JOURNAL OF SOLID AND FLUID MECHANICS
Year:2019 | Volume:9 | Issue:1|Papers Count:20

Forced vibration of a double-beam interconnected by a viscoelastic layer is investigated under two constant acceleration moving loads. These forces are standing for a vehicle rear and front axis loads; hence their values depend on the vehicle acceleration. The Euler-Bernoulli equations and Winkler model are used for the beams and the viscoelastic layer, respectively. With deriving the equations, the modal expansion and modes orthogonality are used to obtain the dynamic response of the beam. Middle point deflections of both beams are presented considering various accelerations, damping ratios and stiffness values of viscoelastic layer. The present work is validated with the results of other authors. It is observed that the damping ratio has not a considerable effect on middle point deflection of the upper beam, whereas it has a significant effect on that of the lower one. Meanwhile, increasing the stiffness leads into decreasing the effect of damping ratio in middle point of the double-beam, decreasing the deflection of the upper beam and increasing that of the lower beam. Increasing the acceleration has not any considerable effects on the general trends. In higher accelerations, increasing the stiffness will decrease the effect of damping ratio with a lower intensity.

Linear particle chain impact damper (LPCID) is a kind of impact dampers that the impact masses are placed in a chain along the straight line. This damper is one of a kind of multi-mass impact damper whose performance is superior to single-mass impact dampers. Researches on the performance of the linear-particle chain impact damper have been numerically and laboratorial conducted so far. In addition, no research has ever been done on the type of mass layout at this demurrage. In this paper, an analytical analysis of the performance of the rigid LPCID in free vibrations of a 1-DOF system is carried out parametrically. In this regard, the effect of parameters such as mass number, mass ratio, distance gap, restitution coefficient and type of mass layout on the damper function have been investigated. In order to investigate the effect of mass layout, two types Impact Damper, three-mass and five-mass, are considered. The layouts are uniform, eight, linear, and diamond. After review, it has been determined that the efficiency of diamond layout is better than other layouts.

In the present article, a numerical procedure is developed for dynamic analysis of residual stress in the process of autofrettage under working pressure. The governing dynamical equations are discretized using finite difference method. Toward This end, differential equations are integrated and by employing divergence theorem surface integrals are converted to boundary integrals. Finally, the C/C++ numerical programming is prepared using the explicit Lagrangian formalism. The effect of transient loading and geometry is investigated in the process of autofrettage on functionally graded cylinders considering elastoplastic stress wave propagation. The residual stress resulting from internal pressure changes structural load bearing capacity of the cylinder. For functionally graded materials whose material properties change continuously, dynamical analysis yield results which are entirely different as compared with their static counterparts due to the change in wave length and acoustic impedance. In the static analysis the dimensionless forms of equations can be developed from the onset, while in the dynamic analysis the physical dimensions gain importance due to inherent properties of the stress waves.

In recent years, laser drilling is used as a new process for micro drilling with high precision, less time and high aspect ratio in various industries, particularly in the aerospace industry. To improve the quality of drilling process, identification of the process parameters and investigation of their influence on the output characteristics are necessary. In present study, laser percussion drilling process was performed on Hastelloy X nickel-based superalloy and the effect of process parameters including laser frequency, pulse width and laser beam keeping time was investigated on the hole geometry characteristics (hole entrance and exit diameter, hole entrance and exit circularity and hole taper). The results indicate that by increasing the laser frequency, hole entrance and exit diameter increases but hole entrance and exit circularity and hole taper decrease. By increasing the pulse width, hole entrance and exit diameter increases but hole entrance and exit circularity decreases. Also, with increasing the pulse width, hole taper decreases. When the laser beam keeping time increases, hole entrance and exit diameter increases but hole entrance and exit circularity and hole taper decrease.

Thin-walled sections absorb impact energy very efficiently that were considered in the studies in different shapes such as square profiles and cylindrical tubes by various methods as axial collapse or oblique loading. These structures are used in a variety of industries, such as aerospace, railways and road transport, especially to reduce road accident injuries in vehicles. To improve the crashworthiness properties of the structures, the peak load of the absorbers that ultimately shocks the occupant is also of importance. In this study, the cylindrical tubes of ultra-light aluminum alloys AA7075 that have a high-energy absorbing property were used for empirical tests. By considering the relationships of plastic hinge formation in thin-walled sections, a new geometry has been proposed that combined the axial and oblique loadings, then the peak load was controlled completely. By changing the end-cap of the tubes to the nozzled shape, after conducting empirical tests and validation of the finite element simulation results, according to analytical relation, the effect of this change was 30% reduction of initial peak load. Also, the effect of the geometry parameters has been studied. In this regard, to control the initial peak load, acceptable results are obtained. By changing the arc height by double and half, the peak load increased by 15% and decreased by 20%, respectively.

