubble shape modes,and motion characteristics of the interaction between the two bubbles.Various complex bubble jetting behaviors were observed,including the presence of multiple types of bubble jetting directions,bubble splitting,and multidirectional jets.Four types of air bubble shapes were defined,namely inclined cup cover-shaped(with and without splitting),double-peaked cup cover-shaped,and inclined L-shaped air bubbles.The formation of different types of bubble jets was analyzed using the vector synthesis principle of the Bjerknes force exerted by the inclined attached air bubble and a steel plate.To describe the diverse orientations of bubble jetting and air bubble shapes,new parameters namely the dimensionless spark bubble oscillation time T^(*)and volume ratio V^(*)that consider the inclination angle are proposed.The findings of this investigation contribute to the existing knowledge and have the potential to further enhance methods for mitigating cavitation damage in marine,hydraulic machinery systems,and medical fields.l fields.展开更多
In this paper,we focus on the two-dimensional pulsating nanofluid flow through a parallel-plate channel in the presence of a magnetic field.The pulsating flow is produced by an applied pressure gradient that fluctuate...In this paper,we focus on the two-dimensional pulsating nanofluid flow through a parallel-plate channel in the presence of a magnetic field.The pulsating flow is produced by an applied pressure gradient that fluctuates with a small amplitude.A kind of proper transformation is used so that the governing equations describing the momentum and thermal energy are reduced to a set of non-dimensional equations.The analytical expressions of the pulsating velocity,temperature,and Nusselt number of nanofluids are obtained by the perturbation technique.In the present study,the effects of the Cu-H2O and Al_(2)O_(3)-H2O nanofluids on the flow and heat transfer in pulsating flow are compared and analyzed.The results show that the convective heat transfer effect of Cu-H2O nanofluids is better than that of Al_(2)O_(3)-H2O nanofluids.Also,the effects of the Hartmann number and pulsation amplitude on the velocity,temperature,and Nusselt number are examined and discussed in detail.The present work indicates that increasing the Hartmann number and pulsation amplitude can enhance the heat transfer of the pulsating flow.In addition,selecting an optimal pulsation frequency can maximize the convective heat transfer of the pulsating flow.Therefore,improved understanding of these fundamental mechanisms is conducive to the optimal design of thermal systems.展开更多
To develop and utilize marine resources in the deep sea, the higher requirements for floating structures, which are operated in marine environment for a long term, have been put forward. Reasonable structure type and ...To develop and utilize marine resources in the deep sea, the higher requirements for floating structures, which are operated in marine environment for a long term, have been put forward. Reasonable structure type and accurate force analysis are favorable guarantees to improve the survival performance and working performance of the floating structures. Floating spheres fastened by mooring cable were widely used in floating structures. In this paper, the wave forces of the floating sphere are efficiently and accurately calculated by solving the geometric relationship between the non-submerged floating sphere and wave surface. Combined with the hydrodynamic calculation of mooring cables based on the lumped mass method, the coupled motion model of multi-floating spheres fastened by multi-mooring cable was established under wave action. Furthermore, according to the floating structures fastened by mooring cable in the actual ocean engineering, the topological method of multi-mooring cables fastening the multifloating spheres was expounded from simple to complex. Finally, the modeling method and preliminarily hydrodynamic characteristics of the fastened floating structures, including the mooring system of renewable energy devices, ocean buoy, and coral nursery, were presented and analyzed in detail. The obtained results showed that the method for calculating the wave force on the floating sphere developed in this paper can accurately describe the motion process of the floating mooring sphere and the force on the mooring cable. Also, the topological method of multiple buoys and multiple mooring cables could efficiently establish various numerical hydrodynamic models of fastened buoys in ocean engineering.展开更多
The present study establishes a simple numerical model for the coupled response of a steel catenary riser(SCR) subjected to coplanar vessel motion and vortex-induced vibration(VIV). Owing to the large deflection of th...The present study establishes a simple numerical model for the coupled response of a steel catenary riser(SCR) subjected to coplanar vessel motion and vortex-induced vibration(VIV). Owing to the large deflection of the SCR, the geometric nonlinearity is considered in this model. The hydrodynamic force comprises the excitation force and hydrodynamic damping, where the excitation force that only exists when the non-dimensional frequency is located in the lock-in range, is associated with the VIV. The hydrodynamic force model is validated based on the published VIV test data.As for the seabed resistance at the touchdown zone(TDZ), integrated with an initial seabed trench, the hysteretic feature is modeled. Based on the model, the study emphasizes on the coupled response characteristics near the touchdown point(TDP) induced by coplanar vessel heave and VIV, and analyzes the sensitivity of the coupled response to the heaving amplitude and frequency. It is found that with the increase of the heave amplitude and frequency, the VIV can be obviously mitigated, but the heave-related response in the coupled analysis seems to be close to that in the heave-only simulation. Finally, the fatigue damage near TDP is parametrically investigated based on the separate analysis and the coupled analysis. The results demonstrate that the coupled effect plays a significant role in the fatigue assessment near TDP. Besides, the proportion of the coupled effect accounting for the total fatigue damage decreases with the increasing seabed stiffness, while increases with the increasing seabed trench depth.展开更多
