Vibration
M. Moradi; M. Bagheri Nouri
Abstract
In this paper, a new algorithm for studying elastic wave propagation in the phononic crystals is presented. At first, the displacement-based forms of elastic wave equations are derived and then the forms are discretized using finite difference method. So the new algorithm is called the displacement-based ...
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In this paper, a new algorithm for studying elastic wave propagation in the phononic crystals is presented. At first, the displacement-based forms of elastic wave equations are derived and then the forms are discretized using finite difference method. So the new algorithm is called the displacement-based finite difference time domain (DBFDTD). Three numerical examples are computed with this method and the results are compared with experimental measurements and the conventional FDTD method. Also, the computational cost of the new approach is compared with the conventional FDTD method. The comparison showed that the calculation time of the DBFDTD method is 37.5 percent less than that of the FDTD method.
Optimization
Omid Fathi; Hadi Kargarsharifabad
Abstract
Improving the efficiency of compressors has been one of the most important goals of researchers over the years. In this paper, three different methods are presented for parameterization and blade optimization of axial flow compressor. All methods consist of flow analysis tool, optimization algorithms, ...
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Improving the efficiency of compressors has been one of the most important goals of researchers over the years. In this paper, three different methods are presented for parameterization and blade optimization of axial flow compressor. All methods consist of flow analysis tool, optimization algorithms, and parametric geometry generation tool, that are different in each approach. Objective function is defined based on the aerodynamic performance of blade in the acceptable incidence angles range. A DCA blade is used as the initial guess for all methods. The performance of optimized blades and the initial blade are compared for evaluating the capability of various methods that a good agreement has been achieved. The results show that the value of performance improvement in each method depends on the number and type of the chosen parameters. All three methods have improved blade performance at the design incidence angle. However, only the first method shows significant performance improvement in off-design conditions.
Micro and Nano Systems
Yaghoub Tadi Beni; Seyyed Mohammad Fatemi
Abstract
Using differential quadrature method (DQM), this study investigated pull-in instability of beam-type nano-switches under the effects of small-scale and intermolecular forces including the van der Waals (vdW) and the Casimir forces. In these nano-switches, electrostatic forces served as the driving force, ...
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Using differential quadrature method (DQM), this study investigated pull-in instability of beam-type nano-switches under the effects of small-scale and intermolecular forces including the van der Waals (vdW) and the Casimir forces. In these nano-switches, electrostatic forces served as the driving force, and von-Karman type nonlinear strain was used to examine nonlinear geometric effects. To derive nonlinear governing equations as well as the related boundary conditions for the nano-beam, variation method was used. Besides, to study the influence of size effect, the nonlocal elasticity theory was employed and the resulting governing equations were solved using DQM. Finally, the pull-in parameters were studied using the nonlocal theory and the results were compared with the numerical results of the classical continuum theory as well as experimental results contained in the references. Results demonstrated that taking into consideration the von-Karman type nonlinear strain increases the beam stiffness and hence, the pull-in voltage. Besides, use of the small scale, compared with the classical theory of elasticity, yields results much closer to experimental results.
Vibration
Henry Ogbemudia Omoregbee; Modestus O. Okwu; Mabel U. Olanipekun; Bright A Edward
Abstract
This paper presents the detection of fault prognostics in bearings with the application of extended Takagi-Sugeno fuzzy recursive least square algorithms (exTSFRLSA). The nonlinear system is decomposed into a multi-model structure, consisting of linear models that are not inherently independent, due ...
