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    An investigation on the effects of gas pressure drop in heat exchangers on dynamics of a free piston stirling engine

    , Article International Journal of Engineering, Transactions B: Applications ; Volume 30, Issue 2 , 2017 , Pages 1243-1252 ; 1728144X (ISSN) Zare, S ; Tavakolpour Saleh, A. R ; Aghajanzadeh, O ; Sharif University of Technology
    Materials and Energy Research Center  2017
    This paper is devoted to study the effects of pressure drop in heat exchangers on the dynamics of a free piston Stirling engine. First, the dynamic equations governing the pistons as well as the gas pressure equations for hot and cold spaces of the engine are extracted. Then, by substituting the obtained pressure equations into the dynamic relationships the final nonlinear dynamic equations governing the free piston Stirling engine are acquired. Next, effects of the gas pressure drop in heat exchangers on maximum strokes of the pistons and their velocities and accelerations are investigated. Furthermore, influences of pressure drop increase in the heat exchangers on maximum and minimum gas... 

    A novel revolving piston minipump

    , Article Sensors and Actuators, B: Chemical ; Volume 218 , October , 2015 , Pages 237-244 ; 09254005 (ISSN) Ashouri, M ; Shafii, M. B ; Moosavi, A ; Amiri Hezave, H ; Sharif University of Technology
    Elsevier  2015
    In this study, a novel prototype high-efficiency miniature pump that uses magnetic properties of a ferrofluid in both pumping and valving mechanisms is presented. The minichannel consisting of a cylindrical pumping chamber, a check valve, an inlet and an outlet, comprises six bonded layers of PMMA. A cylindrical permanent magnet that is placed inside the chamber and is externally actuated by a motorized off-center permanent magnet, functions as a revolving piston which sweeps the perimeter of the cylinder. Ferrofluid is used to cover the gaps between the magnetic piston and the channel walls, also serves as a separating plug between the inlet and the outlet of the chamber preventing... 

    Evaluation and Simulation of Tunnel Mid-shaft Effects on the Natural and Normal Ventilation Performance in a Subway Tunnel

    , M.Sc. Thesis Sharif University of Technology Mahmoodi, Ghasem (Author) ; Farhanieh, Bijan (Supervisor)
    Necessity of a public transport network, environmental protection and a highly land cost in urban areas have increased the desire for underground transportation systems. On the other hand, ventilation system design should be done precisely specially for longer tunnels, large undergrounds spaces and crowded places. Rate of energy reduction for vent systems operation is dependent on their proper implementation. Tunnel design efficiently is influenced by ventilation system. The tunnel mid shaft is complementary part of the underground railway systems that is required for exchange air between the tunnel and the railway station with ambient fresh air. An important application of the tunnel mid... 

    The Effect of Cobalt on Thermal Expansion and Metallurgical Properties of LM13 Alloy

    , M.Sc. Thesis Sharif University of Technology Ejlali, Saeed (Author) ; Varahram, Naser (Supervisor)
    LM13 Aluminum alloys contain Silicon, Copper, magnesium and Nickel. This alloys have been widely used in automobile pistons. For this application thermal expansion coefficient is one important characteristics other than mechanical properties. In this project replacing Cobalt with Nickel to improve alloy thermal and mechanical properties in piston applications by different cobalt contents. Cobalt contents is 0, 0.15, 0.55 and 0.77 Wt%. Because of oxidation magnesium content decrease into 0.98, 0.74, 0.61 and 0.48 Wt%. Thermal expansion coefficient and UTS first increase and after 0.55 Cobalt Wt% show decrease But yield strength and hardness increase as cobalt content increase. Microscopic... 

    Modeling and NVH Analysis of a Four-Cylinder Gasoline Engine and Providing a way to Reduce it

    , M.Sc. Thesis Sharif University of Technology Khorshidi, Mohammad (Author) ; Saadat Foumani, Mahmoud (Supervisor)
    Millions of people are exposed to noise every day in their work and life, and their physical and mental health is at risk due to this issue. Hence, the issue of noise and vibration has become an important factor in car quality. One of the sources of noise and vibration in the vehicle is the engine. The engine is the heart of the car and its most important part. Therefore, reducing Engine noise can have a significant effect on the noise emitted by the vehicle. Engine noise can be divided into three categories: 1 - combustion noise 2 - mechanical noise 3 - aerodynamic noise. This project is in line with a project defined between the university and industry aimed at improving all sources of... 

