Lightweight Research On Complex Shell Frame Structure Based On Structure Optimization Theory

The shell frame structure discussed in this paper is composed of the inner(or outer)skeleton structure acting as the main supports and the outer(or inner)shell structure acting as the minor supports whose sizes in length and width direction is much larger than the size in thickness direction,usually including a number of accessory parts that play an unimportant role for the structure stiffness.It is usually called complex shell frame structure when the number of parts is very high and the structure has many kinds of working conditions.Energy problems of China are faced with a huge challenge.Light weight research on complex shell frame structure is not only useful for the improvement of product quality but also important for reducing energy consumption.Inspired by that the hollow shaft is more lighter in weight than solid shaft when they are subjected to the same torsional load,the view that size optimization will eventually reach what extent depends not only on the choices of optimal design variables and optimization methods,but also on the rationality of original structure is put forward.And considering the fully stressed design criterion,the reasonable design of complex shell skeleton structure which is called equally stressed design criterion is brought up.That is in the premise of meeting the using requirement,making the stress value of the most area of the structure reach or close to the allowable stress value as far as possible.On the basis of these,the lightweight of a compound garbage bin of road sweeping vehicle was taken for example and the following works were done.①According to the characteristics of shell skeleton type structure,the effects of different element types,joint modeling method and constraint set on finite element results were discussed.The finite element model of the initial design scheme of compound garbage bin was established and the linear static analysis was performed then.The results showed that the initial design scheme had many stress concentration areas and huge deformation areas and the scheme needed to be modified.②Put forward three principles for the equally stressed design of complex shell frame structure to make the stress value of its parts in a certain region: redesign the bigger parts,minimize the load transfer path and reduce the stress concentration structures.Applied these principles to the modifications of the compound garbage bin and obtained a design scheme which met the using requirement and the equally stressed design criterion,which verified the correctness of the three principles.③Put forward a new method of choosing and group design variables based on equal strength theory and manufacturing technology.Put forward a method of dealing with the smaller parts in size optimization: regard them as dependent design variables.22 design variables of the size optimization of compound garbage bin and their value ranges were obtained.The stress characteristics of the compound garbage bin were analyzed and four of the eight working conditions were selected as the constraint conditions of the optimization analysis,which greatly simplified the complexity of the optimization problem.The maximum allowable value of structural stress and strain was determined.The size optimization mathematical model is established.④Put forward a way to deal with the thickness of shell welding elements in size optimization.The optimization converged after 32 iterations.The finite element analysis results showed that the optimal design scheme was feasible and the weight of the compound garbage bin was reduced by 562.7kg(about 22.05%).Three design schemes were compared and analyzed.Feasible optimization direction of the subsequent work was pointed out when the design variables reached their upper limits or lower limits in size optimization.The equally stressed design principle of complex shell frame structure proposed in this paper is of great practical significance for the lightweight development of this kind of structure.The methods of choosing and group design variables based on equal strength theory and manufacturing technology and dealing with the smaller parts in size optimization are worth referencing.