# مقالههای Ahmadian

**توجه:**محتویات این صفحه به صورت خودکار پردازش شده و مقالههای نویسندگانی با تشابه اسمی، همگی در بخش یکسان نمایش داده میشوند.

##### ۱IDENTIFICATION OF NONLINEAR INTERFACE MODELS

اطلاعات انتشار:
سیزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۴

تعداد صفحات:
۶

A nonlinear model for joints interfaces is proposed capable of representing the dominant physics involved in a mechanical joint such as micro\macro slip. The joint interface is modelled using a combination of linear and cubic springs. The coefficient of nonlinear spring is assumed to be complex to simulate the softening as well as damping effects of the joint during slipage. An estimate of the response of the structure with the joint under external excitations is obtained using the method of multiple scales. The parameters of the model, i.e. the spring constants are functions of normal and tangential stresses at the joint interface and may be identified by minimizing the difference between the obtained qualitative nonlinear solution and the experimentally measured data.<\div>

##### ۲APPLICATION OF DIFFERENT CONTROL APPROACHES TO THE DESIGN OF SEMI–ACTIVE SUSPENSTION SYSTEMS

اطلاعات انتشار:
سیزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۴

تعداد صفحات:
۸

Design of modern car suspension systems with contradictory limitations on ride comfort and handling is a challenging task. In this paper, Application of different control methods and effect of combining these methods on semi–active suspension systems are examined. Considering a quarter car model, semi–active suspension with Optimal Controller, Fuzzy Controller and Adaptive Optimal Fuzzy Controller (AOFC) is analyzed. Due to the limitation of design methods for non–linear systems, the design of the suspension is done on the base of linear multivariable model. Results of different control approaches are compared. Findings indicate Adaptive Optimal Fuzzy Control leads to smooth ride with optimal amplitude and acceleration transformation, while keeping the holding force at minimum variation.<\div>

##### ۳Dynamic Modeling of Moving Load on a Rail Track with a Visco–Elastic Foundation Using Finite Element Method

اطلاعات انتشار:
سیزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۴

تعداد صفحات:
۷

For many years, motion of moving load on beams has been an interesting subject for researchers. The train running on the rail is an example of moving load on a beam resting the visco–elastic foundation. Most of the simulated models consider only effects of vertical interaction of rail track and wagon systems. They usually ignore the effects of longitudinal forces and bending moments acting on the rail by the wheels due to the wheel interaction with the rail the effects on both longitudinal forces and bending moments on dynamic of the rail resting on visco–elastic foundation are investigated by using finite element method. According to simulated results , by increasing the longitudinal force acting on the rail, longitudinal and vertical displacements of the rail increase. Also, the effects of train speed on longitudinal and vertical direction of the wheel are discussed.<\div>

##### ۴Vibration Analysis of Timoshenko Beam Carrying Non Uniform Partially Distributed Moving Mass Using Mode Summation Method

اطلاعات انتشار:
چهاردهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۵

تعداد صفحات:
۷

vibrational behavior of Timoshenko and Euler–Bernoulli simply supported beams subjected to partially distributed moving mass is analyzed by mode summation method. Numerical results for Timoshenko beam obtained by mode summation method are compared to previous works done based on Finite Difference Method and Discrete Element Method. Good agreement is achieved on examined test problems. Numerical results are also obtained for both Timoshenko and Euler–Bernoulli beams and compared. Effect of the length and velocity of distributed moving mass on the mid–point deflection of Timoshenko beam is investigated<\div>

##### ۵Dynamic Response of an Overhead Cam Valve Train

اطلاعات انتشار:
چهاردهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۵

تعداد صفحات:
۶

This paper presents the dynamic analysis of a complete overhead cam (OHC) type valve train configuration of an internal combustion engine to predict its dynamic response. The valve train model is developed using flexible component approach. Within this approach, each component of the valve train is modeled as an object with the 3D geometry having stiffness, mass, and damping properties. The stiffness properties of the valve train components are calculated using the 3–D finite element model of each component. The dynamic behavior of the valve train is analyzed for the rated speed and over speed of the internal combustion engine to determine the dynamic forces acting in the interface of the valve train components. The results in the form of nodal displacements and valve acceleration are studied to distinguish the occurrence of the jump phenomenon at the rated speed and\or over speed. The model predictions are compared with the experimental observations to insure the validity of the obtained model. Having established the validity of the model, the dynamic forces acting in the interface of the valve train components are estimated which can be used as input for the sustainability analysis of the valve train components at rated and over speeds. The effect of variation in the cam profile on dynamic forces acting on the valve is also studied.<\div>

