مجله مکانیک سازه ها و شاره ها
سال نهم شماره 2 (تابستان 1398)

Understanding of the hydrodynamic performance of an Autonomous Underwater Vehicle (AUV) is essential to investigate of its capability to perform a mission. Dynamic simulation of the equations of motion and analyzing the vehicle maneuverability is a useful tool for performing these evaluations. To achieve this aim the sensitivity of maneuvering of an underwater vehicle to changes of hydrodynamic coefficients can be investigated. In the current study the sensitivity of maneuverability of an AUV to changes of added mass coefficients is considered. In the first step the hydrodynamic coefficients of the AUV are calculated using analytical-semi empirical method. Next the six degree freedom of dynamic equation for this vehicle is solved and the behavior of turning maneuverer is simulated. In the following by changing the different added mass coefficients the behavior change of the underwater vehicle is evaluated. The results shows that the steady turning radius of the maneuver is insensitive to added mass elements, where the advance length which is the character of the transient phase has the most sensitivity to added mass elements. While tactical diameter which is the combination of steady and transient phases has average sensitivity to added mass parameters.

In this research, a series of experiments were first performed to evaluate the plastic deformation of rectangular aluminum plates reinforced by polymeric coating under gas mixture detonation loading. Four different types of thickness configurations were chosen to investigate the effect of front and back layer thicknesses on the deformation resistance of metal-elastomer bilayer structures. In the analytical modelling, a model for predicting the maximum permanent deflection of metal-elastomer bilayer structures was presented. Also, in the empirical modelling, a number of new dimensionless numbers were presented by nondimensionalizing the governing equations of plate based on dimensional analysis in which each dimensionless number represents the geometry of the structure, the ratio of applied dynamic loads to the resistance ability of material, and the dynamic resistance ability of material against plastic deformation. Mathematical functions were presented to predict the maximum permanent deflection of structures by converting the experimental data into the form of dimensionless numbers as well as using singular value decomposition method. Subsequently, the presented empirical models were verified by the conducted experimental results. The results indicated an encouraging agreement between the experimental results and empirical predictions in terms of the maximum permanent deflection.

Nowadays, in impact mechanics, ceramic is especially important. It is used to produce bullet-proof targets due to its low density and high hardness. In this article, we presented a new and complete modified analytical model for semi-infinite ceramic-metal targets, based on the Fellows analytical model, which is one of the most important models in the field of penetration. The new analytical model includes modifications such as considering the variations in the projectile's velocity at each time interval, the calculation of the ceramic cone formation time, the change in the half-angle of the ceramic cone, the change in the compression strength of the ceramic during the penetration process, the calculation of the ceramic mass reduction based on the time of the formation of the ceramic cone, the decrease in the projectile's length depends on the variation in the projectile and ceramic velocity at each time interval and the calculation of the suppression mass reduction. In addition, flowchart of determining the depth of penetration process, regarding to the modifications of the new analytical model and the clarification of the Fellows model ambiguous, was presented. The results of the new analytical model have been compared with the results of the Fellows and Woodward analytical models and experimental data. These results improve the predictions of the Fellows model in determining the penetration depth at low velocities and also have good agreement with experimental data.

In this paper, oscillations of a flexible stabilizer attached to three dimensional body in viscous subsonic flow are investigated. The purpose is firstly to analyze fluid structure interactions using a proper coupling algorithm that can couple the fluid and structure solvers and provide the data exchange between them and secondly to perform the stability analysis of body with its flexible stabilizer. For this purpose, iterative partitioned coupling algorithm is used for data exchange between structure and fluid. Then, the results of vibration characteristics including the amplitude and frequency and forces and moments variations are presented with respect to different bending stiffness and strip masses. Results show that the developed framework captures the physics of fluid-structure interaction with errors less than 10%. Finally, body stability analysis is performed with respect to the pitch damping coefficient using body forced vibrations and the obtained results showed the capability of strip stabilizer for providing the desired body stability.

In this article, the creep behavior of the AlSiCuNiMg alloy, which has been widely utilized in the piston component of the vehicle engine, has been modelled at different temperatures and various stresse levels. For this objective, the creep test was done on casted standard specimens, under a constant temperature and a constant tensile loading condition. Temperatures in creep testing were considered as 250, 275 and 300°C and stress levels were 75, 100 and 125 MPa. Experimental data showed that at a constant stress level, by increasing the temperature, the minimum true strain rate increased and the final true strain decreased; however, at a constant temperature, by increasing the stress level, both mentioned values increased. Based on modeling results, the temperature-dependent power law was the superior strain rate-based model, with the lowest value for the relative error and the scatter-band. In addition, the Bailey-Norton model had better modeling results between strain-based models.

