Effects of Second-Order Sum-and Difference-Frequency Wave Forces on the Motion Response of a Tension-Leg Platform Considering the Set-down Motion

This paper presents a study on the motion response of a tension-leg platform(TLP) under first-and second-order wave forces, including the mean-drift force, difference and sum-frequency forces. The second-order wave force is calculated using the full-field quadratic transfer function(QTF). The coupled effect of the horizontal motions, such as surge, sway and yaw motions, and the set-down motion are taken into consideration by the nonlinear restoring matrix. The time-domain analysis with 50-yr random sea state is performed. A comparison of the results of different case studies is made to assess the influence of second-order wave force on the motions of the platform. The analysis shows that the second-order wave force has a major impact on motions of the TLP. The second-order difference-frequency wave force has an obvious influence on the low-frequency motions of surge and sway, and also will induce a large set-down motion which is an important part of heave motion. Besides, the second-order sum-frequency force will induce a set of high-frequency motions of roll and pitch. However, little influence of second-order wave force is found on the yaw motion.

Investigation on the Radial Micro-motion about Piston of Axial Piston Pump

The limit working parameters and service life of axial piston pump are determined by the carrying ability and lubrication characteristic of its key friction pairs. Therefore, the design and optimization of the key friction pairs are always a key and difficult problem in the research on axial piston pump. In the traditional research on piston/cylinder pair, the assembly relationship of piston and cylinder bore is simplified into ideal cylindrical pair, which can not be used to analyze the influences of radial micro-motion of piston on the distribution characteristics of oil-film thickness and pressure in details. In this paper, based on the lubrication theory of the oil film, a numerical simulation model is built, taking the influences of roughness, elastic deformation of piston and pressure-viscosity effect into consideration. With the simulation model, the dynamic characteristics of the radial micro-motion and pressure distribution are analyzed, and the relationships between radial micro-motion and carrying ability, lubrication condition, and abrasion are discussed. Furthermore, a model pump for pressure distribution measurement of oil film between piston and cylinder bore is designed. The comparison of simulation and experimental results of pressure distribution shows that the simulation model has high accuracy. The experiment and simulation results demonstrate that the pressure distribution has peak values that are much higher than the boundary pressure in the piston chamber due to the radial micro-motion, and the abrasion of piston takes place mainly on the hand close to piston ball. In addition, improvement of manufacturing roundness and straightness of piston and cylinder bore is helpful to improve the carrying ability of piston/cylinder pair. The proposed research provides references for designing piston/cylinder pair, and helps to prolong the service life of axial piston pump.

基于COSMOSMotion的轴向柱塞泵运动仿真

利用三维SolidWorks软件建立轴向柱塞泵三维模型,并利用其插件CAE软件COSMO-SMotion对轴向柱塞泵进行运动仿真,以验证设计参数的合理性,得出相关曲线,为轴向柱塞泵的设计提供指导,提高轴向柱塞泵设计的形象性和直观性。

基于Pro/E MECHANIC MOTION的活塞压缩机运动仿真

在Pro/E环境中,Pro/E的Mechanism能方便地对任何实际的二维或三维机构进行较复杂的运动学分析,并且结合Pro/Mechanic的motion模块对运动构件进行设计仿真。活塞压缩机的运动仿真从运动的角度保证了所设计的压缩机结构的合理性和可靠性。

Theoretical Analysis of Noise of Piston Knocking Cylinder Wall in Automotive Engines

Based on the loading conditions of engine, applying difference method to solve the hydrodynamic lubrication equation of piston skirt movement, the force acting on piston skirt and the moment on wrist pin were obtained. A computer program for simulating the piston second order motion was conducted to calculate the lateral motion of the upper part and the bottom part of piston skirts of the engine of automotive model CA1091. From the simulated result, the maximal impacting phase and the maximal impacting region of the piston were obtained. The result can be used for designing engine, diagnosing the noise of piston knocking cylinder wall and explaining many practical fault phenomena in theory.

A Method for Calculation of Low-Frequency Slow Drift Motions Based on NURBS for Floating Bodies

Through a higher-order boundary element method based on NURBS （Non-uniform Rational B-splines）, the calculation of second-order low-frequency forces and slow drift motions is conducted for floating bodies. In the floating body＇s inner domain, an auxiliary equation is obtained by applying a Green function which satisfies the solid surface condition. Then, the auxiliary equation and the velocity potential equation are combined in the fluid domain to remove the solid angle coefficient and the singularity of the double layer potentials in the integral equation. Thus, a new velocity potential integral equation is obtained. The new equation is extended to the inner domain to reheve the irregular frequency effects; on the basis of the order analysis, the comparison is made about the contribution of all integral terms with the result in the second-order tow-frequency problem; the higher-order boundary element method based on NURBS is apphed to calculate the geometric position and velocity potentials; the slow drift motions are calculated by the spectrum analysis method. Removing the solid angle coefficient can apply NURBS technology to the hydrodynamic calculation of floating bodies with complex surfaces, and the extended boundary integral method can reduce the irregular frequency effects. Order analysis shows that free surface integral can be neglected, and the numerical results can also prove the correctness of order analysis. The results of second-order low-frequency forces and slow drift motions and the comparison with the results from references show that the application of the NURBS technology to the second-order low-frequency problem is of high efficiency and credible results.