Target strength(TS)and circular synthetic aperture sonar(CSAS)images provide essential information for active acoustic detection and recognition of non-cooperative unmanned undersea vehicles(UUVs),which pose a signifi...Target strength(TS)and circular synthetic aperture sonar(CSAS)images provide essential information for active acoustic detection and recognition of non-cooperative unmanned undersea vehicles(UUVs),which pose a significant threat to underwater preset facilities.To access them,we propose an iterative physical acoustics(IPA)-based method to simulate the multiple acoustic scattered fields on rigid surfaces in high-frequency cases.It uses the Helmholtz integral equation with an appropriate Green's function in terms of the Neumann series,and then incorporates the ideas of triangulation and iteration into a numerical implementation.Then two approximate analytic formulae with precise physical meanings are derived to predict the TS and CSAS images of concave targets,respectively.There are no restrictions on the surface's curvature and the order of multiple scattering.The method is validated against the finite element method(FEM)for acoustic scattering from a sphere segment and against an experiment involving an X-rudder UUV's stern.On this basis,we simulate and analyze the TS and CSAS images of an X-rudder UUV.In addition,the influence of the angle of adjacent rudders on the multiple scattering characteristics is discussed.Results show that this method can potentially predict accurate UUV features,especially the multiple scattered features.展开更多
Numerical simulations of the non-spherical evolution of a pulsating bubble interacting with a stationary air bubble attached to a fixed structure were performed using a three-dimensional boundary integral method by im...Numerical simulations of the non-spherical evolution of a pulsating bubble interacting with a stationary air bubble attached to a fixed structure were performed using a three-dimensional boundary integral method by implementing the mirror image method to simplify the processing of the numerical model. Code validation was accomplished by comparing the numerical results with the laboratory experimental data obtained in our previous study. Complex phenomena were observed, including three types of bubble jet forms, which depended strongly on the distance parameter with respect to the initial location of the bubble from the plate, the bubble strength parameter and the initial air bubble radius parameters. The results of the simulations provide detail insight into interesting bubble jetting phenomena,such as bubble splitting, jets moving away from the plate, and bubble shedding. The dimensionless distance parameter and the initial air bubble radius parameter play a major role in determining the shapes of two bubbles and the jetting direction. The air bubble strength parameter did not change the bubble jet direction but influenced the bubble shape.The detachment of the attached air bubble under oscillating bubble suction was easily observed for a small initial air bubble. These results showed that bubble jetting toward the plate was manipulated through the effect of attached air bubble, and that cavitation-based applications and underwater explosion bubble may benefit from this erosion mitigation approach.展开更多
In this work,a novel fluid-structure coupling method called the common node discrete element-smoothed particle hydrodynamics(DS-SPH)method is introduced.This framework combines the principles of the common node discre...In this work,a novel fluid-structure coupling method called the common node discrete element-smoothed particle hydrodynamics(DS-SPH)method is introduced.This framework combines the principles of the common node discrete element method(DEM)and smoothed particle hydrodynamics(SPH)to construct DEM-SPH particles situated on the same node.By doing so,the DEM particles can interact with the SPH particles within their support domain,enabling fluid-structure interaction(FSI).To determine the DEM microscopic parameters required for this method,uniaxial compression and three-point bending tests are conducted on sea ice.To verify the proposed model,we select the interaction between sea ice and structures as a case study.Through simulation,the model's capability of accurately depicting sea ice deformation and fracture has been demonstrated.The results indicate that the inclusion of SPH particles with fluid properties in the DEM model has minimal impact on the main mechanical parameters of sea ice.Additionally,it helps prevent the occurrence of particle splashing during cement failure.However,it is observed that the size of DEM particles and the friction between DEM particles and the structure significantly influence the macroscopic mechanical behavior of the common-node DEM-SPH model.Finally,we compare the fracture behavior of sea ice and the ice forces acting on structures obtained from the current model with on-site measured results.The agreement between the two sets of data is excellent,further validating the effectiveness of the proposed model in practical applications.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.52372356).
