- Experimental study and theoretical analysis show that the critical value of relative wave height (H/ d)b given by Goda and the critical wave steepness (H/ L)b given by Michell and Miche can be adopted as the spillin...- Experimental study and theoretical analysis show that the critical value of relative wave height (H/ d)b given by Goda and the critical wave steepness (H/ L)b given by Michell and Miche can be adopted as the spilling breaking indices of regular waves. According to the same principle, a systematic theoretical analysis and experiment of irregular waves have been done by the authors in order to solve the breaking problem of irregular waves. It is indicated that the authors’ method for determining wave breaking of regular waves can also be used for irregular waves.展开更多
Based on the linear analysis of stability,a dispersion equation isdeduced which delineates the evolution of a general 3-dimensional disturbance onthe free surface of an incompressible viscous liquid jet.With respect t...Based on the linear analysis of stability,a dispersion equation isdeduced which delineates the evolution of a general 3-dimensional disturbance onthe free surface of an incompressible viscous liquid jet.With respect to the spatialgrowing disturbance mode,the numerical results obtained from the solution of thedispersion equation reveal that a dimensionless parameter J_e exists.As J_e】1,theaxisymmetric disturbance mode is most unstable;and when J_e【1,the asymmetricdisturbances come into being,their growth rate increases with the decrease of J_e,tillone of them becomes the most unstable disturbance.The breakup of a low-speedliquid jet results from the developing of axisymmetric disturbances,whose instabilityis produced by the surface tension;while the atomization of a high-speed liquid jetis brought about by the evolution of nonaxisymmetric disturbance,whose instabilityis caused by the aerodynamic force on the interface between the jet and the ambientgas.展开更多
The study of the behavior of concrete under biaxial stresses is essential to the design of offshore concrete platforms. Using the multiaxial test apparatus developed by the authors, the deformation and strength of con...The study of the behavior of concrete under biaxial stresses is essential to the design of offshore concrete platforms. Using the multiaxial test apparatus developed by the authors, the deformation and strength of concrete under biaxial stresses are studied experimentally. Based on the test data, an endochronic damage constitutive model and a failure criterion are proposed. According to the above model, an incremental nonlinear iterative programme is developed, and a plate sample in plane stress state is analyzed.展开更多
Contacting state between molten metal and a mold and initial solidification process of continuously cast metals can be controlled by imposing an intermittent magnetic field.In this study, effect of the intermittent ma...Contacting state between molten metal and a mold and initial solidification process of continuously cast metals can be controlled by imposing an intermittent magnetic field.In this study, effect of the intermittent magnetic field on the initial solidification ofcontinuoasly cast metals was investigated by measuring the temperature distribution in the melt pool and the initial solidification starting position of shells. It was found that under the condition with intermittent magnetic field, the melt near meniscns is in slow cooling state, the initial solidification starting position descends, initial solidification shell thickens and the liquid-solid interface becomes smooth.展开更多
It is found that the anomalous eutectics can be separated on macroscopic scale by flow caused by electromagnetic stirring, and the separated phase is the leading faceted phase with the solution entmpy over 23J/(mol.K)...It is found that the anomalous eutectics can be separated on macroscopic scale by flow caused by electromagnetic stirring, and the separated phase is the leading faceted phase with the solution entmpy over 23J/(mol.K). By using this technology, a new kind of composite pipe ond gear with good abrasive properties are made without adding any reinforced particles. Emphases are paid on the researehes about formation mechanism of seporated eutectic and abrasive property of the composite pipe or gear. The result shows that the entropy of solution controlling the eutectic microstructure is also valid and useful as a criterion of separated eutectic, and the kind and its chemical scope of the off-eutectic used to make composite can be calculated accoofing to this theory.展开更多
