Modares Mechanical Engineering
Year:2019 | Volume:19 | Issue:5 |Papers Count:28

Aeroacoustics is one of the key issues in the design of high-speed modern devices such as giant aircraft and high-speed trains. In this regard, it is tried to design these devices in such a way to have at least aerodynamic noise. The cylinder, as a bluff body, is widely used in the design of various devices, such as a landing gear. Therefore, the reduction of cylinder noise can be widely used. In the present study, numerical solution is used to present a method for reducing the noise generated by flow on the cylinder. This is done by flow suction from the grooves on the cylinder. Acoustic numerical calculations were performed, using LightHill’ s acoustic analog approach in the form of wave equations of Ffowcs-Williams & Hawkings model. The numerical solution is performed in the three-dimensional unsteady form, using the large eddy simulation turbulence model. The characteristics of the grooves, such as their dimensions and distance on the generated acoustic noise have been studied. The results show that the active control method presented in this paper is an effective and yet simple way to control noise. The cylinder used in the present study produces a noise of about 110 dB at a speed of 250 km/h. According to the results, it can be said that by optimally arranging the number of slots and creating a proper flow suction, its sound level can be reduced to about 60 dB.

Applying numerical methods for predicting cake formation and development in cross-flow membrane filtration has been an area of research. The solutions, which are mainly based on the development of zero, one, or two-dimensional methods for estimating filtration parameters, have always suffered from an obvious need for some calibration steps. In this paper, an independent two-way solving method is presented to determine the time variation of the geometry of the cross-flow filtration cake, so that by simultaneously solving the flow through the lattice Boltzmann (LB), it is possible to solve the convection-diffusion equation, using another mesoscopic method (LB-CA) in a two way coupling manner between flow changes and cake growth. Applying LB-CA provides it for all kinds of internal and external forces effects on particles trajectories to be explicitly taken into account. The proposed model was validated against both of theory of Romero and Davis and some experimental results. Moreover, the model was used to determine external effects which are arisen from static imposition of a DC electric field, on cross-flow filtration outcomes. The calculated results exhibits considerable improvements in flux decline curve and removing of fouling in some areas along the membrane length, as DC voltage rises. Also, optimal conditions with considering the electric poles’ size as an optimization parameter shows that with considering the maximum improvement in the flux curve as the target parameter, the electric poles’ size has an optimal value.

Fuel-air mixing is one of the challenging issues in supersonic velocities that is mostly used in scramjet engine combustors. Sufficient mixing between the supersonic airstream and the fuel jet is critical for designing of scramjet engines, and this is due to the very short residence timescale for the mixture in supersonic flows. Various studies and investigations have been conducted on enhancing the fuel-air mixture. One way to improve fuel-air mixture is to employ step before the injection point, so a low-speed recirculation zone is created before the injection point and causes to improve fuel-air mixture. Employing step causes to increase stagnation pressure loss and we should compromise between mixing efficiency and stagnation pressure loss. In this paper, the effects of step on Gaseous sonic transverse injection in supersonic crossflow are investigated numerically. Two-dimensional Reynolds Averaged Navier-Stokes equations and k-ω sst turbulence model and the perfect gas equation have been solved, using Fluent software. The results of the numerical solution are compared and validated with available experimental data. Numerical results showed good agreement with the experimental values. Then, the effects of varying step heights and distance of step from injection point on Mach disc height and stagnation pressure loss are considered numerically.

Because of the fact that cable-driven parallel robot possess limited moment resisting/ exerting capabilities and relatively small orientation workspaces, in this paper, a method for determination of optimal configuration of reconfigurable cable-driven parallel robots is presented to improve their performance. In such robots, actuators can move the cable attachment points on the base with respect to the motion of the end-effector in its trajectory. In the determined configuration, any external wrench on the end-effector can be balanced, using cable forces for all poses near to a pose of the robot. The largest wrench-closure circular zone centered at an arbitrary point of a trajectory for a given range of orientation around a reference orientation of the end-effector is computed. Taking the area of such zone into account and with the aim of enlarging them, the optimal configuration of the robot is determined. The optimal configuration is found by appropriately changing the position of the moving attachment points on the base of the robots. By applying this procedure on a number of points on a given trajectory iteratively, proper actuation schemes are obtained. In this paper, this method is utilized for reconfigurable planar cable-driven parallel robots and the quality of their actuation schemes is compared with the robots with fixed cable attachment points on base.

