JOURNAL OF SOLID AND FLUID MECHANICS
Year:2019 | Volume:9 | Issue:3|Papers Count:20

Electro-magnetic engine mounts are among active mounts which considered in the recent years. Vibration analysis is one of important techniques in fault detection and condition monitoring. Due to this fact, in this study with application of dynamic responses and frequencies responses diagram, significant results in fault detection in electro-magnetic active engine mount system, it's life-time increase, and repairing cost decline, will obtain. In order to achieve these purposes, after introduction of the engine mount structure and system modeling, different faults especially those caused by thermal and corrosion interactions have been introduced. Finally, qualitative and quantitative states of both separate and combined fault diagnosis systems will be presented. According to these tables, six separate faults and three combined ones will identified.

Traumatic brain injury states to the brain damage causing from sudden trauma. Undrestanding the mechanism and effects of such damages to the brain is of importance toward the treatment. In this research, a computational framework for considering the response of a neuronal cell is presented. The neuronal cell consists of three components including nucleus, cytoplasm, and membrane, and also the network of microtubules with the different arrays including crossing, stellate as well as random. In the simulation of blast loads, the pressure load driven by laser-induced and finite elements setup with fluid-structure interactions are considered. Cell components are assumed to follow viscoelastic and elastic mechanical behavior. The obtained results as compared to those of the experimental works showed different levels of cell damage. The presence of the microtubles network in cytoplasm, regardless of the types of array, reduces the total displacement of the cell and the von Mises stress in the other cell components. Furthermore, the network of microtubules plays a significant role in the total strength of the cell under the external imposed pressure. The membrane von Mises stress decrease 50 percent from 30 to 165 Pascals in presence of the network of microtubules.

Kinematic and Kinetic Modeling of a 3PRS mechanism is performed in this paper and its related controller is designed according to Computed Torque Method (CTM). This mechanism is a kind of spatial parallel robot with 6 DOFs, which is controlled using three active prismatic joints and three passive revolute joints and thus the system is categorized as constrained mechanism. Kinematic modeling of the robot is performed using Homogenous transformation matrix and its related Jacobian matrix is exracted. Therefore the position and velocity relation between the joint space and workspace are provided both in its direct and inverse modes. Dynamic equation of the system is also derived using Lagrange equation in the joint space of the robot. Thus both of forward and inverse kinetic of the system are solved for the presented system. Finally, by the aid of the extracted dynamic equation, the robot is controlled using Computed Torque Method (CTM). All of the modeling are verified by simulating the equations in MATLAB and comparing the direct and inverse modes. It is shown that using the extracted modeling and the designed controller for this parallel robot, the desired path can be easily tracked within the workspace of the robot.

Due to the ability of the spot-welding process to create a quality connection between metal plates, especially those with very different mechanical properties, this process has been taken into consideration in recent years. In this method, when two metallic plates welded together under high applied pressure, an atomic bonding is created at the surface of the plates. A single stage compressed gas gun impact test facility was used for carrying out Impact Spot Welding tests. In this study the steel plate with a thickness of 4 mm was considered as a base plate and copper, brass, and aluminum plates were used as front layers and they are under direct contact with flat-and conical-nosed metallic projectiles within the velocity ranging from 100 to 150 m/s. In order to investigate the effect of various parameters in this process, different combination of bilayer metals with 0. 1, 0. 2 and 0. 5 mm gaps were used. The welded interface was studied by Scanning Electron Microscopy (SEM). The results of this study showed that in the collision zone, especially in the central areas a complete bonding has occurred.

This paper is concerned with the problem of designing fractional-order time-delay systems with closedloop eigenvalues in a prescribed region of stability. The main idea is to convert the fractional-order systems with time-delays into an equivalent fractional-order systems without delays. At the first, we compute a state feedback matrix which assigns all the eigenvalues to zero, then by using the method based on similarity transformation and assign the eigenvalues to fractional-order systems without delays compute state feedback matrix in a sector of the complex plane. This method is achieved by implementing properties of vector companion forms. The proposed algorithm can be used for the placement of closedloop eigenvalues in a specified sector in plane and can be employed for fractional-order linear systems with large-scale. Also, the considerations can be easily extended for two-dimensional (2D) and descriptor fractional-order systems. Also, simulation results are presented to demonstrate the effectiveness of the proposed method.

