• Journal of the Korean Society for Precision Engineering
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• v.12 no.5
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• pp.126-135
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• 1995

An exhaust muffler is one of the simple and effective means to meet the demand for a quiet vehicle, and it deserves a close attention to effectively reduce the engine noise. The transfer function technique is one of the tools that have been used to analyze the noise characteristics of the exhaust muffler. In this paper we obtained a transfer function using the forward-going and backward-going components of sound pressure in the exhaust muffler, which is compatible wiht lattice filter algorithm. This form of transfer function is obtained for the basic elements of a muffler, such as uniform tube, open termin- ation, closed termination, anechoic termination, expansion, contraction, extended-tube resonator, hole, Helmholtz resonator, and concentric hole-cavity resonator. The results are combined to produce the transfer function of various types of mufflers. With this transfer function we calculate the transmission and insertion losses of mufflers, and examined the effects of various design parameters. Comparisons were made between the calculation and experimental results, which showed a good agreement, and we conclude that the transfer function of lattice form can be used to analyze the noise characteristics of the exhaust mufflers.

• Wind and Structures
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• v.28 no.4
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• pp.255-270
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• 2019

Aerodynamic configurations of bridge decks have significant effects on the aerostatic torsional divergence and flutter forsuper long-span bridges, which are onset for selection of suitable bridge decksfor those bridges. Based on a cable-stayed bridge with double main spans of 1500 m, considering typical twin-box, stiffening truss and closed-box section, which are the most commonly used form of bridge decks and assumed that the rigidity of those section is completely equivalent, are utilized to investigate the effects of aerodynamic configurations of bridge decks on aerodynamic instability performance comprised of the aerostatic torsional divergence and flutter, by means of wind tunnel tests and numerical calculations, including three-dimensional (3D) multimode flutter analysis and nonlinear aerostatic analysis. Regarding the aerostatic torsional divergence, the results obtained in this study show twin-box section is the best, closed-box section the second-best, and the stiffening truss section the worst. Regarding the flutter, the flutter stability of the twin-box section is far better than that of the stiffening truss and closed-box section. Furthermore, wind-resistance design depends on the torsional divergence for the twin-box and stiffening truss section. However, there are obvious competitive relationships between the aerostatic torsional divergence and flutter for the closed-box section. Flutter occur before aerostatic instability at initial attack angle of $+3^{\circ}$ and $0^{\circ}$, while the aerostatic torsional divergence occur before flutter at initial attack angle of $-3^{\circ}$. The twin-box section is the best in terms of both aerostatic and flutter stability among those bridge decks. Then mechanisms of aerostatic torsional divergence are revealed by tracking the cable forces synchronous with deformation of the bridge decksin the instability process. It was also found that the onset wind velocities of these bridge decks are very similar at attack angle of $-3^{\circ}$. This indicatesthat a stable triangular structure made up of the cable planes, the tower, and the bridge deck greatly improves the aerostatic stability of the structure, while the aerodynamic effects associated with the aerodynamic configurations of the bridge decks have little effects on the aerostatic stability at initial attack angle of $-3^{\circ}$. In addition, instability patterns of the bridge depend on both the initial attack angles and aerodynamic configurations of the bridge decks. This study is helpful in determining bridge decksfor super long-span bridges in future.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.133-151
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• 1991

In this paper an analytic discussion was made for a finite element analysis performed for the case study of Seoul subway NATM tunnel. The effects mainly discussed on the ground deformation analysis were the staged tunnel excavation and the excavated distance from a tunnel facing. The concept of ground characteristic line has been applied to properly consider the loading condition given by staged tunnel excavation so that the imaginary supporting pressure is applied on the excavated tunnel face. Discussions on the results of the performed finite element analysis were mainly made with respect to the ground settlement, tunnel displacement, earth pressure, stress mobilized in supporting members. And the three dimensional supporting effect due to the tunnel facing was evaluated based on an elastic closed-form solution and a result of two dimensional axisymmetric finite element analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.299-303
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• 2004

In our pervious paper, a new parallel-type spherical 3-degree-of-freedom mechanism consisting of a two-degree-of-freedom parallel module and a serial RRR subchain was proposed[1]. In this paper, its improved version is suggested and implemented. Differently from the previous 3-dof spherical mechanism, gear chains are incorporated into the current version of the mechanism to drive the distal revolute joint of the serial subchain from the base of the mechanism and in fact, the modification significantly improves kinematic characteristics of the mechanism within its workspace. Firstly, after a brief description on its structure, the closed-form solutions of both the forward and the reverse position analysis are derived. Secondly, the first-order kinematic model of the mechanism for the inputs which are assumed to be located at the base is derived. Thirdly, through the simulations of the kinematic analysis via. kinematic isotropic index, it is confirmed that the mechanism has much more improved isotropic properties throughout the workspace of the mechanism than the previous mechanism in [1]. Lastly, the proposed mechanism is implemented to verify the results from this analysis.

• Journal of Power Electronics
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• v.9 no.4
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• pp.553-566
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• 2009

In-phase control and energy-optimized control are the two major control strategies proposed for series power quality controllers (SPQC). However quantitative analysis and comparison between these two control strategies is quite limited in previous publications. In this paper, an extensive quantitative analysis is carried out on these two control strategies through phasor diagram approach, and a detailed quantitative comparison is conducted accordingly. The load current is used as the reference phasor, and this leads to a simpler and clearer phasor diagram for the quantitative relationship. Subsequently detailed analysis of SPQC using in-phase control and energy-optimized control are provided respectively, under different modes both for under voltage/voltage sag and for over voltage/voltage swell. The closed form analytic expressions and the curves describing SPQC compensation characteristics are obtained. The detailed system power flow is figured out for each mode, and the detailed quantitative comparison between the two control strategies is then carried out. The comparison covers several aspects of SPQC, such as required compensating voltage magnitude, required capacity of energy storage component, and maximal ride-through time. In the end, computer simulation and prototype experimental results are shown to verify the validity of all the analysis and the result of the comparison.

