利用白车身振动模态试验对车身动态设计的评价与分析

在建立白车身的三维几何模态试验模型的基础上,采用多点激振多点拾振方法对车身的模态进行实测.利用Test.lab软件进行模态参数识别,并利用模态参数识别结果,为整车的动态特性的分析和结构设计的修改提供方法和理论依据.     

汽车发动机悬置安装点最佳位置的优化研究

动力总成是车身振动的主要来源,合理的悬置刚度和安装点位置对于降低车身振动,提高汽车乘坐舒适性十分重要。根据车身、悬置和动力总成参数,考虑车身悬置点动力学特征,建立整车悬置系统振动传递简化模型,分析车身悬置点导纳对动力总成传递到车身振动能量灵敏度,查找对输出功率流影响最大的导纳所对应悬置及方向,在车身车架有限元模型中计算悬置点位置改变对导纳影响大小,进而找出最能降低向车身传递功率流的悬置最优位置。灵敏度分析及有限元模型中的计算结果表明合理选择悬置安装点位置对于降低传递到车身功率流有一定的效果,对悬置最优位置的确定给出了合理的建议。     

《车身阻尼层结构的声灵敏度分析及优化》

车身多层阻尼结构的振动特性及隔吸声特性是影响车室空腔声响应的重要因素。一个简化的车身模型用于研究车身多层结构对车内声压级的影响。通过这个模型，研究了车室空腔声响应与阻尼结构之间的关系。对车身阻尼结构进行了声－结构灵敏度分析，并对优化了阻尼层结构参数。     

高速工业平缝机台板声振分析与降噪研究

本文采用测量高速工业平缝机各部件声辐射功率的方法，识别出台板是该机主要噪声辐射源。应用功率谱和相干分析相结合的方法，探讨了高速工业平缝机台板、底板的振动与标准点噪声之间的声振关系。以此为基础，在台板与底板进行隔振设计，减小了台板的振动及其声辐射，取得了整机降噪的良好效果。     

混合工质热声发动机起振及消振特性试验研究

基于驻波热声发动机,开展了热声发动机在不同安装倾角下起振及消振特性的试验研究。试验结果表明,热声发动机的安装倾角对热声系统的起振温度、消振温度等参数的影响程度与充注工质种类有很大关系。当系统中充注1 MPa氮气时,在试验的5种角度下,最高起振温度484℃,最低起振温度428℃。当系统充注1 MPa氦气时,热声发动机的起振温度和消振温度并无明显变化。该特性为选择合适角度和工质以降低系统起振温度提供了试验参考,并为太阳能驱动的热声发动机的设计和工质的选择提供了试验依据。     

舰船水下辐射噪声快速预报方法

提出一种高精度舰船水下辐射噪声快速预报方法。首先分析设备基座振动、船体表面振动与辐射声场之间的传递规律,然后建立设备基座振动与水下辐射声压之间的传递函数,并通过理论分析、数值及试验验证设备基座至结构水下辐射声压之间存在着只与频率相关的声振传递函数,即声振传递函数具有不变性。研究表明,基于声振传递函数不变性的舰船水下辐射噪声快速预报方法较有限元法具有较高的预报精度和预报效率,预报速度达到分钟级。     

Rijke型燃烧器热声振动特性的试验研究

为研究燃烧过程中的热声振动特性,搭建了Rijke型预混燃烧器热声振动特性试验台架,并进行了化学当量Ф为0.8、1.0和1.2的三组试验研究.Rijke型预混燃烧器为直径40 mm,管长1 066 mm的不锈钢圆管,下端封闭,上端开口.致密堇青石材质的多孔介质稳燃体位于燃烧器四分之一管长处,甲烷与空气的预混气体在稳燃体上方燃烧.试验获得的燃烧温度位于611 K-943 K之间;热声振动频率在440 Hz-476 Hz之间;热声振动声压级位于131 dB-146 dB之间.试验发现,Rijke型预混燃烧器的燃烧温度在同一燃烧功率下基本一致,不受化学当量比的影响.热声振动频率随燃烧功率的增加轻微上升,不同化学当量比下振动频率的变化幅度不相同,贫燃和富燃时频率随燃烧功率的增加有较大的增加,且贫燃大燃烧功率时出现了低频大振幅振动与高频振动并存的现象.热声振动强度强烈依赖于燃烧功率和化学当量比,同一燃烧功率不同化学当量下的热声振动强度相差可达50%.     

热声斯特林发动机系统的起消振过程研究

在自行研制的1台行波型热声斯特林发动机上考察其起振和消振行为.针对不同的加热功率和充气压力下,系统地研究了起消振过程中的温度、压力变化特性,着重分析了滞后回路形成的过程和影响热声系统滞后回路的因素,指出滞后回路存在的条件,对深入理解热声系统的起消振行为具有参考意义.     

