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1
Snyder, Gregory Frantz. "Modeling Spatially and Spectrally Resolved Observations to Diagnose the Formation of Elliptical Galaxies." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:10893.
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In extragalactic astronomy, a central challenge is that we cannot directly watch what happens to galaxies before and after they are observed. This dissertation focuses on linking predictions of galaxy time-evolution directly with observations, evaluating how interactions, mergers, and other processes affect the appearance of elliptical galaxies. The primary approach is to combine hydrodynamical simulations of galaxy formation, including all major components, with dust radiative transfer to predict their observational signatures. The current paradigm implies that a quiescent elliptical emerges following a formative starburst event. These trigger accretion onto the central supermassive black hole (SMBH), which then radiates as an active galactic nucleus (AGN). However, it is not clear the extent to which SMBH growth is fueled by these events nor how important is their energy input at setting the appearance of the remnant. This thesis presents results drawing from three phases in the formation of a typical elliptical: 1) I evaluate how to disentangle AGN from star formation signatures in mid-infrared spectra during a dust-enshrouded starburst, making testable predictions for robustly tracing SMBH growth with the James Webb Space Telescope ; 2) I develop a model for the rate of merger-induced post-starburst galaxies selected from optical spectra, resolving tension between their observed rarity and merger rates from other estimates; and 3) I present results from Hubble Space Telescope imaging of elliptical galaxies in galaxy clusters at 1 < z < 2, the precursors of present-day massive clusters with \(M \sim10^{15}M_{\odot}\), demonstrating that their stars formed over an extended period and ruling out the simplest model for their formation history. These results lend support to a stochastic formation history for ellipticals driven by mergers or interactions. However, significant uncertainties remain in how to evaluate the implications of galaxy appearance, in particular their morphologies across cosmic time. In the final chapter, I outline an approach to build a "mock observatory" from cosmological hydrodynamical simulations, with which observations of all types, including at high spatial and spectral resolutions, can be brought to bear in directly constraining the physics of galaxy formation and evolution.<br>Astronomy
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Issa, Nader. "Modes and propagation in microstructured optical fibres." University of Sydney. Physics and Optical Fibre Technology Centre, 2005. http://hdl.handle.net/2123/613.
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Microstructured optical fibres (MOFs), also commonly called photonic crystal fibres or holey fibres, describe a type of optical fibre in which continuous channels of (typically) air run their entire length. These `holes' serve to both confine electromagnetic waves within the core of the fibre and to tailor its transmission properties. In order to understand and quantify both of these functions, a new computational algorithm was developed and implemented. It solves for the eigenvalues of Maxwell's wave equations in the two-dimensional waveguide cross-section, with radiating boundary conditions imposed outside the microstructure. This yields the leaky modes supported by the fibre. The boundary conditions are achieved exactly using a novel refinement scheme called the Adjustable Boundary Condition (ABC) method. Two implementations are programmed and their computational efficiencies are compared. Both use an azimuthal Fourier decomposition, but radially, a finite difference scheme is shown to be more efficient than a basis function expansion. The properties of the ABC method are then predicted theoretically using an original approach. It shows that the method is highly efficient, robust, automated and generally applicable to any implementation or to other radiating problems. A theoretical framework for the properties of modes in MOFs is also presented. It includes the use of the Bloch-Floquet theorem to provide a simpler and more efficient way to exploit microstructure symmetry. A new, but brief study of the modal birefringence properties in straight and spun fibres is also included. The theoretical and numerical tools are then applied to the study of polymer MOFs. Three types of fibres are numerically studied, fabricated and characterised. Each is of contemporary interest. Firstly, fabrication of the first MOFs with uniformly oriented elliptical holes is presented. A high degree of hole ellipticity is achieved using a simple technique relying on hole deformation during fibre draw. Both form and stress-optic birefringence are characterized over a broad scaled-wavelength range, which shows excellent agreement with numerical modelling. Secondly, an analysis of leaky modes in real air core MOFs, fabricated specifically for photonic band gap guidance, is then used to identify alternative guiding mechanisms. The supported leaky modes exhibit properties closely matching a simple hollow waveguide, weakly influenced by the surrounding microstructure. The analysis gives a quantitative determination of the wavelength dependent confinement loss of these modes and illustrates a mechanism not photonic band gap in origin by which colouration can be observed in such fibres. Finally, highly multimode MOFs (also called `air-clad' fibres) that have much wider light acceptance angles than conventional fibres are studied. An original and accurate method is presented for determining the numerical aperture of such fibres using leaky modes. The dependence on length, wavelength and various microstructure dimensions are evaluated for the first time for a class of fibres. These results show excellent agreement with published measurements on similar fibres and verify that bridge thicknesses much smaller than the wavelength are required for exceptionally high numerical apertures. The influence of multiple layers of holes on the numerical aperture and capture efficiency are then presented. It shows that a substantial increase in both these parameters can be achieved for some bridge thicknesses. Simple heuristic expressions for these quantities are given, which are based on the physical insight provided by the full numerical models. The work is then supported by the first fabrication attempts of large-core polymer MOFs with thin supporting bridges. These fibres exhibit relatively high numerical apertures and show good agreement with theoretical expectations over a very wide scaled-wavelength range.
