Computational fluid dynamics(CFD)provides a powerful tool for investigating complicated fluid flows.This paper aims to study the applicability of CFD in the preliminary design of linear and nonlinear fluid viscous dam...Computational fluid dynamics(CFD)provides a powerful tool for investigating complicated fluid flows.This paper aims to study the applicability of CFD in the preliminary design of linear and nonlinear fluid viscous dampers.Two fluid viscous dampers were designed based on CFD models.The first device was a linear viscous damper with straight orifices.The second was a nonlinear viscous damper containing a one-way pressure-responsive valve inside its orifices.Both dampers were detailed based on CFD simulations,and their internal fluid flows were investigated.Full-scale specimens of both dampers were manufactured and tested under dynamic loads.According to the tests results,both dampers demonstrate stable cyclic behaviors,and as expected,the nonlinear damper generally tends to dissipate more energy compared to its linear counterpart.Good compatibility was achieved between the experimentally measured damper force-velocity curves and those estimated from CFD analyses.Using a thermography camera,a rise in temperature of the dampers was measured during the tests.It was found that output force of the manufactured devices was virtually independent of temperature even during long duration loadings.Accordingly,temperature dependence can be ignored in CFD models,because a reliable temperature compensator mechanism was used(or intended to be used)by the damper manufacturer.展开更多
The bamboo scrimber is an anisotropic material.The elastic constant values of the bamboo scrimber specimens measured by the dynamic and static methods are consistent,and the dynamic test method has the advantages of r...The bamboo scrimber is an anisotropic material.The elastic constant values of the bamboo scrimber specimens measured by the dynamic and static methods are consistent,and the dynamic test method has the advantages of rapidity,simplicity,good repeatability,and high precision.Bamboo scrimber has strong potential as a building material,and its elastic constant is an important index to measure its mechanical properties.To quickly,simply,non-destructively,and accurately detect the elastic constant of the bamboo scrimber,they were dynamically tested by the free plate transient excitation method and cantilever plate torsional vibration method.The static four-point bending method was used to verify the accuracy and reliability of the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber.The mechanism analysis and evaluation of the quality grade,homogeneity,and size effect of the bamboo scrimber whole board were carried out.The main results show that the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber are 12 GPa,1500 MPa,and 0.31,respectively,which meet the requirements of GB/T 40247-2021 for structural bamboo scrimber.展开更多
Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed ...Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed with undesired interference components,often featuring as high-frequency fluctuations.Previous studies have revealed that sectional geometry(shape and size)greatly affects the high-frequency interference.In this study,low strain dynamic testing on full-scale X-section concrete is conducted in order to investigate the influences of high-frequency interference on velocity responses at the pile head.Emphasis is placed on the frequency and peak value of interference waves at various receiving points.Additionally,the effects of the geometrical,and mechanical properties of the pile shaft on high-frequency interference are elaborated on through the three-dimensional finite element method.The results show that the measured wave is obscured by interference waves superposed by two types of high-frequency components.The modulus and cross-sectional area are contributing factors to the frequency and peak value of the interference waves.On the other hand,the position with the least interference is determined,to some extent,by the accurate shape of the X-section.展开更多
Impact drop tests are routinely used to examine the dynamic performance of rockbolts.Numerous impact tests have been carried out in the past decades on independently designed,constructed and operated testing rigs.Each...Impact drop tests are routinely used to examine the dynamic performance of rockbolts.Numerous impact tests have been carried out in the past decades on independently designed,constructed and operated testing rigs.Each laboratory has developed testing procedures;thus,the results are often reported in different ways by various laboratories.The inconsistency in testing procedures and reporting formats presents a challenge when comparing results from different laboratories.A series of impact tests of identical rockbolts was carried out using the direct impact method(i.e.the mass free-fall method)on the rigs in four laboratories in different countries.The purpose of these tests was to investigate the level of consistency in the results from the four rigs.Each rig demonstrated a high level of repeatability,but differences existed between the various rigs.The differences would suggest that there is noticeable equipment-dependent bias when test results obtained from different laboratories are compared.It was also observed that the energy dissipated for the plastic displacement of the bolt was smaller than the impact energy in the tests.The average impact load(AIL)and the ultimate plastic displacement(D)of the bolt describe the ultimate dynamic performance of the bolt.In the case where the bolt does not rupture,the specific plastic energy(SPE)is an appropriate parameter in describing the impact performance of the bolt.Two other relevant parameters are the first peak load(FPL)and the initial stiffness(K)of the bolt sample.The information from this test series will guide the formulation of standardised testing procedures for dynamic impact tests of rockbolts.展开更多
In dynamic test,sampling rate is high and noise is strong,so a signal sparse decomposition method based on Gabor dictionary is put forward.This method iteratively decomposes the signal with the matching pursuit(MP)alg...In dynamic test,sampling rate is high and noise is strong,so a signal sparse decomposition method based on Gabor dictionary is put forward.This method iteratively decomposes the signal with the matching pursuit(MP)algorithm and takes the coherence ratio of the threshold as a condition of iteration termination.Standard MP algorithm is time-consuming,thus an adaptive genetic algorithm is introduced to MP method,which makes computation speed accelerate effectively.Experimental results indicate that this method not only can effectively remove high-frequency noise but also can compress the signal greatly.展开更多
