JOURNAL OF SOLID AND FLUID MECHANICS
Year:2020 | Volume:10 | Issue:1|Papers Count:21

In this paper, determination of the fracture onset by the ductile fracture criteria was studied and the effect of damage function, calibration method, and calibration tests were investigated on the fracture prediction accuracy. Based on the stress state analysis, three different tension tests including the uniaxial, plane strain, and notched tension tests were conducted to determine the critical value of the ductile fracture criteria. In order to investigate the fracture behavior of AA6061-T6 aluminum alloy sheets, The Ayada, Rice-Tracey, and normalized Cockroft-Latham phenomenological ductile fracture criteria were calibrated through a hybrid experimental-numerical method. The finite element (FE) method were used to simulate the process and calibrated fracture criteria were implemented using an appropriate user subroutine. Experimental forcedisplacement curve and the fracture displacement were used to validated the numerical simulation and investigate the fracture prediction accuracy. According to the result, calibration method based on the history of the stress state lead to higher fracture prediction accuracy compared to average value method (3. 4% decrease in average value of the fracture prediction error). Among all the possible condition, the normalized Cockroft-Latham fracture criteria with the plane strain tension test are the most suitable fracture criterion and calibration test to predict the fracture in the positive value of the stress triaxiality.

Reaction forces at the locating points of the machining fixture are considered as one of the important input parameters in different stages of fixture design procedure including fixture planning, unit design, and verification. In the present study, an agile tool is proposed for calculation of the reaction forces based on the minimum norm principle. For validation of the results, finite element analysis is performed in Abaqus ® software on a rigid workpiece with polyhedral geometry. The reaction forces are calculated from the numerical analysis and compared to the theoretical predictions. In comparison to the numerical results, the worst-case error of 3. 9% is obtained for the theoretical predictions of the normal-to-surface components of reaction forces. The theoretical predictions of the tangential components of reaction forces are not accurate. However, their effects are negligible by considering that the intensity of these forces is low in comparison to the normal components. It was concluded that the theoretical predictions of the normal components of reaction forces agreed well to the numerical data and results that were published in the previous studies. The agreement between the theoretical predictions, results of the previous studies, and the finite element analysis confirmed the accuracy of the suggested model.

In the present study, nonlinear free vibration analysis of bi-directional functionally graded simply supported rectangular plates is investigated analytically for the first time. For this purpose, with the aid of Hamilton's principle and von Karman nonlinear strain-displacement relations, the partial differential equations of motion are developed. Afterward, the nonlinear partial differential equations are transformed into the timedependent nonlinear ordinary differential equations by applying the Galerkin method. The nonlinear equation of motion is then solved analytically by the Modified Lindstedt-Poincare method to determine the the plate nonlinear frequencies. The volume fraction distribution is assumed to be continuously graded in both the length and width directions of the plate. Finally, the effects of some system parameters such as the vibration amplitude, FG indexes and aspect ratio on the nonlinear frequency are discussed in detail. To validate the analysis, the results of this paper are compared with both the published data and numerical method, and good agreements are found.

In this study, the effects of adhesive type (Epon 828 and Araldite EA 1103), the overlapping area (12. 5 and 25 mm), and the surface treatment of the polymer composite on the shear behavior of the sandwich panels with a foam core of polyvinyl chloride (PVC) C7075 and a polymer composite skin (glass fibersvinyl ester) were investigated by finite element simulation and experiment. The results revealed that the sample with Epon adhesive exhibited higher shear strength and lower strain percentage value compared to the sample containing the Araldite adhesive. The samples with an overlapping area of 12. 5 mm showed higher shear properties compared to those with a 25 mm overlapping area which is due to the presence of more bubbles and imperfections on the overlapping surface. Due to increased contact area and penetration of the adhesive into the porosities, surface-modified polymer composites with 100-grit sandpapers exhibited higher shear properties in comparison with those surface modified with 60-grit sandpapers. Also, the investigation of the fracture mechanism showed that the two mechanisms of the adhesive fracture and the rupture of the PVC foam led to the destruction of the sandwich panel. Since the foam rupture mechanism overcame the adhesive fracture, the shear properties of the sandwich panel were increased. The results showed that there was a good agreement between the experimental and simulation results.

