http://hdl.handle.net/10125/880 Wed, 22 May 2013 21:39:06 GMT 2013-05-22T21:39:06Z http://hdl.handle.net/10125/20496 Thesis (Ph.D.)--University of Hawaii at Manoa, 2008.; Design of composite structures in many important industrial applications requires good understanding of the fracture behavior in the vicinity of material interfaces. In this study, near-interfacial and interfacial fractures are modeled by the extended finite element method (XFEM), a numerical technique developed recently to model crack propagation. In the XFEM, a crack, or a discontinuity in displacements, is represented by enriching the nodes around the crack with additional degrees of freedom associated with enrichment interpolation functions. Among the advantages of the XFEM are that no remeshing is needed; the crack path is independent of the finite element mesh; it is applicable to preexisting cracks as well as evolving cracks; and it is numerically robust although extra implementation efforts are needed. In order to deal efficiently with changes in the geometry and mesh topology, the level set method (LSM), an algorithm used to track evolving interfaces, is introduced and combined with the XFEM.; The XFEM is first applied to the simulation of near-interfacial crack propagation in a metal-ceramic layered structure. Experimental evidence indicates that, in a ceramic-metal-ceramic sandwich structure, a near-interfacial crack in the ceramic layer can be drawn to or deflect away from the metal layer depending on the difference in elastic properties across the interface. To model near-interfacial fracture, only the Heaviside functions are used for the XFEM, and the vector LSM method, an improvement to the original LSM, where the LSM is adapted to the nature of crack propagation problems, is employed for efficient evaluation of the enrichment functions. The crack propagation paths predicted by the XFEM simulation are found to be consistent with the experimental observation. In the simulation of the interfacial fracture, a bi-material plate with a crack on the interface is modeled. In the proposed scheme, the nodes on the crack are enriched with only the Heaviside functions. The stress intensity factor analysis demonstrates that such an enrichment strategy can produce satisfactory results for interfacial fracture problems.; Includes bibliographical references (leaves 75-83).; Also available by subscription via World Wide Web; 83 leaves, bound 29 cm Tue, 01 Jan 2008 00:00:00 GMT http://hdl.handle.net/10125/20496 2008-01-01T00:00:00Z Yan, Yuhai http://hdl.handle.net/10125/20479 Thesis (Ph.D.)--University of Hawaii at Manoa, 2008.; A joint theoretical, numerical and experimental study is carried out to develop an improved wave model for predicting water waves and fluid current generated by underwater landslides. In the theoretical study, a fully nonlinear and higher-order dispersive depth-integrated hydrodynamic model by Gobbi and Kirby (1999) and Gobbi et al. (2000) is extended to include the time variation in bathymetry. Upon this extension, the new model can be applied to simulate both wave propagation and the dynamic process of wave generation by a submerged moving object such as an underwater landslide. Compared with the lower-order (first- or second-order) traditional long wave models, the higher-order model improves the modeling of the dispersive effect to the fourth-order, thus extending the validity of the wave model from long waves (wavelength-to-water depth ratio larger than 10) to shorter waves (wavelength comparable to the water depth). In addition, it also improves the approximation of the vertical fluid velocity profile from the second-order parabolic assumption to a fourth-order polynomial function for more accurate prediction of the fluid current induced by waves. A finite difference scheme is applied to solve the model equations in one spatial dimension. The new model developed in this thesis is derived independently from the fourth order model by Ataie-Ashtiani and Najafi-Jilani (2007) which is similar but differs from the new model in this thesis.; Experiments also are carried out in a wave flume in the Hydraulics Laboratory of the Department of Civil and Environmental Engineering at the University of Hawaii. Waves are generated by rigid landslide models sliding down an incline with adjustable slopes. The wave elevation is measured by resistance-type wave gauges and the fluid velocity with particle image velocimetry (PIV). The present higher-order model then is applied to simulate the experimental cases and the numerical results are compared with the experimental data as well as with the results based on two existing lower-order wave models. The results show that the present higher-order model agrees with the experimental measurement better for both the wave elevation and especially the fluid velocity induced by the waves and the landslide motion. Most existing studies focus on wave measurement and prediction. This study is among the first to