- The characteristics of deformation and strength of concrete under the plane strain condition are studied experimentally with the triaxial apparatus designed by the authors and are compared with those under the plane...- The characteristics of deformation and strength of concrete under the plane strain condition are studied experimentally with the triaxial apparatus designed by the authors and are compared with those under the plane stress condition. A formula of stress transformation between plane stress and plane strain conditions is proposed for the elasto-plastic state, and it provides a theoretical basis for simplifying nonlinear analysis and fully using the strength of concrete.展开更多
Multi-directional irregular waves are simulated on the basis of the given directional spectrum using a double summation model, a single direction per frequency model and a single summation model. Their results are com...Multi-directional irregular waves are simulated on the basis of the given directional spectrum using a double summation model, a single direction per frequency model and a single summation model. Their results are compared. It is shown that the single direction per frequency model proposed in this paper can generate a realistic wave field. The effects of the model parameters on the simulated results are also studied in this paper and corresponding suggestions are given.展开更多
With respect to the subjective factors and nonlinear characteristics inherent in the important identifi-cation of fault tree analysis (FTA), a new important measure of FTA is proposed based on possibilistic informatio...With respect to the subjective factors and nonlinear characteristics inherent in the important identifi-cation of fault tree analysis (FTA), a new important measure of FTA is proposed based on possibilistic information entropy. After investigating possibilistic information semantics, measure-theoretic terms, and entropy-like models, a two-dimensional framework has been constructed by combining both the set theory and the measure theory. By adopting the possibilistic assumption in place of the probabilistic one, an axiomatic index of importance is defined in the possibility space and then the modelling principles are presented. An example of the fault tree is thus provided, along with the concordance analysis and other discussions. The more conservative numerical results of importance rankings, which involve the more choices can be viewed as "soft" fault identification under a certain expected value. In the end, extension to evidence space and further research perspectives are discussed.展开更多
Electrochemical CO2 reduction to chemicals or fuels presents one of the most promising strategies for managing the global carbon balance, which yet poses a significant challenge due to lack of efficient and durable el...Electrochemical CO2 reduction to chemicals or fuels presents one of the most promising strategies for managing the global carbon balance, which yet poses a significant challenge due to lack of efficient and durable electrocatalyst as well as the understanding of the CO2 reduction reaction(CO2RR) mechanism.Benefiting from the large surface area, high electrical conductivity, and tunable structure, carbon-based metal-free materials(CMs) have been extensively studied as cost-effective electrocatalysts for CO2RR.The development of CMs with low cost, high activity and durability for CO2RR has been considered as one of the most active and competitive directions in electrochemistry and material science.In this review article,some up-to-date strategies in improving the CO2RR performance on CMs are summarized.Specifically, the approaches to optimize the adsorption of CO2RR intermediates, such as tuning the physical and electronic structure are introduced, which can enhance the electrocatalytic activity of CMs effectively.Finally, some design strategies are proposed to prepare CMs with high activity and selectivity for CO2RR.展开更多
The effect of mechanical cyclings on the stress-strain(S-S) curves was studied systematically using tensile tests over a widetemperature range.Two-stage yielding was observed in the temperature range between M_s and t...The effect of mechanical cyclings on the stress-strain(S-S) curves was studied systematically using tensile tests over a widetemperature range.Two-stage yielding was observed in the temperature range between M_s and the ultimate temperature to in-duce martensite,denoted by M_d.The first stage was confirmed to be associated with stress-induced martensite(SIM) and the sec-ond stage was associated with the yielding of SIM.When the samples were mechanically cycled between M_s and M_d.astress-softening phenomenon was observed.The cyclings made the martensite amount increase,critical stress σ_c of SIM de-crease according to exponential law,and the entropy(also enthalpy) of the parent to martensite transformation also decrease.Thevariations of SIM relative amount were determined by recording the changes of electrical resistances in the course of tension.展开更多
A typical example of the seawall construction for industrial use in China-the seawall construction for Shanghai Petrochemical Complex (SPC)-is introduced in this paper.