The objective of this paper is an experimental investigation and numerical modelling of large plastic deformation of metallic-polymeric bilayer plates under gas mixture detonation load. For this, gas detonation forming apparatus was used in the experimental section to perform 40 experiments under various experimental conditions. The experimental results include the effect of impulse value, thickness of the metal plate and polymeric coating and areal density on the maximum permanent transverse deflection of bilayer plates. In the modelling section, multi-objective optimal design of training data and evaluation the prediction capability of the obtained model has been achieved by adaptive neuro-fuzzy inference system (ANFIS) and genetic algorithm. In proceeding of multi-objective optimization procedure from the aspect of two objective functions, a set of optimum non-dominated points, namely, Pareto front was constructed considering as designing points. The application of the genetic algorithm is the optimum design of Gaussian membership function parameters in preceding and least square method for calculation of linear coefficient vectors in the consequent part of the neuro-fuzzy structure. The evaluation of the accuracy of the proposed model has been investigated by comparing the experimental results with modeling data sets using the coefficient of determination (R2) and root-mean-square error for training and prediction data sets.

In order to improve the properties of aluminum and its alloys, various solutions have been considered. In this regard, the use of solid-state processes such as FSP to create surface composite is very suitable. Hence, considering the FSP ability as a thermo-mechanical process and its advantages in the production of surface composite, in the present study, the Al7075 surface composites with the use of reinforcing particles (Al2O3) were produced in accordance with the DOE principles. To this end, the RSM was selected as the experiment design technique. So, the factors such as: tool rotational speed, tool feed rate, tool shoulder diameter, and reinforcing particle size were identified as the input variables. Then, statistical analysis of variables affecting the mechanical properties of surface composite Al7075/Al2O3 was performed. The obtained results from ANOVA and regression analysis of experimental data, confirmed the accuracy of regression equations. Furthermore, it is shown that the linear, interactional and quadratic terms of the input variables are effective on the yield strength and hardness of the composite samples. Also, the tool feed rate and the reinforcing particle size were introduced as the most effective linear factors on the yield strength and hardness of the composite components, respectively.

In this paper, an analytical solution for the asymmetric temperature distribution in a long orthotropic cylinder, considering Cattaneo theory, is presented. The temperature distribution, due to the nonaxisymmetric initial condition, is obtained by using the separation of variable method. In order to verify analytical results, the governing equations are solved numerically using finite difference method. In presented results, the effect of the motion of heat wave from the external face to the center of the cylinder, simultaneously moving the other wave from the center to the external surface, as well as their interference on the temperature distribution is studied. Additionally, the effect of fiber angle on the temperature distribution in both radial and circumferential directions is investigated. Furthermore, the temperature distribution in terms of time is investigated. The results show that the temperature distribution in terms of time at one point has a periodic behavior. The time history of the non-Fourier temperature, which has a wavy form in contrast to the Fourier one, is presented. According to the results, the non-Fourier temperature distribution does not converge to the Fourier one before reaching to the steady state. Also, the temperature distribution at different times in radial and circumferential directions has been investigated.

This paper presents a comprehensive process of designing series elastic actuators to be used in active joints of assistive exoskeleton robots. In this process, the stiffness parameter of torsional spring is selected based on two main criteria to satisfy all the requirements of human motions. The first criterion is an appropriate frequency response for the actuator, according to human motion needs. The second criterion is to provide a sufficient protection of actuator hardware against collision and impact. By determining the desired value for the stiffness parameter, spring architecture is designed to have sufficient mechanical strength and provide the desired stiffness in practice while occupying a minimum space. Along with motor and gearbox, the designed spring is assembled to be used in active joints of exoskeleton robots. The considerations in the optimization of the spring has led to a very compact series elastic actuator which can be used in different human motions such as stair ascend and descend, sit to stand and walking.

In this paper, the dynamic response of electro actuated viscoelastic microbeam is investigated and micropolar theory of elasticity has been used to consider the effects of size in microstructure. Euler-Bernoulli beam theory and Hamilton’ s principle with considering viscoelastic integral constitutive equations, the midplane stretching effect, the axial residual stress and electrostatic force has been used to obtain the equation of motion and the boundary condition of fixed-fixed viscoelastic microbeam. Therefore, the nonlinear integro-differential equation in Volterra integral equation form is obtained. Galerkin method will be used, in order to solve the nonlinear partial integro-differential governing equation and then it converted to the ordinary integro-differential equation. By using the fourth order Runge-Kutta method, we can obtain the response (transverse displacement) of the electro actuated viscoelastic microbeam. In the following, the effect of initial gap value and material length scale parameter on the viscoelastic microbeam behavior are investigated. In the end, the viscoelastic microbeam is simulated in the FE software and the problem is analyzed in quasi-static form. In order to validate, the simulation result is compared with the result obtained from the quasi-static solution of the viscoelastic microbeam.