conduct experiments to measure the landslide induced velocity field and compare the measured velocity with the predicted results.; Tsunami sensitivity to landslide features also is investigated through numerical experiments. Empirical equations are derived for predicting the tsunami wave amplitude and water velocities under the waves, based on the numerical experiments.; With its improved wave dispersion relation and more accurate prediction for the fluid velocity field, the new model developed in this study can be useful to study a wider range of coastal and hydraulic engineering problems including landslide-generated tsunamis and the associated fluid current which is important in the study of sediment transport and seabed erosion during a tsunami attack. Other problems that can also apply the present higher-order model may include prediction of water surface evolution for open channel flows over different bottom disturbances, and surface waves generated by submerged moving vehicles in the shallow ocean in naval applications.; Includes bibliographical references (leaves xxx-xxx).; Also available by subscription via World Wide Web; 103 leaves, bound 29 cm Tue, 01 Jan 2008 00:00:00 GMT http://hdl.handle.net/10125/20479 2008-01-01T00:00:00Z Zhou, Hongqiang http://hdl.handle.net/10125/12119 Mode of access: World Wide Web.; Thesis (Ph. D.)--University of Hawaii at Manoa, 2005.; Includes bibliographical references (leaves 410-414).; Electronic reproduction.; Also available by subscription via World Wide Web; xxxi, 414 leaves, bound ill. (some col.), col. maps 29 cm Sat, 01 Jan 2005 00:00:00 GMT http://hdl.handle.net/10125/12119 2005-01-01T00:00:00Z Gica, Edison http://hdl.handle.net/10125/12118 Thesis (Ph. D.)--University of Hawaii at Manoa, 2004.; Includes bibliographical references (leaves 211-220).; Also available by subscription via World Wide Web; xviii, 220 leaves, bound ill. 29 cm Thu, 01 Jan 2004 00:00:00 GMT http://hdl.handle.net/10125/12118 2004-01-01T00:00:00Z Zhang, Lin, 1956 Sept. 25 http://hdl.handle.net/10125/12117 Mode of access: World Wide Web.; Thesis (Ph. D.)--University of Hawaii at Manoa, 2004.; Includes bibliographical references (leaves 145-149).; Electronic reproduction.; Also available by subscription via World Wide Web; x, 149 leaves, bound ill. 29 cm Thu, 01 Jan 2004 00:00:00 GMT http://hdl.handle.net/10125/12117 2004-01-01T00:00:00Z Huang, Linlin http://hdl.handle.net/10125/994 The trends for analysis and design of steel frames are indicated in this dissertation. The current practice consists of applying the first-order elastic analysis with amplification factors or second-order elastic analysis in combination with the AISC-LRFD interaction equations. Determination of the effective length factors and individual member capacity checks are necessary to select adequate structural member sizes. The direct analysis method is a second-order elastic analysis approach that eliminates the determination of effective length factors from the current AlSC-LRFD method. Unsupported member length is used to calculate the axial strength of a member. Equivalent notional loads and/or modified stiffness are applied together with the external loads to account for the effects of initial out-of-plumbness and inelastic softening. For both AlSC-LRFD and direct analysis methods, a structure is analyzed as a whole, but the axial and flexural strength of each member is examined individually. Inelastic redistribution of internal forces in the structural system cannot be considered. As a result, determined member forces are not correct and more conservative member sizes will be obtained. Moreover, member-based approaches cannot predict structural behaviors such as failure mode and overstength factor. The advanced analysis method considered in this work is a second-order refined plastic hinge analysis in which both effective length factors and individual member capacity checks are not required. In addition, advanced analysis is a structure systembased analysis/design method that can overcome the difficulties of using member-based design approaches. Thus, advanced analysis is a state-of-the-art method for steel structure design. Several numerical examples are provided to show the design details of all three methods. The design requirements corresponding to each analysis approach are illustrated in these examples. The pros and cons of each method are discussed by comparing the design results. Advanced analysis is also a computer-based analysis and design procedure consistent with the features of performance-based design. Applying advanced analysis to performance-based fire resistance and seismic design are proposed. This dissertation shows advanced analysis is efficient in predicting the duration that structures could support load under elevated temperature and capable of determining the performance level of a structure subjected to seismic forces. Thu, 01 May 2003 00:00:00 GMT http://hdl.handle.net/10125/994 2003-05-01T00:00:00Z Hwa, Ken