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In this research, thin-walled steel energy absorbers were investigated. The introduced structures absorb energy through the processes of inversion, folding and expansion. Each absorber consists of two end-capped frusta and a cylindrical shell. The intended absorbers were experimentally made and then tested. The mechanical properties of the used materials were extracted by performing tensile tests and then used for simulation. The simulations of this research were carried out using LS-DYNA software. After comparing the experimental and numerical results, a good agreement between the results was observed and then the obtained results were discussed. The intended absorbers were examined in terms of the thickness of the lower frustum, the height of the middle shell and the angle of the upper frustum. The obtained results showed that by increasing the thickness of the lower frustum, energy absorption in the inversion process increased. In addition, the investigations related to the effect of height on the collapse properties showed that increasing the height of the middle shell with a thickness of 2 mm for the lower frustum led to a decrease in energy absorption. Also, in the investigations carried out on the half angle of the frustum, it was found that the contribution of energy absorption in the expansion process was low.

Newly, energy storage systems and harvesting energy equipment are modern and important topics in engineering problems, but they still face the efficiency problem. Using the advantages of micro-scale flow and metal porous materials can be applied to improve the performance of these systems. So, the present investigation provides a numerical study on a heatsink employing various arrangements of metal foams inside a heat sink (in the direction and against the fluid flow). The influences of diverse fluid flow characteristics, metal foams' permeability and thermophysical properties of the coolant (using CuO-MgO/water nanofluids) on the thermal efficiency of the heatsink are examined. Then, the variations of convective heat transfer coefficient and pressure loss for all variables are investigated, and performance evaluation criteria are defined to distinguish the simultaneous impacts of improving heat exchange against incrementing the pressure loss. It indicates the metal foams located in the direction of the flow perform better than those located against the flow, which increases the performance evaluation criteria (PEC) of the heatsink between 1.18 and 1.55 depending upon the permeability of porous media. Also, using the nanofluids in the presence and absence of metal foams decreases the heatsink performance. Investigating the impacts of volumetric flow rate illustrates that thermal performance increases by increasing the flow rate. In addition, outcomes reveal that although adding metal foams and nano-additives and increasing volumetric flow rate enhance the frictional entropy generation rate, the total amount of entropy generation rate decreases due to more contribution of the thermal entropy generation rate, that reduces by those variables.