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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.
1

Modeling and simulation of tool induced soil resistance with application to excavator machine

LIU, HENG 13 September 2016 (has links)
To evaluate and test control systems designed for heavy duty hydraulic excava-tor, it is important to simulate the force acting on the bucket during its excavation process. The study of soil-tool interaction contributes to the prediction and simula-tion of resistive forces experienced at the tool during digging. Even though many different finite element (FE) models have been developed in the past to study soil-tool interaction process, there is still needs to study the effects of soil-tool friction coefficient. The main objective of this thesis is to utilize finite element model to simulate the soil-tool interaction process, with the focus on the application of excavation, to study the effects of soil-tool friction coefficient on soil failure zone, soil resistive force, and stress distribution on the cutting tool by utilizing finite element model to simulate the soil-tool interaction process. / October 2016
2

Finite Element Analysis of Breast Implants

Wilson, Kelly A. 25 May 1999 (has links)
The Breast Implant Lifetime Study at Virginia Tech, on which this thesis is based, seeks to develop methods and data for predicting the lifetime of saline-filled implants. This research developed Finite Element Analysis (FEA) models to evaluate the stresses that are present in the silicone breast implant material under different loading situations. The FEA work was completed using the commercial codes PATRAN and ABAQUS. PATRAN was used for pre- and post-processing, while ABAQUS was used for the actual analysis and to add fluid and contact elements not supported by PATRAN. Many different loading situations and constraints were applied to these models, as well as variations in the material and model properties. Varying the Poisson's ratio of the implant material from 0.45 to 0.49 did not make a significant difference in the results. Changing the elastic modulus of the implant material from the modulus of a Smooth implant to the modulus of a Siltex implant had a noticeable effect on the stress results, increasing the maximum stresses by almost 8%. Changing the modulus of the surrounding tissue had marked effects as well, with stiffer tissue (E=300 psi) decreasing the implant's stresses by about 60% as compared to softer tissue (E=100 psi). A ten percent decrease in implant thickness yielded a 17% average increase in stress experienced by the implant. For both the 2.5" radius and the 4" radius tissue models, using CAX4 elements produced higher overall stresses in the tissue with the same loading conditions. However, in the 2.5" tissue model, the implant itself experienced less stress with the CAX4 tissue than the CAX3 tissue. In the 4" tissue model, the implant experienced more stress when surrounded by the CAX4 tissue elements. These models will be combined with implant fatigue data to develop a life prediction method for the implant membrane. / Master of Science
3

Three-dimensional nonlinear finite element model for single and multiple dowel-type wood connections

Hong, Jung-Pyo 05 1900 (has links)
A new three-dimensional finite solid element (3D FE) model for dowel-type wood connections was developed using the concept of a beam on a nonlinear wood foundation, which addresses the intricate wood crushing behaviour under the connector in a dowel type connection. In order to implement the concept of wood foundation with solid elements, a 3D FE wood foundation model was defined within a prescribed foundation zone surrounding the dowel. Based on anisotropic plasticity material theory, the material model for the foundation zone was developed using effective foundation material constants that were defined from dowel-embedment test data. New 3D FE single nail connection models were developed that incorporated the wood foundation model. The 3D wood foundation model was justified and validated using dowel-embedment test data with a range of dowel diameters, from a 2.5-mm nail to a25.4-mm bolt. The connection models provided successful results in simulating the characteristics of load-slip behaviour that were experimentally observed. Based on the success of the single nail connection models, several applications of the3D FE connection models were investigated including statistical wood material models, bolted connection models and a multiple nail connection model. Throughout the application studies, discussion of the benefits and limitations of the new model approach using the 3D FE wood foundation are presented. Also, future areas of study are proposed in order to improve the 3D FE dowel-type wood connections models.
4

An evaluation of piano sound and vibration leading to improvements through modification of the material properties of the structure