In this article,dynamic method and static method of testing Poisson's ratio of OSB(Oriented Strand Board)were proposed.Through modal and static numerical analyses,the position where the transverse stress is equal ...In this article,dynamic method and static method of testing Poisson's ratio of OSB(Oriented Strand Board)were proposed.Through modal and static numerical analyses,the position where the transverse stress is equal to zero was determined.The binary linear regression method was applied to express the gluing position of the strain gauge as a relational express ion that depended on the length-width ratio and width-thickness ratio of the canti-lever plate.Then the longitudinal and transverse Poisson's ratios of OSB were mea sured by the given dynamic and static methods.In addition,the test results of OSB Poisson's ratio were analyzed with the probability distribution of random variables.The results showed that using the proposed dynamic method and static method,the test results for longitudinal and transverse Poisson's ratios of OSB were quite consistent,despite the gluing position of the strain gauges being different.And these OSB Poisson's ratios were accorded with that obtained by the axial tensile method and the four-point bending method.OSB longitudinal and transverse Poisson's ratios followed Weibull distribution.展开更多
Dynamic visual acuity test(DVAT)plays a key role in the assessment of vestibular function,the visual function of athletes,as well as various ocular diseases.As the visual pathways conducting dynamic and static signals...Dynamic visual acuity test(DVAT)plays a key role in the assessment of vestibular function,the visual function of athletes,as well as various ocular diseases.As the visual pathways conducting dynamic and static signals are different,DVATs may have potential advantages over the traditional visual acuity tests commonly used,such as static visual acuity,contrast sensitivity,and static perimetry.Here,we provide a review of commonly applied DVATs and their several uses in clinical ophthalmology.These data indicate that the DVAT has its unique clinical significance in the evaluation of several ocular disorders.展开更多
Volatile organic compounds(VOCs) emitted from three types of carpets used in aircrafts were compared by using headspace and dynamic chamber tests. The headspace samples contained many compounds that were not detected ...Volatile organic compounds(VOCs) emitted from three types of carpets used in aircrafts were compared by using headspace and dynamic chamber tests. The headspace samples contained many compounds that were not detected in the dynamic chamber test; in addition, the dominant VOCs found by these two methods were different. The findings indicate that for highly sorptive materials such as carpets, headspace analysis may give inaccurate indication of actual VOC emissions, and it is necessary to conduct dynamic chamber tests over a certain period of time in order to identify the true emission characteristics. From the dynamic chamber tests, 2-ethyl-1-hexanol was the main VOC emitted from all three carpets. The study also examined the emission characteristics of aircraft carpets. In all experiments, total VOC(TVOC) concentration peaked within a few hours after the start of the experiment and was followed by rapid decay. The emission parameters of TVOC emitted by all three carpets were calculated and the simulated data matched the measured data well.展开更多
With the continuous advancement of China’s infrastructure construction to the west,according to the geographic situation in the southwest region,such as mountainous areas and complex terrain,the road construction pro...With the continuous advancement of China’s infrastructure construction to the west,according to the geographic situation in the southwest region,such as mountainous areas and complex terrain,the road construction process is inevitably accompanied by earth and rock blasting.To improve the quality and safety of the project,this paper addresses the problems of land and rock blasting faced in the construction of mountain road projects,taking the research of rock dynamic mechanics test as the starting point,and using a combination of theoretical analysis and experimental research methods.The specific research content includes the following parts:dynamic impact compression test(SHPB),dynamic splitting tensile test,and stress-strain curve analysis of the test results,which provides the theoretical basis and numerical parameters for the numerical simulation of future engineering blasting.展开更多
Degradability of bone tissue engineering scaffold that matching the regeneration rate could allow a complete replacement of host tissue.However,the porous structure of biodegradable Mg scaffolds certainly generated hi...Degradability of bone tissue engineering scaffold that matching the regeneration rate could allow a complete replacement of host tissue.However,the porous structure of biodegradable Mg scaffolds certainly generated high specific surface area,and the three-dimensional interconnected pores provided fast pervasive invasion entrance for the corrosive medium,rising concern of the structural integrity during the degradation.To clarify the structural evolution of the three-dimensional(3D)porous structure,semi-static immersion tests were carried out to evaluate the degradation performance in our previous study.Nevertheless,dynamic immersion tests mimicking the in vivo circulatory fluid through the interconnected porous structure have yet been investigated.Moreover,the effects of dynamic flow rates on the degradation deposition behavior of 3D porous Mg scaffolds were rarely reported.In this study,Mg scaffolds degraded at three flow rates exhibited different degradation rates and deposition process.A flow rate of 0.5 m L/min introduced maximum drop of porosity by accumulated deposition products.The deposition products provided limited protection against the degradation process at a flow rate of 1.0 m L/min.The three-dimensional interconnected porous structure of Mg scaffold degraded at 2.0 m L/min well retained after 14 days showing the best interconnectivity resistance to the degradation deposition process.The dynamic immersion tests disclosed the reason for the different degradation rates on account of flow rates,which may bring insight into understanding of varied in vivo degradation rates related to implantation sites.展开更多
As a widely-applied engineering material in cold regions, the frozen subgrade soils are usually subjected to seismic loading, which are also dramatically influenced by the freeze-thaw(F-T)cycles due to the varying tem...As a widely-applied engineering material in cold regions, the frozen subgrade soils are usually subjected to seismic loading, which are also dramatically influenced by the freeze-thaw(F-T)cycles due to the varying temperature. A series of dynamic cyclic triaxial experiments were conducted through a cryogenic triaxial apparatus for exploring the influences of F-T cycles on the dynamic mechanical properties of frozen subgrade clay.According to the experimental results of frozen clay at the temperature of-10℃, the dynamic responses and microstructure variation at different times of F-T cycles(0, 1, 5, and 20 cycles) were explored in detail.It is experimentally demonstrated that the dynamic stress-strain curves and dynamic volumetric strain curves of frozen clay are significantly sparse after 20F-T cycles. Meanwhile, the cyclic number at failure(Nf) of the frozen specimen reduces by 89% after 20freeze-thaw cycles at a low ratio of the dynamic stress amplitude. In addition, with the increasing F-T cycles,the axial accumulative strain, residual deformation,and the value of damage variable of frozen clay increase, while the dynamic resilient modulus and dynamic strength decrease. Finally, the influence of the F-T cycles on the failure mechanisms of frozen clay was discussed in terms of the microstructure variation. These studies contribute to a better understanding of the fundamental changes in the dynamic mechanical of frozen soils exposed to F-T cycles in cold and seismic regions.展开更多
