小型模块化压水核反应堆堆内构件模态特性研究

小型模块化压水核反应堆的结构形式与常规的压水核反应堆不同.除了吊篮组件以外,还有小型模块化压水核反应堆独有的压紧组件、压紧筒组件和分流环板等结构.为了对小型模块化压水核反应堆堆内构件流致振动行为进行准确的评估,首先应该确定堆内构件在空气和静水中的模态特征.本文以国内自主研发的小型模块化压水核反应堆堆内构件为研究对象,采用ANSYS软件对小型模块化压水核反应堆堆内构件在空气和静水中进行了干模态和湿模态分析,获得了吊篮组件、压紧组件、压紧筒组件以及分流环板在空气和静水中的固有频率及相应的振型,并开展模态试验验证了该分析方法的正确性.该方法可运用到常规压水核反应堆堆内构件的模态分析中.     

潜艇发射装置故障诊断系统的设计与实现

为解决潜艇鱼雷发射装置组成复杂,建立故障诊断模型和提取规则困难的问题,将案例推理诊断技术引入潜艇鱼雷发射装置故障诊断领域.针对潜艇鱼雷发射装置的结构层次特点,采用层次结构与网状结构相结合的案例组织方法进行了工程化实现,应用结果表明:该方法诊断推理高效、可信,能很好地满足潜艇鱼雷发射装置故障诊断的有效性和实用性要求.     

通过应变阵列测量位移模态与曲率模态

针对模态试验中使用加速度计时附加质量大、不易安装且对于结构曲率变化不敏感等问题,提出使用应变阵列测量位移模态与曲率模态.以悬臂梁为例,通过改变应变阵列的布置方法测量梁的位移和曲率模态,并与使用加速度计的模态分析结果进行对比.实验结果表明:通过改变应变阵列布置方法,可有针对性地提取结构的位移模态与曲率模态,且模态识别效果...     

基于单元模态应变能和剩余模态力的结构损伤识别方法在某塔式桁架中的应用

为快速、准确定位工程结构损伤位置,有效提高工程结构安全性能和使用寿命,以某塔式桁架结构为研究对象,运用单元模态应变能法和剩余模态力法对其进行损伤识别.利用MSC Marc对该桁架完整结构和几种不同损伤程度下的损伤结构进行模态分析,通过MATLAB编程从模态分析结果中提取这些结构的模态参数,计算损伤结构单元模态应变能的变化率和损伤结构各节点自由度对应的剩余模态力,并进行结构损伤识别.结果表明单元模态应变能变化率和剩余模态力是有效和准确的结构损伤标志量.     

SolidWorks Simulation在水轮机转轮模态分析中的应用

SolidWorks Simulation作为一款强大的有限元分析软件,其便捷性与易用性已得到公认。本文利用SolidWorks Simulation对某模型水轮机的转轮分别进行了零件状态下的干模态分析,并试算转轮与水体装配体状态下的湿模态分析。分析证明SolidWorks Simulation可以方便、快速的进行零件相关的设置和分析,计算结果可以为转轮的优化设计提供理论依据,但在湿模态分析中还存在不足。     

基于MSC Dytran的潜艇结构撞击强度分析

提出潜艇碰撞问题,对其碰撞特征进行分析,并针对某型潜艇舯部典型结构的撞击极限强度特性进行数值计算,结果表明由于准静压载荷的附连耦合作用,随着静水压力的增加,潜艇舯部耐压壳体结构的防撞能力大幅下降,而耐压壳体内部的平台和舱壁结构能有效提高壳体结构的横向失稳临界应力,改善潜艇结构的径向耐撞能力.     

基于Patran和MSC Nastran的压电智能桁架结构振动模态分析

用Patran和MSC Nastran分析压电智能桁架结构振动模态,验证基于有限元法建立的智能桁架结构机电耦合动力学模型的正确性和有效性.结果表明：采用Patran和MSC Nastran针对2种典型压电智能桁架结构开展振动模态分析的结果,与采用基于有限元法建立的数学模型计算得到的模态频率及实验测试模态频率近似相等,验证基于有限元法模型的正确性和有效性,为开展主动振动控制器的设计提供模型和技术支持.     

对接圆柱壳结构模态特性分析

对接圆柱壳结构在航空航天、船舶、土木和机械等工程领域得到广泛应用,对其模态特性的分析是研究其动力学特性的重要方向.本文简要介绍了模态分析技术和最小二乘复频域法(PolyMAX)的基本原理,并对对接圆柱壳结构进行了计算模态分析和实验模态分析.实验模态分析过程中,针对自由边界的实验实现、分析结果的正确性进行了讨论,并将实验结果与计算模态分析结果进行对比,对比结果表明：对接圆柱壳结构具有圆柱壳结构一般振动特性的同时,由于对接形式的存在出现了以法兰面为分界的非对称振动.     

