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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.


Wang, Peiding 01 January 2014 (has links)
Drop-on-demand (DOD) inkjet print-head has a major share of the market due to simplicity and feasibility of miniature system. The efficiency of droplet generation from DOD print-head is a result of several factors, include viscosity, surface tension, nozzle size, density, driving waveform (wave shape, frequency, and amplitude), etc. Key roles in the formation and behavior of liquid jets and drops combine three dimensionless groups: Reynolds number, Weber number and Ohnesorge number. These dimensionless groups provide some bounds to the “printability” of the liquid. Adequate understanding of these parameters is essential to improve the quality of droplets and provide guidelines for the process optimization. This thesis research describes the application of computational fluid dynamics (CFD) to simulate the creation and evolution process of droplet generation and transport of a highly viscous Newtonian fluid. The flow field is governed by unsteady Navier-Stokes equations. Volume of Fluid (VOF) model is used to solve this multi-phase (liquid-gas) problem.

Data-Driven Adaptive Reynolds-Averaged Navier-Stokes <em>k - ω</em> Models for Turbulent Flow-Field Simulations

Li, Zhiyong 01 January 2017 (has links)
The data-driven adaptive algorithms are explored as a means of increasing the accuracy of Reynolds-averaged turbulence models. This dissertation presents two new data-driven adaptive computational models for simulating turbulent flow, where partial-but-incomplete measurement data is available. These models automatically adjust (i.e., adapts) the closure coefficients of the Reynolds-averaged Navier-Stokes (RANS) k-ω turbulence equations to improve agreement between the simulated flow and a set of prescribed measurement data. The first approach is the data-driven adaptive RANS k-ω (D-DARK) model. It is validated with three canonical flow geometries: pipe flow, the backward-facing step, and flow around an airfoil. For all 3 test cases, the D-DARK model improves agreement with experimental data in comparison to the results from a non-adaptive RANS k-ω model that uses standard values of the closure coefficients. The second approach is the Retrospective Cost Adaptation (RCA) k-ω model. The key enabling technology is that of retrospective cost adaptation, which was developed for real-time adaptive control technology, but is used in this work for data-driven model adaptation. The algorithm conducts an optimization, which seeks to minimize the surrogate performance, and by extension the real flow-field error. The advantage of the RCA approach over the D-DARK approach is that it is capable of adapting to unsteady measurements. The RCA-RANS k-ω model is verified with a statistically steady test case (pipe flow) as well as two unsteady test cases: vortex shedding from a surface-mounted cube and flow around a square cylinder. The RCA-RANS k-ω model effectively adapts to both averaged steady and unsteady measurement data.

The Development of a Hybrid Optimization Algorithm for the Evaluation and Optimization of the Asynchronous Pulse Unit

Inclan, Eric 01 January 2014 (has links)
The effectiveness of an optimization algorithm can be reduced to its ability to navigate an objective function’s topology. Hybrid optimization algorithms combine various optimization algorithms using a single meta-heuristic so that the hybrid algorithm is more robust, computationally efficient, and/or accurate than the individual algorithms it is made of. This thesis proposes a novel meta-heuristic that uses search vectors to select the constituent algorithm that is appropriate for a given objective function. The hybrid is shown to perform competitively against several existing hybrid and non-hybrid optimization algorithms over a set of three hundred test cases. This thesis also proposes a general framework for evaluating the effectiveness of hybrid optimization algorithms. Finally, this thesis presents an improved Method of Characteristics Code with novel boundary conditions, which better characterizes pipelines than previous codes. This code is coupled with the hybrid optimization algorithm in order to optimize the operation of real-world piston pumps.