Dynamic tensile failure is a common phenomenon in deep rock practices,and thus accurately evaluating the dynamic tensile responses of rocks under triaxial pressures is of great significance.The Brazilian disc(BD)test ...Dynamic tensile failure is a common phenomenon in deep rock practices,and thus accurately evaluating the dynamic tensile responses of rocks under triaxial pressures is of great significance.The Brazilian disc(BD)test is the suggested method by the International Society for Rock Mechanics and Rock Engineering(ISRM)for measuring both the static and dynamic tensile strengths of rock-like materials.However,due to the overload phenomenon and the complex preloading conditions,the dynamic tensile strengths of rocks measured by the BD tests tend to be overestimated.To address this issue,the dynamic BD tensile strength(BTS)of Fangshan marble(FM)under different preloading conditions were measured through a triaxial split Hopkinson pressure bar(SHPB).The fracture onset in BD specimen was captured through a strain gage around the disc center.The discrepancy between the traditional tensile strength(TTS,determined by the peak load P_(f) of the BD specimen)and the nominal tensile strength(NTS,obtained from the load P_(i) when the diametral fracture commences in the tested BD specimen)was applied to quantitatively evaluating the overload phenomenon.The Griffith criterion was used to rectify the calculation of the tensile stress at the disc center under triaxial stress states.The results demonstrate that the overload ratio(s)increases with the loading rate(σ)and decreases with the hydrostatic pressure(σ_(s)).The TTS corrected by the Griffith criterion is independent of theσ_(s)due to the overload phenomenon,while the NTS corrected by the Griffith criterion is sensitive to both the andσ.Therefore,it is essential to modify the tensile stress in dynamic confined BD tests using both the overload correction and the Griffith criterion rectification to obtain the accurate dynamic BTS of rocks.展开更多
Al_(2)O_(3)-MgO and Al_(2)O_(3)-spinel low cement castables(LCC-AM and LCC-AS)have been extensively used in steel ladles as working linings.Nevertheless,the use of alumina-magnesia gunning mixes has been mainly kept f...Al_(2)O_(3)-MgO and Al_(2)O_(3)-spinel low cement castables(LCC-AM and LCC-AS)have been extensively used in steel ladles as working linings.Nevertheless,the use of alumina-magnesia gunning mixes has been mainly kept for maintaining these castable linings,because of high rebound loss,poor green strength,high porosity and short life-span.Thanks to a high BET alumina(MC-G),it is now possible to develop a series of high-performance no-cement or low-cement Al_(2)O_(3)-MgO gunning mixes(NCG-AM or LCG-AM).The paper focuses on the BOF slag resistance of NCG-AM,LCG-AM,LCC-AM and LCC-AS.The corrosion mechanisms of rotary slag samples were studied by scanning electron microscopy(SEM/EDS).The results reveal different microstructures around MgO particles,depending on the four used compositions.Continuous and thicker spinel phases were formed in NCG-AM,which was proved to have the best corrosion resistance after the dynamic slag test.MC-G can provide a high diffusion flux of Al^(3+)in terms of kinetics and hence inhibits Kirkendall porosity around MgO particles.In addition,a continuous spinel phase acts like a pinning nail to reinforce the matrix and thus decreases erosion by slag.In contrast to NCG-AM,the porous spinel phase was found around unreacted MgO particles and some particles were carried away near the interface of LCC-AM and slag.The NCG-AM containing MC-G had been tested in two steel plants,and it extended the service life of the ladles up to 50%.In addition,this study suggests the potential application of NCG-AM as steel ladle linings.展开更多
The hydrostatic or confining pressure of deep rocks has a significant impact on the mechanical behavior of brittle materials.Especially when confining pressure is applied,the mechanical properties of rock materials will ...The hydrostatic or confining pressure of deep rocks has a significant impact on the mechanical behavior of brittle materials.Especially when confining pressure is applied,the mechanical properties of rock materials will undergo significant changes.Considering that the process of shale sample subjected to impact load is in a closed container in the dynamic triaxial SHPB test,the failure process of the sample cannot be observed.Meanwhile,the activation volume of the shale sample would be large and local failure would occur in the test under the high strain rate loading.Therefore,thefinite element model of shale considering the bedding effect under confining pressure was established in this study.Taking shale materials with different bedding dip angles as simulation objects,the dynamic failure characteristics of shale were studied using the dynamic analysis software ANSYS/LS‐DYNA from three aspects:stress‐strain curve,failure growth process,and failure morphology.The research results obtained can serve as the key technical parameters for deep resource extraction.展开更多
Based on three kinds of dynamic test of MEMS,a dynamic system for the vibration test of micro machined gyroscope based on high speed photography is introduced.Firstly,the architecture of the system hardware is introdu...Based on three kinds of dynamic test of MEMS,a dynamic system for the vibration test of micro machined gyroscope based on high speed photography is introduced.Firstly,the architecture of the system hardware is introduced.Secondly,the image tracking performance is compared by the test using the template matching algorithm,the mean shift algorithm and the SURF algorithm.The vibration curve shows that high speed photograph combined with SURF algorithm is faster,more accurate,and more suitable for the vibration test of micro machined gyroscope.After the frequency analysis and related interpolation,more characteristics of micro gyroscope can be obtained.展开更多
The dynamic characteristics of high sensitivity temperature sensor are studied by using siphon method to fill the air hole near the core of the hollow photonic crystal fiber with Cargille matching liquid,and the two e...The dynamic characteristics of high sensitivity temperature sensor are studied by using siphon method to fill the air hole near the core of the hollow photonic crystal fiber with Cargille matching liquid,and the two ends are fused with single-mode fiber in this work.We analyzed the working principle of filled photonic crystal fiber sensor by using the standard coupling mode theory of directional coupler.The coupling process was simulated by COMSOL software.When the photonic crystal fiber filled with 10 mm liquid was scanned by tunable laser,the temperature sensitivity was 7.50 nm /℃,the average temperature response time was 0.317 s,the average release time was 3.732 s,and the temperature variation linearity was 100%.The experimental results show that the liquid filled photonic crystal fiber has the advantages of high temperature sensitivity,fast response time and good linearity.展开更多
