Quasi-Hamiltonian principle of liquid-filled elastic body dynamics

Liquid-filled elastic body dynamics is an important branch of fluid-solid coupling mechanics. It deals with the study of motion of a body and the liquid contained in the body under the interaction between the two,for example,a liquid-filled satellite,a fuel tank of an airplane,etc. The research on liquid-filled elastic body dynamics is usually done by the variational method since the method has a feature of treating things as a whole. Considering the elastic motion of the liquid-filled body and the surface tension effect on the liquid-gas interface,liquid-solid interface and gas-solid interface,the present paper establishes a quasi-Hamiltonian variational principle for the above-mentioned system. After finding the stationary-value conditions of its functional obtained,a complete system of governing equations consisting of the stationary value conditions,preconditions and constraint conditions is established,and then the equations are reduced into some known ones in a special case.

Dynamic response of liquid-filled rectangular tank with elastic appendages under pitching excitation

Nonlinear dynamics of liquid-filled rectangular tank with elastic appendages are studied. Based on the assumption of ideal fluid, the coupling dynamic equations of rigid tank, elastic appendages and liquid fuel are derived using H-O principle. In the case of pitch excitation, the modified potential function and wave height function are introduced to describe the moving boundary of fluid, then Galerkin＇s method is used to discretize the dynamic equations into ordinary differential equations. The natural frequencics of the coupling system are formulated in liquid depth, the length of the tank, etc. The formulae are confirmed by numerical simulations, which also show that the effects of liquid and elastic appendages on the attitude angular of rigid.

BOUNDARY ELEMENT METHOD FOR MOVING AND ROLLING CONTACT OF 2D ELASTIC BODIES WITH DEFECTS

A scheme of boundary element method for moving contact of two-dimensional elastic bodies using conforming discretization is presented. Both the displacement and the traction boundary conditions are satisfied on the contacting region in the sense of discretization. An algorithm to deal with the moving of the contact boundary on a larger possible contact region is presented. The algorithm is generalized to rolling contact problem as well. Some numerical examples of moving and rolling contact of 2D elastic bodies with or without friction, including the bodies with a hole-type defect, are given to show the effectiveness and the accuracy of the presented schemes.

STABILITY ANALYSES ON DYNAMIC CONTROL FOR A MOVING BODY LEVITATED MAGNETICALLY OVER ELASTIC GUIDEWAYS

Based on the Floquet theory on ordinary differential equationswith periodically variable coefficients and the bifurcation approachto nonlinear equations, a numerical approach to determining thestability region of control parameters is established for a dynamiccontrol system composed of a moving body levitated magnetically overflexible guideways. The system is nonlinearly coupled among theelastic deformation of guideways, disturbance the levitation positionof the body and electromagnet- ic control forces.

THE SOLVING PROBLEM AND THE DIFFERENCE SOLVING PROCESS FOR THE SHEAR OF A BOUNDED ELASTIC BODIES

A long elastomer with rectangular section bonded between two parallel rigid surfaces will come about deformation because of the role of two opposite shear forces in both the top and bottom plate. The mathematic model of the deformation is deduced and a new difference solving process is proposed. For boundary condition with singularity, a detailed analysis and deduction is given and a new rational and effective discrete boundary condition is proposed. Simulate computation demonstrates that the result is identical with qualitative analysis. Therefore, a new and functional numerical method and quantitative analysis method are provided.

Measurement of elastic modulus and evaluation of viscoelasticity of foundry green sand

Elastic modulus is an important physical parameter of molding sand; it is closely connected with molding sand’s properties. Based on theories of rheology and molding sand microdeformation, elastic modulus of molding sand was measured and investigated using the intelligent molding sand multi-property tester developed by ourselves. The measuring principle was introduced. Effects of bentonite percentage and compactibility of the molding sand were experimentally studied. Furthermore, the essential viscoelastic nature of green sand was analyzed. It is considered that viscoelastic deformation of molding sand consists mainly of that of Kelvin Body of clay membrane, and elastic modulus of molding sand depends mainly on that of Kelvin Body which is the elastic component of clay membrane between sands. Elastic modulus can be adopted as one of the property parameters, and can be employed to evaluate the viscoelastic properties of molding sand.