In this research, thermoelastic analysis of the beams with variable thickness made of functionally graded materials (FGM) has been carried out. The beam geometry is similar to a turbine blade. Loading is composed of a transverse distributed force, a specific temperature field and an inertia body force due to rotation. Tip of the beam is free and root of the beam is fixed. Mechanical and thermal properties are assumed to be variable along the longitudinal direction of the beam based on the power law variation. Using first-order shear deformation theory, linear strain– displacement relations and Generalized Hooke’ s law, a system of second order differential equation is obtained. Using division method, differential equations are solved. For each division, longitudinal and transverse deflections and longitudinal, shear and effective stresses are obtained. For six different nonhomogeneous distributions, analyses were carried out based on the power law variation. The results show that beam made of FGM with positive and further index of non homogeneity, maximum longitudinal and transverse deflections and longitudinal, shear and effective stresses would be less.

In this study, the fractograghy of the inhomogeneous specimen (including seam weld) of API X65 steel was performed for the first time by the drop weight tear test. The fracture surface of the test specimen consisted of three zones of base metal, heat affected zone and weld metal. The test was performed according to the API 5L standard. The crack initiated with a cleavage fracture from the notch root and then transformed to a shear failure with a 45 degree angle change to the surface plate and continued to the inverse fracture zone. SEM images of all three zones showed signs of ductile fracture including dimples of varying size, orientation and shape. Dimples study from beginning to the end of fracture surface showed that loading from the tensile state at the notch root was changed to shear loading at the end of fracture surface. Also, faint chevron marks with high density were observed in the center of fracture surface in the base metal. In the hammer impact zone, an inverse cleavage fracture was observed, which was enclosed on both sides by shear surfaces with an angle of 45 degree. The calculated ductile fracture surface was within the standard range and indicated the confirmed toughness of these steels for the use in gas transportation pipe lines.

Shape Memory Alloys (SMAs) are a group of smart materials which demonstrate two particular non-linear stress-strain behavior, Shape Memory Effect and Super elasticity based on Austenite to Martensite transformation and vice versa. Effects of heat treatment on SMA wire property and the vibration of composite plate with embedded SMA wires are investigated in current study. Heat treatment effects was studied experimentally and transformation temperatures is determined by differential scanning calorimetry (DSC). Since the ABAQUS software is not capable of analysis the shape memory alloy structures, the UMAT subroutine in the software is used to implement the Boyd and Laguodas model to any shape memory alloy finite element analysis in ABAQUS. Extensive numerical results are depicted to provide an insight into the effects of volume fraction, pre-strain and shape memory alloy properties, transformation temperatures and stress-strain curve changing duo to heat treatment on pre and post-buckled composite plate are discussed. Results reveals that temperature and time of heat treatment result in decreasing and increasing of transformation temperatures, respectively. Moreover, the dynamic response is improved significantly due to SMA pre-strain.

Two-layer metallic sheets are very important Alternative for single-layer metal sheets which have many advantages including weight loss and high strength to weight ratio. Using these sheets saves energy. Hence, the replacement of single-layer metal sheets with two-layer metallic sheets is one of the industry's requirements. One of the most important defects in the sheet metal forming is tearing. Heating of the sheet is one of the ways to postpone the tearing. According to previous studies, there has been no research on warm formability of two-layer metallic sheets. In this research, the aim of the study is to determine forming limit diagram of copper-aluminum two-layer sheets at warm temperature range by experimental and numerical methods. In the experimental method, the formability diagram was obtained by Stretch forming tests with hemispherical punch ond Tensile tests. The results of the experimental method showed that with increasing temperature, the formability increases, The maximum deformation force is reduced, also the height of the dome-shaped height increases with increasing temperature. On the other hand, the simulated model in Abaqus software has a fairly good fit with the experimental model. The best model for predicting precisely the necking momentum was the M-K model.

