风荷载作用下大型柔性储液结构动态响应仿真方法研究

风荷载作用下柔性储液结构的动态响应属于典型的非线性流固耦合问题。采用多物质ALE有限元法,建立了大型柔性储液结构的有限元模型,数值模拟风荷载作用下柔性储液结构的动态响应,比较了不同风速对柔性结构的影响。仿真结果表明：风速越大,结构的最大主应力、质心偏移量也越大,当风速达到一定时,结构将会沿地面产生滑动。仿真结果为风荷载作用下柔性储液结构的抗风性研究提供参考依据。     

基于单胞模型复合材料性能预测的储液容器抗冲击性

基于复合材料的性能预测, 对空投柔性储液容器的抗冲击性和动态响应进行了研究。针对该类材料结构具有周期性的特点, 在单胞有限元模型基础上, 应用周期性边界条件加载方法, 通过数值模拟预测了复合材料的宏观性能和力学参数。以此为基础, 采用基于任意拉格朗日欧拉(ALE)描述的流固耦合方法, 通过数值仿真研究了装水量80%(体积分数)的柔性容器空投冲击的动态响应, 并将获得的结果与物理实验进行了对比, 证明了本文中采用的性能预测方法、 有限元模型和流固耦合技术的合理性和有效性。      

储液盒塑件注射模设计

本文分析了储液盒塑件的结构特点,介绍储液盒注射模设计要点及模具的工作过程。重点介绍了储液盒注射模结构的设计方法,分析和阐述模具分型面的确定、注射机的选择方法,排气系统、浇注系统、冷却系统,脱模机构、型芯设计过程。此储液盒塑件注射模设计的结构是点浇口形式的三分型面注射模。     

柔性多体系统碰撞动力学研究

摘 要：针对工程中常见的柔性多体系统碰撞过程,详细的分析了柔性多体系统的接触碰撞条件,基于非线性等效弹簧阻尼模型建立了柔性体的碰撞模型,并基于库仑摩擦模型考虑两体碰撞时的切向摩擦作用。在此基础上把柔性体碰撞模型综合到柔性多体系统动力学方程中,建立了含接触碰撞的柔性多体系统动力学模型,此模型适用于一般含碰撞的多体系统。仿真算例以柔性梁在重力场中的接触碰撞过程为对象进行动力学仿真,研究柔性梁碰撞前、碰撞过程及碰撞后的动力学特性和动态响应,以及碰撞过程碰撞力的变化规律,并与刚性梁在重力场中的接触碰撞过程进行详细的比较和分析,结果表明基于非线性等效弹簧阻尼模型建立的柔性多体系统碰撞动力学模型可以有效的分析接触碰撞过程的动力学性能,验证了模型的有效性和正确性。     

基于两种接触模型的柔性体间多次微碰撞问题研究

由于柔性体的弹性振动,柔性结构间的一次宏观碰撞过程中,可能发生多次"接触-分离-接触"的微碰撞过程。多次碰撞行为往往会对结构造成各种形式的损害。为了能正确预测任意形状柔性体的多次微碰撞过程,基于三维实体有限元模型,分别采用罚函数法和附加约束法的接触模型,对一柔性杆撞击两端固支梁的问题进行研究,并分析了接触刚度、网格尺寸等参数对两种方法仿真结果的影响。数值结果表明,在罚函数法中,只有通过多次试算得到合适的接触刚度及网格尺寸,才能准确预测出多次微碰撞过程的碰撞次数、碰撞力峰值及碰撞持续时间,而附加约束方法无需选取接触刚度并且对网格尺寸的依赖性较小。     

储液容器流固耦合动力响应分析计算

本文采用交替解法对地震条件下储液容器的动态响应问题进行了实例分析和计算。首先推导出流固耦合系统在地震条件下的有限元模型。然后,对在水平地震激励条件下的圆柱形储液容器,采用交替解法进行了计算,并将其与整体解法进行了比较。结果表明交替解法具有更好的计算效率。     