In this paper, the second order steady drift forces on the ships and other floating offshore structures are calculated by the far field method. The amplitudes of diffracted waves and radiated waves at infinity are obt...In this paper, the second order steady drift forces on the ships and other floating offshore structures are calculated by the far field method. The amplitudes of diffracted waves and radiated waves at infinity are obtained by the two-dimensional source distribution and strip-theory method. For the twin hull structure, the hydrodynamic interaction between the two hulls is taken into account. The drift forces on cross sections of Lewis type as well as on the semi-submersibles are computed. The theoretical results obtained by the present method agree fairly well with experimental results.展开更多
The wave forces on pipes near the ocean bottom are studied with model test in this paper. Comparisons of four different methods show that the uncommonly used method - Least Square Mass (LSM) is the most stable one. Th...The wave forces on pipes near the ocean bottom are studied with model test in this paper. Comparisons of four different methods show that the uncommonly used method - Least Square Mass (LSM) is the most stable one. The in-line and transverse forces on the pipe, which is placed at various distances from the bottom of the wave tank, are measured. The force transfer coefficients (CD, CM, CL are much larger when the pipe is near the bottom than when it is free. But the coefficients do not increase unlimitedly: they reach their maxima at ξ (gap ratio = e / D) = 0.1 (gap ratio ξ = e/ D). An interesting result is that the ratio of lift force frequency (fL ) to wave frequency (fw) is 2.0. In the paper, the curves of coefficients are given.展开更多
This paper introduces the process and result of fatigue test of steel (Z direction steel) welded T tubular joints used in offshore engineering. Detailed measurement of stress concentration factor, stress distribution,...This paper introduces the process and result of fatigue test of steel (Z direction steel) welded T tubular joints used in offshore engineering. Detailed measurement of stress concentration factor, stress distribution, fatigue life and crack development has been performed. Through analysis, an empirical formula of stress concentration factor for T tubular joints, fatigue S-N curve and crack propagation rule are obtained.展开更多
- Theoretically speaking, it is impossible to make the differential equation of motion uncoupled for the natural modes of a system in consideration of the attached water. The hydro-elastic structure is equal to the, n...- Theoretically speaking, it is impossible to make the differential equation of motion uncoupled for the natural modes of a system in consideration of the attached water. The hydro-elastic structure is equal to the, non-proportional damping system. In this paper a perturbation analysis method is put forward. The structure motion equation is strictly solved mathematically, and the non-proportional damping problem is transformed into a series of proportional damping ones in the superposition form. The paper also presents the calculation formula of the dyanamic response of the structure being subjected to harmonic and arbitrary load. The convergence of the proposed method is also studied in this paper, and the corresponding convergence conditions are given. Finally, the proposed method is used to analyze the displacement response of a real offshore platform. The calculation results show that this method has the characteristics of high accuracy and fast convergence.展开更多
A spatial finite element model for vibration analysis of crankshaft system was proposed. The crankshaft body was simplified as spatial rigid frame by using beam elements based on Timoshenko beam theory. The main beari...A spatial finite element model for vibration analysis of crankshaft system was proposed. The crankshaft body was simplified as spatial rigid frame by using beam elements based on Timoshenko beam theory. The main bearings in system were simplified as linear springs and dashpots. The natural frequencies of the crankshaft system of a four in-line cylinder engine were calculated and compared with the analytical and experimental values available in other publications. In order to simulate the motion of operating crankshaft system, the gas forces, rotating masses and reciprocating masses were considered, the crankshaft and main bearings were coupled in a rotating coordinate system, and a dynamic model for vibration analysis of crankshaft system was established. By applying the dynamic model, the influence of the mass and moment of inertia of front pulley on the behavior of crankshaft vibration was investigated.展开更多
- A series model tests of wave forces by both regular and irregular waves combined with currents on single piles and bipiles in tandem and parallel arrays have been carried out. Based on Morison Equation, linear wave ...- A series model tests of wave forces by both regular and irregular waves combined with currents on single piles and bipiles in tandem and parallel arrays have been carried out. Based on Morison Equation, linear wave theory and linear wave spectrum theory as well, the characteristics of inline, lift and resultant forces on cylinders have been analyzed respectively. The drag, inertia and lift coefficients CD, CM and CL f皉 single piles related to KC number and the grouping effect coefficients of inline, lift and resultant forces on bipiles in tandem and parallel arrays related to KC number are given in this paper.展开更多
