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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.
31

A Semantic Framework for Reusing Decision Making Knowledge in Engineering Design

Rockwell, Justin A 01 January 2009 (has links) (PDF)
A semantic framework to improve automated reasoning, retrieval, reuse and communication of engineering design knowledge is presented in this research. We consider design to be a process involving a sequence of decisions informed by the current state of information. As such, the information model developed is structured to reflect the conceptualizations of engineering design decisions with a particular emphasis on semantically capturing design rationale. Based on a description logic formalism, the information model was implemented using the Web Ontology Language (OWL), which provides a semantically rich and sufficiently broad specification of design decisions capable of supporting the application of any specific decision-making method. Through this approach knowledge reuse is achieved by communicating design rationale and facilitating semantic-based retrieval of knowledge. A case study is presented to illustrate three key features of the approach: 1) seamless integration of separate modular domain ontologies and instance knowledge related to engineering design that are needed to support decision making, 2) the explicit documentation of design rationale through design decisions, and 3) the application of an automated method for matching and retrieving stored knowledge. The automated retrieval method is implemented using the Semantic Web Rule Language (SWRL) and serves as an example of the type of reasoning services that can easily be achieved by formally and semantically representing design knowledge.
32

Computational Methods for the Analysis of Non-Contact Creep Deformation

Ye, Xiao 01 January 2012 (has links) (PDF)
Currently, various needs from industry, science and national defense strategy demand materials with cutting-edge ultra-high temperature performances. Typical applications of ultra-high temperature materials (UHTMs) are supersonic airplanes, gas turbines and rocket nozzles which usually require continuous service of critical components at temperatures higher than 1600°C. Creep resistance is a critical criterion in designing materials for these applications. Traditional creep characterization methods, however, due to limitations on cost, accuracy and most importantly temperature capability, gradually emerge as a bottleneck. Since 2004, a group of researchers in the University of Massachusetts, Amherst have been designing a new high temperature characterization scheme that can break through the limits of traditional methods. Their method is based on non-contact creep tests conducted with Electrostatic levitation (ESL) facilities in NASA Marshall Space Flight Center in Huntsville Alabama. The tested sample is levitated in electric field and is heated as well as rotated with specially positioned laser beam. After certain amount of time, the sample deforms under centripetal forces. By comparison of the shape of the deformed sample with results from finite element simulation, creep behavior of the tested material can be characterized. Based on the same theory, this thesis presents a computational creep characterization method based on non-contact method. A finite element model was built to simulate non-contact creep behavior and results were compared to ESL experiments to determine the creep characteristic. This method was validated both theoretically and numerically and then applied to creep characterization of a promising ultra-high temperature composite from General electric (GE).
33

Parallel Mesh Adaptation and Graph Analysis Using Graphics Processing Units

Mcguiness, Timothy P 01 January 2011 (has links) (PDF)
In the field of Computational Fluid Dynamics, several types of mesh adaptation strategies are used to enhance a mesh’s quality, thereby improving simulation speed and accuracy. Mesh smoothing (r-refinement) is a simple and effective technique, where nodes are repositioned to increase or decrease local mesh resolution. Mesh partitioning divides a mesh into sections, for use on distributed-memory parallel machines. As a more abstract form of modeling, graph theory can be used to simulate many real-world problems, and has applications in the fields of computer science, sociology, engineering and transportation, to name a few. One of the more important graph analysis tasks involves moving through the graph to evaluate and calculate nodal connectivity. The basic structures of meshes and graphs are the same, as both rely heavily on connectivity information, representing the relationships between constituent nodes and edges. This research examines the parallelization of these algorithms using commodity graphics hardware; a low-cost tool readily available to the computing community. Not only does this research look at the benefits of the fine-grained parallelism of an individual graphics processor, but the use of Message Passing Interface (MPI) on large-scale GPU-based supercomputers is also studied.
34

Additive Manufacturing of Cork, a Cold Spray Technology

Dickey, Kimberly Kay 01 December 2021 (has links) (PDF)
Cold Spray Additive Manufacturing is a technology capable of mass manufacturing components with complicated geometry and coating substrates in hard-to-reach areas. In addition, cold spray also has the ability of conducting a green manufacturing process, with zero waste of renewable feed material, and zero gas and chemical emission. This paper investigates solely cold spray as an additive manufacturing technology with cork as the natural material. CFD results were used to predict the physical behavior of air and the cork particles. After unsuccessful coatings, final results showed that when moisture is added, cork is successfully cold sprayed, and agglomeration is experienced. Following these results, high speed camera and Hopkinson bar tests concluded that pressure is the only significant parameter that drastically effects the disposition quality of the cork coating. This is the first reported result of cork powder being cold sprayed, in addition to groundbreaking results of successfully coating an Aluminum substrate without a binder. Key words: cork, powder, additive manufacturing, natural materials, cold spray, binder, deposition efficiency, coating, high speed camera, Hopkinson bar.
35

