Amelina E.V.   Голушко С.К.   Yurchenko A.  

The problems of analysis and design of hybrid pressure vessels

Reporter: Amelina E.V.

Rocket and Space industry makes extensive use of high-pressure vessels for transport and storage of different kinds of gas. High strength and reliability along with lightweight are critical properties for such structures. The main load applied to such vessels is a high internal pressure amounting for tens and hundreds of atmospheres. A promising solution is to make hybrid composite overwrapped pressure vessels (COPV) of a metal (titanium) liner and reinforced multilayer fibrous composite (CFRP). Such hybrid structures have significantly greater capabilities to manage their stress-strain state and thus durability and weight.
Producing reliable COPV requires developing and testing the technology for forecasting and analyzing the deformation and strength of vessels under typical and high load. It is useful to explore possibilities to control characteristics of deformation and strength by changing the geometry of the vessels and the mechanical and structural parameters of the composite. It is also important to develop and test a technology for optimization of the characteristics of vessels, primarily how to reduce the weight of the tank while maintaining its usable capacity.
Applying methods of mathematical modeling and numerical optimization can significantly reduce the duration of research aimed at finding the best parameters of the hybrid structure and cut down the cost of the research. However, a number of serious problems can occur along this way. They include the lack of reliable methods of solving problems of optimal design of such complexity, the problems of numerical modeling of such hybrid structures associated with the choice of models that describe adequately the behavior of such structures, and which are not too demanding on computational resources.
In this report, we propose approaches to the solution of direct problems with the use of a number of shell theories and of several structural models of composite material. The opportunities for controlling stress-strain state of COPV were shown. Regularities in the behavior of the vessels were found for all studied versions of shell theories and their combinations with different models of composite materials, which allows identifying the ways of making best reinforcement by using simpler theories and models, saving computing resources significantly.
The second part of the study is dedicated to the solution of problems of optimum design of pressure vessels with minimum weight under given constraints on volume and strength. Basing on the results of the first part of research the classical shell theory and structural theory of fibrous composite material with one-dimensional fibres were chosen as the basic theories. To solve these tasks we used the methods of global numerical optimization. The results were verified by solving the direct problem with the obtained parameters.
The research resulted in development of the technological sequence from the analysis of stress and strain to optimal design of vessels with given constraints on the load and the internal volume. To design vessels with capacity V* litres and a permissible pressure P*, a parametric analysis was conducted with account of the strength characteristics depending on the parameters of the composite. The numerical optimizations were performed at different constraints on control functions: the form of a vessel, wall thickness, and reinforcement angles. It was shown that the variable control functions could significantly reduce the weight of the optimal design in comparison with the design with constant characteristics.