A study on flow fields and performance of water wheel turbine using experimental and numerical analyses

In this paper, an analysis of the performance and flow fields of water wheel turbines for tidal energy extraction is carried out using experimental and numerical methods. The purpose of this work is to develop a water turbine suitable for sites, where fast and shallow surface flows are available, such as rivers or tidal currents. For both methods, the water wheel turbine is tested over a range of tip speed ratios with a differing number of rotor blades, ranging between three and twelve. The results indicate that the numerical simulation shows agreement with the experiment in most cases. Also, the water wheel turbine operates effectively at a range of small tip-speed ratios, where the highest turbine efficiency is produced. Under the same working conditions, the turbines using between six and nine blades generate a greater efficiency and cause lesser reverse flows than others when submerged in water. In contrast, the 3-bladed turbine is the least efficient design as it produces the lowest amount of energy and causes intense vibrations and noises. These noises are a result of a collision between the incoming flow of the channel and the wheel blades during the experimentation, especially at high load conditions. By adding more blades, the torque generated is improved considerably; however, the upstream and downstream depths of the turbine, in this case, are also elevated significantly. Furthermore, in the inlet region, the 3-bladed and 6-bladed turbines have a smaller shock loss and a lower resistance to the main flow from the inlet than the others. Meanwhile, it is found that the flow in the outlet region on the turbines with between nine and twelve blades is in the opposite direction to the wheel’s rotation, significantly obstructing the main flow from the inlet.     

Enhanced Photocurrent Performance of Flexible Micro-Photodetector Based on PN Nanowires Heterojunction using All-Laser Direct Patterning

UV micro-photodetectors (mPDs) have received significant attention owing to the increasing demand for application in wearable healthcare devices. However, mPDs often suffer from tiny signals owing to their small size. Although this problem can be overcome by using low-dimensional nanomaterials with high surface-to-volume ratios, such as nanowires (NWs), selective synthesis of functional NWs on the desired position of the specific substrate is challenging. This study introduces, for the first time, the laser-induced hydrothermal growth (LIHG) process, in which a strongly focused laser beam generates a localized high-temperature field, enabling the localized growth of CuO NWs on the desired position of the specific substrate. Also, an all-laser direct patterning process for the fabrication of a flexible mPD based on a p-CuO NW/n-ZnO NW heterojunction is demonstrated. The PN NWs heterojunction exhibits remarkable photocurrent enhancement compared to a homojunction with a single semiconductor material. Furthermore, the all-laser direct patterning process of the flexible PN NWs heterojunction can be applied for the fabrication of other flexible optoelectronic applications.     

STRUCTURAL OPTIMIZATION USING A NEW LOCAL APPROXIMATION METHOD

A new method for solving structural optimization problems using a local function approximation algorithm is proposed. This new algorithm, called the Generalized Convex Approximation (GCA), uses the design sensitivity information from the current and previous design points to generate a sequence of convex, separable subproblems. The paper contains the derivation of the parameters associated with the approximation and the formulation of the approximated problem. Numerical results from standard test problems solved using this method are presented. It is observed that this algorithm generates local approximations which lead to faster convergence for structural optimization problems.