Impedance functions for a rigid foundation on a layered medium

A comparison was made between the vertical, rocking and horizontal impedance functions for a rigid strip foundation placed on homogeneous soil obtained by the finite element approach and the corresponding functions obtained for an elastic half-plane. An attempt was made to determine the overall size of the finite element model and the material damping necessary to approximate the two-dimensional half-plane results over the frequency range of interest. The results of this study indicate that even for large overall sizes of the model, the impedances obtained by the finite element approach present important oscillations depending on the value of the frequency. Such oscillations may be reduced by further increasing the overall size of the model or by increasing the material damping; however, the last approach would lead to an overestimation of the radiation damping. The errors associated with the vertical, rocking and horizontal impedances are of different magnitudes, the largest corresponding to the vertical impedances. The size of the elements was chosen such that the impact on the results obtained was minimal. It is expected that the use of larger size elements would further complicate the modeling problem.     

Periodic response of a viscoelastic cooling tower

The periodic response of a linear viscoelastic cooling tower to a prescribed recurring sequence of pressure fluctuations or earth accelerations is analyzed. An approximate analysis, based on the bending theory of shells, is presented. The problem is reduced to a double sequence of boundary-value problems of linear ordinary differential equations.     

Vibrations of thick plates using a high precision triangular element

In this paper vibrations of thick plates using a high precision triangular element are studied. The effect of transverse shear is included in the derivation of the stiffness matrix and the effect of rotatory inertia is included in the derivation of the mass matrix of the element. Explicit expressions for stiffness and mass matrices of the element are presented. The numerical examples considered show that the natural frequencies obtained are accurate even with a coarse finite element subdivision.     

Dissipative heating in a coated viscoelastic cylinder

The thermomechanical responses of a long coated hollow cylinder made of viscoelastic material subjected to cyclic presure fluctuations at high frequency are studied. The accumulation of the continuous energy dissipation induces a significant temperature increase in the material which affects the material behavior and hence the structural response. The paper adopts a numerical approach with the intention of studying the effect of coating. It is found that the coating has little effect on the dissipative heating due to internal pressure fluctuation. However, the heating effect can be greatly reduced when the cyclic pressure is applied on the outside surface.     

Periodic excitation of a finite linear viscoelastic solid

The response of a finite three-dimensional standard linear viscoelastic solid to periodic excitation is investigated. The theory is specialized for a circular cylindrical body that is bonded to a rigid base at one end and shaken by a prescribed oscillation of a circular rigid plate that is bonded concentrically to the other end. A practical relevance of the theory is the design of vibration absorbers that are made of blocks of viscoelastic materials. Four types of motion of the driving plate are treated: (1) a simple harmonic translation of the plate perpendicular to its plane; (2) an angular oscillation of the plate about its normal axis of symmetry; (3) a simple harmonic translation of the plate in its plane; and (4) an angular oscillation of the plate about a diameter. The theory provides the displacements, stresses, and natural frequencies of the body for the four types of motion. In addition, the mean power input and driving force or driving moment applied to the plate are obtained. Computer programs have been written for the solutions of finite difference approximations of the governing equations. Sample results of the computations are included.     

核电厂管系振动鉴定

本文介绍了核电厂管道振动鉴定概况,讨论了目前使用的管系振动的鉴定方法,给出了鉴定准则。     

Excitation of finite viscoelastic solid on springs

The objective of this study is to predict the dynamic response of a finite three-dimensional cylindrical standard viscoelastic body supported on the bottom by a spring foundation and subjected to periodic axial force, twist, shear and rocking moment disturbances transmitted through a rigid circular plate bonded concentrically to the top of the body. The results of the analysis may be of use to aid in the proper design of foundations for radar towers, massive reciprocating engines or compressors, vibration and earthquake simulators, etc.     

The experimental investigation of the impact of a particle or a rigid body on a cylindrical shell

This paper is devoted to the investigation of the impact of loose or detached parts and components on the body of a primary system of nuclear power plants or in pipelines.

The model task of an impact of a particle or a rigid body on a cylindrical shell is solved. The dependences of force of the impact and the acceleration of a point of the shell on time are received. Theoretical calculations are confirmed with the experiments.

The solution of these tasks and the theoretical calculations are the base for the solution of the inverse problem of the detection of the location of an impact by a particle on the shell and its mass and velocity.

The method of the solution of inverse problem for the impact of a particle is presented below. The experimental installation for measurement parameters of the oscillations of a point of the shell is created. An analogue-to-digital converter is used in the installation, and structural schema is drawn. The installation includes a hardware-software complex based on a personal computer.     

Measurement of Leakage Flow Induced Vibrations of Cylinder

For development of a two-phase flow analysis code by use of two-velocity two-temperature (2V2T) model, six basic equations completely independent and consistent with one another are derived for several possible types of thermodynamical unequilibrium conditions. Characteristic of the basic equations is that evaporation and condensation take place in the saturated water and saturated vapor separately. These phase change equations in the saturated state are rigorously derived using the thermodynamical law.

The energy conservation equation of each phase is derived from the well known total two-phase flow energy equation, using the first law of thermodynamics and conservation equations of mass and momentum of each phase. This derivation method will give assurance that all conservation equations are consistent with one another.

To form simplest 2V2T model, the terms of wall and interphase friction, and heat transfer to the two-phase flow and between phases are considered in this paper.     