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Mancino, Antonio. "On the structural and dynamical properties of a new class of galaxy models with a central BH." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18722/.
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This thesis work focuses on the dynamical properties of two-component galaxy models characterized by a stellar density distribution described by a Jaffe profile, and a galaxy (stars plus dark matter) density distribution following a r^(-3) shape at large radii. The dark matter (hereafter, DM) density profile is defined by the difference between the galaxy and the stellar profiles. The orbital structure of the stellar component is described by the Osipkov-Merritt (OM) radial anisotropy, and that of the DM halo is assumed isotropic; a black hole (BH) is also added at the center of the galaxy.
The thesis is organized as follows. In Chapter 2 the main structural properties of the models are presented, and the conditions required to have a nowhere negative and monothonically decreasing DM halo density profile are derived; a discussion is also given of how the DM component can be built in order to have the same asymptotical behaviour, in the outer regions and near the center, as the Navarro-Frenk-White (NFW) profile. In Chapter 3 an investigation of the phase-space properties of the models is carried out, both from the point of view of the necessary and sufficient conditions for consistency, and from the direct inspection of the distribution function; the minimum value of the anisotropy radius for consistency is derived in terms of the galaxy parameters. In Chapter 4 the analytical solution of the Jeans equations with OM anisotropy is presented, together with the projection of the velocity dispersion profile at small and large radii. Finally, in Chapter 5 the global quantities entering the Virial theorem are explicitly calculated; these can be used for energetic considerations that are briefly mentioned, and allow us to determine the fiducial anisotropy limit required to prevent the onset of Radial Orbit Instability as a function of the galaxy parameters. The main results are summarized in Chapter 6, and some technical details are given in the Appendices.
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Cheng, Chia Hsuan, and 鄭嘉璿. "The Formation of Supermassive Binary Black Holes in Elliptical Galaxies." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/43502072329650587136.
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碩士<br>國立清華大學<br>物理系<br>104<br>We study the evolution of two supermassive black holes in the galaxy. We investigate whether two black holes can form a bound binary system within the age of the universe. Since the dynamical friction is the major physical process to determine the early stage of the formation of binary supermassive black holes, we also investigate its variables and other parameters such as the mass and the initial positions of the black holes. We use the simulation to study the behavior of two black holes in the galaxy. The results show that the evolution in the Hernquist model is faster than the one in the Plummer model. The former’s critical black hole mass to become gravitational bound is roughly one tenth of the latter’s. Hence it is easier for the black holes to become a bound binary in the Hernquist model.
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Chang, Tsang-Huai, and 張蒼懷. "Study of the Characteristic Effect of Elliptical Holes Polishing by Rotating Abrasive Flow Machining." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/28811666725888207114.
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Tsai, Tsungyen, and 蔡宗諺. "BEM Analysis for Stress Concentrations of Bending Problem of Anisotropic Plates Containing Two Elliptical Holes." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/80496427955875267379.
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碩士<br>國立臺灣大學<br>應用力學研究所<br>103<br>This work uses a new boundary integral equation (BIE) and finite element method (FEM) to analyze an infinite anisotropic plate containing two elliptic/circular holes subjected to remote bending or twisting moments. The foundation of the boundary integral equation is the classical plate theory with Cauchy integral formula. The BIE is used to calculate the curvatures and moments on the boundaries directly. Numerical examples are given for orthotropic and isotropic plates with circular or elliptic holes under uniform bending and twisting moments. Comparison of the numerical results with the analytic solution for one hole shows that in general BIE can achieve higher accuracies in evaluating moments while BIEs and FEM have comparable accuracies for computing deflections.