The combustion system used by the Hoffman furnaces for brick factories has a very low efficiency. In the current paper, the performance of the combustion system of Hoffman furnaces of Kolet Pottery Brick Co has improved, using computational fluid dynamics (CFD) by making changes to the Hoffman furnace torch, including the converging the torch head, inserting the spring in the pipe to create the swirl flow, shortening the nozzle length for the better mixing of the fuel and air, and more. The changes were simulated in each step with the FLUENT simulation software. Based on the theoretical results and simulation, optimized torch was made and a field test was carried out on it in a brick factory and the gases from their combustion were analyzed. As a result of these reforms, the combustion efficiency of the Hoffman furnaces has increased from 27% to 47 %, and consumption of fuel oil has decreased by a third. Also, the CO value of 16854 ppm in the old torch was reduced to 298 ppm in the optimized torch and the NO value ranged from 49 to 18 ppm as a result of optimizations.

Prior to entering to the throttling valve of the City Gate Stations (CGS), high-pressure natural gas flow in pipelines is transmitted through Water Bath Indirect Heaters (WBIH), which is increasing its temperature to compensate for the temperature drop caused by the Joule-Thomson effect and preventing the occurrence of the hydration phenomenon, gas freezing, and subsequent blockage of the gas flow path. Because of feeding of processed gas of the network on a large scale, optimizing the WBIHs has a lot of significance. In the present study, each WBIH is simulated by a type of thermodynamic machine, consisting of two distinct thermal systems. According to the problem geometry and governing equations, the thermodynamic analysis of these two systems results in the formulation of a relationship between their thermal efficiencies together and the definition of a parameter was defined as the Thermodynamic Similarity Coefficient (TSC). Then, the results showed that always, a constant logarithmic relationship exists between of the Number of Heat Transfer Units (NTU) values difference of the fire tube and heat coil of the WBIHs with their TSC as well as a constant power relationship between their NTU values ratio with this coefficient too. Finally, by solving the equation system obtained from these two relations, it was possible to determine the optimal values of NTU for the fire tube and heat coil as functions of TSC of the WBIH and to achieve the relationship between their optimum geometric dimensions together in the most ideal heat transfer state with a maximum relative error of about 13%.

An airfoil that is heaving and pitching simultaneously may extract energy from an oncoming flow, acting as a turbine. The extracting energy from a flow is possible if the effective parameter in performance of turbine is selected properly. In this study, the theoretical performance of an oscillating twin-wing wind generator is investigated through unsteady two-dimensional laminar-flow simulations, using the commercial computational fluid dynamics code FLUENT. Computations By examining various geometric, motor, and slippery parameters and investigating the effect of each of these parameters, we present a mapping of power-extraction efficiency in the frequency and pitching amplitude domain for a NACA 0015 airfoil at a Reynolds number of 41000. Results of a parametric study show that motion-related parameters such as heaving amplitude and frequency have a strong effect on airfoil performances, whereas geometry parameters turn out to play a secondary role. A power extraction efficiency of 49% is reached by twin-wing parallel configuration. This configuration improve the efficiency by around 7% as compared to the single foil configuration.

