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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Numerical simulation of compressible gas flow coupled to heat conduction in two space dimensions

Korneeva, Daria Y. 23 June 2011 (has links)
The current thesis studies a model of two dimensional convection of an ideal gas in a rectangular domain having walls of finite thickness. The temperature outside of walls is considered constant. Heat exchange between walls and outside/inside air is computed using Newton's law of cooling. Heat transfer inside walls is modelled with the heat equation. The mathematical model inside enclosure involves Navier-Stokes equations coupled with equation of state for gas. The model is numerically studied using the method of large particles. One of the main goals of the current thesis was to develop a software in C# language for numerical solution of the above-described model. Physically meaningful results, including stream lines and distribution of parameters of gas and temperature inside solid walls were obtained.
12

Numerical simulation of Large Solar Hot Water system in storage tank

Shue, Nai-Shen 06 September 2012 (has links)
This research is aimed to study the storage tank design parameters effects on the efficiency of the large solar hot water system. Detailed CFD simulation for the storage tank coupled with TRNSYS program simulation for the entire solar hot water system will be performed to study the system performance under various thermal stratification baffles design for the storage tank. The study is made for three representative cities of Taiwan by input their typical-meteorological-year data (TMY data). The results indicate the performance of a large solar hot water system can be significantly improved with proper designed thermal stratification baffles in the storage tank.
13

Experimental and Numerical Study of Polymer Scratch Behavior

Jiang, Han 2009 August 1900 (has links)
As part of a larger effort to understand the fundamental knowledge of polymer scratch behavior, this dissertation is focused on both experimental study and numerical analysis of scratch deformation of a broad range of polymers, with an emphasis on the mechanical understanding of how the scratch-induced damage is formed. An instrumented progressive load scratch method recommended by ASTM/ISO standards was adopted for the experimental work. The commercial finite element (FE) method package ABAQUS was employed as a numerical simulation tool to describe the stress-strain fields, and it analyzes the deformation mechanisms during the scratch process. A thorough parametric study has been performed to assess the influence of material parameters and surface properties, such as Young's modulus, yield strength, and friction coefficient, on the polymer scratch behavior. Upon investigation of the scratch behaviors of a broad range of polymer materials, various kinds of scratch damage features are identified and correlated with the mechanical characteristics of the polymers. A generalized scratch damage mechanism map for polymers is presented. Correlation between different material types and scratch damage mechanisms is made. It is found that both the material characteristics and the stress state exerted on the scratched surface are responsible for the observed scratch damage mechanisms. The phenomenological deduction of the scratch damage process based on the stick-slip mechanism is established. A more realistic material law for the scratch analysis is also provided. To evaluate the polymer resistance against scratch visibility quantitatively, an entirely new automated on-set scratch visibility determination methodology is developed based on typical visual characteristics of human eyes. Its application on the evaluation of mar and abrasion of polymer is also explored. This new methodology can quantify polymer scratch resistance consistently and reliably regardless of the sample surface characteristics and color.
14

Numerical Simulations on Long-Term Shoreline Changes behind Detached Breakwaters

Wu, Cheng-chung 24 May 2005 (has links)
In this thesis, a numerical simulation model is applied to investigate the long-term shoreline changes behind detached breakwaters. The model includes three components, namely a wave model, a current model, and a shoreline change model. In the numerical simulations, various combinations of wave conditions and the placement of detached breakwater are chosen to explore the effect of detached breakwaters on the shoreline change. The results of calculation show that with incident wave angles within 0~45, wave height in the range of 0.5~1.5m, or the offshore distance to the detached breakwaters being 60~120m, the larger in any one of these three parameters is, the bigger the erosion distance onshore from the original shoreline and the extent of salient offshore are behind detached breakwaters. When incident angle of the wave increases, shoreline plan form becomes skewed, and the time required to arrive at equilibrium also increases, in addition to the position of the top of salient moves downcoast. Within the wave periods of 7~10 seconds tested, waves with large period are found to show slight decrease of the erosion distance onshore and the extent of salient offshore behind detached breakwaters. The plan form of the salient is not affected by wave period. However, the larger the wave period is, the sooner the long-tern shoreline will result. Moreover, for a detached breakwater constructed in the range of offshore distances within 1.0¡ÕS/B¡Õ2.0, variable offshore distances do not produce much difference in the erosion distance onshore and the extent of salient offshore behind detached breakwaters, and salient only will form. In the case of the S/B =< 0.8, a tombolo will result. Finally, the results of shoreline plan form from the numerical modeling are verified by the empirical parabolic bay shape equation of Hsu and Evans (1989), a small-scale hydraulic model, and two numerical models based on GENESIS and LITPACK. Overall, the result are in good agreement with these four different approaches, and therefore, the present model is suitable for practical engineering applications.
15