Vibrations of two coaxial cylindrical shells containing fluid

This paper considers the vibrational behavior of two long, elastic, coaxial cylindrical shells containing (or conveying) fluid. Both exact and approximate formulas for the added (attached, virtual) mass of the fluid are derived. The method of analysis is illustrated using appropriate shell equations.     

Rocking of rigid blocks on randomly shaking foundations

The rocking of a rigid rectangular block on two types of shaking foundations is examined. The foundation is either a rigid plane, or a flexible (Winkler) foundation whose independent springs and dashpots separate from the block base when the springs are going into tension. Horizontal random excitation of the form of modulated white noise, which represent idealized earthquake records, are used to shake both types of foundations. Simulation shows that for each model there is an excitation intensity threshold below which no toppling of the block occurs. Above that threshold the chance of toppling increases with the intensity. It is also observed that toppling almost always follows whenever the center of mass is tilted pass the vertical through the base corners of the block.     

Vibrations of prismatic shells with hexagonal cross section

Presented is an approximate method for the vibration analysis of nuclear reactor subassembly ducts in form of slender thin-walled polygonal shells with hexagonal cross section. The method is based on the semimembrane shell theory. Inadequacies of this approximate theory are not expected to play a significant role in the determination of fundamental natural frequencies. According to the simplified theory employed, three basic types of motion appear as independent: purely longitudinal vibrations, flexural vibrations and distortional vibrations.     

Flow Induced Vibrations in Gas Tube Assembly of Centrifuge

A centrifuge essentially consists of a rotor rotating at very high speed. Gas tube assembly, located at the center of the rotor, is used to introduce feed gas into the rotor and remove product and waste streams from it. The gas tube assembly is thus a static component, the product and waste scoops of which are lying in the high pressure region of a fluid rotating at very high speed. This can cause flow induced vibrations in the gas tube assembly. Such vibrations affect not only the mechanical stability of the gas tube assembly but may also reduce the separative power of the centrifuge. In a cascade, if some of the centrifuges have gas tube vibration, then cascade performance will be affected.

A theoretical analysis of the effect of waste tube vibrations on product and waste flow rates and pressures in the centrifuge is presented. A simple stage consisting of two centrifuges, in which one has tube vibration, is considered for this purpose. The results are compared with experiment. It is shown that waste tube vibration generates oscillations in waste and product flow rates that are observable outside the centrifuge.     

Thermal stresses in a cylindrical shell containing a circular hole or a rigid inclusion

The thermal stress problem of a circular discontinuity in a cylindrical shell has been solved by continuum approach. Two types of discontinuities are considered: (i) a circular hole and (ii) a circular regid inclusion. The effect of a uniform temperature or a linearly varying temperature across the thickness has been studied. The problem is converted into an equivalent boundary value problem and boundary conditions are specified around the discontinuity. The results are presented in a graphical form for ready use.     

The Hall effect on an unsteady flow due to a rotating infinite disc

An analysis of the effects of Hall currents on the unsteady flow of an electrically conducting, viscous, incompressible fluid due to a rotating disk has been carried out. It is assumed that the flow is under the action of a transverse magnetic field and the magnetic Reynolds number is small. Approximate solutions to the velocity and the torque are derived for small values of the time t. They are shown graphically. It is observed that the torque-coefficient decreases with an increase in the Hall parameter.     

Mechanism of the Excitation of Vibrations in RBMK Fuel Assemblies

It is shown that the high intensity of the vibrations of RBMK fuel assemblies is due to the parametric excitation of oscillations when an axial flow of the coolant interacts with the fuel elements. The periodicity of this coolant action is due to plug-flow regimes of the two-phase coolant, pumped-induced oscillations of the coolant flow rate, and turbulization of the flow by the spacing lattices and fittings. It is shown that an in-reactor experiment must be performed in order to obtain a relation between the steam-content distribution and the vibrations in the RBMK fuel assemblies. For this, it is suggested that the steam-content distribution and the vibrations of the fuel elements be measured by using a standard system of measurements of the thermohydraulic and neutron-physical parameters of RBMK reactors and by analysing the noise in the indications of the sensors monitoring the height distribution of the energy release.     

An experimental study of natural convection in a volumetrically heated spherical pool bounded on top with a rigid wall

Flooding of the reactor cavity is being considered as a cooling strategy to prevent vessel thermal failure in the case of severe core damage accidents in which relocation of core material into lower vessel head occurs. A recent study carried out at UCLA showed that the flooding of cavity could indeed be a viable option. However, one important factor contributing to uncertainty in that study was the internal natural convection heat transfer coefficient. In the present work, experiments were conducted to examine natural convection heat transfer in internally heated hemispherical pools with external cooling. In the experiments, Freon-113 contained in a Pyrex bell jar, was used as a test liquid and the vessel was cooled from the outside with water. The pool was bounded with a rigid wall at the top, and was heated with a 750 W magnetron taken from a conventional microwave oven. The vessel inner wall temperature was not held constant and varied from the stagnation point to the equator. A series of chromel alumel thermocouples was used to measure the pool and wall temperatures at different locations.Experiments were performed for pools with nearly insulated and cold rigid walls at the top. The depth of the pool was varied parametrically. Both local and average heat transfer coefficients based on maximum pool temperature were obtained. The results have been compared with the correlations obtained for pools with free surface.