Phased Array Ultrasonic Testing (PAUT) is one of the most efficient and economic methods for inspecting weld joints. In some industrial applications, Dissimilar Metal Welds (DMW) are used for connecting the austenitic stainless steel pipes to the ferritic steel. Inhomogeneity and anisotropy of DMW causes ultrasonic waves to skew and attenuate. This issue can decrease the defects echo and reduce the probability of detecting them. Therefore, PAUT is used for inspection of DMW due to its ability to steering and focusing the ultrasonic waves. Conventional focusing technique is used for focusing waves in the homogenous and isotropic media. However, this technique can’t be used for focusing wave in DMW. In this paper, the conventional focusing technique developed for focusing ultrasonic waves in inhomogeneous and anisotropic media. Results of ultrasonic waves focused on defect in DMW media by the developed conventional focusing technique are compared and validated by adaptive focusing technique. Simulation results have been shown that developed conventional focusing technique has acceptable accuracy operation for focusing waves in inhomogeneous and anisotropic media such as DMW. In addition, the amplitudes of the defect echoes has increased about 235% , compared to conventional ultrasonic testing which indicates that the waves is correctly focused on defect.

In this paper, an active control strategy based on the cylinder forced rotary oscillation is considered to reduce the flow-induced vibration of an elastically mounted two-degree-of-freedom circular cylinder free to vibrate in both transverse and in-line directions. The fluid flow governing equations are two-dimensional incompressible Navier-Stokes model which discretized by means of the finite volume method. The frequency ratio〖 f〗_rot/f_n, and rotation rate α, are two important adjustable parameters which must be selected in such a way that the vortex shedding frequency locked on associated rotational forcing frequency, and the cylinder transverse and in-line vibrations will be suppressed accordingly. Based on comprehensive simulations accomplished in this paper, three different active open-loop control systems is selected in order to effectively reduce the cylinder vibrations for reduced velocities in synchronization region with the following input parameters: (for V_r=5: α=1,f_rot/f_n=1.1), (for V_r=6: α=1,f_rot/f_n=1.3), and (for V_r=7: α=1,f_rot/f_n=1.5). These three control systems are found to decrease the maximum transverse cylinder vibration amplitudes by 88%, 92%, and 92% while the corresponding in-line vibration amplitudes decrease by 93%, 90%, and 82%, respectively.

In the present article, a high-order global-local theory with three-dimensional elasticity corrections is employed to trace the local and instantaneous variations of lateral deflections and stress components of sandwich plates with auxetic (negative Poisson ratio) cores under static loads. The governing equations are extracted based on Hamilton’s principle. The main novelties of the present research in comparison to the available literature are the presenting a higher-order global-local plate theory with equilibrium-based 3D-elasticity corrections, incorporation of the transverse flexibility of the core (a fact that is crucial when studying behaviors of thick or soft core sandwich plates) and investigation of the negative Poisson ratio (auxeticity) effects of the core material on the static (stress and displacment) responses. All these items are accomplished here, for the first time. Since the transverse shear stresses are extracted based on the 3D elasticity theory, in contract the traditional constitutive-based theories, the interlaminar continuity condition of the transverse shear stresses is met. The verification results show that the presented finite element formulation leads to highly accurate results, even for thick or soft core sandwich plates. Results reveal that auxeticity of the core material decreases the global and relative stresses and lateral deflections of the face sheets.

Nano particle manipulation is composed of two phases. First phase is critical force and time investigations and the second phase is nano particle motion and displacements. In this paper the first phase of nano particle manipulation was investigated. Critical force is the amount of force required for overcoming the friction and surface adhision forces. Also critical time is the duration for partical to change from static to dynamic state. Two noticeable categories of parameters are chiefly effecting on two significant factors: 1- peripheral parameters and 2- dimensional parameters. In this paper by utilizing sensitivity analysis, which A-fest method is one of them, and HK precise friction model effect of peripheral parameters on critical rolling's time and force was studied. Surface energy, work adhision, elastic modulus of needle and particle and poissan coefficients of needle and particle, are the studied peripheral parameters. With nano particle considered to be rigid and without its deformation, elastic modulus of particle and needle was known as the most effective factor on critical rolling force and time in x-axis direction and y-axis direction in nano manipulation using Hk model respectively.