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Shih, Tzu-Hsien, and 石子賢. "Effects of Different Semi-Elliptical Bolt Holes on the Stress Concentration of Tensile Wooden Members." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/38273044366339721678.
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碩士<br>國立臺灣大學<br>森林環境暨資源學研究所<br>98<br>Generally, the tensile strength of wood is larger than that of compression strength in longitudinal direction. Because wood tissue could be damaged by metal connector or fastener, stress concentration always occurred at wood near the interface between wood and metal. This is the reason why the tensile strength value is almost close to or even lower than compression value in structural design.
In previous reviews, pioneers usually solved many problems by finite element analysis (FEA) simulation and assumed that the wood was isotropic. However, the wood is a kind of anisotropic material rather than isotropic. In fact, it is orthotropic.
In this study, a software called Solid Works2008 was used to find the results by FEA. The computer simulation is a tool that an assumed force can apply on a new type of bolt connection in order to reduce stress concentration.
Douglas fir (Pseudotsuga menziesii) was selected as the wood member. The material of the bolt was common steel. In this computer simulation, steel was set as an isotropic material. In Cartesian coordinate, the x-direction was assumed in longitudinal direction of the wood. The y- and z-direction represented radial and tangential directions of the wood respectively.
The total length of the member is 250 mm, and the width and the thickness are 60 and 12 mm. The hole is drilled in the central. The right side of the hole is a semicircle with 9.5 mm radius a, and the left side is a semiellipse with b mm semimajor axis (or with semiminor axis, if b&lt;a). All the initial sizes are constant, but the length of the semi axis of the semiellipse is variable, so that the definition of the axis ratio R is b/a, where a is the radius of the semicircle. R is set starting from 0.75, and each model with an increment of 0.25 for R was built and analyzed.
The applied load was a concentrated force of 980.67 N（100 kgf） on the metal bolt towards the left. The right side of the member would be fixed and could not be moved and there was no deformation or displacement at the end surface.
The interface between the wood and the metal bolt was set to free. There was neither glue nor adhesive between them, so there was a clearance while the deformation and displacement happened. Friction was neglected, however.
Compared with simulation results, it is evident that the distribution of stress is quite different between isotropic and orthotropic member. But stress concentration still exists in both models at same locations.
To enhance the utilization of wood material, the good property of tensile strength of wood should be considered. But stress concentration around the hole will reduce this property. Adjusting the ratio of the axes of R can find a way to reduce the stress concentration. One of the concentrated stresses must be increased while another must be decreased whether the ratio increases or decreases. The simulation show that a good result can be obtained when the ratio R is about 1.2 to 1.25.
In the experiment, strain gauges and the universal testing machine were used. Signals were measured and converted through the written computer program. Basically, some of the results are similar with computer simulations. While the applied load is constant, the value of strain at the tensile area by the bolt hole decreases with R increasing, and the value of strain at the compression area by the bolt hole increases with R increasing. However, there were some disadvantages for mechanism such as nodes of wood, grain. And the dimension of the models was too small (limited by the testing machine) that the disadvantages appeared obviously. Because of the small dimension, the scale of strain gauges was enlarged, so that a part of the results were not so accuracy.
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Wager, David. "The Influence of Elliptical Nozzle Holes on Mixing and Combustion in Direct Injection Natural Gas Engines." Thesis, 2008. http://hdl.handle.net/1807/17235.
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Experiments were conducted to compare mixing and combustion of natural gas jets from round and elliptical nozzle holes in an optically accessible combustion bomb. A flame ionization detector was used to measure the concentration fields of the two jet types. Pressure data, combustion imaging, and hydrocarbon measurements of exhaust gas were used to compare the ignition delay, heat release, and combustion efficiency of the two nozzles.
Concentration measurements indicated that the elliptical nozzle produced jets with smaller rich core regions and lower peak concentrations at all conditions. Firing tests indicated that the two nozzles produced equivalent ignition delays. Peak heat release rates were higher for the round nozzle, while the elliptical nozzle produced smoother transitions from premixed to diffusion burning. Combustion efficiency was slightly higher for the round nozzle. Results indicate that elliptical nozzles could potentially lower NOx and particulate emissions, but further experiments are required to test this hypothesis.