Analysis of Centrifugal Titanium Compound Metal Casting by Computer Aided Engineering

Lai, Jian-zhi 22 August 2006 (has links)
The present study aims to explore flow behavior in the mold during centrifugal casting process by numerical simulations. The theoretical model comprises two groups of steady conservation equations of mass and momentum and the governing equations are solved numerically with k-£` turbulence model and iterative SIMPLE(Semi-Implicit for Pressure-Linked Equations) algorithm to determine the flow property. The numerical results indicate that the melt liquids of titanium compound metal flow near the walls in the high rotation rate. With the high rotation rate, the outflow velocity is rapid. The products depend on the flow of the melt liquids. The flow is rapid, the filled process is quick, and the temperature is uniform. But if the flow is slow, the temperature is not uniform in the filled process. Therefore, the products may result in faults. When the rotation rate is up to 50 rpm, the melt liquids flow near the walls with the affect of centrifugal force. The velocity is larger than the velocity with zero rotation rate . Thus the flow with rotation rate can help to fill quickly, and reduce the temperature loss.
16

Simulation study for a stack of micro-PEMFC

Huang, Chun-Hui 21 August 2008 (has links)
Proton exchange membrane (PEM) fuel cell possesses the characteristics of microminiaturization and low temperature operation. For this reason, the proton exchange membrane fuel cell is very suitable to serve as power source of portable electronic products. In this paper, a three-dimensional numerical model to evaluate the voltage and the total current density of a PEM fuel cell stack was developed. The polarization curves of the PEM fuel cell stack under three different operating temperatures were investigated. In this study, the micro PEM fuel cell stack contains two single cells. Pure H2 gas stream was supplied as the anode inlet flow and air as the cathode inlet flow under constant pressure at 97 kPa and constant cell temperate (298K¡B308K¡B323K) conditions. Because the cell temperature may affect the chemical reaction rate on the cathode side, we discussed the influences of different temperatures on the cell performance. Solutions were compared with the experimental data. Both the value of power density and the tendency of polarization curve are in good agreement with the experimental data.
17

On understanding the physics and source conditions of the Enceladus South Polar Plume via numerical simulation

Yeoh, Seng Keat 10 August 2015 (has links)
Enceladus, a tiny moon of Saturn, is found to be geologically active. In 2005, Cassini detected an anomalously warm region and a plume, consisting of mostly water vapor and ice grains, at its south pole. The plume has far-reaching effects on the Saturnian system and offers clues into the moon’s interior, particularly as to whether liquid water exists underground. Consequently, understanding the physics and source conditions of the plume is crucial, which is the focus of this work. The plume is not only two-phase but also multi-regime in nature and can be divided into three distinct regions: a subsurface region, a collisional near-field and a free-molecular far-field. To study it, a hybrid model of the plume, which treats each region separately, is constructed. Two subsurface models are considered. Using the resulting vent conditions from these models, the plume is propagated from the surface vents out to several Enceladus radii using the direct simulation Monte Carlo (DSMC) method in the near-field and a free-molecular model in the far-field. The model is used to examine the plume flow, with and without grains. Collisions are found to be important in various processes, including grain condensation and flow acceleration. Since collision rates drop away from the vent, they must be high enough at the vent to enable significant condensation to occur and the gas to accelerate to the maximum speed possible by allowing energy stored in internal modes to be converted into translational energy as the gas expands. When slower grains are present, however, they may decelerate and push the gas out more laterally. Moreover, grains may form a thick column and restrict the free expansion of the gas. Smaller grains have greater and more extensive effects on the gas, but are also more strongly affected by the gas. Their motions decouple from the gas motions higher above the vent. They are also more likely to spread with the gas and be accelerated to the gas speeds. By constraining the plume far-field using Cassini data, the H2O and grain production rates from the plume are estimated to be ~100–1000 kg/s and < 10 kg/s respectively, which agree with other estimates. Based on fit results, the gas jets appear to be narrow, suggesting high Mach numbers at the vents. / text
18

Simulation of hydrodynamics of the jet impingement using Arbitrary Lagrangian Eulerian formulation

