Computational Methods in Engineering

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The objective of this study is to design a robust direct model reference adaptive controller (DMRAC) for a nonlinear cardiovascular model over a range of plant parameters representing a variety of physical conditions. The direct adaptive controllers used in thisd study require the plant to be almost strictly positive real (ASPR) that is, for a plant to be controlled there must exist a feedback gain such that the resulting closed loop system is strictly positive real. We designed a new compensator so that the system composed of the cardiovascular plant and the compensator satisfy the ASPR condition. Numerous studies in the past have considered a small range of gain variations of the cardiovascular system. In most cases, the controller was designed based on variations in either time delay or plant gains. Many of these workers treated the cardiovascular system as a single-input single output (SISo) plant in which the control output was Mean Arterial Pressure (MAO). We treated the cardiovascular system as a multi-input multi-output (MIMO) plant in which both the MAP and Cardiac Output (CO) are simultaneously controlled. In this study, a new linear model is presented that provides a better approximation thanthe one the original linear model does. By doing so and utilizing the DMRAC algorithm, we could satisfy the stability conditions for the nonlinear model while satisfactory responses obtained under every possible condition for the cardiovascular nonlinear model.

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In this paper, first the theory of Improved Applied Element Method (IAEM) is proposed and then an appropriate algorithm and software are developed for analyzing structures behavior until collapse by this method. Then, some examples of structural analysis by the above method and a software developed for this study are presented. The results show that IAEM has the ability to solve the discussed problems more accurately in less time than Finite Element Method (FEM). Moreover, the efficiency of the method for solving large displacements problems is enhanced in this research by introducing nonlinear response indicators. For modification of the stiffness matrix in the nonlinear range, a new method is presented that increases the accuracy of calculation up to 30%.