文摘To realize the low-resistance shape optimization design of amphibious robots,an efficient optimization design framework is proposed to improve the geometric deformation flexibility and optimization efficiency.In the proposed framework,the free-form deformation parametric model of the flat slender body is established and an analytical calculation method for the height constraints is derived.CFD method is introduced to carry out the high-precision resistance calculation and a constrained Kriging-based optimization method is built to improve the optimization efficiency by circularly infilling the new sample points which satisfying the constraints.Finally,the shape of an amphibious robot example is optimized to get the low-resistance shape and the results demonstrate that the presented optimization design framework has the advantages of simplicity,flexibility and high efficiency.
基金The research work described herein was funded by the National Nature Science Foundation of China(Grant No.41877213).This financial support is gratefully acknowledged.
文摘The boundary condition is a crucial factor affecting the permeability variation due to suffusion.An experimental investigation on the permeability of gap-graded soil due to horizontal suffusion considering the boundary effect is conducted,where the hydraulic head difference(DH)varies,and the boundary includes non-loss and soil-loss conditions.Soil samples are filled into seven soil storerooms connected in turn.After evaluation,the variation in content of fine sand(ΔR_(f))and the hydraulic conductivity of soils in each storeroom(C_(i))are analyzed.In the non-loss test,the soil sample filling area is divided into runoff,transited,and accumulated areas according to the negative or positive ΔR_(f) values.ΔR_(f) increases from negative to positive along the seepage path,and Ci decreases from runoff area to transited area and then rebounds in accumulated area.In the soil-loss test,all soil sample filling areas belong to the runoff area,where the gentle-loss,strengthened-loss,and alleviated-loss parts are further divided.ΔR_(f) decreases from the gentle-loss part to the strengthened-loss part and then rebounds in the alleviated-loss part,and C_(i) increases and then decreases along the seepage path.The relationship between ΔR_(f) and Ci is different with the boundary condition.Ci exponentially decreases with ΔR_(f) in the non-loss test and increases with ΔR_(f) generally in the soil-loss test.
基金supported by the Research on the Prediction Mechanism of Corrosion for High Strength Steel in Deep Sea Service Driven by Multi-Scale,High-Dimension and Small-Sample Data(C2301002635)Research on the Influence of Nozzle Structure on the Scouring Effect of Submerged Water Jet(2023R411045)+1 种基金the Zhejiang Ocean University Outstanding Master’s Thesis Cultivation Project(ZJOUYJS20230018)the Scientific Research Project of Zhejiang Graduate Education Society in 2022(2022-021)which was gained by Chen.
文摘Water jet technology is widely used in submerged buried pipes as a non-traditional trenching process,often invol-ving a complex sediment response.An important adjustable and influential engineering variable in this technol-ogy is represented by the impinging distance.In this study,the FLOW-3D software was used to simulate the jet scouring of sand beds in a submerged environment.In particular,four sets of experimental conditions were con-sidered to discern the relationship between the maximum scour depth and mass and the impinging distance.As shown by the results,a critical impinging distance h0 exists by which the static scour depth can be maximized;the scour mass ratio between dynamic and static conditions decreases as the impinging distance increases.Moreover,the profile contours are similar when the erosion parameter Ec is in the range 0.35<Ec<2.Empirical equations applicable for predicting the jet trenching contour under both dynamic and static scour modes are also provided in this study.
基金financially supported by the Hainan Provincial Joint Project of Sanya Yazhou Bay Science and Technology City(Grant No.520LH052)the National Natural Science Foundation of China(Grant No.51909164).
