• 제목/요약/키워드: Hydrodynamic Performance

검색결과 492건 처리시간 0.024초

초소형 HDD용 유체 동압베어링의 동적 성능평가 시스템 (Development of Performance Evaluation System for Hydrodynamic Bearing in Hard Disk Drive)

  • 박성준;이형욱;송정한;이혜진
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2009년도 추계학술대회 논문집
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    • pp.66-68
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    • 2009
  • Most hard disk spindles currently used are supported by oil lubricated hydrodynamic bearings. However, in the trend of increasing spindle speed and reducing size and cost, dynamic behaviors of the bearing such as RRO and NRRO are more important. A novel system evaluating dynamic behavior of hydrodynamic bearings in had disk drive was developed to analyze the effect of groove shapes and parameters.

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시스템 검증에 의한 조종수학 모형의 평가 (Estimation of Maneuvering Mathematical Model by System Identification Techniques)

  • 이호영;신현경
    • 한국해양공학회지
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    • 제13권4호통권35호
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    • pp.118-123
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    • 1999
  • The mathematical model used in the simulation of ship's maneuvering contains the hydrodynamic coefficients, which are usually evaluated based on PMM model tests in the towing tank and used to predict ship's maneuvering performance when applied to the proto-type ship. The proper mathematical model has to be developed to predict ship's maneuvering motions with hydrodynamic coefficients very well. The mathematical model for PMM model tests is analyzed with identification program and the hydrodynamic coefficients and maneuvering motions by system identification we compared with those obtained directly from PMM model tests and sea trial. The mathematical model for PMM model tests was established and the magnitudes of ship's maneuvering coefficients were determined. When the identified values of coefficients were used to simulate the maneuvers, a very good agreement was obtained between the numerically simulated motion responses and those obtained from PMM model tests.

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고하중과 고속 미끄럼 베어링 시스템의 경계윤활에 대한 연구 (Study on Boundary Lubrication in the Sliding Bearing System under High Load and Speed)

  • 장시열
    • Tribology and Lubricants
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    • 제15권3호
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    • pp.248-256
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    • 1999
  • Many tribological components in automobile engine undergo high load and sliding speed with thin film thickness. The lubrication characteristics of the components are regarded as ether hydrodynamic lubrication or boundary lubrication, whereas in a working cycle they actually have both characteristics. Many modem engine lubricants have various additives for better performance which make boundary film formation even under hydrodynamic lubrication regime. Conventional Reynolds equation with the viewpoints of continuum mechanics concerns only bulk viscosity of lubricant, which means that its simulation does not give insights on boundary lubrication characteristics. However, many additives of modern engine lubricant provide mixed modes of boundary lubrication characteristics and hydrodynamic lubrication. Especially, high molecular weight polymeric viscosity index improvers form boundary film on the solid surface and cause non-Newtonian fluid effect of shear thinning. This study has performed the investigation about journal bearing system with the mixed concepts of boundary lubrication and hydrodynamic lubrication which happen concurrently in many engine components under the condition of viscosity index improver added.

외란을 받는 저널 베어링의 비선형 주파수 응답 해석 (Nonlinear frequency Response Analysis of Hydrodynamic Journal Bearing Under External Disturbance)

  • 노병후;김경웅
    • Tribology and Lubricants
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    • 제15권1호
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    • pp.68-76
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    • 1999
  • This paper presents the nonlinear characteristics of the oil lubricated hydrodynamic journal bearing. The traditional approach is to characterize the behavior and performance of fluid film hydrodynamic journal bearings by means of linearized bearing analysis. The objective of this paper is to examine the nonlinear characteristics of the journal bearing when an external sinusoidal shock is given to the system. The oil film force is obtained by solving the finite width Reynolds equation at each time step by the solution of the column method. Frequency response function and journal orbit obtained from both linear and nonlinear bearing simulations are compared with each other.

