This paper discusses the seismic analysis of concrete dams with consideration of material nonlinearity. Based on a consistent rate-dependent model and two thermodynamics-based models, two thermodynamics-based rate-dep...This paper discusses the seismic analysis of concrete dams with consideration of material nonlinearity. Based on a consistent rate-dependent model and two thermodynamics-based models, two thermodynamics-based rate-dependent constitutive models were developed with consideration of the influence of the strain rate. They can describe the dynamic behavior of concrete and be applied to nonlinear seismic analysis of concrete dams taking into account the rate sensitivity of concrete. With the two models, a nonlinear analysis of the seismic response of the Koyna Gravity Dam and the Dagangshan Arch Dam was conducted. The results were compared with those of a linear elastic model and two rate-independent thermodynamics-based constitutive models, and the influences of constitutive models and strain rate on the seismic response of concrete dams were discussed. It can be concluded from the analysis that, during seismic response, the tensile stress is the control stress in the design and seismic safety evaluation of concrete dams. In different models, the plastic strain and plastic strain rate of concrete dams show a similar distribution. When the influence of the strain rate is considered, the maximum plastic strain and plastic strain rate decrease.展开更多
Road material constitutive model is the essential condition of pavement structure design,calculation,and maintenance decision.Experts have conducted in-depth studies on the problems and proposed many meaningful consti...Road material constitutive model is the essential condition of pavement structure design,calculation,and maintenance decision.Experts have conducted in-depth studies on the problems and proposed many meaningful constitutive models.However,these constitutive models have not been summarized and no uniform conclusion on the applicability of them is reported in the academic circle.The linear elastic model based on Hooke's law is still used in pavement structure design.This paper systematically reviewed the existing constitutive models that reflect the materials'mechanical properties and used for pavement structure calculation.These constitutive models were divided into three categories:linear,nonlinear,and damage models under repeated loads.The applicable conditions,parameter determination methods,advantages,and disadvantages of each model were introduced.Moreover,the model's feasibility in structural design and calculation was analyzed.Follow-up studies should focus on the parameter determination standard of viscoelastic constitutive models,the extension of the 1D constitutive model to 3D state,and the nonlinear constitutive models related to stress-strain state to drive the application of the constitutive models in pavement structure calculation and design.Furthermore,to evaluate the life cycle service performance of road materials and structures,establishing the pavement damage model from the structure perspective will be the future direction.展开更多
SiO_(2)-particle reinforced silicon rubber composite(SP-RSRC)is a widely utilized material that offers shock absorption protection to various engineering structures in impact environments.This paper presents a compreh...SiO_(2)-particle reinforced silicon rubber composite(SP-RSRC)is a widely utilized material that offers shock absorption protection to various engineering structures in impact environments.This paper presents a comprehensive investigation of the mechanical behavior of SP-RSRC under various strain rates,employing a combination of experimental,theoretical,and numerical analyses.Firstly,quasi-static and dynamic compression tests were performed on SP-RSRC utilizing a universal testing machine and split Hopkinson pressure bar(SHPB)apparatus.Nonlinear stress-strain relationships of SP-RSRC were obtained for strain rates ranging from 1×10^(−3) to 3065 s^(−1).The results indicated that the composite showed evident strain rate sensitivity,along with nonlinearity.Then,a nonlinear visco-hyperelastic constitutive model was developed,consisting of a hyperelastic component utilizing the 3rd-order Ogden energy function and a viscous component employing a rate-dependent relaxation time scheme.The model accurately characterized the dynamic mechanical response of SP-RSRC,effectively mitigating the challenge of calibrating an excessive number of material parameters inherent in conventional viscoelastic models.Furthermore,the simplified rubber material(SRM)model,integrated within the LS-DYNA software,was chosen to depict the mechanical properties of SP-RSRC in numerical simulations.The parameters of the SRM model were further calibrated based on the strain-stress relationships of SP-RSRC,as predicted by the developed nonlinear visco-hyperelastic constitutive model.Finally,an inverse ballistic experiment using a single-stage air gun was conducted for SP-RSRC.Numerical simulations of SHPB experiments and the inverse ballistic experiment were then performed,and the reliability of the calibrated SRM model was verified by comparing the results of experiments and numerical simulations.This study offers a valuable reference for the utilization of SP-RSRC in the realm of impact protection.展开更多