In this study, a novel processing technique, namely gas mixture detonation method, was used for large plastic deformation of thin rectangular aluminum plates reinforced by polymeric coating. Based on this new idea, a series of experimental tests were conducted on plastic behavior of metal-elastomer bilayer structures with the aim of increasing the threshold of the impulsive load. In these structures, polyurea coating with different thicknesses of 3 mm and 4 mm was used as a reinforcing layer for aluminum plates. In this series of experiments, the effects of the back and front layer thicknesses on the behavior of the structure subjected to five different impulsive loads have been studied. The experimental results indicated that addition of polymeric coating with thicknesses of 3 mm and 4 mm to the 2 mm thick aluminum sheet led to a decrease in the permanent deflections of structure by 12. 7% and 21. 1% at impulse of 19. 1 N· s, 22. 2% and 30. 9% at impulse of 28. 1 N· s, and eventually, 23. 3% and 31. 3% at impulse of 32. 3 N· s, respectively. For 1 mm thick aluminum sheet, using polymeric coating of 3 and 4 mm led to increase of the threshold of the impulsive load 2. 1 and 2. 4 times, respectively.

The structure of marine vessels is usually being subjected to the dynamic loading conditions of sea-surface waves. The dynamics and vibrational characteristics of such structures is expected to be affected by sea environmental loadings. In this paper, a rectangular plate, that was immersed with water at different immersion depths and different boundary conditions was numerically analyzed by the Abaqus software, and the results have been presented and discussed in details. For validation the numerical method, the effects of immersion depth on the natural frequency of circular plate, which is parallel to the free surface of water, have been investigated experimentally and numerically. By evaluating 81 extracted vibrational modes, it became clear that a natural drop in natural frequencies begins with a rise in the fluid's height from a specific position, which is directly related to the type of boundary conditions. In the modal analysis of structures, it can be admitted that the major decreasing frequency due to increased mass is caused by one-way contact of the fluid and the structure and then, if the other side of the structure is in contact with the fluid, it will have a very small effect on the natural frequency reduction, which is clearly apparent in this study.

In this study, stress analysis of circular plate with variable thickness with clamped and simply-supported edge are presented. In the most previous research on the variable thickness plates, midplane symmetric plates were analyzed but as a first time in this study, by using two independent functions for top and bottom surfaces, transverse asymmetric plates can be analyzed. By using the combination of first order shear deformation plate theory and 3D elasticity method the shear and normal stress components such as transverse shear and normal stresses are extracted. For examination of the accuracy of the obtained results based on the presented analysis, the obtained results are compared with those obtained by 3D elasticity of ABAQUS software based on the finite element method. The comparisons show that the presented solution has very good accuracy and presented procedure for stress analysis of circular plates are very effective. Based on the presented procedure in this is study, 3D figures of stresses in the radial and thickness directions can be easily extracted and the stress components can be investigated more effectively.

In this paper, a new method is presented for removing the noise from the vibration signals of the rotating machinery based on the empirical wavelet transform (EWT) and the soft thresholding function. The EWT is a new signal processing method that decomposes each signal into its constituent components based on its frequency information. After decomposing each signal, the soft thresholding method is performed to empirical modes and the denoised signal is reconstructed. For evaluating the proposed denoising approach, this technique is used for detecting the bearing fault. For this purpose, the kurtosis factor and the envelope spectrum of each denoised signal are calculated for detecting the presence of fault and diagnosing the fault type, respectively. The results illustrate that the proposed technique increases the quality of the vibration signals so that the obtained kurtosis value is more sensitive to the presence of fault in the inner ring and the outer ring. On the other hand, the type of fault is diagnosed by observing the appeared frequencies in the envelope spectrum of signals denoised with EWT. The results show that the EWT-based denoising approach is superior to the empirical mode decomposition-based denoising method in the rotating machinery fault diagnosis procedure.

Compared to the resistance spot welding (RSW) process, Friction stir spot welding (FSSW) is an ideal process for aluminum alloys. In this study, the effect of welding parameter such as tool penetration depth, tool rotational speed, tool penetration speed and the arrangement of aluminum alloy sheets of 7075-T6 and 2024-T3 on the shear strength of the joining zone in the friction stir spot welding process have been investigated. By properly choosing these parameters, the optimum shear strength of the joint can be attainable. The result of the shear test showed that the increase of tool rotational speed from 800 up to 1250 rpm caused the increase of shear force, However further increase up to at 1600 and 2000 rpm resulted in the decrease of the shear force. By increasing in tool penetration depth, shear force increases. If the alloy Al2024-T3 is selected to be the upper plate, the connection will have better shear strength.

