Changes In Stiffness Matrix Research Articles

Real-Time FEM Computation of Nonlinear Magnetodynamics of Moving Structures on FPGA for HIL Emulation

Finite-element method (FEM) based hardware-in-the-loop emulation provides the most accurate and fast prototype platform for real-time design and testing of electric machines in a nondestructive environment. The application of transmission line modeling (TLM) can expeditiously reduce the FEM execution time by decoupling the nonlinear elements of the FEM equivalent network using transmission lines to keep the stiffness matrix unchanged through the simulation for static cases. However, in electric machines the TLM method suffers from the change of stiffness matrix in the time-stepped procedure due to movement. Furthermore, time consumption for the solution of numerous decoupled nonlinear equations for a fairly large number of TLM iterations in comparison with the conventional Newton–Raphson method remains a challenge. This paper proposes a novel real-time TLM method based on finite precalculated lower and upper triangular decompositions and field programmable gate array hardware implementation to exploit TLM parallelism for real-time simulation of magnetodynamics in electric machines. A two-dimensional FEM simulation of a single-sided linear induction machine is emulated in hardware and the results are validated experimentally and with Jmag-Designer software to show the effectiveness of the proposed method.

Методические особенности анализа накопления повреждений и достижения предельных состояний объектов при комбинированных многопараметрических воздействиях силовых факторов и среды

The paper proposes a new methodological approach, coupled with complex analysis of reaching damages and limit states
 of materials and structural elements under multi-parameter actions of various kinds of loads and the environment, taking
 into account changes in the stress-strain state, material properties and the kinetics of components damageability as well
 as time factor. We propose to consider damageaccumulation as a multi-level analysis, uniting a group of micro, mesoand
 macroscales and analyze it in probabilistic setup.
 During the damageextentestimation we invite to use the method of modulus of rupture variationand a method based
 on the analysis of changes in stiffness matrix in model studies. Also in this regard, are considered the probability matrix
 methods of scripting to achieve the ultimate states, which provide construction of macro- vulnerability matrix, mezovulnerability
 matrix and vector of threats.

Расчет железобетонных конструкций методом конечных элементов с учетом реального описания действующих физических процессов

It is well known, that buildings and their bearing structures are subject to ageing, including corrosion, deterioration, etc. When faults in bearing structure are detected, disposal-at-failure maintenance should be made. But before that, it is necessary to assess the rate of deterioration.The author suggests to use finite element method for calculation of the safety margin of reinforced concrete bearing structures, because the finite element method is widely used in engineering practice of structural design. In the process of engineering inspection of reinforced concrete structures all defects of the inspected structure should be clearly specified. The article suggests to create the FEM-Model of the inspected structure in view of the fact that this structure is defected. In order to achieve this effect, the stiffness matrix of some finite elements should be changed and the FEM-Model must be created of volumetric finite elements (the article speaks about eight-node parallelepiped elements).At first the FEM-Model will be created of eight-node parallelepiped elements with standard descriptions for the reinforced concrete; then finite elements in damage area must be changed. On the basis of integral estimation of the mode of deformation, deformation ratio will be calculated, which is essential for the description assignment of the changes in stiffness matrix. The formulation of the deformation ratio includes all the possible defects of structure through indexes, which must be analytically calculated depending on the concrete defect.The method described in the article is useful in the process of engineering inspection of the reinforced concrete structures. Using this method can sufficiently specify the safety margin of a defected structure and forecast the future operational integrity of this structure under the acting load.

동특성 변화를 이용한 감쇠 구조물의 손상예측

A damage in structure alters its dynamic characteristics. The change is characterized by changes in the modal parameter, i.e., modal frequencies, modal damping value and mode shape associated with each modal frequency. Changes also occur in some of the structural parameters; namely, the mass, damping, stiffness matrices of the structure. In this paper, evaluation of changes in stiffness matrix of a structure is presented as a method not only for identifying the presence of the damage but also locating the damage. It is shown that changed stiffness matrix can be accurately estimated a sensitivity coefficient matrix derived from modifying mode shapes, First, with 4 story shear structure models, the effect of presence of damage in a structure on its stiffness matrix is studied. By using these analytical model, the effectiveness of using change of stiffness matrix in detecting and locating damages is demonstrated. To validate the predicted changing stiffness and its location, the obtained results are compared to the reanalysis result which shows good agreement.

Efficient structural health monitoring for a benchmark structure using adaptive RLS filters

Structural health monitoring is the process of implementing a damage detection strategy for civil and mechanical engineering infrastructure. In this research, the structure’s health or the level of damage is monitored by identifying changes in structural parameters, by comparing the stiffness matrix of a structure with the undamaged model matrix. The two methods developed employ adaptive recursive least squares (RLS) filtering using measured or estimated structural responses and a reasonable estimate of the input force, such as an earthquake, to directly identify changes in structural stiffness for the ASCE benchmark structure health monitoring (SHM) problem. These methods focus on minimal computation to enable real-time implementation and are computationally simple, requiring 0.03 Mcycles of computation for a 4 degree of freedom (DOF) structure at a 100 Hz sampling rate and 520 Mcycles for 120-DOF at 100 Hz. These values assume no parallelisation for super-scalar digital signal processing chips and are within the capability of current digital signal processing devices. The identified changes in stiffness matrix converge to within 1.5% of the true value within 1.6 s, with an average of 0.56 s for the twelve 4-DOF and 12-DOF cases and damage patterns examined from the ASCE SHM benchmark problem.

有限要素法を用いた木材の破壊過程のシミュレーション

An existing FEM program for elastic-plastic problems was converted to the one which can be accomodated to the change of stiffness matrix and the release of stress at fractured elements. With this program, the fracturing processes of two testing types of wood (spruce) were simulated; the standard JIS shearing test (JIS Z2114) and the standard JIS bending test (JIS Z2113). The results are summarized as follows.(1) The shearing strength obtained by the calculation was 90.6kgf/cm2. This value agreed with the actual testing data. The fracture initiated and propagated along the grains. This simulated result accorded well with the real fracturing process in the shearing test.(2) The bending strength obtained by the calculation was 1297kgf/cm2, which was larger than the actual value because the finite element mesh was rough and thus the scale factors for yielding were estimated as large values. The fracture initiated at the bottom of the specimen, grew to the neutral axis and turned its direction to the grain. This simulated result accorded well with the real fracturing process in the bending test.