• Journal of the Korean Society for Precision Engineering
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• v.5 no.2
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• pp.33-42
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• 1988

In a large scale oil hydraulic system having repeatedly operated actuator, such as a large scale forging press, pressure surges often due to the recombination of oil column in a return line attached to the downstream side of a directional control valve. Expecially, the pressure surges appear very severe ones at a certain valve operating frequency. These pressure surges restrict the operating frequency of the hydraulic system. But related reports on the above mentioned phenomenon are rarely to be found. In this study, therefore, the authors investigate the exact reason why such severe pressure surges occur at a certain range of valve operating frequency. The study is performed by experiment and numerical computation on the relationship between pressure surges and valve operating frequency.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.12
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• pp.4513-4532
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• 2014

Motivated by the Weber's Law, this paper proposes an efficient and robust shape descriptor based on the perceptual stimulus model, called Weber's Law Shape Descriptor (WLSD). It is based on the theory that human perception of a pattern depends not only on the change of stimulus intensity, but also on the original stimulus intensity. Invariant to scale and rotation is the intrinsic properties of WLSD. As a global shape descriptor, WLSD has far lower computation complexity while is as discriminative as state-of-art shape descriptors. Experimental results demonstrate the strong capability of the proposed method in handling shape retrieval.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.10a
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• pp.411-420
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• 1999

The computational model and a new eigenvalue solution algorithm for large-scale structures is presented in the form of parallel computation. The computational loads and data storages required during the solution process are drastically reduced by evenly distributing computational loads to each processor. As the parallel computational model, multiple personal computers are connected by 10Mbits per second Ethernet card. In this study substructuring techniques and static condensation method are adopted for modeling a large-scale structure. To reduce the size of an eigenvalue problem the interface degrees of freedom and one lateral degree of freedom are selected as the master degrees of freedom in each substructure. The performance of the proposed parallel algorithm is demonstrated by applying the algorithm to dynamic analysis of two-dimensional structures.

• Journal of the Korean Society for Railway
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• v.9 no.1 s.32
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• pp.12-17
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• 2006

The bridge to be analyzed is a self-anchored suspension bridge which is constructed within the country. Forced vibration test was performed with oscillator for verification of safety, maintenance and management. In this study, the feasibility of deduction was verified with the modified analysis model by comparing natural frequency, natural mode and damping ratio of the real bridge, which are obtained from the vibration test of the whole bridge after construction of 3-dimensional self-anchored cable suspension bridge, with the eigenvalue of analytic computation model and evaluating them. As a result of study, the friction of bridge bearing must be considered to get the natural frequencies of flexural vibration, and evaluating the polar moment of inertia is critical factor in analysis modeling in case of torsional vibration. The logarithmic damping ratio of the test appeared to exceed the ordinary one assumed at the design phase.

• Proceedings of the KIEE Conference
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• 1993.07a
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• pp.76-78
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• 1993

This paper describes an efficient method of computing any desired number of the most unstable eigenvalues and eigenvectors of a large scale multi-machine power system. Approximate eigenvalues obtained by Hessenberg process are refined using Rayleigh quotient iteration with cubic convergence property. If further eigenvalues and eigenvectors are needed, the procedure described above are repeated with deflation. The proposed algorithm can cover all the model types of synchronous machines, exciters, speed governing system and PSS defined in AESOPS. The proposed algorithm applied to New England test system with 10 machines and 39 buses produced the results same with AESOPS in faster computation time. Also eigenvectors computed in Rayleigh quotient iteration makes it possible to make eigen-analysis for improving unstable modes.

• Smart Structures and Systems
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• v.6 no.5_6
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• pp.525-543
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• 2010

Testing and validation processes are critical tasks in developing a new hardware platform based on a new technology. This paper describes a series of experiments to evaluate the performance of a newly developed MEMS-based wireless sensor node as part of a wireless sensor network (WSN). The sensor node consists of a sensor board with four accelerometers, a thermometer and filtering and digitization units, and a MICAz mote for control, local computation and communication. The experiments include calibration and linearity tests for all sensor channels on the sensor boards, dynamic range tests to evaluate their performance when subjected to varying excitation, noise characteristic tests to quantify the noise floor of the sensor board, and temperature tests to study the behavior of the sensors under changing temperature profiles. The paper also describes a large-scale deployment of the WSN on a long-span suspension bridge, which lasted over three months and continuously collected ambient vibration and temperature data on the bridge. Statistical modal properties of a bridge tower are presented and compared with similar estimates from a previous deployment of sensors on the bridge and finite element models.