Axial power flow distributions of ultrasonic guided waves in viscous liquid-filled pipes

The axial power flow (APF) magnitude and attenuation distributions of ultrasonic longitudinal guided waves in viscous liquid-filled elastic pipes are investigated. The optimal location, optimal mode and its frequency-thickness product (fd) for the test of pipes filled with viscous liquid are chosen according to APF and attenuation distributions. The results show that the APF magnitude distribution is an important parameter in choosing the modes and parameters. A particular mode has weak dispersion in ranges of fd values with large group velocity, while other modes with smaller group velocity in the same fd ranges have stronger dispersion. It has been observed that, within these ranges, the chosen mode has a larger APF on the (pipe’s) wall. Therefore, in the region of fd values where a particular mode has a large group velocity, this mode will be effective to be used in testing elastic pipes filled with viscous liquid. The results obtained from both the APF analysis and attenuation distribution are consistent.

MATERIAL MULTIPOLE MECHANICS OF ELASTIC DIELECTRIC COMPOSITES

The overall mechanical and electrical behaviors of elastic dielectric composites are investigated with the aid of the concept of material multipoles. In particular, by introducing a statistical continuum material multipole theory, the effects of the electric-elastic interaction and the microstructure (size, shape, orientation,...) of inhomogeneous particles on the overall behaviors of the composites can be obtained. A basic solution for an ellipsoidal elastic inhomogeneity with electric polarization in an infinite elastic dielectric medium is first given, which shows that classical Eshelby 's elastic solution is modified by the presence of electric-elastic interaction. The overall macroscopic constitutive relations and their overall macroscopic material parameters accounting for electroelastic interaction effect are then derived for the elastic dielectric composites. Some quantitative calculations on the problems with statistical anisotropy, the shape effect and the electric-elastic interaction are finally given for dilute composites.

THE RECIPROCAL THEOREM AND LINEAR ELASTIC VARIATIONAL PRINCIPLES

In this paper classical linear elastic variational principles are systematically derivedfrom the reciprocal theorem and mixed variational principles of variations of boundaryconditions are given.

Motion estimation of elastic articulated objects from image contours

A new method of elastic articulated objects (human bodies) modeling was presented based on a new conic curve. The model includes 3D object deformable curves which can represent the deformation of human occluding contours. The deformation of human occluding contour can be represented by adjusting only four deformation parameters for each limb. Then, the 3D deformation parameters are determined by corresponding 2D contours from a sequence of stereo images. The algorithm presented in this paper includes deformable conic curve parameters determination and the plane, 3D conic curve lying on, parameter determination.

不同盾构施工参数对地表沉降影响的数值分析

为研究盾构隧道施工阶段不同施工参数对地表沉降的影响规律,文中依托杭州某盾构隧道工程,运用Midas GTS NX数值软件建立盾构隧道施工三维模型,分析施工阶段注浆体弹性模量、注浆压力、掌子面推力等施工参数对地表沉降的影响。结果表明,不同施工参数工况下地表横向沉降曲线皆呈现倒V形,且最大值均位于隧道拱顶正上方;适当增大注浆压力、掌子面推力可以减小地表沉降量;注浆体弹性模量大小与地表沉降量成反比;不同施工参数对地表沉降量的影响作用由大到小排列依次为注浆压力、注浆体弹性模量、掌子面推力,研究成果可为相关工程提供参考借鉴。

松辽盆地海力锦铀矿床含矿地层岩石弹性参数特征研究

当前,地震勘探技术在砂岩型铀矿勘查中主要用于查明地层展布、构造和砂体等成矿环境要素,而在分辨地层岩石是否含矿等铀矿信息直接获取方面尚存在欠缺。砂岩型铀矿含矿砂体与围岩的弹性参数差异是开展含矿砂体地震识别技术研究的基础,针对松辽盆地海力锦铀矿床的含矿地层,采集三口钻井的岩心,在实验室采用“线切割+全程样品防护”方式制获岩心样品,通过“量积法+超声脉冲透射法”开展测量,获取钻井岩心样品的纵波速度、横波速度和密度等弹性参数,并计算钻井岩心的纵波阻抗和横波阻抗,在此基础上开展海力锦铀矿床含矿地层岩石的弹性参数特征研究。研究结果表明:在含矿层深度范围内,岩石弹性参数差异主要受岩石岩性影响,而受深度变化的影响可忽略不计;地层岩石不同岩性的速度、密度和波阻抗等弹性参数存在差异,特别是含矿中砂岩的密度和速度参数与围岩存在一定差异,可根据密度和纵波速度差异识别含矿中砂岩,并给出相应的技术方案,为开展岩石岩性及含矿砂体的地震精细识别研究提供依据。

