Modeling in Engineering
Year:2016 | Volume:14 | Issue:44|Papers Count:13

In this paper, the nanofluid forced convection heat transfer in the case of single and two phase approachs is studied. The fully-developed flow and steady Darcy-Brinkman-Forchheimer equation is employed in porous channel and is solved with homotopy perturbation method. The thermal equilibrium model is assumed between nanofluid and solid phases. It is assumed that the nanoparticles are distributed non-uniformly inside the channel. As a result, the volume fraction distribution equation is also coupled with governing equations. It is observed that as the Schmidt number is increased, the wall temperature gradient is decreased and as a consequence the local Nusselt number is decreased. The effects of Lewis number, Schmidt number and modified diffusivity ratio on the volume fraction distribution are also studied and discussed. Heat transfer of single and two phase approaches are also compared.

In this study, two-dimensional pulsating unsteady flow of nanofluid through a rectangular channel with isothermal walls is investigated numerically. The finite volume approach with a staggered grid arrangement is employed to discretize the governing momentum and energy equations. The set of resultant algebraic equations is solved simultaneously using SIMPLE algorithm to obtain the velocity and pressure distribution within the channel. The results are obtained for different pulse parameters, which are Strouhal number (frequency of pulsation), Amplitude of pulsation, Reynolds number and volume fraction of nanoparticles. The results show that increasing the amplitude of pulsation has no effect on cycle period of pulsation, while it can raise the Nusselt number. The analysis also reveals that increasing the Strouhal number reduces the cycle period of pulsation significantly, while its effect on the rate of heat transfer is not more appreciable. Furthermore, it is found that the heat transfer increases, as the volume fraction of nanoparticles and Reynolds number increase. It can also be seen that the maximum value of relative Nusselt number for silver nanoparticles is more than other studied nanoparticles.

To obtain the transient temperature in different parts of the body and the welding pool growing, the continuity and momentum equations are solved along with the energy equation. The analysis for a rectangular plate made of AISI 304 Stainless Steel is done by writing a program with Fortran.90. Because the Fourier heat transfer equation at short times and large dimensions does not have sufficient accuracy a non-Fourier form of heat transfer equation is being used. Gaussian heat source is considered as a heat source model. The governing equations for fluid flows are solved by the finite volume method in which the SIMPLE method is used for calculating pressure-velocity coupling in fluid flows, likewise the Power-Law method and the staggered grid can be used for discretization equations. The finite difference method is also used to solve the energy equation. The effect of heat conduction, fluid flows and force actions at the weld pool is considered. Thermo-physical properties such as thermal conductivity, specific heat and dynamic viscosity are a function of temperature. There are two mechanisms, radiation and convection heat transfer, which actively cause heat transfer to the surroundings. The numerical results were compared with experimental data. Finally, the results obtained from the assumed Fourier heat transfer are compared for the same study. The results bear the fact that the weld pool thick in the cross section of keyhole PAW and the time that molten metal reaches to the end of thick metal, are in good agreement compared to experimental measurements.

Effect of soil-structure interaction (SSI) and site condition on elastic and inelastic seismic demands of structure is investigated in this research. More emphasis is on Effect of soil-structure interaction and site condition is assessed by using earthquakes recorded on different site classes C, D and E (NEHRP [1]) where SSI has a significant effect on the structural demands because of noticeable difference between the stiffness of soil and the structure. In order to develop a comprehensive statistical parametric study, the structure is modeled as an elastic-plastic single degree of freedom (SDOF) system and the soil beneath the foundation is supposed as a homogeneous half space and is idealized by fundamental lumped mass parameters based on the concepts of the cone model (Wolf, 1994 [17]). To consider the frequency dependency of soil’s dynamic stiffness in this model, the soil is represented with a three-DOF system that introducing an internal DOF in the soil can represent this effect. Then the whole of soil-structure model is analyzed under 45 earthquakes recorded on previously mentioned site classes. A parametric study is done for a wide range of non-dimensional parameters controlling the SSI effects on structural demands. It is concluded that SSI affects on structural seismic demands such as elastic and inelastic strength, strength reduction factor, ductility demand, and inelastic displacement ratio especially for structures located on site class E. Results exhibit remarkable differences in comparison to fixed base one. Consequently, in some cases, using parameters derived for fixed base case, lead to non-conservative results in design and assessment parameters of structures located on soft soils.

In this paper, axial crushing of foam-filled cylindrical aluminium tubes with initiator is investigated. For this purpose, an initiator is placed at the top of the foam-filled tube to prevent a sudden force applied to the main part of the structure when the accident occurs. In this new design model, several numerical simulations using ABAQUS 5.6 finite element explicit code are carried out to study the effects of length initiator on crashworthiness characteristics of the foam-filled thin-walled cylindrical tubes. In order to verify these numerical results, a series of quasi-static axial compression tests are performed. Moreover, load-displacement curves and deformation mechanism of the structure under axial compression are described. The results show that the initiator reduces the intensity of damage to the main structure and occupants.

