Time-domain dynamic constitutive model suitable for mucky soil site seismic response

Soil nonlinear behavior displays noticeable effects on the site seismic response.This study proposes a new functional expression of the skeleton curve to replace the hyperbolic skeleton curve.By integrating shear modulus and combining the dynamic skeleton curve and the damping degradation coefficient,the constitutive equation of the logarithmic dynamic skeleton can be obtained,which considers the damping effect in a soil dynamics problem.Based on the finite difference method and the multi-transmitting boundary condition,a 1D site seismic response analysis program called Soilresp1D has been developed herein and used to analyze the time-domain seismic response in three types of sites.At the same time,this study also provides numerical simulation results based on the hyperbolic constitutive model and the equivalent linear method.The results verify the rationality of the new soil dynamic constitutive model.It can analyze the mucky soil site nonlinear seismic response,reflecting the deformation characteristics and damping effect of the silty soil.The hysteresis loop area is more extensive,and the residual strain is evident.

A viscoelastic-plastic constitutive model with Mohr-Coulomb yielding criterion for sea ice dynamics

A new viscoelastic-plastic （VEP） constitutive model for sea ice dynamics was developed based on continuum mechanics. This model consists of four components： Kelvin-Vogit viscoelastic model, Mohr-Coulomb yielding criterion, associated normality flow rule for plastic rehololgy, and hydrostatic pressure. The numerical simulations for ice motion in an idealized rectangular basin were made using smoothed particle hydrodynamics （SPH） method, and compared with the analytical solution as well as those based on the modified viscous plastic（VP） model and static ice jam theory. These simulations show that the new VEP model can simulate ice dynamics accurately. The new constitutive model was further applied to simulate ice dynamics of the Bohai Sea and compared with the traditional VP, and modified VP models. The results of the VEP model are compared better with the satellite remote images, and the simulated ice conditions in the JZ20-2 oil platform area were more reasonable.

Constitutive model of rock under static-dynamic coupling loading and experimental investigation

The importance of study on constitutive model of statically loaded rock experiencing dynamic load is set forth, and the studying methods on dynamic constitutive model are classified according to the current studying status. By way of combining statistic damage model and viscoelastic model, uni-axial and multi-axial constitutive models of statically loaded rock experiencing dynamic load (static-dynamic coupling constitutive model) under intermediate strain rate are established. The verification experiment on 2D constitutive model under different static stress and dynamic stress with different frequencies is designed and performed. It is found that there is a good agreement between the experimental stress-strain curves and the theoretical stress-strain curves.

Dynamic Analysis of Submarine Pipelines on an Elastic / Viscoelastic Foundation

This paper presents a new finite element method for solving static and dynamic problems in laying operation of pipelines. The effect of the viscoelastic soil behavior is considered by using the Pasternak foundation model. Some examples are also presented.

Dynamic properties of structures with dampers modelled using fractional order derivatives

The focus of this paper is on determination of the dynamic parameters of structural systems with viscoelastic (VE) dampers described by Maxwell rheological models. Such parameters could be obtained after solving the appropriately defined nonlinear eigenvalue problem for frames with VE dampers. The solution to the nonlinear eigenvalue problem is obtained by equating to zero the determinant of the considered system of equations. Apart from complex conjugate eigenvalues, the real ones occurred when dampers that are described by the classic Maxwell model, are also determined.

ELASTOPLASTIC MODEL DESCRIBING CYCLIC CREEPING BEHAVIOUR OF SOFT CLAYS

The elastoplastic model in the deviatoric stress space is constructed to describe the cyclic undrained creeping behaviour of soft clays under cyclic stress by using Mises yield criterion and the concept of a field of hardening moduli. Furthermore, the effect of model parameters on the deformation is studied, and a method is given to determine quantitatively model parameters from results of cyclic triaxial tests of the saturated soft clay.

