冲击拉伸实验装置的研制及其试验研究

材料动力学试验技术远比准静态力学中的复杂,为了模拟各种速率的冲击加载过程,试验装置设计就成为关键问题之一.特别是针对材料动态拉伸性能的测试,目前的冲击拉伸装置还没有统一标准,因此本文基于一维弹性应力波原理设计了一套双气室间接杆-杆型冲击拉伸试验装置.该装置采用了双气室对称布置的方式,通过气体转换器实现气路的转换,克服了现有气动式冲击拉伸设备结构复杂、密封要求严格的缺点.本文利用该装置对2A12T4铝合金试件的冲击拉伸性能进行了测试,并数值分析了应力波在杆系和试件中的传播效应.通过试验测试和数值分析论证了该冲击拉伸装置实验的可靠性和设计的合理性.     

三稳态压电俘能器的势能函数及对其性能的影响

基于压电本构方程、牛顿第二定律和基尔霍夫定律,推导了机械式三稳态非线性压电俘能器的数学模型,采用数值方法研究了压电俘能器的势能函数及其对系统动力学响应和俘能特性的影响,同时,分析了刚度比和弹簧位置参数对势能函数性状的影响。研究结果表明:三稳态压电俘能器系统的势能函数具有三个势阱且具有对称性,当系统初始位置位于较浅的势阱附近时,系统将更容易做大幅阱间运动,降低有效俘能的激励幅值阈值,能够在较小的激励幅值下产生较大的均方根电压;在阱间运动情况下,势阱宽度越大,系统的均方根电压越大;弹簧位置参数和刚度比等系统参数会影响势阱深度与势阱宽度的大小,通过合理地设计系统参数,能有效提高系统均方根电压、降低有效俘能的激励幅值阈值。     

基于交叉型双气室空气互联悬架的全地形车侧倾特性研究

设计了一种采用囊式空气弹簧的交叉型双气室空气互联悬架 (PIS 悬架),并应用于侧翻事故发生率极高的全地形车上. 建立了交叉型双气室气体耦合 AMEsim 模型与全地形车整车动力学 ADAMS/Car 模型,通过将前者模型中的空气弹簧弹性力作为整车动力学模型的输入变量,将后者模型中的空气弹簧压缩伸张位移作为气体耦合模型的输入变量,建立了完整的机械-气体耦合多自由度动力学联合仿真模型. 通过 J 型弯高速典型仿真实验对搭载 PIS 悬架、双气室非互联悬架 (UN-PIS 悬架) 和普通螺旋弹簧悬架 (HS 悬架) 的全地形车进行侧倾特性对比研究. 研究结果显示,PIS 悬架若关闭互联管路,则会形成 UN-PIS 非互联状态,使悬架刚度瞬间大幅上升,平顺性瞬间变差,而具有相同垂向刚度的 PIS 悬架与 HS 悬架,前者能够提供更多的侧倾角刚度. 研究了气路系统 中影响动态侧倾特性的相关因子,包括连接管路管长、管径、附加气室容积. 研究表明,互联管路管长越小,越有利于提升全地形车侧倾特性,存在临界管径,管径小于或大于该值时,均会小幅度提升侧倾特性,附加气室容积越小,侧倾角刚度越大,为 PIS 悬架气路系统设计提供理论依据.      

ROLL CHARACTERISTICS OF ALL-TERRAIN VEHICLE BASED ON CROSSING DOUBLE AIR CHAMBER PNEUMATICALLY INTERCONNECTED SUSPENSION$^{\bf 1)}$

设计了一种采用囊式空气弹簧的交叉型双气室空气互联悬架 (PIS 悬架),并应用于侧翻事故发生率极高的全地形车上. 建立了交叉型双气室气体耦合 AMEsim 模型与全地形车整车动力学 ADAMS/Car 模型,通过将前者模型中的空气弹簧弹性力作为整车动力学模型的输入变量,将后者模型中的空气弹簧压缩伸张位移作为气体耦合模型的输入变量,建立了完整的机械-气体耦合多自由度动力学联合仿真模型. 通过 J 型弯高速典型仿真实验对搭载 PIS 悬架、双气室非互联悬架 (UN-PIS 悬架) 和普通螺旋弹簧悬架 (HS 悬架) 的全地形车进行侧倾特性对比研究. 研究结果显示,PIS 悬架若关闭互联管路,则会形成 UN-PIS 非互联状态,使悬架刚度瞬间大幅上升,平顺性瞬间变差,而具有相同垂向刚度的 PIS 悬架与 HS 悬架,前者能够提供更多的侧倾角刚度. 研究了气路系统 中影响动态侧倾特性的相关因子,包括连接管路管长、管径、附加气室容积. 研究表明,互联管路管长越小,越有利于提升全地形车侧倾特性,存在临界管径,管径小于或大于该值时,均会小幅度提升侧倾特性,附加气室容积越小,侧倾角刚度越大,为 PIS 悬架气路系统设计提供理论依据.     