Research on Coupling Transfer Characteristics of Vibration Energy of Free Piston Linear Generator

In order to clarify the mechanism and main influencing factors of the vibration energy coupling transmission with a dual-piston structure,a thermodynamic and dynamic coupling model of the free piston linear generator(FPLG)was established.The system energy conversion,vibration energy coupling transmission,and influencing factors were studied in detail.The coupling transmission paths and the secondary influence mechanism from in-cylinder combustion on vibration energy transmission were obtained.In addition,the influence of the movement characteristics of the dual-piston on the vibration energy transmission was studied,and the typical parameter variation law was obtained,which provides theoretical guidance for the subsequent vibration reduction design of the FPLG.

Mixed Lubrication Analysis and Experiment Validation of Internal Combustion Piston Skirt

A mixed lubrication model was established for piston skirt lubrication. The mathematical model developed in this paper incorporates governing equations of motion with average Reynolds equation. This model considers the surfaceroughness and profile. The corresponding computer program can be used to calculate oscillatory motion of piston during the entire trajectory, which has the excellent convergence.In addition, a set of equipment, which adopt the laser induced fluorescent method, was developed to measure the oil film thickness between the piston and the bore.

基于西门子SIMOTION C240运动控制系统的活塞铸造机自动化控制设计

活塞铸造加工具有精密度高、节拍快以及批量大等有点,在应用过程中不仅需要设定铸造机机械手精准路径,还应该对整机开关量模拟信号与逻辑控制进行监测,并根据工艺要求与产品型号快速切换铸造程序。根据市场发展需要,设计一套满足铸造机与配套浇注机械手控制系统需要的自动化控制系统,该系统采用SIMOTION C240运动控制系统,在完成机械手动作控制的同时,还使铸造机逻辑控制得以实现,实现活塞浇注、出模、凝固、卸料以及淬火等工序自动化操作,为现代化产品制造提供技术支持。

基于COSMOSMotion的活塞压缩机运动仿真分析

建立活塞压缩机的三维模型,并利用COSMOSMotion进行运动仿真,形象地展示活塞压缩机的运动,得出相关参数曲线。理论上推导和分析活塞压缩机的运动参数,以验证仿真结果的精确性。为活塞压缩机的设计提供指导,提高设计的形象性和直观性。

旋转对置活塞发动机运动学特性研究

高功率密度发动机是未来内燃机的发展趋势.旋转对置活塞发动机结构简单,做功频率是传统往复式活塞发动机的两倍,可以显著提高发动机的理论功率密度,是小型无人机、混合动力系统的理想动力源.文中通过建立数学模型,探究了旋转对置活塞发动机的结构参数对活塞运动规律、气缸容积变化规律和压缩比的影响,分析了相邻活塞运动碰撞的边界条件.研究结果表明,活塞线速度对椭圆齿轮节曲线偏心率的变化最为敏感,当线速度大于平均值时,线速度与偏心率成正比,线速度小于平均值时则成反比;偏心率的增大可以减小气缸的余隙容积,且使下止点对应的气缸容积增大,进而调节发动机的压缩比;活塞端面夹角增大可以减小气缸的余隙容积;偏心率和活塞端面夹角在±10%的范围内变化时,压缩比相应的变化范围分别为5.62~12.04和5.01~23.45,当偏心率过大时将导致相邻活塞发生碰撞.

悬架用活塞一体式二级压缩机性能的研究

为了了解空气悬架用大、小活塞一体式二级往复空气压缩机的工作性能,为新机型设计、优化和物理样机实验提供依据。根据整体尺寸建立压缩机运动学数学模型,基于AMESim对空气压缩机整个系统充罐过程进行建模和仿真,仿真得到新型空气压缩机一二级缸充罐过程中压力变化特性;并与传统单级压缩机型进行对比,仿真结果表明;新型二级活塞一体式空气压缩机在充罐压力较高时能保持较高的充气效率,在设定17bar工况下,气体对活塞作用力以及阻力矩峰值为传统机型的56%和47%,并且曲线变化更平缓,说明采用新型二级压缩机型能有效提高容积系数,降低负载波动,提高压缩机运行稳定性。对两种机型进行了物理样机试验,试验结果表明:在储气罐3.7 L,压力由大气压充压至17 bar条件下,新机型升压时间相较传统机型用时少27.3 s,在高压段新机型充气性能优于传统机型,仿真充罐规律与试验结果相吻合。