In this research, taking into account the pressure drop of the streams, a simple and useful method is presented for finding the proper path of hot and cold streams inside shell-tube heat exchangers in the synthesis of heat exchangers networks (HENs). Generally, the HENs synthesis by mathematical programming leads to the problems which are answered by Mixed Integer Non Linear Programming (MINLP) methods. Optimization of such formulations results convergence difficulties due to the existence of both continuous and integer variables. In this study, instead of solving simultaneously integer and continuous variables, the genetic algorithm was used to find optimal HEN structure (integer variables). To find optimal values for continuous variables of the network, by categorizing this type of variables into two groups and using Quasi Linear Programming (QLP) instead of the nonlinear programming model (NLP), the complexity of the NLP model solution is also greatly reduced. The optimal values of continuous and integer variables are obtained with respect to a common objective function that reaches the minimum annual cost of the HEN. The comparison of the proposed method with the references shows that this method has the ability to reduce the cost of pumping flows to about 0. 76%.

Orthopedic implants are one of the most reliable methods for bone injuries treatment. An important issue, which must be considered in the design of orthopedic implants, is that the Young’ s modulus of implants should be near to the host bone to prevent complications such as stress shielding. Porous implants are considered as one of the new and effective methods for this issue and recent technologies such as metal 3D printing made it possible to manufacture different porous structures with various geometries, which could be used to reach the goal. Porous geometries are used to approaching the elastic modulus of implantation with a porous structure to the bone. Mechanical properties of Diamond porous structure have been investigated in this study and an equation for obtaining the modulus of elasticity is presented in terms of the geometric parameters of this structure. Based on the results, the error between finite element analysis and experimental data is between 3. 64% and 18. 51% and it has been shown that the Young’ s modulus obtained from finite element method is more in line with the existing experimental data than the analytical results; by the increase of relative density, the error would be decreased. Furthermore, in the relative density between 0. 06 and 0. 16, the Young’ s modulus of titanium Diamond structure would be the same as bone Young’ s modulus, which is an effective feature in design of orthopedic implants.

In this study, the effect of a cylindrical protuberance on the thrust vector of a supersonic jet was investigated as a new method in thrust vector control. For this purpose, a convergent-divergent nozzle was designed and constructed. This nozzle is such that the Mach number is its nominal output in full expansion conditions 2. The wall of the nozzle is equipped with pressurized holes to measure pressure variations. Also, there is a duct wall in the nozzle wall to apply a protuberance inside the nozzle. Pressure sensors for pressure measurement and also the schlieren system are used to check the outlet flow field. The total pressure of the compartment is constant at all tests and is 5. 7bar. The results of this study show that the depth of penetration of the protuberance in the flow field has a significant effect on the amount of deviation and even the direction of the deviation of the jet stream exited from the convergent-divergent nozzle. The maximum jet outlet flow from the nozzle is 5. 7degrees, which occurred at a rate of H⁄ D* =0. 4. In addition, these results indicate that with the increase in bulge penetration within the nozzle, the nozzle axial thrust has slightly decreased.

An alarm threshold plays an important role in an industrial fault detection system and directly contributes the False Alarm Rate (FAR) and Missed Alarm Rate (MAR). A crucial consideration for designing a threshold is estimating the Probability Density Function (PDF) of both normal and abnormal state based on recorded samples. The existence of measurement error in samples will be the contributors to an inaccurate estimation, following that, the alarm threshold will also be inaccurate. Therefore, grasping and recognizing measurement errors is highly important; in this paper, this problem will be investigated. For this purpose, firstly, a mathematical closedform of statistical parameters will be estimated, and, then, based on error propagation rule, the computation error of estimated parameters will be explored. It is assumed the high limit and low limit values of the measurement error are known or computable. Secondly, an approach is introduced to design a varying alarm threshold adapting to the current value of measurement error computing based on change detection algorithm. The proposed method is confirmed via a Monte Carlo simulation and it is finally applied to an industrial benchmark, Gas Turbine V94. 2, experiencing fouling fault.