双稳态电磁式振动能量捕获器超谐波响应研究

超谐波响应是非线性振动系统在较大激励下表现的特性,在某种条件下双稳态振动能量捕获系统的超谐波响应可使系统产生优越的输出功率。本文将质量-非线性弹簧-阻尼系统与双稳态振动能量捕获器相结合,提出了附加非线性振子的双稳态电磁式振动能量捕获器,建立系统的力学模型及控制方程。采用两项式谐波平衡法,获得了双稳态系统在简谐激励下产生大幅运动的基谐波和超谐波响应的解析解,借助数值仿真分析了质量比和调频比对双稳态振动能量捕获器产生大幅运动的影响规律,获得了双稳态系统的结构参数的最佳配置范围,且当外部激励频率处于低频段时,系统发电主要表现为超谐波发电,随着激励频率的增大,振动发电系统主要呈现基谐波发电。上述研究,为双稳态能量捕获装置的理论研究提供了参考。     

浮台多向运动对水下锚索共振响应影响研究

在复杂的海洋环境中,上部浮式结构受到波、浪、流共同作用,会产生多个方向的运动,进而诱发水下锚索产生复杂的动力学行为,影响海洋工程结构的安全性和稳定性．本文考虑水下锚索垂度效应所带来的二次非线性效应,探究上部浮台纵荡和垂荡运动对水下锚索振动响应的影响．建立上部浮台多方向运动影响下水下锚索的动力学模型,推导其运动微分方程,并采用多尺度法对运动微分方程开展近似分析以及稳定性分析．研究结果表明：系统的共振响应随着垂荡位移的增加而增加,随着垂跨比的增加而减小;随着垂荡位移的增加,系统越发容易失去稳定性;随着倾角和初始张力的变化,系统的不稳定区域也会发生定性和定量的改变;与仅考虑参激作用的情况相比,参强联合作用时水下锚索的振动响应幅值会增加．     

考虑海底接触的钢悬链式立管触地点动力响应以及疲劳损伤分析

基于考虑接触的钢悬链式立管SCR(Steel Catenary Riser)触地点处的结构特性,分别采用了考虑管土分离的线性截断模型以及包含土体吸力效应的帽盖模型来描述P-y曲线。通过改变上端浮体的垂荡运动幅度、土体吸力系数以及海床刚度,对SCR触地点处的动力响应以及疲劳损伤特性进行了分析。分析结果表明,SCR触地点的垂向位移、弯矩、等效应力以及疲劳损伤均随着浮体垂荡运动幅度的增加而呈上升趋势。SCR触地点的垂向位移随着土体吸力系数的增大由高幅低频响应转变为低幅高频响应。SCR触地点的疲劳损伤随着海床刚度的增加呈现先稳定再增加再稳定的趋势。     

双稳态压电俘能器的簇发振荡与俘能效率分析

本文从理论上分析了双稳态压电俘能器在高频激励下的动力学行为和低频激励下的簇发振荡, 旨在为系统找到多条高能轨道从而提高俘能效率. 首先, 介绍了双稳态压电俘能器的结构以及一般模型. 与工程上研究俘能器的目的不同, 本文主要从动力学方面分析了俘能器的运动, 电压输出与效率, 包括高频激励下系统的低能阱内周期运动、阱间混沌运动等, 并说明了单个低频激励下双稳态压电俘能器会在阱间高能轨道上发生簇发振荡, 但在阱内低能轨道上只做周期运动. 同时, 结合振幅以及势阱深度等因素对簇发振荡的存在性和强度进行分析. 为了说明高能轨道与低能轨道对系统俘能效率的影响, 讨论了不同的等效阻尼、负载电阻下俘能器输出电压的变化, 找到了最优匹配. 最后, 对于多个低频外激励的情况, 从不同的轨道组合模式上得到了双高能簇发振荡模式输出的电压最大, 其次是单高能簇发振荡与单低能周期振荡的组合模式, 输出电压最低的是双低能周期振荡模式. 并与单个外激励进行对比, 表现了多个激励的良好性能.      

