Mathematical model to generate near-periodic human jumping force signals

A mathematical modelling procedure has been developed to generate synthetic vertical force signals induced by a single person jumping. The ability to replicate much of the temporal and spectral features of real jumping loads give this model a definite advantage over the conventional half-sine models coupled with Fourier series analysis. This includes modelling of the omnipresent lack of symmetry of individual jumping pulses and jump-by-jump variations in amplitudes and timing. The model therefore belongs to a new generation of synthetic narrowband jumping loads that simulate reality better. The proposed mathematical concept for characterisation of irregular jumping pulses may be utilised in vibration serviceability assessment of civil engineering assembly structures, such as grandstands, footbridges and concert or gym floors, to estimate realistic dynamic structural response due to people jumping.     

Development of a Leg Mechanism for Soft Landing Based on Biological Motion

With jumping mechanisms,soft landing motion is important to protect loads and the mechanisms.This study proposes a leg mechanism for soft landing based on biological motion.Human jumping motion with a load suggests a unique motion for soft landing.The landing model consists of two periods.Jerk is minimized in the first period and force is minimized in the second period.In comparison with other landing models,this model is specialized for soft landing motion protecting an objective part.Given all mechanisms ...     

Inelastic buckling of two-layer composite columns with non-linear interface compliance

A mathematical model for a slip-buckling problem has been proposed and its exact solution has been found for the analysis of materially inelastic two-layer composite columns with non-linear interface compliance. The mathematical model has been carried out to evaluate exact critical buckling loads. It has been demonstrated mathematically exactly, that exact critical buckling loads are influenced by the initial stiffness, and hence on linear portion of the interface force-slip relationship. Besides, it has been shown that material inelasticity can reduce the critical buckling loads significantly and that the interlayer stiffness has an important effect on the transition between the elastic and inelastic buckling.     

连续采煤机垂直方向振动的仿真

为了研究连续采煤机在垂直方向的振动情况,通过假设与简化,建立了连续采煤机的动力学模型和数学模型,求得了12HM10型连续采煤机的固有频率和5阶振型,利用计算机仿真技术,分析了各连接点刚度、各部质量、滚筒的转速和载荷对连续采煤机履带前后接地点处的振动大小与变化。研究表明,靠近机器前面的振动比后面的大,滚筒转速对机体振动的频率有影响,提高各连接点刚度、增大各部质量、降低滚筒转速、减小滚筒载荷可以减轻连续采煤机的振动。     

Analysis of a modular generator for high-voltage, high-frequency pulsed applications, using low voltage semiconductors (< 1 kV) and series connected step-up (1:10) transformers

This article discusses the operation of a modular generator topology, which has been developed for high-frequency (kHz), high-voltage (kV) pulsed applications. The proposed generator uses individual modules, each one consisting of a pulse circuit based on a modified forward converter, which takes advantage of the required low duty cycle to operate with a low voltage clamp reset circuit for the step-up transformer. This reduces the maximum voltage on the semiconductor devices of both primary and secondary transformer sides. The secondary winding of each step-up transformer is series connected, delivering a fraction of the total voltage. Each individual pulsed module is supplied via an isolation transformer. The assembled modular laboratorial prototype, with three 5 kV modules, 800 V semiconductor switches, and 1:10 step-up transformers, has 80% efficiency, and is capable of delivering, into resistive loads, -15 kV1 A pulses with 5 micros width, 10 kHz repetition rate, with less than 1 micros pulse rise time. Experimental results for resistive loads are presented and discussed.     

