Browsing by Author "Kim, Jihwan"
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Item Model reduction in nonlinear structures(Texas Tech University, 2007-05) Kim, Jihwan; Barhorst, Alan; Burton, Thomas D.; Berg, Jordan M.; Seshaiyer, Padmanabhan; Ekwaro-Osire, StephenModel reduction is the method that approximates high order systems by lower order ones in mathematical models. Reduction method is efficient and accurate ways to represent and to simulate the responses of nonlinear structures. The motivation for this work arises in the problem of modeling, analysis, and simulation of very complex structures that may be composed of dozens or hundreds of individual components and that may need the order of millions of degree of freedom to capture necessary geometric detail in a finite element model. The reduction methods (LBR and CMS based reduction) are based on the linear transformation and use the physical coordinates rather than modal coordinates so these reduction methods are easy to apply on the complex nonlinear problems. This dissertation is to study several methods of reduced order modeling for structural systems. The objective of the reduced order methods is to provide a significant reduction in the number of degrees of freedom while retaining essential information from the original model. For the free vibration the numerical integration are perform on the system having various nonlinearities. The reduced order model accurately represents the responses of the original model and very reliable on strong nonlinear damping and weak to moderate nonlinear static effects. For the forced vibration harmonic excitation the reduced model retains nonlinear characteristics in the frequency-response curve such as jump phenomena, backbone curve, and superharmonic resonance. For the variable frequency excitation, both the reduced and original system have good agreement in amplitude and frequency in the steady-state responses. In the random frequency response, the reduced model is in good agreement with the original model in frequency spectrum analysis even though the time responses of the reduced mode with strong nonlinear effect have deteriorated from the responses of the original model. Based on the numerical results of the reduction method, it can be summarized that the reduced model captures the system response of the full model with good accuracy and linear based model reduction and a modified CMS reduction method are very promising to use in various nonlinear structural problems.Item The temporal suffixes in Korean and their interpretations(2007-12) Kim, Jihwan; Beaver, David I., 1966-This report deals with the issue of tense and aspect system in Korean both semantically and syntactically. Previous accounts for tense and aspect in Korean have been based on the assumption that the suffix has a fixed meaning, either temporally or aspectually, and either perfect(ive) or imperfective, and so on. In this report, I argue that the interpretation of the temporal suffix in Korean must be more flexible. The interpretation of the suffix is dependent on the occurrence conditions such as the characteristics of the verbs (or the predicates) and the temporal adverbials. For this claim, I argue how to understand tense and viewpoint aspect in Korean based on ‘twocomponent theory of aspect’ (Smith 1997) along the line of ‘boundedness’ of the grammaticalized aspect (Depraetere 1995) and ‘Event realization’ by Bohnemeyer and Swift (2004): –ess is either past tense or perfective aspect suffix and –nun is a present tense suffix with imperfective aspect meaning, because –nun only occurs with [+dynamic] predicates. Further, I argue how we can reflect the semantic tense and aspect onto the syntactic representation properly. Following Demirdache & Uribe-Etxebarria (1997, 2000), I show how tense and aspect in Korean can be mapped onto the syntactic representation. To treat the temporal adverbials, I follow Thompson (2005) that temporal adverbials are linked to [spec, AspP] position when they play a role as Reference Time (RT). Finally, I argue how the relations of the temporal arguments are syntactically realized in Korean. And –ess is interpreted as perfective aspect when the RT and ST (Speech Time) overlap.