Advanced Materials Research Vols. 33-37

Abstract: The center hole deformation test of rigid bearing plate is an important method for understanding deformation properties of deep weak rock mass. According to the center hole deformation test of rigid bearing plate in dam zone of Dagangshan hydropower station, this paper detailedly recommends test method of this experiment, and the settlement deformation formula of deep rock mass under circular rigid bearing plate is deduced, which could be used to calculate deformation modulus and equivalence deformation modulus of different deep rock mass at test points. According to curves of depth-deformation under different pressures at test points in dam zone, we have analyzed deformation characteristics of deep weak rock mass. By the center hole deformation test of rigid bearing plate, stratum properties in dam zone of Dagangshan hydropower station could be understood further, and it provides important references for the study of creep speciality of weak rock mass in dam zone.

Abstract: In the present paper, to clarify and examine the fundamental buckling behaviours of cylindrically curved plates subjected to axial loading, a series of elastic and elasto-plastic large deflection analyses as well as elastic eigen buckling analysis are performed together with the comparisons with the buckling behaviours of circular cylinder. On the basis of the numerical results, the effects of curvature, magnitude of initial imperfection, slenderness ratio and aspect ratio on the characteristics of the buckling and post buckling collapse behavior of cylindrically curved plates and circular cylinders under axial compression are discussed. The buckling strength and ultimate strength formulae of the cylindrically curved plate are empirically derived based on the FEM series analysis by curve fitting using least square method. The validity of the ultimate strength formulations developed in this study has to some extent been verified through comparison with nonlinear numerical solutions.

Abstract: The dynamic characteristics of a TV tower with 610m in height is actively analyzed by using commercial package ANSYS in this study. The mode selection is carried out by determining the modal mass participation ratio. The observations made based on numerical investigation demonstrate that the natural frequencies of the high rise unsymmetrical tower are substantially close and the modal displacement of the antenna is much larger than that of the major tower. In order to select the major mode shapes, the modal mass participation ratios of the first 30 modes are calculated and at least first 10 mode shapes should be considered when investigating the seismic responses. It is seen that the mode shapes whose vibration directions are paralleled to the short axis of the elliptical core tube are critical to the structural seismic responses. In this direction, the mass participation ratios of the first three mode shapes add up to 0.63, the 10 modes, the sum of whose modal participation ratio is 0.8184, are selected in order. Therefore, at least 10 modes should be involved in the analysis of structural seismic responses.

Abstract: The synchrotron radiation is an important light source used to improve the measurement resolution and efficiency of scientific equipments. The electrons in radio frequency system are accelerated by the synchrotron radiation superconducting cavity. Tensile or compressive loads along the axial direction may be applied on this thin-walled shell cavity for compensating the frequency shift due to the variations of surrounding condition. In order to avoid the failure of the thin-walled shell cavity before the frequency tuning process, the finite element method and experiment were used to predict the deformation behavior and limit load of thin-walled shell cavity. The parameters such as thickness, material properties and radius of round beam tube were discussed. The finite element results show that the limit loads were overestimated when the material properties were assumed to be linear elastic. When the cavity becomes thicker, the limit loads and the maximum compressive displacements of thin-walled shell cavity increase. The analysis method used in this paper can help us find the tunable ranges of synchrotron radiation superconducting cavities with different thicknesses, material properties and geometries.

Abstract: Taylor series numerical method is a novel time integration method for structural dynamics. In comparison with the well-known ones, Taylor series method has high accuracy and good convergence characteristics and thus is a good alternative for solving structural dynamics problems. In the paper, the recursive formulae of Taylor series numerical method in linear and nonlinear structural dynamics are derived. The desired user routine in Fortran 90, which was compiled and linked into the general software ANSYS program, is designed and programmed. User-defined menus are constructed via the User Interface Design Parameter. Numerical examples illustrated the validity of the customized plug-in. The research in this paper promotes the algorithm application in complicated engineering problems.

Abstract: In this article the freely oscillating 3-dimensional parachute-like body sustained at one point is focused. To catch the real phenomenon by numerical simulation, the virtual mass is considered in this study. The flow field is calculated by using the MAC method applying third order upwind scheme for the convex term, and applying central difference for the other terms. ALE method is applied in order to consider a moving boundary problem. The virtual mass is calculated by using a potential flow at every time step. As a result, it has been made clear that the virtual mass has influence on the freely oscillating rigid concave body motion. And the flow structure around the freely oscillating parachute-like body is made clear.

Abstract: Korea Atomic Energy Research Institute (KAERI) is in the process of carrying out a Nuclear Hydrogen Development and Demonstration (NHDD) Program by considering the indirect cycle gas cooled reactors that produce heat at temperatures in the order of 950°C. A coaxial doubletube hot gas duct (HGD) is a key component connecting the reactor pressure vessel and the intermediate heat exchanger (IHX) for the NHDD program. Recently, a preliminary design evaluation for the hot gas duct of the NHDD program was carried out. These preliminary design activities include a preliminary decision on the geometric dimensions, a preliminary strength evaluation, an appropriate material selection, and identifying the design code for the HGD. In this study, a preliminary strength evaluation for the HGD of the NHDD program has been undertaken based on the HTR-10 design concepts. Also, a preliminary evaluation of the creep-fatigue damage for a high temperature HGD structure has been carried out according to the draft code case for Alloy 617. Preliminary strength evaluation results for the HGD showed that the geometric dimensions of the proposed HGD would be acceptable for the design requirements.

Abstract: This paper is disserted to the vibrations of the sandwich panels with pyramidal truss cores. Firstly, based on the Hamilton principle the governing equations of a sandwich panel with pyramidal truss cores are obtained and the eigenfrequencies of the sandwich panel is studied. Then the dynamic response of the sandwich subjected to uniformly distributed sinusoidal loading is studied. The influences of the sizes of the panel on the eigenfrequencies of the panel are discussed. The maximum deflections of the panels of equal mass subjected to the same loading are compared.

Abstract: Characteristics and mechanism of twin-vertical-tail buffet response on airplane configuration with wing root leading edge extension (LEX) were studied by both experiment and computation. Low-speed wind tunnel experiments were carried out to measure the root bending moment and tip acceleration of vertical tail. Vortical flow patterns were visualized via laser light sheet technique. Three-dimensional computation was performed to solve the unsteady Euler equations on rigid model. The results indicate that (1) bursting of vortices emanating from LEX is the main source of twin-vertical-tail buffet; (2) the Euler equations is able to predict the general characteristics of vertical-tail buffet response reasonably.

Abstract: Modern robust flutter method is an advanced technique for flutter margin estimation. It always gives the worst-case flutter speed with respect to potential modeling errors. Most literatures are focused on linear parameter uncertainty in mass, stiffness and damping parameters, etc. But the uncertainties of some structural nonlinear parameters, the freeplay in control surface for example, have not been taken into account. A robust flutter analysis approach in μ-framework with uncertain nonlinear operator is proposed in this study. Using describing function method the equivalent stiffness formulation is derived for a two dimensional wing model with freeplay nonlinearity in its flap rotating stiffness. The robust flutter margin is calculated for the two dimensional wing with flap freeplay uncertainty and the results are compared with that obtained with nominal parameter values. It is found that by considering the perturbation of freeplay parameter more conservative flutter boundary can be obtained, and the proposed method in μ-framework can be applied in flutter analysis with other types of concentrated nonlinearities.