基于AMESim的液压卷带机构动态分析研究

为了研究液压卷带机构的动态特性,建立了液压卷带机构理论分析的数学模型,分析了性能参数对系统的影响,指出起动与负载突变时系统的阻尼系数及固有频率相同,其动态特性也一致。以AMESim为建模环境,建立了液压卷带机构的仿真模型,分析了系统起动及负载突变时的转速动态响应,及有效体积弹性模量和马达输出轴等效转动惯量对系统动态特性的影响,绘制了仿真结果图。结果表明在起动及负载突变时该系统响应较快且精确,油液含气量增加导致系统响应变慢、精确性下降,卷带量增加会在一定程度上减缓系统的响应速度。     

基于动态响应的高速压力机综合平衡优化

针对曲柄式高速压力机动平衡中存在的机身激振力与激振力矩平衡相互制约的问题,提出了一种基于动态响应的综合优化模型。通过有限元模拟获得机身在单位简谐载荷作用下的动态响应向量,通过傅里叶级数分解得到实际激振载荷的振幅向量,以此构造了一个直接以机身振动响应为对象的综合平衡优化模型,该模型能够适用于一般机械系统。     

挖掘机工作装置液压系统动臂油缸的压力跃变研究

以PC02挖掘机工作装置液压系统为例,建立了状态变量数学模型和仿真模型.通过分析动臂油缸活塞杆在伸出和缩回时负载压力pL跃变的规律,提出在压力跃变过程中存在压力冲击和压力空穴阶段;给出了负载压力pL的稳态解析表达式;压力冲击的峰值远大于压力跃变的稳态值.     

Experimental identification of turbulent fluid forces applied to fuel assemblies using an uncertain model and fretting-wear estimation

This paper is devoted to the identification of stochastic loads applied to fuel assemblies using an uncertain computational model and experimental measurements of responses. The stochastic loads applied to the structure are induced by a turbulent flow. The structure is made up of a nonlinear complex dynamical system. The experimental responses of the structure are obtained from strain sensors located on the structure. There are several sources of uncertainties in this experimental identification problem of the stochastic loads: uncertainties on the nonlinear dynamical computational model of the structure (fuel assemblies), uncertainties on the parameters of the mathematical model of the stochastic loads themselves and finally, measurements errors. All these sources of uncertainties are identified and taken into account in the identification process of the stochastic loads. Then, the stochastic nonlinear dynamical computational model of fuel assemblies on which the identified stochastic loads are applied yields interesting results concerning the robustness of the estimation of the fretting-wear of the fuel rods.     

风力发电机桨叶轴承载荷分析模型的研究

在考虑攻角、桨距角、偏航运动、重力和惯性力等因素的情况下,基于静力学分析方法,建立了桨叶轴承系统载荷分析数学模型。通过数值计算,研究了桨叶轴承在攻角、桨距角、偏航角速度及不同风速工况下所承受的载荷。分析结果表明,攻角增加会使不同方向上的载荷有不同程度的增加;桨距角增大到一定程度,载荷会呈现不同的趋势;偏航速度的变化导致陀螺力矩的变化,从而引起轴承载荷的变化。     

简单单腿弹跳机器人的尺度效应仿真

微小型弹跳机器人和其他大型机器人相比,有着自己独特的性能,有很大的科研意义和应用价值。提出一种新颖的设计思路,着手对现有弹跳机器人（包括大型机器人）的抽象、分析和仿真,研究机器人的尺度效应对弹跳高度的影响,得到机器人尺寸变化和弹跳初速、弹跳高度、落地时间、落地速度等弹跳性能之间的关系,并讨论弹跳机器人模型是否可以微小化问题,以便对复杂弹跳机器人的微型化和效率的提高提供思路和改进方案。     

The role of the quadriceps in controlling impulsive forces around heel strike

The damaging effect of transient loads on joints has been observed in vitro and in vivo, and may be an aetiological factor in osteoarthrosis. The events around heel strike, when the velocity of the foot is brought rapidly to zero, may be a source of such loads in normal activity. By modifying the rate at which the limb descends to the ground, quadriceps action influences the magnitude of the heel strike transient. Experiments were carried out to analyse the occurrence of these transients, and a two-dimensional mathematical model of the knee joint and lower leg was used to calculate the forces developed at the knee in response to them. Paralysis of the quadriceps resulted in a large increase in the heel strike transient.     