基于模态灵敏度分析的客车车身优化

针对提高国产某轻型客车的乘坐舒适性,解决车内振动和噪声剧烈问题,本文首先基于有限元仿真和道路试验的阶次跟踪方法进行振动和噪声原因分析,所确定的原因为轮胎激励引起的车身结构共振。为避免共振,以白车身钣金件和骨架的厚度为设计变量,以提高白车身前两阶固有频率为目的,用模态灵敏度理论对白车身进行优化设计和灵敏度分析。然后结合各钣金件和骨架的模态灵敏度和质量灵敏度,设计最优的改进方案并进行试验分析。对比优化前后的试验结果,验证了该优化方案的有效性与合理性。     

基于空间傅里叶变换的柱面结构声学灵敏度分析

声学灵敏度可以用于预测空间声学量随设计变量的变化情况,为低噪声设计提供优化方向和量化依据,对其进行研究具有重要意义。在空间傅里叶变换的基础上,提出了一种用于柱状声源外部声场的声灵敏度计算方法,在已知振速及其对设计变量导数基础上,给出了可用于计算空间任意点的声学量关于声源的结构参数、材料特性等设计变量的灵敏度分析公式。而且空间傅里叶变换的引入,使得文中算法具有计算速度快,稳定性好的优势。数值仿真的结果证明了该方法的正确性和有效性。     

Mixed explicit-implicit iterative finite element scheme for diffusion-type problems: I. Theory

A Galerkin finite element formulation of diffusion processes based on a diagonal capacity matrix is analysed from the standpoint of local stability and convergence. The theoretical analysis assumes that the conductance matrix is locally diagonally dominant, and it is shown that one can always construct a finite element network of linear triangles satisfying this condition. Time derivatives are replaced by finite differences, leading to a mixed explicit-implicit system of algebraic equations which can be efficiently solved by a point iterative technique. In this work the accelerated point iterative method is adopted and is shown to converge when the conductance matrix is locally diagonally dominant. Several examples are included in Part II of this paper to demonstrate the efficiency of the new approach.     

Measurement of thermal relaxation and temperature damping time in a solid

Differential equations of heat conductance of solid body are presented, a result of Fourier, Cattaneo–Vernotte, and two-phase delay hypotheses. The experimental set-up and automated measuring system is described for the study of transient thermal processes in solid. The solution of the boundary problem of the third kind is given with differential equations of heat conductance of parabolic and hyperbolic types. The results of experimental and theoretical study of transient thermal processes in the plate center are given in the sudden immersion into a hot environment. Based on the comparison of theoretical transient processes with recorded automated measuring system, the adequacy of hypotheses and corresponding differential equations of heat conductance are concluded with respect to short-term transient processes. Thermal relaxation and temperature damping constants for polymethyl methacrylate are measured.     

Electrical and mechanical fully coupled theory and experimental verification of Rosen-type piezoelectric transformers

A piezoelectric transformer is a power transfer device that converts its input and output voltage as well as current by effectively using electrical and mechanical coupling effects of piezoelectric materials. Equivalent-circuit models, which are traditionally used to analyze piezoelectric transformers, merge each mechanical resonance effect into a series of ordinary differential equations. Because of using ordinary differential equations, equivalent circuit models are insufficient to reflect the mechanical behavior of piezoelectric plates. Electromechanically, fully coupled governing equations of Rosen-type piezoelectric transformers, which are partial differential equations in nature, can be derived to address the deficiencies of the equivalent circuit models. It can be shown that the modal actuator concept can be adopted to optimize the electromechanical coupling effect of the driving section once the added spatial domain design parameters are taken into account, which are three-dimensional spatial dependencies of electromechanical properties. The maximum power transfer condition for a Rosen-type piezoelectric transformer is detailed. Experimental results, which lead us to a series of new design rules, also are presented to prove the validity and effectiveness of the theoretical predictions.     

Normal phase propagation along a current carrying superconducting wire and its heat transfer to a cooling He II bath

A theoretical and experimental study of the longitudinal propagation velocity of a normal phase along a superconducting cylindrical wire suspended in a superfluid helium bath is presented. The theoretical model supposes a moving nonplanar separating boundary between the normal and superconducting phases and takes into account the latent heat absorbed during the destruction of the superconducting state. The comparison of the measured and calculated normal zone propagating velocities versus the circulating electrical currents shows an excellent agreement for all the bath temperatures considered. A boundary thermal conductance across the wire wall and superfluid helium bath interface is inferred by adjusting the calculated velocities with the experimental data. The deduced boundary thermal conductance is similar to the Kapitza conductance in the sense that both are proportional to the superfluid helium bath temperature raised to a constant power. Furthermore the deduced boundary conductance seems unaffected by the dynamical aspect of the longitudinal destruction process of the superconducting state and by the heat flux range across the solid and He II separating boundary covered by the normal zone propagation velocity versus the circulating electrical current plots. To the authors knowledge this is the first study of heat transfer using the data obtained from longitudinal normal zone propagation experiments.     

Experimental verification of a theoretical model for erbium-doped fibre ring lasers

A simple theoretical model for erbium-doped fibre ring lasers is presented. This model is experimentally verified by means of the comparison between theoretical values and measurements of efficiency, threshold pump power and output laser power employing a wide set of experimental situations. This model provides semi-analytical equations, which characterise the erbium-doped fibre, determining its absorption and emission spectral coefficients.     