The objective of the current study is to investigate the application of smart Magneto/Electro-Rheological (MR/ER) elastomers in vibration suppression and extending the stability region of the rotors system. The rotor is modeled via finite element method based on the Rayleigh beam theory. Proposed model takes the rotary inertia, gyroscopic effects and internal damping of the shaft into account. The stiffness and damping of the elastomers are considered as functions of the applied electric or magnetic fields. The simulation results reveal that the use of MR/ER elastomer leads to down shifting of the critical speeds and a reduction in its corresponding vibration amplitude. Also, the stability limit speed of the system is improved. Simulation results revealed that MR elastomer supports are superior on ER elastomer supports in the vibration suppression and extending the stability region of the rotor system. Finally, to improve the stability of the rotor system to higher operating rotational speeds, an on-off control strategy is employed. The proposed novel idea can be effectively utilized for optimization of the vibration level and widening the stability regions of rotating systems.

In recent years, increase of speed and reduce of weight of railway vehicles is under focus of transportation industries and train factories. This subject may increase the instability and overturning of these vehicles, under blowing crosswind. In this study, numerical simulation of crosswind induced air flow around an ICE2 train model, is performed with aid of computational fluid dynamic methods to obtain effective aerodynamic coefficients. According to the simulations the equilibrium of train is determined under crosswind in various incident angle and train velocity. Then, five geometrical parameters are considered and basic geometry is modified to generate eight new geometries. By comparing aerodynamic results of these 9 nose shapes, influence of each parameter is reported on the overturn of train. Investigations show from considered geometrical parameters, that thickness reduction of train nose and increase length of train nose or angle reduction of train nose tip have more favorable effect on safety of train movement to prevent of overturn.

Aerospoke nozzle is one kind of the converging-diverging nozzle that are more effective than of the Bell nozzle. The aerospike nozzle have high efficiency in the all Number of Pressure Ratio (NPR). Also, the usability as a vector thrust is the other benefits of the aerospike nozzle. The disadvantage of the aerospike nozzle it’ s heavier than as the Bell nozzle and the aerospike nozzle requires cooling system. There are afew studies about the aerospike nozzles and the use of this type of nozzles requires more experimental and theoretical studies. In this study reported the results of numerical simulation an axisymmetric aerospike nozzle. In This study used a structure grid and the K-ε turbulence model. The effected of NPR was investigated and the NPR varied between 2 to 50. The results show linear relation between NPR and nozzle mass flow rate. In the last part of this study the effected of the spike length was studied. The four defferent spikes was modeled by 20, 40, 60 and 80 percent length of the first spike length in 10 NPR and results show the cutting more than 40 percent length of the spike effect in flow quality.

This article contains a numerical simulation of polygonal hydraulic jump using the volume-of-fluid (VOF) method. This phenomenon occurs when a circular jet of a high viscous liquid impinges perpendicularly onto a flat surface. In fact, when a liquid jet hits a surface, a circular hydraulic jump appears around the stagnation point. In a fluid with low viscosity (such as water), the shape of this jump is circular and in a high viscosity fluid (e. g., ethylene glycol), a polygonal structure forms. This structure is due to the presence of mechanical waves around the collision area, which is considered in the numerical method. In this paper, the results of the numerical model are validated with available experimental studies for the shape and structure of the generated hydraulic jump and its radius. Finally, based on numerical results, it is observed that a circular hydraulic jump spreads at the beginning, and after its corresponding wave collides with downstream obstacles, a polygonal shape is gradually formed and stabilized. In addition, the streamlines show that the existing of high-speed flows in some points of the solution domain generates corners in the jump shape leading to the formation of a polygonal hydraulic jump.

The Munk moment may make the vessel unstable in simultaneous Surge and Sway motions. In this paper the munk moment was calculated by computational fluid dynamics (CFD) and finite volume method (FVM) for an autonomous submarine. Furthermore the added mass coefficients were calculated for computation of munk moment using analytical formulation in potential flow. The damping coefficients were also calculated. The unstedy state numerical simulation of real flow for surge and sway motions has been performed. The turbulent effects were considered by using k− ω sst turbulence model. Using Planar Motion Mechanism (PMM) in pure sway situation, the forces and moments were calculated. The overset mesh was used for grid generation in computational domain. The mesh independency has been also prerformed. Using sixth order polynomial interpolation for forces and moments of numerical simulation, the hydrodynamic coefficients were calculated. The results showed good agreement with experimental data. Finally, the munk moment of numerical simulation and analytical formulation have been compared. Furthormore N ̇ was calculated based on potential theory and also compared with numerical and experimental ones.