基于时域解耦算法的多液舱浮式结构物运动模拟

对于带有多个晃荡液舱的浮式结构物,浮体的运动、外场水动力以及各舱内的液体晃荡力会实时相互决定,发生复杂的耦合作用.为准确模拟多液舱浮式结构物的运动,本文引入一种有效的时域解耦算法.该方法以模态分解法为基础,通过对浮式结构物所受外域水动力和各液舱内非线性晃荡力进行模态分解,最终形成时域解耦运动方程,无需迭代求解过程即可显式计算浮式结构物的瞬时加速度.该方法可避免传统迭代求解方法在迭代次数、截断误差和收敛特性等方面的不足,减少解耦过程的计算耗时.本文进一步结合边界元数值方法,分别对单液舱浮式结构物和多液舱浮式结构物的工况开展数值模拟研究.通过与单液舱浮式结构物的实验结果对比,验证了本文时域解耦算法的有效性.本文详细分析了晃荡力对单液舱浮式结构物运动的影响,发现存在一个共振影响区间:当外场波浪频率在该区间之外时,可以在时域计算结果中观察到稳定的浮体运动;在比该区间更低频的波况下,液舱晃荡力与外场波浪力相位相反甚至可以相互抵消,此时晃荡液舱的存在可以减弱浮体运动;在比该区间更高频的波况下,液舱内晃荡力与外场波浪力可以具有相同相位,此时晃荡液舱的存在会加剧浮体的运动.本文进一步研究了四液舱浮式结构物在波浪中的纵荡、垂荡和纵摇运动情况,发现非线性液舱晃荡可对纵荡和纵摇运动产生影响,但对垂荡运动影响很小.     

基于时域解耦算法的多液舱浮式结构物运动模拟

对于带有多个晃荡液舱的浮式结构物, 浮体的运动、外场水动力以及各舱内的液体晃荡力会实时相互决定, 发生复杂的耦合作用. 为准确模拟多液舱浮式结构物的运动, 本文引入一种有效的时域解耦算法. 该方法以模态分解法为基础, 通过对浮式结构物所受外域水动力和各液舱内非线性晃荡力进行模态分解, 最终形成时域解耦运动方程, 无需迭代求解过程即可显式计算浮式结构物的瞬时加速度. 该方法可避免传统迭代求解方法在迭代次数、截断误差和收敛特性等方面的不足, 减少解耦过程的计算耗时. 本文进一步结合边界元数值方法, 分别对单液舱浮式结构物和多液舱浮式结构物的工况开展数值模拟研究. 通过与单液舱浮式结构物的实验结果对比, 验证了本文时域解耦算法的有效性. 本文详细分析了晃荡力对单液舱浮式结构物运动的影响, 发现存在一个共振影响区间: 当外场波浪频率在该区间之外时, 可以在时域计算结果中观察到稳定的浮体运动; 在比该区间更低频的波况下, 液舱晃荡力与外场波浪力相位相反甚至可以相互抵消, 此时晃荡液舱的存在可以减弱浮体运动; 在比该区间更高频的波况下, 液舱内晃荡力与外场波浪力可以具有相同相位, 此时晃荡液舱的存在会加剧浮体的运动. 本文进一步研究了四液舱浮式结构物在波浪中的纵荡、垂荡和纵摇运动情况, 发现非线性液舱晃荡可对纵荡和纵摇运动产生影响, 但对垂荡运动影响很小.      

Numerical study on the dynamics of a two-raft wave energy conversion device

This paper presents a dynamic analysis of a two-raft wave energy conversion device based on the three-dimensional wave radiation-diffraction method. The device consists of two hinged cylindrical rafts of elliptical cross section and a power take-off system at the joint. The effect of raft length, linear damping and spring coefficient in the power take off (PTO) system, axis ratio (ratio of minor axis to major axis of raft elliptical cross section) and raft radius of gyration on wave energy capture factor has been investigated in frequency domain, while the effects of a nonlinear Coulomb power take-off, raft radius of gyration and latching control have been studied in time domain. The difference in the performance of a raft-typed device obtained using a linear damping and a Coulomb damping is also illustrated.     