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This paper presents the detection of fault prognostics in bearings with the application of extended Takagi-Sugeno fuzzy recursive least square algorithms (exTSFRLSA). The nonlinear system is decomposed into a multi-model structure, consisting of linear models that are not inherently independent, due to the fuzzy regions defined in exTSFRLSA. The exTSFRLSA was developed to tune, adjust and adapt the parameters involved in the propagation model, as it tends to update itself with the availability of new data. This method is suitable for the online identification of systems because of its unsupervised learning pattern which dwells on a mechanism cantered on rule-based evolution. Scenarios considered for the rule-based modification and upgrade are quite diverse, thereby ensuring effective comparison of measured and predicted defect size. An estimation of the remaining useful life was determined successfully with the proposed method, showing that the system performance health indicator reflects bearing degradation, and it was concluded that exTSFRLSA can be used for fault prediction of bearing where rolling element are involved, especially while its operation is associated with fluctuating speed and load conditions
Manufacturing Processes
Mehrdad Nasrollahzade; Seyed Jalal Hashemi; Hassan Moslemi Naeini; Amirhosein Roohi; Shahryar Imani Shahabad
Abstract
Aluminum alloys are considered a lot in the automotive and aerospace industry because of their high strength to weight ratio. In this manuscript, the gas forming process of aluminum AA6063 tubes at high temperatures up to 500°C is investigated, through experimental and numerical tests. Therefore, ...
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Aluminum alloys are considered a lot in the automotive and aerospace industry because of their high strength to weight ratio. In this manuscript, the gas forming process of aluminum AA6063 tubes at high temperatures up to 500°C is investigated, through experimental and numerical tests. Therefore, an experimental setup is prepared and so, tube specimens are formed in a die with square cross section. Finite element simulation of the hot gas forming process is carried out to investigate the effects of process parameters including time period of forming process, temperature, and loading path. Uniaxial tensile tests under various temperatures and strain rates is performed, in order to obtain flow stress curves of the material. Corner radius and thickness distribution of tubular formed parts is investigated. The results show smaller corner radii could be formed at higher temperatures, whereas lower forming pressure is necessary. Increasing the time period of the process enhances the corners of the specimens to be formed. In addition, the maximum of formability is obtained when the gas pressure increases rapidly at the beginning of the process. However, the increasing rate of gas pressure must be reduced to form a smaller corner radius.
Impact Mechanics
Farshid Kholoosi; Saman Jafari; Mahdi Karimi
Abstract
In this study, the crushing behavior and energy absorption of various thin-walled structures under quasi-static loading are investigated. Some experimental data from similar work are used for the validation of a simulated model. Some samples are designed and considered with different combined geometries. ...
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In this study, the crushing behavior and energy absorption of various thin-walled structures under quasi-static loading are investigated. Some experimental data from similar work are used for the validation of a simulated model. Some samples are designed and considered with different combined geometries. It was found from simulated model that the most ability of specific energy absorption and crushing force efficiency are related to the circle-square sample. For the circle-square sample, the analytic equations for calculating the mean crushing force are obtained. The mean crushing force result is compared with the result of simulations, showing a good agreement. The multi-objective optimization process for the circle-square structure is performed using non-dominated sorting genetic algorithms for two statuses. The purpose of optimization is to increase the specific energy absorption and to decrease the peak crushing force, which causes the increase of the crushing force efficiency amount. The amount of specific energy absorption in the second status compared to the first status is improved by 17%. The amount of crushing force efficiency is improved by 12% after the optimization process.
Perturbation Technique
Abbas Kosarineia
Abstract
The entropy generation analysis of non-Newtonian fluid in rotational flow between two concentric cylinders is examined when the outer cylinder is fixed and the inner cylinder is revolved with a constant angular speed. The viscosity of non-Newtonian fluid is considered at the same time interdependent ...
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The entropy generation analysis of non-Newtonian fluid in rotational flow between two concentric cylinders is examined when the outer cylinder is fixed and the inner cylinder is revolved with a constant angular speed. The viscosity of non-Newtonian fluid is considered at the same time interdependent on temperature and shear rate. The Nahme law and Carreau equation are used to modeling dependence of viscosity on temperature and shear rate, respectively. The viscous dissipation term is adding elaboration to the formerly highly associate set of governing motion and energy equations. The perturbation method has been applied for the highly nonlinear governing equations of base flow and found an approximate solution for narrowed gap limit. The effect of characteristic parameter such as Brinkman number and Deborah number on the entropy generation analysis is investigated. The overall entropy generation number decays in the radial direction from rotating inner cylinder to stationary outer cylinder. The results show that overall rate of entropy generation enhances within flow domain as increasing in Brinkman number. It, however, declines with enhancing Deborah number. The reason for this is very clear, the pseudo plastic fluid between concentric cylinders is heated as Brinkman number increases due to frictional dissipation and it is cooled as Deborah number increases which is due to the elasticity behavior of the fluid. Therefore, to minimize entropy need to be controlled Brinkman number and Deborah number.