Keane, Martin January 2006 (has links)
A study of vibrations and sound radiation in upright and grand pianos has been made to determine whether the piano may be improved by altering the materials of the component parts which are traditionally fabricated in timber. Modal analysis and sound level measurements of an upright piano has shown that the radiation from the case is at least 20 dB lower than the radiation from the soundboard, and therefore the case is not a significant determinant of piano tone. A method was developed for separating piano sound and vibrations into broadband and tonal components and used to compare the performance of upright and grand pianos. Using this method it was found that the broadband vibration level was twice as high in the uprights as in the grands. A finite element model of an upright piano was developed and used to demonstrate that replacing the keybed with a higher impedance material than conventionally used would reduce the key vibration level, and hence bring the uprights closer in performance to grand pianos, and improve the 'feel' of the instrument for the player. The keybed of one of a pair of identical pianos was replaced with high density fibreboard, and subsequent objective measurements showed that the broadband component of key vibrations was reduced by 3.2 dB while the radiated sound was unchanged. A controlled subjective comparison between the modified and unmodified pianos undertaken by experienced players showed that a statistically significant number preferred the modified piano, and that the upright piano had been improved. / Acoustics Research Centre, Department of Mechanical Engineering, Foundation for Research Science and Technology, Fletcher Wood Panels.
5

An evaluation of piano sound and vibration leading to improvements through modification of the material properties of the structure

Keane, Martin January 2006 (has links)
A study of vibrations and sound radiation in upright and grand pianos has been made to determine whether the piano may be improved by altering the materials of the component parts which are traditionally fabricated in timber. Modal analysis and sound level measurements of an upright piano has shown that the radiation from the case is at least 20 dB lower than the radiation from the soundboard, and therefore the case is not a significant determinant of piano tone. A method was developed for separating piano sound and vibrations into broadband and tonal components and used to compare the performance of upright and grand pianos. Using this method it was found that the broadband vibration level was twice as high in the uprights as in the grands. A finite element model of an upright piano was developed and used to demonstrate that replacing the keybed with a higher impedance material than conventionally used would reduce the key vibration level, and hence bring the uprights closer in performance to grand pianos, and improve the 'feel' of the instrument for the player. The keybed of one of a pair of identical pianos was replaced with high density fibreboard, and subsequent objective measurements showed that the broadband component of key vibrations was reduced by 3.2 dB while the radiated sound was unchanged. A controlled subjective comparison between the modified and unmodified pianos undertaken by experienced players showed that a statistically significant number preferred the modified piano, and that the upright piano had been improved. / Acoustics Research Centre, Department of Mechanical Engineering, Foundation for Research Science and Technology, Fletcher Wood Panels.
6

An evaluation of piano sound and vibration leading to improvements through modification of the material properties of the structure

Keane, Martin January 2006 (has links)
A study of vibrations and sound radiation in upright and grand pianos has been made to determine whether the piano may be improved by altering the materials of the component parts which are traditionally fabricated in timber. Modal analysis and sound level measurements of an upright piano has shown that the radiation from the case is at least 20 dB lower than the radiation from the soundboard, and therefore the case is not a significant determinant of piano tone. A method was developed for separating piano sound and vibrations into broadband and tonal components and used to compare the performance of upright and grand pianos. Using this method it was found that the broadband vibration level was twice as high in the uprights as in the grands. A finite element model of an upright piano was developed and used to demonstrate that replacing the keybed with a higher impedance material than conventionally used would reduce the key vibration level, and hence bring the uprights closer in performance to grand pianos, and improve the 'feel' of the instrument for the player. The keybed of one of a pair of identical pianos was replaced with high density fibreboard, and subsequent objective measurements showed that the broadband component of key vibrations was reduced by 3.2 dB while the radiated sound was unchanged. A controlled subjective comparison between the modified and unmodified pianos undertaken by experienced players showed that a statistically significant number preferred the modified piano, and that the upright piano had been improved. / Acoustics Research Centre, Department of Mechanical Engineering, Foundation for Research Science and Technology, Fletcher Wood Panels.
7

An evaluation of piano sound and vibration leading to improvements through modification of the material properties of the structure