    Identification Dynamic Modeling and Analysis of a Variable Displacement Axial Piston Pump

    , M.Sc. Thesis Sharif University of Technology Pooyafar, Payam (Author) ; Salarieh, Hassan (Supervisor)
    According to high nominal pressure and controllable flow, variable displacement axial piston pumps are used widely in hydraulic industry. However, there still exist many problems and limitations in the areas of design, controllers and performance. To solve the problems without wasting time and money in making prototypes, an accurate dynamic model of the pump is required which predicts pump behavior under various control signals and loads. The lack of simple and practical methods of measuring describing parameters of pump dynamics, makes investigation and verification of such a model very challenging. In this thesis, literature review is presented in a wide range. After investigating of... 

    Diffuser miniature pump with an extra ferrofluidic valve

    , Article Microfluidics and Nanofluidics ; Volume 19, Issue 5 , November , 2015 , Pages 1235-1244 ; 16134982 (ISSN) Ashouri, M ; Shafii, M. B ; Moosavi, A ; Sharif University of Technology
    Springer Verlag  2015
    This paper presents the prototype design and fabrication of a magnetically actuated miniature pump that utilizes self-sealing capability of ferrofluid-covered permanent magnets in both pumping and valving mechanisms. The valving action is performed by employing one active valve along with two nozzle/diffuser elements. Two cylindrical permanent magnets are placed inside the flat-wall channels: One magnet acts as the active valve and the other one serves as a reciprocating piston actuating the working fluid. In order to seal the gaps between the channel walls and the permanent magnet of the valve/piston, ferrofluid is used to cover the surfaces of both magnets. The valve and the piston are... 

    Design and construction of a two-phase fluid piston engine based on the structure of fluidyne

    , Article Energy ; Volume 127 , 2017 , Pages 660-670 ; 03605442 (ISSN) Moazami Goudarzi, H ; Yarahmadi, M ; Shafii, M. B ; Sharif University of Technology
    Elsevier Ltd  2017
    Engines that extract energy from low-grade heat sources, e.g., from other processes, have received considerable attention recently. The use of Fluidyne, which is a liquid piston Stirling engine, is quite popular. Herein, we explore the use of liquid-to-vapor phase change in a Fluidyne. This provides two considerable differentiators; (1) exploitation of very low temperature difference ΔT≈30 K, and (2) relatively low temperature ΔT≈330 K heat sources, for producing mechanical work, and thus electrical energy. The influence of three operating parameters, i.e., input heat flux, working fluid, and filling ratio, on the performance of the engine was characterized. Their optimum values, which yield... 

    On the nonlinear dynamic responses of FG-CNTRC beams exposed to aerothermal loads using third-order piston theory

    , Article Acta Mechanica ; Volume 229, Issue 6 , 2018 , Pages 2413-2430 ; 00015970 (ISSN) Asadi, H ; Rabiei Beheshti, A ; Sharif University of Technology
    Springer-Verlag Wien  2018
    The purpose of this study is to analyze the nonlinear dynamic responses of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beams exposed to axial supersonic airflow in thermal environments. The dynamic model of the FG-CNTRC beam is developed with regard to the first-order shear deformation theory incorporating the von Kármán geometrical nonlinearity. The thermomechanical properties of the constituents are assumed to be temperature dependent. The third-order piston theory is adopted to estimate the nonlinear aerodynamic pressure induced by the supersonic airflow. Harmonic differential quadrature method is implemented to discretize the equations of motion in the spatial... 

    Effect of casting process on microstructure and tribological behavior of LM13 alloy

    , Article Journal of Alloys and Compounds ; Volume 475, Issue 1-2 , 2009 , Pages 321-327 ; 09258388 (ISSN) Ashiri, R ; Niroumand, B ; Karimzadeh, F ; Hamani, M ; Pouranvari, M ; Sharif University of Technology
    LM13 alloy is widely used in piston industry, due to its low coefficient of thermal expansion, excellent castability and hot tear resistance. In this research effect of casting process on wear behavior of LM13 alloy was investigated. First, samples were produced using two casting processes and heat treated. Then wear behavior of these samples under dry sliding condition was examined. Results of hardness and strength tests indicated that squeeze cast specimens exhibited higher mechanical properties. Wear experiment results showed that in both squeeze and gravity cast specimens, amount of weight loss increases with increase in sliding distance which is accompanied by reduction in wear rate and... 

