• Title/Summary/Keyword: Magnitude factor

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Exploring the effects of speed and scale on a ship's form factor using CFD

  • Terziev, Momchil;Tezdogan, Tahsin;Demirel, Yigit Kemal;Villa, Diego;Mizzi, Simon;Incecik, Atilla
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.13 no.1
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    • pp.147-162
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    • 2021
  • The problem of predicting a ship's form factor and associated scale effects has been subject to many investigations in recent years. In this study, an attempt is made to investigate whether the form factor is influenced by a change in the ship's speed by numerically modelling a geosim series of the KCS hull form by means of a RANS solver. The turbulence dependence of the problem is also studied by altering the closure model among three widely used approaches (the k-𝜔, k-𝜔 SST, and k-𝜀 models). The results show that at very low speeds (Froude numbers in the range of 0.02-0.06) the numerical model predicts changes in the form factor of a ship between 10% and 20%, depending on the turbulence model and scale factor choices. As the speed is increased further, the form factor exhibits little change, usually in the range of 1% or less. Simulations where the Reynolds number is changed by approximately two orders of magnitude, achieved by altering the value of viscosity, confirmed that the form factor can be considered Froude-dependent only for low speeds, predicting essentially identical values when high speed cases are considered.

Implementation of the Self-tuning Control Algorithm with an Input- amplitude Constraint (제어입력 크기가 제한되는 자기동조 제어알고리즘의 구현에 관한 연구)

  • 장효환;정회범
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.9
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    • pp.2153-2161
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    • 1993
  • Self-tuning control algorithms for an input-amplitude constrained system are developed and implemented. Magnitude of control input for small motors is generally restricted to narrow bound due to actuator saturation. The gain-adjusted control algorithm and the bounded-gain control algorithm proposed in this study yield smoother control input variations within the magnitude constraints comparing with the existing Clarke's suboptimal control algorithm. In the gain-adjusted control algorithm, the feedforward gain is adjusted using maximum gain, while in the bounded-gain control algorithm, the feedforward gain is bounded using weighting factor. For the DC servo motor control, the system performances of the proposed algorithms are compared with those of the existing algorithm by computer simulation and experiment. It is shown that the input variations of the proposed algorithms are smoother as compared with the existing algorithm.

A Study on the 2nd exitation method for CVCF Generation of doubly-fed induction Generator (권선형 유도 발전기 CVCF 발전을 위한 2차 여자 제어법에 관한 연구)

  • Ahn, Jin-Woo;Kim, Chul-Woo;Hwang, Young-Moon
    • Proceedings of the KIEE Conference
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    • 1988.11a
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    • pp.341-344
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    • 1988
  • This paper derives a condition foe constant voltage i constant frequency generation of doubly-fed induction generator. The condition is varied by the magnitude of output voltage, load current and its power factor, slip of the machine. Magnitude of output voltage is controlled by exiting voltage which is caculated by derived equation from operating condition. frequency of output voltage is controlled by injecting slip frequency to the rotor which is the difference between wanted output frequency and rotor frequency.

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On-Line and Off-Line Partial Discharge Properties in the Pumped Storage Generator Stator Windings (양수발전기 고정자 권선에서 운전중 및 정지중 부분방전 특성)

  • Kim, Hee-Dong;Ju, Young-Ho;Yoon, Dea-Hen
    • Proceedings of the KIEE Conference
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    • 1999.07e
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    • pp.2089-2092
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    • 1999
  • Partial discharge(PD) tests were performed both when the pumped storage generator(rated 13.8kV and 220MVA) was on-line and off-line. This generator has been equipped with 12 bus coupler sensors in directional mode. PD tests were conducted using partial discharge analyzer(PDA), partial discharge meter(PDM) and digital partial discharge detector. PDA showed that the patterns of the normalized quantity number(NQN) and the partial discharge magnitude are in accord with on-line and off-line. The insulation condition was estimated by diagnostic tests(off-line) such as PD magnitude and dissipation factor.

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Study on Plastic Deformation of Cohesionless Soil through Cyclic Triaxial Test (반복삼축압축실험을 통한 사질토의 소성변형 특성에 관한 연구)

  • Shin, Eun-Chul;Kang, Hyoun-Hoi;Choi, Chan-Young;Yang, Hee-Aaeng
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.10a
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    • pp.1370-1376
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    • 2008
  • The structure of railroad or subway is that low fare transportation system of the large traffic volume. Like this structure is subjected to the cyclic load of moving vehicle. Consequently the result of the settlement analysis or plastic deformation prediction of railroad bed could be used as an important factor in safety of the railroad. The results of cyclic triaxial test were used in the numerical analysis of power model which Li and Selig(1994) developed. The soil samples were obtained from the construction site of railroad. Cyclic triaxial test was conducted with the variation of the magnitude of cyclic load and soil types. The large magnitude of plastic deformation in the railroad bed is caused of structure failure of the railroad.