##### ۶Dynamic Analysis of Non–uniform Cross–Section Beam under Moving Mass Using Finite Element Method

اطلاعات انتشار:
چهاردهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۵

تعداد صفحات:
۹

The analysis of a variable cross–section beam subjected to a moving concentrated force and mass is investigated. Finite element method with cubic Hermitian interpolation functions is used to model the structure based on Euler–Bernoulli beam and Wilson–Ө direct integration method is implemented to solve time dependent equations. Effects of cross–section area variation, boundary conditions, and moving mass inertia on the deflection, natural frequencies and longitudinal stresses of beam are investigated. Results indicates using a beam of parabolically varying thickness with constant mass can decrease maximum deflection and stresses along the beam while increasing natural frequencies of the beam. Effect of moving mass inertia at high velocity of moving load is also investigated and findings indicate effect of inertia is significant at high velocity.<\div>

##### ۷MINIMIZATION OF THE DISCRETIZATION ERROR IN PLANE STRESS ELEMENT FORMULATION BY AN INVERSE METHOD

اطلاعات انتشار:
پانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۶

تعداد صفحات:
۶

Common methods in determination of element mass and stiffness matrices are minimization of the energy function, the residues of the equation of motion and etc. In these methods, by using assumed shape function for element behavior and by minimization of some functions, we can determine the element formulation. Alternatively, we may construct the formulation by using an inverse approach. The purpose of inverse method is minimization of the difference between the numerical (discrete model) and the analytical (continuous model) models. In the inverse method, we

obtain the optimum value of independent parameters for stiffness (and mass) matrix, so that the minimum discretization error accurse. In this paper, it is shown that more accurate models can be obtained by the inverse method, also the relation between inverse method and deformation modes of the element is developed and with the aid of this relation, an optimum model for the rectangular plane stress element is obtained.<\div>

obtain the optimum value of independent parameters for stiffness (and mass) matrix, so that the minimum discretization error accurse. In this paper, it is shown that more accurate models can be obtained by the inverse method, also the relation between inverse method and deformation modes of the element is developed and with the aid of this relation, an optimum model for the rectangular plane stress element is obtained.<\div>

##### ۸OFF LINE MONITORING OF TRACK INDUCED EXCITATION OF CAR BODY USING OPERATIONAL RESPONSES

اطلاعات انتشار:
پانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۶

تعداد صفحات:
۸

There are methods for determination of track induced excitation of a car body and almost in all of them direct responses of the structure on the location of the excitation have to be measured which is not always possible. From another point of view there are some indirect force determination techniques with ability to determine excitation force of a system without measuring direct responses of the excitation point. These methods are called Indirect Force Determination methods. In this study some of the indirect force determination methods are introduced and possibility of applying them on a car body is discussed. Different aspects of problem such as noise contamination of measurements and stability of the problem with their treatments are explained and a suitable method for determination of excitation forces of a car body is proposed. For case study responses of a real car body during operation are recorded using 20 accelerometers mounted on the side panels of the structure. Finite Element model of the car body is used together with its measured responses and track induced excitations between car body and its boogies are reconstructed in three principal x,y and z axes using Transfer Path Analysis.<\div>

##### ۹BACKLASH EFFECT ON SIDEBAND STRUCTURES OF GEAR PAIRS’ VIBRATION SPECTRUM

اطلاعات انتشار:
پانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۶

تعداد صفحات:
۸

A gear pair model including local tooth defects and backlash is considered and its response to parametric excitation is evaluated to include the sideband structures due to local tooth defects. Piecewise–linear and hysteresis formulations are considered for impact forces due to backlash. The response with hysteresis energy dissipation is shown to have a clear and stronger appearance of sideband structures. The model resembles the physical merits of the system and can be used for fault detection exercises with more confidence.<\div>

##### ۱۰DETERMINATION OF THE LOCATION OF AN UNKNOWN CONCENTRATED FORCE

اطلاعات انتشار:
پانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۶

تعداد صفحات:
۷

In this paper a novel method for determination of location of a concentrated force acting on a structure is proposed. The method uses the relations between outputs for identification of the force location. Uniqueness of the predicted location of the force is discussed and a method for appropriate selection of a measurement set is introduced which guarantees the uniqueness of the predicted force location. Eventually three cases of simulation are carried out to exemplify various aspects of the discussion.<\div>

##### ۱۱DESIGN AND ANALYSIS OF A NOVEL PERISTALTIC MICROPUMP

اطلاعات انتشار:
پانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۶

تعداد صفحات:
۶

Micropumps are one of the gravest and versatile outcomes of EMMS technology which have vast applications in industries. In this paper different types of micropumps, their characteristic and usage in precise engineering are presented then a novel design of micropumps with peristaltic motion, actuated with annular piezoelectric cells is introduced and its high efficiency was observed. Behavior and working parameters of mechanical micropumps are also studied.<\div>