弹力带抗阻训练对绝经女性骨密度和体质指数的影响

探讨弹力带抗阻训练对绝经女性骨密度和体质指数的影响,为预防治疗绝经女性骨质疏松症提供理论依据。本研究共招募30名绝经女性为实验对象,进行12周的弹力带抗阻训练,1~8周为低等强度,8~12周为中等强度,每周3次。利用超声骨密度仪等对实验对象干预前、干预中期和干预后期进行骨密度、体质指数、心率等检测。结果表明,12周弹力带抗阻训练后绝经女性的骨密度较干预前有显著增高,体质指数得到了有效控制,说明弹力带抗阻训练对预防和治疗绝经女性骨质疏松症有积极作用。

多模态超声评估产次对会阴体及肛提肌功能影响的研究

目的运用二维灰阶超声联合实时剪切波弹性成像(SWE)探究产次对自然分娩产后早期会阴体(PB)及肛提肌(LAM)功能的影响。方法选取南充市中心医院产后6~8周自然分娩产妇为研究组,根据产次分为二次经产妇组46例及初产妇组55例。选择同期到本院做检查有性生活史未育的健康女性50例作为对照组。分别测量三组静息和最大收缩状态下会阴体长度、高度、杨氏模量值,静息、最大收缩以及Valsalva状态下双侧肛提肌杨氏模量值,计算差值,比较各组不同状态下超声参数变化情况。结果静息及最大收缩状态下二次经产妇组会阴体长度、高度、收缩幅度和杨氏模量值低于初产妇组和对照组,差异有统计学意义(P<0.05)。三组组间相同状态下肛提肌杨氏模量值与差值比较,差异均有统计学意义(P<0.05),对照组以及初产妇组组内不同状态下肛提肌杨氏模量值差异有统计学意义(P<0.05),二次经产妇组组内最大收缩状态下肛提肌杨氏模量值较Valsalva及静息状态增大,而Valsalva与静息状态比较,差异无统计学意义(P>0.05)。结论二次自然分娩对产后早期会阴体及肛提肌功能的影响较初次自然分娩更明显,二维灰阶超声联合实时剪切波弹性成像技术可以评估自然分娩不同产次会阴体及肛提肌功能的差异性。

低强度抗阻结合血流限制训练12周青年人体成分、肌肉力量及动脉弹性功能

背景:高强度抗阻训练能有效提高肌肉力量,但动脉硬化风险较高;高强度抗阻训练结合有氧运动可有效降低动脉硬化水平;低强度抗阻结合血流限制训练不需要高负荷力量刺激肌肉,或许是提高肌肉力量、保持动脉弹性的科学训练方法。目的:探讨12周的低强度抗阻训练结合血流限制训练对青年人体成分、肌肉力量及动脉弹性功能的影响,为制定个性化训练方案提供理论支撑。方法:随机招募55名大学生并通过抽签的方式随机分为高强度抗阻训练组、高强度抗阻结合有氧运动组及低强度抗阻结合血流限制训练组,分别进行为期12周的高强度抗阻训练、高强度抗阻训练结合有氧运动、低强度抗阻训练结合血流限制训练,训练结束后进行身体成分、肌肉力量及动脉弹性功能测试。结果与结论:12周的训练干预后,高强度抗阻训练组、低强度抗阻结合血流限制训练组的瘦体质量显著增加(P<0.05),3组的最大重复次数(1RM)和膝关节等速肌力均显著增加(P<0.05),高强度抗阻结合有氧运动组、低强度抗阻结合血流限制训练组的动脉弹性功能显著改善(P<0.05)。结果表明:12周的高强度抗阻训练、低强度抗阻训练结合血流限制训练能显著改善身体成分;3种训练方式均能增加肌肉力量;12周的高强度抗阻训练结合有氧运动、低强度抗阻训练结合血流限制训练均能改善动脉弹性功能,且低强度抗阻训练结合血流限制训练的效果优于高强度抗阻训练结合有氧运动。因此,建议将低强度抗阻训练结合血流限制训练作为首选训练方式,以改善动脉弹性,降低动脉硬化的风险。

