نشریه علوم کاربردی و محاسباتی در مکانیک
سال بیست و هفتم شماره 1 (پاییز و زمستان 1394)

In most engineering structures the energy absorption systems are used to prevent or reduce damages. In this paper, performance of a crushing element of ER24PC locomotive is investigated. The numerical modeling of this crushing element, after introducing its operation, is performed using the Abaqus finite element software in order to evaluate its crushing characteristics. Since the shape of crushing element of ER24PC locomotive is tapered, an analytical solution has been used to validate the numerical results. Because of the thickness of crushing element, rupture may be occur in this element and using of a proper damage model is essential in order to simulate this rupture. From three damage models introduced in this paper, one damage model is already provided in Abaqus and the other two models have been coded. By comparing numerical results with experimental test results, proper damage model in software is developed and used in order to properly simulate the crashing process of considered element. The desirable damage model is verified by using ECE R66 standard. Finally in order to improve the energy absorption capacity metallic foam is used as a filler in energy absorber element. Through comparing the energy absorption behavior of foam filled crushing element with the non-filled element the foam performance in crushing element is evaluated.

In order to diagnose the faults of industrial rotating machines automatically, an expert system is used in this paper. A tri-lobe roots blower compressor is used as a test rig to represent an industrial machine. The proposed method for training the expert system includes: data acquisition, signal processing and intelligent pattern recognition stages. Acceleration signals of healthy and faulty compressor components were acquired in the first stage. The signals were conditioned to be used for the signal processing as the next stage. It is necessary to find pattern recognition criterion of the compressor fault diagnosis. Therefore feature extraction of data was performed as part of the second stage. In the third stage, a support vector machine tool was trained and employed to classify the faults. The proposed procedure was tested and the obtained results showed that this algorithm works very well and it fully classifies the faults automatically.

In this paper, the implementation of the variable-span Morphing wing(VSMW) on the wings of a UAV to achiev the optimal performance for various flight regimes is studied in wind tunnels. For the implementation of this plan, a morphing wing with its related mechanism is designed, built and tested. Tests were carried out at a low- speed wind tunnel with speeds of 35, 60 and 80 m/s in the range of Reynolds Number between 250×〖10〗^3 to 620×〖10〗^3. For the implementation of the morphing wing plan, the maximum deviation of wing span relative to Basewing (BW) is 38 percent and change of aspect ratio is 74% percent. Experimental results showed the improved aerodynamic properties of VSMW compared to BW. These improvements are in the form of reduction of induced drag, thrust required and increasing of lift coefficient, aerodynamic efficiency, endurance and rang. According to the results, endurance and range for VSMW comparison to BW, respectively 17 and 5 percent increased. The experimental studies show that the maximum aerodynamic efficiency of the wing model occurs at 4 degree angle of attack with the maximum value being 14.8 for the base wing, 16.3 for the morphing wing with 50 percent (5 cm) extension in wing span, and 17.4 % for the morphing wing with 100 percent (10 cm) span extension. This research also shows how VSMW can be used as an alternative method of roll control instead of the regular method (i.e. using aileron control surfaces) as it provides more roll control power than the regular method.

In this study, the free vibration analysis of a functionally graded rotating double tapered beam is performed. The analysis is based on Euler-Bernoulli beam theory. The Material properties of the beam vary continuously in the thickness direction according to the power-law function. The governing differential equation of motion is derived using the Hamilton’s principle. Natural frequencies are obtained using differential transformation (DTM) technique. The effects of the taper ratios, nondimensional rotational speed, nondimensional hub radius and material volume fraction index on the natural frequencies are discussed. Numerical results are tabulated in several tables and figures. To verify the present analysis, the results of this study are compared with the available results from the existing literature. It is shown that the natural frequencies of a functionally graded rotating double tapered Euler-Bernoulli beam can be obtained with high accuracy by using DTM. It was observed that nondimensional rotational speed, height taper ratio and power-law exponent significantly affect the natural frequency. The effects of hub radius and breadth taper ratio on the natural frequencies are negligible.

The effect of sail position on the downstream flow field of the sail is investigated in the wind tunnel. A five-hole pressure probe is used to measure the 3D flow field. The investigation of the five-hole results shows that the five-hole measurements can determine the horseshoe vortex structure. Also, the results show that the horseshoe vortexes become smaller by forward moving of the sail on the body to the nose. Therefore, if the sail is mounted on the hull near the bow, the performance of the impeller increases and nose level decreases.

