seyed hamed hashemi mehne

Nowadays, wind energy is considered one of the cleanest sources of energy, and the capacity of wind power plants is growing around the world. In particular, the design and construction of small wind turbines have been the subject of much research. This article deals with the Savonius wind turbine, a well-known vertical axis turbine. First, the mechanical principles of operation of this type of wind turbine are explained. Then, the criteria for determining its efficiency and performance, such as power and torque coefficients, are stated. The sequel discusses the geometric and technical factors affecting its efficiency. These factors include the overlap ratio, number of blades, number of stages, twist angle, shaft diameter, and the installation of end plates. The current paper can be helpful for those trying to improve the performance of this type of turbine. In this regard, there are some proposed innovative designs to enhance the performance of the Savonius turbine concerning experimental results and their numerical simulations. These designs increase the maximum power coefficient to 38%, although they complicate the turbine structure. Some of these innovative designs are also reviewed.

This paper deals with active vibration control (AVC) and structural health monitoring of a maneuvering flexible spacecraft with a cracked panel using piezoelectric (PZT) sensor/actuator patches and strain rate feedback (SRF) method. The cracked panel is modeled using the Euler-Bernoulli beam theory and the finite element method (FEM). The nonlinear equations of motion of the fully coupled rigid-flexible system are extracted using the Lagrangian formulation and solved with Newmark-β algorithm. Two approaches of structural health monitoring; first, trial and error, and second, maximum strain rates (online measurement) along with AVC (applying control signals based on the maximum values of strain rates to the predefined number, but unknown locations of PZT actuators), are performed. The strain rates change directly with mission conditions and crack locations, and the corresponding actuators are activated simultaneously. Moreover, to identify the dynamic behavior of the whole, cracked system, an energy function with different weighting coefficients is introduced to propose a suitable criterion for the performance evaluation of the second approach. Simulations for different crack numbers and locations and external disturbances as a comparative study (in MATLAB/Simulink) demonstrate suitable criteria to determine the number and locations of actuators and reduce the power costs in modern spacecraft in high-precision missions.

‎Continuous stirred tank reactor (CSTR) is an important and constructive part in various chemical and process industries and therefore it is necessary to control the process in optimal temperature and concentration conditions. Because of the nonlinear nature and limits of the control input‎, ‎solving this problem is very difficult. To achieve a sub-optimal control policy for chemical processes‎, ‎we focused on a new construction model‎.  Then‎, ‎a two-phase algorithm‎, ‎denoted as modified sequential general variable neighborhood search (MSGVNS) algorithm based on three local searches that use efficient neighborhood interchange has been employed to solve CSTR problems numerically. The results of the proposed method show that its convergence to the exact solution is achieved by the accuracy comparable to other numerical algorithms in few times‎.

In this paper, using the concepts related to the information theory, the model of interaction between human and machine in a standard simulator of piloting tasks is created. For this purpose, baud rate generated in all subsystems of the simulator is calculated and by summing them, the total baud rate is obtained. Next, output baud rate produced by human during working with the simulator is computed and subsequently, a unique index facilitating human performance investigation is proposed. Finally, the capability of this index is examined in the simulator of piloting tasks via a practical test performed by some subjects for different levels of workload (low, medium, and high). Results demonstrate that when a substantial growth in the workload level occurs, subjects try to show extra effort through increasing their generated output baud rate. On the other hand, according to the statistics analysis it can be concluded that there is a significant difference between performance of subjects across low, medium, and high levels of workload, i.e. a severe growth in the workload level causes considerable drop in performance index.

One of the most interesting topics in the field of human machine interaction is workload. In this paper, using information theory concepts, baud rates generated in all subsystems of a generic simulator of piloting tasks were calculated and then, a unique numerical index presenting an estimation of overall workload was extracted. To examine the effectiveness of offered criteria, three tests with different levels of autopilot failure were designed in which existing workload were labeled based on involving baud rates. A group of subjects performed these tests as the pilots while recording their own idea about perceived workload. Results confirmed that there were statistically significant differences between the averages of scores assigned by subjects to the overall workload for three levels of difficulty. Consequently, the proposed quantitative index is effective enough for determination of workload levels in the simulator environment and facilitates creation of needed scenario noticeably.

A shape optimization problem of cooling fins for computer parts and integrated circuits is modeled and solved in this paper. The main purpose is to determine the shape of a two-dimensional pin fin, which leads to the maximum amount of removed heat. To do this, the shape optimization problem is defined as maximizing the norm of the Nusselt number distribution at the boundary of the pin fin's connection profile. The governing differential equations are solved in solid and fluid phases separately. In order to formulate the optimization problem with finite dimensions, the shapes of the profiles are parameterized with cubic polynomials. Due to the lack of an explicit relation between the objective function and the geometric parameters, an approximate modeling method is used for the optimization process. The proposed method starts with three initial points. Then, the governing differential equations are solved for each of the profiles related to the initial points. The new step in this iterative process involves calculations based on a polynomial interpolation within the resulting Nusselt number norms. A numerical example is given to show the implementation and accuracy of the method.