文摘Deepsea mining has been proposed since the 1960s to alleviate the lack of resources on land.Vertical hydraulic transport of collected ores from the seabed to the sea surface is considered the most promising method for industrial applications.In the present study,an indoor model test of the vertical hydraulic transport of particles was conducted.A noncontact optical method has been proposed to measure the local characteristics of the particles inside a vertical pipe,including the local concentration and particle velocity.The hydraulic gradient of ore transport was evaluated with various particle size distributions,particle densities,feeding concentrations and mixture flow velocities.During transport,the local concentration is larger than the feeding concentration,whereas the particle velocity is less than the mixture velocity.The qualitative effects of the local concentration and local fluid velocity on the particle velocity and slip velocity were investigated.The local fluid velocity contributes significantly to particle velocity and slip velocity,whereas the effect of the local concentration is marginal.A higher feeding concentration and mixture flow velocity result in an increased hydraulic gradient.The effect of the particle size gradation is slight,whereas the particle density plays a crucial role in the transport.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51809209 and 11702244)the Open Fund of Key Laboratory of Water-Sediment Sciences and Water Disaster Prevention of Hunan Province(Grant No.2021SS04).
文摘The scattering of normally incident water waves by two surface-piercing inclined perforated barriers in water with a uniform finite depth is investigated within the framework of linear water wave theory.Considering that thin barriers are zero-thickness,a novel numerical method involving the the coupling of the dual boundary element method(DBEM)with damping layers is applied.In order to effectively damp out the reflected waves,two damping layers,instead of pseudoboundaries are implemented near the two side boundaries of the computational domain.Thus,the modified linearized free surface boundary conditions are formulated and used for solving both the ordinary boundary integral equation as well as the hypersingular boundary integral equation for degenerate boundaries.The newly developed numerical method is validated against analytical methods using the matched eigenfunction expansion method for the special case of two vertical barriers or the inclined angle to the vertical being zero.The influence of the length of the two damping layers has been discussed.Moreover,these findings are also validated against previous results for several cases.After validation,the numerical results for the reflection coefficient,transmission coefficient and dissipation coefficient are obtained by varying the inclination angle and porosity-effect parameter.The effects of both the inclination angle and the porosity on the amplitudes of wave forces acting on both the front and rear barriers are also investigated.It is found that the effect of the inclination angle mainly shifts the location of the extremal values of the reflection and the transmission coefficients.Additionally,a moderate value of the porosity-parameter is quite effective at dissipating wave energy and mitigating the wave loads on dual barriers.
基金supported by the Research and Development Center of Transport Industry of New Generation of Artificial Intelligence Technology(Grant No.202202H)the National Key R&D Program of China(Grant No.2019YFB1600702)the National Natural Science Foundation of China(Grant Nos.51978600&51808336).
文摘Structural Health Monitoring(SHM)systems have become a crucial tool for the operational management of long tunnels.For immersed tunnels exposed to both traffic loads and the effects of the marine environment,efficiently identifying abnormal conditions from the extensive unannotated SHM data presents a significant challenge.This study proposed amodel-based approach for anomaly detection and conducted validation and comparative analysis of two distinct temporal predictive models using SHM data from a real immersed tunnel.Firstly,a dynamic predictive model-based anomaly detectionmethod is proposed,which utilizes a rolling time window for modeling to achieve dynamic prediction.Leveraging the assumption of temporal data similarity,an interval prediction value deviation was employed to determine the abnormality of the data.Subsequently,dynamic predictive models were constructed based on the Autoregressive Integrated Moving Average(ARIMA)and Long Short-Term Memory(LSTM)models.The hyperparameters of these models were optimized and selected using monitoring data from the immersed tunnel,yielding viable static and dynamic predictive models.Finally,the models were applied within the same segment of SHM data,to validate the effectiveness of the anomaly detection approach based on dynamic predictive modeling.A detailed comparative analysis discusses the discrepancies in temporal anomaly detection between the ARIMA-and LSTM-based models.The results demonstrated that the dynamic predictive modelbased anomaly detection approach was effective for dealing with unannotated SHM data.In a comparison between ARIMA and LSTM,it was found that ARIMA demonstrated higher modeling efficiency,rendering it suitable for short-term predictions.In contrast,the LSTM model exhibited greater capacity to capture long-term performance trends and enhanced early warning capabilities,thereby resulting in superior overall performance.
基金supported by the Natural Science Foundation of Zhejiang Province(Grant No.LHZ21E090003)the National Nature Science Foundation of China(Grant No.52171279)+1 种基金Zhoushan Science&Technology Project(Grant No.2021C21002)supported by CNPq(Conselho Nacional de Desenvolvimento Científico e Tecnológico,Grant No.301474/2017-6).