基于Pasternak海床模型的椭圆余弦波浪荷载作用下埋置管线动力响应解析解

通过两阶段分析方法,针对椭圆余弦波作用下埋置管线的动力响应进行了探究。基于椭圆余弦波理论,采用Biot固结方程推导了非线性波浪作用下浅水区埋置管线所受的周期波浪压力;将管线考虑为动力Pasternak海床模型上的Euler-Bernoulli梁,将波浪动荷载施加到管线上获得无限长管线的动力响应偏微分控制方程;利用Fourier变换和Laplace变换并借助卷积定理得到管线挠度、速度、加速度、转角、弯矩和剪力的动力响应解。通过与三维有限元数值算例及既有试验结果对比验证了解析解的正确性与适用性。对椭圆余弦波作用下埋置管线的动力响应特性进行了敏感参数分析,结果表明:波浪高度H显著影响了波面形状与海床内波浪力大小,不同浪高下管线转角、弯矩和剪力的变化更明显,而挠度、速度和加速度响应敏感性则较低。

DRUCKER-PRAGER YIELD CRITERIA IN VISCOELASTIC-PLASTIC CONSTITUTIVE MODEL FOR THE STUDY OF SEA ICE DYNAMICS

Based on the characteristics of sea ice drifting and ridging at meso-small scale, the Drucker-Prager (D-P) yield criteria was introduced into the Viscoelastic-Plastic (VEP) constitutive model for the study of sea ice dynamics. In this model, the Kelvin–Vogit viscoelastic model was adopted in the elastic stage, and the associated normal flow rule was used in the plastic stage. Using the VEP model, the sea ice ridging process was simulated in an idealized rectangular basin, and the simulation results show that the simulated ice ridge thickness is consistent with the analytical solution. Moreover, the VEP model with the D-P yield criteria was also applied for the sea ice simulation of Bohai Sea, and the ice thickness, concentration, velocity, and ice stress were obtained in 48 h. The simulated thickness distributions agree well with the satellite images. The singular problem in the Mohr–Coulomb (M-C) yield criteria was overcome by the D-P yield criteria, and the computational efficiency was also improved. In the numerical simulations described above, the smoothed particle hydrodynamics was applied.

考虑细观损伤的推进剂粘弹性多尺度本构模型研究

为了深入研究固体推进剂细观损伤行为及对其宏观力学性能的影响,在223~333 K温度下对硝酸酯增塑聚醚推进剂(NEPE)推进剂开展了单轴拉伸和应力松弛试验,获得了相应的应力应变曲线及松弛模量主曲线。在有限变形下开发了考虑细观损伤的非线性粘弹性本构模型,该模型通过将微空洞演化与温度、应变率、围压及循环加载损伤等因素关联实现对推进剂力学性能的多尺度分析。通过有限元软件ABAQUS对模型进行了二次开发,并基于试验数据确定了模型参数,之后将模型应用于预测推进剂在不同加载下的力学响应。结果表明,该模型能够准确预测推进剂在宽温(223~333 K)和加载速率(1~200 mm·min^(-1))下的单轴拉伸响应,并且适用于循环加载、围压试验和双轴加载试验,验证了该模型在复杂应力状态下的有效性。该模型所需参数较少且易于嵌入商用软件,可为发动机推装药结构完整性的多尺度分析提供一定的理论指导。

各向同性磁流变弹性体磁相关非线性动态力学行为的本构模型

各向同性磁流变弹性体是一种将磁性颗粒随机掺入到聚合物基体中制备而成的智能材料。在磁场作用下,其模量发生快速、可逆、连续变化,在振动控制领域显示出良好的应用前景。实验结果表明,各向同性磁流变弹性体的动态力学行为具有很强的频率、应变幅值和磁场相关性。尽管上述行为对于其潜在应用具有重要的影响,但目前关于各向同性磁流变弹性体磁相关非线性动态力学行为的理论研究则关注不够。为准确评价各向同性磁流变弹性体的动态力磁耦合行为,并指导其相关产品的设计,本文建立了一个基于连续介质力学理论,反映各向同性磁流变弹性体磁相关非线性动态力学行为的本构模型。随后,开发了和本构模型对应的数值实现算法,并对模型的预测能力进行了验证。该模型有助于深入理解各向同性磁流变弹性体磁相关非线性动态力学行为的潜在力学机制。此外,该模型有助于指导基于各向同性磁流变弹性体产品的设计和应用。

冻土动力学研究综述

冻土动力学是寒区岩土工程所要考虑的重要内容,是研究冻土抗震和抗长期循环荷载的理论基础。本文主要介绍了冻土动力学参数的测试方法,回顾了冻土动力学参数、冻土动强度、冻土动蠕变破坏特征和冻土动蠕变强度的研究进展,并对部分冻土动态本构模型和动蠕变模型进行了简单的介绍,最后对冻土动力学的发展趋势进行了展望。