The most important challenge in the bilateral teleoperation systems is to achieve the operator's true sense of the environment and guarantee the stability of the system. Until now, various approaches have been developed to design such systems in which the passivity condition for environmental forces and operators have been used to prove the stability of the Lyapunov function. These conditions can impose serious restrictions, especially in the field of medical applications on teleoperation systems. The existence of timevarying delay in the master-slave communication channel and also uncertainties (external disturbances and un-modeled dynamics), which sometimes may destabilize the control system, are important factors and underlie in attracting researchers attention. The main purpose of this paper is to propose a robust backstepping fuzzy adaptive controller for the control of uncertain nonlinear bilateral teleoperation system in the presence of time delay and parametric uncertainty. The stability analysis is based on Lyapunov and the simulation results demonstrate the success of the proposed method in achieving the control goals.

In this study, numerical investigation and non-dimensional modeling of the dynamic response of steel and aluminum alloy plates reinforced with polymeric layers impacted by rigid projectiles with different geometries were investigated. In the numerical modeling section, the ABAQUS finite element software and PolyUMod were used to simulate the process. The Johnson-Cook plasticity and fracture models were used to define the metallic material as well as the Mooney– Rivlin model for the polymeric material. To validate the numerical model, a comparison was made between the results of numerical simulations and the experimental ones available in the open literature. The results showed good accuracy of the numerical model in predicting the plastic behavior of the structure as well as the residual velocity of the projectile. A rigorous parametric study was performed using the validated numerical model on the behavior of metalpolymer structures impacted by projectiles with different geometries and moreover, the results were used to provide a mathematical model to estimate the residual velocity of the projectile. For mathematical modeling, new dimensionless numbers were introduced for the penetration process of a rigid projectile to metal-polymer targets using the non-dimensional dynamic equilibrium equations for plates.

Since DC motors have simple structure and long life, the precise speed control for increasing performance and industrial applications is of great importance. This paper is devoted to designing a fractional PID controller in order to speed control of a DC motor by considering the drive and chopper dynamics. As a novelty, chopper dynamic is also considered. From a control point of view, the dynamics of the chopper could complicate the system dynamics, and from a practical point of view, it could reduce the ripple of the armature current. This improves the transient response and results in better speed regulation. In addition, as a novelty, to adjust the fractional order PID controller coefficients a new optimization approach called watercycle optimization (WCA) algorithm by considering a multi-objective criteria is employed. The results obtained are compared with the artificial bee colony and particle swarm optimization algorithm. The results show that the fractional order PID controller optimized by the WCA algorithm performs better in terms of rise-time, overshoot and steady state error.

In present paper, after optimizing the capacity of the CCHP system equipment using the three-yearly relative annual benefit method, the CO2, CH4, CO, NOx and SOx emissions are studied. Optimization is carried out, assuming operation in the off-design points and ability to sell electricity to the network. The performance of the system will be evaluated in real conditions (under the influence of ambient temperature and pressure) and ideal, as well as two views on the production of pollutants at the place of consumption (Local) and total emissions (Global). Optimization process suggests an internal combustion engine with a nominal capacity of 2440 kW as a prime mover for the case study of the hotel, which despite the significant reduction of CO2, CO, NOx and SOx emissions in global mode, increases the CH4, CO and NOx in comparison with the traditional system at local mode by 92. 5%, 0. 79% and 84. 1%. On the other hand, the economic performance of the power unit of the CCHP system with a change in environmental conditions indicates that if the actual performance of the gas engine in the system is not considered, the system incomes will not have the required certainty.