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Habbaky, Charles. "A Comparative Study between Circular and Elliptical Nozzle Holes on Natural Gas Combustion and Soot Formation in a Direct Injection Engine." Thesis, 2012. http://hdl.handle.net/1807/33230.
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The effects of changing nozzle hole patterns and hole geometry in a direct injection natural gas optically accessible engine was investigated. Six nozzles were studied having a 1 hole, 3 hole, and 9 hole pattern; each having either elliptical or circular hole geometries. Combustion images were taken with a high speed camera and the nozzles were compared on the basis of their ignition delay time, rate of heat release, net heat release, fuel utilization, gross indicated thermal efficiency, and particulate emissions. The best performance in all categories was achieved by the 9 hole nozzles which was largely attributed to better fuel mixing as a result of its hole distribution. The elliptical hole geometry exhibited characteristics of improved mixing mainly through reduced ignition delay time and reduced elemental carbon emissions.
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Glass, Lisa Anne. "The Central regions of early-type galaxies in nearby clusters." Thesis, 2012. http://hdl.handle.net/1828/4188.
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Remarkably, the central regions of galaxies are very important in shaping and influencing galaxies as a whole. As such, galaxy cores can be used for classification, to determine which processes may be important in galaxy formation and evolution. Past studies, for example, have found a dichotomy in the inner slopes of early-type galaxy surface brightness profiles. Using deprojections of the galaxies from the ACS Virgo and Fornax Cluster Surveys (ACSVCS/FCS), we show that, in fact, this dichotomy does not exist. Instead, we demonstrate that the brightest early-type galaxies tend to have central light deficits, a trend which gradually transitions to central light excesses – also known as compact stellar nuclei – as we go to fainter galaxies. This effect is quantified, and can be used to determine what evolutionary factors are important as we move along the galaxy luminosity function. The number of stellar nuclei that we observe is, in fact, an unexpected result emerging from the ACSVCS/FCS. Being three times more common than previously thought, they are present in the vast majority of intermediate and low-luminosity galaxies. Conversely, it has been known for over a decade that there is likely a supermassive black hole weighing millions to billions of solar masses at the center of virtually every galaxy of sufficient size. These black holes are known to follow scaling relations with their host galaxies. Using the ACSVCS, along with new kinematical data from long-slit spectroscopy, we measure the dynamical masses of 83 galaxies, and show that supermassive black holes and nuclei appear to fall along the same scaling relation with host mass. Both represent approximately 0.2% of their host’s mass, implying an important link between the two types of central massive objects. Finally, we extract elliptical isophotes and fit parameterized models to the surface brightness profiles of new Hubble Space Telescope imaging of the ACSVCS galaxies, observed in infrared and ultraviolet bandpasses. Taken together, the two surveys represent an unprecedented collection of isophotal and structural parameters of early-type galaxies, and will allow us to learn a great deal about the stellar populations and formation histories of galaxy cores.<br>Graduate
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Wang, Rui-Sheng, and 王瑞聖. "Analysis of Elliptical-Hole Photonic Crystal Fiber." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/31748481091071152828.
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碩士<br>義守大學<br>電機工程學系<br>101<br>Through Vector Boundary Element Method, this thesis is analyzing and simulating elliptical-hole photonic crystal fiber. For the propagation modes, we change the air hole radius, elliptical ratio, wavelength, and turn the angle of air hole structure. In here, we analyze not only in the characteristics of mode also including polarization. As shown in the result, we will discuss the effective index of the EPCF, we knows inversely proportional to relationship of effective index and wavelength. At η=1.2, the effective index is the maximum value. Therefore, we will discuss the polarization of the EPCFs, the relationship between the birefringence and the wavelength is direct ration. By analyzing turn the angle of air hole’s 90-degrees-polarization, it’s found that the birefringence is clearly more obvious than its original structure. The highest birefringence rate is 0.0008.
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Wang, Yuhsiang, and 王昱翔. "An Analysis of Sheet Metal Elliptical Cup Drawing and Elliptical Hole-flanging Processes." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/06237532778782981816.
