A.K.W. Ahmed

Optimization of thermocontrolled tank for hydrogen storage in vehicles

There is growing concern about the environmental pollution caused by vehicular engines and the tendency to replace the dominant liquid hydrocarbon fuels with cleaner alternative energy sources. Hydrogen is a promising alternative to liquid hydrocarbon fuels. It has many advantages when injected directly into the cylinder of an internal combustion engine. However, when using compressed hydrogen gas for automotive applications, large and heavy tanks are required and when used in liquid form, expensive insulating materials and cryogenic pumps are required to create the high pressure. A prototype composite vessel has been developed to supply hydrogen gas at high pressure required for direct injection without compressing gas or using any cryogenic pumps. This vessel, called the thermocontrolled tank has been simulated and then tested to determine the rate of pressure and temperature rise in the tank. The test results indicated that the liquid hydrogen can be brought from atmospheric pressure to the high pressure in a reasonable time period. The composite vessel design has been optimized for use in vehicles. The design problem was formulated as a multi-objective optimization case because of the presence of different conflicting objectives. Weighting factors have been attached to the various objectives and then solved. Conclusions have been drawn from the tests, simulation and optimization results which would allow the most effective storage of hydrogen in thermocontrolled tanks on vehicles equipped with direct gas injection.

An algorithm for simulation of nonlinear mechanical systems using energy and force similarity of its elements

Abstract An algorithm, based upon energy and force equilibrium, is proposed to evaluate the frequency response characteristics of nonlinear mechanical systems with symmetric and asymmetric dissipative and restoring elements. Dual stage dampers and hardening springs with symmetric or asymmetric characteristics are characterized by an array of local equivalent linear coefficients, using the methodology based upon principle of energy similarity. Frequency response characteristics of a dynamical system comprising nonlinear symmetric and asymmetric damping and hardening spring are evaluated, and compared to those determined from direct integration of the nonlinear system equations. An error analysis is performed to determine the magnitude of error between the nonlinear and local equivalent linear forces. The average force error is then integrated within the local equivalent algorithm to achieve the force similarity between the nonlinear and linear elements. The results revealed that the proposed algorithm can accurately estimate the frequency response characteristics of the nonlinear systems in a highly efficient manner. The algorithm based upon energy similarity alone yields slight error near the resonant frequencies, while the analysis based on the combined energy and force similarity can reduce this error considerably.