The flow quality inside a supersonic axisymmetric mixed compression air intake designed for the freestream Mach number of 2. 0 has been investigated experimentally and numerically in this study. The numerical study was used to analyze the shock configurations inside the intake. The flow in a supersonic intake is always irreversible due to the shock waves and boundary layers. A useful tool for studying flow quality entering the engine is the investigation of entropy generation due to various factors. In this study, the accuracy of the numerical results is evaluated by the experimental data at first and then the entropy generation inside intake is studied for different back pressures. Results indicated that reduction of the pseudo-shock length results in the significant decrease of entropy generation. Furthermore, role of the pressure fluctuations in the entropy generation was examined and it is observed that pressure fluctuations could have a significant effect on the irreversibility of the flow. According to the results, by increasing the exit blockage ratio from 55% to 62. 5%, the rate of entropy generation will be reduced by 33% due to the reduction of peuso-shock length, reduction in the flow separation at the end of diffuser and reduction of pressure fluctuations.

The practical and prolonged implementation of pulse detonation engines implies the control of temperature in detonation tubes. The nature of the detonation itself, plus the rapid repetition of different processes within the working cycle, are accompanied by variations of speed, temperature and pressure and create a heating environment which is different from conventional engines and difficult to specify and control. In this paper the various processes of the working cycle are studied and a template is proposed for the loading and thermal boundary conditions. In continuation, the analytical and thermal models have been developed based on the described assumptions and the thermal responses have been obtained for sequential loadings. The severe thermal gradients in the tube wall and the short duration of each detonation can cause high sensitivity of the response to solution parameters and affect the solution convergence. The validation and verification of the results have been carried out through comparisons of the analytical and numerical results with the experimental results reported in the literature. The obtained results not only provide the thermal condition for control design, but also give the required data for other related aspects of pulse detonation engine, like thermoelastic and thermal fatigue analyses.

Water softening and preventing of scaling in evaporators are very important in industrial water treatment processes. Lamella clarifiers improve the treatment process and decrease its related costs. In the present study, by using a CFD approach, the flow inside the sedimentation tank equipped with lamella has been studied. By using the Discrete Phase Model (DPM) and due to the two-way coupling between the main phase (fluid) and the discrete phase (particles), the particles motion has been traced. The turbulence model k-ε RNG is used to simulate the flow inside the sedimentation tank. The influence of employing lamella plates and their inclination angle as well as size of particles have been conducted. Results showed that using lamella inside the tank, by tuning the rising velocity of water, turbulent flow energy, and reduction of the rotational area volume, leads to increase of the tank particle removal efficiency by 6. 47 percent. In addition, the presence of lamella causes a stability in the removal efficiency of sedimentation tank at different flow rates. A parametric study with the aim of investigating the effect of different angles of lamella on the tank efficiency shows that changing the angles of the plates from 60 to 45 degrees increases the efficiency by 14. 66 percent.

In the present study, mixing of two fluids of different viscosities in a micromixer with oscillating stirrer was simulated by MRT-LBM and the effect of aspect ratio (AR) of stirrer on mixing efficiency was analyzed. The simulation was performed at Re=50, Sc=10. The results showed, at low values of amplitude (K), at low values of Strouhal number (St), increase of AR causes increase in mixing efficiency and at others, it decreases and then increases. At intermediate values of K, at low and intermediate St, mixing efficiency decreases with the increase of AR and at high values of St, it first decreases and then increases. At high values of K, at low and high St, increasing AR causes no improvement in mixing efficiency and at intermediate values of St, mixing efficiency decreases and then increases. In this research, the best mixing efficiency for viscosity logarithmic ratio (R) =2 is at AR=0. 7, St=1, K=0. 5. Also results revealed that for two fluids of different viscosities, at very low values of St, mixing efficiency increases with the increase of R and at others decreases considerably. In general, for two fluids of different viscosities, stirrer with low values of AR has better mixing efficiency.

Two-phase flow of oil and air in the journal bearing of Shahid Abbaspour dam power plant is simulated. The problem is considered as unsteady and it is investigated at different times from the generator starts up. The geometry is 3D and the flow is laminar. This geometry consists of several separate sections, including a rotary oil reservoir, a journal bearing, and a steel shaft, where all sections are connected by pipes and the flow is passed through them. Regarding the repetition of the computational domain, a quarter of the geometry is modeled. Due to the complexity of geometry, the geometric model is divided into smaller volumes and is gridded with the structured mesh. The velocity field, pressure distribution and volume fraction are obtained by solving the equations of continuity, and momentum. Two-phase flow is modeled by VOF model. Results are evaluated with the data obtained from the pressure gage of bearing. Results indicate that the oil movement is consistent with the actual physical condition. In order to improve the cooling system of bearing, it is necessary to identify the high-pressure locations of bearing for branching, which it is achieved by calculating and analyzing the distribution of pressure in the bearing.

