• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.5
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• pp.475-482
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• 2010

In this paper, an efficient two-level parallel domain decomposition algorithm is suggested to solve large-DOF structural problems. Each subdomain is composed of the coarse problem and local problem. In the coarse problem, displacements at coarse nodes are computed by the iterative method that does not need to assemble a stiffness matrix for the whole coarse problem. Then displacements at local nodes are computed by Multi-Frontal Sparse Solver. A parallel version of PCG(Preconditioned Conjugate Gradient Method) is developed to solve the coarse problem iteratively, which minimizes the data communication amount between processors to increase the possible problem DOF size while maintaining the computational efficiency. The test results show that the suggested algorithm provides scalability on computing performance and an efficient approach to solve large-DOF structural problems.

• Steel and Composite Structures
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• v.29 no.3
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• pp.379-389
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• 2018

In this research, the explicit closed-form local buckling solution of steel plates in contact with concrete, with both loaded and unloaded edges elastically restrained against rotation and subjected to eccentric compression is presented. The Rayleigh-Rize approach is applied to establish the eigenvalue problem for the local buckling performance. Buckling shape which combines trigonometric and biquadratic functions is introduced according to that used by Qin et al. (2017) on steel plate buckling under uniform compression. Explicit solutions for predicting the local buckling stress of steel plate are obtained in terms of the rotational stiffness. Based on different boundary conditions, simply yet explicit local buckling solutions are discussed in details. The proposed formulas are validated against previous research and finite element results. The influences of the loading stress gradient parameter, the aspect ratio, and the rotational stiffness on the local buckling stress resultants of steel plates with different boundary conditions were evaluated. This work can be considered as an alternative to apply a different buckling shape function to study the buckling problem of steel plate under eccentric compression comparing to the work by Qin et al. (2018), and the results are found to be in consistent with those in Qin et al. (2018).

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.4
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• pp.449-459
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• 2000

The original Mindlin-type degenerated shell element perform reasonably well for moderately thick shell structures. However, when full integration for analysis of thin shell is used to evaluate the stiffness matrix, the stiffness of shell element is often over-estimated due to shear or membrane locking phenomena. To correct this problem, the formulation of the new degenerated shell element is derived by the combination of two different techniques. The first type of elements(TypeⅠ) has used assumed shear strains in the natural coordinate system to overcome the shear locking problem, the reduced integration technique in in-plane strains(membrane strains) to avoid membrane locking behaviour. Another element(TypeⅡ) has applied the assumed strains to both of membrane strain and transverse shear strains. The improved degenerated shell element has been tested by several numerical problems of shell structures. Numerical results indicate that this shell element shows fast convergence and reliable solutions.

• Structural Engineering and Mechanics
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• v.40 no.5
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• pp.637-654
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• 2011

The present paper studies the variation of the natural frequencies and mode shapes of rectangular plates carrying a three degree-of-freedom spring-mass system (subsystem), when the subsystem changes (stiffness, mass, moment of inertia, location). An analytical approach based on Lagrange multipliers as well as a finite element formulation are employed and compared. Numerically reliable results are presented for the first time, illustrating the convenience of using the present analytical method which requires only the solution of a linear eigenvalue problem. Results obtained through the variation of the mass, stiffness and moment of inertia of the 3-DOF system can be understood under the effective mass concept or Rayleigh's statement. The analysis of frequency values of the whole system, when the 3-DOF system approaches or moves away from the center, shows that the variations depend on each particular mode of vibration. When the 3-DOF system is placed in the center of the plate, "new" modes are found to be a combination of the subsystem's modes (two rotations, traslation) and the bare plate's modes that possess the same symmetry. This situation no longer exists as the 3-DOF system moves away from the center of the plate, since different bare plate's modes enable distinct motions of the 3-DOF system contributing differently to the "new' modes as its location is modified. Also the natural frequencies of the compound system are nearly uncoupled have been calculated by means of a first order eigenvalue perturbation analysis.

• The Journal of the Society of Korean Medicine Diagnostics
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• v.13 no.1
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• pp.1-9
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• 2009

Objectives : If patients notice a symptom indicating inveterate dyspepsia but they don't have any problem around gastroscope, they get diagnosed as a functional dyspepsia or an imaginary stomach disease, but to overcome the limitations of these diagnoses, we are analyzing them for the common feature and are looking for a new diagnostics for them. Methods : Based on our survey with 122 patients with inveterate dyspepsia, we analyzed the period of onset, eating habits, the main symptoms, and observations on the gastroscope. We also analyzed the function of the stomach and intestines by EAV examinations, and the outer walls of the stomach and intestines by subdividing the level of coagulation into six with abdominal palpation. Results : We figured out that people who appeals about inveterate dyspepsia have had long period of onset, and that they had bad eating habits, shoulder stiffness, neck stiffness, headache, dizziness, etc. These are all the similar symptoms beside dyspepsia, which indicates that it is a syndrome. From about 70%, they didn't had particular problem in gastroscope, and as to be seen from the result of EAV examination, their stomachs and intestines had become functionless. Also, we were able to feel a stiffened tissue through abdominal palpation. Conclusion : Through this investigation, we found out that what the gastroscope can not find so that gets diagnosed as a functional dyspepsia or an imaginary stomach disease can be diagnosed as a syndrome called damjeok by overcoming the limitation utilizing the survey, EAV examinations, and abdominal palpation. We can find a mighty significance from the fact that it can be diagnosed as a syndrome.