- In the time domain method the dynamic load is successfully identified when the accelerations, velocities and displacements or velocities and displacements of the structure are known. But in engineering practice or e...- In the time domain method the dynamic load is successfully identified when the accelerations, velocities and displacements or velocities and displacements of the structure are known. But in engineering practice or experiments usually only the acceleration response is recorded. In this paper an improved time domain method is proposed for dynamic load identification. In this method by using of Duhamel integral, only the acceleration response is required for load identification. As an application of the present method, the dynamic ice load on a Bohai offshore platform is identified based on some measured acceleration. The identified values of ice load are in good agreement with the measured ones.展开更多
Multiattribute decision making(MADM) problems, in which the weights and ratings of alternatives are expressed with intuitionistic fuzzy(IF) sets, are investigated.Firstly, the relative degrees of membership and the re...Multiattribute decision making(MADM) problems, in which the weights and ratings of alternatives are expressed with intuitionistic fuzzy(IF) sets, are investigated.Firstly, the relative degrees of membership and the relative degrees of non-membership are formulated as IF sets, the weights and values of alternatives on both qualitative and quantitative attributes may be expressed as IF sets in a unified way.Then a MADM method based on generalized ordered weighted averaging operators is proposed.The proposed method is illustrated with a numerical example.展开更多
文摘- Experimental study and theoretical analysis show that the critical value of relative wave height (H/ d)b given by Goda and the critical wave steepness (H/ L)b given by Michell and Miche can be adopted as the spilling breaking indices of regular waves. According to the same principle, a systematic theoretical analysis and experiment of irregular waves have been done by the authors in order to solve the breaking problem of irregular waves. It is indicated that the authors’ method for determining wave breaking of regular waves can also be used for irregular waves.
基金The project supported by the National Natural Science Foundation of China
文摘Based on the linear analysis of stability,a dispersion equation isdeduced which delineates the evolution of a general 3-dimensional disturbance onthe free surface of an incompressible viscous liquid jet.With respect to the spatialgrowing disturbance mode,the numerical results obtained from the solution of thedispersion equation reveal that a dimensionless parameter J_e exists.As J_e】1,theaxisymmetric disturbance mode is most unstable;and when J_e【1,the asymmetricdisturbances come into being,their growth rate increases with the decrease of J_e,tillone of them becomes the most unstable disturbance.The breakup of a low-speedliquid jet results from the developing of axisymmetric disturbances,whose instabilityis produced by the surface tension;while the atomization of a high-speed liquid jetis brought about by the evolution of nonaxisymmetric disturbance,whose instabilityis caused by the aerodynamic force on the interface between the jet and the ambientgas.
文摘The study of the behavior of concrete under biaxial stresses is essential to the design of offshore concrete platforms. Using the multiaxial test apparatus developed by the authors, the deformation and strength of concrete under biaxial stresses are studied experimentally. Based on the test data, an endochronic damage constitutive model and a failure criterion are proposed. According to the above model, an incremental nonlinear iterative programme is developed, and a plate sample in plane stress state is analyzed.
文摘Contacting state between molten metal and a mold and initial solidification process of continuously cast metals can be controlled by imposing an intermittent magnetic field.In this study, effect of the intermittent magnetic field on the initial solidification ofcontinuoasly cast metals was investigated by measuring the temperature distribution in the melt pool and the initial solidification starting position of shells. It was found that under the condition with intermittent magnetic field, the melt near meniscns is in slow cooling state, the initial solidification starting position descends, initial solidification shell thickens and the liquid-solid interface becomes smooth.
文摘It is found that the anomalous eutectics can be separated on macroscopic scale by flow caused by electromagnetic stirring, and the separated phase is the leading faceted phase with the solution entmpy over 23J/(mol.K). By using this technology, a new kind of composite pipe ond gear with good abrasive properties are made without adding any reinforced particles. Emphases are paid on the researehes about formation mechanism of seporated eutectic and abrasive property of the composite pipe or gear. The result shows that the entropy of solution controlling the eutectic microstructure is also valid and useful as a criterion of separated eutectic, and the kind and its chemical scope of the off-eutectic used to make composite can be calculated accoofing to this theory.