扫地机器人触发式液压辅助越障机构的设计

针对扫地机器人越障高度较低的问题,设计了一种触发式液压辅助越障机构。该机构无须额外驱动即可使机器人在正常行驶和越障模式之间来回切换,减小了控制单元的复杂度。首先,介绍了机构各模块的结构组成和工作原理;其次,利用UG软件绘制了辅助越障机构的三维结构图,分析了驱动轮在越障临界点的受力,给出了辅助驱动力的计算公式;再次,对其易损件——液压杆进行静力学分析,并对装有触发式液压辅助越障机构的扫地机器人进行了越障仿真,从理论上验证了该机构的可行性;最后,根据扫地机器人的产品参数,结合实际工况,制作了辅助越障机构,并将其搭载在扫地机器人上进行实验。理论分析与实验结果表明,触发式液压辅助越障机构能提供足够的辅助驱动力,提高了扫地机器人的越障高度,有效解决了扫地机器人在越障时因动力不足而被卡死的问题。研究结果可为扫地机器人的结构优化提供参考。     

下肢外骨骼助力机器人动力学建模及实验研究

下肢外骨骼助力机器人存在人?机关节是否匹配、主动关节设计是否满足人体关节运动的驱动力要求等问题。为解决上述问题,基于所设计的电液伺服驱动下肢外骨骼助力机器人,将其简化为七连杆结构,并结合步态平衡理论,采用牛顿?欧拉法构建了其摆动相与支撑相瞬时动力学模型。然后,将不同步态相位下人体运动时的角度数据、速度数据及机器人结构参数代入牛顿?欧拉动力学迭代方程,求得机器人各关节的理论驱动力矩。最后,开展ADAMS（automatic dynamic analysis of mechanical systems,机械系统动力学自动分析）仿真实验和人机协同助行实验,通过对机器人各关节的驱动力矩峰值进行比较,验证了所构建动力学迭代方程的正确性和有效性。结果表明,通过采用牛顿?欧拉法来求解下肢外骨骼助力机器人关节的驱动力矩,可为其结构优化与控制策略制定提供重要的理论支撑。     

混凝土湿喷机臂架系统的动力学建模与分析

 针对混凝土湿喷机臂架系统的液压油缸驱动力难以显式计算的问题,采用解析几何法和拉格朗日方程建立混凝土湿喷机臂架系统的动力学模型．将驱动油缸等效为活塞杆沿着套筒运动的二连杆机构,这样臂架成为不完全开链的十连杆机构．采用解析几何法,推导臂架杆件转角与液压油缸行程的函数关系,即臂架系统的运动学方程．在运动学基础上根据拉格朗日动力学方程,建立广义力（液压油缸驱动力）对广义坐标（油缸行程）的数学模型．仿真分析时选择了湿喷机的一个典型工作过程,利用符号运算工具MAPLE求解广义力的解析式,并导入MATLAB进行数值求解．同时,利用PRO/E的机构动力学仿真工具对臂架进行分析．对比可见MATLAB与PRO/E仿真结果相吻合,验证了混凝土湿喷机臂架系统动力学模型的正确性．最后,结合动力学模型分析驱动油缸铰点位置变化对油缸工作过程中最大驱动力的影响,结果表明原湿喷机臂架系统结构有待进一步优化．因此,该动力学模型为油缸选型和油缸受力优化提供了理论依据．     

Simulation of the transient response of heat driven refrigerators with continuous temperature control Simulation de la réponse transitoire des réfrigérateurs utilisant une source de chaleur avec maîtrise de la température en continu

A theoretical and experimental study is presented and a mathematical model is introduced for a heat driven refrigeration system operating with continuous temperature control. The model consists of a refrigerated space, an absorption refrigerator, operating irreversibly, a temperature sensor and a reference signal, and a power law control action. The steady-state behavior of the absorption refrigerator model is validated by direct comparison between theoretical results and experimental data. The model is then used to identify an optimal thermal conductance allocation, for a fixed total thermal conductance inventory, such that the refrigeration rate is maximized and the ‘pull-down' time is minimized. A simulation of the system operating in a transient mode is carried out to show that closed-loop operation results in a large reduction of fuel consumption, with respect to the ‘on–off' operation. Appropriate dimensionless groups are identified and the generalized results reported in charts using dimensionless variables.     

Tunable ultrashort electro-optical power divider using coupled photonic crystal waveguides

Photonic crystals (PCs) have many potential applications because of their ability to control lightwave propagation. We have investigated a tunable ultrashort electro-optical power divider in two-dimensional PC structures. The power divider, composed of a dielectric cylinder in air, is studied by solving Maxwell's equations using the plane wave expansion method and finite-difference time-domain method. The power-splitting mechanism is analogous to that of conventional directional couplers, utilizing coupling between guided modes supported by line defect waveguides. To increase the coupling coefficient of the PC coupler, the radius of the rods between two waveguides is reduced. The switching mechanism is a change in the conductance in the coupling region between the waveguides and hence modulating the coupling coefficient, and eventually switching is achieved. Such a mechanism of wavelength multiplexing should open up a new application for designing components in photonic integrated circuits.