Capturing the experimental behaviour of a point-absorber WEC by simplified numerical models

The paper presents a wave basin experiment of a direct-driven point-absorber wave energy converter moving in six degrees of freedom. The goal of the work is to study the dynamics and energy absorption of the wave energy converter, and to verify under which conditions numerical models restricted to heave can capture the behaviour of a point-absorber moving in six degrees of freedom. Several regular and irregular long-crested waves and different damping values of the power take-off system have been tested. We collected data in terms of power output, device motion in six degrees of freedom and wave elevation at different points of the wave basin. A single-body numerical model in the frequency domain and a two-body model in the time domain are used in the study. Motion instabilities due to parametric resonance observed during the experiments are discussed and analysis of the buoy motion in terms of the Mathieu instability is also presented. Our results show that the simplified models can reproduce the body dynamics of the studied converter as long as the transverse non-linear instabilities are not excited, which typically is the case in irregular waves. The performance of the more complex time domain model is able to reproduce both the buoy and PTO dynamics, while the simpler frequency domain model can only reproduce the PTO dynamics for specific cases. Finally, we show that the two-body dynamics of the studied wave energy converter affects the power absorption significantly, and that common assumptions in the numerical models, such as stiff mooring line or that the float moves only in heave, may lead to incorrect predictions for certain sea states.     

Effect of the stiffness,inertia and oscillation kinematics on the thrust generation and efficiency of an oscillating-foil propulsion system

This paper presents an experimental study that has investigated the effects of the foil stiffness, inertia and oscillation kinematics on the thrust generation and efficiency of a flexible oscillating-foil propulsion system. A semi-empirical damped-oscillator model, which included a quadratic damping element, was developed and fitted to the experimental results. The model was used to develop explanations for the observed trends in the propulsive performance. For all of the foils constructed for the study, a consistent relationship between the efficiency and frequency ratio was observed. The maximum efficiency occurred at the same frequency ratio that resulted in both a beneficial phasing of the deformation with respect to the driven motion and also the maximum overall amplitude of the motion. For foils of equivalent resonant frequency operating at the same frequency ratio, the stiffer and heavier foils were found to develop greater thrust, likely because the lower effective damping allowed for a greater amplitude of the motion. Increasing the amplitude of the driven motion was found to cause the frequency ratio providing the maximum efficiency to shift towards lower values. The use of combined pitch and heave motions was shown to increase efficiency while reducing thrust compared to the heave-only case.     

Hybrid analytical/numerical modeling of nanosecond laser-induced micro-jets generated by liquid confining devices

The generation of micro-jets with pulsed laser irradiation is a key enabling technique for microfluidic devices, printers and needle-free drug injectors. Modeling approaches for such devices are essential to optimize their design and performance. Here we present a hybrid analytical/numerical model to simulate nanosecond laser-induced micro-jets generated by a dual-chamber liquid confining device. The simulated device consists of two chambers; the first one is closed and filled with a propellant liquid and the second is filled with the liquid to be ejected and equipped with a nozzle. Laser-induced cavitation is generated in the first chamber, which is separated by an elastic membrane from the second one, to reduce the thermo-mechanical impact of the absorbed laser energy on the liquid to be ejected. By modifying the generalized form of the Rayleigh–Plesset equation to account for the pressure variation inside the chamber, we show that the geometry of the liquid confining device affects drastically laser-induced bubble dynamics and the resulting jet ejection dynamics. We also demonstrate the effect of the membrane size, laser energy and nozzle size variation on the micro-jet dynamics. We found that such devices can generate micro-jets (velocity: 0.93 m/s to 48.39 m/s) suitable for micro-drop printing (volume: 0.097 nL to 7.68 nL). Although we focused on printing applications, the modeling approach presented here can be widely adapted for designing and optimizing needle-free drug injectors and microfluidic devices.     