##### ۱۲FREE VIBRATION ANALYSIS OF STIFFENED LAMINATED COMPOSITE PLATES UNDER AXIAL LOADS

اطلاعات انتشار:
پانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۶

تعداد صفحات:
۶

In this study‚ the free bending vibration of orthotropic laminated composite plates with stiffeners subjected to axial loads is carried out using first shear deformation theory and finite element method. Effect of axial tension and compression loads on the natural frequencies of the structure is investigated. Adding stiffeners under the plate increases the natural frequency. The displacements are based on C0 –nine plate bending element and each node has three degree of freedom. Effect of both shear deformation and rotary inertia are implemented in the modeling of plate. The equations of motion are derived using Hamilton's principle. Results indicate the tension loads and stiffeners will increase the natural frequency

while the compression loads reduce the natural frequency. The buckling force of plate is computed by increasing the absolute value of ompressive force until the natural frequency tends to zero. Results of simple cases are compared with finding in literature and good agreements were achieved.<\div>

while the compression loads reduce the natural frequency. The buckling force of plate is computed by increasing the absolute value of ompressive force until the natural frequency tends to zero. Results of simple cases are compared with finding in literature and good agreements were achieved.<\div>

##### ۱۳BUCKLING ANALYSIS AND DAMAGE DETECTION OF CRACKED COLUMNS

اطلاعات انتشار:
چهارمین کنگره ملی مهندسی عمران،
سال ۱۳۸۷

تعداد صفحات:
۸

A new method for computation of buckling load of non–uniform cracked columns is presented. The governing equations in the form of differential equations and boundary conditions are derived. The crack is modeled by a mass less rotational spring. Based on the principles of calculus of variations a minimization problem is defined as an alternative for the governing differential equations. Solution of this minimization problem leads to the buckling load and mode shape of the column. The concept of fractal dimension is used for detecting the position and depth of the crack, from the mode shape. Several examples solved and the method is verified.<\div>

##### ۱۴Dynamic pull–in analysis of Circular and Rectangular microplates under the squeeze–film damping effect

اطلاعات انتشار:
شانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۷

تعداد صفحات:
۷

In this paper, effect of squeeze film damping on the Dynamic response of rectangular and circular singlelayer micro plates is studied. To simulate the squeeze film damping effect, squeezed fluid and plate equations are coupled and implemented to the problem. Application of finite element method, first–order shear deformation theory and Reynolds equations are used to model dynamical system. Using finite element method (FEM) dynamic pull–in phenomenon of circular and rectangular micro plates under the actuation of nonlinear electrostatic force andsqueeze film damping is studied. Comparing the results shows these analyses in good agreement with available literatures.<\div>

##### ۱۵Synthesis of submicron alumina powder via a new wet chemical method

اطلاعات انتشار:
پنجمین کنگره بین المللی مهندسی شیمی،
سال ۱۳۸۶

تعداد صفحات:
۷

Basic aluminium sulphate (BAS) was prepared by forced hydrolysis of aluminium salt solution followed by precipitation with a sulphate solution. The BAS powder was transformed into crystalline basic ammonium aluminum carbonate (ammonium dawsonite) by treating BAS with ammonium carbonate solution. FTIR spectroscopy was used for the identification of materials. Submicron α–alumina with mean particle size of 0.23 μm was obtained by heating ammonium dawsonite at 1150°C for 1 h. Phase transformation sequence of ammonium dawsonite was investigated by means of XRD. SEM micrograph confirms formation of submicron powder.<\div>

##### ۱۶Fabrication and Characterization of Multilayer α–Alumina NF Membranes

اطلاعات انتشار:
پنجمین کنگره بین المللی مهندسی شیمی،
سال ۱۳۸۶

تعداد صفحات:
۹

Multilayer ceramic membranes were successfully fabricated via a controlled method. Tubular alumina porous support systems with an open porosity about 48% dip–coating and pore size in the range of 100–600 nm were used as membranes substrate. Submicron and nano alumina powders were used to prepare membranes intermediate and top layers, respectively. The effects of the several parameters on the structural properties of the prepared membranes were studied to get an appropriate pore size and defect–free surface. The morphology and multilayer structure of the final NF membranes were characterized using SEM and optical microscopy (OM). The pore size distribution of multilayer NF membranes was measured by mercury porosimetry (MP).<\div>

##### ۱۷Estimating Total Economic Value of Coral Reefs of Kish Island (Persian Gulf)

اطلاعات انتشار:
International Journal Of Environmental Research،
ششم،شماره۱، Winter ۲۰۱۲،
سال ۰

تعداد صفحات:
۱۰

This paper is concerned with the economic valuation of the coral reef within Kish Island in Persian Gulf of Iran. For calculating this value, all components of use and non–use values are estimated and then according to each of them, suitable method has applied. Many different evaluation tools such as contingent valuation method, zonal travel cost method, replacement cost, avoided cost method, value at risk method are used. The semi non parametric distribution free estimator for calculating the contingent valuation method is applied. The probability of willingness to pay the same as the probability of accepting bids is estimated by using data based on questioners approach using stated preference method. The result indicates that the total economic value of this unique ecosystem in Kish Island is at least 14.6 million dollar per year, showing the importance of conservation value of the ecosystem. Its largest component of total economic value is about 62 percent attributed to the recreational value. This is followed by conservation value which is about 23 percent of the economic value. Since coastal protection and waste assimilation functions of coral reef are 10 percent, it is also suitable factor in illustrating total economic value. The economic value for each hectare of this ecosystem in Kish Island is US$ 237,000 in 2009.

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