文摘In this study,the frequency characteristics of the turbulent wind and the effects of wind-wave coupling on the low-and high-frequency responses of semi-submersible floating offshore wind turbines(FOWT)are investigated.Various wave load components,such as first-order wave loads,combined first-and second-order difference-frequency wave loads,combined first-and second-order sum-frequency wave loads,and first-and complete second-order wave loads are taken into consideration,while different turbulent environments are considered in aerodynamic loads.The com-parison is based on time histories and frequency spectra of platform motions and structural load responses and statistical values.The findings indicate that the second-order difference-frequency wave loads will significantly increase the natural frequency of low-frequency motion in the responses of the platform motion and structure load of the semi-submersible platform,which will cause structural fatigue damage.Under the action of turbulent wind,the influences of second-order wave loads on the platform motion and structural load response cannot be ignored,especially under extreme sea conditions.Therefore,in order to evaluate the dynamic responses of semi-submersible FOWT more accurately,the actual environment should be simulated more realistically.
基金supported by the National Natural Science Foundation of China(Grant No.51911530205)the Natural Science Foundation of Jiangsu Province(Grant No.BK20201455)+4 种基金the Guangdong Basic and Applied Basic Research Foundation(Grant No.2023A1515010890)the Key Laboratory of Port,Waterway and Sedimentation Engineering of MOT(Grant No.YK222001-2)the Open Research Fund of Key Laboratory of Water Security Guarantee in Guangdong-Hong Kong-Marco Greater Bay Area of Ministry of Water Resources(Grant No.WSGBA-KJ202309)the Qing Lan Project of Jiangsu UniversitiesThe authors also thank the Royal Society(Grant No.IEC\NSFC\181321)for providing partial support for this work。
文摘The current study investigates the hydrodynamic characteristics of gap resonance within a narrow gap formed by two adjacent boxes subjected to incident focused transient wave groups.A two-dimensional(2D)numerical wave tank based on the OpenFOAM package is utilized for this purpose.The weather-side box is fixed while the lee-side box is allowed to heave freely under wave actions.The effects of the focused wave amplitude and spectral peak period on the wave amplification within the gap,motion of the lee-side box,and wave forces(including horizontal and vertical wave forces)acting on each box are systematically examined.For comparison,another structural layout consisting of two fixed boxes is also considered.The results reveal that the release of the heave degree of freedom(DoF)of the lee-side box results in remarkably distinct resonance features.In the heave-box system,both its fluid resonant period and the period corresponding to the maximum heave displacement of the lee-side box are significantly larger(i.e.,1.6-1.7 times)than the fluid resonant period of the fixed-box system.However,the wave amplification factor inside the gap in the heave-box system is significantly lower than that in the fixed-box one.Both the variations of the maximum horizontal and vertical wave forces with the spectral peak period and their magnitudes are also significantly different between the two structural systems.
基金supported by the National Natural Science Foundation of China(Grant Nos.52171250,52371277,and 51909027).
文摘Fluid resonance in moonpool formed by twin boxes under wave actions is investigated by using a viscous numerical wave flume with ReNormalization Group(RNG)turbulent model.The accuracy of the numerical model is validated by available experimental data.Three types of edge profiles,the sharp edge,concave edge and convex edge are con-sidered.Numerical simulations show that the normalized resonant amplitude in moonpool decreases with the decrease of moonpool opening or increase of incident wave amplitude.The increased reflection coefficients are the major reason for the phenomena,implying less wave energy is able to support the wave resonance in moonpool.With the increase of incident wave height,the energy coefficients increase for convex edges around resonant fre-quency,which are oppositely with those of sharp and concave edges.Various flow patterns of the wave resonance in the vicinity of the moonpool entrance are also identified,which are mainly dependent on the edge profiles.
