فهرست مطالب

Scientia Iranica - Volume:26 Issue: 3, May-Jun 2019

Scientia Iranica
Volume:26 Issue: 3, May-Jun 2019

  • Transactions on Mechanical Engineering (B)
  • تاریخ انتشار: 1398/03/11
  • تعداد عناوین: 15
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  • H. Ghaebi *, M.N. Bahadori, M.H. Saidi Pages 1281-1292
    In this research, a confined aquifer with low groundwater flow was considered to meet the cooling and heating requirement of residential complexes. The complexes were located in the cities of Ahvaz, Ardabil, Bandar Abbas, Esfahan, Kerman, Rasht, Tehran and Zahedan. The complex in Ardabil required mostly heating, the ones in Ahvaz and Bandar Abbas required mostly cooling, whereas the complex in other cities required both heating and cooling. Four different alternatives of aquifer thermal energy storage (ATES) were analyzed in this study. These alternatives were:1) using ATES alone for cooling 2) for cooling coupled with a conventional refrigeration system or a chiller 3) for heating by employing flat plate solar collectors and 4) for heating by employing flat plate solar collectors and a heat pump. Thermal energy recovery factor and the annual coefficient of performance (COP) of the alternatives were determined. The results showed that, for buildings located in cities with mild climatic conditions(such as Esfahan), where the annual heating and cooling energy requirements are early equal, the use of ATES is highly recommended when employing any of the alternatives considered in this investigation.
    Keywords: Aquifer thermal energy storage, climate, solar energy, heat pump
  • Mohammad Shojaeefard *, Kian Tafazzoli Pages 1293-1298
    Heat transfer has considerable applications in different industries such as designing of heat exchanger, nuclear reactor cooling, control system for spacecraft and designing of microelectronics cooling. As the surfaces of two metals contact each other, this issue becomes so crucial. Thermal contact resistance is one of the key physical parameters in heat transfer of mentioned surfaces. Measuring the experimental value of thermal contact resistance in laboratory is highly expensive and difficult. As an alternative, numerical modeling methods could be engaged. In this study, Inverse problem method solution is utilized as a proper method for estimation of thermal contact resistance value. In this order, three different configurations (flat-flat, flat-cylinder, and cylinder-cylinder) were utilized in two steady and unsteady state conditions to predict the value of thermal contact resistance. In conclusion, the final results establish the fact that the inverse problem method solution can predict thermal contact resistance values between contacting surfaces.
    Keywords: thermal contact resistance, thermal contact conductance, transient numerical simulation, curvilinear contact, interface interaction
  • Rafa Grzejda * Pages 1299-1306
    This article concerns modeling, computation and analysis of multi-bolted joints in the assembly stage. The physical joint model is introduced as the assembly of the following three basic subsystems: a set of fasteners (bolts), a flexible joined flange and a contact layer between it and a rigid support. The finite element method (FEM) is used for modeling. Bolts are replaced by the bolt models of the spider type. The joined flange is modeled with spatial finite elements. As a model of the contact layer, the Winkler contact layer model is adopted. The truth of the theorem has been tested, according to which nonlinear characteristics of the contact layer may have an insignificant impact on computational final values of bolt preloads in the case of sequential tightening of the joint. The results of the calculations for the selected multi-bolted joint are given and compared with the experimental results. Conclusions of paramount importance to the engineering practice are comprised.
    Keywords: Multi-bolted joint, Nonlinearity, FE-modeling, Assembly stage, Preload
  • S. S. Madinei, N. Arjmand * Pages 1307-1315
    Previous studies have measured thoracic range of motion (RoM) using either skin-mounted devices or supine CT-imaging and have reported quite different RoMs. Given the inherent shortcomings of measurements of vertebrae movements from the overlying skin, the present study aims to measure normal RoM of the thoracic spine in the sagittal plane using the upright digital radiography. Lateral radiographs of the thoracic spine were acquired from eight asymptomatic male subjects in upright standing and full forward flexion using a mobile U-arm digital radiographic system. Total (T1-T12), upper (T1-T6), and lower (T6-T12) thoracic RoMs were measured. A throughout comparison with available skin-based measurements in the literature was carried out. Mean of total (T1-T12) thoracic RoM was 22.5° (SD 4.1°), most of which was generated by the lower (T6-T12) as compared to upper (T1-T6) thoracic spine (15.5° versus 7.1°, p measurements suffer from the inter sensor-skin-vertebra movements and supine imaging techniques do not allow maximal trunk flexion, standing radiography remains as the gold-standard technique. Evaluation of thoracic spine RoM has implications in both patient discrimination for diagnosis and in biomechanical models for estimation of spinal loads.