A new fatigue life prediction method based on nonlinear fatigue cumulative damage generalized expression

Ye’s nonlinear cumulative damage model has been widely used in engineering because of its simple mathematical form and clear physical meaning. However, it does not consider the interaction between two different loads, so its prediction accuracy has large room for improvement. In this paper, the k-th power of load ratio is introduced into Ye’s model to reflect the influence of the interaction between two different loads on fatigue damage during the damage evolution process, and a generalized expression of the model is obtained. Based on this generalized expression, a new fatigue life prediction method is proposed. The proposed method is validated by comparison with existing versions based on the experimental data of typical engineering materials under two-level and multilevel loads. The results show that the prediction method proposed here can well reflect the load interaction effect, and compared with other models, this method has a more accurate prediction effect on the fatigue life of four materials.

     

Computational results of a dynamic simulation of the conforming shell gas journal bearing

A time-dependent mathematical model for the conforming shell gas journal bearing is presented. A computational simulation of the mathematical model is used to investigate the dynamic behaviour and steady state characteristics of the bearing. The onset of dynamic instabilities, violation of the minimum film thickness criteria and component separations are found to be the three factors which form upper and lower bounds on the range of acceptable loads.     

Transient effects in the quasi-static and dynamic internal inversion and nosing of metal tubes

The plastic deformation mechanisms of metal tubes during quasi-static nosing and internal inversion are analysed. Rigid-plastic analyses which incorporate an assumption of full conformity between the deforming tube and the forming die predict accurately the nosing load-displacement curve. Details of the deformation processes during internal inversion are examined using the non-linear facilities of the finiteelement code ABAQUS. The early stages of the forced inversion characteristic are more complex than for nosing, with different deformation modes dominating the behaviour at different times. Each of these is also examined using rigid, perfectly plastic models.The quasi-static behaviour is used to provide insight into features of the load pulses generated during dynamic/impact loading of the tubes. The peak impact loads can only be assessed through a full dynamic analysis since inertial effects strongly influence the magnitude of the dynamic loads. It is shown that measured dynamic force pulses for both nosing and internal inversion can be accurately predicted fusing appropriate finite element models and the source of the high dynamic force peaks in inversion is discussed. It has been found both experimentally and numerically that the steady-state inversion force is lower under dynamic loading conditions than under quasi-static loading. A simple analytical model provides an explanation for this and highlights the importance of the ratio of the mass of the striker to that of the inverted portion of the tube in this phenomenon.     

受生物启发的扑翼飞行器弹跳机构概念设计

针对扑翼飞行器自主起降能力缺失、严重影响其适用场景的问题，开展了仿生弹跳机构设计研究。对鸟类跳跃起飞过程中典型的运动状态进行分析，结合其各阶段的后肢骨骼结构、重心、力、速度等运动变化规律，对扑翼飞行器弹跳起飞动态过程进行了设计。基于鸟腿的骨骼解剖学结构，设计了闭链齿轮-五杆仿鸟腿弹跳机构，并基于D-H法推导出弹跳机构运动学方程，利用拉格朗日方程建立了弹跳机构起跳阶段的动力学方程。对弹跳机构进行了详细结构设计，采用ADAMS对简化的弹跳模型进行了仿真分析。仿真结果显示，借助该仿生弹跳机构，扑翼飞行器系统质心速度达到8.4 m/s，大于“信鸽”飞行器起飞所需的速度7.9 m/s，具备弹跳起飞的可能性。     

A Highly Stable Source of Current Pulses with an Adjustable Amplitude of up to 350 A for a Nonlinear Complex Load

