• Journal of Advanced Marine Engineering and Technology
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• v.10 no.4
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• pp.31-40
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• 1986

With the tendency toward high speed and high pressure in centrifugal pumps, the problem of sub-synchronous vibration has arisen, caused by the hydraulic forces of the working fluid, such as wearring, balance piston, impeller, etc.. These forces can drastically alter the rotor critical speeds and stability characteristics, and can be acted significant destabilizing forces. For preventing such self-excited vibration, the desing of the rotor system needs, which would secure the stability of the machine. In this paper, a procedure is presented for dynamic modeling of rotor-bearing-seal-impeller systems which consist of rigid disks, distributed parameter finite rotor elements and discrete bearings, seals and impellers. A finite element model including the effects of rotatory inertia and gyroscopic moments is developed using the consistent matrix approach. The technique of dynamic matrix reduction is applied to the shaft matrices to reduce them to a set of matrices of dynamic of significantly fewer degrees of freedom. The representation of bearing, seal and impeller elements is in term of linearized stiffness and damping matrices by reasonably small perturbations from equilibrium. The stability behavior of a typical double suction centrifugal pump is presented. Results show the influence of clearance and flow conditions on running speeds and stability characteristics.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.338-338
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• 2006

Equilibrium behavior of ABA triblock copolymer with different lengths of endblock A chains was examined using self-consistent field theory by Matsenl. It was found that at small asymmetries, the A block bidispersity reduces the stretching energy of the A domains. This effect causes a slight increase in the domain spacing and shifts the order-order transitions toward higher A volume fractions. At large asymmetries, the short A blocks pull free of their domains allowing their B blocks to relax. A feature of microphase-separated structure of asymmetric poly(methyl acyrylate) (PMA)-b-polystyrene-b-PMA using SAXS, DSC and ESR was experimentally examined. These measurements gave an evidence of the solubilization of short A chains to the B domains.

• Ocean and Polar Research
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• v.26 no.3
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• pp.515-521
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• 2004

The processes of formation and dissociation of gas hydrates were investigated by monitoring pressure and temperature variations in a pressure cell in order to understand the kinetic behavior of gas hydrate and the controlling factors fur the phase transition of gas hydrate below freezing. Gas hydrates were made kom guest gases ($CH_4,\;CO_2$, and their mixed-gas) and fine ice powder. We found that formation and dissociation speeds of gas hydrates were not controlled by temperature and pressure conditions alone. The results of this study suggested that pressure levels at the formation of mixed-gas hydrate determine the transient equilibrium pressure itself.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1530-1537
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• 1991

본 연구에서는 반무한 직선 계면균열의 상하면에 임의로 분포하는 어떠한 하 중에 대해서도 그 해석이 가능한 그린함수(Green's function)를 구하고자 한다. 이 를 위하여 반무한 직선 계면균열상의 임의의 한 점에 평면 집중하중이 작용하는 문제 와 비평면 집중전단하중이 작용하는 문제를 각각 택하였고, 이때 계면균열의 선단은 열려있다고 가정하였다. 이 문제를 풀므로써 균열선단부근의 응력성분을 결정하고 이로부터 그린함수의 의미를 지니는 응력강도계수에 대한 폐형해를 얻었다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.174-178
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• 1999

This paper describes an investigation on bearing failure due to spragging that has been continuously occurred in turbine hearings. The spragging is defined as the damage found on the leading edge of unloaded pads in the tilting pad journal bearing, In general, the damage mechanism by spragging is classified into fatifgue failure, The principle cause of spragging could be thought as the self-excited vibration by the absence of a stable static equilibrium position of upper pads with no preload. Because of serious consequences of system breakdowns due to bearing failures, determination ar the causes of failure and effective method for countermeasures are very important. This paper describes both the causes of spragging and countermeasures for prevention of such failure, which are taken place in the electric power plants.

• Korean System Dynamics Review
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• v.1 no.1
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• pp.133-157
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• 2000

This paper deals with the social system from the point of system thinking consisting the fundamental construct of system dynamics. The Bertalanffy's general system theory, having been criticized because of its ambiguity, and the complex science theory, emerging system theory, are integrated by using the system thinking which is characterized with three concepts, 'feedback thinking', 'dynamic thinking', 'operational thinking'. In the integration, system thinking suggests the dynamic pattern of the social system have not only an equilibrium status but also complex status. The science of complexity gives an implication to system dynamics the important of the uncertainty and complexity if we interpret the social system as an open system. To show more concrete description, I simulate the cooperation model based on the iterated prisoner dilemma. The simulation results show the diverse patterns of cooperation and betrayal. Especially the sensitivity of initial payoff will cause the chaotic strategic landscapes as the game gose on. These results mean that we should not give the hasty prescription to control social system artificially. Because social system retains the self-organizing force in itself.

• Journal of Korean Association for Spatial Structures
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• v.18 no.2
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• pp.25-34
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• 2018

This study investigated a bio-tensegrity structural system that combines the characteristics of a general tensegrity structural system with a biological system. The final research objective is to accomplish a changeability for the structural system as like the movement of the natural bio-system. In the study, we present a shape finding procedure for the two stage bio-tensegrity system model inspired by the movement pattern of animal backbone. The proposed system is allowing a dynamic movement by introducing the concept of "saddle" for the variable bio-tensegrity structure. Several shape finding analysis example and results are presented and shows a efficient validation and suitability.

• Structural Engineering and Mechanics
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• v.43 no.5
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• pp.583-605
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• 2012

This paper presents a spatial catenary cable element for the nonlinear analysis of cable-supported structures. An incremental-iterative solution based on the Newton-Raphson method is adopted for solving the equilibrium equation. As a result, the element stiffness matrix and nodal forces are determined, wherein the effect of self-weight and pretension are taken into account. In the case of the initial cable tension is given, an algorithm for form-finding of cable-supported structures is proposed to determine precisely the unstressed length of the cables. Several classical numerical examples are solved and compared with the other available numerical methods or experiment tests showing the accuracy and efficiency of the present elements.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.10a
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• pp.176-183
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• 1999

This paper describes the application of discretized continuum-type optimality criteria (DCOC) for the reinforced concrete continuous beams. The cost of construction as objective function which includes the costs of concrete, reinforced steel, formwork is minimized. The design constraints include limits on the maximum deflection in a given span, on bending and shear strengths, optimality criteria is given based on the well known Kuhn-Tucker necessary conditions, followed by an iterative procedure for designs when the design variables are the depth and the steel ratio. The self-weight of the beam is included in the equilibrium equation of the real system. Two numerical examples of reinforced concrete continuous beams with rectangular cross-section are solved to show the applicability and efficiency for the DCOC-based technique

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.10a
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• pp.134-141
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• 1997

A geometrically non-linear finite element formulation of spatial cable networks is presented using three cable elements. Firstly, derivation procedures of tangent stiffness and mass matrices for the space truss element and the elastic catenary cable element, and the isoparametric cable element are summarized. The load incremental method based on Newton-Raphson iteration method and the dynamic relaxation method are presented in order to determine the initial static state of cable nets subjected to self-weights and support motions. Furthermore, static non-linear analysis of cable structures under additional live loads are performed based on the initial configuration. Challenging example problems are presented and discussed in order to demonstrate the feasibility of the present finite element method and investigate static non-linear behaviors of cable nets.