Papers by Keyword: Modal Analysis

Abstract: Metamaterials are controlled arrangements of material structures in which their mechanical properties can be tailored by tuning their geometrical parameters. A parametrization based on cubic Bézier curves is employed here to generate cantilever lattice-beams by changing the position of a free control point. The apparent stiffness of these lattice-beams is numerically analyzed by means of tensile, bending, and free vibration simulations. Results expose the influence of shear deformation in the mechanical behavior of beams made from a cellular material; different degrees of variation depending on the loading conditions and lattice topology are observed and discussed.

Abstract: Turbine blade failures are among the leading causes of steam turbine failure. Failure types typically include cracking, rubbing, blade fouling, and foreign object damage. There is currently a range of non-destructive testing methods used to detect damage at the blade-disk attachment zone, all of which involve disassembling of the blade from the disk for periodic inspection. Evidence indicate that a method to detect damage at the blade-disk attachment zone using a non-contact, non-destructive in-situ off-line modal-based structural health monitoring technique could be useful under some circumstances. Such a technique would have the advantage of eliminating the necessity to disassemble blades during inspection. This would result in significant cost savings. Also, defects associated with the disassembly and reassembly of blades would be avoided. Thus, the aim of this study was to develop a modal-based turbomachinery blade disk attachment inspection technique. Modal parameters were acquired from a robust experimental modal analysis of freely supported low-pressure steam turbine blade-disk segment assemblies. Artificial single-location cracks were intentionally introduced into the turbine blades by cutting a 1 mm thickness notch at three probable damage locations, namely, at the upper pinhole on the leading-edge pressure side, above the root at the base of the aerofoil on the leading-edge and on the trailing-edge. In this work, a finite element analysis of the bladed disk segment assemblies was carried out with and without damage. To validate the reliability of the numerical models, the numerical results were correlated with the measured values, the results of which showed a strong correlation. Finally, a parametric study was conducted in which various healthy and damaged blade-disk cases were systematically investigated. This was done to examine the sensitivity of the blade natural frequency to damage. The artificial damage above the root was found to cause the largest changes in natural frequency. These changes were even more pronounced for assemblies with two blades. Receiver operating characteristic curves were used to assess the discriminatory ability of the results. Each damage case was found to be unique and therefore identifiable from its corresponding healthy case.

Abstract: This paper addresses to a dynamic modal analysis of a crank-type mechanism. The proposed mechanism will have all the components considered as deformable bodies. Thus, the proposed research consists on two methods, namely an analytical and a numerical one. The analytical method allows to identify the static and dynamic components of the matrices that from the equation of motion based on the Kane formalism and the finite element modeling. The numerical method is based on the virtual prototyping of the whole assembly with the ADAMS software. In this case, for the deformable bodies analysis, will be used the method of superposition which have on its base the modal analysis and the RR Craig and MCC Bampton procedure.

Abstract: In this paper we were looking for the production of a physical car body part (the left side fender of a Peugeot 206) made from composite materials based on epoxy resin and reinforced carbon fiber and kevlar woven. On the newly created fender model, a modal analysis has been made in order to determine its own frequencies on a certain direction, and an harmonic analysis with Finite Element Method.

Abstract: In order to improve the dynamic stability of precision micro slitting turn-milling machine tools, reduce or avoid the vibration problem during the cutting process, optimize the machine structure and processing parameters, the modal analysis of precision micro slitting turn-milling machine tool based on hammer experimental method was researched. In this paper, by analyzing the mechanism of precision micro slitting turn-milling machine tools, the multi degree-of-freedom mathematical vibration model of precision slitting turn-milling machine tools is constructed. The precision micro turn-milling machine tool is analyzed based on the hammer experiment analysis. The modal analysis obtained the first five natural frequencies and resonance speeds of the precision micro slitting turn-milling machine tool,including ST26, NN-25UB8K2 and NN-20UB87. The research results show that hammer experimental method can evaluate the vibration modal analysis of precision micro slitting turn-milling machine tools to some extent. The experimental modal analysis results guide and optimize the structural design and processing technology of precision micro slitting turn-milling machine tools.