    Investigating Effect of Nano Ceramic Coating of Combustion Chamber on the Performance of Internal Combustion Engines

    , M.Sc. Thesis Sharif University of Technology Sharifi, Masoud (Author) ; Naghdabadi, Reza (Supervisor)
    Thermal barrier coatings (TBCs) are used for increasing the efficiency and reducing pollutants of internal combustion engines (ICEs). In this paper, an optimization framework is developed in order to obtain the optimal dimensions for conventional coat, and the optimal dimensions and material property for functionally graded (FG) coat of a partially coated piston. A thermo mechanical analysis is investigated for Nano coat by finite element method. The conventional and Nano coats are made of MgZrO_3 as the insulating ceramic overlay and NiCrAl as the metallic bond-coat. The properties of the FG coat is assumed to vary according to power law through the thickness. For all tree conventional, FG... 

    Aeroelastic Topology Optimization of a Supersonic Wing

    , M.Sc. Thesis Sharif University of Technology Same, Hossein (Author) ; Hadadpour, Hassan (Supervisor) ; Dehghani Firouzabadi, Rouhollah (Supervisor) ; Noorian, Mohammad Ali (Co-Advisor)
    A series of algorithms developed for performing aeroelastic topology optimization applying stress constraint on a three dimentional structure of a supersonic wing. The structure modeled using finite element method by three dimentional solid hexahedron elements. Bi-directional evolutionary structural optimization method used for developing optimization algorithms. In order to apply supersonic aerodynamic loading and developing aeroelastic model algorithms, the piston aerodynamic theory utilized. In order to apply static pressure loading, the maximum angle of attack of the wing performance is proposed. Using developed MATLAB code by modeling and meshing wing structure in ABAQUS a software... 

    Aeroelastic Analysis of Sandwich Plates with Viscoelastic Core and Functionally Graded Materials in Supersonic Flow

    , M.Sc. Thesis Sharif University of Technology Gholamalizadeh, Vajiheh (Author) ; Haddadpour, Hassan (Supervisor)
    This study investigates the aeroelastic instability of functionally graded sandwich plate with viscoelastic core in supersonic airflow. The classical plate theory, first order shear deformation theory, Hamilton's principle and linear first-order piston theory have been employed to extract the governing equations of motion of the structure. The Ritz method and State space notation is used to solve the derived equations and identify the instability boundary of the sandwich plate with simply-supported boundary conditions. The derived are solved using a computer program which is validated and verified by comparing the results with available literature. Our attention is focused on analyzing the... 

    Design, Analysis and Prototyping of Cylindrical Electropump with Radial Space Limit

    , M.Sc. Thesis Sharif University of Technology Modarressi, Vala (Author) ; Arghavani Hadi, Jamal (Supervisor)
    Inflatable packers are a class of downhole equipments that are used for oilwell pluging operations. To set the packer inside the well, it is necessary to apply hydraulic pressure to it. By using the setting tool and installing an electropump in it, it is possible to transfer the fluid into the packer and supply the required pressure. In this research, an electropump has been designed and built that, firstly, is dimensionally suitable for the conditions of oil wells and, secondly, can have a good performance in the environmental conditions inside the well. This electropump, which can be used in a 2.125-inch setting tool, consists of a brushless direct current motor and a piston pump. To test... 

    Molecular dynamics simulation of orientation dependency in the shock-induced phase transition of C60 fullerene single crystals into amorphous diamond

    , Article Phase Transitions ; Vol. 87, Issue. 3 , 2014 , Pages 271-285 ; ISSN: 01411594 Mahnama, M ; Naghdabadi, R ; Sharif University of Technology
    A molecular dynamics simulation of the shock-wave propagation in the face-centered cubic (FCC) structured C60 fullerene along the <100>, <110> and <111> crystallographic directions is performed. For this purpose, the response of the material under different shock-wave loadings is studied through Hugoniot curves. Three regimes of the material behavior have been observed from fully elastic to elastic-plastic to plastic. The Hugoniot elastic limit and the phase transition are also investigated along different crystallographic directions. It is shown that the shock wave travels faster along the <110> and <111> directions than in the <100> direction in the material. Comparing the results with the... 