In this paper, black powder of the separation from air flow by a helical one-channel dust concentrator have been experimentally studied and the efficiency and pressure drop have been investigated by Computational fluid dynamics (CFD) simulations in different operating conditions. Experimental set-up is a helical one-channel including 29 branches for exporting diluted stream out. It also has two suction devices at the ends of channels in order to provide testing in high inlet flow. Black powder particles with certain particle size distribution have been tested, whose average particle size has been determined 0. 327 μ m by DLS and SEM images processing. CFD simulation of helical one-channel dust concentrator for air-black powder separation has been done with FLUENT software. The Realizable k-ε turbulent model, as an optimal turbulence model in terms of accuracy and speed in simulation, has been used. According to evaluation of the results, the experimental results have been compared and it showed 5. 2% error. To investigate the effect of operating condition, the various air flow rate and solids mass fractions were investigated and the results showed that the simulation efficiency has increased more than 4. 1% by increasing 58% of the inlet volumetric flow rate. The separation efficiency had no change by increasing the solid mass fraction from 7% up to 20%.

Heat transfer phenomenon and location prediction as well as hotspot temperature in disc-type transformer windings have attracted many researches in recent years. The motivation is based on noticeable effects of these issues on transformers endurance, reliability, and functionality. This paper focuses on developing a sufficiently accurate CFD model to carry out paremetric studies and address some guidelines for disc-type transformer windings with zigzag cooling path with a reasonable computional resource demands. The discs composed from copper wires and paper insulators wrapped around them. Accounting for this inhomogeneity by zone distinction in CFD model results in many computational subdomains in very small size, which makes model development and mesh generation difficult and also computational costs, very high. In this paper, using properties definition functions, a method is introduced that accounts for different material properties with no need to resolve solution subdomains. Also temperature dependency of thermo-physical properties such as conductivity, viscousity, and density have been taken care of. Results show that using current method, model development, and also solution time noticeably reduced without any considerable descripancies in numerical results. Furthermore, using Ansys Workbench capabilities for automatic parameters study, i. e. automatic geometry reconstruction and mesh generation, effects of several parameters on transformer cooling condition have been investigated. Finally, some guidelines for such transformers design have been addressed.

One of the new approaches to produce nanoscale metals with ultera fine grains is applying severe plastic deformation on initial sample with coarse grains. In this method, by applying intense strain to the sample in several steps, the size of the grain decreases to a nanoscale, which results in the improvement of the mechanical and physical properties of the metals. One of the most important methods for this purpose is the constrained groove pressing (CGP) method. Due to the need for a small weight of space structures, sheets of aluminum alloys, aluminum7075-T6, and steel 4130 were selected. The mechanical behavior of the sheets was studied experimentally. The simulation of the interaction between the fluid and the structure was performed for a curved fin model with three different alloys and the deformation of the flying rocket was compared. The results show that the size of the aluminum7075-T6 block decreases from 60 microns to 270 nm with increasing the stages of the process, while the yield strength in the fourth pass increases compared to the annealed sample by 38%. The tensile strength increased by 34%, and the length elongation in the fourth passes reduced by 40%. The total deformation in the fin of the aluminum 7075-T6 improved to 99. 9% with the CGP process. However, the amount of deformation in the steel 4130 fin compared to the CGPed aluminum7075-T6 is less than 0. 1% of the total deformation.

Metal injection molding (MIM) is a novel process classified in powder metallurgy. This process can produce complex metallic parts with high rate of production and consists of four stages, including mixing, injection, debinding, and sintering, where the properties of the final part highly depends on the parameters of each of these stages. In this study, the parameters of injection pressure, injection and mold temperature, holding pressure, holding time, injection speed, and cooling time on the density, strength, and hardness of the final MIM compact have been investigated. By the design of experiments and response surface methodology (RSM) method, 50 samples have been injected using different parameters. In order to measure the density, tensile strength, ad hardness of the samples, the debinding and sintering procedures have been done on the injected samples. The results show that the injection pressure, injection temperature, and mold temperature have the highest effect on the strength and density of the final part, respectively, and on the other hand, holding pressure, holding time, and cooling time have a negligible effect. Within the measured properties, density and strength are more affected by the injection parameters compared to hardness. Finally, the optimum injection parameters for samples made of 4605 low alloy steel include injection pressure of 133 bar, injection temperature of 158oC, mold temperature of 60oC, the holding pressure of 70 bar, holding time of 8 second, injection speed of 112 mm/min, and cooling cycle of 17 second.