Development of a Coupling Model for Fluid-Structure Interaction using the Mesh-free Finite Element Method and the Lattice Boltzmann Method

Mudrich, Jaime 15 November 2013 (has links)
In the presented thesis work, the meshfree method with distance fields was coupled with the lattice Boltzmann method to obtain solutions of fluid-structure interaction problems. The thesis work involved development and implementation of numerical algorithms, data structure, and software. Numerical and computational properties of the coupling algorithm combining the meshfree method with distance fields and the lattice Boltzmann method were investigated. Convergence and accuracy of the methodology was validated by analytical solutions. The research was focused on fluid-structure interaction solutions in complex, mesh-resistant domains as both the lattice Boltzmann method and the meshfree method with distance fields are particularly adept in these situations. Furthermore, the fluid solution provided by the lattice Boltzmann method is massively scalable, allowing extensive use of cutting edge parallel computing resources to accelerate this phase of the solution process. The meshfree method with distance fields allows for exact satisfaction of boundary conditions making it possible to exactly capture the effects of the fluid field on the solid structure.

A Consistent Algorithm for Implementing the Space Conservation Law

Pillalamarri Narasimha Rao, Venkata Pavan 29 August 2014 (has links)
Fluid flows occurring in moving and/or deforming environments are influenced by the transient nature of their containment. In Computational Fluid Dynamics (CFD), simulating such flow fields requires effort to maintain the geometric integrity of the transient flow domain. Convective fluxes in such domains are evaluated with respect to the motion of the boundaries of the control volume. These simulations demand conservation of space in addition to the conservation of mass, momentum and energy as the solution continues in time. The Space Conservation Law in its continuous form can be inferred by using the rules of fundamental calculus. However, implementing it in a discrete form poses substantial challenges. During mesh motion, the surfaces enclosing the control volumes sweep through three-dimensional space. As per the Space Conservation Law, the change in the control volume has to match the sum of the swept volumes of all its faces exactly. The Space Conservation Law must be satisfied accurately and consistently in order to avoid the occurrence of non-physical masses and to prevent the violation of the continuity equation. In this work we have attempted to address the consistency issues surrounding the implementation of the Space Conservation Law in OpenFOAM. The existing method for calculation of swept volumes falls short in terms of consistency. Moreover, its capabilities are limited when it comes to complex three-dimensional mesh motions. The existing method of calculation treats swept volumes as net fluxes emanating from cell faces. We have implemented an alternate algorithm in which the swept volumes are treated as intermittent virtual cells whose volumes can be calculated in a unique and consistent manner. We will conclude by validating our approach for mesh motions of varying degrees of complexity.

Numerical Simulation of High Velocity Impact of a Single Polymer Particle during Cold Spray Deposition

Shah, Sagar P 07 November 2016 (has links)
Abstract The cold spray process is an additive manufacturing technology primarily suited for ductile metals, and mainly utilized in coating surfaces, manufacturing of freeform parts and repair of damaged components. The process involves acceleration of solid micro-particles in a supersonic gas flow and coating build-up by bonding upon high velocity impact onto a substrate. Coating deposition relies on the kinetic energy of the particles. The main objective of this study was to investigate the mechanics of polymer cold spray process and deformation behavior of polymers to improve technological implementation of the process. A finite element model was created to simulate metal particle impact for copper and aluminum. These results were compared to the numerical and experimental results found in the literature to validate the model. This model was then extended to cover a wide range of impact conditions, in order to reveal the governing mechanisms of particle impact and rebound during cold spray. A systematic analysis of a single high-density polyethylene particle impacting on a semi-infinite high density polyethylene substrate was carried out for initial velocities ranging between 150m/s and 250m/s by using the finite element analysis software ABAQUS. A series of numerical simulations were performed to study the effect of a number of key parameters on the particle impact dynamics. These key parameters include: particle impact velocity, particle temperature, particle diameter, and particle density, composition of the polyethylene particle, surface composition and the thickness of a polyethylene film on a hard metal substrate. The effect of these parameter variations were quantified by tracking the particle temperature, deformation, plastic strain and rebound kinetic energy. The variation of these parameters helped define a window of deposition where the particle is mostly likely to adhere to the substrate.