Parameter identification of Pasternak foundation models(PFM)is never satisfactory,which discourages the application and popularization of PFM.In the present study,an energy-based model to predict the dynamic foundatio...Parameter identification of Pasternak foundation models(PFM)is never satisfactory,which discourages the application and popularization of PFM.In the present study,an energy-based model to predict the dynamic foundation coefficients was proposed using the vibration kinetic energy and potential energy of a Pasternak foundation-rigid plate system.On the basis of the Pasternak foundation,the relationship among the natural frequency,dynamic foundation coefficients,rigid plate configuration,and vibrating soil equivalent mass per unit area was considered.To obtain the natural frequencies of the Pasternak foundation-rigid plate system,dynamic tests were performed.Using two or more dynamic test results of various rigid plates on a foundation,a set of equations of dynamic foundation coefficients was set up to directly identify the foundation coefficients and equivalent mass per unit area of vibrating soil.The feasibility of the proposed method was verified by comparing it with the outdoor and indoor test results and finite element analysis results.When the proposed method is used to obtain the dynamic parameters,PFM can be generalized and applied more widely in engineering practice.展开更多
In deep underground engineering,rock burst and other dynamic disasters are prone to occur due to stress concentration and energy accumulation in surrounding rock.The control of dynamic disasters requires bolts and cab...In deep underground engineering,rock burst and other dynamic disasters are prone to occur due to stress concentration and energy accumulation in surrounding rock.The control of dynamic disasters requires bolts and cables with high strength,high elongation,and high energy-absorbing capacity.Therefore,a constant resistance energy-absorbing(CREA)material is developed.In this study,the dynamic characteristics of the new material are obtained via the drop hammer tests and the Split Hopkinson Pressure Bar(SHPB)tests of the new material and two common bolt(CB)materials widely used in the field.The test results of drop hammer test and SHPB test show that the percentage elongation of CREA material is more than 2.64 and 3.22 times those of the CB material,and the total impact energy acting on CREA material is more than 18.50 and 21.84 times,respectively,indicating that the new material has high elongation and high energy-absorbing capacity.Subsequently,the CREA bolts and cables using the new material are developed,which are applied in roadways with high stress and strong dynamic disturbance.The field monitoring results show that CREA bolts and cables can effectively control the surrounding rock deformation and ensure engineering safety.展开更多
To effectively improve the poor engineering properties of loess and enhance its seismic performance,the industrial by-product lignin is used as a modified material.Based on lots of dynamic triaxial tests,the dynamic e...To effectively improve the poor engineering properties of loess and enhance its seismic performance,the industrial by-product lignin is used as a modified material.Based on lots of dynamic triaxial tests,the dynamic elastic modulus and damping ratio of lignin-modified loess were tested.The effects of lignin content on the dynamic elastic modulus and damping ratio of lignin-modified loess were analyzed.Combined with scanning electron microscopy(SEM)and X-ray diffraction(XRD),the microscopic mechanism of lignin to improve the dynamic properties of loess was studied.The results show that lignin can effectively modify the dynamic deformation of loess under dynamic load.Under the same dynamic stress condition,the dynamic strain of lignin-modified loess is smaller than compacted loess.The dynamic elastic modulus of modified loess with different lignin content are quite different,but both decrease with the increase of dynamic strain.And the dynamic elastic modulus of modified loess is greater than compacted loess.The maximum dynamic elastic modulus of modified loess with a lignin content of 1%are significantly greater than others.Under the same dynamic strain condition,the damping ratio of lignin-modified loess is smaller than compacted loess.Lignin can effectively fill loess pores and cement loess particles.Compared with compacted loess,no new mineral components are generated in the lignin-modified loess.The optimum lignin content of dynamics characteristic of modified loess is present,and the optimum lignin content is 1%.展开更多
Research to reliably predict the seismic response of nuclear power stations with a pile-raft foundation is needed to meet the high safety requirements of nuclear power stations.In this study,a scaled superstructure wi...Research to reliably predict the seismic response of nuclear power stations with a pile-raft foundation is needed to meet the high safety requirements of nuclear power stations.In this study,a scaled superstructure with a 4×3 pile-raft foundation,which is constructed in Shanxi kaolin clay,is modelled.Accordingly,the characteristics of seismic response for nuclear power stations with a pile-raft foundation are analyzed using dynamic centrifuge tests.In particular,multiple earthquake motions with different magnitudes and frequency properties are utilized to map the relationship between structural response and properties of earthquake motions.The results show that the seismic response of the soil,raft,and structure are significantly affected by the natural frequency and magnitude of the earthquake motion.The soil surface acceleration is lower than the raft acceleration.The results provide a reliable reference to better understand the seismic response of nuclear power stations.展开更多
文摘Computational fluid dynamics(CFD)provides a powerful tool for investigating complicated fluid flows.This paper aims to study the applicability of CFD in the preliminary design of linear and nonlinear fluid viscous dampers.Two fluid viscous dampers were designed based on CFD models.The first device was a linear viscous damper with straight orifices.The second was a nonlinear viscous damper containing a one-way pressure-responsive valve inside its orifices.Both dampers were detailed based on CFD simulations,and their internal fluid flows were investigated.Full-scale specimens of both dampers were manufactured and tested under dynamic loads.According to the tests results,both dampers demonstrate stable cyclic behaviors,and as expected,the nonlinear damper generally tends to dissipate more energy compared to its linear counterpart.Good compatibility was achieved between the experimentally measured damper force-velocity curves and those estimated from CFD analyses.Using a thermography camera,a rise in temperature of the dampers was measured during the tests.It was found that output force of the manufactured devices was virtually independent of temperature even during long duration loadings.Accordingly,temperature dependence can be ignored in CFD models,because a reliable temperature compensator mechanism was used(or intended to be used)by the damper manufacturer.