传统Spar平台垂荡主共振时非线性耦合响应的研究

考虑瞬时波面影响,建立了Spar平台垂荡-纵摇运动的参数激励耦合运动方程,应用多尺度法导出了波浪频率接近垂荡固有频率时响应方程的一阶摄动解并做数值验证。计算结果显示:当波浪高度达到一定值时,纵摇运动中出现大量的亚谐频率成分;随着波浪高度进一步增大,纵摇运动将出现明显的幅值跳跃现象。研究结果表明,能量渗透现象是纵摇运动失稳的主要原因,波浪激励力矩对于纵摇本身的贡献很小。由于垂荡模态存在能量饱和现象,多余的垂荡能量将会向纵摇模态转移,导致出现大幅值的纵摇运动。     

Wave flume experiments on two-dimensional oscillating water column wave energy devices

Experiments were performed in a wave flume with regular waves of very small amplitude-to-wavelength ratio (less than 0.01). Their purpose was mainly the validation of the oscillating surface pressure theory of Sarmento and Falcão (1985) applied to wave energy absorption by oscillating water column (OWC) devices. Experimental and theoretical curves for the efficiency and for the reflection and transmission coefficients were obtained and compared. The test also included the validation of the two-wave-gauge experimental procedure used to decouple direct and reflected wave trains, as well as the effects of increasing the depth of immersion of the OWC overhang on the efficiency-wave period curves.     

波浪与新型双排开孔圆筒防波堤相互作用三维数值模拟

双排开孔圆筒防波堤是基于圆筒、板式结构的一种复合式新型结构型式;基于不可压缩两相流模型建立三维数值波浪水槽,通过RNG k-ε湍流模型进行湍流封闭,并采用TruVOF方法捕捉自由液面,开展波浪与双排开孔圆筒防波堤相互作用数值模拟,探究相对排间距、开孔率对新型双排开孔圆筒防波堤消浪性能的影响,分析了后排开孔圆筒防波堤附近的复杂水动力现象和流动特性.结果表明,在本文研究工况范围内,沿程平均波高随相对排间距的增大先增大后减小,随开孔率的增大而增大,周期对沿程平均波高的影响没有明显规律;当B/D=9, e=23.11%时,新型双排开孔圆筒防波堤消浪效果最优,反射系数在0.4～0.46之间,透射系数在0.3～0.35之间,耗散系数在0.8～0.85之间;自由液面破碎、水气掺混、环状涡运动演化是新型双排开孔圆筒防波堤紊动耗能消波的主要原因;相对排间距会引起后排防波堤附近涡量分布以及剪切层形态的变化,从而导致不同的紊动特性,影响双排开孔圆筒防波堤消浪特性.研究结果可以为新型双排开孔圆筒防波堤工程设计与消浪机理研究提供理论支撑.     

Shock waves in an elliptical cavity with varying height

Transient shock waves in a confined elliptical chamber are experimentally investigated. Quantitative results of the pressure distribution are obtained for an air-filled cavity. Lower bounding surfaces of different geometrical shapes can be inserted making it possible to get chambers with varying height. An electrical discharge across a pair of electrodes inside the cavity gives rise to the shock waves. Double pulsed holographic interferometry is used to study the propagation and focusing process of the waves. The results are quantitatively evaluated by using the method of two-reference-beam holography. The angular pressure distribution behind the converging wave front is presented for different geometries of an air-filled cavity. The pressure distribution is non-homogeneous but symmetric along the wave front. The pressure level is higher for the geometry where the height of the chamber decreases with the radial distance from the outgoing focus and lower for increasing height of the chamber. In addition, shock waves in a water-filled cavity are studied. In this case qualitative results are obtained. Received 3 November 1996 / Accepted 5 January 1997     

高速破片撞击充液容器时容器壁面的损伤

为研究高速破片（钨球）撞击充液容器（贯穿前后壁面）时容器壁面的毁伤情况，利用ANSYS/LS-DYNA对该过程进行了数值模拟，分析了破片撞击动能对充液容器前后壁面毁伤程度的影响，并进行实验验证。结果表明:高速破片撞击充液容器形成的液压水锤对充液容器前后壁面的破坏程度可分为3个等级，即前后壁面均未出现裂纹、前壁面没有出现裂纹后壁面出现裂纹和前后壁面均出现裂纹且后壁面呈花瓣式开裂；破片撞击充液容器过程中，前后壁面的最大变形量和前后壁面的裂纹总数随破片撞击动能的增加而增大。     

爆轰产物驱动飞片运动数值模拟研究

利用数值模拟方法,研究了主装药与飞片之间的空气隙厚度变化对飞片中载荷幅度和载荷上升时间、飞片速度和飞片变形量的影响。数值模拟与验证实验结果吻合得较好。结果表明,带空气隙的化爆加载装置可以在飞片中获得较小的载荷幅度和较长的载荷上升时间,并且可以降低飞片击靶速度,从而实现较低的冲击压力,但飞片变形量随着空气隙厚度增大而增大。