开关电源设备的抗地震性能分析

建立某开关电源设备机柜的模型,通过HyperWorks对其进行结构模态分析和谐响应分析,得到机柜模态频率值和模态频率响应值,且与实际测试结果相差较小,说明仿真所采用的模拟连接和模拟结构部件的方法基本符合实际.由分析结果可知,结构的固有频率较低,模态频率响应值较大.用仿真软件进行机柜结构优化,结构的固有频率提高,模态频率响应值降低,从而提高开关电源设备机柜的抗地震性能.     

基于结构高阶局部模态的损伤诊断研究

结构振动测试和损伤诊断中,较易得到结构的低阶模态信息,但低阶模态信息主要反映结构的整体性能,对结构局部损伤不敏感.本文主要研究框架结构高阶模态特性,并通过高阶模态来反映结构的局部特征,实现框架结构损伤诊断.研究中采用理论模态分析和实验模态分析相结合的方法.理论模态分析表明框架结构存在模态密集区且高阶模态具有局部特征.采用局部激振方法对一个钢筋混凝土框架结构模型施加激励,通过实验模态分析获取高阶局部模态信息.结果表明最大能量高阶模态可以识别框架柱的刚度变化.     

Doubly asymptotic approximations as non-reflecting boundaries in fluid-structure interaction problems

Acoustic approximations are differential relations between induced fluid pressure and velocity in an acoustic medium. The plane wave approximation (PWA) is valid for high frequency response while doubly asymptotic approximations (DAA) are valid at very high and very low frequencies and, in advanced versions, at selected intermediate frequencies.These relations have been applied extensively on the wet surface of submerged structures to completely uncouple the equations of motion of the structure from those of the surrounding fluid. If DAA are used, a different virtual mass matrix and, in the advanced versions, fitting matrices must be evaluated for each structural geometry.In this paper, the approximations are used on a fluid surface which encloses the structure and has a geometry for which virtual mass and fitting matrices are known. The response is obtained by solving numerically the coupled fluid-structure equations within this approximation to a non-reflecting boundary.A numerical example of the dynamic response of a spheroidal shell is solved using a sphere as the absorbing boundary and the response obtained is compared to exact results.     

An immersed boundary approach for shape and topology optimization of stationary fluid-structure interaction problems

This paper presents an approach to shape and topology optimization of fluid-structure interaction (FSI) problems at steady state. The overall approach builds on an immersed boundary method that couples a Lagrangian formulation of the structure to an Eulerian fluid model, discretized on a deforming mesh. The geometry of the fluid-structure boundary is manipulated by varying the nodal parameters of a discretized level set field. This approach allows for topological changes of the fluid-structure interface, but free-floating volumes of solid material can emerge in the course of the optimization process. The free-floating volumes are tracked and modeled as fluid in the FSI analysis. To sense the isolated solid volumes, an indicator field described by linear, isotropic diffusion is computed prior to analyzing the FSI response of a design. The fluid is modeled with the incompressible Navier-Stokes equations, and the structure is assumed linear elastic. The FSI model is discretized by an extended finite element method, and the fluid-structure coupling conditions are enforced weakly. The resulting nonlinear system of equations is solved monolithically with Newton’s method. The design sensitivities are computed by the adjoint method and the optimization problem is solved by a gradient-based algorithm. The characteristics of this optimization framework are studied with two-dimensional problems at steady state. Numerical results indicate that the proposed treatment of free-floating volumes introduces a discontinuity in the design evolution, yet the method is still successful in converging to meaningful designs.     

Continuum shape sensitivity analysis for aeroelastic gust using an arbitrary lagrangian-eulerian reference frame

Continuum Sensitivity Analysis (CSA), a method to determine response derivatives with respect to design variables, is derived here for the first time in an arbitrary Lagrangian-Eulerian (ALE) reference frame. CSA differentiates nonlinear governing system of equations to arrive at a linear system of partial differential continuum sensitivity equations (CSEs), here, for fluid-structure interaction (FSI). The CSEs and associated sensitivity boundary conditions are derived here for the first time for FSI, using the boundary velocity formulation, carefully distinguishing design velocity from flow velocity and ALE mesh velocity. Whereas boundary conditions must be differentiated using the material (total) derivative, it is sometimes advantageous to derive the CSEs using local (partial) derivatives. The benefit is that geometric sensitivity, known as design velocity, may not be required in the domain. It is shown here that this advantage is realized when the ALE frame undergoes only the rigid body motion associated with the structure to which it is attached. It is further shown that the advantage is not realized when the ALE mesh deforms due to the flexible motion of the fluid-structure interface. The equations for the transient gust response of a two-dimensional airfoil in compressible flow, flexibly attached to a rigid body mass, are presented as a model problem to illustrate a detailed derivation.     

