考虑接触非线性的航行体出水结构动力学分析

水下发射航行体在出水过程中,随着沾湿表面积减少,航行体与周围流体相互作用而产生时变流固耦合效应,并引起结构动力学特性的变化。同时,考虑到航行体通常采用舱段式结构,各舱段在连接处存在非线性接触问题,对结构动力学特性也存在实质性影响。在考虑上述因素影响的情况下,将航行体简化为Timoshenko梁模型并利用有限元方法对结构动特性和动响应进行计算分析,得到了出水过程时变流固耦合效应及连接刚度非线性对航行体结构固有频率及动力响应的影响规律,在此基础上进一步分析了连接结构、载荷及出水速度的变化对结构动响应特性的影响。     

侧滑角对超空泡航行体转弯运动沾湿区域的影响

为了提高通气超空泡航行体在转弯运动过程中空泡和航行体的运动一致性,基于有限体积法和VOF多相流模型,采用动态网格技术对航行体转弯运动的空泡形态特性进行了非定常数值模拟研究。通过对航行体沾湿区域的分析,揭示了沾湿区域形成的原因,利用空化器对空泡轴线的定向效应,提出了合理改变侧滑角减缓沾湿区域出现的具体方法。通过分析侧滑角和侧滑角速度对航行体沾湿区域的影响,提出了超空泡航行体转弯运动过程中,在给定偏航角条件下避免出现沾湿区域的侧滑角和侧滑角速度的适用范围,为进一步研究超空泡航行体机动运动问题提供参考。     

结构化流道近壁区软性磨粒流流动仿真及实验研究

为了揭示结构化流道近壁区软性磨粒流的压力场及速度场的分布规律,有效预测其软性磨粒流的材料去除特性,采用VOF多相流模型和RNG 湍流模型,通过对结构化流道的结构进行合理的网格划分和特殊边界条件设置,对结构化流道内部的软性磨粒流流动进行数值模拟。仿真结果表明：不同的软性磨粒流入口位置对工件加工会产生影响;结构化流道中软性磨粒流的压力场、速度场和软性磨粒流的去除率随着加工区域位置的不同而不同;加工区域入口区域的压力、速度值存在突变,为此在实际加工用引入了引流模块。流场数值模拟和实验研究结果趋势是一致的,数值模拟为深入研究软性磨粒流的基本规律提供一种理论工具     

含气空泡出水过程数值模拟研究

含气空泡在出水过程中会发生溃灭,形成较为复杂且剧烈变化的流场。首先基于含气理想球形空泡溃灭模型,理论上分析了空泡溃灭特性,而后基于均质多相流模型,对航行体出水过程中含气空泡溃灭现象进行了数值模拟分析。计算分析表明,含气空泡溃灭过程存在回弹现象,会在航行体表面形成冲击载荷,空泡内压提高使空泡尺度增大并且可在一定程度上减小空泡内外压差,缓解由空泡周围流体强烈拍击航行体壁面而产生的压力激励。     

航行体加速运动对空泡形态影响研究

基于均质平衡流理论,采用Mixture 多相流模型,通过设置来流速度边界条件随时间的变化,并考虑动坐标系流体体积力,在动量方程中加入源相,实现了超空泡航行体加速过程的数值模拟,得到了航行体加速运动,自然超空泡与通气超空泡形态变化规律.结果表明:航行体加速运动达到匀速状态速度相同的条件下,自然超空泡滞后时间随着加速度减小而减小;在加速度相同的条件下,空泡滞后时间随着速度的增大而减小;航行体加速运动引起通气超空泡形态连续脉动.     

基于VOF法的平底结构自由落体入水砰击载荷模拟

应用动网格技术和VOF方法模拟了平底结构的自由落体入水过程和气-液两相流,得到了平底物体自由落体入水过程的运动特性、砰击载荷特性以及入水空泡演化过程。结果表明:整个入水过程中,平底物体在入水瞬间受到来自液面的砰击载荷最大,砰击面的载荷压力分布中间高两端低;砰击载荷随入水初速的增加而增大;平底物体入水空泡破裂后对上表面造成冲击压力。数值计算方法和结果对入水结构安全性和适应性评估具有实际意义。     

变速超空泡航行体壳结构的动力响应分析

通过对变速超空泡水下航行体壳结构受力模型的分析,建立了恒定推力下航行体的平面运动方程,确定了变速过程中的阻力和冲击力。利用有限元方法,进行了结构响应计算,分析了减速过程中节点时域上的最大应力值在轴向的分布情况及典型节点处的响应。结果表明：航行体所需推力和所受应力较大,对其结构强度要求较高;运动过程中,节点时域上的最大应力在空间域上的极大值主要分布在首尾端部和柱壳中部;存在一些振动频率对航行体结构响应影响显著。结果对超空泡航行体壳结构受力和强度分析以及优化设计有着重要的指导意义。&;#61472;     

