拉载下环向穿透裂纹位于圆柱壳固定端的弹塑性解

基于薄壳半膜力理论和Dugdale模型,针对环向穿透裂纹位于其固定端的圆柱壳,推导了其在轴拉载荷作用下的裂纹尖端张开位移(CTOD)、J积分、由裂纹所引起的附加变形等一套相对完整的弹塑性解。除少数数值求根外,均为显式计算,并可涵盖塑性破坏。该解可方便地用于不同断裂参数、裂纹长度以及几何参数的系列计算,弥补了目前缺乏本问题理论解析解的不足。     

计入气穴的水下爆炸作用下结构流固耦合三维数值模拟

水下爆炸在结构物面附近产生的气穴现象,严重影响水下爆炸作用下的流固耦合动响应,是舰船水下爆炸领域的难点,传统的边界元方法、有限元方法(FEM)难以解决水下爆炸气穴现象这类强非线性问题．针对此问题,计及流体中的气穴现象,考虑流体的可压缩型,忽略流体粘性,建立水下爆炸瞬态强非线性流固耦合三维数值模型,采用流体谱单元方法(SEM)和结构有限元方法求解该模型．计算结果表明:相对有限元法,谱单元法具有更高的计算精度,且谱单元解与解析解、试验值吻合良好．在此基础上,结合ABAQUS软件,分别探讨三维球壳、船体板架在水下爆炸作用下的瞬态流固耦合机理,给出气穴区域及其对水中结构物动响应的影响特征,旨在为舰船水下爆炸瞬态流固耦合问题的相关研究提供参考．     

一种适用于并行运算处理的实时高动态范围图像合成算法研究

针对目前现有高动态范围图像(HDRI)的合成算法因复杂度高而难以应用于强实时系统的缺点,本文提出了一种适用于并行运算处理硬件的基于多曝光时间的实时HDRI合成算法。该方法首先完成探测器光照响应曲线的生成与标定,然后在现场可编程门列阵(FPGA)中通过数字信号处理技术完成多曝光图像序列的场景照度恢复以及像素的实时融合。仿真验证结果表明,该算法能够正确有效地在FPGA中执行,可达到实时HDRI获取的设计要求。     

Nonlinear dynamics of cantilevered pipes conveying fluid: Towards a further understanding of the effect of loose constraints

The nonlinear dynamics of a fluid-conveying cantilevered pipe with loose constraints placed somewhere along its length is investigated. The main objective of this study is to determine the effects of several geometrical and physical parameters of the loose constraints on the characteristics and behavior of pipes conveying fluid. Based on the full nonlinear equation of motion, the dynamical behavior of the pipe system is investigated. Phase portraits and bifurcation diagrams are constructed for a selected set of system parameters. Typical results are firstly compared to numerical ones reported previously and excellent agreement is obtained. Then, the threshold flow velocities for several key bifurcations including pitchfork, period doubling, chaos, and sticking behaviors are predicted, showing that in many cases, the gap size, stiffness, and asymmetry of the loose constraints have remarkable effects on the nonlinear responses of the cantilevered pipe conveying fluid. For a pipe system with small/large constraint gap sizes, small constraint stiffness, or large constraint offset, some of the complex dynamical behaviors including chaos and period-doubling bifurcations would disappear, at least in the flow velocity range of interest.     

Post-flutter response of a flexible cantilever plate in low subsonic flows

Numerical simulations on the post-flutter response of a flexible cantilever plate are carried out by establishing a nonlinear aeroelastic model. The present study shows that chaotic movements may exist in the three-dimensional panel flutter problems in case of low subsonic flows. In the analysis, time traces, phase-plane plots, Poincare maps as well as power spectral densities are employed to identify the dynamic behavior of the system. It is observed that the plate undergoes period-1, period-3 and non-periodic motions with the increase of inflow velocity. The post-flutter behavior is dominated by both geometric and aerodynamic nonlinearities. Numerical results show that wingtip vortexes are in fact an important source of aerodynamic nonlinearities, which have not been fully studied before. The study also provides a criterion on how to choose a coupling strategy in the nonlinear aeroelastic simulation of a low-aspect-ratio flexible structure in low subsonic flows when the dominant nonlinear effect is different in the post-flutter response.     

航空油料在舱室内燃爆危害的数值分析

不同舱室结构内航空油料的燃爆参数存在差异,为了解和掌握不同结构舱室内航空油料的燃爆危害性,运用计算流体动力学（computational fluid dynamics,CFD）方法对不同结构航空油料舱室内的航空油料蒸汽燃爆问题进行了数值模拟。结果表明:密闭航空油料舱中的航空油料蒸汽预混燃爆时,油舱各处压力分布较均匀,无隔板密闭舱室和含不完全分割隔板密闭舱室内航空油料的最大燃爆压力分别为0.76、0.74 MPa,即舱室内的不完全分割隔板对航空油料燃爆时所产生的最大压力无显著影响;隔板等特殊结构的存在使舱室内部产生了气流漩涡,增大了燃料消耗的速率,导致火焰面传播速度及压力上升速率增大,舱室内各处燃料的质量分数由火焰面决定。     

Vibration of a circular disk as a test method for damping characteristics of constrained layer material

The theoretical analysis of free vibrations of a disk of constrained layer sandwich material is considered. The results enable the real and imaginary parts of the shear parameter to be determined from experimental data. A correction for a small mass attached to the centre of a disk is introduced. An example of test results illustrates the method. An exact method involving numerical solution of the governing differential equation has been checked by approximate formulae based on potential energy of deformation.     

Molecular structure,hydrostability and stabilization of polyurethane acetals

The effect of the nature and ratio of initial comonomers, the method of synthesis, hydrolysis level and the stabilizer type on the molecular-mass parameters of nonisocyanate polyurethane acetals (PUA) has been studied. The nature of active centres of polymerization has been suggested. The course of hydrolytic degradation of various PUAs has been investigated. It has been shown that the hydrostability of PUA can be increased by salt additives.     

大尺寸太赫兹平顶波束的产生研究

为了实现低频段太赫兹高斯波束整形为大尺寸平顶波束,提出了一种利用双相位板结构设计大尺寸平顶波束整形系统的方法.基于Input-Output算法,利用角谱理论计算系统参数,同时对所设计系统进行了数值仿真并搭建了实验系统,验证了出射光场的横向强度分布是否符合预期.结果表明,所设计的双相位板整形系统能够成功将0.1 THz高...     

Model experiments of the transient response to flooding of the box shaped barge

Coupling of the flooded water and ship motions was studied experimentally. Roll decay tests for one flooded compartment and transient abrupt flooding tests were performed for the box shaped barge model. The tests were conducted to obtain information on the flooding process for the development of numerical tools and to provide validation data. Quantitative values on the effect of flooded water on the roll damping were obtained. Flooded water behaves in a different manner in undivided and divided compartments. Flooded water in divided compartment increases roll damping significantly. In undivided compartment roll damping was high at low amount of flooded water. For higher amounts damping was of the same order as for the intact model. Initial flooding is a complex process where the ship and flooded water motions are coupled. Propagation of the flooding water inside the compartment, at a dam-break type abrupt flooding, was studied by tracking the surface of the flooded water. An image processing algorithm was used to obtain the tracked surface. Flooded water volume and its center of gravity were estimated from the tracked surface. Different internal layouts of the flooded compartment can lead to a totally different roll response. The inflooding jet plays an important role in the response in case of the undivided compartment. While, for a divided compartment, asymmetric flooding due to the obstructions causes high heel angle on the damage side.