In this study, electromechanical behavior of the micro scaled capacitive pressure sensors is investigated and ‎the effect of electrostatic actuation on the performance of the device is analyzed. The sensor is considered as ‎a circular microplate with an initial distance from a fixed substrate. Due to electrostatic load and external ‎pressure, the plate deflects and the capacitance of the device changes. The external pressure can be estimated ‎by measuring this change of capacitance. Hence, in this research, the relation between the capacitance and ‎external pressure is studied. To this goal, the equation governing static deflection of the microplate is derived ‎in polar coordinates. This equation is converted to an algebraic equation using Galerkin approach and then ‎solved utilizing an iterative method. Finally, the effects of external pressure and applied voltage on the ‎capacitance and sensitivity of the device are investigated and the convergence of the proposed iterative ‎algorithm is analyzed.‎

A three-dimensional hybrid method is developed for transient analysis of functionally graded thick hollow cylinders subjected to asymmetric dynamic pressure and thermal shock loads. The material properties of the shell are temperature dependent and graded continuously in the radial direction. The hybrid solution method is composed of the layerwise theory, differential quadrature method, and Fourier series expansion. This research shows some interesting results that can be helpful for design of FG shells subjected to transient pressure and thermal shock simultaneously. To verify the precision of this method, the developed results are compared with the experimental and numerical results presented in the available literatures. Then, by employing the proposed method for a selected FG cylinder, the temperature dependent dynamical behavior of the shell subjected to thermal shock and asymmetric transient pressure was studied. Finally, the effect of different parameters on this behavior was studied. Also the fast convergence rate of the presented solution is demonstrated.

In present study, the velocity and pressure of two-phase flow in flow field and the effect of inlet turbulence on trajectory and breakup of liquid jet in crossflow are investigated numerically. Large eddy simulation method is used to discriminate Navier Stokes equations. A hybrid fluid volume model and level set are applied for two-phase modeling. Results show, with increasing the turbulence intensity, the vortices in the flow field store more energy. According to breakup mechanism changes the breakup length and breakup height are closed to injector output 33% and 11% respectively. Also, due to the very small amount of dynamic energy present in the turbulent fluctuations, the jet trajectory equation doesn’t change in the different turbulence intensity. Liquid jet trajectory has been studied in different nozzle geometries. The results indicate that liquid jet trajectory is different for elliptic and circular geometries. Results are in good agreement with the results of other researchers.

In the present work, the performance of water-based Fe3O4 (magnetite) nanofluid and graphene nanoplatelet (GNP) nanofluid in solar steam generation has been evaluated. For this purpose, a solar simulator, a beaker containing nanofluid, an electronic balance and temperature sensors were employed. In the first place, magnetite nanofluid with different mass fractions (0.01, 0.02 and 0.04 %) and GNP nanofluid with mass fractions of 0.001, 0.002 and 0.004% were separately exposed to solar illumination at intensity of 3.5 sun kW/m2. Then the most efficient concentration of magnetite nanofluid was mixed with different concentrations of GNP nanofluid and the photothermal conversion and solar evaporation behavior of the mixed nanofluid was studied. The results showed that adding the nanoparticles mentioned above to pure water, Highly increases the light absorption so that the solar vapor generation efficiency of magnetite nanofluid with concentration of 0.04 % mass weight and GNP nanofluid with the mass fraction of 0.004 % were 1.97 and 2.69 times as high as that of pure water. And the mixed nanofluid containing 0.01% mass weight of magnetite and 0.004% mass weight of GNP has a solar evaporation efficiency of 32.4% which is while the evaporation efficiency of pure water is 14.13%.

In the present work, we offer a novel numerical algorithm based on the lattice Boltzmann method (LBM) to consider the motion of many circular particles in a non-Newtonian power law fluid in Couette flow and it is combined with the smoothed profile method which explains the movement of particles. At first, the velocity variation of shear-thickening has been analyzed and the results was compared with the numerical results of the previous works. The present study is a first report, which investigate flow behavior of circular particles with the same and different size in power law medium in Couette flow on the LBM framework. The effective viscosity of a particulate suspension that are placed randomly inside two parallel walls is considered for 0.04

The Aids-related non-Hodgkin’s lymphomas are the second most frequent cancer. A proposed treatment strategy should be implemented as short as possible. A long time treatment protocol not only devitalizes the immune system but also cause to drug resistance. It is observed in many cases that the immune system is able to diminish the tumor cells without any external treatment. Based on these, an extended model for cancer during the treatment has been proposed. A mixed chemo-immunotherapy proposed which the chemotherapy limits the tumor cell growth and the immunotherapy modifies the dynamics of the system. Hence, the equilibrium points of the system, their stabilities and the bifurcation of the system investigated. In order to obtain an optimal dose and considering the conditions of a patient the SDRE method combined with a fuzzy system. The simulation results show an efficient treatment should not only reduce the population of cancer cells but also must modify the dynamics of the system.