文摘The bamboo scrimber is an anisotropic material.The elastic constant values of the bamboo scrimber specimens measured by the dynamic and static methods are consistent,and the dynamic test method has the advantages of rapidity,simplicity,good repeatability,and high precision.Bamboo scrimber has strong potential as a building material,and its elastic constant is an important index to measure its mechanical properties.To quickly,simply,non-destructively,and accurately detect the elastic constant of the bamboo scrimber,they were dynamically tested by the free plate transient excitation method and cantilever plate torsional vibration method.The static four-point bending method was used to verify the accuracy and reliability of the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber.The mechanism analysis and evaluation of the quality grade,homogeneity,and size effect of the bamboo scrimber whole board were carried out.The main results show that the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber are 12 GPa,1500 MPa,and 0.31,respectively,which meet the requirements of GB/T 40247-2021 for structural bamboo scrimber.
基金National Natural Science Foundation of China under Grant Nos.51622803 and 51878103China Postdoctoral Science Foundation under Grant No.2021M692689。
文摘Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed with undesired interference components,often featuring as high-frequency fluctuations.Previous studies have revealed that sectional geometry(shape and size)greatly affects the high-frequency interference.In this study,low strain dynamic testing on full-scale X-section concrete is conducted in order to investigate the influences of high-frequency interference on velocity responses at the pile head.Emphasis is placed on the frequency and peak value of interference waves at various receiving points.Additionally,the effects of the geometrical,and mechanical properties of the pile shaft on high-frequency interference are elaborated on through the three-dimensional finite element method.The results show that the measured wave is obscured by interference waves superposed by two types of high-frequency components.The modulus and cross-sectional area are contributing factors to the frequency and peak value of the interference waves.On the other hand,the position with the least interference is determined,to some extent,by the accurate shape of the X-section.
文摘Impact drop tests are routinely used to examine the dynamic performance of rockbolts.Numerous impact tests have been carried out in the past decades on independently designed,constructed and operated testing rigs.Each laboratory has developed testing procedures;thus,the results are often reported in different ways by various laboratories.The inconsistency in testing procedures and reporting formats presents a challenge when comparing results from different laboratories.A series of impact tests of identical rockbolts was carried out using the direct impact method(i.e.the mass free-fall method)on the rigs in four laboratories in different countries.The purpose of these tests was to investigate the level of consistency in the results from the four rigs.Each rig demonstrated a high level of repeatability,but differences existed between the various rigs.The differences would suggest that there is noticeable equipment-dependent bias when test results obtained from different laboratories are compared.It was also observed that the energy dissipated for the plastic displacement of the bolt was smaller than the impact energy in the tests.The average impact load(AIL)and the ultimate plastic displacement(D)of the bolt describe the ultimate dynamic performance of the bolt.In the case where the bolt does not rupture,the specific plastic energy(SPE)is an appropriate parameter in describing the impact performance of the bolt.Two other relevant parameters are the first peak load(FPL)and the initial stiffness(K)of the bolt sample.The information from this test series will guide the formulation of standardised testing procedures for dynamic impact tests of rockbolts.
文摘In dynamic test,sampling rate is high and noise is strong,so a signal sparse decomposition method based on Gabor dictionary is put forward.This method iteratively decomposes the signal with the matching pursuit(MP)algorithm and takes the coherence ratio of the threshold as a condition of iteration termination.Standard MP algorithm is time-consuming,thus an adaptive genetic algorithm is introduced to MP method,which makes computation speed accelerate effectively.Experimental results indicate that this method not only can effectively remove high-frequency noise but also can compress the signal greatly.
基金This research was sponsored by the Science and Technology Project for Policy Guidance of Jiangsu Province(SZ-LYG 2020016).