轴向载荷下超空泡航行体动力稳定性的数值研究

考虑超空泡航行体头部受到的轴向扰动载荷作用,推导了水下航行体动力失稳控制方程,进而利用Bolotin方法对水下航行体的动力稳定性问题进行了数值计算,得到了相应的临界频率曲线,并分析了载荷参数和航行体参数变化对主动力不稳定区域的影响规律,计算结果可为水下航行体的安全评估提供一定的理论依据。     

基于温度体模型的动网格生成方法及在流固耦合振动中的应用

提出温度体模型动网格生成方法,并将其应用于流固耦合算法,生成物体振动过程中的动态网格。温度体模型动网格方法将运动边界的位移映射为求解域的温度边界条件,以流体能量方程或固体导热方程作为控制方程求解得到计算域内的温度分布,将求解得到的温度分布作为网格节点的动态位移。基于温度体模型的动网格方法物理意义清晰,算法实现简单,能够快速而有效地生成高品质的动态网格,特别在边界位移大的情况下与其他网格生成方法相比有较大的优势。最后采用流固耦合有限元算法求解了定浆式轴流泵强迫振动过程中连锁特性和柱体由于旋涡脱落诱发自激振动两个工程问题。其中流场采用基于特征线方程的分离算法进行求解,固体场采用Newmark方法进行求解,在计算过程中采用温度体模型生成动态网格。结果表明该发展的算法性能优异,能有效解决流固耦合中的振动问题。     

超空泡航行器三维流场仿真及性能分析

提出了带进水管路超空泡航行器基本结构和性能评价方法.基于三维Reynolds平均N-S方程、Mixture 多相流模型和完全空化模型,建立了超窄泡航行器内外流仿真模型.开展了不同航行状态和空化器攻角下流场仿真,分析了航速、航行攻角和空化器攻角对空泡形态、航行器水动力特性和进水管路性能等影响规律.研究表明:航行攻角严重影...     

用于环形正负电子对撞机探测器超导磁体的小型氦虹吸回路实验与数值模拟研究

在探测器超导磁体的低温系统预研中,搭建了小型的氦虹吸冷却回路实验系统,进行了气-液两相沸腾和传热特性实验研究,并利用VOF多相流模型模拟计算了氦的热虹吸自然冷却循环过程和过热烧干过程。在相同条件下,模拟计算结果与实验数据进行了比较,模拟计算得到的的温度分布、璧面过热度与实验测量数据符合度较好。     

Hybrid model for prediction of welding distortions in large structures

The paper presents a short overview of the contemporary approaches for calculating welding distortions. In order to meet the existing challenges, an advanced hybrid model for prediction of welding distortions in large structures is described. For the purpose of illustrating the capability of this model, a simulation case is put into discussion. The results are validated by comparison with experimental data, as well as with common simulation technique. Analysis of the calculation costs is also presented. The directions for development of calculation technique, based on the presented model, are also suggested.     

基于小波奇异性理论的水轮机空化检测

空化噪声谱分析中常采用的功率谱分析在研究空化噪声这种具有很强突变性的信号时具有明显的缺陷,文中提出了一种基于小波奇异性理论的水轮机空化检测方法,并提出了小波基选择方案、突变点检测条件和最佳检测阈值。进行了混流式水轮机的模型转轮试验,观测了模型转轮额定工况下的涡带形态和空化发展情况,并采集存储了大量空化噪声数据。对照观测结果分析实际的检测数据,结果表明该方法的有效性,并很好的检测出空化初生和空化形态转变。     

Dynamic response of deformable structures subjected to shock load and cavitation reload

The dynamic response of deformable structures subjected to shock load and cavitation reload has been simulated using a multiphase model, which consists of an interface capturing method and a one-fluid cavitation model. Fluid–structure interaction (FSI) is captured via a modified ghost fluid method (Liu et al. in J Comput Phys 190: 651–681, 2003), where the structure is assumed to be a hydro-elasto-plastic material if subjected to a strong shock load. Bulk cavitation near the structural surface is captured using an isentropic model (Liu et al. in J Comput Phys 201:80–108, 2004). The integrated multiphase model is validated by comparing numerical predictions with 1D analytical solutions, and with numerical solutions calculated using the cavitation acoustic finite element (CAFé) method (Sprague and Geers in Shocks vib 7:105–122, 2001). To assess the ability of the multiphase model for multi- dimensions, underwater explosions (UNDEX) near structures are computed. The importance of cavitation reloading and FSI is investigated. Comparisons of the predicted pressure time histories with different explosion center are shown, and the effect on the structure is discussed.     

