Sharif Digital Repository

In this paper using classical beam theory, the dynamical governing differential equations of a vibrating shaft are derived then by using lumped parameter technique and method of transfer matrix (TM) the induced eigen value problem is solved. In calculating natural frequencies of a vibrating shaft under different boundary conditions, primarily the shaft was divided into number of segments. In each segment different number of lumped properties like mass, damping and flexibility on overall massless elastic or rigid shaft were applied. One of the aims of this study was to find out the optimum value for number of segments under different aforementioned conditions. In order to estimate the natural... 

This study developed and validated a lumped parameter model for the FLEXI-BAR, a popular training instrument that provides vibration stimulation. The model which can be used in conjunction with musculoskeletal-modeling software for quantitative biomechanical analyses, consists of 3 rigid segments, 2 torsional springs, and 2 torsional dashpots. Two different sets of experiments were conducted to determine the model's key parameters including the stiffness of the springs and the damping ratio of the dashpots. In the first set of experiments, the free vibration of the FLEXI-BAR with an initial displacement at its end was considered, while in the second set, forced oscillations of the bar were... 

Effects of fringing electrostatic fields on the behavior of a double clamped initially curved microbeam are investigated. Galerkin's decomposition method is applied on the governing Euler-Bernoulli equation with distributed electrostatic force to obtain the lumped-parameter model of the system. The resulting single degree of freedom model is obtained with the Palmer's formula as a model for the fringing field effects. To derive an applied form of the fringing field effect in lumped model, we have used Genetic Algorithms as an optimization method. Then using the lumped model, we have investigated the system nonlinear dynamics. Comparison of the obtained bifurcation diagrams with the... 

Micropumps are among useful equipment in microsystems. The magnetically actuated mercury micropump, which has been introduced for less than a decade, is an innovative kind of micropumps which uses mercury droplets motion as a pumping agent. The equations governing this micropump are complex and their numerical solution is a time-consuming process, due to electromagnetic, hydrodynamic, and unsteady effects. In the present study, for the first time, using simplifying assumptions, the performance of a Magneto Mercury Reciprocating (MMR) micropump with electromagnetic actuation is studied through electrical analogy and then, the components and operational stages of the micropump are simulated... 

Problem statement: Modeling Human cardiovascular system was always an important issue from long past because by doing such modeling, investigation in cardiovascular system and its abnormities would be simpler. One of the most effective ways to do such modeling is using lumped method (Electrical analogy). Approach: Lumped method was used for simulating a complete model in this approach. A 36-vessel model was chosen to make equivalent circuit of lumped method from it. This complicated circuit includes equivalent segment for arteries, pulmonary, atrium, left and right ventricles. Furthermore, in this complex circuit some additional points were considered to improve this method. Some of the most... 

This study investigates the possibility of sequential failure analysis of Tension Braced Moment Resisting Frames (TBMRFs) by examining its performance in the linear and nonlinear stages under idealized seismic loading conditions. The results obtained from rigorous analyses by means of numerical methods are utilized to set up and calibrate an analytical model which would appropriately differentiate the contribution shares of the frame and the bracing elements. The paper provides information on key response parameters, including interaction value between frame and brace elements, as well as tensile strength capacity and ductility capability of such systems. © 2008 American Institute of Physics... 

The disposal of used tires is a major environmental problem. With increasing interest on recovery of wastes, pyrolysis is considered as an alternative process for recovering some of the value in scrap tires. An accurate kinetic model is required to predict product yields during thermal or catalytic pyrolysis of scrap tires. Pyrolysis products contain a variety of hydrocarbons over a wide boiling range. A common approach for kinetic modeling of such complex systems is lumping where each lump is defined by a boiling point range. Available experimental data for thermal and catalytic pyrolysis of scrap tires from the literature were used to evaluate two types of lumping models; discrete and... 

The effect of complexity level of a lumped kinetic model for heavy residue hydroconversion on estimated values of kinetic parameters was investigated in this work by imposing constraints for the parameter estimation algorithm of a complex six-lump kinetic model and deriving a simpler modified model from the complex model. Kinetic analysis was performed using available experimental data reported in the literature from a study on hydrocracking of Chinese Gudao vacuum residue in a bench-scale reactor using ammonium phosphomolybdate (APM) as a dispersed catalyst. The kinetic models also included coke formation reactions that had previously been ignored by most investigators due to the rather... 