In the high-pressure gas-turbines, with hot-flowing gas through the stator channels with a high mass-flow rate, even slight variation in the blade geometry will have significant effects on the downstream flow-field. These minor changes can be compared to corrosion rates. The first occurrence of this corrosion is the non-uniformity of flow in the stator-rotor axial distance. This non-uniform flow, due to the complex pattern of vortices, prevents the complete transfer of fluid energy to the rotor and greatly reduces the turbine performance. In this research, a high-pressure turbine is considered to be at high risk of corrosion. The main goal is to predict these variations due to corrosion. Firstly, a 3D numerical analysis of the turbine initial model was conducted to accurately observe the flow field and the results were validated by the existing experimental results. Then, in order to investigate the effects of corrosion on the turbin performance, the blades geometrical changes were applied in stator blade profile and the flow distribution was analyzed. Results show that the highest corrosion risk is at the trailing-edge of the blades. Due to reduction in the stator inlet-outlet area ratio, the axial-velocity is reduced. But simultaneously, with increasing the stator channels outlet area, the mass-flow rate is increased by 7. 31%. Therefore, the turbine undergoes to an off-design condition. The flow pattern will be more complicated in the rotor’ s entrance, and corrosion will develop rapidly due to temperature rise as the flow separates from the rotor blades.

Industrial sector is always recognized as one of the largest energy consumers in each country. Besides the high energy consumption of industrial sector, a significant amount of energy is lost due to inefficient use and old machines. Combined heat and power (CHP) systems have always been considered as an efficient system to reduce energy consumption and increase productivity in the industry. The aim of this paper is techno-economic analysis of application of CHP systems in a few samples of different types of almost high energy consumer industries, considering the different approaches, on which the electrical capacity of the system is designed. In this study, a combination of various parameters such as different types of prime movers (gas turbine or reciprocating engine), different types of fuel (natural gas and diesel fuel), and guaranteed selling of generated electric power (GSGEP) in different industries are considered. Finally, after determining the capacity of the simultaneous production system for the selected factories, some important economic indicators like net present value (NPV), simple payback periods (SPB), and levelized cost of electricity (LCOE) were considered by two coupled software, MATLAB and Excel. The results showed that in all scenarios, the use of reciprocating engine as the prime mover and natural gas as its fuel is the best choice to satisfy the technoeconomical goals.

Piezoelectric bending actuators have been extensively utilized in recent years. Two major modeling methods, lumped and continuous, have been generally proposed in previous researches for these actuators. The lumped method can only express the transverse vibration of one specified point on the actuator. In addition, the effect of higher vibrational modes has been ignored. Hence, continuous dynamic models have been proposed to rectify the mentioned drawbacks. In this method, linear constitutive equations for low voltage applications are usually applied. But, the main challenge in continuous modeling of piezoelectric actuators is the hysteresis nonlinear phenomenon caused by high excitation voltages. In this paper, piezoelectric nonlinear hysteretic constitutive equations have been employed to carry out the continuous dynamic model for two general types of bimorph bending actuators i. e. Series and Parallel. In addition, zero dynamic analysis for nonlinear systems has been applied to clarify the effect of higher vibrational modes on the actuator dynamic behavior based on the location of target point. Experimental results show the maximum error 1. 44 and 1. 2% in the identification of first and second vibrational modes, respectively, and the maximum error 2. 89% in the modeling of actuator nonlinear behavior by two vibrational modes. These results validate the efficiency of the proposed dynamic model to express the actuator nonlinear behavior, dynamic analysis, and its superiority over conventional models with one vibrational mode.