Film cooling is one of the most effective methods for protecting turbine blades from thermal overheating. For steady gas flow, the film cooling has been extensively investigated, but there is insufficient knowledge of how the pulsation affects the film cooling performance. In this study, the effects of air coolant injection with sinusoidal pulsations on temperature distribution and film cooling effectiveness of a turbine blade is numerically investigated. Cooling air is injected through the three plenums to leading edge, pressure and suction sides of the blade at five blowing ratios of 0.5, 0.75, 1, 1.5, 2, and 2.5 with frequency of 50Hz. Also, the effect of main flow Reynolds number on cooling performance is studied. Finite volume method was used to solve flow governing equations. Obtained results show that pulsating the blade cooling mass flow rate causes the size of counter vortex rotating pair to be varied, resulting in change of temperature distribution of the surface at each time steps. The averaged centerline pulsed film cooling effectiveness distribution is maximized on downstream of the injection hole of leading edge, pressure side and suction side at blowing ratio of 0.75, 0.5 and 1, respectively.

In this paper, the inception, growth and development of cavitation are investigated around the combined body experimentally. The diameter of afterbody and the length of model are 25 and 210 mm respectively. The angles of conic nose are 〖30〗^° and 〖45〗^°. Models were tested in a high speed closed circuit cavitation tunnel. A peripheral groove is established on the afterbody and then one conic nose, experiments are repeated in these cases. A comparison was done between all cases. For 〖30〗^° model with groove on afrebody and without groove, cavitation is initiated at a small distance behind the body. If the groove is established on the nose then cavitation is initiated into it. In 〖45〗^° model, cavitation is initiated on the interface of the nose and afterbody. Into the groove and behind of afterbody, cavitation will be initiated at the center of vortex resulted by separation. By developing the length of cavitation on the afterbody, regular longitudinal oscillations will be occurred. Behind the model, inside the wake of body, cavitation initiates at the center of annular vortex. After developing the length of cavitation area ,bubble shedding occurs at the end of cavitation region. During the fluctuating of cavitation area, bubble shedding occurs randomly. In these cases, intense noise is heard.

In this study, the impacts of three different inflow conditions on turbulent boundary layer characteristics over a flat plate was numerically investigated. The investigated boundary conditions are uniform velocity profile at inlet with turbulent generation using strip, precursor-based simulation model (TVMF) and rescaling/recycling model purposed by Lund, which are applicable in large-eddy simulation (LES). The simulations are done using LES with dynamic smagorinsky coefficient in OpenFOAM software. Validation of the numerical method was done using direct numerical data and analytical solution. Comparison of the skin friction coefficient with analytical equation shows that the maximum deviation in simulations with precursor-based, Lund and strip model are 4.3%, 4.5%, 19.2% accordingly. The numerical values and development trend of intergral thicknesses, velocity components and the other characteristics obtained through simulations using precursor-based and Lund inlet models, are in good agreement with direct numerical simulation (DNS) results while the results obtained by using the strip model are more diverse from the DNS results. The results of this study indicate that using precursor-based and Lund inflow generation models in LES produces more realistic results accompanied with reduced computational cost.

While aircraft fuel systems are not generally regarded as the most glamorous feature of aircraft functionality, they are an essential feature of all aircraft. Their implementation and functional characteristics play a "critical role" in the design, certification and operational aspects of both military and civil aircraft. In this article, our concentration is to numerical analysis of baffle shape effects in aircraft fuel tank sloshing. Sloshing is meant the standing wave formed on the surface of a liquid when a tank partially filled with liquid is oscillated. In this study, sloshing analysis with VOF method in ANSYS FLUENT software. One fuel tank without baffle & four fuel tank with different baffle shapes analysed. Results with regard to tank filling, gravity acceration & tank geometry in tank 1 indicate baffle is necessary equipment for safe engine operation. In addition, results in the other tanks indicate position of baffle’s holes is important and affect in velocity of fluid in tanks. Finally, after analysis some recommandations suggested for future works.