文摘- The characteristics of deformation and strength of concrete under the plane strain condition are studied experimentally with the triaxial apparatus designed by the authors and are compared with those under the plane stress condition. A formula of stress transformation between plane stress and plane strain conditions is proposed for the elasto-plastic state, and it provides a theoretical basis for simplifying nonlinear analysis and fully using the strength of concrete.
基金A part of the project supported financially by National Natural Science Foundation of China
文摘Multi-directional irregular waves are simulated on the basis of the given directional spectrum using a double summation model, a single direction per frequency model and a single summation model. Their results are compared. It is shown that the single direction per frequency model proposed in this paper can generate a realistic wave field. The effects of the model parameters on the simulated results are also studied in this paper and corresponding suggestions are given.
基金supported by the National Natural Science Foundation of China (60674078).
文摘With respect to the subjective factors and nonlinear characteristics inherent in the important identifi-cation of fault tree analysis (FTA), a new important measure of FTA is proposed based on possibilistic information entropy. After investigating possibilistic information semantics, measure-theoretic terms, and entropy-like models, a two-dimensional framework has been constructed by combining both the set theory and the measure theory. By adopting the possibilistic assumption in place of the probabilistic one, an axiomatic index of importance is defined in the possibility space and then the modelling principles are presented. An example of the fault tree is thus provided, along with the concordance analysis and other discussions. The more conservative numerical results of importance rankings, which involve the more choices can be viewed as "soft" fault identification under a certain expected value. In the end, extension to evidence space and further research perspectives are discussed.
基金supported by the National Key R&D Program of China (2016YFB0600902)the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB17000000)+2 种基金Dalian National Laboratory for Clean Energy (DNL180401)the Youth Innovation Promotion Association CASthe Singapore Ministry of Education Academic Research Fund (AcRF) Tier 1: RG9/17, RG115/17, RG115/18 and Tier 2: MOE2016-T2-2-004
文摘Electrochemical CO2 reduction to chemicals or fuels presents one of the most promising strategies for managing the global carbon balance, which yet poses a significant challenge due to lack of efficient and durable electrocatalyst as well as the understanding of the CO2 reduction reaction(CO2RR) mechanism.Benefiting from the large surface area, high electrical conductivity, and tunable structure, carbon-based metal-free materials(CMs) have been extensively studied as cost-effective electrocatalysts for CO2RR.The development of CMs with low cost, high activity and durability for CO2RR has been considered as one of the most active and competitive directions in electrochemistry and material science.In this review article,some up-to-date strategies in improving the CO2RR performance on CMs are summarized.Specifically, the approaches to optimize the adsorption of CO2RR intermediates, such as tuning the physical and electronic structure are introduced, which can enhance the electrocatalytic activity of CMs effectively.Finally, some design strategies are proposed to prepare CMs with high activity and selectivity for CO2RR.
文摘The effect of mechanical cyclings on the stress-strain(S-S) curves was studied systematically using tensile tests over a widetemperature range.Two-stage yielding was observed in the temperature range between M_s and the ultimate temperature to in-duce martensite,denoted by M_d.The first stage was confirmed to be associated with stress-induced martensite(SIM) and the sec-ond stage was associated with the yielding of SIM.When the samples were mechanically cycled between M_s and M_d.astress-softening phenomenon was observed.The cyclings made the martensite amount increase,critical stress σ_c of SIM de-crease according to exponential law,and the entropy(also enthalpy) of the parent to martensite transformation also decrease.Thevariations of SIM relative amount were determined by recording the changes of electrical resistances in the course of tension.
文摘A typical example of the seawall construction for industrial use in China-the seawall construction for Shanghai Petrochemical Complex (SPC)-is introduced in this paper.
文摘In this paper, the second order steady drift forces on the ships and other floating offshore structures are calculated by the far field method. The amplitudes of diffracted waves and radiated waves at infinity are obtained by the two-dimensional source distribution and strip-theory method. For the twin hull structure, the hydrodynamic interaction between the two hulls is taken into account. The drift forces on cross sections of Lewis type as well as on the semi-submersibles are computed. The theoretical results obtained by the present method agree fairly well with experimental results.