In the present paper, a new penalization method is proposed for implementation of the rigid surfaces on the Navier-Stokes equations in the vorticity-stream function formulation. In this method, a rigid body is considered as a region in the fluid flow, where the time is stopped. Therefore, by stopping the fluid particles, this region plays the role of a rigid body. In this regard, a new transformation is introduced and applied to the governing equations and a set of modified equations are obtained. Then, in the modified equations, the time dilation of the solid region is approached to infinity, while the time dilation of the fluid region remains unit. In the article, the physical and mathematical properties of modified equations are investigated and satisfaction of the no-slip and no-penetration conditions are justified. Then, a suitable numerical algorithm is presented for solving the modified equations. In the proposed algorithm, the modified vorticity equation is time integrated via the Crank– Nicolson method, and the spatial discretization is performed with the second-order finite differencing on a uniform Cartesian grid. The method is applied to the fluid flow around a square obstacle placed in a channel, the sudden flow perpendicular to a thin flat plate, and the flow around a circular cylinder. The results show that the no-slip and no-penetration conditions are satisfied accurately, while the flow fields are also solenoidal high level of accuracy.

Penetration into ceramic-aluminum targets is of prime importance for researchers in defense and non-defense industries. In this study, the effect of a blunt projectile having a specified speed and penetrating into a ceramic-aluminum target at angles of 0, 15, 30, and 45 degrees is investigated. In this research, 8 experiments were carried out at Ballistic Laboratory of Imam Hossein University and the design of the experiments was carried out in such a way that the facilities of the laboratory could be used. The results of the study showed that by increasing the angle of obliquity, penetration depth is decreased substantially in ceramic-aluminum target, and when the angle of obliquity is increased beyond a certain limit, projectile will ricochet. Also, in this study, numerical investigation was performed, using Autodyne software. In this numerical simulation, the impact of the blunt projectile at 700 m/s on ceramic-aluminum target was carried out to determine the penetration depth into the given target. The blunt projectile penetration was simulated with oblique ceramic silicon carbide plates supplemented with aluminum 2024-T3 and the residual velocity and mass values of the projectile were determined at the exit of the combined target. The projectile was assumed to be rigid and the Johnson– Holmquist structural model was used to describe ceramic behavior and Johnson-Cook material model was used for projectile and target. The results of the experiments and numerical simulation were compared and there was a good agreement between these two modes of investigations, indicating the validity and accuracy of simulation assumptions.

This paper investigates a kind of KNTU1 non-diaphragm shock tube equipped with an innovative design valve within a driven tube. The shock tube is capable of generating a flat shock wave in its driven tube with a length to diameter ratio of 41/6. The KNTU1 shock tube is diaphragm-type and some limitations of this kind of shock tube such as the lack of repeatability without disassembling, the inability to adjust pressure ratio at a specified interval, and the inability to automate the shock tube caused a development on an automated shock tube. In this study, an innovative mechanism to achieve high-speed opening valve with an opening time of 8ms and 10ms is proposed. The unique feature of this automatic valve, compared with existing valves, is its opening from the center to the sides, such as the camera aperture. This is the best way to open the valve and smooth the wave and compensates for a part of the opening time of the valve. Also, the alignment of the driver and the drain prevents disturbances caused by the redirection or rotation of the gas seen in most valves. These help optimize the shock tube. Another initiative in this paper is the design and construction of an optical system to measure the speed and the moment of shock wave arrival to check the shape surface of the shock wave. This system has the ability to move in driven. This paper has been compiled to compare theoretical and experimental data of shock wave.