Aerodynamic heating and drag reduction in hypersonic flying is one of the most important challenges in this speed range. In decades, the use of the spike method has been considered by the experts as an appropriate tool for aerodynamic drag reduction and a lot of research is done to optimize the geometry, dimensions and type of spike aerodisk. In this study, the effect of spike length on the wave drag reduction of a standard nose, HB1, in hypersonic flow regime was evaluated using two methods of numerical simulation and experimental test of hypersonic wind tunnel in Mach number 6. 4. For this purpose, the amount of drag force applied to the model was investigated in four types of spikes with length to diameter ratios of 0. 5, 1. 0, 1. 5 and 2. 0. The results indicate that the numerical solution has a significant adaptation with experimental results and, according to expectations, Spike has a considerable effect on the nose hypersonic drag reduction. It was also observed that the increase in spike length caused a further decrease in the nose wave drag and the length to diameter ratio of 2 with the drag reduction of 43% has shown the best performance.

n this study, the comparison of the heat transfer of heat exchanger of the spiral tube and the direct pipe using the hybrid nanofluid in the turbulent flow has been empirically investigated. The nano fluid used in this study consists of a mixture of titanium oxide, silicon oxide and magnesium oxide with a medium diameter (20-30 nm) in a base water fluid at a temperature range of 60 to 30 ° C. Nanoparticles have been used in the volume fractions range of 0. 25, 0. 5, 0. 75 and 1%. The results showed that the Nusselt number increased by increasing the Reynolds number and the concentration in the spiral tube compared to the direct tube by 6. 6% on average. Also, the results are reported as temperature difference, the use of nanoparticles in the spiral tube is higher than the direct tube in the volume fraction of 0. 25% and the temperature of 60 ° C, 37. 6%. The percentage increase in the optimal temperature difference of the hybrid nano fluid in the spiral tube in the volume fraction is 0. 25% and 60 ° C, which is 10% higher than the base fluid and in the direct tube in the volume fraction of 0. 75% and 60 ° C Compared to the base fluid, the temperature difference is increased by 6%.

The transient pool boiling of deionized water was studied under saturation condition and atmospheric pressure at time periods of 1, 10, 100 and 1000s. Iron-aluminum-chromium alloy wire was used in the horizontal position as a surface heater and two permanent ceramic magnets were used to investigate the magnetic field effect on the deionized water boiling. Voltage difference on the wire heater was used to increase heat flux during periods of time, and this voltage difference increases linearly with time. The increase of heat flux was obtained by a quadratic polynomial function with increasing the voltage from zero to 50 volts over time periods. The critical heat flux with the presence of the magnetic field happens at higher superheat temperatures of wire. The critical heat flux values for periods of 100 and 1000s in the presence of the magnetic field are more than the same values in the absence of the magnetic field which could be due to the change in the chemical-physical properties of magnetized water. The magnitudes of the heat flux enhancement due to the magnetic field relative to the absence of the magnetic field for the period of 100 and 1000s were 12. 74% and 7. 3%, respectively.

In this study, the wake behind a cylinder with helical strakes at Re = 20000 is experimentally investigated. Three helical strakes with a pitch of 3D and equal distances were installed on the cylinder. The ratios of strakes heights (thicknesses) to cylinder diameter (H/D) were 0. 1, 0. 09, 0. 07 and 0. 05. The effects of helical strakes on the mean velocity profile, turbulence intensity, velocity defect and Strouhal number of the cylinder on its center line were studied. The results showed that using helical strakes with varying heights results in different effects on the wake structure, which can be demonstrated in near (x≤ D) and far (x>D) regions downstream, behind the model. In the near regions, planes with higher thickness resulted in improved wake and reduced velocity defect, while in the far regions, using the plane with an H/D of 0. 07 led to up to 35% decrease in velocity deficit. Rotating planes helical strakes were also seen to reduce maximum turbulence by 14%.