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碩士<br>聖約翰科技大學<br>自動化及機電整合研究所<br>99<br>This essay is base on I-DEAS to build a module and to grid computing, and adopting the conception of the Prandtl-reuss plasticity equations, the von Mises yield criterion, large deformation finite element model, and updated Lagrangian formulation (ULF) to use the DYNAFORM Finite Element Method, FEM simulator.
Using the values of tensile testing on cold rolled steel (SPCC-SD) to be the standard values of production procedure simulation analyzing, and simulating the deep drawing process of elliptical cup and the elliptical hole convex axis forming. Then the relationship of punch loading and stroke, deformation history, thickness change history, and forming limit.
Using 50-ton hydraulic machine to examine the deep drawing of elliptical cup and the elliptical hole-flanging process. And compare simulation values with examined values.
Regarding to the deep drawing process of cylindrical cup, the minimum thickness is at the contact area of parts and long punch axle. That is because the material Withstand the maximum tensile stress at this area.
From the limit drawing ratio of perimeter of Convex axis and perimeter of material, we can know that the limit drawing rate is 2.136. During process, the perimeter of material will affect the limit of forming,
Regarding to the elliptical hole-flanging forming, the maximum stresses and minimum thickness is at the contact area of parts and long punch axle. That is because the material withstand the maximum tensile stress at the area of internal elliptical hole, and force the thickness become thin. Regarding to short axle, the Radius of curvature is big, so the thickness is not changed.
From the limit drawing ratio of circumference of elliptical punch profile and the circumference of the minimal initial elliptical punch profile of the minimal initial elliptical hole of the blanks. We can know that the limit drawing rate of elliptical hole-flanging is 1.463. During process, the bore diameter of material will affect the material’s limit of forming,
This essay is base on I-DEAS module design and DYNAFORM finite element method, FEM simulator to analysis the authenticity and reliability. It can provide the reference for the staffs who are in mold design and process analysis field. As process improvement, mold design, and simulation analysis of defects estimated reference.
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Seshagiri, Sanjeev. "Identification of Force Coefficients in Two Squeeze Film Dampers with a Central Groove." Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-05-9430.
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Squeeze Film Dampers (SFD) provide viscous damping in rotor bearing systems to reduce lateral vibration amplitudes and to isolate mechanical components. Aircraft engine shafts, often supported on roller bearings, operate at high rotational speeds and are susceptible to large amplitude shaft whirl due to rotor imbalance. SFDs aid to reduce such large whirl amplitudes while also eliminating rotor instabilities.
he current work quantifies experimentally the forced performance of two parallel squeeze SFDs separated by a central groove. Force coefficients are identified in a specialized SFD test rig constructed to undergo similar operating and loading conditions as in jet engines. Of interest is to quantify the effect of a central feed groove on the forced performance of SFDs and to validate predictions from a computational tool. The test rig comprises of an elastically supported bearing structure and one of two journals. Tests are conducted on two open ends SFDs, both with diameter D and nominal radial clearance c; each damper with two parallel film land lengths L= 1/5 D and 2L, separated by a feed groove of width L and depth 3/4 L. ISO VG 2 grade lubricant oil flows into the central groove via 3 orifices, 120 degrees apart, and then through the film lands to finally exit to ambient. In operation, a static loader pulls the bearing to various static off center positions with respect to the stationary journal, and electromagnetic shakers (2,200 N) excite the test system with single frequency loads over a frequency range to generate rectilinear, circular and elliptical orbits with specified motion amplitudes. A frequency domain method identifies the SFD mechanical parameters, viz., stiffness, damping, and added mass coefficients.
The long damper generates 7 times more direct damping and 2 times more added mass compared to the short length damper. The damping coefficients are sensitive to the static eccentricity (up to 50 percent c) while showing lesser dependency on the amplitude of whirl motion (up to 20 percent c). On the other hand, added mass coefficients are nearly constant with static eccentricity and decrease with higher amplitudes of motion. The magnitudes of identified cross-coupled coefficients are insignificant for all imposed operating conditions for either damper.
Large dynamic pressures recorded in the central groove demonstrate the groove does not isolate the film lands by merely acting as a source of lubricant, but contributes to the generation of large added mass coefficients. The recorded dynamic pressures in the film lands and central groove do not evidence lubricant vapor or gas cavitation for the tested static eccentricities and amplitudes of motion.
