Analysis and Improvement of Virtual Work Criteria for Structure Optimization
An improvement of virtual work criteria for structure optimization is presented to overcome the shortcomings caused by the neglect of dead weight and inertial load of structure in solution of criteria equations. Deduction of criteria equations is analyzed to prove that the shortcomings lead to the error of structure optimization. Therefore, new criteria equations are formulated using the displacement representation of algebraic sum and matrices. According to the characteristics of the improved criteria equations, an improved Aitken algorithm is applied to solve the equations in order to implement the complete automatization of iterative solution for structure optimization. The algorithm is proved to be an accelerated iterative method, and its convergence order is estimated. The feasibility of improved criteria equations and the merits of improved Aitken algorithm are demonstrated by an illustrative example showing five-bar truss. The results show that the improvement of virtual work criteria provides a structure optimization method for precision machine.
New linear iterative algorithm and its application in seeking solution of criterion equations of structural optimization
Aitken algorithm,exploited to solve nonlinear equations with one variable,is an automatic linear iterative algorithm,in which each iteration needs computing function values twice.Extending it to iterative solution of structural optimization nonlinear criterion equations,complete automatization of iterative seeking solution for structural optimization can be implemented.To eliminate the defects of requiring two structural analysis for one iteration,a new type of linear iterative algorithm,called Atiken-Chen algorithm,is constructed.This algorithm utilizes the information of the last iteration and merely needs one structural analysis for each iteration,through which the computing efficiency and degree of automatization of structural optimization interaction computation are greatly enhanced.Feasibility and superiority of this algorithm have been demonstrated by illustrations.
Thrombus formation after aortic valvular replacement using Björk-Shiley valve occluding the right coronary orifice.
We describe a patient with unstable angina due to occlusion of the orifice of the right coronary artery by thrombus formation after aortic valvular replacement using a Björk-Shiley valve. After strict anticoagulant treatment, transesophageal echocardiography demonstrated disappearance of the thrombus formation around the orifice of the right coronary artery.