In this paper presents a digital filter method for online estimation of heat flux on a one-dimensional plate. Two inverse problems are designed to investigate this method. In the first problem, the unknown heat flux and the boundary condition on the other side of the plate are not known and in the second problem, the heat flux on the sides of a two-layers plate is unknown. in both cases, two sensors have been used to measure the temperature history of the plate. In the proposed algorithm, one of the two sensors is used as a boundary condition. To evaluate the accuracy and capability of digital filter, several experiments were designed. The filter coefficients are calculated only once in the proposed method and used in all experiments. The results show that this algorithm is very successful in estimating different forms of heat flux with different noise intensity at measured temperatures and different thermocouple positions in the plate and the Tikhonov digital filter method has more precision compared to Beck's method. Also, using the mollified data in the proposed algorithm increases the accuracy and efficiency of the proposed algorithm.

The present study investigates the effect of using exhaust smoke extractors as an alternative to traditional manifolds in a spark ignition engine designed to maximize engine power. To investigate the effect of the extractors on the engine performance and selection of superior design, the proposed geometric model of proposed manifolds in a numerical simulation process has been investigated and after optimization has been constructed and installed on the engine. At the next step, the engine was experimentally tested in the test cell. Results were compared with the base engine. It was observed that the designed exhaust extractors would increase the maximum engine power up to 15%.

In this study in order to study the effect of secondary flow on the efficiency of solar collectors, a circular collector with helical tube and a regular collector is constructed and tested at the same time. The assessment was based on the ASHRAE standard and in southern Iran. Experiments were carried out based on different environmental conditions using normal water agent and zinc oxide/ water nanofluid. The results of this study show that with variation in ambient conditions as well as increasing the efficiency and increasing the efficiency of the efficiency of both the circular and rectangle flat plate solar collector performance, the main reason is the secondary flow effect on the enhancement of heat transfer from the tubes to the operating fluid. Also, while using nanofluid instead of water as a factor fluid, although the efficiency of both solar collector is increased, the secondary effect on heat transfer in the use of nanofluid is significantly enhanced due to the motion of particles particles in suspension. In addition, the maximum number of registered solar collector efficiency by using nanofluid was about 77. 6% in circular collector.

Separation of blood cells has a widespread application in medical sciences. Separation of these cells helps identifying their properties. Knowing the properties of circulating tumor cell's (CTC) and the effect of different drugs on them can significantly help to develop and improve patient's treatment methods. During recent years, microfluidic devices for separation and sorting of these cells have been significantly developed. There are different methods for cell sorting. In this research, the size and the electrical properties of cells have been considered as the main criteria for cell separation and by combining pinched flow fractionation (PFF) as a passive method with dielectrophoresis as an active method, the separation of MDA-435 mammalian circulating tumor cell from white and red blood cells is investigated. These cells have small size differences where in pinched flow fractionation, incapability to separate particles of similar sizes is a major challenge. In this research, dielectrophoresis force creates a gap between circulating tumor cells and white blood cells in the pinched segment and after hydrodynamic expansion in the broadened segment, circulating tumor cells, white blood cells, and red blood cells will be collected in their specific outlet branches. Results show that this hybrid method can separate tumor cells effectively.

Turbocharger turbine blade are exposed to damage because of High pressure and Pulsating inlet charge. In recent designed blades, thickness is reduced and loading was increased, these caused the higher probability of blades failiure. Therefore the blades thickness distribution should be defined according to the combination of higher efficiency and higher resistance against failiure. In this paper the Aero static efficiency of the turbin according to different thickness parameters is studied. And the most volnurable area of the bades is identified by the result of the fluid behavior simulation and structural analysis. A 3D CFD model in ANSYS CFX for fluid side, and a FEA model in ANSYS Static Structural module for the blade structural responses were used then the results were coupled. Validation was performed by reference to experimental data. Resuls show that thinner blades are more proper for this kind of turbomachine but in partial admission ticker blades have higher efficiency than thinner blades.