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    Developing a Method for Fatigue Life Assessment of Vehicle Biw by Considering Spot Welding Connections

    , M.Sc. Thesis Sharif University of Technology Ahmadi, Alireza (Author) ; Farrahi, Gholamhossein (Supervisor) ; Chizari, Mahmoud (Supervisor) ; Reza Kashyzadeh, Kazem (Co-Supervisor)
    One of the most important considerations in the vehicle design procedure is the durability of the components. Among different parts of a vehicle, the body is the main load-bearing component and as a result, its durability is critical. Due to the expensive and time-consuming nature of fatigue tests, finite element based durability analysis is of great interest among automotive industry. The aim of this research is to provide an algorithm for a more accurate and efficient durability analysis of the vehicle body by considering inertia effects. By using the multi-body dynamics model of the full vehicle and the finite element model of the vehicle body, the vehicle body structure is analyzed from... 

    Effect of Different Defects of Spot Welded Joint in Automotive Body on Fatigue Strength: Experimental and Numerical Investigation

    , M.Sc. Thesis Sharif University of Technology Ganjabi, Mohammad Amin (Author) ; Farrahi, Gholamhossein (Supervisor) ; Mehmanparast, Ali (Supervisor) ; Reza Kashyzadeh, Kazem (Co-Supervisor)
    On average there are to resistance spot welding connections per vehicle. The quality of these welding directly affects the quality of the finished product and the strength of the vehicle against various loads, including road roughness, different maneuvers and even sudden impacts from accidents. During the spot welding process, unintentional failures occur due to the wrong choice of current, force and time. The aim of this study is to investigate the fatigue strength of three-sheets welding joints in numerical and laboratory methods, considering the defects of (Undersize weld, Stick, edge of sheet metal and Edge of sheet metal-SECANT) . For this purpose, a healthy spot welding model was first... 

    Experimental and numerical investigation of drag force over tubular frustum

    , Article Scientia Iranica ; Volume 18, Issue 5 , 2011 , Pages 1133-1137 ; 10263098 (ISSN) Niknafs Abrebekooh, Y ; Rad, M ; Sharif University of Technology
    There are different ways in order to achieve higher velocity in underwater vehicles. One of these methods is using a body with special form. This paper presents a towing tank based experimental study on drag forces for different Reynolds Numbers of a special underwater model. This paper investigates drag force and drag coefficient in a different flow direction over the model. Obtained experimental results in towing tank are explained. Computational Fluid Dynamic (CFD) simulation also is performed using commercial CFD software package FLUENT 6.3.26. There is a significant decrease in drag coefficient of model moving with small diameter at upstream  

    Aeroelastic behavior of a slender body considering free fittings

    , Article Journal of Mechanical Science and Technology ; Volume 24, Issue 9 , 2010 , Pages 1755-1762 ; 1738494X (ISSN) Ehramianpour, M ; Haddadpour, H ; Ahmadian, M. T ; Sharif University of Technology
    This paper presents dynamic and vibration analysis of a flight vehicle with consideration of the free fitting between its two sections. Using the Lagrangian approach, a general analytical model is developed for a non-spinning elastic vehicle in planar motion. The model contains rigid body motions and bending deformations of two sections of the flight vehicle and a nonlinear rotational spring that models the freeplay between the two sections. To express bending deformation, the mode summation method is applied. It is shown that freeplay in the joints significantly affects the trajectory of the flight vehicle. Numerical examples reveal the effect of a joint's nonlinearity on the trajectory and... 

    NVH analysis and improvement of a vehicle body structure using DOE method

    , Article Journal of Mechanical Science and Technology ; Volume 23, Issue 11 , 2010 , Pages 2980-2989 ; 1738494X (ISSN) Azadi, S ; Azadi, M ; Zahedi, F ; Sharif University of Technology
    The improvement of a vehicle body structure under the constraint of noise, vibration and harshness (NVH) behavior is investigated by using design of experiments (DOE) method. First, car body geometry is modeled in CATIA and meshed in HYPERMESH software. Then, a modal analysis between 0-50 Hz is done by MSC NASTRAN. A frequency map of the body is extracted and compared with a reference map to identify shortcomings. By using factorial and response surface Methods (RSM), optimization of the NVH performance is accomplished. An algorithm is proposed to improve the car NVH behavior. At last, in order to verify the present algorithm, forced vibration is analyzed under real road inputs for the model... 