基于触发式黏塑性元件的黏性土黏弹塑性动本构模型

基于黏性、弹性和塑性元件构造的动本构模型往往存在预测效果较差,不能完全反映黏性土的黏性、弹性、塑性的缺点。通过引入一种触发式的黏塑性元件Ψ,以残余变形为切入点,提出了一个考虑振动稳定和振动衰化现象的黏性土黏弹塑性动本构模型,并通过动三轴试验进行了验证。该动本构模型不但能够描述动荷载作用下黏性土残余应变的发展规律,且能合理地预测动应变的发展情况。结果表明,试样在动荷载作用下,存在元件Ψ的黏滞系数随振动周期增长而衰减的现象,且衰减情况和含水率密切相关。最优含水率是影响振动稳定和振动衰化现象的重要参数,当含水率小于最优含水率时,试样变形表现为振动稳定,此时元件Ψ黏滞系数的变化可以忽略不计;当含水率大于最优含水率时,试样变形表现为振动衰化,此时元件Ψ黏滞系数的变化不可忽略。

河道淤泥气泡混合轻质土动力特性及本构模型研究

河道淤泥气泡混合轻质土(FMLSS)是一种较新颖的疏浚淤泥在工程领域废物再利用方式。利用室内动三轴试验分析了不同的围压、含水率、水泥掺入量和气泡含量条件下FMLSS动应力应变骨干曲线的变化规律。结果表明,FMLSS动应力应变骨干曲线呈现先线性增加然后逐渐趋稳的规律,符合双曲线模型;相比围压、含水率和气泡含量的影响,水泥掺入量对FMLSS动应力应变关系的影响更显著。考虑到FMLSS力学性质的复杂性,对原有Hardin-Drnevich模型进行改进,提出修正系数k及其函数表达,再由拟合曲线反推求出k值并对其变化规律进行分析,发现k值随围压、水泥掺入量和气泡含量的增加而减小,随含水率的增加而增大。根据拟合结果对k值函数中的待定系数进一步优化,最后建立起符合FMLSS动力特性的修正Hardin-Drnevich模型,为其稳定分析、灾变预测及工程应用提供支撑。

垂直弹射系统中缓冲及反后坐效应的建模方法

针对垂直弹射过程中,由缓冲以及弹射后坐引发的对发射性能与阵地产生的负面影响问题,从缓冲吸能角度,提出按缓冲器的塑性应变能-压缩量关系曲线拟合并求导解算缓冲力-压缩量关系模型的方法,有效规避了缓冲力波动所造成的拟合漂移问题,并据此构造了模拟缓冲器的线弹性-塑性弹簧模型;依据弹射试验数据,反演了反后坐效应的动态数据,据此构造了模拟反后坐效应的非线性粘弹性-塑性弹簧模型;通过力元、状态变量及牛顿迭代法的有机结合,在动力学模型中实现了上述二模型的高效解算。仿真结果表明:两模型计算稳定高效且缓冲特性与有限元仿真结果高度吻合、反后坐效应和试验数据符合良好,这验证了数据处理方法的有效性和建模方法的可信性,为后续含缓冲和反后坐效应的弹射动力学仿真提供了一种稳定而又可信的建模思路。

Dynamic Deformation of Frozen Soil at a High Strain Rate:Experiments and Damage-Coupled Constitutive Model

The dynamic compressive deformation of frozen soil was investigated by conducting the split-Hopkinson pressure bar(SHPB)experiments at three temperatures and different high strain rates,and the dynamic stress–strain responses and failure modes of the frozen soil were analyzed.The experimental results demonstrate that the frozen soil exhibits evident dependence on the strain rate and temperature under the dynamic loading condition.The dynamic compressive stress–strain curve of the frozen soil was divided into three parts:the linear,nonlinear rising,and strain softening parts.The nonlinear rising and strain softening parts were both caused by the damage attributed to the debonding between the ice particles and soil matrix,from which a rate-dependent damage evolution equation was obtained.Moreover,a damage-coupled dynamic viscoelastic constitutive model of frozen soil at high strain rate was derived.A comparison between the theoretically predicted results and the experimental ones showed that the developed dynamic viscoelastic model could well describe the dynamic mechanical behavior of frozen soil at high strain rate.