浸没排气过程声信号与流场振荡规律研究

采用流体体积(Volume of Fluid,VOF)模型和威廉姆斯-霍金斯(Ffowcs Williams and Hawkings,FW-H)模型对浸没排气过程声信号进行数值模拟,研究竖直向下浸没排气过程声信号产生机制及理论依据。将模拟结果与实验结果进行对比,验证模型的适用性和准确性。研究结果表明,声信号与流场流动状态相关,气泡间分离和气体再注入过程引起的气泡体积剧烈振动是影响气泡流声信号产生的关键因素。在同一深度处,在径向上声压随位置的变化服从指数衰减,在周向上声信号呈现球源信号传播特点。     

通气空化多相流动特性的实验与数值研究

为了进一步分析通气空化多相流的特性,采用实验和数值模拟相结合的方法,对绕带空化器回转体的通气两相流动和通气三相流动的结构进行了对比分析。实验中采用高速全流场流动显示技术获得了通气空化多相流动的空泡形态;数值模拟中采用滤波器湍流模型（FBM）进行了数值计算,获得了空泡形态和流线分布,数值模拟获得的空泡形态与实验一致。结果表明,由于空化数的不同,在相同通气率下,绕回转体通气空化三相流动的空泡形态不同于通气两相流动;同时空泡的非定常行为也发生了大的变化。     

湿工况下翅片表面冷凝水滴运动的数值模型

了解析湿过程中冷凝水对换热器翅片侧换热和压降的影响机制,需要首先建立湿工况下翅片表面冷凝水滴的运动模型。通过对翅片表面上冷凝水滴进行受力分析,得出了水滴运动的判断条件;建立了水滴接触角预测模型,并结合VOF界面追踪方法来描述气液相界面、计算表面张力,从而建立了预测冷凝水滴在竖直翅片表面运动过程的数值模型。通过水滴运动实验对模型的可靠性进行了验证：水滴与翅片表面接触角的模拟值与实验值的平均误差为2.11%,最大误差为2.51%;水滴运动速度的模拟值与实验值的平均误差为6.5%,最大误差为10%。结果表明：水滴运动模型能够准确的预测水滴在翅片表面的运动规律。     

Numerical simulation of cryogenic cavitating flow by an extended transport-based cavitation model with thermal effects

Thermodynamic effects on cryogenic cavitating flow is important to the accuracy of numerical simulations mainly because cryogenic fluids are thermo-sensitive, and the vapour saturation pressure is strongly dependent on the local temperature. The present study analyses the thermal cavitating flows in liquid nitrogen around a 2D hydrofoil. Thermal effects were considered using the RNG k-ε turbulence model with a modified turbulent eddy viscosity and the mass transfer homogenous cavitation model coupled with energy equation. In the cavitation model process, the saturated vapour pressure is modified based on the Clausius-Clapron equation. The convection heat transfer approach is also considered to extend the Zwart-Gerber-Belamri model. The predicted pressure and temperature inside the cavity under cryogenic conditions show that the modified Zwart-Gerber-Belamri model is in agreement with the experimental data of Hord et al. in NASA, especially in the thermal field. The thermal effect significantly affects the cavitation dynamics during phase-change process, which could delay or suppress the occurrence and development of cavitation behaviour. Based on the modified Zwart-Gerber-Belamri model proposed in this paper, better prediction of the cryogenic cavitation is attainable.     

水下平面爆炸冲击作用下空化区域形成及其特征

在水下平面冲击波基本理论基础上,导出在弱冲击波条件下,平面冲击波的空化深度和空化区域高度计算模型.利用LS-DYNA有限元程序对空化区域的密度和速度等特征进行了数值模拟分析.     

Damage effects of adhesives in modern glass façades: a micro-mechanically motivated volumetric damage model for poro-hyperelastic materials

This paper presents a micro-mechanically motivated volumetric damage model accounting for cavitation effects in modern glass connections, e.g. laminated glass connections. The volumetric part of an arbitrary Helmholtz free energy function is equipped with an isotropic damage formulation. To develop a micro-mechanical damage model, the porous micro-structure of a transparent structural silicone adhesive is analyzed numerically applying hydrostatic loading conditions. Based on the structural responses of different types of cubic representative volume elements incorporating an initial void fraction, three damage parameters are fitted utilizing the Levenberg–Marquard algorithm. The present volumetric damage model is implemented into ANSYS FE Code using a UserMat subroutine, where the algorithmic setting is described in detail in the present paper. To compare the structural responses of cubic equivalent homogeneous materials with representative volume elements, benchmark tests under hydrostatic loading are performed. The results indicate that the novel damage model accounts adequately for volumetric damage due to the cavitation effect. A special form of the pancake test is described briefly. The test allows for visualizing the cavitation effect during experimental testing. The experimental results of the pancake test are compared with numerical results, where the pancake test is simulated incorporating the micro-mechanical damage model. The micro-mechanically motivated scalar, internal damage variable is equipped with the obtained damage parameters from the structural response of the representative volume elements. The results show an adequate approximation of the experiment through the simulation. However, to optimize the results of the simulation, an optimization study on the damage parameters is conducted utilizing the Downhill-Simplex algorithm. Using the optimized damage parameters, the simulation of the pancake tests is further improved. Hence, it is shown that the novel micro-mechanically motivated volumetric damage model is excellently suited to represent the cavitation effect in poro-hyperelastic materials.