医用注射泵检定设备存在的问题及对策研究

正一、注射泵检定装置的工作原理及其特点本文提供的注射泵检定装置,用于对注射泵的堵塞压力和流速进行测量,大体上包括相互串联的第一管段、第二管段和第三管段,所述第一管段与所述第二管段之间设置有堵塞阀,所述第二管段通过所述第三管段连接至一储液容器。所述第一管段具有一进液口,其上设置有用于测量管路内测试液体压力的压力传感器,所述第二管段为透光管路且外侧设置有光学传感器,所述储液容器设置有一出液口。所述注射泵的输出端连接至所述第二管段,且其输入端通过一气体管路连接至所述储液容器。     

多体系统斜碰撞动力学中的结构柔性效应

本文针对重力场下作大范围回转运动的柔性梁与一固定斜面发生斜碰撞的情况,建立起系统含碰撞的一致线性化的动力学方程。根据Ｈｅｒｔｚ接触理论和线性切线接触刚度建立碰撞接触模型。针对结构不同刚度的情况进行了仿真计算,由仿真算例的计算结果可以看出,结构的柔性对碰撞过程中的微运动具有明显的作用,同时对降低由于碰撞而引起的能量损耗和减少碰撞作用力起到一定的效果。     

船舶摇摆振动对传热和制冷系统的影响研究述评

渔船发动机尾气制冷系统和核动力舰船的自然冷却系统在海洋条件下的安全稳定性是关乎其应用的重要问题。研究海洋条件下的流动与换热特性对提高制冷系统的稳定性具有重要意义。文中综述了海洋条件下船舶的摇摆与晃动对储液容器、换热器的热传递以及制冷系统影响的研究现状。大量研究表明,海洋条件下摇摆与晃荡会对流动与换热造成影响,而传热传质的强化或削弱依具体海况(摇摆和晃荡的剧烈程度)而不同。渔船尾气吸收式制冷系统在比较恶劣的海洋条件下将受到较大的影响。通过在储液容器(如吸收器、发生器)中增加阻尼板或阻尼网,可有效抑制储液容器内部液面波动,提高系统运行稳定性。     

储液结构隔震优化模型及其影响参数分析

针对储液结构地震响应包括储液部分的刚体运动、中高频的冲击运动和低频的对流运动以及下部支撑部分的结构运动,导致该系统对频带宽、随机性强的地震动响应敏感,该文从概率优化的角度探讨基础隔震、层间隔震和非隔震储液结构的地震响应及其参数影响规律。基于Haroun-Housner储液结构动力模型,建立并给出了非隔震模型、层间隔震模型、基础隔震模型的动力控制方程。提出以其基底剪力的均值和标准差作为优化目标函数,以隔震层周期作为优化变量的优化模型,并在MATLAB软件平台上实现了该模型。通过单参数影响分析,研究了水箱结构与下部支撑结构的重量比、下部支撑结构的刚度、水箱结构储液高度与半径比、场地变化等因素对各种模型地震响应的影响。该研究成果对隔震技术在储液结构中的应用、提高储液结构的抗震性能等方面具有参考价值。     

轨道交通动态客流对轮轨力特征影响研究

为了研究轨道交通动态客流对轮轨力特征的影响,通过对列车实际线路进行试验分析动态客流对列车轮轨力、脱轨系数及频谱特征参数的影响。在线路曲线段位置钢轨上粘贴应变片,获得列车在不同客流工况下通过该区间段时的轮轨力大小,分析比较客流高峰期、客流非高峰期典型工况下轮轨力幅值大小、幅值变化趋势、脱轨系数大小及主频范围与频率变化规律。结果表明：动态客流对轮轨力幅值影响较大,随着客流增大轮轨垂向力幅值增大12.9 %,轮轨横向力幅值增大7.5 %。列车正常运营状态下脱轨系数在0.12～0.16 之间变化,动态客流对脱轨系数影响较小,均在安全行车范围内。动态客流引起轮轨力主频幅值大小变化,钢轨内轨横向力共振频率由175 Hz偏移到155Hz,共振频率出现了偏移,但轮轨力频谱特征趋势基本保持一致。     