基金National Natural Science Foundation of China under Grant No.51978397。
文摘This paper describes the quasi-static testing and analytical modelling of the hysteretic behavior of aluminum alloy rigid bus-flexible connectors of 220 kV electrical substations.The main objective of the study is to experimentally investigate the hysteretic behavior of six different types of rigid bus-flexible connectors 220 kV electrical substations when subjected to cyclic loading.Another objective is to theoretically study the flexibility and effectiveness of a previously proposed analytical model in fitting the experimental hysteresis loops of the tested rigid bus-flexible connectors.The experimental investigation indicates that the tested rigid bus-flexible connectors exhibit highly asymmetric hysteresis behavior along with tension stiffening effect.The theoretical study demonstrates that the generalized Bouc-Wen model has high flexibility and is effective in fitting the experimental hysteresis resisting force-displacement curves of the six tested rigid bus-flexible connectors.
基金financially supported by the Natural Science Foundation of Jiangsu Province of China (Grant No.BK20200998)the National Natural Science Foundation of China (Grant Nos.52171311,52271279,and 51579130)。
文摘The estimation of ship speed in ice ridge fields is important for both route planning and prediction of emergency response time.An analytical method for estimating ship motion in first-year ice ridge is developed based on ice resistance models and ship motion equations,in which the effect of ship speed on ridge resistance is taken into account.Two model tests in level ice and one model test in ice ridge for an icebreaking multipurpose vessel are used to validate and benchmark the presented method.The predicted results including level ice resistances,net thrust and ship motion in the ice ridge field are compared with the model test data.The comparisons show that the presented method can generate reasonable results.The effects of input parameters on ship speed,penetration depth and number of necessary rams to transit ridge have been studied.Based on the calibrated model,insights into the ice resistance and the ship motion are obtained.It is found that the energy consumption of the keel obtained by integral calculation of the keel resistance at the penetration distance is with the same magnitude as the result of the maximum keel resistance multiplied by the ridge length.In addition,the effect of ridge width and keel depth on keel resistance and average transit speed is investigated.
基金financially supported by the National Natural Science Foundation of China (Grant Nos.52271276,52271319,and 52201364)the Natural Science Foundation of Jiangsu Province (Grant No.BK20201006)。
文摘A higher order boundary element method(HOBEM)is presented for inviscid flow passing cylinders in bounded or unbounded domain.The traditional boundary integral equation is established with respect to the velocity potential and its normal derivative.In present work,a new integral equation is derived for the tangential velocity.The boundary is discretized into higher order elements to ensure the continuity of slope at the element nodes.The velocity potential is also expanded with higher order shape functions,in which the unknown coefficients involve the tangential velocity.The expansion then ensures the continuities of the velocity and the slope of the boundary at element nodes.Through extensive comparison of the results for the analytical solution of cylinders,it is shown that the present HOBEM is much more accurate than the conventional BEM.
基金financially supported by Natural Scienceof University of Jiangsu Province (Grant No.22KJB580004)the Key R&D Projects in Guangdong Province (Grant No.2020B1111500001)the Jiangsu Province“Six Talents Peak”High-Level Talents Support Project (Grant No.2018-KTHY-033)。
文摘Unsteady wash waves generated by a ship with constant speed moving across an uneven bottom topography are investigated by numerical simulations based on a Mixed Euler–Lagrange(MEL) method. The transition is accomplished by the ship traveling from the depth h1 into the depth h2 via a step bottom. A small tsunami would be created after this transition. However, the unsteady wave-making resistance induced by this new phenomenon has not been well documented by literature. Therefore, the main purpose of the present study is to quantify the effects of an uneven bottom on the unsteady wash waves and wave-making resistance acting on the ship. An upwind differential scheme is commonly used in the Euler method to deal with the convection terms under free-surface condition to prevent waves in the upstream. Evidently, it cannot be applied to the present problem due to upstream waves generated by the ship would be dampened by the upwind scheme. The central differential scheme provides more accurate results,but it is not unconditionally stable. An MEL method is therefore employed to investigate the upstream wave generated by the ship moving over the uneven bottom. Simulation results show that the hydrodynamic interaction between the ship and the uneven bottom could initiate an upstream tsunami, as well as unsteady wave-making resistance on ships.The unsteady wave-making resistance oscillates periodically, and the amplitude and period of the oscillations are highly dependent on speed and water depth.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52171311,52271279)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No.20KJB510046)。
文摘Experiments were conducted to investigate the dynamics of an oscillating bubble generated by a spark in the presence of an inclined attached air bubble.The study primarily focused on the influence of the inclination angle on the behavior of bubble jetting orientation,air bubble shape modes,and motion characteristics of the interaction between the two bubbles.Various complex bubble jetting behaviors were observed,including the presence of multiple types of bubble jetting directions,bubble splitting,and multidirectional jets.Four types of air bubble shapes were defined,namely inclined cup cover-shaped(with and without splitting),double-peaked cup cover-shaped,and inclined L-shaped air bubbles.The formation of different types of bubble jets was analyzed using the vector synthesis principle of the Bjerknes force exerted by the inclined attached air bubble and a steel plate.To describe the diverse orientations of bubble jetting and air bubble shapes,new parameters namely the dimensionless spark bubble oscillation time T^(*)and volume ratio V^(*)that consider the inclination angle are proposed.The findings of this investigation contribute to the existing knowledge and have the potential to further enhance methods for mitigating cavitation damage in marine,hydraulic machinery systems,and medical fields.l fields.