The direct damping coefficients for both dampers are independent of excitation frequency over the frequency range of the tests. Predictions derived from a novel SFD computational tool that includes flow interactions in the central groove and oil supply orifices agree well with the experimental force coefficients for both dampers.
The current work advances the state of the art in SFDs for jet engines.
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Kuo, Yu-Ting, and 郭育廷. "Stress Concentration of Laminated Composite Plate with an Elliptical Hole." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/24916817542251186532.
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碩士<br>逢甲大學<br>機械工程學所<br>94<br>The characteristic of its structure laminated composite plate with an Elliptial hole, while building up model necessarily needing to first understand laminate composite material the stress around distribute in the condition. Because an Elliptial hole under loaded as the structure investigate the stress distribution and the stress concentration factor around an Elliptial hole of a laminated composite plate with an Elliptial hole. The laminated composite plate under loads behavior then the maximum normal stress as 90° , and the maximum compressive stress as 0° around an Elliptial hole . The objective of this paper inquires to effect of the fiber ply orientations under loaded laminated composite plate with an Elliptial hole investigate the stress distribution around an Elliptial hole by using ANSYS Finite Element program. The laminated composite plate with an Elliptial hole under loaded behavior analysis consult the basis in the future.
The laminated composite plate with an Elliptial hole under loaded investigate the stress distribution and the stress concentration factor can change because around an Elliptial hole go to the plate of the distance of size. The stress distribution and the stress concentration factor obvious , so all strength isn’t ideal.
The Quasi-Isotropic laminated composite plate with an Elliptial hole laminate ply way effect all composite plate strength. All laminated plate thickness isn’t change and changed every a laminated thickness. Example： ， laminate ply. Each fiber ply is the same for the stress distribution as under loaded condition. Two kinds of Quasi-Isotropic laminated composite plate comparisons , , both 0° layer in order to mainly bears the stress structure, but have the more fiber ply. Therefore 0° layer the stress distribution and the stress concentration factor
comparisons , and laminated 0 ° layer the stress distribution and the stress concentration factor seems to is lower.
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Huang, Po-Jung, and 黃柏融. "A Study of stress concentration forOrthotropic plates containing elliptic holes." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/22759632672979992774.
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碩士<br>國立臺灣大學<br>應用力學研究所<br>101<br>With dual boundary integral equation, combined from Cauchy''s formalism and anisotropic elastic mechanics, this thesis is aimed to analyze the maximum stress concentration on the inner plate or boundary by five different types of elliptic holes in an orthotropic plate. First, the analytic solution of the infinite plate with single elliptic hole under uniform tensile stress is used to confirm the accuracy of the numerical method. Second, five different types of elliptic holes are compared with literature numerical solution for isotropic material to further confirm the accuracy of the method. And then, this thesis takes Silicon, a cubic materials, for example, when the ratio of minor axes to major axes and the distance between two or more than two elliptic holes are smaller, the maximum stress value will be larger, and it would be slightly smaller than that for isotropic material. Last, when the material constant A formed by elastic constant is smaller, the maximum stress value would be larger, but the value would not change obviously with material constant B. This thesis constructs a method for computing the maximum stress concentration value by inputting the elastic constant, the size of holes, and distance between each holes.
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Huang, Chih-hsiung, and 黃鋕雄. "An Analysis of Elliptical Hole-flanging Forming Process of Sheet Metal." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/j9h3ek.
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碩士<br>國立臺灣科技大學<br>機械工程系<br>94<br>A methodology of formulating an elasto-plastic three-dimensional finite element model, which is based on Prandtl-Reuss flow rule and Hill’s yield criterion respectively, associated with an updated Lagrangian formulation, is developed to simulation sheet metal flanging process. The shape function derived from a four-node quadrilateral degenerated shell element associated into the stiffness matrix to constitute the finite element model. An extended rmin algorithm is proposed to formulate the boundary condition, such as nodal penetration and separation, strain increment and rotation increment and altered elasto-plastic state of material.
In order to verify the reliability and accuracy of the FEM code, the fractured thickness of a specimen in the simple tension test is adopted as the fracture criterion of forming limit in simulation. The numerical simulation results include relationship between punch load and punch stroke, distribution of the thickness, distribution of the stress, distribution of the strain, deformation history and the forming limit etc. in elliptical hole-flanging forming process.