复合材料薄壁管冲击断裂分析与吸能特性优化

为实现不同冲击载荷下的吸能管结构逆向设计, 应用复合材料强度和刚度理论, 计算得到树脂基纤维增强复合材料正交各向异性的力学参数, 同时应用非线性显式有限元算法模拟了轴向冲击载荷作用下管件的动态断裂过程。根据正交设计原理, 得到了管件比吸能与其几何参数之间的非线性映射关系, 并构造出了相应的响应表面。按照汽车正面碰撞对冲击加速度的要求, 应用序列二次规划算法对吸能管进行了优化设计, 得到了具有较优吸能效率和较小冲击力峰值的吸能管结构参数。结果显示: 方管的变形模式、吸能量、冲击载荷-位移曲线变化趋势、冲击载荷峰值等与试验结果吻合很好; 当管件的壁厚、截面长度、管长分别选取2.1、44、200 mm时, 可得到设计域内的最大比吸能29.23 J/g。      

Impact of traffic states on freeway crash involvement rates

Freeway traffic accidents are complicated events that are influenced by multiple factors including roadway geometry, drivers’ behavior, traffic conditions and environmental factors. Among the various factors, crash occurrence on freeways is supposed to be strongly influenced by the traffic states representing driving situations that are changed by road geometry and cause the change of drivers’ behavior. This paper proposes a methodology to investigate the relationship between traffic states and crash involvements on the freeway. First, we defined section-based traffic states: free flow (FF), back of queue (BQ), bottleneck front (BN) and congestion (CT) according to their distinctive patterns; and traffic states of each freeway section are determined based on actual measurements of traffic data from upstream and downstream ends of the section. Next, freeway crash data are integrated with the traffic states of a freeway section using upstream and downstream traffic measurements. As an illustrative study to show the applicability, we applied the proposed method on a 32-mile section of I-880 freeway. By integrating freeway crash occurrence and traffic data over a three-year period, we obtained the crash involvement rate for each traffic state. The results show that crash involvement rate in BN, BQ, and CT states are approximately 5 times higher than the one in FF. The proposed method shows promise to be used for various safety performance measurement including hot spot identification and prediction of the number of crash involvements on freeway sections.     

Dynamic response of flexible container during the impact with the ground

In order to understand and improve the crashworthiness of airdropped flexible containers, this paper presents the work of numerical simulations about the dynamic behaviour of the container under impact loading. A finite element model of the container is constructed and used to predict the dynamic response of the container. Water movement and sloshing in the container are modelled using the multi-material ALE method; interaction between the container and the fluid is studied by the penalty method. Mechanical properties of the fabric composite are obtained by applying periodic boundary conditions on the unit cell model. Numerical results are compared with experiment data for the validation of the model and the approaches. With a range of system parameters, numerical tests show that the shoulder of the container is the most vulnerable part during the impact. Both the drop heights and the amount of water have great effects on the crashworthiness of the container. The maximum dynamic stress of the container is proportional to the drop height. The amount of water in the container influences the failure of the container.     

Fluid oscillations in an open,flexible container

In this paper we study normal oscillation modes of an incompressible fluid in an open container, part of the wall of which may be flexible. The flexible part of the container wall is modelled by a membrane. We first investigate the eigenfrequencies of an inviscid fluid in a flexible container. We are able to show, by analytical means, that the eigenfrequencies of an inviscid fluid decrease when part of the rigid container wall is replaced by a membrane. The problem of viscous fluid oscillations in a flexible container is then studied numerically using the finite-element technique. Two different types of eigenmodes are observed: free-surface oscillation modes and structural vibration modes. The dependence of the two modes on the Bond number (measure of the ratio of gravitational and tension forces) and the Reynolds number is investigated.     