Computational Fluid Dynamics (CFD)
Tohid Adibi
Abstract
In this paper the characteristics of unsteady three-dimensional incompressible flows with heat transfer are obtained along with artificial compressibility of Chorin. At first, compatibility equations and pseudo characteristics for three-dimensional flows are derived from five governing equations (continuity ...
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In this paper the characteristics of unsteady three-dimensional incompressible flows with heat transfer are obtained along with artificial compressibility of Chorin. At first, compatibility equations and pseudo characteristics for three-dimensional flows are derived from five governing equations (continuity equation, Momentum equations in three directions, and energy equation) and then results are simplified to two dimensional flows. Pseudo Mach hyper-cone (four dimensional cone) are found and its cross-section with physical axis is calculated numerically. Unlike compressible flow, this is not a sphere. It is found that the pseudo acoustic speed within the incompressible flow is function of artificial compressibility parameter and the directions. In two dimensional, Pseudo Mach cone is obtained by numerical solution of characteristic equations. Unlike compressible flow, the cross section of Mach cone with x-y plane is not circle. This shape is not oval, too. The influence of artificial compressibility parameter on convergence history and accuracy was surveyed by simulation of cavity flow as a benchmark
Fracture Mechanics
Mahdi Yazdani
Abstract
In fracture mechanics and failure analysis, cracked media energy and consequently stress intensity factors (SIFs) play a crucial and significant role. Based on linear elastic fracture mechanics (LEFM), the SIFs and energy of cracked media may be estimated. This study presents the novel modification of ...
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In fracture mechanics and failure analysis, cracked media energy and consequently stress intensity factors (SIFs) play a crucial and significant role. Based on linear elastic fracture mechanics (LEFM), the SIFs and energy of cracked media may be estimated. This study presents the novel modification of decoupled scaled boundary finite element method (DSBFEM) to model cracked media. In this method, only the boundaries of problems are discretized using specific higher-order sub-parametric elements and higher-order Lagrange polynomials as mapping functions. Implementing the weighted residual method and using Gauss-Lobatto-Legendre numerical integration yield diagonal Euler’s differential equations. The chief modifications among the research conducted and the previous studies concerning DSBFEM is that here in, generation of geometry process of the functional interpolation, integration of the diverse is chosen, and by current technic, the difficulty of the DSBFEM is decreased. Therefore, when the local coordinates origin is located at the crack tip, the geometry of crack problems are implemented directly without further processing. Validity and accuracy of the proposed method are fully illustrated through three benchmark problems, whose results agree very well with those of other numerical and/or analytical solutions existing in the literature.
Sarallah Abbasi
Abstract
The purpose of this paper is to investigate the effect of aspect ratio on vortex shedding, and transient flow-induced noise over a rectangular cylinder is presented. The freestream velocity is assumed 50 m/s. URANS equations with turbulence model are employed to flow analysis. Aerodynamic noise ...
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The purpose of this paper is to investigate the effect of aspect ratio on vortex shedding, and transient flow-induced noise over a rectangular cylinder is presented. The freestream velocity is assumed 50 m/s. URANS equations with turbulence model are employed to flow analysis. Aerodynamic noise calculations are performed using the FW-H analogy. The rectangular cross-section with various lengths and widths is considered. A comparison of the results extracted in the present study with the experimental results of other references indicates the accuracy of the present research. The aspect ratios from 0.6 to 6 (equivalent to Reynolds numbers from 2.5 × 104 to 5.6 × 104) are studied. The simulations can be divided into two categories. In the first category, the ratio of length to width (R = B/H) is less than one, and in the second one, this ratio is greater than one. In the first case, noise is reduced by a relatively low slope. But in the second condition, the behavior of noise is different in various ratios and the slope of noise variations is high. The flow structure is also discussed in this paper. It is founded that for the first category, by increasing the aspect ratio, both the fluctuations and aerodynamic forces are reduced, and the longitudinal wake zone is increased. But in the second category, fluctuations of flow may be increased or decreased in various aspect ratios.