    Keywords: Thoracic spine, Range of motion, Kyphosis (Cobb) angle, Digital radiography, Imaging, Biomechanical modelling
  • Parviz Ghadimi *, Sayyed Mahdi Sajedi, Sasan Tavakoli Pages 1316-1334
    In this paper, effects of a wedge on the performance of planing craft in calm water are experimentally investigated. Experiments are carried out on three different cases distinguished by the wedge type. The model, built of fiberglass, is a prismatic planing hull with deadrise angle of 24 degrees. Towing tests are conducted at different Froude numbers ranging from 0.21 to 2.1. The total trim angle, resistance, rise up at the CG as well as stern and bow, keel wetted length, chine wetted length, stagnation angle, and the length of stagnation line are measured. They are used to study the effect of installing a wedge on the performance as well as the effect of height on the hydrodynamic characteristics. Based on the observations made, it is concluded that, when the wedge is applied to the hull, the risk of model exhibiting instability diminishes, while total trim angle largely decreases, keel wetted length is enlarged, wetted surface becomes thinner, CG rise up is lowered, and the resistance is reduced. Moreover, experimental measurements and theoretical 2D+T theory are combined to bring deeper insight about physics of the flow and pressure distribution when a wedge is installed on the bottom of a planing hull.
    Keywords: Experimental Study, Planing hull, Wedge, Performance, Calm water, Combination of Experimental, Theoretical studies
  • A. Nouri Borujerdi *, F. Sepahi Pages 1335-1349
    In this study, turbulent natural convection in a square enclosure including one or four hot and cold bodies is numerically investigated in the range of Rayleigh numbers of . The shape of the internal bodies is square or rectangular with the same surface areas and different aspect ratios.  In all cases, the horizontal walls of the enclosure are adiabatic and the vertical ones are isothermal. It is desired to investigate the influence of different shapes and arrangements of internal bodies on the heat transfer rate inside the enclosure with wide-ranging applications such as ventilation of buildings, electronic cooling and industrial coldbox packages. Governing equations including Reynolds-averaged-Navier-Stokes equations have been solved numerically with finite volume method and  turbulence model in a staggered grid. The boundary condition for turbulence model is based on the standard wall function approach. Strongly implicit method is employed to solve the discretized systems of algebraic equations with a remarkable rate of convergence. The effects of several parameters such as distance between the bodies, aspect ratio and Rayleigh number on heat transfer rate have been investigated. The most change in heat transfer rate at high values of Rayleigh numbers is associated with alteration in distance between square bodies.  Moreover, the horizontal installation of rectangular bodies with h/w = 1/3 is accompanied by a maximum reduction of heat transfer at low Rayleigh numbers. The present results have been compared with previous experimental and numerical works regarding enclosures with or without internal bodies and reasonable agreement is observed.
    Keywords: Natural convection, enclosure, interior bodies, turbulent flow, numerical method
  • S. Eswaramoorthi, S. Sivasankaran *, S. Rajan, Ali Saleh Alshomrani, M. Bhuvaneswari Pages 1350-1357
    The effects of viscous dissipation and convective boundary condition on the two-dimensional convective flow of a second grade liquid over a stretchable surface with suction/injection and heat generation are investigated. The governing partial differential equations are reduced into a dimensionless coupled system of nonlinear ordinary differential equations by appropriate similarity transformation. Then, they are solved analyticallyby homotopy analysis method (HAM) and by numerically with fourth order Runge-Kutta method with shooting technique. The HAM and numerical results of the local skin friction and local Nusselt number are compared for various emerging parameters. It is found that the momentum boundary layer thickness grows with rising the values of the viscoelastic parameter.