• Bulletin of the Society of Naval Architects of Korea
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• v.13 no.2
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• pp.13-43
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• 1976

A potential flow approach is used to develop a method and an associated computer program for floating marine structures of general configuration in wave of all water depths with arbitrary heading. It computes the total force distributions and six degrees-of-freedom motion. The hydrodynamic-force equations and derived become identical under certain assumptions to the equations commonly used by the offshore industry, and the two methods are compared in detail. The computed motions of all six degree agree quite well with model-scale and full-scale experimental data for two typical semisubmersible drilling rigs in finite-depth water. Also the presented motion computations are more accurate than a previous work by the second approach. The present computations use experimentally validated or determined values of frequency-dependent hydrodynamic coefficients with the effects of the free surface and both finite and infinite water depths. The present method generates sufficient computation accuracy to use for practical design applications.

• Journal of the Korean Society of Safety
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• v.31 no.5
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• pp.95-101
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• 2016

This study proposes a multi-scale dynamic system reliability analysis of control system as a method of quantitative evaluation of its performance in probabilistic terms. In this second paper, we discuss the control effect of the viscous damper on the seismic performance of the structure-level failure. Since the failure of one structural member does not necessarily cause the collapse of the structural system, we need to consider a set of failure scenarios of the structural system and compute the sum of the failure probabilities of the failure scenarios where the statistical dependence between the failure scenarios should be taken into account. Therefore, this computation requires additional system reliability analysis. As a result, the proposed approach takes a hierarchial framework where the failure probability of a structural member is computed using a lower-scale system reliability with the union set of time-sequential member failures and their statistical dependence, and the failure probability of the structural system is again computed using a higher-scale system reliability with the member failure probabilities obtained by the lower-scale system reliability and their statistical dependence. Numerical results demonstrate that the proposed approach can provide an accurate and stable reliability assessment of the control performance of the viscous damper system on the system failure. Also, the parametric study of damper capacity on the seismic performance has been performed to demonstrate the applicability of the proposed approach through the probabilistic assessment of the seismic performance improvement of the damper system.

• Journal of Advanced Navigation Technology
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• v.18 no.5
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• pp.468-475
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• 2014

The recommend system is getting more difficult real time recommend by lager preference data set, computing power and recommend algorithm. For this reason, recommend system is proceeding actively one's studies toward distribute processing method of large preference data set. This paper studied distribute processing method of large preference data set using hadoop distribute processing platform and mahout machine learning library. The recommend algorithm is used Co-occurrence Matrix similar to item Collaborative Filtering. The Co-occurrence Matrix can do distribute processing by many node of hadoop cluster, and it needs many computation scale but can reduce computation scale by distribute processing. This paper has simplified distribute processing of co-occurrence matrix by changes over from four stage to three stage. As a result, this paper can reduce mapreduce job and can generate recommend file. And it has a fast processing speed, and reduce map output data.

• Journal of Intelligence and Information Systems
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• v.9 no.3
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• pp.117-135
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• 2003

This study is to propose a procedure solving scale problem of traditional collaborative filtering (CF) approach. The CF approach generally uses some similarity measures like correlation coefficient. So, as the user of the Website increases, the complexity of computation increases exponentially. To solve the scale problem, this study suggests a clustering model-based approach using Self-Organizing Map (SOM) and RFM (Recency, Frequency, Momentary) method. SOM clusters users into some user groups. The preference score of each item in a group is computed using RFM method. The items are sorted and stored in their preference score order. If an active user logins in the system, SOM determines a user group according to the user's characteristics. And the system recommends items to the user using the stored information for the group. If the user evaluates the recommended items, the system determines whether it will be updated or not. Experimental results applied to MovieLens dataset show that the proposed method outperforms than the traditional CF method comparatively in the recommendation performance and the computation complexity.