• Title/Summary/Keyword: Hydrodynamic Performance

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Application of multi objective genetic algorithm in ship hull optimization

  • Guha, Amitava;Falzaranoa, Jeffrey
    • Ocean Systems Engineering
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    • v.5 no.2
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    • pp.91-107
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    • 2015
  • Ship hull optimization is categorized as a bound, multi variable, multi objective problem with nonlinear constraints. In such analysis, where the objective function representing the performance of the ship generally requires computationally involved hydrodynamic interaction evaluation methods, the objective functions are not smooth. Hence, the evolutionary techniques to attain the optimum hull forms is considered as the most practical strategy. In this study, a parametric ship hull form represented by B-Spline curves is optimized for multiple performance criteria using Genetic Algorithm. The methodology applied to automate the hull form generation, selection of optimization solvers and hydrodynamic parameter calculation for objective function and constraint definition are discussed here.

Feasibility Study on the New Structure of a Spindle Motor for Hard Disk Drive

  • Kim, Tae-Woo;Chang, Jung-Hwan
    • Journal of international Conference on Electrical Machines and Systems
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    • v.2 no.3
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    • pp.295-299
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    • 2013
  • This paper presents the new structure of a spindle motor for hard disk drive (HDD). It can produce axial force as well as torque without a pulling plate or a pulling magnet required for the normal operation of a hydrodynamic bearing in rotating-shaft structure. The proposed models have different air gap length along the axial direction by changing the thickness of permanent magnet (PM). One has a single slope and the other has double slopes on the surface of PM. For the design of the proposed models, variables are defined and its effects on the motor performances are investigated by 3-demensional finite element analysis (FEA). The equi-performance curves are investigated for the main characteristics of the spindle motor such as generated torque, axial force and torque ripple ratio. The validity of the proposed models is verified by the feasibility study and performance evaluation.

Numerical Analysis of Hydrodynamic Performance of a Movable Submerged Breakwater (가동식 잠수 방파제의 유체동력학적 성능 수치해석)

  • Koo, Weon-Cheol;Kim, Do-Hyun
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.1
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    • pp.23-32
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    • 2011
  • Numerical analysis of hydrodynamic performance of a movable submerged breakwater was carried out as an eco-friendly marine structure for coastal and harbor protection. Using boundary elements method with two-dimensional frequency-domain reflection and transmission coefficients and wave forces acting on the submerged flat plate were calculated with various submerged depths and respective motion allowable modes. The movable breakwater was found to be more efficient in wave-blocking than the fixed structure. Variation of reflection coefficients was significantly influenced by vertical motion of the body.

Hydrodynamic performance of a vertical slotted breakwater

  • George, Arun;Cho, Il Hyoung
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.12 no.1
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    • pp.468-478
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    • 2020
  • The wave interaction problem with a vertical slotted breakwater, consisting of impermeable upper, lower parts and a permeable middle part, has been studied theoretically. An analytical model was presented for the estimation of reflection and transmission of monochromatic waves by a slotted breakwater. The far-field solution of the wave scattering involving nonlinear porous boundary condition was obtained using eigenfunction expansion method. The empirical formula for drag coefficient in the near-field, representing energy dissipation across the slotted barrier, was determined by curve fitting of the numerical solutions of 2-D channel flow using CFD code StarCCM+. The theoretical model was validated with laboratory experiments for various configurations of a slotted barrier. It showed that the developed analytical model can correctly predict the energy dissipation caused by turbulent eddies due to sudden contraction and expansion of a slotted barrier. The present paper provides a synergetic approach of the analytical and numerical modelling with minimum CPU time, for better estimation of the hydrodynamic performance of slotted breakwater.

Experimental Evaluation for Hydrodynamic Performance of a Hybrid Supported Type Fast Craft

  • Yang, S.I.;Koh, C.D.;Ahn, J.W.;Kim, Y.G.;Lee, J.-T.
    • Journal of Ship and Ocean Technology
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    • v.4 no.4
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    • pp.34-44
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    • 2000
  • This paper deals with the sea trial results of a fast craft with the hybrid supported type hul form. waterjet propulsion system and motion control system. The hybrid-type container ship operable in the sea with a wave height of y6 m, a speed of 50 knots and a payload of 1,500 tons were designed. A 1/8 scale 10 m- long test craft was constructed and tested in open seas. The hydrodynamic performance such as speed, turning, motion control in waves and waterjet thrush was analyzed.

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Skill Assessments for Evaluating the Performance of the Hydrodynamic Model (해수유동모델 검증을 위한 오차평가방법 비교 연구)

  • Kim, Tae-Yun;Yoon, Han-Sam
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.14 no.2
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    • pp.107-113
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    • 2011
  • To evaluate the performance of the hydrodynamic model, we introduced 10 skill assessments that are assorted by two groups: quantitative skill assessments (Absolute Average Error or AAE, Root Mean Squared Error or RMSE, Relative Absolute Average Error or RAAE, Percentage Model Error or PME) and qualitative skill assessments (Correlation Coefficient or CC, Reliability Index or RI, Index of Agreement or IA, Modeling Efficiency or MEF, Cost Function or CF, Coefficient of Residual Mass or CRM). These skill assessments were applied and calculated to evaluate the hydrodynamic modeling at one of Florida estuaries for water level, current, and salinity as comparing measured and simulated values. We found that AAE, RMSE, RAAE, CC, IA, MEF, CF, and CRM are suitable for the error assessment of water level and current, and AAE, RMSE, RAAE, PME, CC, RI, IA, CF, and CRM are good at the salinity error assessment. Quantitative and qualitative skill assessments showed the similar trend in terms of the classification for good and bad performance of model. Furthermore, this paper suggested the criteria of the "good" model performance for water level, current, and salinity. The criteria are RAAE < 10%, CC > 0.95, IA > 0.98, MEF > 0.93, CF < 0.21 for water level, RAAE < 20%, CC > 0.7, IA > 0.8, MEF > 0.5, CF < 0.5 for current, and RAAE < 10%, PME < 10%, CC > 0.9, RI < 1.15, CF < 0.1 for salinity.