According to the simulation and experiment results, the maximum stress and the minimum thickness are concentrated on the contact regions between workpiece and punch major axis. The maximum punch load decrease, as the profile radius of elliptical punch and initial hole of blank increase remarkably. The initial hole of blank has great influence on the forming limit, but it is independent of the profile radius of elliptical punches. The limiting forming ratio (LFR) is defined between the circumference of elliptical punch profile and the circumference of the minimal initial elliptical hole of the blanks. The LFR amounts to about 1.4627 for penetration in the elliptical hole-flanging process of this study. The different of the ratio of the punch major axis to the punch minor axis, as the aspect ratio of punch increase, the punch major axis regions is closed to the fractured thickness and the expanding height is low too.
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王廷軒. "The Strength of Braided Composite Plates Each with an Inclined Elliptical Hole." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/49941383892006376911.
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碩士<br>逢甲大學<br>機械與電腦輔助工程學系<br>104<br>In the work, the Finite Element software —ANSYS— and Point Stress Criterion are used for studying the fracture strength of braided composite plates each with an elliptical hole of inclined angle 45o. First, carbon fiber braid was impregnated with epoxy resin to make braided composite plates by hot-press method. Then, by means of metallographic microscope, we observed the cross-section of a specimen along the direction of fiber yarn weaving, and got the high length ratio and the fiber volume fraction. Furthermore, the Stiffness Averaging Method was adopted to calculate the equivalent engineering moduli of the braided composite plates, and the calculated axial Young’s modulus was then verified by experimental data. Carrying out the tension experiment with the specimens with various major axes (miner radius is fixed) which incline an angle of 45° to the horizontal is to get fracture strength of specimens. Next, the engineering moduli and the resulting fracture strengths of the experimental group are input into ANSYS for analysis to obtain the stress distribution beside the hole in this plate. Meanwhile, the characteristic length from the Point Stress Criterion is derived. Furthermore, the Least-squares method is adopted to set up a functional relationship between characteristic length and major radius.
Finally, in order to verify the accuracy of this study, specimens with different radius were made, and the functional relationship mentioned above was used to calculate the characteristic length and the predicted fracture strength. By comparison to experimental data, it is shown that our method can accurately predicted the notched strength of braided composite plates each containing an inclined elliptical hole with a maximum error of only 2.23%.
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莊啟揚. "A Study on the Strength of Composite Laminates each with an Elliptical Hole." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/88603940195379749401.
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Sun, Han-Yun, and 孫涵筠. "A Study on the Strength of Braided Composite Laminates with a Central Inclined Elliptical Hole." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/35jyux.
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碩士<br>逢甲大學<br>纖維與複合材料學系<br>105<br>In this study, we used both Finite Element Based Point Stress Criterion (FEBPSC) and experiments to investigate the notched strengths of braided composite laminates each with an inclined elliptical hole of inclined angle 30o. First, carbon braided fabrics were reinforced with epoxy resin to make composite plates by hot-press method. Then,braided composite plates were made into tensile specimens each with an central inclined elliptical hole. Tensile tests were applied to the specimen to obtain their notched strengths. The finite element analysis based point stress criterion was used to calculate the characteristic length for each specimen. Least-squares method is adopted to set up a functional relationship between the characteristic lengths and the elliptical hole radii. Finally the predicted notched strength for each specimen can be obtained. According to the comparison results the predicted notched strengths were well matched with the experimental notched strengths for all specimens. The maximum error for all specimen between the predicted notched strengths and the experimental notched strengths is only within 3.84%. Therefore it can be concluded that the finite element analysis based point stress criterion is very effective to predict the notched strengths of braided composite plates each with an central inclined elliptical hole.
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江志言. "A Study of the Notched Strength of Braided Composite Plates with a Central Elliptical Hole." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/52119972250958503007.
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WIKARTA, ALIEF, and 維佳達. "Antiplane Interaction of a Crack with a Reinforced Elliptical Hole Embedded in an Infinite Matrix." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/27749310318686189396.