Due to the inaccessibility to rotating parts of the rotor the only way to flaw detection is measuring vibrations on the fixed portions such as surfaces of housing the bearings. It is common that in industry with measure vibrations of surfaces the housings at three direction and analyze it, predict and solve the created bug type. Take the effects of the housing can be help to accurately predict the rotor behavior at the measured response of the rotor using the analytical methods. Aims of this paper are modeling a full system of rotor-bearing-housing and considering the housing effects. For this, firstly subsystem of rotor-bearings is modeling using the Riley’s continuous beam theory and assumed modes method. Also a complete finite element model and a simple spring-mass model of the housing is made. Then, the forces exerted from the subsystem of rotor-bearing is calculated using the Newmark method and by applying on model of the housing, the responses time, curves of the deformation and frequency spectrums are drawn. The present study has been able to modeling properly the complete rotor-bearings-housing system. Furthermore the inadequate of the simple spring-mass model due to large errors and inability to accurately modeling the vibrating behavior of housing has acknowledged. Studies have shown that despite the lack of the axial force in the rotor-bearing subsystem, the housing will vibrate in axial direction. In addition with despite the equality of all conditions in the rotor-bearings, will not be expected an equal response in all direction of the housing. Also by considering the housing effects, domain the graphs of frequency spectrum will be reduced, particularly at high frequencies.

Designing and manufacturing of technical systems and devices in refineries, oil and gas pipelines and gas booster stations is associated with huge costs from an economic point of view. Hence, managers at industry section, especially oil and gas industry, seek ways to control the production and distribution costs. Generally speaking, at distribution section, selection of operational appliances by operators in gas booster stations to be run, would be done without considering various kinds of cost. In this research, a deterministic mixed integer program is presented to minimize the operational costs in gas booster stations of a gas distribution network. The objective is to select operational appliances, turbo-compressors here, such that minimize the operational costs while customer demands are met. Operational costs are include consumed fuel costs (fuel exploded in gas turbine combustion chambers to yield the torque power to run the gas compressor), maintenance and repair costs, startup costs (generally the electrical costs used for running the electro air compressors which provide the compressed air), and penalty costs. Considering the gas transmission operating region no.9 as a case study, the result is that the model could minimize the total costs about 14% in comparison with the selection of two chief operators.

Seismic base isolation is an earthquake resistant design method that is based on decreasing the seismic demand instead of increasing the seismic capacity. In this paper, the seismic response of base-isolated structures is numerically investigated. The effectiveness of an isolation system depends upon the dynamic characteristics of earthquake ground motion and the building superstructure. In order to evaluate the dynamic response of nonlinear base-isolated structures, different detailed 3D nonlinear analytical models with different characteristics are developed and analyzed under significant and strong motion earthquakes. Also in order to have the optimized behavior of system, different types of isolators including Lead-Rubber Bearing (LRB) and Friction-Pendulum (FPS) isolators were simulated between the superstructure and the foundation so as to provide lateral flexibility and energy dissipation capacity. Providing an optimized arrangement of different types of isolators in the structure is important since it affects the structural responses to earthquakes. The parametric study is concentrated on base shear, accelerations and displacements of isolated models. Also the comparison between hysteretic responses of models as a main criterion for energy dissipation of system has been investigated and evaluated. Results show that the model with FPS ratio of 25% has the best structural response against seismic loads.

Significantly velocity profile in tubular reactors is affect in outlet products. In order to obtain velocity profile, rheological models can be used. One of them is Power law model. One of the most important and effective parameters that it can be observed in this model is the n parameter. In this work, investigations of influence n on velocity profile in laminar flow and on conversion of a tubular reactor that Methyl Methacrylate polymerization occurs in the reactor are presented. Furthermore, this study is investigated rheological properties of outlet and inlet solution of the reactor with a rheometer and the value of n is estimated 0.8403 by curve fitting. The results indicate that with increasing the value of n, the pattern of motion is close to mixed. In addition, it can be observed that the conversion increases with decreasing the value of n and there exist maximum of conversion for the reactor in n=0. In other words, the conversion in n=0 is very close to the conversion in plug flow pattern and this means that in this situation velocity profile is plug flow. In the last part of this work, by the value of n that has been estimated, a modeling of the reactor is presented. The obtained conversion from modeling is 69.66 % and this value is very close to empirical conversion from paper Fan et al (65 %), and this means the modeling is acceptable.

Creation and installation of DG in distribution networks, a source of new challenges in maintaining and protecting the network that has attracted much attention in research and practice. In this regard, we need to all cases and incidents in the system are investigated and simulation. The purpose of the technical review and how to implement security settings, need to develop new tools and methods for the study of certain or probable sequence of conservation practices in the system. Sequence analysis of the distribution network protection, will be promoting in the presence of distributed provided. This paper presents a new approach to model the performance of a distributed network security system using generalized stochastic Petri nets, to evaluate the protective systems of distribution network, the models are dealt with. The proposed method is a 32 bus IEEE distribution network with high penetration of DG to study the impact of DG on distribution network protection systems have been applied.

This paper presents a comprehensive model for dynamic expansion planning of distribution grids (DDGEP) considering distributed generation technologies. The proposed model determines the optimal location, capacity and dynamics (i.e. timing) of DG investment as well as optimal time schedule of reinforcement of distribution feeders. The objective function of this model encompasses both investment and operation costs of distribution grids and DG units along a specified planning horizon. To solve the suggested model, a new two-level solution method composed of Binary Enhanced Imperialist Competition Algorithm (BEICA) and Improved Particle Swarm Optimization (IPSO) is introduced. BEICA optimizes the location, capacity and timing of DG investment and also timing of existing feeders' reinforcement while IPSO optimizes the operation point of distributed generator-integrated distribution system. In order to demonstrate the effectiveness of proposed two-level solution approach (BEICA+IPSO), it is applied on a radial distribution test system and the obtained results are compared with several other solution methods.