薄壁四点接触球轴承-腕部关节系统接触动力学分析

在机器人实际工况中,针对含有薄壁四点接触球轴承的机器人腕部关节系统的运动稳定性问题,对腕部系统模型进行了简化设计和仿真研究。在考虑薄壁结构的弹性变形和动态接触作用耦合影响的基础上,建立了刚柔耦合工业机器人腕部关节系统模型,分析了不同受载工况和正反转驱动下的变形规律和动态特性。首先,基于多体动力学和Hertz接触理论,设计了包含薄壁四点接触球轴承和中空轴及基座的腕部关节系统刚柔耦合接触动力学仿真模型;然后,考虑薄壁中空轴、基座、轴承套圈和保持架的结构弹性变形、钢球和套圈滚道、保持架的动态接触作用,研究了机器人腕部关节系统两种实际工况对保持架和钢球角速度、保持架和薄壁基座振动位移、钢球与套圈的动态接触力的影响;最后,计算分析了两种工况下腕部关节系统的动态载荷规律和振动响应特性。研究结果表明:在相对较大的径向载荷作用下,保持架和钢球会出现打滑现象,速度呈现周期波动,保持架和基座具有更好的运动稳定性,其薄壁轴承内部载荷降低,主副接触对均承担联合载荷,轴承内部载荷稳定性也更好。该仿真模型及结果可以为薄壁腕部关节系统的动力学分析与设计提供参考。

刚体完全弹性碰撞中e=1的简单证明

本文给出了三维刚体与刚体完全弹性碰撞中,动能不损失等价于恢复系数e=1的证明,推广了以往在质点间碰撞、质点与刚体碰撞中得到的结果的适用范围.本文避开了碰撞中刚体转动能量的计算,以冲量和做功入手完成了一种简单的证明.

一种新型一体压铸车身静态弯扭刚度数值分析

为提升车辆刚度和性能、减少零件数量,提出一种采用高压压铸铝合金材料的A00级纯电平台新型压铸车身。对该车身进行刚度校核并研究刚度性能提升的方法。通过CAE对该新型车进行自由模态及弯曲和扭转刚度校核;应用基于均匀弹性应变能的方法对白车身进行优化,以提升车身的扭转刚度。优化后车身的扭转刚度及弯曲刚度分别为11485(N·m)/(°)和17329 N·mm,满足性能目标要求。

Analysis of Skin Parameters of Korean Men According to the Parts of the Body for Integumentary Physiotherapy Research

Studies have demonstrated that some cutaneous biophysical properties vary with the part of the body. The results to date of skin conditions in human skin of multiple parts of the body have not yet been well established. In this study, we assessed the differences in the skin’s sebum, moisture, pores, wrinkles, pigmentation, and elasticity of each body part in Korean men in their 20s. A total of 34 healthy men were enrolled. A Skin Diagnosis Meter was used to measure the skin’s surface sebum, moisture, pores, wrinkles, pigmentation, and elasticity of each body part. The sebum content was significantly higher on the face than at other sites. Moisture was significantly high on the feet. Pores were significantly high on the face. Wrinkles were significantly high on the face. Pigmentation was high on the face and neck, but not significantly. Elasticity was significantly high on the hands. In the correlation analysis results, sebum and pore were positively correlated, but sebum and moisture and wrinkle and elasticity were negatively correlated. For nearly the first time, this study resulted in systematic reference values for standardized biophysical measuring methods and body parts reflecting the skin physiology of healthy South Korean men. The results show that skin’s surface sebum, moisture, pores, wrinkles, pigmentation, and elasticity vary with the part of the body.

Some Methods of Solution of Problems of Sound Diffraction on Bodies of Non-Analytical Form

This review analyzes following numerical methods of a solution of problems of a sound diffraction on ideal and elastic scatterers of a non-analytical form: a method of integral equations, a method of Green’s functions, a method of finite elements, a boundary elements method, a method of Kupradze, a T-matrix method and a method of a geometrical theory of a diffraction.