Refined theories based on non-polynomial kinematics for the thermoelastic analysis of functionally graded plates

This article presents an analytical solution for the thermoelastic analysis of simply supported functionally graded sandwich plates using the Carrera unified formulation, which allows the automatic implementation of various structural theories. The governing equations for plates under thermal loads are obtained using the principal of virtual displacement and solved using the Navier method. Linear and nonlinear temperature fields through the thickness are taken into account. Particular attention is focused on plate theories with nonpolynomial refined kinematics. The results of the present displacement fields are compared with the classical polynomial ones, proposed by Carrera, for several orders of expansion.     

基于频响函数辨识鼓筒-轮盘结合部连接参数的选点原则

基于频响函数的辨识方法被广泛用于识别结合部动态参数,其中如何选择频响数据是关键问题。本文针对结合部采用弹簧和阻尼器连接的鼓筒-轮盘模型提出了频响数据选取原则和对应于该原则的量化标准。具体选点原则为所选取的局部信噪比最高的频点所对应的模态对连接刚度的综合灵敏度应该最高。为了定量比较不同模态对连接刚度的综合灵敏度,建立了具体的量化指标和标准。理论分析表明本文所提出的频响数据选取原则和量化标准是有效的,具有一定的工程应用价值。     

饱和哈密顿控制系统可镇定性分析(英文)

研究了一类具有饱和的耗散哈密顿控制系统的有限增益可镇定性问题.在一定条件下运用静态输出反馈使得系统达到全局渐近稳定.另外,针对哈密顿系统中的非线性函数提出进一步的演变条件,利用相同的反馈律使得闭环系统达到有限增益L2镇定,同时获得有限增益的估计值.仿真结果验证了所提结论的有效性.     

Application of hierarchical matrices to boundary element methods for elastodynamics based on Green's functions for a horizontally layered halfspace

This paper presents the application of hierarchical matrices to boundary element methods for elastodynamics based on Green's functions for a horizontally layered halfspace. These Green's functions are computed by means of the direct stiffness method; their application avoids meshing of the free surface and the layer interfaces. The effectiveness of the methodology is demonstrated through numerical examples, indicating that a significant reduction of memory and CPU time can be achieved with respect to the classical boundary element method. This allows increasing the problem size by one order of magnitude. The proposed methodology therefore offers perspectives to study large scale problems involving three-dimensional elastodynamic wave propagation in a layered halfspace, with possible applications in seismology and dynamic soil–structure interaction.     

New Explicit Green's Function and Poisson's Integral Formula for a Thermoelastic Quarter-Space

In this paper a new Green's function and a new Poisson-type integral formula for a boundary value problem (BVP) in thermoelasticity for a quarter-space with mixed homogeneous mechanical boundary conditions are derived. The thermoelastic displacements are generated by a heat source, applied in the inner points of the quarter-space and by heat flux, prescribed on its boundary half-planes. All results are obtained in closed forms that are formulated in a special theorem. A closed form solution for a particular BVP of thermoelasticity for a quarter-space also is included. The main difficulties to obtain these results are in deriving the functions of influence of a unit concentrated force onto elastic volume dilatation Θ^(k) and, also, in calculating a volume integral of the product of function Θ^(k) and Green's function in heat conduction. Using the proposed approach it is possible to extend the obtained results not only for any canonical Cartesian domain, but also for any orthogonal one.     

Free Vibration Analysis of an Eccentric Thermoelastic Hollow Cylinder

The three-dimensional free vibrations in a simply supported homogeneous isotropic, thermally conducting, circular cylinder of finite length with an eccentrically located inner circular cavity have been studied. The surfaces of the cylinder are subjected to stress free and thermally insulated or isothermal boundary conditions. The three-dimensional linear theory of coupled thermoelasticity has been employed to model the problem. The displacement potential functions have been introduced to decouple purely shear and longitudinal motions. The purely transverse wave has been found to remain unaffected due to thermal field. The translation addition theorem for cylindrical wave functions along with orthogonal series expansions has been used to develop the exact solution. To illustrate the analytical results, the numerical solution of some relations and equations have been obtained to compute lowest frequency and dissipation factor versus eccentricities, for selected length to radius ratio and radius ratio of hollow cylinder. The computer simulated results have been carried out with the help of MATLAB software and are presented graphically.     

Using Discontinuity Method in Plane Thermoelastic Problems of Fracture Mechanics

The boundary element method is used for solving stationary plane thermoelastic problem for heat-conductive crack. The influence functions for a segment with elementary discontinuities of temperature, its normal derivative (an analogue of heat flow) and displacements are obtained. The results of test problem correspond to a physical picture of the process. The illustrative problem is devoted to a question about the necessity to take into account the heat conductivity of cracks in the longitudinal direction in the thermoelastic problems of fracture mechanics. Recommendation for choosing thermal model of the cracks for metal structures is made.     

Some Relations of Neutronic Noise with Fluctuation of Inlet Coolant Temperature and Vibration of a Control Rod Obtained by Simultaneous Measurements at KUR

Experiments on reactor noise were conducted at KUR. Depending on the operating condition of the reactor, the cause of the noise are classified into the following four types.

1. Zero-power noise source due to the branching process of fission neutrons and/or due to random bombardment of neutrons to the detector—under natural circulation of coolant and at essentially zero-power level.

2. Coolant temperature fluctuation due to natural convection—under natural circulation and at relatively high power level.

3. Flow induced vibration of shim control rods—under forced circulation of coolant and at low power level.

4. Fluctuation of inlet coolant temperature—under forced circulation and near the maximum power level.

Vibration of a spare shim control rod and fluctuation of inlet coolant temperature were measured simultaneously with the neutronic noise. Then the noise sources of the types (3) and (4) were verified. The vibration of a control rod has a broad spectrum in low frequency region besides the large peak at 14 Hz. The fluctuation of inlet coolant temperature is non-white noise and consists of large low frequency component. The theoretically predicted sink structures in the neutronic PSD relating to the transit time of inlet coolant temperature fluctuation through the core were not observed in the experimental results.     

Exact Solutions of Two Point Time Correlations on Point Reactor Kinetics with Gaussian Reactivity Fluctuations

Station blackout is reported to be a sequence that would likely be a significant contributor to the accident risk at a boiling water reactor (BWR). The occurrence frequency of station blackout is evaluated in probabilistic safety assessment (PSA) to be 6×10^?6 per reactor year at Limerick and less than 10^?7 per reactor year at BWR in Japan.

This report describes an analytical study of thermal-hydraulic and radionuclide behavior during a postulated severe accident of station blackout at a reference BWR plant. The analytical approach was shown in both of hand calculation and the THALES/ART code calculation to better understand wide physical and chemical phenomena in the processes of severe accidents.

We evaluated timing of key events, core cooling and core temperature, reactor vessel failure, debris temperature, containment pressure, and release and deposition of radionuclide in the containment. The THALES and CORCON models on the chemical reactions in the core-concrete interaction lead to great differences in the increasing rate of containment pressure and the release rate of fission products from the core debris.