• Cross-Cultural Studies
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• v.36
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• pp.37-59
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• 2014

William Wordsworth's "The Thorn" revolves around the following questions: Who is Martha? Why does she go to the mountain top and repeat her doleful cry? To these questions, it gives us two different kinds of answers; one derives from the villagers, and the other from the narrator. This essay attempts to examine how the answers exemplify two different critical approaches to the problem of community, using Jacques Lacan's account of sexual difference in his seminar on Encore as a guiding thread of analysis. The important thing to retain here is that sexual difference in Lacan's seminar on Encore does not so much indicate biological determinations as two distinct forms of relating to the other which are intimately bound up with the question of how a community is constructed and maintained. The first form, called "masculine," suggests that it is a radical exception to a community that makes possible the community as a field of totality or sameness; the second form, called "feminine," shows that each of the subjects cannot be regarded as a member of a closed community which is guaranteed by the exceptionality, but as an exception that is radically singular. This in turn leads us to consider the possibility that the masculine form has to do with the villagers' effort to distinguish themselves from Martha and the feminine form with the way in which the narrator confronts and represents her. In the course of his formulation of sexuation graph, Lacan stresses that the masculine side must be supplemented by the feminine side, which allows us to elaborate on why, concerning Martha, the narrator does not just keep the completely different position from the villagers'. This is to say that the villagers' representation of Martha as an exception to the community should be supplemented by the narrator's attempt to tell Martha's story as the villagers do and at the same time to capture something of her enigmatic unrepresentability. Bearing in mind Charles Shepherdson's elaboration of traumatic memory, this essay also tries to clarify how the narrator preserves and even transmits something of Martha's truth that is embodied in her uncontrollable and unassimilable cry.

• Journal of Advanced Research in Ocean Engineering
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• v.1 no.1
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• pp.55-62
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• 2015

Floating structure such as tension leg platform, semi-submersible and spar are widely used in field of oil exploration and renewable energy system. All of these structures have the base cylinder support structure which have effective rule in overall dynamic of response. So the accurate and reliable modeling is needed for optimum design and understanding the physical background of these systems. The aim of this article is an analytical discussion on stochastic modeling of floating cylinder based support structure but an applicable one. Due to this a mathematical mass-damper-spring system of a floating cylinder of HAWAII WTG offshore wind as an applicable and innovative system is adopted to model a coupled degrees using random vibration in analytical way. A fully develop spectrum is adopted to solve the stochastic spectrum analytically by a proper approximation. Some acceptable assumption is adopted. The simplified but analytical and innovative hydrodynamic analysis of this study not only will help researcher to concentrate more physically on hydrodynamic analysis of floating structures but also can be useful for any quick, simplified and closed form analysis of a complicated problem in offshore engineering.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.7
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• pp.664-672
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• 2010

This paper provides the target observability analysis of time-to-go polynomial guidance law with bearing-only measurement. In this study, a direct approach is used to analyze the target observability. Since the observability condition of a constant-velocity target is given by the function of LOS angle only, the target observability characteristic is determined by substituting the closed form solution of LOS angle to the observability condition directly. The analysis results show that the target observability is depended on the choice of guidance gain, initial intercept condition and guidance command shape. After that this mathematical analysis result is evaluated and demonstrated by number of simulation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.12
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• pp.1471-1481
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• 2009

In diesel engines, it is inevitable that the torsional vibration is produced by the fluctuation of engine torque. Therefore, it is necessary to establish preventive measures to diminish the torsional vibration. The sleeve spring type damper is one of the preventive measures for reducing the torsional vibration. In this study, the closed form equations to predict the spring constant of a sleeve spring and the torsional characteristics of the torsional vibration damper are proposed to calculate stiffness of the damper and verified their availability through the finite element analysis and experiments. And the stability of the sleeve spring torsional vibration damper is verified by analyzing the inner star and outer star, which are the core parts of the damper, and 2-roll bending process is proposed to manufacture sleeve spring. The program to calculate the initial radius including spring-back effect is developed, and the FEA method to analyze elasto-plastic problem was verified through analysis of 90$^{\circ}$bending process. The results of the analysis are in good agreements with those of the experiments. The newly proposed method can be used as an advanced technique that remarkably curtails cost of production and replaces the conventional forming.

• Journal of The Korean Association For Science Education
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• v.19 no.4
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• pp.585-594
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• 1999

The purpose of this study is to examine the concept of Greenhouse Effect as understood by middle school high school university students using a closed-form questionnaire. Based on results of the questionnaire which was administered to 619, the extent to which alternative concepts were held was quantified and compared the difference of various group based on grade level. gender, text and major. Also, subjects were divided into two groups, one is middle school students and the other is high school university students and common themes within conceptual framework of each group were identified by factor analysis. The result showed that students confused Greenhouse Effect with ozone layer depletion in stratosphere and linked familiar contamination around everyday life. acid rain. radioactive contamination, nuclear arsenal to Greenhouse Effect. These trends were more appreciable in female than male, biology major than any other major and text did not make any significant difference. In addition, the result of factor analysis showed that two groups linked familiar contamination around everyday life to Greenhouse Effect and high school university students understand the consequences of an increase in the Greenhouse Effect more systematically than middle school student, perceived the relation between the origin of an increase in the Greenhouse Effect and human activity but confused Greenhouse Effect with ozone layer depletion in stratosphere.