The application of high-power semiconductor lasers for creating a population inversion in active gaseous media is an integral part of studies that are aimed at the achievement of a sufficient level of laser-radiation energy to initiate a thermonuclear reaction. The stability of the laser radiation and, thus, the repeatability of experimental results, depend on the stability of the parameters of current pulses for pumping laser-diode arrays with a pulse amplitude of up to several hundred amperes. The flow of current pulses with such an amplitude through a cable that connects the load to the output of the current-pulse source must not lead to the formation of voltage pulses of opposite polarity across the load, which can damage it. This can be prevented by correcting the current pulse edges. It is proposed to develop a source of current pulses with a high amplitude on the basis of several modules of fast linear current amplifiers with individual control loops, whose outputs are connected in parallel. It is established that a compensation-type current sensor on the basis of the Hall effect is operable at high frequencies and can be used in these modules, but it has pronounced resonance properties, which must be canceled. It is shown that analog driving pulses of each module can be formed using aperiodic chains with parameters that eliminate oscillatory processes in the load circuit. A dynamic model of a module of the linear current amplifier and the calculation relationships for the parameters of its components, which follow from this model, are presented. The experimental results that confirm stability of the parameters of the formed current pulses are presented.     

变桨和偏航运动对风力发电机桨叶轴承载荷的影响

在考虑攻角、桨距角、偏航运动、重力和惯性力等因素的情况下,基于静力学分析方法,建立了桨叶轴承系统载荷分析数学模型。通过数值计算,研究了桨叶轴承在风速和桨距角、偏航角速度和桨叶转速同时发生变化的工况下所承受的载荷。分析结果表明,风速的增大会使载荷不断增加,而桨距角的增大只能使载荷在局部有所增大;桨叶轴承系统的陀螺力矩幅值大小、桨叶在空间的旋转角度以及偏航速度有着直接的关系。     

基于改进卡尔曼滤波的叉车载重快速准确估计方法

针对工作环境恶劣、操作工况复杂的伸缩臂叉车载重实时快速准确估计需求,对伸缩臂叉车的载重估计数学模型及其求解算法进行了研究。首先,利用叉车现有功能模块中已装配的各类传感器,提出并分析了三种载重估计方案,在综合比较各方案的优缺点之后,确定并建立了基于动力学原理的载重估计数学模型;然后,将载重作为估计系统的状态变量,将液压系统压力、臂架变幅角度和伸缩臂伸缩长度等实时信号作为测量值,将基于转动定律建立的载重计算公式作为状态变量与测量值之间的观测方程,运用卡尔曼滤波算法对该数学模型进行求解;同时,为解决卡尔曼滤波算法在递推过程中状态变量发生改变从而导致大量新测量数据对状态变量失去校正能力的问题,提出了一种基于改进卡尔曼滤波的载重估计算法;最后,对某企业超长载重伸缩臂叉车进行了不同载重的离线试验和在线试验。研究结果表明：对于454 kg的轻载荷,该算法的估计结果的最大绝对误差小于91 kg,而对于1100 kg、2268 kg、3368 kg和4536 kg的重载荷,其平均绝对百分比误差小于3%;趋于稳定估计值的响应时间可在1 s之内,完全优于实际应用需求。该方法模型简单、可移植强,可推广应用到起...     

超分子作用阻尼材料的动态力学模型修正

为提高飞机起落架载荷实测精度,以支柱式起落架结构为研究对象,探讨处理其载荷标定数据的工程方法。首先,对实际受载情况和单向加载工况标定数据的分析,挖掘出三向载荷、缓冲支柱压缩行程与应变码值间的数学关系,将预测的数学关系代入到多向工况的标定数据中,验证了它们的准确性;其次,根据两种标定数据回归方法,提出了对应使用的支柱式起落架载荷-应变标定方程的数学模型;最后,将两种标定方程代回到标定数据中,计算起落架三向载荷,所有反算载荷的误差均在可控范围内,表明标定方程满足精度要求。将标定方程代入实测数据中,实测曲线符合变化规律。该处理方法的应用能有力提高支柱式起落架的起飞-着陆载荷实测和载荷谱编制的准确度。