文摘In this article,dynamic method and static method of testing Poisson's ratio of OSB(Oriented Strand Board)were proposed.Through modal and static numerical analyses,the position where the transverse stress is equal to zero was determined.The binary linear regression method was applied to express the gluing position of the strain gauge as a relational express ion that depended on the length-width ratio and width-thickness ratio of the canti-lever plate.Then the longitudinal and transverse Poisson's ratios of OSB were mea sured by the given dynamic and static methods.In addition,the test results of OSB Poisson's ratio were analyzed with the probability distribution of random variables.The results showed that using the proposed dynamic method and static method,the test results for longitudinal and transverse Poisson's ratios of OSB were quite consistent,despite the gluing position of the strain gauges being different.And these OSB Poisson's ratios were accorded with that obtained by the axial tensile method and the four-point bending method.OSB longitudinal and transverse Poisson's ratios followed Weibull distribution.
基金Supported by Chinese Capital’s Funds for Health Improvement and Research(No.CFH2018-2-4093)National Science and Technology Major Project(No.2018ZX10101-004)。
文摘Dynamic visual acuity test(DVAT)plays a key role in the assessment of vestibular function,the visual function of athletes,as well as various ocular diseases.As the visual pathways conducting dynamic and static signals are different,DVATs may have potential advantages over the traditional visual acuity tests commonly used,such as static visual acuity,contrast sensitivity,and static perimetry.Here,we provide a review of commonly applied DVATs and their several uses in clinical ophthalmology.These data indicate that the DVAT has its unique clinical significance in the evaluation of several ocular disorders.
基金Funded by the National Basic Research Program of China(973 Program) under Grant No.2012CB720100
文摘Volatile organic compounds(VOCs) emitted from three types of carpets used in aircrafts were compared by using headspace and dynamic chamber tests. The headspace samples contained many compounds that were not detected in the dynamic chamber test; in addition, the dominant VOCs found by these two methods were different. The findings indicate that for highly sorptive materials such as carpets, headspace analysis may give inaccurate indication of actual VOC emissions, and it is necessary to conduct dynamic chamber tests over a certain period of time in order to identify the true emission characteristics. From the dynamic chamber tests, 2-ethyl-1-hexanol was the main VOC emitted from all three carpets. The study also examined the emission characteristics of aircraft carpets. In all experiments, total VOC(TVOC) concentration peaked within a few hours after the start of the experiment and was followed by rapid decay. The emission parameters of TVOC emitted by all three carpets were calculated and the simulated data matched the measured data well.
文摘With the continuous advancement of China’s infrastructure construction to the west,according to the geographic situation in the southwest region,such as mountainous areas and complex terrain,the road construction process is inevitably accompanied by earth and rock blasting.To improve the quality and safety of the project,this paper addresses the problems of land and rock blasting faced in the construction of mountain road projects,taking the research of rock dynamic mechanics test as the starting point,and using a combination of theoretical analysis and experimental research methods.The specific research content includes the following parts:dynamic impact compression test(SHPB),dynamic splitting tensile test,and stress-strain curve analysis of the test results,which provides the theoretical basis and numerical parameters for the numerical simulation of future engineering blasting.
基金supported by grants from National&Local Joint Engineering Research Center of Orthopaedic Biomaterials(XMHT20190204007)Shenzhen Key Medical Discipline Construction Fund(No.SZXK023)+4 种基金Shenzhen“San-Ming”Project of Medicine(No.SZSM201612092)Shenzhen Research and Development Project(No.Z2021N054)Guangdong Basic and Applied Basic Research Foundations(No.2019A1515011290,2021A1515012586,2019A1515110983)China Postdoctoral Science Foundation(No.2020M672756)Bethune Charitable Foundation and CSPC Osteoporosis Research Project(No.G-X-2020–1107–21)。
文摘Degradability of bone tissue engineering scaffold that matching the regeneration rate could allow a complete replacement of host tissue.However,the porous structure of biodegradable Mg scaffolds certainly generated high specific surface area,and the three-dimensional interconnected pores provided fast pervasive invasion entrance for the corrosive medium,rising concern of the structural integrity during the degradation.To clarify the structural evolution of the three-dimensional(3D)porous structure,semi-static immersion tests were carried out to evaluate the degradation performance in our previous study.Nevertheless,dynamic immersion tests mimicking the in vivo circulatory fluid through the interconnected porous structure have yet been investigated.Moreover,the effects of dynamic flow rates on the degradation deposition behavior of 3D porous Mg scaffolds were rarely reported.In this study,Mg scaffolds degraded at three flow rates exhibited different degradation rates and deposition process.A flow rate of 0.5 m L/min introduced maximum drop of porosity by accumulated deposition products.The deposition products provided limited protection against the degradation process at a flow rate of 1.0 m L/min.The three-dimensional interconnected porous structure of Mg scaffold degraded at 2.0 m L/min well retained after 14 days showing the best interconnectivity resistance to the degradation deposition process.The dynamic immersion tests disclosed the reason for the different degradation rates on account of flow rates,which may bring insight into understanding of varied in vivo degradation rates related to implantation sites.
基金the National Natural Science Foundation of China (NSFC)(Grant Nos.U22A20596 and 41771066)the Science and Technology Project of Qinghai-Tibet Railway Company (QZ2021-G03)。
文摘As a widely-applied engineering material in cold regions, the frozen subgrade soils are usually subjected to seismic loading, which are also dramatically influenced by the freeze-thaw(F-T)cycles due to the varying temperature. A series of dynamic cyclic triaxial experiments were conducted through a cryogenic triaxial apparatus for exploring the influences of F-T cycles on the dynamic mechanical properties of frozen subgrade clay.According to the experimental results of frozen clay at the temperature of-10℃, the dynamic responses and microstructure variation at different times of F-T cycles(0, 1, 5, and 20 cycles) were explored in detail.It is experimentally demonstrated that the dynamic stress-strain curves and dynamic volumetric strain curves of frozen clay are significantly sparse after 20F-T cycles. Meanwhile, the cyclic number at failure(Nf) of the frozen specimen reduces by 89% after 20freeze-thaw cycles at a low ratio of the dynamic stress amplitude. In addition, with the increasing F-T cycles,the axial accumulative strain, residual deformation,and the value of damage variable of frozen clay increase, while the dynamic resilient modulus and dynamic strength decrease. Finally, the influence of the F-T cycles on the failure mechanisms of frozen clay was discussed in terms of the microstructure variation. These studies contribute to a better understanding of the fundamental changes in the dynamic mechanical of frozen soils exposed to F-T cycles in cold and seismic regions.