Nowadays, simulation of viscoelastic flows at high Weissenberg numbers is one of the most obstacles and important issues for rheologists to observe the rheological properties at sufficiently high weissenberg number. It is well known that the conformation tensor should, in principle, remain symmetric positive definite (SPD) as it evolves in time. In fact, this property is crucial for the well-posedness of its evolution equation. In practice, this property is violated in many numerical simulations. Most likely, this is caused by the accumulation of spatial discretization errors that arise from numerical integration of the governing equations. In this research, we apply a mathematical transformation, the so-called hyperbolic tangent, on the conformation tensor to bound the eigenvalues and prevent the generation of negative spurious eigenvalues during simulations. The flow of FENE-P fluid through a 2D channel is selected as the test case. Discrete solutions are obtained by spectral/hp element methods which based on the high orders polynomials and have high accuracy for physical instability problems. This enhanced formulation, hyperbolic tangent, prevails the previous numerical failure by bounding the magnitude of eigenvalues in a manner that positive definite is always satisfied. Under this new transformation, the maximum accessible Weissenberg number increases 100% comparing the classical constitutive equation (FENE-P classic).

In this paper, an integrated control system of longitudinal, lateral and yaw vehicle dynamics is presented using active braking and active front steering (AFS) systems. The proposed active braking system based on sliding mode controller, includes two kinds of working modes of anti-locked brake and (ABS) and an electronic stability control (ESC) and a fuzzy controller has been used in the AFS system. Also, a nonlinear estimator utilising unscented Kalman filter is applied to estimate the vehicle dynamics variables. According to the estimated values and Dugoff tire model, the tire-road friction coefficient is calculated. An adaptive neuro-fuzzy inference system (ANFIS) is proposed to obtain optimum wheel slip ratio. In the simulation part, first, the hard braking action in straight line on the roads with various friction coefficients is investigated, which results in high precision of the estimator for the friction coefficient and optimum wheel slip ratio, and greatly reduced the distance and stopping time in comparison to the vehicle without estimator. Then, simulation of split-μ roads has been carried out which demonstrates the integrated control of ABS, ESC and AFS systems can, in addition to improving the lateral and yaw stability, also decrease the stopping distance.

In this work, it is focused on the configurations of Gas Diffusion Layers and their influences on the performance of Polymer Electrolyte Membrane Fuel Cell. At first, effect of prominent GDLs is studied. For this purpose, radius (R) of prominences is grown gradually. The optimal performance is obtained in the R=0. 45. In addition, the inlet velocity of gas flow is surveyed. The results indicates that when the inlet velocity of gases is set about 0. 2 m/s, the species diffusion is optimized. Also, the height of channels is investigated to find out the optimal channel height. It is found that the higher performance is achieved in channel height about h=1mm and R=0. 45mm. The number of prominences on GDLs is investigated as the last parameter. The results demonstrates that by rising the number of prominences, output current density is grown. To validating numerical results, a set of experimental tests is carried out, which is seen favorable accordance between them. Moreover, the results of base model, has been compared with the result of published papers.

The flow behavior over a diamond wing was experimentally investigated in a smoke tunnel, using laser sheet technique. The effects of Leading Edge Extension (LEX) were also studied. The experiments were conducted at the velocity of 2. 5 (m/s) and the angles of attack of 5 to 45 degrees. The results showed that a vortex structure was formed above the wing surface. Increasing the angle of attack increased the size and strength of the vortices and the height of the vortex core to the wing surface as well. At a specific angle of attack the structure of the vortices was changed rapidly and the vortex break down was occurred. The location of vortex break down moved toward the wing apex by increasing the angle of attack. The LEX caused formation of another vortex above the wing surface which was merged with the main wing vortex and formed a stronger one. The stronger vortex energized the boundary layer of the wing surface, delayed the flow separation and moved the break down further down-stream. Using LEX also decreased the width of the wake region behind the wing, up to 14% compared to the original wing which can improve the aerodynamic performance of the control surfaces behind the wing.

In this paper, DPD method is used to simulate the polymer chain in a micrometers channel with respect to fluid motion using electrosomalic micro pump. In this study, the displacement of a polymeric chain at the two fixed ends in an electro-osmotic flow in a simple microchannel is investigated and the influence of the effective parameters are studied on the displacement of the polymeric chain. In the following, a two fixed ends polymeric chain is placed in the channel and the fluid flow will cause the polymer chain to move reciprocatingly. It has been shown that with the change of electric field from 50 to 150 V / m with 20 beads, the amount of chain movement would be twice, while if the number of beads is added to 40, at electric field of 100 V / m, the displacement rate will be increased approximately 3 times. Also, the effect of the position of the installation has been checked and shown by changing the position of the installation from the vertical coordinates 4 and 4 to 9. 5 and-9. 5, with consideration of the same chain movement, the electric field strength decreased by half, and the amount of oscillation decreases.