    Keywords: second grade fluid, convective boundary, heat generation, suction, injection, viscous dissipation
  • Navid Asmari Saadabad, Hamed Moradi *, Gholamreza Vossoughi Pages 1358-1377
    Due to flexibility of thin plates, high amplitude vibrations are observed when they are subjected to severe dynamic loads. Due to the extensive application of circular plates in industry, attenuating the undesired vibrations is of foremost importance. In this paper, adaptable vibration suppressors (AVSs) as a semi-active control approach, are utilized to suppress the vibrations in a free circular plate; under the concentrative harmonic excitation. Using mode summation method, mathematical model of the hybrid system, including the plate and an arbitrary number of vibration suppressors is analyzed. By developing a complex multiple-loops algorithm, optimum values for the AVSs’ parameters (stiffness and position) are achieved such that the plate deflection is comprehensively minimized. According to the results, AVSs act efficiently in suppressing the vibrations in resonance/non-resonance conditions. It is also observed that optimum AVSs reduce the plate deflection over a broad spectrum of excitation frequencies. Finally, since the algorithm is developed in a general user friendly style, AVSs’ design can be extended to other shapes of plates with various boundary conditions and excitations.
    Keywords: Circular plates, Adaptable vibration suppressor, Semi-active control, Advanced algorithm, Optimal design
  • Himayat Ullah, Baseer Ullah *, Abdul Rauf, Riaz Muhammad Pages 1378-1387
    Shot peening is one of the surface treatment processes usually used for the improvement of fatigue strength of metallic parts by inducing residual stress field in them. The evaluation of shot peening parameters experimentally is not only very complex but costly as well. An attractive alternative is the explicit dynamics finite element (FE) analysis having the capability of accurately envisaging the shot peening process parameters using a suitable material’s constitutive model and numerical technique. In this study, ANSYS/LS-DYNA software was used to simulate the impact of steel shots of various sizes on 2618-T61 aluminium alloy plate described with strain rate dependent elasto-plastic material model. The impacts were carried out at various incident velocities. The effect of shot velocity and size on the induced compressive residual stress and plastic deformation were investigated. The results demonstrated that increasing the shot velocity and size yielded in an increase in plastic deformation of the aluminium target. However, as observed, the effect of shot velocity and size was small in magnitude on the target's subsurface compressive residual stress.
    Keywords: Surface treatment, Finite Element Analysis, Residual stress, Plastic deformation
  • Abd Elnaby Kabeel *, Mofreh.H. Hamed, Zm Omara, A.W. Kandeal Pages 1388-1399
    The performance of a flat plate single-pass solar air heater (SAH) modified at the entrance region of the heater was experimentally investigated. The entrance region was covered with glass cover instead of steel cover. The aim of using glass at the entrance region is increasing the heating area exposed to solar irradiation. In addition, replacing the steel cover with glass reduces the shading effect occurred due to steel which decreases the temperature of the surface of the absorber and hence the outlet temperature of the air. Also, guide blades were placed in the entry region to ensure well air distribution on the absorber surface and hence enhancing the thermal performance of SAH. The modified SAH was compared with another one without air blades and without glass cover at the entrance. The experiments were performed at four air flow rates ranged from 0.013 kg/sec to 0.04 kg/sec. The modifications led to good enhancement in both the air temperature difference and the efficiency. The glazed-bladed SAH showed a good improvement in the daily thermal efficiency by 6.72 % to 10.5 % over the conventional heater and by 2.16 % to 3.25 % over the glazed SAH.
    Keywords: Single-pass solar air heater, Entrance region, Thermal efficiency, Air flow rate, Air distribution, Guide blades
  • M. Kurtulmu * Pages 1400-1404
    A-TIG welding is a welding method in which TIG welding is conducted by covering a thin layer of activating flux on the weld bead beforehand. The most benefit of this process is the gain in weld penetration depth. A-TIG welds were produced on mild steel plates with TiO2 flux. The emphasis of this paper lies in introducing the effects of various process parameters (welding current, welding speed, powder/acetone ratio of the flux, arc length and electrode angle) in mild steel A-TIG welding. The weld penetration depth was the measured metallographically. An optimum value was determined for each welding parameter.