• Structural Monitoring and Maintenance
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• v.5 no.4
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• pp.463-488
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• 2018

In the last decades, research efforts have been spent to investigate the effect of prestressing on the dynamic behaviour of prestressed concrete (PSC) beams. Whereas no agreement has been reached among the achievements obtained by different Researchers and among the theoretical and the experimental results for simply supported beams, very few researches have addressed this problem in continuous PSC beams. This topic is, indeed, worthy of consideration bearing in mind that many relevant bridges and viaducts in the road and railway networks have been designed and constructed with this structural scheme. In this paper the attention is, thus, focused on the dynamic features of continuous PSC bridges taking into account the effect of prestressing. This latter, in fact, contributes to the modification of the distribution of the bending stress along the beam, also by means of the secondary moments, and influences the flexural stiffness of the beam itself. The dynamic properties of a continuous, two spans bridge connected by a nonlinear spring have been extracted by solving an eigenvalue problem in different linearized configurations corresponding to different values of the prestress force. The stiffness of the nonlinear spring has been calculated considering the mechanical behaviour of the PSC beam in the uncracked and in the cracked stage. The application of the proposed methodology to several case studies indicates that the shift from the uncracked to the cracked stage due to an excessive prestress loss is clearly detectable looking at the variation of the dynamic properties of the beam. In service conditions, this shift happens for low values of the prestress losses (up to 20%) for structure with a high value of the ratio between the permanent load and the total load, as happens for instance in long span, continuous box bridges. In such conditions, the detection of the dynamic properties can provide meaningful information regarding the structural state of the PSC beam.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.4
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• pp.76-83
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• 2005

With the acceleration of the miniaturization of products, especially in recent years, machining technologies for these products is in need of improvement. Conventional technologies have limitations in realizing the miniaturization due to the downsizing effects of the tools, which lack sufficient cutting stiffness during machining. The application of ultrasonic vibration is one of the most useful solutions in dealing with the problem. This study focused on the difference of ultrasonic drilling from conventional one in geometrical machining mechanism and the corresponding machining results. In detailed, some mathematical equations for drill cutting edge paths during drilling were extracted and new method to find uncut chip thickness from above equations was suggested. The experiments were carried out through the comparison between the results (disposed chips and internal surface states of holes) of conventional drilling and those of ultrasonic drilling. It was determined that the geometrical paths of cutting edges and analyzed uncut chip thickness agree with the appearance of disposed chips. Furthermore, the change in tool path by ultrasonic vibration resulted in the improvement of surface statement.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10b
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• pp.202-207
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• 1993

A theoretical and experimental study is presented for the force holding control of a miniature robotic ringer which is driven by a pair of piezoelectric unimorph cells. In the theoretical analysis, one finger is modeled as a flexible cantilever with a tactile force sensor at the tip and the mate of the finger is a solid beam supposed with sufficient stiffness. Further, the force sensor is modeled by a one-degree-of-freedom, mass-spring system and the output of sensor is then described by the sensor stiffness multiplied by the relative displacement. The problem investigated in this paper is that two typical holding tasks of the human finger are picked up and applied to the robotic finger. One is the work holding a stationary object with a prescribed, time-varying force and the other one is to keep the contacted force constant even if the object is in motion. The simple PID feedback control scheme is used to control the minute gripping force of order 0.01 Newton. It is shown both experimentally and theoretically that the artificial finger with the piezoelectric actuator works well in the minute force holding of the tiny object.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.264-269
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• 2008

This paper presents the summary of control of abnormal vibration found in the COP motors of a nuclear power plant. All six identical units of COP pump-motor assemblies showed unstable vibration pattern of which one or two showed higher vibration enough to exceed the allowable level from the installation stage. Many trials of test, measurement, overhaul and replacement had been repeated to investigate and solve the problem but only to reach unsatisfactory settlement. Recently several times of site tests are made and followed by significant diagnostic actions in which the authors group participated. It was found that the coupled shafting system of motor and pump is in close resonance with the $1^{st}$ shaft rotating speed. Redesign of topside motor bearing clearance is made to increase bearing stiffness and hence to avoid the resonance which consequently led to reduce the troubled vibration to allowable and stable status.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.4
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• pp.465-472
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• 2008

An automotive windshield wiper system is modeled mainly for vibration analysis purpose. The model is composed of solid links, ideal joints, imperfect joints to simulate unavoidable manufacturing defects and bushings having stiffness, contact between a wiper blade and a wind screen glass, friction, a spring and an actuator. Main stream of wiper dynamics analysis has been obtaining a closed form of system of equations using Newton's or Lagrange's formula and doing a numerical simulation study to understand and predict the behavior of it. However, the modeling process is complex since a wiper system is of multibody and a contact problem occurs. When imperfection, such as dead zone of a joint and stiffness of a rubber bushing, should be included, the added complexity makes the modeling difficult. Since the imperfection is understood as main cause of problematic vibration, the dynamics model of a wiper system aiming vibration analysis should include such unavoidable manufacturing defects in the model. An open form of dynamic model of a automotive windshield wiper system with imperfect joints using a commercial software is obtained and a simulation analyssis is conducted for vibration reduction study.