    Investigation of switching time and pressure head effects on hydro magnetic micro-pump and flow controller

    , Article 2008 Proceedings of the ASME Fluids Engineering Division Summer Conference, FEDSM 2008, 10 August 2008 through 14 August 2008, Jacksonville, FL ; Volume 2 , 2009 , Pages 463-470 ; 9780791848418 (ISBN) Esmaily Moghadam, M ; Shafii, M. B ; Fluids Engineering Division, ASME ; Sharif University of Technology
    The significant importance of micro-scaled devices in medicine, lab-on-a-chip, and etc resulted in a vast variety of researches. The idea behind the novel hydro magnetic micro-pump and flow controller is that ferromagnetic particles, mixed and dispersed in a carrier fluid, can be accumulated and retained at specific sites to form pistons in a micro-tube using some external magnetic field sources along the micro-tube. This external magnetic field is related to some solenoids, which are turned on and off alternatively. Depending upon dragging speed of these pistons, which itself is a function of switching time, this device can be used to either increase (pumping) or decrease (valving) the flow... 

    Experimental and numerical evaluation of piston metallic damper (PMD)

    , Article Journal of Constructional Steel Research ; Volume 154 , 2019 , Pages 99-109 ; 0143974X (ISSN) Jarrah, M ; Khezrzadeh, H ; Mofid, M ; Jafari, K ; Sharif University of Technology
    Elsevier Ltd  2019
    In this paper, a metallic yielding damper, called piston metallic damper (PMD) is introduced for the first time. The PMD is comprised of a set of parallel hollow circular plates that interconnect inner shaft of the PMD to its outer pipe. Experiments and numerical models are used to examine its applicability as a seismic energy dissipating device. In this novel damper seismic input energy will be dissipated through flexural yielding of circular steel plates when system experiences small to medium displacements. At large displacements, tensile behavior will dominate and causes significant increase in stiffness of the system. In experimental program, different specimens were tested and the... 

    Aero-thermoelastic stability of functionally graded plates

    , Article Composite Structures ; Volume 80, Issue 4 , 2007 , Pages 580-587 ; 02638223 (ISSN) Navazi, H. M ; Haddadpour, H ; Sharif University of Technology
    In this paper, an analytical investigation intended to determine the aero-thermoelastic stability margins of functionally graded panels is carried out. For this purpose, piston theory aerodynamics has been employed to model quasi-steady aerodynamic loading. The material properties of the plate are assumed to be graded continuously across the panel thickness. A simple power-law and the Mori-Tanaka scheme are used for estimating the effective material properties such as temperature-dependent thermoelastic properties. The effects of compressive in-plane loads and both uniform and through the thickness non-linear temperature distributions are also considered. Hamilton's principle is used to... 

    Nonlinear oscillations of a fluttering functionally graded plate

    , Article Composite Structures ; Volume 79, Issue 2 , 2007 , Pages 242-250 ; 02638223 (ISSN) Haddadpour, H ; Navazi, H. M ; Shadmehri, F ; Sharif University of Technology
    In this paper, the nonlinear aeroelastic behavior of functionally graded plates is studied in supersonic flow. For this purpose, the von Karman strains and piston theory have been employed to model structural nonlinearity and quasi-steady aerodynamic panel loading, respectively. The material properties of the plate are assumed to be graded continuously in the direction of thickness. The variation of the properties follows a simple power-law distribution in terms of the volume fractions of constituents. The Hamilton's principle is used to construct the coupled nonlinear partial differential equations of motion. The derived equations are transformed into a set of coupled ordinary differential... 

    Applicability of the FSEM for analyzing wire flat rolling process

    , Article Engineering Computations (Swansea, Wales) ; Volume 23, Issue 5 , 2006 , Pages 515-524 ; 02644401 (ISSN) Kazeminezhad, M ; Taheri, A. K ; Sharif University of Technology
    Purpose - The purpose of this paper is to present an assessment of the ability of combined finite and slab element method (FSEM) for analyzing the wire flat rolling process. Design/methodology/approach - Using the FSEM, the effective strain field of flat rolled wire is predicted for different reductions in height and frictional conditions. The validity of the method is assessed by performing the Vickers microhardness measurements on the flattened wire cross section. Also, the creation of macroscopic shear bands in cross section of the flat rolled wire is investigated and confirmed by microhardness and metallographic examinations. Moreover, the lateral spread and width of contact area are...