    Keywords: A-TIG welding parameters, Mild steel A-TIG welding, A-TIG flux, A-TIG flux solvent, A-TIG flux compositions
  • Mohsen Sheikholeslami, D. D.Ganji *, Zhixiong Li, R. Hosseinnejad Pages 1405-1414
    Electrohydrodynamic Fe3O4- Ethylene glycol nanofluid forced convection is simulated in existence of thermal radiation. The porous lid driven cavity has one moving positive electrode. Single phase model has been applied to simulate nanofluid behavior. Control Volume based Finite Element Method is employed to obtain the results which are the roles of Darcy number , radiation parameter , Reynolds number , nanofluid volume fraction and supplied voltage . Results depict that maximum values for temperature gradient is obtained for platelet shape nanoparticles. Nusselt number enhances with rise of Darcy number and supplied voltage. Convection mode enhances with increase of permeability of porous media and nanofluid volume fraction but it decreases with rise of Hartmann number.
    Keywords: Electric field, Shape of nanoparticles, Nanofluid, porous media, thermal radiation
  • Nikolay Dudak, Galiya Itybaeva, Asylbek Kasenov *, Zhanara Mussina, Aizhan Taskarina, Kairatolla Abishev Pages 1415-1426
    This paper deals with hole-enlarging multiflute drill processing. The analysis of existing structures, their advantages and disadvantages is carried out. Cutting conditions during hole-enlarging multiflute drill processing are shown. A new design of hole-enlarging multiflute drill as a hole-enlarging multiflute drill-broaching tool from broaching-speed steel with carbide plates, as well as a new way of handling the new tools is offered. Hole-enlarging multiflute drill-broaching combines the features of hole-enlarging multiflute drill (in cross section) and the features of broaching tool (in longitudinal section). In this way, it was possible to increase the quality of hole making (size variance, surface roughness), to facilitate the cutting conditions and to increase the durability. The results of prototypes testing are presented.
    Keywords: multiflute drill processing, the quality of hole making, hole enlarging, hole surface microstructure
  • Reza Masoudi Nejad, Mahmoud Shariati *, Khalil Farhangdoost, Amir Atrian Pages 1427-1437
    This study aims to analyze the rolling contact fatigue influenced by residual stresses caused by the contact of the wheel and rail and its manufacturing process. For this purpose, a rail available in Iran railway is used with an exact profile geometry. The location of maximum stress caused by the contact of wheel/rail for rail profiles can be calculated by three-dimensional elastic-plastic finite element model. Then, in order to estimate the stress distribution caused by rail manufacturing process, a thermal analysis with finite element method will be performed. Afterwards, the results of performed stress analysis will be used as input for three-dimensional crack growth and rail fatigue life estimation model to calculate the stress intensity factors and fatigue life according to the set of related parameters with boundary element method. Finally, three-dimensional finite element analysis results obtained show good agreement with those achieved in field measurements.
    Keywords: Rolling contact fatigue, Manufacturing process, Finite Element, Fatigue crack growth, Boundary element
  • Somaye Yaghoubi *, Ebrahim Shirani, Ahmad Reza Pishevar Pages 1438-1445
    In this paper, flow past a single Dissipative Particle Dynamics (DPD) particle with low Reynolds number is investigated and it is inquired that whether a single DPD particle immersed in a fluid, has an intrinsic size. Then a minimum length scale is determined such that the hydrodynamic behavior based on standard DPD formulation is modeled correctly. Almost all of the previous studies assume the DPD particles as point centers of repulsion with no intrinsic size. Hence to prescribe the size of a simulating sphere, a structure of frozen DPD particles is created. In this paper two effective radii, Stokes-Einstein radius and a radius based on the Stokes law, for DPD particles are introduced. For small Reynolds numbers; it is proved that the two radii approach each other. Finally in spite of the typical simulations which assume DPD particles as point centers of repulsion, it is concluded that each of the individual DPD particles interact with other particles as a sphere with non-zero radius. It results the reduction of the required number of particles and eventuates more economical simulations. Moreover contemplating the radius of the particles is necessary for the new Low-Dimensional model which is derived based on the DPD method.
    Keywords: Dissipative Particle Dynamics, Low-Dimensional model, Low Reynolds number, Stokes-Einstein equation