An explicit dynamics extended finite element method (X-FEM) is applied to the problems with material interfaces. To this end, the available X-FEM element mass matrix lumping techniques have been identified and assessed. It is shown that all the methods have their own limitations and are not general enough to handle the enrichment functions specifically developed for the elements with material interfaces. Hence, a general element mass matrix lumping technique has been introduced which exactly preserves the kinetic energies of the basic rigid body and enrichment modes. The idea is borrowed from the previously published method for a specific range of enrichment functions and extended to... 

Volumetric and equilibrium calculations for the natural gas and oil defined by a large number of components are not feasible in applications like compositional reservoir simulation. Therefore, the fluid mixture is grouped to reduce computational load and to make faster calculations. However, for several reasons, it is required to have the detailed fluid composition rather than the lumped one. In this work, an improved delumping method is presented to retrieve the phase composition of the detailed mixture based on the grouped mixture thermodynamic calculations. The method is based on previously proposed delumping techniques for non-cubic equation of state (Assareh et al. in Fluid Phase... 

The structural instability of an array of cantilevers, each of which interacts with two neighbouring beams through electrostatic and van der Waals forces, is studied. Distributed and lumped parameter modelling of the array result in a set of coupled nonlinear boundary value problems and a set of coupled nonlinear equations, respectively. These coupled nonlinear systems are solved numerically for different numbers of beams in the array to obtain the pull-in parameters. The pull-in parameters converge to constant values with an increase in the number of beams in the array. These constants, which are important in the design of cantilever arrays, are compared for the distributed and lumped... 

Tapered piezoelectric beams, because of their more efficiency to generate power, are required to be analyzed by simple models. In this paper, single degree of freedom (SDOF) relations are used to model transvers vibration of an exponentially tapered piezoelectric beam. For this purpose, first, response of the damped cantilevered Euler–Bernoulli beam with base excitation is obtained. Then, lumped parameters of the beam are extracted in order to calculate the SDOF model response. Comparing the Euler-Bernoulli beam model with the SDOF model shows that the lumped parameter model is not accurate enough to predict the beam’s response. Therefore, a tapering parameter dependent correction factor is... 

Electrical analogy (Lumped method) is an easy way to model human cardiovascular system. In this paper Lumped method is used for simulating a complete model. It describes a 36-vessel model and cardiac system of human body with details that could show hydrodynamic parameters of cardiovascular system. Also this paper includes modeling of pulmonary, atrium, left and right ventricles with their equivalent circuits. Exact modeling of right and left ventricles pressure increases the accuracy of our simulation. In this paper we show that a calculated pressure for aorta from our complex circuit is near to measured pressure by using advanced medical instruments  

The strong bases statistical associated fluid theory (SAFT) equations of state allow modeling for a wide range of scales and applications. The equilibrium calculations are very time-consuming in SAFT-based family of equations of state; therefore the number of components used in describing a fluid mixture must be reduced by grouping. On the other hand, in some applications it is required to retrieve the detailed fluid description from equilibrium calculation performed on the lumped fluid description. The purpose of this paper is to develop a systematic approach for lumping and delumping with equilibrium calculations using the Perturbed Chain (PC)-SAFT equation of state. The methodology... 

Atomic force microscopy (AFM), as an indispensable tool for nanoscale characterization, presents major drawbacks for operation in a liquid environment arising from the large hydrodynamic drag on the vibrating cantilever. The newly introduced 'Trolling mode' (TR-mode) AFM resolves this complication by using a specialized nanoneedle cantilever that keeps the cantilever outside of the liquid. Herein, a mechanical model with a lumped mass was developed to capture the dynamics of such a cantilever with a nanoneedle tip. This new developed model was applied to investigate the effects of the needle-liquid interface on the performance of the AFM, including the imaging capability in liquid  

Nitric Oxide (NO) provides myocardial oxygen demands of the heart during exercise and cardiac pacing and also prevents cardiovascular diseases such as atherosclerosis and platelet adhesion and aggregation. However, the direct in vivo measurement of NO in coronary arteries is still challenging. To address this matter, a mathematical model of dynamic changes of calcium and NO concentration in the coronary artery was developed for the first time. The model is able to simulate the effect of NO release in coronary arteries and its impact on the hemodynamics of the coronary arterial tree and also to investigate the vasodilation effects of arteries during cardiac pacing. For these purposes, flow...