柔性极板电容式液位传感器的研究和应用

目的 为了解决传统硬质极板电容式液位传感器在曲面容器上性能不佳的问题.方法 从寄生电容的基本原理出发,研发一种可以包覆于圆柱面容器的柔性极板电容式液位传感器,建立液位与电容量间的数学关系,完成相应的软、硬件设计,通过STM32与柔性极板电容式液位传感器之间的I2C通信,实现液位传感器的在线水位检测,完成传感器性能测试实验,包括线性度、重复性、迟滞特性,并提出一种基于该传感器的流量测量方法.结果 该传感器工作稳定,具有良好线性度,重复性误差为2.70％,在有效测量范围的迟滞特性参数都小于1.69％.结论 该柔性极板电容式液位传感器安装使用便捷、与容器外壁贴合度较好,且测量结果不受容器水平横截面积、待测液体成分的限制,可以实时监测连续液位的变化.制作的传感器可以用在直径20 mm和更小的待测容器上,也可用作微小流量测量.     

A joint-probability approach to crash prediction models

Many road safety researchers have used crash prediction models, such as Poisson and negative binomial regression models, to investigate the associations between crash occurrence and explanatory factors. Typically, they have attempted to separately model the crash frequencies of different severity levels. However, this method may suffer from serious correlations between the model estimates among different levels of crash severity. Despite efforts to improve the statistical fit of crash prediction models by modifying the data structure and model estimation method, little work has addressed the appropriate interpretation of the effects of explanatory factors on crash occurrence among different levels of crash severity. In this paper, a joint probability model is developed to integrate the predictions of both crash occurrence and crash severity into a single framework. For instance, the Markov chain Monte Carlo (MCMC) approach full Bayesian method is applied to estimate the effects of explanatory factors. As an illustration of the appropriateness of the proposed joint probability model, a case study is conducted on crash risk at signalized intersections in Hong Kong. The results of the case study indicate that the proposed model demonstrates a good statistical fit and provides an appropriate analysis of the influences of explanatory factors.     

Exploring a Bayesian hierarchical approach for developing safety performance functions for a mountainous freeway

While rural freeways generally have lower crash rates, interactions between driver behavior, traffic and geometric characteristics, and adverse weather conditions may increase the crash risk along some freeway sections. This paper examines the safety effects of roadway geometrics on crash occurrence along a freeway section that features mountainous terrain and adverse weather. Starting from preliminary exploration using Poisson models, Bayesian hierarchical models with spatial and random effects were developed to efficiently model the crash frequencies on road segments on the 20-mile freeway section of study. Crash data for 6 years (2000–2005), roadway geometry, traffic characteristics and weather information in addition to the effect of steep slopes and adverse weather of snow and dry seasons, were used in the investigation. Estimation of the model coefficients indicates that roadway geometry is significantly associated with crash risk; segments with steep downgrades were found to drastically increase the crash risk. Moreover, this crash risk could be significantly increased during snow season compared to dry season as a confounding effect between grades and pavement condition. Moreover, sites with higher degree of curvature, wider medians and an increase of the number of lanes appear to be associated with lower crash rate. Finally, a Bayesian ranking technique was implemented to rank the hazard levels of the roadway segments; the results confirmed that segments with steep downgrades are more crash prone along the study section.     

Bootstrap resampling approach to disaggregate analysis of road crashes in Hong Kong

Road safety affects health and development worldwide; thus, it is essential to examine the factors that influence crashes and injuries. As the relationships between crashes, crash severity, and possible risk factors can vary depending on the type of collision, we attempt to develop separate prediction models for different crash types (i.e., single- versus multi-vehicle crashes and slight injury versus killed and serious injury crashes). Taking advantage of the availability of crash and traffic data disaggregated by time and space, it is possible to identify the factors that may contribute to crash risks in Hong Kong, including traffic flow, road design, and weather conditions. To remove the effects of excess zeros on prediction performance in a highly disaggregated crash prediction model, a bootstrap resampling method is applied. The results indicate that more accurate and reliable parameter estimates, with reduced standard errors, can be obtained with the use of a bootstrap resampling method. Results revealed that factors including rainfall, geometric design, traffic control, and temporal variations all determined the crash risk and crash severity. This helps to shed light on the development of remedial engineering and traffic management and control measures.