Compressible Flow
Sarallah Abbasi; ali joodaki
Abstract
The choice of geometrical shape of the blades has a considerable effect on aerodynamic performance and flow characteristics in axial compressors. In this paper, the effects of the blades shape on the aerodynamic design characteristics are investigated based on Streamline Curvature Method (SCM). Initially, ...
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The choice of geometrical shape of the blades has a considerable effect on aerodynamic performance and flow characteristics in axial compressors. In this paper, the effects of the blades shape on the aerodynamic design characteristics are investigated based on Streamline Curvature Method (SCM). Initially, the Streamline Curvature Method (SCM) is used for designing a two-stage axial compressor. Comparing the current results with experimental ones indicates good agreement. The first stage of the axial compressor is selected with three different blade profiles. The first case (case I) has the polynomial camber with naca thickness distribution series 6. The second case (case II) has the standard naca profile series 6 and the third case (case III) has the modified standard naca profile series 4. Results reveal that using the standard airfoils in the stators leads to improved flow conditions such as loss coefficient and pressure ratio. On the contrary, this profile selection may cause an increase in the stagger angle that is not favorable. Aerodynamic Design with a polynomial camber line in the rotor demonstrates a better aerodynamic behavior in loss coefficient, pressure ratio and diffusion factor. Whilst the use of such a camber line in the stator leads to the formation of less favorable aerodynamics conditions in comparison to the standard airfoil.
Nonlinear Solution
Harsh Kumar Dixit; T.C Gupta
Abstract
The simplified analytical method has developed to analyze the effect of bearing geometrical parameters, i.e. eccentricity ratio, journal rotation speed, slenderness ratio, bearing radial clearance, pad pivot offset and the number of pads on tilting pad journal bearing (TPJB) properties, i.e. fluid film ...
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The simplified analytical method has developed to analyze the effect of bearing geometrical parameters, i.e. eccentricity ratio, journal rotation speed, slenderness ratio, bearing radial clearance, pad pivot offset and the number of pads on tilting pad journal bearing (TPJB) properties, i.e. fluid film thickness, fluid film forces and fluid film stiffness and damping coefficients of TPJB. Reynolds equation was solved for each pad to determine fluid film pressure on pads. The infinite short bearing assumption used to determine pressure distribution on pads integrated over the pad surface to find fluid film forces. The pressure distribution and fluid film forces validated with previous researches. Error bars presented to indicate accuracy measurement. The maximum error found was not more than 6 percent corresponding to loaded pads. The percentage error found maximum when the eccentricity ratio is 0.25 while it found a minimum when the eccentricity ratio is 0.62. The Matlab code has been developed for the solution of non-linear equations. Results produced in the form of design curves which compares changes in fluid film properties corresponding to TPJB geometric parameters. The results obtained in this manuscript are applicable in other similar researches to find appropriate and limiting values of fluid film properties at different geometrical and parametric conditions. The generated plots and data are helpful in dynamic analysis to find the value of a specific parameter corresponding to a specific value of fluid film coefficient, which makes an easier selection of suitable numerical integration technique and boundary conditions to avoid non-significant results, which save time and effort in the nonlinear analysis.
Automation
Ali Mirmohammad Sadeghi; Abdollah Amirkhani; Behrooz Mashadi
Abstract
Recognizing a driver’s braking intensity plays a pivotal role in developing modern driver assistance and energy management systems. Therefore, it is especially important to autonomous and electric vehicles. This paper aims at developing a strategy for recognizing a driver’s braking intensity ...