    Stability analysis of elastic launch vehicles with fuel sloshing in planar flight using a BEM-FEM model

    , Article Aerospace Science and Technology ; Volume 53 , 2016 , Pages 74-84 ; 12709638 (ISSN) Noorian, M. A ; Haddadpour, H ; Ebrahimian, M ; Sharif University of Technology
    Elsevier Masson SAS  2016
    A numerical model is developed for investigation of coupled dynamics of fuel contained elastic launch vehicles in planar atmospheric flight. Finite element method along with the linear quasi-steady piston aerodynamic theory is used for developing an aeroelastic model. A reduced order boundary element model is used for modeling the liquid sloshing in tanks. The interaction of sloshing and aeroelasticity is studied using stability analysis of the coupled system. Results show that the slosh-aeroelastic coupling in an elastic launch vehicle occurs for low tank filling ratios and may lead to decreasing the system damping. Due to more interactions between the slosh and rigid body modes, larger... 

    Biomechanical simulation of eye-airbag impacts during vehicle accidents

    , Article Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine ; Volume 232, Issue 7 , 2018 , Pages 699-707 ; 09544119 (ISSN) Shirzadi, H ; Zohoor, H ; Naserkhaki, S ; Sharif University of Technology
    SAGE Publications Ltd  2018
    Airbags are safety devices in vehicles effectively suppressing passengers’ injuries during accidents. Although there are still many cases of eye injuries reported due to eye-airbag impacts in recent years. Biomechanical approaches are now feasible and can considerably help experts to investigate the issue without ethical concerns. The eye-airbag impact–induced stresses/strains in various components of the eye were found to investigate the risk of injury in different conditions (impact velocity and airbag pressure). Three-dimensional geometry of the eyeball, fat and bony socket as well as the airbag were developed and meshed to develop a finite element model. Nonlinear material properties of... 

    A comparative study on the fatigue life of the vehicle body spot welds using different numerical techniques: Inertia relief and modal dynamic analyses

    , Article Frattura ed Integrita Strutturale ; Volume 14, Issue 52 , 2020 , Pages 67-81 Ahmadi, A ; Farrahi, G. H ; Kashyzadeh, K. R ; Azadi, S ; Jahani, K ; Sharif University of Technology
    Gruppo Italiano Frattura  2020
    Owing to the expensive and time-consuming nature of durability experiments, finite element based durability analysis is quite prevalent in the automotive industry. Numerical fatigue life analyses are typically divided into two different categories, the quasi-static methods which are faster and the dynamic methods which are more accurate. The aim of this paper is to compare the inertia relief and modal dynamic approaches in terms of formulation, accuracy and computation time. The chosen case study is the fatigue life of the vehicle body which is considered the main load-bearing component in a vehicle. By utilizing multi-body dynamics model and driving the vehicle on different standardized... 

    Toward design and fabrication of wind-driven vehicles: Procedure to optimize the threshold of driving forces

    , Article Applied Mathematical Modelling ; Volume 37, Issue 1-2 , 2013 , Pages 50-61 ; 0307904X (ISSN) Mirzaei, P. A ; Rad, M ; Sharif University of Technology
    Wind energy has been continuously considered as a green, available, and economical alternative source of energy. For centuries, the transformed wind energy to drag-force has been used for transportation in watercrafts. With improvement of aerodynamics, the airfoil was invented to create and use a higher magnitude aerodynamic force, lift-force, in order to elevate airplanes. Later, the lift-force was horizontally applied as the thrust force in land/water wind-crafts. Whereas in airplanes horizontal airfoils (wing) create a vertical lift-force, installed vertical airfoils (wing-sail) produce a horizontal lift-force in wind-crafts. Therefore, this force can be used as thrust (driving) force in... 