A 3D model of computational fluid dynamics for an anode solid oxide fuel cell is presented. This model incorporates important transport phenomena in a fuel cell such as heat transfer, mass transfer, electrode kinetics, and potential field. The simulation results of the model were compared with the available laboratory data in the same conditions that shows good agreement with other references. In this model, the effect of different parameters such as temperature, pressure, stoichiometry and electrolyte thickness on the fuel cell performance was investigated. The results of this model clearly describe the distribution of species, including reactants and products, temperature distribution, distribution potential, and distribution of current density. The results showed that the temperature, pressure and stoichiometry of the anode have a great effect on the performance of the cell so that each parameter increases the performance of the fuel cell performance. On the other hand, increasing the thickness of the electrolyte can have a negative effect on the performance of the fuel cell.

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 C-D nozzle was designed and constructed. The nozzle exit Mach number is 2. The wall of the nozzle is equipped with pressure holes to measure pressure variations. Also, there are several holes in the divergence portion of nozzle wall to apply a protuberance inside the nozzle. Pressure sensors for pressure measurement and also the Schliern system are used to check the outlet flow field. The nozzle pressure ratio in all experiments is constant and in two cases is equal to NPR=6. 6 and NPR=9. The protuberance is installed in the nozzle divergence section, at position ⁄ and with a constant penetration ratio of ⁄ . The results of this study show that using the protuberance can control the angle of the thrust vector. Also, installing location ⁄ is the best position which, in this case the angle of the trusted vector reaches 3. 1 degrees. Also, the results reveals that the change in the nozzle pressure ratio in different installing positions has different effects on the thrust vector angle and axial thrust losses.

In recent years trends towards designing axial fan with low aspect ratio have been increased. Application of this kind of blades leads to higher rotor efficiency relative to blade with high aspect ratios. In contrast, applying this kind of blade causes to intensify 3D flows, increasing secondary losses and creating losses due to shock occurrence. In the current study, designing of a two stage axial fan with low aspect ratio is carried out. To obtain losses in the axial fan, appropriate models have been employed for profile loss, secondary loss shock loss and tip clearance loss. For extracting blade’ s profile, polynomial camber and naca 65 thickness distribution have been used. Comparing the obtained results including loss estimation, meridional velocity, pressure and diffusion factor distribution and blade geometrical parameters such as stagger angle, chord length, solidity and camber angle show good agreement. The 3D shape of the blade have been extracted by calculating the stagger angle and thickness distribution in each section.

Viscous fingering instability in porous media is one of the natural processes which is widely used in many different type of problems, such as Enhanced oil recovery process. In this paper nonlinear simulation of viscous fingering instability of miscible reactive interface through homogeneous porous medium is examined. In this case, the fluid produced at the interface can be considered similar to the coastline, so mono and multi fractal analysis can be performed. First the concentration contours are plotted in differnet models of instability, then by using image processing, the fractal dimension of image is computed for both fractal and multifractal cases in different times. It can be seen that the fractal dimension in the instability problems can be one of the important parameters that describes the complexity of the patterns. The multifractal spectrum curves are plotted for different image of instability and the results show that when the leading or trailing front is unstable the growth of disturbances over the time lead to an increase in the amount of fractal dimension. However when both leading and trailing fronts are unstable, the interaction between the fingers and different fingers pattern may lead to a decrease in fractal dimension.

In this article, we extracted the forces and moment of a supercavtation projectile according to the former experimental work that is exist within literature. regards to the projectile high-speed and the illustration technique, it's safe to say that this experiment is one of the most attractive examples which is exists in the literature. In this test, projectile after leaving the launcher and moving a short path in the air, enters at a low angle to the free surface of the fluid (water). Due to the availability of the experiment test multimedia and thank to the image processing techniques in this paper, speed and acceleration values of the projectile were extracted. In the next step, forces, moments and hydrodynamic coefficients of the projectile were evaluated. The results in this study show that the value of the drag coefficient ( ) are in good agreement with existing predictions, but the results related to the values of the lift and moment coefficients ( and ), contain new and important information in which it will change some of the former assumptions in the literature. The present study also provides useful information about projectile angular velocity which is used in the study of the stability of motion of such devices.