Finite Element Modeling of Ballistic Impact on a Glass Fiber Composite Armor

Davis, Dan M 01 June 2012 (has links) (PDF)
Finite Element Modeling of Ballistic Impact on a Glass Fiber Composite Armor Dan Davis Experiments measuring the ballistic performance of a commercially available fiberglass armor plate were used to guide the development of constitutive laws for a finite element model of the impact. The test samples are commercially available armor panels, made from E-glass fiber reinforced polyester rated to NIJ level III. Quasi-static tensile tests were used to establish material properties of the test panels. These properties were then used to create models in the explicit finite element code LSDYNA. Ballistic impact testing of the panels was conducted using a compressed gas gun firing spherical steel projectiles oriented normal to the test panel surface. The V50 ballistic limit of these panels was found to be approximately 560 m/s. Tuning parameters in the finite element models were adjusted to match the experimentally measured penetration depths and ballistic limits. Models were created in LSDYNA by adjusting the available material library types 3 and 59 for the target, and material type 15 for the projectile. Type 3 models are isotropic, and resulted in shear punch-out type failures of the plate that poorly replicated the test results. Type 59 takes orthotropic properties into consideration, and can analyze delamination when used with solid elements. Results with model type 59 were significantly better than those using type 3, however, this model was found to vastly underestimate the impact resistance of the plate. With significant adjustments to the material properties in the type 59 model, the LSDYNA simulations were found to better replicate the experimentally observed response of the panels. However, these deformations are questionable since they required quite unrealistic adjustments to the material properties.
36

The Effect Of Magnetic Bearing On The Vibration And Friction Of A Wind Turbine

Vorwaller, Mark Ryan 01 January 2012 (has links)
Demands for sustainable energy have resulted in increased interest in wind turbines. Thus, despite widespread economic difficulties, global installed wind power increased by over 20% in 2011 alone. Recently, magnetic bearing technology has been proposed to improve wind turbine performance by mitigating vibration and reducing frictional losses. While magnetic bearing has been shown to reduce friction in other applications, little data has been presented to establish its effect on vibration and friction in wind turbines. Accordingly, this study provides a functional method for experimentally evaluating the effect of a magnetic bearing on the vibration and efficiency characteristics of a wind turbine, along with associated results and conclusions. The magnetic bearing under examination is a passive, concentric ring design. Vibration levels, dominant frequency components, and efficiency results are reported for the bearing as tested in two systems: a precision test fixture, and a small commercially available wind turbine. Data is also presented for a geometrically equivalent ball bearing, providing a benchmark for the magnetic bearing’s performance. The magnetic bearing is conclusively shown to reduce frictional losses as predicted by the original hypothesis. However, while reducing vibration in the precision test fixture, the magnetic bearing demonstrates increased vibration in the small wind turbine. This is explained in terms of the stiffness and damping of the passive test bearing. Thus, magnetic bearing technology promises to improve wind turbine performance, provided that application specific stiffness and damping characteristics are considered in the bearing design.
37

Optimization and Modeling Tools for Telescope Hexapod Structures

Feeney, Michael Edward 01 June 2011 (has links) (PDF)
Hexapod trusses are an important element in many mechanical design systems. The natural frequency and stiffness behavior under geometric and mass variations of such structures is largely undocumented. Furthermore, the ability to quickly model hexapod designs and explore a large design-space in finite element software packages is, in general, time consuming and inefficient. The purpose of this project was to develop software tools that made design-space exploration (modeling and simulation processes) for hexapod structures drastically more efficient. Secondly, the project included an experimental analysis portion to demonstrate the various modal study techniques and to validate finite element analysis predictions. Lastly, the project investigated a specific hexapod design problem as a means of exhibiting the modeling/optimization software tools and to develop an understanding of the natural frequency behavior of hexapods. To this end, the research could be used for the design of telescope secondary support structures and other hexapod optimization engineering problems.
38

Simulation of an Oxidizer-Cooled Hybrid Rocket Throat: Methodology Validation for Design of a Cooled Aerospike Nozzle