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Recognizing a driver’s braking intensity plays a pivotal role in developing modern driver assistance and energy management systems. Therefore, it is especially important to autonomous and electric vehicles. This paper aims at developing a strategy for recognizing a driver’s braking intensity based on the pressure produced in the brake master cylinder. In this regard, a model-based, synthetic data generation concept is used to generate the training dataset. This technique involves two closed-loop controlled models: an upper-level longitudinal vehicle dynamics model and a lower-level brake hydraulic dynamic model. The adaptive particularly tunable fuzzy particle swarm optimization algorithm is recruited to solve the optimal K-means clustering. By doing so, the best number of clusters and positions of the centroids can be determined. The obtained results reveal that the brake pressure data for a vehicle traveling the new European driving cycle can be best partitioned into two clusters. A driver’s braking intensity may, therefore, be clustered as moderate or intensive. With the ability to automatically recognize a driver’s pedal feel, the system developed in this research could be implemented in intelligent driver assistance systems as well as in electric vehicles equipped with intelligent, electromechanical brake boosters.
Vibration
M. Talebitooti; M. Ghasemi; S. M. Hosseini
Abstract
In the present work, study of the vibration of a functionally graded (FG) cylindrical shell made up of stainless steel, zirconia, and nickel is presented. Free vibration analysis is presented for FG cylindrical shells with simply supported-simply supported and clamped–clamped boundary condition ...
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In the present work, study of the vibration of a functionally graded (FG) cylindrical shell made up of stainless steel, zirconia, and nickel is presented. Free vibration analysis is presented for FG cylindrical shells with simply supported-simply supported and clamped–clamped boundary condition based on temperature independent material properties. The equations of motion are derived by Hamilton’s principle. Material properties assume to be graded in the thickness direction according to a simple power law distribution in terms of the volume fraction of the constituents. Effects of boundary conditions and volume fractions (power law exponent) on the natural frequencies of the FG cylindrical shell are studied. Frequency characteristics of the FG shell are found to be similar to those of isotropic cylindrical shells. Furthermore, natural frequencies of these shells are observed to be dependent on the constituent volume fractions and boundary conditions. Strain displacement relations from Love's and first-order shear deformation theories are employed. Galerkin method is used to derive the governing equations for clamped boundary conditions. Further, analytical results are validated with those reported in the literature and excellent agreement is observed. Finally, in order to investigate the effects of the temperature gradient, functionally graded materials cylindrical shell with high temperature specified on the inner surface and outer surface at ambient temperature,1D heat conduction equation along the thickness of the shell is applied and the results are reported.
Nonlinear Solution
saeed mahmoudkhani
Abstract
An efficient and accurate analytical solution is provided using the homotopy-Pade technique for the nonlinear vibration of parametrically excited cantilever beams. The model is based on the Euler-Bernoulli assumption and includes third order nonlinear terms arisen from the inertial and curvature nonlinearities. ...
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An efficient and accurate analytical solution is provided using the homotopy-Pade technique for the nonlinear vibration of parametrically excited cantilever beams. The model is based on the Euler-Bernoulli assumption and includes third order nonlinear terms arisen from the inertial and curvature nonlinearities. The Galerkin’s method is used to convert the equation of motion to a nonlinear ordinary differential equation, which is then solved by the homotopy analysis method (HAM). An explicit expression is obtained for the nonlinear frequency amplitude relation. It is found that the proper value of the so-called auxiliary parameter for the HAM solution is dependent on the vibration amplitude, making it difficult to rapidly obtain accurate frequency-amplitude curves using a single value of the auxiliary parameter. The homotopy-Pade technique remedied this issue by leading to the approximation that is almost independent of the auxiliary parameter and is also more accurate than the conventional HAM. Highly accurate results are found with only third order approximation for a wide range of vibration amplitudes.
Computational Fluid Dynamics (CFD)
Shuvam Mohanty; Om Parkash; Rajesh Arora
Abstract
This paper presents a comprehensive and exclusive thermodynamic analysis of counter flow heat exchanger under various operating and geometrical conditions. Analysis system (ANSYS) workbench 14.0 has been used for computational analysis and comparison with previous literature has been carried out in view ...