This article aims to develop a head pursuit （HP） guidance law for three-dimensional hypervelocity interception, so that the effect of the perturbation induced by seeker detection can be reduced. On the basis of a no...This article aims to develop a head pursuit （HP） guidance law for three-dimensional hypervelocity interception, so that the effect of the perturbation induced by seeker detection can be reduced. On the basis of a novel HP three-dimensional guidance model, a nonlinear variable structure guidance law is presented by using Lyapunov stability theory. The guidance law positions the interceptor ahead of the target on its tlight trajectory, and the speed of the interceptor is required to be lower than that of the target, A numerical example of maneuvering ballistic target interception verifies the rightness of the guidance model and the effectiveness of the proposed method.展开更多
This paper presents ordered rate nonlinear constitutive theories for thermoviscoelastic fluids based on Classical Continuum Mechanics (CCM). We refer to these fluids as classical thermoviscoelastic polymeric fluids. T...This paper presents ordered rate nonlinear constitutive theories for thermoviscoelastic fluids based on Classical Continuum Mechanics (CCM). We refer to these fluids as classical thermoviscoelastic polymeric fluids. The conservation and balance laws of CCM constitute the core of the mathematical model. Constitutive theories for the Cauchy stress tensor are derived using the conjugate pair in the entropy inequality, additional desired physics, and the representation theorem. The constitutive theories for the Cauchy stress tensor consider convected time derivatives of Green’s strain tensor or the Almansi strain tensor up to order n and the convected time derivatives of the Cauchy stress tensor up to order m. The resulting constitutive theories of order (m, n) are based on integrity and are valid for dilute as well as dense polymeric, compressible, and incompressible fluids with variable material coefficients. It is shown that Maxwell, Oldroyd-B, and Giesekus constitutive models can be described by a single constitutive theory. It is well established that the currently used Maxwell and Oldroyd-B models predict zero normal stress perpendicular to the flow direction. It is shown that this deficiency is a consequence of not retaining certain generators and invariants from the integrity (complete basis) in the constitutive theory and can be corrected by including additional generators and invariants in the constitutive theory. Similar improvements are also suggested for the Giesekus constitutive model. Model problem studies are presented for BVPs consisting of fully developed flow between parallel plates and lid-driven cavities utilizing the new constitutive theories for Maxwell, Oldroyd-B, and Giesekus fluids. Results are compared with those obtained from using currently used constitutive theories for the three polymeric fluids.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 90510018)
文摘This paper discusses the seismic analysis of concrete dams with consideration of material nonlinearity. Based on a consistent rate-dependent model and two thermodynamics-based models, two thermodynamics-based rate-dependent constitutive models were developed with consideration of the influence of the strain rate. They can describe the dynamic behavior of concrete and be applied to nonlinear seismic analysis of concrete dams taking into account the rate sensitivity of concrete. With the two models, a nonlinear analysis of the seismic response of the Koyna Gravity Dam and the Dagangshan Arch Dam was conducted. The results were compared with those of a linear elastic model and two rate-independent thermodynamics-based constitutive models, and the influences of constitutive models and strain rate on the seismic response of concrete dams were discussed. It can be concluded from the analysis that, during seismic response, the tensile stress is the control stress in the design and seismic safety evaluation of concrete dams. In different models, the plastic strain and plastic strain rate of concrete dams show a similar distribution. When the influence of the strain rate is considered, the maximum plastic strain and plastic strain rate decrease.
基金funded by the National Key of Research and Development Plan under grant no.2020YFA0714300.
文摘Road material constitutive model is the essential condition of pavement structure design,calculation,and maintenance decision.Experts have conducted in-depth studies on the problems and proposed many meaningful constitutive models.However,these constitutive models have not been summarized and no uniform conclusion on the applicability of them is reported in the academic circle.The linear elastic model based on Hooke's law is still used in pavement structure design.This paper systematically reviewed the existing constitutive models that reflect the materials'mechanical properties and used for pavement structure calculation.These constitutive models were divided into three categories:linear,nonlinear,and damage models under repeated loads.The applicable conditions,parameter determination methods,advantages,and disadvantages of each model were introduced.Moreover,the model's feasibility in structural design and calculation was analyzed.Follow-up studies should focus on the parameter determination standard of viscoelastic constitutive models,the extension of the 1D constitutive model to 3D state,and the nonlinear constitutive models related to stress-strain state to drive the application of the constitutive models in pavement structure calculation and design.Furthermore,to evaluate the life cycle service performance of road materials and structures,establishing the pavement damage model from the structure perspective will be the future direction.