基金We acknowledge the funding support from the National Natural Science Foundation of China(Grant Nos.42141010,51879184 and 12172253).
文摘Dynamic tensile failure is a common phenomenon in deep rock practices,and thus accurately evaluating the dynamic tensile responses of rocks under triaxial pressures is of great significance.The Brazilian disc(BD)test is the suggested method by the International Society for Rock Mechanics and Rock Engineering(ISRM)for measuring both the static and dynamic tensile strengths of rock-like materials.However,due to the overload phenomenon and the complex preloading conditions,the dynamic tensile strengths of rocks measured by the BD tests tend to be overestimated.To address this issue,the dynamic BD tensile strength(BTS)of Fangshan marble(FM)under different preloading conditions were measured through a triaxial split Hopkinson pressure bar(SHPB).The fracture onset in BD specimen was captured through a strain gage around the disc center.The discrepancy between the traditional tensile strength(TTS,determined by the peak load P_(f) of the BD specimen)and the nominal tensile strength(NTS,obtained from the load P_(i) when the diametral fracture commences in the tested BD specimen)was applied to quantitatively evaluating the overload phenomenon.The Griffith criterion was used to rectify the calculation of the tensile stress at the disc center under triaxial stress states.The results demonstrate that the overload ratio(s)increases with the loading rate(σ)and decreases with the hydrostatic pressure(σ_(s)).The TTS corrected by the Griffith criterion is independent of theσ_(s)due to the overload phenomenon,while the NTS corrected by the Griffith criterion is sensitive to both the andσ.Therefore,it is essential to modify the tensile stress in dynamic confined BD tests using both the overload correction and the Griffith criterion rectification to obtain the accurate dynamic BTS of rocks.
文摘Al_(2)O_(3)-MgO and Al_(2)O_(3)-spinel low cement castables(LCC-AM and LCC-AS)have been extensively used in steel ladles as working linings.Nevertheless,the use of alumina-magnesia gunning mixes has been mainly kept for maintaining these castable linings,because of high rebound loss,poor green strength,high porosity and short life-span.Thanks to a high BET alumina(MC-G),it is now possible to develop a series of high-performance no-cement or low-cement Al_(2)O_(3)-MgO gunning mixes(NCG-AM or LCG-AM).The paper focuses on the BOF slag resistance of NCG-AM,LCG-AM,LCC-AM and LCC-AS.The corrosion mechanisms of rotary slag samples were studied by scanning electron microscopy(SEM/EDS).The results reveal different microstructures around MgO particles,depending on the four used compositions.Continuous and thicker spinel phases were formed in NCG-AM,which was proved to have the best corrosion resistance after the dynamic slag test.MC-G can provide a high diffusion flux of Al^(3+)in terms of kinetics and hence inhibits Kirkendall porosity around MgO particles.In addition,a continuous spinel phase acts like a pinning nail to reinforce the matrix and thus decreases erosion by slag.In contrast to NCG-AM,the porous spinel phase was found around unreacted MgO particles and some particles were carried away near the interface of LCC-AM and slag.The NCG-AM containing MC-G had been tested in two steel plants,and it extended the service life of the ladles up to 50%.In addition,this study suggests the potential application of NCG-AM as steel ladle linings.
基金National Key Research and Development Project of China,Grant/Award Number:2020YFA0711800National Natural Science Foundation of China,Grant/Award Numbers:12072363,12372373。
文摘The hydrostatic or confining pressure of deep rocks has a significant impact on the mechanical behavior of brittle materials.Especially when confining pressure is applied,the mechanical properties of rock materials will undergo significant changes.Considering that the process of shale sample subjected to impact load is in a closed container in the dynamic triaxial SHPB test,the failure process of the sample cannot be observed.Meanwhile,the activation volume of the shale sample would be large and local failure would occur in the test under the high strain rate loading.Therefore,thefinite element model of shale considering the bedding effect under confining pressure was established in this study.Taking shale materials with different bedding dip angles as simulation objects,the dynamic failure characteristics of shale were studied using the dynamic analysis software ANSYS/LS‐DYNA from three aspects:stress‐strain curve,failure growth process,and failure morphology.The research results obtained can serve as the key technical parameters for deep resource extraction.
文摘Based on three kinds of dynamic test of MEMS,a dynamic system for the vibration test of micro machined gyroscope based on high speed photography is introduced.Firstly,the architecture of the system hardware is introduced.Secondly,the image tracking performance is compared by the test using the template matching algorithm,the mean shift algorithm and the SURF algorithm.The vibration curve shows that high speed photograph combined with SURF algorithm is faster,more accurate,and more suitable for the vibration test of micro machined gyroscope.After the frequency analysis and related interpolation,more characteristics of micro gyroscope can be obtained.