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This paper presents a comprehensive and exclusive thermodynamic analysis of counter flow heat exchanger under various operating and geometrical conditions. Analysis system (ANSYS) workbench 14.0 has been used for computational analysis and comparison with previous literature has been carried out in view of variable temperature and mass flow rate of hot and cold fluids. An analytical and statistical method of computational fluid dynamics (CFD) analysis is used for simulation and validation of the heat exchanger under steady and dynamic operating conditions. A 3-D model of a heat exchanger having 1000 mm and 1200 mm outside and inside tube lengths with diameter 12.7 mm is designed in ANSYS environment using Renormalization Group (RNG) k-ε approach in order to get the better effectiveness of the system. The variable effects of the steady-state temperature and mass flow rate are investigated. The influence of turbulence over the temperature and pressure profiles is also studied. Moreover, the analytical outcome of the present investigations is compared with that of previous existing literature and found to be in agreement with the previous studies. The proposed analysis presents an in-depth perspective and simulation of temperature gradient profile through the length of heat exchanger. The proposed modified design of heat exchanger along with changing flow direction yields much better results with small computational error 0.66% to 1.004% and 0.83% to 1.05% with respect to change in temperature and mass flow rate respectively.
Abdulnaser Mohammed Alshoaibi; Omar Yasin
Abstract
This paper proposes a combination of FRANC2D/L (2D crack growth simulation program) and ANSYS mechanical program (3D structural analysis for fracture mechanic analysis). The comparisons between the two software are performed for different case studies for stress intensity factors (SIFs) and crack growth ...
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This paper proposes a combination of FRANC2D/L (2D crack growth simulation program) and ANSYS mechanical program (3D structural analysis for fracture mechanic analysis). The comparisons between the two software are performed for different case studies for stress intensity factors (SIFs) and crack growth trajectory. Crack growth is numerically simulated by a step-by-step 3D and 2D finite element method. The SIFs are calculated by using the displacement correlation technique. The procedure consists of computing SIFs, the crack growth path, stresses, and strain distributions via an incremental analysis of the crack extension, considering two and three-dimensional analysis. The finite element analysis for fatigue crack growth is performed for both software based on Paris's law, and the crack orientation is determined using maximum circumferential stress theory. The simulation results obtained in this study, using the finite element method, provide a good agreement with experimental results for all the case studies reviewed.
Vibration
RAJASEKHARA REDDY MUTRA; Srinivas J
Abstract
Turbochargers are most widely used in automotive, marine and locomotive applications with diesel engines. To increase the engine performance nowadays, in aerospace applications also turbochargers are used. Mostly the turbocharger rotors are commonly supported over the fluid film bearings. With the operation, ...
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Turbochargers are most widely used in automotive, marine and locomotive applications with diesel engines. To increase the engine performance nowadays, in aerospace applications also turbochargers are used. Mostly the turbocharger rotors are commonly supported over the fluid film bearings. With the operation, lubricant properties continuously alter leading to different load bearing capacities. This paper deals with the diagnostic approach for prediction of shaft unbalance and the bearing parameters using the measured frequency responses at the bearing locations. After validating the natural frequencies of the rotor finite element model with experimental analysis, the response histories of the rotor are recorded. The influence of the parameters such as bearing clearance, oil viscosity and casing stiffness on the unbalance response is studied. By considering three levels each for shaft unbalance and oil viscosity, the output data in terms of four statistical parameters of equivalent Hilbert envelopes in the frequency domain are measured. The data is inversely trained using Radial Basis Function (RBF) neural network model to predict the unbalance and oil viscosity indices from given output response characteristics. The outputs of the RBF model are validated thoroughly. This approach finds changes in the rotor bearing parameters from the measured responses in a dynamic manner. The results indicate that there is an appreciable effect of lubricant viscosity at two different temperatures compared to other parameters within the operating speed range. The identification methodology using the neural network is quite fast and reliable
Heat and Mass Transfer
Amit Parmar; Shalini Jain
Abstract
The current article has investigated unsteady convective flow for MHD non-Newtonian Powell-Eyring fluid embedded porous medium over inclined permeable stretching sheet. We have pondered the thermophoresis parameter, chemical reaction, variable thermal conductivity, Brownian motion, variable heat source ...
