h. golparvar

In this paper, theoretical and experimental simulations of the UAV hull’s structural strength in the landing phase on the water surface have been studied. In the seaplane design, calculating the strength of the hull structure against impact from the water surface is of special importance. Initially, the hull was numerically simulated using the finite element method, the interaction of the structure with the fluid (two-phase). Then, by performing an experimental study with variable speed, the results of numerical solution and experimental experiment are compared and evaluated. Comparing the results and graphs obtained from the numerical method with experimental experiments, it has been observed that throwing the seaplane free fall on the water surface can be a simulation of the most critical state for landing. The results show that increasing the descent height and velocity of the device when colliding with the water surface, causes the highest strain gradient along the axis perpendicular to the floor of the waterfowl and the least changes along the axis tangential to the water surface. According to the data obtained from the Tsai Hill and Tsai Wu rupture criteria for numerical solution and experimental testing, the values of stress and strength of the seaplane hull structure are within the allowable design range.

Piezoelectric cantilevers are mostly used for vibration energy harvesting. Changing the shape of the cantilevers could affect the generated output power and voltage. In this work, vibration energy harvesting via piezoelectric resonant unimorph cantilevers is considered. Moreover, a new design to obtain more wideband piezoelectric energy harvester is suggested. This study also provides a comprehensive analysis of the output voltage relationships and deducing an essential precise rule of thumb to calculate resonance frequency in cantilever-type unimorph piezoelectric energy harvesters using the Rayleigh-Ritz method. The analytical formula is then analyzed and verified by experiment on a fabricated prototype. The analytical data was found in an agreement with the experimental results. An important finding is that among all the unimorph tapered cantilever beams with uniform thickness, the triangular cantilever, can lead to highest resonance frequency and by increasing the ratio of the trapezoidal bases, the resonance frequency decreases. It is concluded that the shape can have a significant effect on the output voltage and therefore maximum output power density. Some triangular cantilever energy harvesters can arrange in pizza form using cantilever arrays. This arrangement decreases the occupied space and can lead to increasing the power density and also operating bandwidth.