Maghzian, Hamid 05 1900 (has links)
Controlled cooling is an important part of steel production industry that affects the properties of the outcome steel. Many of the researches done in controlled cooling are experimental. Due to progress in the numerical techniques and high cost of experimental works in this field the numerical work seems more feasible. Heat transfer analysis is the necessary element of successful controlled cooling and ultimately achievement of novel properties in steel. Heat transfer on the surface of the plate normally contains different regimes such as film boiling, nucleate boiling, transition boiling and radiation heat transfer. This makes the analysis more complicated. In order to perform the heat transfer analysis often empirical correlations are being used. In these correlations the velocity and pressure within the fluid domain is involved. Therefore in order to obtain a better understanding of heat transfer process, study of hydrodynamics of the fluid becomes necessary. Circular jet due to its high efficiency has been used vastly in the industry. Although some experimental studies of round jet arrays have been done, yet the characteristics of a single jet with industrial geometric and flow parameters on the surface of a flat plate is not fully understood. Study of hydrodynamics of the jet impingement is the first step to achieve better understanding of heat transfer process. Finite element method as a popular numerical method has been used vastly to simulate different domains. Traditional approaches of finite element method, Lagrangian and Eulerian, each has its own benefits and drawbacks. Lagrangian approach has been used widely in solid domains and Eulerian approach has been widely used in fluid fields. Jet impingement problem, due to its unknown free surface and the change in the boundary, falls in the category of special problems and none of the traditional approaches is suitable for this application. The Arbitrary Lagrangian Eulerian (ALE) formulation has emerged as a technique that can alleviate many of the shortcomings of the traditional Lagrangian and Eulerian formulations in handling these types of problems. Using the ALE formulation the computational grid need not adhere to the material (Lagrangian) nor be fixed in space (Eulerian) but can be moved arbitrarily. Two distinct techniques are being used to implement the ALE formulation, namely the operator split approach and the fully coupled approach. This thesis presents a fully coupled ALE formulation for the simulation of flow field. ALE form of Navier-Stokes equations are derived from the basic principles of continuum mechanics and conservation laws in the fluid. These formulations are then converted in to ALE finite element equations for the fluid flow. The axi-symmetric form of these equations are then derived in order to be used for jet impingement application. In the ALE Formulation as the mesh or the computational grid can move independent of the material and space, an additional set of unknowns representing mesh movement appears in the equations. Prescribing a mesh motion scheme in order to define these unknowns is problem-dependent and has not been yet generalized for all applications. After investigating different methods, the Winslow method is chosen for jet impingement application. This method is based on adding a specific set of partial differential Equations(Laplace equations) to the existing equations in order to obtain enough equations for the unknowns. Then these set of PDEs are converted to finite element equations and derived in axi-symmetric form to be used in jet impingement application. These equations together with the field equations are then applied to jet impingement problem. Due to the number of equations and nonlinearity of the field equations the solution of the problem faces some challenges in terms of convergence characteristics and modeling strategies. Some suggestions are made to deal with these challenges and convergence problems. Finally the numerical treatment and results of analyzing hydrodynamics of the Jet Impingement is presented. The work in this thesis is confined to the numerical simulation of the jet impingement and the specifications of an industrial test setup only have been used in order to obtain the parameters of the numerical model.
19

Validation of the Lattice Boltzmann Method for Direct Numerical Simulation of Wall-Bounded Turbulent Flows

BESPALKO, DUSTIN JOHN 18 September 2011 (has links)
In this work, the lattice Boltzmann method (LBM) was validated for direct numerical simulation (DNS) of wall-bounded turbulent flows. The LBM is a discrete-particle-based method that numerically solves the Boltzmann equation as opposed to conventional DNS methods that are based on the Navier-Stokes (NS) equations. The advantages of the LBM are its simple implementation, its ability to handle complex geometries, and its scalability on modern high-performance computers. An LBM code was developed and used to simulate fully-developed turbulent channel flow. In order to validate the results, the turbulence statistics were compared to those calculated from a conventional NS-based finite difference (FD) simulation. In the present study, special care was taken to make sure the computational domains for LBM and FD simulations were the same. Similar validation studies in the literature have used LBM simulations with smaller computational domains in order to reduce the computational cost. However, reducing the size of the computational domain affects the turbulence statistics and confounds the results of the validation. The turbulence statistics calculated from the LBM and FD simulations were found to agree qualitatively; however, there were several significant deviations, particularly in the variance profiles. The largest discrepancy was in the variance of the pressure fluctuations, which differed by approximately 7%. Given that both the LBM and FD simulations resolved the full range of turbulent scales and no models were used, this error was deemed to be significant. The cause of the discrepancy in the pressure variance was found to be the compressibility of the LBM. The LBM allows the density to vary, while the FD method does not since it solves the incompressible form of the NS equations. The effect of the compressibility could be reduced by lowering the Mach number, but this would come at the cost of significantly increasing the computational cost. Therefore, the conclusion of this work is that, while the LBM is capable of producing accurate solutions for incompressible turbulent flows, it is significantly more expensive than conventional methods for simple wall-bounded turbulent flows. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2011-09-15 23:24:09.968
20

Numerical simulation of Ricci flow on a class of manifolds with non-essential minimal surfaces

Wilkes, Jason Unknown Date
No description available.

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