In this study, effective diffusion coefficient of drying clay of ceramics drying clay ceramics have been studied. In this study, the effects of temperature (40-60-80 °C), relative humidity (30-50-70%) and air velocity (1-2-3 ms-1) on the drying behavior of clay ceramics were investigated. A full factorial design of experiments on a cubic sample was performed. In each trial mass and volume reduction using balance and camera was registered and the drying curve was plotted. Effective diffusion coefficient of moisture using drying curves were calculated using the newly developed algorithm of firefly. In this algorithm, the goal is to reduce the error between the analytical values and experimental values. Statistical analysis and analysis of variance showed that in calculation of the effective diffusion coefficient the velocity, temperature and humidity are independent of each other. The greatest impact on the effective diffusion coefficient is respectively related to the temperature, velocity and environment humidity. The comparison between this study and other studies show that 97% similarity and applicability of this method in calculating the effective diffusion coefficient of the ceramic drying processes.

Reinforcement learning is a method in which agent/agents obtain a positive or negative reward to do an efficient operation. In this way, the performance will be very suitable for the systems which are naturally complicated for deriving the differential equations. This can be a good alternative to other control areas. One of the main disadvantages of this method is considering the discrete actions during it. However, many of dynamical systems couldnt be optimized by this approach. To remedy this deficiency, different approaches have emerged, including approximate methods. In this paper, fuzzy logic is used to continually optimize the operations. In this case, the reinforcement learning method sets the fuzzy control rules which are the principles of optimal control. Two approaches, stabilizing the pendulum and both of pendulum and cart are considered to control the pole- cart problem in this paper. The results show that the applied artificial intelligence can be used as a proper solution for the taken policy.

In this study, the boiler of Mashhad Toos power plant is studied numerically in order to investigate the possibility to improve its efficiency and reduce its pollutants emission. In this regard, first the current status of the boiler is simulated and the numerical results are compared with the available experimental data, where a good agreement is observed. Next, the effects of the injected fuel droplets’ diameters, air flow rate and the inlet air swirl direction arrangement on the boiler thermal efficiency and pollution emissions are studied. An appropriate arrangement of the inlet air swirl directions for the nine liquid-fueled burners of the boiler is proposed that will lead to a higher boiler thermal efficiency and lifetime.

In this study, a low Reynolds flow around a blade is studied by experimental and numerical methods and characteristic curves are extracted. In the experimental static test, the results of thrust force, engine power, current and voltage in different speed for a rotor were recorded. Considering the importance of the flow field around the blade, the static and dynamic numerical simulations of the flow through a blade of Quadrotor are investigated. In addition to the blade aerodynamic results, the statistical of the computational domain are also analyzed. For the numerical simulation, a commercial software (Fluent) is used with the assumption of compressible viscous flow and turbulence model simulations. In this study, the characteristic curves of the rotor blade are extracted by the two mentioned methods. Comparison of numerical and experimental results show good agreement and confirm the accuracy of the measurement. According to the simulation of the flow field around the blade using the numerical method, the effective distance of the blades in order to find the optimum Quadrotor structure is studied.

In this paper, by defining an appropriate free energy function and integrate that with a Lattice Boltzmann algorithm; a two-phase system of vapor and liquid is modeled where the flow is governed by the continuity and Navier-Stokes equations. Using the developed model, initially a planar interface is modeled and outputs are compared with theoretical results. Then a droplet which is suspended in bulk vapor is investigated and equilibrium conditions of the droplet are compared with theoretical results.

Unlike serial manipulators, forward kinematic problem (FKP) of parallel robots is highly complicated and its analytical solution is not generally le. Therefore, in most cases numerical methods are used to solve this problem which are relatively time consuming. On the other hand, reducing the duration of FKP analysis is an essential task for applications like real-time control. In this paper, artificial neural networks and a 3rd-order numerical algorithm are combined and a new hybrid strategy is proposed for forward kinematics analysis of parallel manipulators which significantly increases the speed of the FKP solution. In the proposed method, an approximate solution of the FKP is first produced by the neural network. This solution is next considered as an initial guess for the 3rd-order numerical technique which solves the nonlinear forward kinematics equations and obtains the answer with a desired level of accuracy. The proposed method is applied to a spatial 3-PSP parallel manipulator. The results show that using this method will lead to a 35 percent reduction in number of iterations and a 12 percent reduction in the FKP analysis time, while maintaining high level of solution accuracy.

In this paper, the motion capability of wheeled mobile robot is increased by providing a new structure. Due to the special design, converting a two-wheeled robot to a four-wheeled robot is possible in the proposed multi-mode robot. This design has the ability to simultaneously and interchangeably provide locomotion and manipulation capability in motion on uneven terrain. Unlike most other mobile robot designs that have a separate manipulator arm module attached on top of the mobile platform, the central axis in this design can manipulate like a robotic arm. The robot midpoint as an end-effector is a passive joint. The part which could carry the guidance and visual equipments follows the height control, easily and without a new actuator. The basic requirement of stability and acceptable performance could be guaranteed through this simple, novel design. Finally, the simulation is used to study the robot’s enhanced mobility characteristics through animations of different trajectories for end-effector on uneven terrain.