Keane, Martin January 2006 (has links)
A study of vibrations and sound radiation in upright and grand pianos has been made to determine whether the piano may be improved by altering the materials of the component parts which are traditionally fabricated in timber. Modal analysis and sound level measurements of an upright piano has shown that the radiation from the case is at least 20 dB lower than the radiation from the soundboard, and therefore the case is not a significant determinant of piano tone. A method was developed for separating piano sound and vibrations into broadband and tonal components and used to compare the performance of upright and grand pianos. Using this method it was found that the broadband vibration level was twice as high in the uprights as in the grands. A finite element model of an upright piano was developed and used to demonstrate that replacing the keybed with a higher impedance material than conventionally used would reduce the key vibration level, and hence bring the uprights closer in performance to grand pianos, and improve the 'feel' of the instrument for the player. The keybed of one of a pair of identical pianos was replaced with high density fibreboard, and subsequent objective measurements showed that the broadband component of key vibrations was reduced by 3.2 dB while the radiated sound was unchanged. A controlled subjective comparison between the modified and unmodified pianos undertaken by experienced players showed that a statistically significant number preferred the modified piano, and that the upright piano had been improved. / Acoustics Research Centre, Department of Mechanical Engineering, Foundation for Research Science and Technology, Fletcher Wood Panels.
8

Flutter Analysis of Stonecutters Cable-stayed Bridge using Finite Element Model

Feng, Fan January 2015 (has links)
The current research analyzed the flutter response of the Stonecutters Cable-Stayed Bridge in Hong Kong, which has a twin deck configuration, under the effect of wind. The aerodynamic instability response of the bridge steel deck of the main span is mainly the focus of the current project. Initially, a complete finite element bridge model was created in ABAQUS finite element software, representing all the structural elements of the Stonecutters Cable-Stayed Bridge in a lumped mass bridge model. The natural frequencies and the vibration modes were validated against the data available in the literature at first. Secondly, the effect of the mean wind loading for wind speeds between 35 m/s and 211 m/s were determined. The vertical and horizontal displacements and the torsional angle at mid-span are indicated to determine the bridge performance under mean wind load. Moreover the flutter instability was modeled based on Scanlan’s theory and the response of the bridge model at several different locations along the main and the side span and the top of the tower, were determined for wind speeds of 35 m/s and higher, where this critical aerodynamic instability is expected to occur. In addition, the responses of the bridge under natural wind data were also determined by applying a wind speed recorded data to the bridge model. Finally, the critical flutter wind speed and the flutter frequency were determined by Fast Fourier Transform in MATLAB program. The flutter onset wind speed was also determined.
9

Stochastic Galerkin Model Updating of Randomly Distributed Parameters

Nizamiev, Kamil 10 May 2011 (has links)
No description available.
10

Finite Element Modelling and Molecular Dynamic Simulations of Carbon nanotubes/ Polymer Composites

Gaddamanugu, Dhatri 2009 May 1900 (has links)
Modeling of single-walled carbon nanotubes, multi-walled nanotubes and nanotube reinforced polymer composites using both the Finite Element method and the Molecular Dynamic simulation technique is presented. Nanotubes subjected to mechanical loading have been analyzed. Elastic moduli and thermal coefficient of expansion are calculated and their variation with diameter and length is investigated. In particular, the nanotubes are modeled using 3D elastic beam finite elements with six degrees of freedom at each node. The difficulty in modeling multi walled nanotubes is the van der Waal's forces between adjacent layers which are geometrically non linear in nature. These forces are modeled using truss elements. The nanotube-polymer interface in a nano-composite is modeled on a similar basis. While performing the molecular dynamic simulations, the geometric optimization is performed initially to obtain the minimized configuration and then the desired temperature is attained by rescaling the velocities of carbon atoms in the nanotube. Results show that the Young's modulus increases with tube diameter in molecular mechanics whereas decreases in molecular dynamics since the inter-atomic potential due to chemical reactions between the atoms is taken into consideration in molecular dynamics unlike in molecular mechanics.

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