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The current article has investigated unsteady convective flow for MHD non-Newtonian Powell-Eyring fluid embedded porous medium over inclined permeable stretching sheet. We have pondered the thermophoresis parameter, chemical reaction, variable thermal conductivity, Brownian motion, variable heat source and variable thermal radiation in temperature and concentration profiles. Using similar transformation, the PDEs are converted by couple ODEs and solve by R–K–Fehlberg 4th–5th order method. The physical features of non-dimensional radiation parameter, non-Newtonian fluid parameters, suction /injection parameter, mass Grashof number porosity parameter, temperature ratio parameter, thermal Grashof number, Biot number of temperature and Biot number of concentration have been analyzed by plotting the graphs of graphical representations of momentum, heat, and mass profiles. , and have been analyzed. The transfer rate of temperature is decreased whereas the flow rate offluid grows with an enhancement in (K) and (Gr).The transfer rate of the temperature is distinctly boosted whereas the fluid flow rate is distinctly declined with an enhancement in (M) , (Kp).
Hanan EL BHILAT; Khalid El Had; Houda SALMI; Abdelilah Hachim
Abstract
In this study, the effect of six successive recycling cycles of the recycled material including high impact polystyrene disposable cups on tensile properties, glass transition temperature, flexural, impact strength tests and fluidity were studied. It has been found that after increasing recycling, the ...
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In this study, the effect of six successive recycling cycles of the recycled material including high impact polystyrene disposable cups on tensile properties, glass transition temperature, flexural, impact strength tests and fluidity were studied. It has been found that after increasing recycling, the molar mass and the viscosity decrease (a slight increase of melt flow index) until the fifth cycle; the maximum yielding stress decreased due to material brittleness.The impact strength has only been relatively influenced by a 17% increase, whereas the elongation at break and the Young’s modulus dropped with reprocessing cycles. Glass transition temperature has undergone a remarkable decrease: It dropped in a consistent way by the sixth cycle we measured a drop of almost 11°C was compared to the virgin material, with a notable increase in flexural modulus and hardness. The resulted curves show the reliability of this material to be used after a specific number of processing in several industrial applications.
Fatigue
M. Jooybari; J. Shahbazi Karami; M. Sheikhi
Abstract
In the present study, mechanical properties and low cycle fatigue behavior of a solid-solutionized AA6061 aluminum alloy produced by equal channel angular pressing (ECAP) process were investigated. The grain refinement after two passes of ECAP significantly increased the yield stress and ultimate tensile ...
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In the present study, mechanical properties and low cycle fatigue behavior of a solid-solutionized AA6061 aluminum alloy produced by equal channel angular pressing (ECAP) process were investigated. The grain refinement after two passes of ECAP significantly increased the yield stress and ultimate tensile stress and decreased the ductility of the alloy. However, the improvement of low cycle fatigue strength was not as remarkable as expected. Post-ECAP aging heat treatment to the peak-aging condition imposed a notable change in the strength and ductility of the alloy so that its fatigue strength partly enhanced. An optimized combination of grain refinement and distributed fine precipitates in the matrix of the alloy was achieved by conducting aging heat treatment between passes of ECAP. The proposed procedure was proved to yield the best combination of strength and ductility, better distribution and size of precipitates, and thus a remarkable improvement in the low cycle fatigue response of the investigated material.
Fluid Mechanics
A Hassanvand; Mojtaba Saei Moghaddam; M. Barzegar Gerdroodbary; Y Amini
Abstract
Finding the solutions for heat and mass transfer problems is significant to reveal the main physics of engineering issues. In this work, the Adomian decomposition method is chosen as a robust analytical method for the investigation of temperature and flow features in a viscous fluid that moves between ...
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Finding the solutions for heat and mass transfer problems is significant to reveal the main physics of engineering issues. In this work, the Adomian decomposition method is chosen as a robust analytical method for the investigation of temperature and flow features in a viscous fluid that moves between two parallel surfaces. To ensure the validation of results, the outcome of the Adomian decomposition method is compared with that of the Runge-Kutta method, and reasonable agreement is observed. The comparison confirms that the Adomian decomposition method is a robust and reliable approach for solving this problem. Then, diverse parameters such as Prandtl number and squeeze number are studied. Besides, the effect of chemical reaction parameter, Eckert number, and Schmidt number are comprehensively discussed. Findings reveal that the Sherwood number rises when the chemical reaction parameter and Schmidt number increase. Also, it declines with growths of the squeeze number. Likewise, The findings confirm that the Nusselt number enhances with the rising of the Eckert number and Prandtl number, and it declines when the squeeze number increases.