基金Funded by the National Natural Science Foundation of China(No.61675137)。
文摘The dynamic characteristics of high sensitivity temperature sensor are studied by using siphon method to fill the air hole near the core of the hollow photonic crystal fiber with Cargille matching liquid,and the two ends are fused with single-mode fiber in this work.We analyzed the working principle of filled photonic crystal fiber sensor by using the standard coupling mode theory of directional coupler.The coupling process was simulated by COMSOL software.When the photonic crystal fiber filled with 10 mm liquid was scanned by tunable laser,the temperature sensitivity was 7.50 nm /℃,the average temperature response time was 0.317 s,the average release time was 3.732 s,and the temperature variation linearity was 100%.The experimental results show that the liquid filled photonic crystal fiber has the advantages of high temperature sensitivity,fast response time and good linearity.
文摘Parameter identification of Pasternak foundation models(PFM)is never satisfactory,which discourages the application and popularization of PFM.In the present study,an energy-based model to predict the dynamic foundation coefficients was proposed using the vibration kinetic energy and potential energy of a Pasternak foundation-rigid plate system.On the basis of the Pasternak foundation,the relationship among the natural frequency,dynamic foundation coefficients,rigid plate configuration,and vibrating soil equivalent mass per unit area was considered.To obtain the natural frequencies of the Pasternak foundation-rigid plate system,dynamic tests were performed.Using two or more dynamic test results of various rigid plates on a foundation,a set of equations of dynamic foundation coefficients was set up to directly identify the foundation coefficients and equivalent mass per unit area of vibrating soil.The feasibility of the proposed method was verified by comparing it with the outdoor and indoor test results and finite element analysis results.When the proposed method is used to obtain the dynamic parameters,PFM can be generalized and applied more widely in engineering practice.
基金This work was supported by the National Natural Science Foundation of China(Nos.41941018,52074164,and 42077267);the Natural Science Foundation of Shandong Province,China(Nos.2019SDZY04 and ZR2020JQ23)the Project of Shandong Province Higher Educational Youth Innovation Science and Technology Program,China(No.2019KJG013).
文摘In deep underground engineering,rock burst and other dynamic disasters are prone to occur due to stress concentration and energy accumulation in surrounding rock.The control of dynamic disasters requires bolts and cables with high strength,high elongation,and high energy-absorbing capacity.Therefore,a constant resistance energy-absorbing(CREA)material is developed.In this study,the dynamic characteristics of the new material are obtained via the drop hammer tests and the Split Hopkinson Pressure Bar(SHPB)tests of the new material and two common bolt(CB)materials widely used in the field.The test results of drop hammer test and SHPB test show that the percentage elongation of CREA material is more than 2.64 and 3.22 times those of the CB material,and the total impact energy acting on CREA material is more than 18.50 and 21.84 times,respectively,indicating that the new material has high elongation and high energy-absorbing capacity.Subsequently,the CREA bolts and cables using the new material are developed,which are applied in roadways with high stress and strong dynamic disturbance.The field monitoring results show that CREA bolts and cables can effectively control the surrounding rock deformation and ensure engineering safety.
基金This study was supported in part by the Funding of Science for Earthquake Resilience(Grant Nos.XH20057,XH21034,XH21036Y)the National Natural Science Foundation of China(Nos.51778590,51408567)+1 种基金the grant of the Fundamental Research Funding for the Institute of Earthquake Forecasting,China Earthquake Administration(Grant Nos.2018IESLZ06,2016IESLZ01)the Science and Technology Projects Funding for Lanzhou City(Grant No.2018-1-123).
文摘To effectively improve the poor engineering properties of loess and enhance its seismic performance,the industrial by-product lignin is used as a modified material.Based on lots of dynamic triaxial tests,the dynamic elastic modulus and damping ratio of lignin-modified loess were tested.The effects of lignin content on the dynamic elastic modulus and damping ratio of lignin-modified loess were analyzed.Combined with scanning electron microscopy(SEM)and X-ray diffraction(XRD),the microscopic mechanism of lignin to improve the dynamic properties of loess was studied.The results show that lignin can effectively modify the dynamic deformation of loess under dynamic load.Under the same dynamic stress condition,the dynamic strain of lignin-modified loess is smaller than compacted loess.The dynamic elastic modulus of modified loess with different lignin content are quite different,but both decrease with the increase of dynamic strain.And the dynamic elastic modulus of modified loess is greater than compacted loess.The maximum dynamic elastic modulus of modified loess with a lignin content of 1%are significantly greater than others.Under the same dynamic strain condition,the damping ratio of lignin-modified loess is smaller than compacted loess.Lignin can effectively fill loess pores and cement loess particles.Compared with compacted loess,no new mineral components are generated in the lignin-modified loess.The optimum lignin content of dynamics characteristic of modified loess is present,and the optimum lignin content is 1%.
基金Supported by:Scientific Research Program of China General Nuclear Power Corporation(CGN)under Grant No.K-A2017.054Postgraduate Research and Practice Innovation Program of Jiangsu Province under Grant No.KYCX19_0093。
文摘Research to reliably predict the seismic response of nuclear power stations with a pile-raft foundation is needed to meet the high safety requirements of nuclear power stations.In this study,a scaled superstructure with a 4×3 pile-raft foundation,which is constructed in Shanxi kaolin clay,is modelled.Accordingly,the characteristics of seismic response for nuclear power stations with a pile-raft foundation are analyzed using dynamic centrifuge tests.In particular,multiple earthquake motions with different magnitudes and frequency properties are utilized to map the relationship between structural response and properties of earthquake motions.The results show that the seismic response of the soil,raft,and structure are significantly affected by the natural frequency and magnitude of the earthquake motion.The soil surface acceleration is lower than the raft acceleration.The results provide a reliable reference to better understand the seismic response of nuclear power stations.