A method for static aeroelastic analysis based on the high-order panel method and modal method

A method for static aeroelastic analysis based on the high-order panel method and modal method is presented. The static aeroelastic characteristics of flexible wings are investigated using this method. Three-dimensional aerodynamic models of flexible wings are constructed based on the geometry of wing configuration, and the modal method is adopted to achieve the fluid-structure coupling. The static aeroelastic characteristics of the AGARD445.6 wing and a low-aspect-ratio wing are investigated in this study....     

Ultra sensitive in-situ acoustic characterization system for HDD head disc interface defectoscopy

An ultra sensitive drive level acoustic characterization system has been developed for in-situ Head Disc Interface defectoscopy. Multimode acoustic emission (AE) sensor installed on the drive cover is designed for tracking air bearing (AB) and slider modes. Monitored modal changes at the AB and slider bandwidth correlate to the weak head disc interface (HDI) interactions such as lubricant modulation and particles induced defects. Two or three orders of magnitude increase in sensitivity can be achieved by a combination of advanced sensors, data acquisition hardware and digital signal processing algorithms. Continuous and Discrete Wavelet Transform and Joint Time-Frequency analyses are implemented for the AB modal data mining process. Performance of the newly developed technology is demonstrated on a normally operating hard disc drive (HDD).     

Three-dimensional fluid-structure coupling in transient analysis

The numerical simulation of nonlinear, transient fluid-structure interactions (FSI) is a current area of concern by researchers in various fields, including the field of nuclear reactor safety. This paper primarily discusses the formulation used in an algorithm that couples three-dimensional hydrodynamic and structural domains. Here, both the fluid and structure are discretized using finite elements. The semi-discretized equations of motion are solved using an explicit temporal integrator.Coupling is accomplished by satisfying interface mechanics. The structure imposes kinematic constraints to the moving fluid boundary, and the fluid in turn provides an external loading on the structure. At each interface node, normals are computed from the nodal basis functions of only the hydrodynamic nodes. By defining the interface normal in this manner, it becomes independent of the type of structural boundary (i.e. shell, plate, continuum, etc.) and thus makes this aspect of the coupling independent of the structure type. A penalty type gap-impact element is developed to model the impact region between the fluid and structure.Results for several problems are presented and these include a comparison between analytical results for a FSI problem and numerical predictions.     

Review of coupling methods for non-matching meshes

Domain decomposition is nowadays a common way to speed up complex computations. However, the discrete meshes used in the different domains do not have to match at their common interface, especially when different physical fields are involved such as in fluid-structure interaction computations. Exchange of information over this interface is therefore no longer trivial. In this paper six methods that can deal with the information transfer between non-matching meshes in fluid-structure interaction computations are compared for different criteria. This is done for analytical test cases as well as a quasi-1D fluid-structure interaction problem. Two methods based on radial basis functions, one with compact support and one using thin plate splines, are favoured over the other methods because of their high accuracy and efficiency.     

Finite element analysis of shock-induced hull cavitation

The paper describes the theoretical formulation and computational implementation of a method for treating hull cavitation in underwater-shock problems. In addition, the method can be applied to the analysis of submerged structures that contain internal fluid volumes. In the present implementation, the Doubly Asymptotic Approximation (DAA) serves to simulate a radiation boundary that is located away from the fluid-structure surface at a distance sufficient to contain any cavitating region. The enclosed fluid is discretized with volume finite elements that are based upon a displacement-potential formulation. An explicit time-integration algorithm is used to advance the solution in the fluid-volume region, implicit algorithms are used for the structure and DAA boundary, and a staggered solution procedure has been developed to treat the interface conditions. Results for two example problems obtained with the present implementation show close agreement with those obtained by other methods.     

A non-reflecting boundary in fluid-structure interaction

A very efficient non-reflecting boundary condition is derived for the seismic response analysis of a submerged structure, such as a dam or an offshore structure, interacting with a compressible fluid domain of unbounded extent. The fluid-structure system is assumed to be two-dimensional and the analysis is conducted in the frequency domain. In the finite element discretization, pressure and displacements are considered to be the basic nodal unknowns for the fluid domain and the structure, respectively. The implementation of the proposed boundary condition in any existing finite element code, based on such a formulation, is extremely simple. Some fluid-structure systems are analysed to demonstrate the effectiveness and efficiency of the proposed method.     

Time domain computation of flow induced sound

We present a recently developed numerical scheme for computational aeroacoustics (CAA). Therewith, we solve the flow field by a large eddy simulation (LES) and the generation as well as propagation of acoustic noise by Lighthill’s analogy applying the finite element method. The developed scheme allows a direct coupling in time domain as well as a sequential coupling in frequency domain and provides the acoustic sound field not only in the far field but also in the region of the flow. Furthermore, we can directly investigate the acoustic source terms in the flow region. The scheme is well suited for interior aeroacoustic problems with complex geometries as well as for fluid-structure interaction problems. Implementation is validated and a two-dimensional simple application example is used to investigate the acoustic sources and to evaluate the acoustic pressure field from both transient and harmonic analyses.