Brennen, Peter Alexander 01 June 2009 (has links) (PDF)
A study was undertaken to create a finite element model of a cooled throat converging/diverging rocket nozzle to be used as a tool in designing a cooled aerospike nozzle. Using ABAQUS, a simplified 2D axisymmetric model was created featuring only the copper throat and stainless steel support ring, which were brazed together for the experimental test firings. This analysis was a sequentially coupled thermal/mechanical model. The steady state thermal data matched closely to experimental data. The subsequent mechanical model predicted a life of over 300 cycles using the Manson-Halford fatigue life criteria. A mesh convergence study was performed to establish solution mesh independence. This model was expanded by adding the remainder of the parts of the nozzle aft of the rocket motor so as to attempt to match the transient nature of the experimental data. This model included variable hot gas side coefficients in the nozzle calculated using the Bartz coefficients and mapped onto the surface of the model using a FORTRAN subroutine. Additionally, contact resistances were accounted for between the additional parts. The results from the preliminary run suggested the need for a parameter re-evaluation for cold side gas conditions. Parametric studies were performed on contact resistance and cold side film coefficient. This data led to the final thermal contact conductance of k=0.005 BTU/s•in.•°R for contact between metals, k=0.001 BTU/s•in.•°R for contact between graphite and metal, and h=0.03235 BTU/s2•in.•°R for the cold side film coefficient. The transient curves matched closely and the results were judged acceptable. Finally, a 3D sector model was created using identical parameters as the 2D model except that a variable cold side film condition was added. Instead of modeling a symmetric one or two inlet/one or two outlet cooling channel, this modeled a one inlet/one outlet nozzle in which the coolant traveled almost the full 360° around the cooling annulus. To simplify the initial simulation, the model was cut at the barrier between inlet and outlet to form one large sector, rather than account for thermal gradients across this barrier. This simplified nozzle produced expected data, and a 3D full nozzle model was created. The cold side film coefficients were calculated from previous experimental data using a simplified 2D finite difference approach. The full nozzle model was created in the same manner as the 2D full nozzle model. A mesh convergence study was performed to establish solution mesh independence. The 3D model results matched well to experimental data, and the model was considered a useful tool for the design of an oxidizer cooled aerospike nozzle.
39

Hybrid III 95th Percentile Large Male Finite Element Model Neck Alteration

Day, Eric Riley 01 December 2019 (has links) (PDF)
The motivation behind the project was to update the Livermore Software Technology Corporation (LSTC) Hybrid III 95th percentile finite element model, such that the neck assembly response under varying simulated loading conditions equals that of the federally regulated Hybrid III 95th percentile anthropomorphic testing device (ATD). The family of Hybrid III crash test dummies approximate the physical properties and response of the human body in a frontal automotive crash. The Hybrid III is used to assess the effectiveness of vehicle restraint systems. LSTC offers Hybrid III finite element models for use in their Multiphysics simulation software package, LS-DYNA. The Hybrid III models are used as cost-effective alternative to physical crash tests in the development of vehicle crashworthiness. However, the neck response of the LSTC Hybrid III 95th percentile model in simulation was poorly correlated to that of the physical Hybrid III neck in corresponding tests. The source of the dissimilarity was inadequate dimensions, element behavior, and material properties of the neck. To improve correlation to the physical ATD, a number of modifications were made to the LSTC Hybrid III 95th percentile neck. Development of the neck model began with improvements in mass and geometry. Element formulation and element discretization were altered to improve model durability and accuracy. A mesh convergence study and simulation under extreme-severity loading were completed to validate the foregoing model alterations. Test data from a physical compression test and NASA-performed Neck Sled Tests were collated with data from simulation to adjust material type and material properties. The model was further calibrated according to Code of Federal Regulations neck calibration test response requirements. The resulting neck model developed in LS-DYNA exhibited improved dynamic characteristics and reliability under both low and high-severity loading. Computational efficiency was enhanced along with model tendency to normally terminate under excessive loading. The updated model moreover demonstrated consistent element behavior and realistic feedback in bending. The revised neck model will be adopted by NASA for use in predicting potential occupant injury during spacecraft landing. A similar model with reworked material properties attuned to higher loading will be implemented into the full consumer version of the Hybrid III 95th percentile model for employment in high-severity frontal crash simulation.
40

Implementation of Topology Optimization into the Mechanical Design Process

Clapp, Nolan 01 June 2023 (has links) (PDF)
Topology Optimization is a lightweighting method based on finite element analysis that produces a part with optimum material distribution in the design space. Results from topology optimization often have organic shapes and curves that are difficult if not impossible to machine with traditional subtractive manufacturing methods. This paper analyzes the implementation of the Solidworks® Topology Optimization add-in into the mechanical design process and discusses required postprocessing to ensure manufacturability of the optimized part though a case study on two example parts. Results of traditional optimization, topology optimization and “selective” optimization (optimization using the results from topology optimization to selectively remove material to ensure manufacturability) were compared in terms of weight reduction and time required for optimization. In addition, simplified lightweighted parts were experimentally tested to validate the results of Solidworks® FEA and Topology Optimization to ensure physical part performance and increase confidence in future model results. Overall, it was determined that due to the large amount of time to setup and run, topology optimization may not be the most effective lightweighting method if time is a significant design constraint. However, for some specific applications where part weight is of major importance or where additive manufacturing may be a possible manufacturing process, the benefits of topology optimization’s material removal capability outweigh the required solution time.

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