基金Project supported by the China Postdoctoral Science Foundation(No.2018M631909)the Doctor of Entrepreneurship and Innovation Project of Jiangsu Province(No.JSSCBS20221300)。
文摘In this paper,we focus on the two-dimensional pulsating nanofluid flow through a parallel-plate channel in the presence of a magnetic field.The pulsating flow is produced by an applied pressure gradient that fluctuates with a small amplitude.A kind of proper transformation is used so that the governing equations describing the momentum and thermal energy are reduced to a set of non-dimensional equations.The analytical expressions of the pulsating velocity,temperature,and Nusselt number of nanofluids are obtained by the perturbation technique.In the present study,the effects of the Cu-H2O and Al_(2)O_(3)-H2O nanofluids on the flow and heat transfer in pulsating flow are compared and analyzed.The results show that the convective heat transfer effect of Cu-H2O nanofluids is better than that of Al_(2)O_(3)-H2O nanofluids.Also,the effects of the Hartmann number and pulsation amplitude on the velocity,temperature,and Nusselt number are examined and discussed in detail.The present work indicates that increasing the Hartmann number and pulsation amplitude can enhance the heat transfer of the pulsating flow.In addition,selecting an optimal pulsation frequency can maximize the convective heat transfer of the pulsating flow.Therefore,improved understanding of these fundamental mechanisms is conducive to the optimal design of thermal systems.
基金financially supported by the National Natural Science Foundation of China (Grant No.52101330)the Basic Scientific Research Foundation of Zhejiang Provincial Universities (Grant No.2022J004)。
文摘To develop and utilize marine resources in the deep sea, the higher requirements for floating structures, which are operated in marine environment for a long term, have been put forward. Reasonable structure type and accurate force analysis are favorable guarantees to improve the survival performance and working performance of the floating structures. Floating spheres fastened by mooring cable were widely used in floating structures. In this paper, the wave forces of the floating sphere are efficiently and accurately calculated by solving the geometric relationship between the non-submerged floating sphere and wave surface. Combined with the hydrodynamic calculation of mooring cables based on the lumped mass method, the coupled motion model of multi-floating spheres fastened by multi-mooring cable was established under wave action. Furthermore, according to the floating structures fastened by mooring cable in the actual ocean engineering, the topological method of multi-mooring cables fastening the multifloating spheres was expounded from simple to complex. Finally, the modeling method and preliminarily hydrodynamic characteristics of the fastened floating structures, including the mooring system of renewable energy devices, ocean buoy, and coral nursery, were presented and analyzed in detail. The obtained results showed that the method for calculating the wave force on the floating sphere developed in this paper can accurately describe the motion process of the floating mooring sphere and the force on the mooring cable. Also, the topological method of multiple buoys and multiple mooring cables could efficiently establish various numerical hydrodynamic models of fastened buoys in ocean engineering.
基金financially supported by the National Natural Science Foundation of China (Grant No. 51979129)。
文摘The present study establishes a simple numerical model for the coupled response of a steel catenary riser(SCR) subjected to coplanar vessel motion and vortex-induced vibration(VIV). Owing to the large deflection of the SCR, the geometric nonlinearity is considered in this model. The hydrodynamic force comprises the excitation force and hydrodynamic damping, where the excitation force that only exists when the non-dimensional frequency is located in the lock-in range, is associated with the VIV. The hydrodynamic force model is validated based on the published VIV test data.As for the seabed resistance at the touchdown zone(TDZ), integrated with an initial seabed trench, the hysteretic feature is modeled. Based on the model, the study emphasizes on the coupled response characteristics near the touchdown point(TDP) induced by coplanar vessel heave and VIV, and analyzes the sensitivity of the coupled response to the heaving amplitude and frequency. It is found that with the increase of the heave amplitude and frequency, the VIV can be obviously mitigated, but the heave-related response in the coupled analysis seems to be close to that in the heave-only simulation. Finally, the fatigue damage near TDP is parametrically investigated based on the separate analysis and the coupled analysis. The results demonstrate that the coupled effect plays a significant role in the fatigue assessment near TDP. Besides, the proportion of the coupled effect accounting for the total fatigue damage decreases with the increasing seabed stiffness, while increases with the increasing seabed trench depth.