Analysis of a Carbon Fiber Reinforced Polymer Impact Attenuator for a Formula SAE Vehicle Using Finite Element Analysis

Rappolt, John T 01 June 2015 (has links)
The Hashin failure criteria and damage evolution model for laminated fiber reinforced polymers are explored. A series of tensile coupon finite element analyses are run to characterize the variables in the physical model as well as modeling techniques for using an explicit dynamic solver for a quasi-static problem. An attempt to validate the model on an axial tube crush is presented. It was found that fiber buckling was not occurring at the impactor-tube interface. Results and speculation as to why the failure initiation is incorrect are discussed. Lessons learned from the tube crush are applied successfully to the quasi-static Formula SAE nosecone crush test. The model is validated by experimental data and the impact metrics between the test and model are within 5%. Future work and possible optimization techniques are discussed.

Design and Analysis of the Impact Diffusion Helmet Through a Finite Element Analysis Approach

Warnert, Steven Paul 01 October 2016 (has links)
By applying the finite element approach to the design and analysis of the impact diffusion helmet, many helmet configurations were able to be analyzed. Initially it was important to determine what design variables had an influence on the impact reducing abilities of the helmet design. The helmet was run through a series of Abaqus simulations that determined that a design with two oval shaped channels running along the length of the helmet was best. Next, these options were optimized to generate the helmet that produced the greatest impact reduction. The optimization simulations determined that a helmet that pushed the channels as far from the impact zone as possible reported the lowest acceleration. This indicated that removing the channels from play was most advantageous from an impact reduction perspective. Finally, a 3-D printed experimental helmet was impact tested and compared to a 3-D printed control helmet. The experimental helmet brought the channels back into the impact zone in order to judge if they had a physical effect on the acceleration. Both the simulations and the subsequent physical testing indicated that the Impact Diffusion Helmet design has a negative influence on the concussion reducing properties of a football helmet.

A Methodology for Verification of Structural Standards for a Seating System by Finite Element Analysis

Dworaczyk Wiltshire, Zachary Kelly 01 June 2019 (has links)
Currently California Polytechnic State University has a patent pending on a new type of seating system designed to increase the functionality of public transportation vehicles. The patent is based on the work completed by a senior project group in 2016, whose design showcased the feasibility of the idea. Further development was completed by a second senior project group, the Adjustable Seating Systems, in 2019. The intent of the Adjustable Seating Systems group was to develop a seating system with the intent of commercialization and implementation in paratransit vehicles with future development into large buses and trains. Seating systems used in public transportation are required to meet strict geometric and structural standards by the federal government under FMVSS 207, 208, 209 and 210 to be comfortable and protect the passenger in a wide variety of situations. Included in these standards are quasi-static and dynamic tests developed to simulate the loading conditions of a crash event. Seating systems must be able to withstand the loading conditions with no obvious signs of failure to ensure the safety of the passengers. The work of this thesis was to simulate the loading conditions outlined by the safety standards on the design developed by the Adjustable Seating Systems group using finite element analysis. The results confirm the seating system meets the required safety standards. The largest stresses induced in the system are between the yield stress and ultimate stress of the material, indicating plastic deformation without failure due to fracture.

Direct design of a portal frame

Ugaz, Angel Fajardo 01 January 1971 (has links)
This investigation was undertaken to develop plastic design aids to be used in the direct design of optimum frames. It uses the concept of minimum weight of plastically designed steel frames, and the concept of linear programming to obtain general solutions. Among the special characteristics of this study are: A. The integration of both gravity and combined loading conditions into one linear programming problem. B. The application of the revised simplex method to the dual of a parametric original problem. C. The application of A and B above in the development of design aids for the optimum design of symmetrical single-bay, single-story portal frame. Specifically, design graphs for different height to span ratios and different vertical load to lateral load ratios are developed. The use of these graphs does not require the knowledge of linear programming or computers on the part of the designer.

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