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碩士<br>國立臺灣科技大學<br>機械工程系<br>97<br>Analytical exact solutions of a fundamental anti-plane interaction problem for a reinforced elliptical hole embedded in an infinite matrix with an arbitrarily oriented crack located in the matrix under a remote uniform shear load are provided in this paper. Investigations on the present anti-plane problem are tedious due to the presence of material in-homogeneities and geometric discontinuities. Based on the technique of conformal mapping and the method of analytical continuation in conjunction with the alternating technique, the general expressions of the stress function in the coated layer and the matrix are derived explicitly in a closed form. By applying the existing solutions for dislocation functions, the integral equations for a line crack are formulated and the mode-III stress intensity factors are obtained numerically. Several numerical examples are given to demonstrate the effects of geometrical parameters and material property combinations on the strength of the anti-plane stress singularity.
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WANG, JING-XING, and 王淨行. "FEM computational methods of the endochronic plasticity on the thin plate with central elliptical hole." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/74018223415161355763.
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陳威穎. "A Study of the Strength of Nano-silica/Braided Composite Plates with a Central Elliptical Hole." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/53600034520425263196.
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Wu, Jiunn-Shyan, and 吳俊賢. "A 3-D Anal. of Anisotropic Plates Containing an Elliptic Hole." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/29097283645007855184.
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Sun-Chih, Tsai, and 蔡尚志. "Thermal stresses in an infinite body with a partially reinforced elliptic hole." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/87089871312465203087.
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碩士<br>國立臺灣科技大學<br>機械工程系<br>87<br>This paper provides an analytical exact closed-form solution for a partially reinforced elliptic hole embedded in an infinite isotropic or anisotropic medium under a remote uniform heat flow. Based on the method of analytical continuation which can staisfy the boundary conditions and the technique of conformal mapping, the full field solutions for the temperature and stresses are obtained in compact complex form. The rotation angle of a reinforced portion on the hole due to the application of a remote uniform heat flow is determined analytically which is dependent of the material property, geometric configuration and the magnitude of applied loading. Comparison of the present results with the existing ones shows that our derived solutions are exact and general. Finally, in order to check answer correctness the stress functions corresponding to anisotropic problems are successfully reduced to those corresponding to isotropic problems. Some numerical results are carried out and shown in graphic form to illustrate the physic behavior of the present problem.
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WONG, WEI-ZE, and 翁維澤. "Prediction of the Notched Strength of Braided Composite plates Each with an Elliptical Hole of 15 inclining Angle." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/7v7w58.
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碩士<br>逢甲大學<br>機械與電腦輔助工程學系<br>106<br>In this paper, we mainly investigate the failure strength of braided composite plates each with an elliptical hole of 15o inclining angle. The Finite Element Analysis software ANSYS and the point stress criterion are used to predict the notched strength. First, we put the carbon fiber braid into the mixed liquid with epoxy resin, and then use hot-press method to make braided composite plates. Next, we use the tensile testing machine to obtain the experimental data and employ the diamond cutter to cut a sample along the direction of fiber yarn weaving. Then, we observe fracture mechanism by putting the sample under the metallographic microscope. Finally, we can see the fluctuating of yarn weaving together with crack and delamination.
By ANSYS and point stress criterion, the characteristic length and notched strength can be predicted. By comparison to experimental data, it is shown that our method can accurately predict the notched strength of braided composite plates with a maximum error of only 3.49%.
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CHEN, LI-PING, and 陳麗萍. "Plane stress analysis of A 2-D finite-length plate containg a circular/elliptical inclusion/hole using BEM." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/88237124856160666185.
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WANG, ZHAO-LIN, and 王兆麟. "Failure prediction of a plate weakened by an ellptic hole or elliptic rigid inclusion under thermal or mechanical load." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/69677236204945237610.
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Tupholme, Geoffrey E. "Row of shear cracks moving in one-dimensional hexagonal quasicrystalline materials." 2014. http://hdl.handle.net/10454/9236.
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No<br>Representations for the stress fields created around an infinite row of collinear, antiplane shear cracks moving within one-dimensional hexagonal quasicrystals, and the resulting stress intensity factors and the J-integral, are determined in closed-form and discussed, using an extended method of dislocation layers. The solutions for a finite quasicrystalline plate containing a single moving crack and a plate with a moving edge crack are also provided by this analysis. (C) 2014 Elsevier Ltd. All rights reserved.