Computational Fluid Dynamics (CFD)
Omid Khayat; Hossein Afarideh
Abstract
One of the challenging problems in the Oil & Gas industry is accurate and reliable multiphase flow rate measurement in a three-phase flow. Application of methods with minimized uncertainty is required in the industry. Previous developed correlations for two-phase flow are complex and not capable ...
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One of the challenging problems in the Oil & Gas industry is accurate and reliable multiphase flow rate measurement in a three-phase flow. Application of methods with minimized uncertainty is required in the industry. Previous developed correlations for two-phase flow are complex and not capable of three-phase flow. Hence phase behavior identification in different conditions to designing and modeling of three-phase flow is important. Numerous laboratory and theoretical studies have been done to describe the Venturi multiphase flow meter in both horizontal and vertical flow. However, it is not possible to select the measurement devices for all similar conditions. In this study a new venturi model was developed that implemented in Simulink/Matlab for predicting mass flow rate of gas, water and oil. This models is simple and semilinear. Several classified configurations of three phase flow were simulated using Computational Fluid Dynamics (CFD) analysis to get hydrodynamics parameters of the flows to use as inputs of the model. The obtained data, used as test and train data in Least squares support vector machine (LSSVM) algorithm. The pressure drop, mass flow rate of gas, oil and water have been calculated with LSSVM method. Two tuning parameters of LSSVM, namely γ and σ^2, obtained as 1150954 and 0.4384, 53.9199 and 0.18163, 8.8714 and 0.14424, and 10039130.2214 and 0.74742 for pressure drop, mass flow rate of oil, gas mass flow rate, water mass flow rate, respectively. Developed models was found to have an average relative error of 5.81%, 6.31% and 2.58% for gas, oil and water respectively.
Composite Materials
Erfan Mirshekari; Arash Reza
Abstract
In this work, transient dynamic stress concentration in a hybrid composite laminate subjected to a sudden internal crack is examined. It is assumed that all fibers lie in one direction and the applied load acts along direction of fibers. Two types arrangements are considered for the fiber; square and ...
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In this work, transient dynamic stress concentration in a hybrid composite laminate subjected to a sudden internal crack is examined. It is assumed that all fibers lie in one direction and the applied load acts along direction of fibers. Two types arrangements are considered for the fiber; square and hexagonal arrangement. Using shear lag model, equilibrium equations are deduced and upon proper application of initial and boundary conditions, the complete field equations are obtained using finite difference method. The results of dynamic effect of fiber breakage on stress concentration are well examined in presence of a second type fiber. These results are compared to those of their static values in both models. The effect of surface cracks on stress concentration, as a result of fiber breakage, is also examined. The values of dynamic stress concentrations is deduced and compared to those of a lamina. Also, the peak stress concentration during transition time for fibers to reach static equilibrium is calculated and compared with those of static values.
Casting
Ehsan Barati; Javad Akbari
Abstract
Thermal expansion and hot deformation are two phenomena causing dimensional errors in investment casting. This error occurs in dimensions between the die and wax pattern. Therefore, the wax's thermo-physical and thermo-mechanical properties, the metal die features, and the process parameters affect the ...
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Thermal expansion and hot deformation are two phenomena causing dimensional errors in investment casting. This error occurs in dimensions between the die and wax pattern. Therefore, the wax's thermo-physical and thermo-mechanical properties, the metal die features, and the process parameters affect the dimensions of the wax pattern. Some important effective process parameters are the injection temperature, die temperature, and holding time. In this paper, the effect of injection parameters on the dimensional accuracy of the wax model created by a metallic die is studied. The Taguchi formulation based on the design of experiments is applied to obtain the optimum condition in achieving the best dimensional accuracy. The studied specimen has an “F” shape with 10 dimensions. The root mean square (RMS) of dimensional differences is considered for accuracy analysis. The results show that if the injection temperature, injection pressure, and holding time are considered as 80oC, 20 bar, and 2.5 min, respectively, the best accuracy may be achieved.
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