文摘SiO_(2)-particle reinforced silicon rubber composite(SP-RSRC)is a widely utilized material that offers shock absorption protection to various engineering structures in impact environments.This paper presents a comprehensive investigation of the mechanical behavior of SP-RSRC under various strain rates,employing a combination of experimental,theoretical,and numerical analyses.Firstly,quasi-static and dynamic compression tests were performed on SP-RSRC utilizing a universal testing machine and split Hopkinson pressure bar(SHPB)apparatus.Nonlinear stress-strain relationships of SP-RSRC were obtained for strain rates ranging from 1×10^(−3) to 3065 s^(−1).The results indicated that the composite showed evident strain rate sensitivity,along with nonlinearity.Then,a nonlinear visco-hyperelastic constitutive model was developed,consisting of a hyperelastic component utilizing the 3rd-order Ogden energy function and a viscous component employing a rate-dependent relaxation time scheme.The model accurately characterized the dynamic mechanical response of SP-RSRC,effectively mitigating the challenge of calibrating an excessive number of material parameters inherent in conventional viscoelastic models.Furthermore,the simplified rubber material(SRM)model,integrated within the LS-DYNA software,was chosen to depict the mechanical properties of SP-RSRC in numerical simulations.The parameters of the SRM model were further calibrated based on the strain-stress relationships of SP-RSRC,as predicted by the developed nonlinear visco-hyperelastic constitutive model.Finally,an inverse ballistic experiment using a single-stage air gun was conducted for SP-RSRC.Numerical simulations of SHPB experiments and the inverse ballistic experiment were then performed,and the reliability of the calibrated SRM model was verified by comparing the results of experiments and numerical simulations.This study offers a valuable reference for the utilization of SP-RSRC in the realm of impact protection.
文摘This article aims to develop a head pursuit （HP） guidance law for three-dimensional hypervelocity interception, so that the effect of the perturbation induced by seeker detection can be reduced. On the basis of a novel HP three-dimensional guidance model, a nonlinear variable structure guidance law is presented by using Lyapunov stability theory. The guidance law positions the interceptor ahead of the target on its tlight trajectory, and the speed of the interceptor is required to be lower than that of the target, A numerical example of maneuvering ballistic target interception verifies the rightness of the guidance model and the effectiveness of the proposed method.
文摘This paper presents ordered rate nonlinear constitutive theories for thermoviscoelastic fluids based on Classical Continuum Mechanics (CCM). We refer to these fluids as classical thermoviscoelastic polymeric fluids. The conservation and balance laws of CCM constitute the core of the mathematical model. Constitutive theories for the Cauchy stress tensor are derived using the conjugate pair in the entropy inequality, additional desired physics, and the representation theorem. The constitutive theories for the Cauchy stress tensor consider convected time derivatives of Green’s strain tensor or the Almansi strain tensor up to order n and the convected time derivatives of the Cauchy stress tensor up to order m. The resulting constitutive theories of order (m, n) are based on integrity and are valid for dilute as well as dense polymeric, compressible, and incompressible fluids with variable material coefficients. It is shown that Maxwell, Oldroyd-B, and Giesekus constitutive models can be described by a single constitutive theory. It is well established that the currently used Maxwell and Oldroyd-B models predict zero normal stress perpendicular to the flow direction. It is shown that this deficiency is a consequence of not retaining certain generators and invariants from the integrity (complete basis) in the constitutive theory and can be corrected by including additional generators and invariants in the constitutive theory. Similar improvements are also suggested for the Giesekus constitutive model. Model problem studies are presented for BVPs consisting of fully developed flow between parallel plates and lid-driven cavities utilizing the new constitutive theories for Maxwell, Oldroyd-B, and Giesekus fluids. Results are compared with those obtained from using currently used constitutive theories for the three polymeric fluids.
基金supported by the National Natural Science Foundation of China (12102424, 12202434, and 11972343)the Anhui Key R&D Program of China (202104a5020009)+1 种基金the Fundamental Research Funds for the Central Universities(WK2090000030)the Fellowship of China Postdoctoral Science Foundation (2022M713045)。