基于AMESim的多液缸合流式压裂泵流量脉动特性研究

传统的机械式压裂泵存在冲次高、冲程短、曲轴易于失效等问题,为此,提出了一种多液缸合流式液压驱动压裂泵,并对其产生流量脉动的机理进行了研究。首先,详细阐述了多液缸合流式压裂泵的工作原理,基于液压流体力学等理论,建立了多液缸合流式压裂泵的数学模型,并进行了理论分析;其次,采用AMESim仿真软件搭建了多液缸合流式压裂泵工作仿真模型,选择了合理的仿真参数设置,进行了变负载压力下的仿真研究;最后,对液压动力传递链中的活塞-柱塞运动特性、泵腔流量特性、输出流量和压力脉动特性进行了研究,并对仿真结果进行了分析。研究结果表明:在25 MPa工况下,多液缸合流式压裂泵的输出压力和流量脉动率分别为36.8%和20.61%,冲次只有42次/min,符合实际工况;多液缸合流式压裂泵输出流量脉动的主要原因是各组液缸的频繁换向、泵送行程和吸入行程的切换,导致活塞-柱塞做减速停止运动和加速启动运动。

Motion de-blurring by second-order intensity-correlated imaging

For a Hanbury Brown and Twiss system, the influence of relative motion between the object and the detection plane on the resolution of second-order intensity-correlated imaging is investigated. The analytical results, which are backed up by experiments, demonstrate that the amplitude and mode of the object＇s motion have no effect on the second-order intensity-correlated imaging and that high-resolution imaging can be always achieved by using a phase-retrieval method from the diffraction patterns. The use of motion de-blurring imaging for this approach is also discussed.

活塞动力学二阶运动的仿真方法与试验研究

采用多体动力学在时间域内迭代计算活塞、缸套及润滑油膜相互耦合子系统的运动学与动力学方程,在考虑活塞体径向刚度、活塞体及缸套冷热态型面的影响下,得到活塞主、副推力侧实际工况下的热态配缸间隙;动力学仿真方法计算出活塞二阶运动结果,包括:活塞主、副推力面间换向的径向运动和绕活塞销的转动;二阶运动对缸套的动态敲击力作为载荷边界条件施加在有限元模型上,计算出气缸体在活塞敲击下的振动响应;同时,在发动机台架上对气缸体两侧的活塞敲击处布置加速度传感器、以及布置缸内爆压传感器和上止点位置测量得到气缸体结构振动响应,试验结果验证了仿真模型的有效性。

活塞裙部的润滑分析及活塞系统2阶运动的研究

基于平均流量模型分析了活塞裙部的润滑问题，并且与活塞运动方程结合，求解了活塞系统２阶运动的轨迹，探讨了活塞结构参数对２阶运动的影响，计算和比较了在不同参数下活塞裙部的摩擦力。

单活塞式液压自由活塞发动机运动特性研究

研究单活塞式液压自由活塞发动机运动特性。根据单活塞式液压自由活塞发动机样机结构,采用AMESim建立了发动机性能预测模型并进行试验研究,发动机性能预测结果与试验数据基本一致。单活塞式液压自由活塞发动机稳定工作时输出特性单一,运动过程重复性好,循环过程不对称且压缩冲程较膨胀冲程耗时长。活塞运动加速度大,在上止点停留时间短。发动机压缩比可无级变化,其工作频率可控且受极限频率限制,输出流量具有间歇性特征且输出压力基本恒定。

汽车发动机活塞裙部-缸套系统摩擦学仿真分析和减摩设计

摩擦学在降低发动机摩擦损失和提高系统可靠性方面具有很大的潜力.本文以汽车发动机活塞裙部-缸套系统为对象,以寻求降低该系统摩擦损失的技术方案为目标,考虑各种因素建立了内燃机活塞裙部混合润滑模型.利用该模型,对活塞裙部型面的改进设计进行了探索,并据此确定了某款发动机活塞的改进方案.仿真结果表明:所提出的改进方案,均能实现显著降低活塞裙部-缸套系统摩擦损失的目标,最大降幅达到45.5%.

活塞裙部型线对活塞系统二阶运动和摩擦功率的影响

从活塞的动力学分析开始，结合流体动力润滑方程，建立了缸套活塞裙部间的润滑模型。该模型采用优化的数值分析方法，使计算程序有较好的收敛性，能计算出整个四冲程范围内的活塞二阶运动和摩擦功率的轨迹。此外，作者将原始的直线型线和国外先进机型的中凸型线输入计算程序中，探讨了其对活塞裙部型面的作用和优劣。结果表明：中凸型线可以使活塞在上行和下行冲程中均能形成双向油楔。

活塞二阶运动及活塞裙部摩擦的瞬态分析

为分析不同工况下内燃机活塞-缸套系统的摩擦学和动力学行为,本文从内燃机系统动力学分析入手,结合流体润滑方程,建立了考虑系统变惯量影响的活塞二阶运动与摩擦学行为的瞬态分析模型.以某型号单缸机为例,计算和比较了整个启动过程中曲轴转速、二阶运动及摩擦功耗的变化;对比分析了启动时第一周期与稳定运行时某一周期内活塞二阶运动和活塞裙部摩擦学行为的差别.结果表明:该模型可应用于内燃机动力学和摩擦学行为的稳态及瞬态分析.