基金supported by the National Youth Science Foundation of China(Grant No.52001211).
文摘Target strength(TS)and circular synthetic aperture sonar(CSAS)images provide essential information for active acoustic detection and recognition of non-cooperative unmanned undersea vehicles(UUVs),which pose a significant threat to underwater preset facilities.To access them,we propose an iterative physical acoustics(IPA)-based method to simulate the multiple acoustic scattered fields on rigid surfaces in high-frequency cases.It uses the Helmholtz integral equation with an appropriate Green's function in terms of the Neumann series,and then incorporates the ideas of triangulation and iteration into a numerical implementation.Then two approximate analytic formulae with precise physical meanings are derived to predict the TS and CSAS images of concave targets,respectively.There are no restrictions on the surface's curvature and the order of multiple scattering.The method is validated against the finite element method(FEM)for acoustic scattering from a sphere segment and against an experiment involving an X-rudder UUV's stern.On this basis,we simulate and analyze the TS and CSAS images of an X-rudder UUV.In addition,the influence of the angle of adjacent rudders on the multiple scattering characteristics is discussed.Results show that this method can potentially predict accurate UUV features,especially the multiple scattered features.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 52171311 and 52271279)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant No. 20KJB510046)。
文摘Numerical simulations of the non-spherical evolution of a pulsating bubble interacting with a stationary air bubble attached to a fixed structure were performed using a three-dimensional boundary integral method by implementing the mirror image method to simplify the processing of the numerical model. Code validation was accomplished by comparing the numerical results with the laboratory experimental data obtained in our previous study. Complex phenomena were observed, including three types of bubble jet forms, which depended strongly on the distance parameter with respect to the initial location of the bubble from the plate, the bubble strength parameter and the initial air bubble radius parameters. The results of the simulations provide detail insight into interesting bubble jetting phenomena,such as bubble splitting, jets moving away from the plate, and bubble shedding. The dimensionless distance parameter and the initial air bubble radius parameter play a major role in determining the shapes of two bubbles and the jetting direction. The air bubble strength parameter did not change the bubble jet direction but influenced the bubble shape.The detachment of the attached air bubble under oscillating bubble suction was easily observed for a small initial air bubble. These results showed that bubble jetting toward the plate was manipulated through the effect of attached air bubble, and that cavitation-based applications and underwater explosion bubble may benefit from this erosion mitigation approach.
基金financially supported by the National Natural Science Foundation of China (Grant No.52201323)。
文摘In this work,a novel fluid-structure coupling method called the common node discrete element-smoothed particle hydrodynamics(DS-SPH)method is introduced.This framework combines the principles of the common node discrete element method(DEM)and smoothed particle hydrodynamics(SPH)to construct DEM-SPH particles situated on the same node.By doing so,the DEM particles can interact with the SPH particles within their support domain,enabling fluid-structure interaction(FSI).To determine the DEM microscopic parameters required for this method,uniaxial compression and three-point bending tests are conducted on sea ice.To verify the proposed model,we select the interaction between sea ice and structures as a case study.Through simulation,the model's capability of accurately depicting sea ice deformation and fracture has been demonstrated.The results indicate that the inclusion of SPH particles with fluid properties in the DEM model has minimal impact on the main mechanical parameters of sea ice.Additionally,it helps prevent the occurrence of particle splashing during cement failure.However,it is observed that the size of DEM particles and the friction between DEM particles and the structure significantly influence the macroscopic mechanical behavior of the common-node DEM-SPH model.Finally,we compare the fracture behavior of sea ice and the ice forces acting on structures obtained from the current model with on-site measured results.The agreement between the two sets of data is excellent,further validating the effectiveness of the proposed model in practical applications.