Abstract: The SMPC (Shape Memory Polymer Composite) is used for space deployable structuredue to their excellent properties. In this paper, the space deployable antenna was designed, whichincludes the design of the basic configuration, the antenna substrate, the SMPC hinge and its location.The modal of the hinge was studied with finite element software ABAQUS. The hinges with differentthickness were analyzed and compared. The modal of single piece antenna was calculated. Thevibration types and natural frequencies of the single piece antenna in connection are obtained. Theeffects of different hinge structures on the overall mode and the natural frequencies of the hinge werestudied. The influence of hinge location on the natural frequencies of deployable antenna was alsostudied. The mode of four pieces antenna in unfolding was calculated, the main vibration types wereobtained, and the natural frequencies were analyzed and compared with that of the single pieceantenna. In unfolding, the natural frequencies of the four pieces antenna are lower than that of thesingle piece one.

Abstract: The following study involves designing of a go-kart chassis using CAD and CAE tools. The chassis is the supporting base for every automobile and chassis is subjected to various loads due to self-weight, acceleration, braking, bumps and cornering. CATIA Software was used for designing the CAD model of the chassis and ANSYS software was used for the FEA analysis of the chassis under different loading conditions. The calculations of these forces due to impacts are required to design a functional chassis for go-kart and having an adequate stiffness to avoid any vibration or resulting resonance. Ten mode shapes and natural frequencies are studied for vibration characteristics using Modal analysis in ANSYS. For impact analysis the loads in terms of gravitational acceleration are applied for the front, side and rear impact as 4g, 2g and 2g respectively and the results are compared to get the best material among the four selected materials AISI 4130, AISI 1080, AISI 1020 and AISI 1026.

Abstract: This paper presents the results of the simulation experiment performed in Lira-SAPR. The purpose of the experiment is modal analysis of various structural schemes of the high-rise reinforced concrete frame under pulsation and earthquake action. Calculations have been made for three series of samples, differing in the stiffness ratio of the frame and diaphragm of the scheme (from 20% to 65.9%), considering seismic rating of 7, 8 and 9 magnitude and subsoils of the 1^st, 2^nd and 3^rd categories of seismic activity. It has been established, that the ratio of stiffness influences the distribution of the modal mass. The acceleration of the cover nodes does not depend on the stiffness ratio – they grow as seismic activity of the site increases. Stiffness ratio influences the total reinforcement requirement. This influence is significant in the range of ratio values from 20.5% to 42.5%. Further increase in the stiffness ratio has little influence on the reinforcement requirement.

Abstract: This paper presents dynamic analysis of a three stage planetary gear reducer for operate a tower crane. Ordinary and planetary gears have been designed respecting the coaxial, neighboring and mounting conditions. Harmonic analysis has been processed to identify frequency response for displacements, strains and deformations. The aim of the study was to determine critical frequencies to avoid mechanical resonance phenomenon. The obtained results are based on the superposition method for solving the systems of differential equations resulting from the analysis with finite elements.

Abstract: Steam turbine generator unit, water pump and other high speed revolution symmetric flexible rotor were regarded as research objects in this paper. According to variation characteristic of rotor shaft in rigid and flexible working mode, nine-reel high pressure water pump rotor was analyzed. The former four-order intrinsic frequency of flexible rotor was obtained by modal analysis and harmonic response analysis. The methods of reaction force response and unbalance response were been studied after first order and second order resonance region eliminating in different modes of simple harmonic exciting force. Based on above theoretical research results, trapezoid counterweight method was proposed for dynamic balance of flexible rotor. This method solved problem that rigid dynamic balance of low speed rotor was destroyed after first order and second order resonance region counter weight in dynamic balance of flexible rotor. The dynamic balancing techniques of flexible rotor could be improved the qualities of rotor and its relative products by this method, eliminating the vibration of unbalance mass of products radically.