Scientia Iranica
Volume:18 Issue: 3, 2011

A series of low speed wind tunnel tests were conducted on a section of a 660 kW wind turbine blade to examine the effects of distributed surface contamination on its performance characteristics. The selected airfoil was tested with a clean surface, two types of zigzag roughness, strip tape roughness and distributed contamination roughness. The straight and zigzag leading edge roughness models simplify the contamination results in an early turbulence transition. In this study, surface contamination was simulated by applying 0.5 mm height roughness over the entire upper surface of the airfoil. The distribution density varied from the leading edge to the trailing edge of the model. Our data show that this particular airfoil was very sensitive to surface contamination and its maximum lift coefficient decreased up to 35%, while the stall angle of attack increased slightly. The surface contamination, however, caused very smooth stall characteristics and less lift drop in the post stall region. In contrast to the clean model, the maximum lift coefficient of the roughened airfoil increased with Reynolds number. The effects of zigzag roughness and strip tape roughness were less than that of the distributed contamination roughness.

In this study, a pure Lagrangian algorithm for numerical simulation of fluid-structure interaction problems is proposed based on the Smoothed Particle Hydrodynamics (SPH) method. A new treatment of boundary conditions at the interfaces is introduced that provides the possibility of simultaneous integration of governing equations for all particles, regardless of its material type. The proposed algorithm is capable of dealing with large deformations of hypo elastic solids. The method is validated by comparison of numerical results with other numerical simulations and also examining the consistent behaviors of the algorithm for different parameters.

The friction drive principle, which is based on the superposition of two synchronized perpendicular vibrations at the interface of the robot and the work floor, plays a fundamental role in the locomotion of miniaturized robots. In this paper, the iteration perturbation method proposed by He is used to generate a periodic solution for this type of friction drive microrobot. The equation of motion for the system reveals a parametrically excited oscillator with discontinuity, the elastic force term for which is proportional to a signum function. The obtained solutions are in excellent agreement with those achieved from numerical integration and experiments reported in the literature. Results show that for a wide range of variation of system parameters, a phase shift near 90°between the perpendicular vibrations leads to the maximum achievable velocity of the slider. Besides, we have shown that driving frequency and the relative amplitude of vibrations are the best parameters for the control purposes of this type of microrobot.

The flow over a supersonic inlet has been investigated experimentally and numerically at a free stream Mach number of 2 and a zero degree angle of attack. Wind tunnel tests were performed to obtain the performance parameters of the inlet and were used as a baseline and validation tools for the numerical code. A heat source was added to the flow field at a distance ahead of the inlet. The effect of heat source addition on the main performance parameters of the inlet is investigated numerically. Results show that the heat source considerably reduces drag coefficient; however, its effect on pressure recovery is not favorable. This unfavorable effect was then minimized by controlling heat source parameters, such as its location, size and shape. For the optimum condition, drag coefficient reduces considerably, inlet mass flow rate increases, but pressure recovery slightly decreases.

Morphing Evolutionary Structural Optimization (MESO) is a soft-kill version of Evolutionary Structural Optimization (ESO). This paper proposes a new optimality criteria-based performance index for monitoring the optimization process of the conventional MESO method. Also, a quantitative verification of the MESO for some benchmark problems with equality constraints is presented. For some structures like Michell trusses, a qualitative verification of the ESO method has been already reflected in the literature. However, in this study, a quantitative verification of the MESO method in the shape optimization is shown by comparing the results with analytical solutions. An excellent convergence of the MESO method in stiffness, frequency and weight optimization problems with equality constraints to optimum clearly reveals that this method is a robust optimization technique, which can be easily implemented and applied to a wide range of problems.

Periodic orbits have been studied more extensively by space mission designers in recent years. These orbits are usually described as planar in three-body-problems. In this article, in addition to introducing a new orbit that turns around a secondary mass, applications in Moon-based, Earth-based, and interplanetary missions are also described. Floquet exponents as chaos indicators and normal potential levels for orbits are also calculated. The advantages of their use as space station orbits are studied at the end of the article.

Preheating treatment and employing a proper welding sequence are introduced as two efficient approaches for reducing residual stresses in welding processes. Selecting a right welding sequence and a proper preheating temperature for a weld system are crucial tasks, since welding residual stresses are inevitably produced in a welded structure. However, obtaining residual stresses is very complex, and much time is needed in some cases, particularly for the modeling and prediction of residual stresses in welded structures. So in this work, we attempt to show that these stresses depend on generated entropy during the arc welding process. Thus by obtaining thermal irreversibility effects from temperature distribution, due to a variation of different welding parameters, selection of optimum factors to achieve minimum residual stress is not only possible, but easier to undertake. In the proposed method, it is not a necessity to obtain residual stress values, and one can predict the behavior of residual stress qualitatively. To do so, 3D numerical models are employed to study the similar behavior of created residual stresses and entropy due to a variation of different preheating temperatures and three common welding sequences.

Extensive wind tunnel tests were performed on several wing- body-tail combinations in subsonic flow to study the effects of wing geometric parameters on the flow field over the tail. For each configuration, tail surface pressure distribution, as well as the velocity contour at a plane perpendicular to the flow direction behind the wing was measured. The results show a strong effect of wing to tail span ratio, as well as wing aspect ratio, on the flowfield downstream of the wing. For low sweep wings, as those considered here, wing and body interference effects on the tail are associated with the wing tip vortex and nose-body vortex.

Extensive wind tunnel tests were performed on several wing- body-tail combinations in subsonic flow to study the effects of wing geometric parameters on the flow field over the tail. For each configuration, tail surface pressure distribution, as well as the velocity contour at a plane perpendicular to the flow direction behind the wing was measured. The results show a strong effect of wing to tail span ratio, as well as wing aspect ratio, on the flowfield downstream of the wing. For low sweep wings, as those considered here, wing and body interference effects on the tail are associated with the wing tip vortex and nose-body vortex.

The paper addresses a new QRS complex, geometrical feature extraction technique, as well as its application in supervised electrocardiogram (ECG) heart-beat hybrid (fusion) classification. To this end, after detection and delineation of the major events of an ECG signal via an appropriate algorithm, each QRS region and also its corresponding Discrete Wavelet Transform (DWT) are supposed as virtual images, and each one is divided into eight polar sectors. Then, the curve length of each excerpted segment is calculated and used as an element of the feature space. To increase the robustness of the proposed classification algorithm versus noise, artifacts and arrhythmic outliers, a fusion structure consisting of four different classifiers, namely Support Vector Machine (SVM), Probabilistic Neural Network (PNN) and two Multi Layer Perceptron-Back Propagation (MLP-BP), with different topologies, were designed. To show the merit of the new proposed algorithm, it was applied to all MIT-BIH arrhythmia database records, and the discriminative power of the classifier in isolation of different beat types of each record was assessed. As a result, the average accuracy value, Acc=98.18%, was obtained. Also, the proposed method was applied to 8 arrhythmias and an average value of Acc=97.37% was achieved.