    Mechanical characteristics improvement of spot-welded dissimilar steels in different thickness

    , Article Proc. of the Int. Conf. on Advances in Welding Science and Technology for Construction, Energy and Transportation, AWST 2010, held in Conj. with the 63rd Annual Assembly of IIW 2010, 11 July 2010 through 17 July 2010, Istanbul ; 2010 , Pages 803-810 ; 9786056141911 (ISBN) Farhangdoust, S ; Kokabi, A. H ; Adineh, A ; Mansourzadeh, S. A ; Ghasemzadeh, H ; Ardakani, R. T ; Sharif University of Technology
    Resistance spot welding of dissimilar materials especially in different thickness is generally more challenging than that of similar materials due to differences in the physical, chemical and mechanical properties of the base metals. And also when the part is under static and dynamic forces the health of spot-welds is crucial. Hence, the influence of welding parameters such as current, time, applied force and hold time on the shear-tensile load has been investigated in this study. Moreover, in this research the case study is one of the most important body parts of the vehicle which is front wheel house, and effect of above-mentioned parameter on the strength of spot-welds has been... 

    Semi analytical prediction of automobile body temperature distribution in the top coat paint oven

    , Article Proceedings of the ASME Summer Heat Transfer Conference 2009, HT2009, 19 July 2009 through 23 July 2009 ; Volume 3 , 2009 , Pages 655-660 ; 9780791843581 (ISBN) Hanafizadeh, P ; Sajadi, B ; Saidi, M. H ; Khalkhali, H ; Taherraftar, M ; Sharif University of Technology
    Automotive industry frequently needs to test new products, according to different production parameters, in order to determine the actual thermal behavior of bodies before mass production is implemented. Numerical simulation of these processes can reduce the very expensive and time consuming experimental procedures. For the drying and hardening process of the top paint applied in the coating process, the body temperature must be raised according to the paint manufacturer regulations. Consequently, prediction of temperature distribution of the car body during various zones of ovens is very vital in the design and performance analysis of the paint dryers. In this research, a novel... 

    Modeling and validation of a detailed FE viscoelastic lumbar spine model for vehicle occupant dummies

    , Article Computers in Biology and Medicine ; Volume 99 , 2018 , Pages 191-200 ; 00104825 (ISSN) Amiri, S ; Naserkhaki, S ; Parnianpour, M ; Sharif University of Technology
    Elsevier Ltd  2018
    The dummies currently used for predicting vehicle occupant response during frontal crashes or whole-body vibration provide insufficient information about spinal loads. Although they aptly approximate upper-body rotations in different loading scenarios, they overlook spinal loads, which are crucial to injury assessment. This paper aims to develop a modified dummy finite element (FE) model with a detailed viscoelastic lumbar spine. This model has been developed and validated against in-vitro and in-silico data under different loading conditions, and its predicted ranges of motion (RoM) and intradiscal pressure (IDP) maintain close correspondence with the in-vitro data. The dominant frequency... 

    Experimental and analytical studies on the prediction of forming limit diagrams

    , Article Computational Materials Science ; Volume 44, Issue 4 , 2009 , Pages 1252-1257 ; 09270256 (ISSN) Ahmadi, S ; Eivani, A. R ; Akbarzadeh, A ; Sharif University of Technology
    Metal forming processes are widely used in industrial productions, automobile bodies, food industries, oil refineries, and liquid and gas transmission systems. Analyzing these processes is very important to reduce wastes and optimize the processes. Study of some main factors such as physical and mechanical properties of material and its formability, die geometry, die material, lubrication and pressing speed has been the topic of many research projects. In this paper, forming limit diagrams (FLDs) for LC and ULC steels and the effect of different parameters like the work-hardening exponent, n, and the plastic strain ratio, r, on these diagrams have been evaluated and simulated using... 

    Effect of whole-body vibration and sitting configurations on lumbar spinal loads of vehicle occupants

    , Article Computers in Biology and Medicine ; Volume 107 , 2019 , Pages 292-301 ; 00104825 (ISSN) Amiri, S ; Naserkhaki, S ; Parnianpour, M ; Sharif University of Technology
    Elsevier Ltd  2019
    Whole-body vibration (WBV) has been identified as one of the serious risk factors leading to spinal disorders, particularly in professional drivers. Although the influential factors in this area have been investigated epidemiologically, finite element (FE) modeling can efficiently help us better understand the problem. In this study, a modified HYBRID III dummy FE model which was enhanced by detailed viscoelastic discs in the lumbar region was utilized to simulate the effect of WBV on lumbar spine loads. Spinal responses to the vertical sinusoidal vibrations of a generic seat were obtained and spinal injury risk factors were calculated. Effects of variation of excitation frequencies, three...