In two-dimensional measurements using hot wire anemometer, the sensitivity of the sensor to change the flow direction (sensitivity of direction or angular response of sensor) is of particular importance. Sensitivity of direction of sensor, relation between flow velocity vector and heat transfer from the hot wire sensor is determined, using the Yaw sensitivity function and its coefficient. In some cases, negative values of Yaw sensitivity coefficient k^2 are encountered, for which no specific reason has been presented. In this paper, reason of negative values of k^2 for un-plated sensors of hot wire anemometer in two-dimensional measurements have been investigated experimentally. For this purpose, flow velocity field between the prongs of a model of a normal probe (SN) at different velocities and Yaw angles have been studied. Results show that the probe’ s prongs produce flow disturbances, which cause a reduction in flow velocity and the deviation (rotation) of the flow adjacent to the prongs and the sensor. At different Yaw angles, the maximum reduction in flow velocity amounts to 3% and the deviation of flow direction has a maximum of 6. 3° . It is supposed that this phenomenon affects the amount of heat transfer from the sensor and the effective velocity obtained by the hot wire anemometer, which eventually produces the reported negative k2 values.

In this paper, an improved, real-time, highly accurate control-oriented style, named Neuro Mean Value Modeling, is presented for IC engine modeling. This model is a combination of neural networks and mean value model, and is able to overcome the shortcomings of both styles. In other words, taking advantage of both methods, this grey-box extension will be of more reliability than a mere black-box neural network, and also of more accuracy than roughly white-box mathematical relations of mean value model. In this paper, the model is modified to become suitable for designing an engine controller. Thanks to the sophisticated methods applied (such as committee method, improved partitioning, and especially, simplifying neural networks’ tasks), neural networks of high accuracy with line-like regressions will be achieved. As will be seen, the model is precisely validated based on experimental-software data and it is capable of accurately predicting the engine’ s outputs (such as pollutant emissions, manifold pressure, knock probability, and engine speed) all in real time. In the end, the effect of engine control inputs on pollutant emissions and fuel consumption will be examined. The engine employed to establish the model is a ported fuel injection SI engine.

In this study, the performance of a ducted wind turbine is compared with a bare one using wind tunnel results. Ducted turbines are a type of small wind turbines, which consist of a diffuser surrounding the rotor. The duct makes more air flow in rotor plain and as a result augments power production. The blade was fabricated, using resin polyester armed by glass fiber. Duct is formed by sheet metal rolling in slope to have an acceptable appearance. According to BEM design, predicted power for the bare turbine is 300W in wind velocity 10 m/s considering 20% loss due to bearing resistant, rotor inertia, and generator efficiency. Wind tunnel investigation revealed 165W power experimentally for bare wind turbine. The evaluation of the system in the wind tunnel showed that the power augmentation of the ducted system compared to the bare one was 37% higher on average. The maximum power augmentation of the ducted turbine was 286W. The rotor speed of ducted turbine was 61% more than the bare turbine, which increased the speed of the tip of the blade.

The aim of this paper is identifying the parameters of parametric Spencer model for a doubleended magnetorheological damper with different sizes of iron-carbonyl powders suspended in magnetorheological fluid. There is not any published work in literature about identification of parameters of Spencer model for spherical iron particles with different particle diameters in magnetorheological fluids. Hence, in present work, at first, two different magnetorheological fluids with different diameters of iron particle and same volume percentage are prepared. Then, using a double-ended magnetorheological damper, dynamic displacement tests with harmonic excitation in different frequencies and using different electric currents are conducted. The parametric Spencer model is selected for modeling the damper and identifying its parameters. 10 parameters of this model are identified, using nonlinear least square solver and implementing Sequential Quadratic Programming method for damper, using two different magnetorheological fluids in different frequencies and different electric currents. The appropriate polynomials are extracted for identified parameters that have systematic trends with increasing electric current. With generating theoretical and experimental hysteresis curves in different electric currents, excitation frequencies and different fluids, it is tried to assess the capability of Spencer model in regenerating the experimental counterparts. The comparisons of the hysteresis curves obtained from Spencer model with identified parameters by the experimentally achieved counterparts show that this model has adequate compatibility with experiments in predicting force-velocity hysteresis curves. However, the implemented model has not enough success in predicting the force-displacement hysteresis curves, especially in sharp ends of the curves and force delaying regions.