文摘The wave forces on pipes near the ocean bottom are studied with model test in this paper. Comparisons of four different methods show that the uncommonly used method - Least Square Mass (LSM) is the most stable one. The in-line and transverse forces on the pipe, which is placed at various distances from the bottom of the wave tank, are measured. The force transfer coefficients (CD, CM, CL are much larger when the pipe is near the bottom than when it is free. But the coefficients do not increase unlimitedly: they reach their maxima at ξ (gap ratio = e / D) = 0.1 (gap ratio ξ = e/ D). An interesting result is that the ratio of lift force frequency (fL ) to wave frequency (fw) is 2.0. In the paper, the curves of coefficients are given.
文摘This paper introduces the process and result of fatigue test of steel (Z direction steel) welded T tubular joints used in offshore engineering. Detailed measurement of stress concentration factor, stress distribution, fatigue life and crack development has been performed. Through analysis, an empirical formula of stress concentration factor for T tubular joints, fatigue S-N curve and crack propagation rule are obtained.
文摘- Theoretically speaking, it is impossible to make the differential equation of motion uncoupled for the natural modes of a system in consideration of the attached water. The hydro-elastic structure is equal to the, non-proportional damping system. In this paper a perturbation analysis method is put forward. The structure motion equation is strictly solved mathematically, and the non-proportional damping problem is transformed into a series of proportional damping ones in the superposition form. The paper also presents the calculation formula of the dyanamic response of the structure being subjected to harmonic and arbitrary load. The convergence of the proposed method is also studied in this paper, and the corresponding convergence conditions are given. Finally, the proposed method is used to analyze the displacement response of a real offshore platform. The calculation results show that this method has the characteristics of high accuracy and fast convergence.
文摘A spatial finite element model for vibration analysis of crankshaft system was proposed. The crankshaft body was simplified as spatial rigid frame by using beam elements based on Timoshenko beam theory. The main bearings in system were simplified as linear springs and dashpots. The natural frequencies of the crankshaft system of a four in-line cylinder engine were calculated and compared with the analytical and experimental values available in other publications. In order to simulate the motion of operating crankshaft system, the gas forces, rotating masses and reciprocating masses were considered, the crankshaft and main bearings were coupled in a rotating coordinate system, and a dynamic model for vibration analysis of crankshaft system was established. By applying the dynamic model, the influence of the mass and moment of inertia of front pulley on the behavior of crankshaft vibration was investigated.
文摘- A series model tests of wave forces by both regular and irregular waves combined with currents on single piles and bipiles in tandem and parallel arrays have been carried out. Based on Morison Equation, linear wave theory and linear wave spectrum theory as well, the characteristics of inline, lift and resultant forces on cylinders have been analyzed respectively. The drag, inertia and lift coefficients CD, CM and CL f皉 single piles related to KC number and the grouping effect coefficients of inline, lift and resultant forces on bipiles in tandem and parallel arrays related to KC number are given in this paper.
文摘- In the time domain method the dynamic load is successfully identified when the accelerations, velocities and displacements or velocities and displacements of the structure are known. But in engineering practice or experiments usually only the acceleration response is recorded. In this paper an improved time domain method is proposed for dynamic load identification. In this method by using of Duhamel integral, only the acceleration response is required for load identification. As an application of the present method, the dynamic ice load on a Bohai offshore platform is identified based on some measured acceleration. The identified values of ice load are in good agreement with the measured ones.
基金supported by the National Natural Science Foundation of China (70871117 70571086)
文摘Multiattribute decision making(MADM) problems, in which the weights and ratings of alternatives are expressed with intuitionistic fuzzy(IF) sets, are investigated.Firstly, the relative degrees of membership and the relative degrees of non-membership are formulated as IF sets, the weights and values of alternatives on both qualitative and quantitative attributes may be expressed as IF sets in a unified way.Then a MADM method based on generalized ordered weighted averaging operators is proposed.The proposed method is illustrated with a numerical example.