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A psychophysical evaluation of passenger preferences of coach interior design (Psychophysics를 이용한 고속전철 객실내장설계의 승객 선호도 평가)

  • 한성호;정의승;박성준;곽지영;최필성
    • Proceedings of the ESK Conference
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    • 1993.04a
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    • pp.134-144
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    • 1993
  • The psychophysical magnitude estimation thechnique can provide a useful tool for determining the best design features of a product in terms of user preference, especially when it is difficult or almost impossible to obtain objective and quantitative data on the user performance. In this research, several interior design features of a high speed train such as arrangement of passenger seats, and availability of interior facilities were examined quantitatively to provide interior design recommendations for the high speed train. A train simulator was built to provide a realistic interior enviror enviroment of the high speed train, and individual design features were manipulated by using a three-factor within-subject experimental design. At the same time, a psychophysical scale of verbal descriptors ranging from "extremly like" to "extremly dislike" was developed to explain the magnitude estimates of the design features in ordinary language.n ordinary language.

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Flexural Pinching and Energy Dissipation Capacity (휨핀칭과 에너지 소산능력)

  • 박흥근;엄태성
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 2003.03a
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    • pp.275-285
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    • 2003
  • Pinching is an important property of reinforced concrete member which characterizes its cyclic behavior. In the present study, numerical studies were performed to investigate the characteristics and mechanisms of pinching behavior and the energy dissipation capacity of flexure-dominated reinforced concrete members. By analyzing existing experimental studies and numerical results, it was found that energy dissipation capacity of a member is directly related to energy dissipated by re-bars rather than concrete that is a brittle material, and that it is not related to magnitude of axial compressive force applied to the member. Therefore, for a member with specific arrangement and amount of re-bars, the energy dissipation capacity remains uniform regardless of the flexural strength that is changed by the magnitude of axial force applied. Due to the uniformness of energy dissipation capacity pinching appears in axial compression member. The flexural pinching that is not related to shear force becomes conspicuous as the flexural strength increases relatively to the uniform energy dissipation capacity. Based on the findings, a practical method for estimating energy dissipation capacity and damping modification factor was developed and verified with existing experiments.

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Prediction of earthquake-induced crest settlement of embankment dams using gene expression programming

  • Evren, Seyrek;Sadettin, Topcu
    • Geomechanics and Engineering
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    • v.31 no.6
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    • pp.637-651
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    • 2022
  • The seismic design of embankment dams requires more comprehensive studies to understand the behaviour of dams. Deformations primarily control this behaviour occur during or after earthquake loading. Dam failures and incidents show that the impacts of deformations should be reviewed for existing and new embankment dams. Overtopping erosion failure can occur if crest deformations exceed the freeboard at the time of the deformations. Therefore, crest settlement is one of the most critical deformations. This study developed empirical formulas using Gene Expression Programming (GEP) based on 88 cases. In the analyses, dam height (Hd), alluvium thickness (Ha), the magnitude-acceleration-factor (MAF) values developed based on earthquake magnitude (Mw) and peak ground acceleration (PGA) within this study have been chosen as variables. Results show that GEP models developed in the paper are remarkably robust and accessible tools to predict earthquake-induced crest settlement of embankment dams and perform superior to the existing formulation. Also, dam engineering professionals can use them practically because the variables of prediction equations are easily accessible after the earthquake.

Behavior of Fatigue Crack Propagation from Surface Flaw (表面欠陷 에 發생하는 疲勞크랙擧動)

  • 송삼홍;오환섭
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.9 no.2
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    • pp.150-157
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    • 1985
  • In terms of behavior of fatigue cracks propagated after build-up around the artificial drilled miro-hole, this study has been made of the build-up process of slips and micro cracks, behavior of micro-crack propagation and the definition of fatigue limit under the rotating bending stress with low carbon steel. The results of this study are as follows: (1) The fatigue limit is the repropagating critical stress for the nonpropagating cracks which have grown to some limit around the micro-hole in regard of the magnitude of micro-hole. (2) Behavior of the slips and micro-cracks initiation are occurring simultaneously in front and in rear of micro-hole tips in the view of the rotational direction, regardless of the magnitude of micro-hole. (3) Behavior of fatigue crack propagation is different from magnitude of micro-hole, its behavior is propagation of single crack about respectively large hole, but about respectively small hole, fatigue crack propagated joining phenomena of micro-cracks. (4) The behavior of fatigue fracture is affected by the factor of its defects in the view of magnitude of micro-hole when the diameter of the micro-holes are smaller than 50.mu.m, and this is also affected with the size effect of micro-hole diameter.

Stress intensity factors for periodic edge cracks in a semi-infinite medium with distributed eigenstrain

  • Afsar, A.M.;Ahmed, S.R.
    • Structural Engineering and Mechanics
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    • v.21 no.1
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    • pp.67-82
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    • 2005
  • This study analyzes stress intensity factors for a number of periodic edge cracks in a semiinfinite medium subjected to a far field uniform applied load along with a distribution of eigenstrain. The eigenstrain is considered to be distributed arbitrarily over a region of finite depth extending from the free surface. The cracks are represented by a continuous distribution of edge dislocations. Using the complex potential functions of the edge dislocations, a simple as well as effective method is developed to calculate the stress intensity factor for the edge cracks. The method is employed to obtain the numerical results of the stress intensity factor for different distributions of eigenstrain. Moreover, the effect of crack spacing and the intensity of the normalized eigenstress on the stress intensity factor are investigated in details. The results of the present study reveal that the stress intensity factor of the periodic edge cracks is significantly influenced by the magnitude as well as distribution of the eigenstrain within the finite depth. The eigenstrains that induce compressive stresses at and near the free surface of the semi-infinite medium reduce the stress intensity factor that, in turn, contributes to the toughening of the material.