地震作用下大直径嵌岩单桩动力响应数值分析

以大直径嵌岩单桩为研究对象,对地震荷载作用时桩、土、岩的变形规律及桩基刚度进行分析,在有限元-无限元耦合数值模拟中引入土体非线性黏弹性本构模型与岩体损伤本构模型来描述桩周土、岩介质刚度随应变衰减的特性。数值模拟结果表明,大直径嵌岩单桩位移、加速度等动力响应,土体非线性滞回特性以及岩石损伤程度等显著受到桩基嵌岩深度、岩石风化程度和地震烈度等因素的影响,在设计时应深入分析。

考虑围压效应的冻结砂土动态本构模型研究

为描述主动围压作用下冻结砂土的动态力学特性,通过在朱-王-唐模型的非线性体上串联塑性体,建立了能够考虑围压效应的冻结砂土动态损伤本构模型;分析了损伤参数对应力-应变曲线特征、屈服点、峰值应力和峰值应变的影响规律,基于冻结砂土动力学试验数据确定了模型参数;通过将模型和试验数据进行对比,并对不同试验条件下模型的预测误差进行分析,验证了模型的适用性和准确性。结果表明,损伤参数对应力-应变曲线弹性阶段和屈服点无明显影响,而对塑性阶段和破坏阶段的影响较为显著,本构模型预测的应力-应变曲线与试验结果具有较好的一致性。模型能够预测围压引起冻结砂土塑性阶段占比大和屈服点明显的特征,且能够描述围压对冻结砂土动态强度的增强效应;不同负温和主动围压条件下,模型对峰值应力和屈服强度的预测效果优于峰值应变和屈服应变。

基于细观结构的复合固体推进剂含损伤黏弹性本构模型

复合固体推进剂的宏观力学性能与其细观组分及损伤密切相关,基于复合固体推进剂变形过程中细观结构的演化,开发复合固体推进剂含孔洞损伤的宏细观本构模型。该模型考虑了推进剂温度和应变率的相关性,并能够描述推进剂拉伸和压缩状态下不同的力学响应。通过不同温度和不同应变率下的拉伸和压缩试验,验证本构模型的有效性。基于有限元分析软件提供的用户材料子程序接口UMAT,对非线性黏弹性本构模型进行二次开发,并应用于低温点火工况下药柱结构完整性分析,结果表明药柱在低温点火条件下安全系数为2.56,结构完整性满足要求。与基于Prony级数的线性黏弹性本构模型进行对比分析,表明新建立的本构模型能够更准确地进行复合固体推进剂药柱的结构分析。

循环加载下复合推进剂的非线性热粘弹性本构模型

复合推进剂在动态加载下伴随着自热效应,即存在明显的温度升高现象。为了定量描述这种热力耦合特性,基于不可逆热力学理论建立了非线性热粘弹性本构模型和相应的数值算法,编写了基于Abaqus的用户子程序,并通过实验验证了数值算法的正确性。研究结果发现,非线性本构模型成功地描述了复合推进剂在不同加载模式下的非线性力学行为和自热效应,自热效应对复合推进剂的力学行为有着直接影响,与不考虑自热效应相比,循环加载下应力-应变滞回圈的斜率降低显著,表明力学性能已受到自身温度升高的影响。结果表明,考虑自热效应的热力耦合本构模型能更准确地描述复合推进剂的循环力学行为,滞回圈的形状与实验结果更为吻合,斜率误差在10%以内。

基于CT动态扫描的冻土细观二元介质本构模型

开展荷载作用下冻土的宏-细观力学特性试验研究,对揭示冻土细观力学特性和建立宏-细观力学性质之间的联系具有重要的意义。利用重新研制的可配合医用CT进行扫描的冻土三轴仪开展了不同温度、围压条件下的饱和冻土常规三轴压缩试验研究,其中在轴向加载过程中共对试样进行了8次CT扫描。通过对CT数平均值和应力应变曲线的分析发现:当应力应变曲线表现为应变硬化时,冻土试样CT数平均值随着轴向应变的增加而线性降低;当应力应变曲线表现为应变软化时,试样CT数平均值在软化阶段加速降低。结合动态扫描过程中试样CT数平均值的变化规律,提出利用试样CT数平均值对体积破损率进行表征,建立了饱和冻土的二元介质细观本构模型,并利用试验数据对建立的本构模型进行了验证,结果表明提出的本构模型能够很好的预测冻土在常规三轴应力路径下的应力应变行为。