Evaluation of Course Stability Performance for Tanker using CFD (CFD를 이용한 Tanker의 침로안정성 평가)

  • Hong, Chun-Beom;Yang, Hee-Jun
    • Journal of the Society of Naval Architects of Korea
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    • v.45 no.5
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    • pp.523-529
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    • 2008
  • The course stability performance for tankers is evaluated by computational fluid dynamics. In the present work, a Reynolds averaged Navier-Stokes (RANS) code is applied to a maneuvering problem covering the pure drift and yaw motions. The purposes of this study are to evaluate the hydrodynamic force in the bare hull (AFRAMAX) in pure drift and yaw motion and to provide information about the trends in the forces and moments when the rudder angles are varied. The flow simulation is performed by FLUENT. The CFD code is examined to find the optimistic computational condition such as size of grid, turbulence model and initial condition. The hydrodynamic derivatives in drift and pure yaw motion are estimated by the numerical simulation, and then the stability levers are calculated. It is confirmed that the computations show the superiority and inferiority of course stability performance according to the hull forms. Finally, the CFD code is applied to the estimation of the rudder forces when the rudder angles are varied. The propeller effect expressed by the body force distribution is also included.

The Effect of Leaflet Elasticity on the Hydrodynamic Performance of Trileaflet Prosthetic Valves (삼엽인공판막 leaflet 탄성도가 수력학적 성능에 미치는 영향)

  • Seo, J.C.;Rhee, K.H.;Lee, S.H.;Ahn, H.
    • Proceedings of the KOSOMBE Conference
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    • v.1997 no.11
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    • pp.109-112
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    • 1997
  • The Hydrodynamic performance of the trileaflet polymer prosthetic valves depends on the design of the leaflet and the physical properties of the leaflet membrane. In order to study the effect of leaflet membrane elasticity on the hemodynamic performance of trileaflet prosthetic valve, leaflet membranes are manufactured using two different polymers - Biospan and Tecoflex SG-93A. The hemodynamic performance parameters are measured under steady and physiological pulsatile flow, and compared with monoleaflet polymer valve(floating valve) and bileaflet mechanical valve(St. Jude Medical valve). Well designed trileaflet valve shows the lowest mean pressure drop among the tested valves. The trileaflet valves with Biospan membrane show lower pressure drop and back low comparing to those with Tecoflex membrane. More elastic membrane may provide wide opening area during systole and close membrane ree edge contact during diastole. Durability of trileaflet valves are also tested in vitro. Trileaflet valves with non-uniform membrane thickness ail within 17 days because of stress concentration. Trileaflet polymer valves with uniform membrane thickness perform well over 55 days without failure.

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Hydrodynamic Performance Test of a Turbopump (터보펌프의 수력 성능시험)

  • Hong Soon-Sam;Kim Dae-Jin;Kim Jin-Sun;Choi Chang-Ho;Kim Jin-Han
    • Journal of the Korean Society of Propulsion Engineers
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    • v.10 no.1
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    • pp.18-22
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    • 2006
  • Hydrodynamic performance test was conducted for a fuel pump of a liquid rocket engine turbopump. The pump driven by an electric motor was tested using water. It is experimentally shown that the inducer had very small effect on the pump's head and efficiency but great effect on the pump's cavitation performance. Additionally, inducer test was carried out to investigate the effect of the inducer on the pump in detail, and it was found that the pump reached a critical cavitation number when the inducer head dropped by 55%.

Shallow Water Effect on Resistance Performance of Large Container Ship Based on CFD Analysis (천수 효과가 대형 컨테이너선의 저항 성능에 미치는 영향에 관한 전산유체역학 해석 연구)

  • Sun-kyu, Lee;Youngjun, You;Jinhae, Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.59 no.6
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    • pp.345-354
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    • 2022
  • It is easy for a ship passing through confined waters to be exposed in dangers of collisions and grounding due to different hydrodynamic responses. Since marine accidents can cause significant impacts on environments, global economy, and human lives, it is necessary to study the effect of shallow water on hydrodynamic performance of a ship. In this paper, the effect of water depth on resistance performance was investigated using CFD analysis as an initial study for improving navigational safety of a large container ship under confined waters. After a CFD set-up for deep water condition was validated and verified by comparing CFD analysis with model test results, CFD calculations according to ship speed and water depth were conducted. The features were investigated in terms of tendency and physical knowledge related to resistance performance. The increase of resistance due to shallow water effect was reviewed with empirical formula suggested from SWABE JIP. Speed loss due to shallow water effect was additionally reviewed from estimated delivered power according to ship speed and water depth.