수치해석을 통한 콘크리트 부유구조체 길이에 따른 운동 및 구조성능 검토 (Hydrodynamic Motion and Structural Performance of Concrete Floating Structure by Length Using Numerical Analysis)

  • 이두호;유영준
    • 콘크리트학회논문집
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    • 제25권4호
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    • pp.401-409
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    • 2013
  • 이 연구에서는 부유구조체의 단면특성은 동일하지만, 길이가 서로 다른 4가지의 대형 콘크리트 부유구조체에 대하여 운동 특성 및 구조성능의 해석적 연구를 수행하였다. 부유구조체 설치해역은 수심이 35 m인 연안을 대상으로 하였으며, 설치해역에서 발생할 수 있는 파랑주기 3초~10초 34개 규칙 파랑하중을 적용하였다. ANSYS-AQWA를 통하여 부유구조체의 동수역학 해석을 수행하였으며, 운동 특성을 검토하였다. 또한, 34개 파랑하중에서 부유구조체에 최대 응답진폭을 나타내는 위험 파랑하중을 선정하였으며, 선정된 위험파랑하중으로 인해 부유구조체에 도입되는 파압을 도출하였다. 위험 파랑하중으로 인해 도출된 파압을 부유구조체에 매핑(mapping)하여 구조성능을 검토하였다. 해석 결과를 종합해볼 때, 부유구조체의 길이가 증가할수록 부유구조체의 운동이 감소하는 것을 알 수 있다. 이것은 부유구조체와 파랑하중의 상호작용의 효과는 파랑주기와 구조물 길이에 지배적인 것으로 사료된다. 또한, 위험 파랑하중으로 인해 부유구조체의 하부슬래브는 인장응력이 발생하며, 부유구조체 길이는 단면력에 영향을 미치지 못하는 것을 알 수 있다.

유체-구조 반복해석법에 의한 유연 프로펠러의 설계 알고리듬 개발 (Design Algorithm of Flexible Propeller by Fluid-Structure Interactive Analysis)

  • 장현길;노인식;홍창호;이창섭
    • 대한조선학회논문집
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    • 제49권6호
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    • pp.528-533
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    • 2012
  • Flexible composite propellers are subject to large deformation under heavy loading, and hence the hydrodynamic performance of deformed propeller might deviate from that of the metallic propeller under negligible deformation. To design the flexible propeller, it is therefore necessary to be able to evaluate the structural response of the blades to the hydrodynamic loadings, and then the influence of the blade deformation upon the hydrodynamic loadings. We use the lifting-surface-theory-based propeller analysis and design codes in solving the hydrodynamic problem, and the finite-element-method program formulated with 20-node iso-parametric solid elements for the analysis of the structural response. The two different hydrodynamic and structural programs are arranged to communicate through the carefully-designed interface scheme which leads to the derivation of the geometric parameters such as the pitch, the rake and the skew distributions common to both programs. The design of flexible propellers, suitable for manufacturing, is shown to perform the required thrust performance when deformed in operation. Sample design shows the fast iteration scheme and the robustness of the design procedure of the flexible propellers.

A numerical study on hydrodynamic maneuvering derivatives for heave-pitch coupling motion of a ray-type underwater glider

  • Lee, Sungook;Choi, Hyeung-Sik;Kim, Joon-Young;Paik, Kwang-Jun
    • International Journal of Naval Architecture and Ocean Engineering
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    • 제12권1호
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    • pp.892-901
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    • 2020
  • We used a numerical method to estimate the hydrodynamic maneuvering derivatives for the heave-pitch coupling motion of an underwater glider. It is very important to assess the hydrodynamic maneuvering characteristics of a specific hull form of an underwater glider in the initial design stages. Although model tests are the best way to obtain the derivatives, numerical methods such as the Reynolds-averaged Navier-Stokes (RANS) method are used to save time and cost. The RANS method is widely used to estimate the maneuvering performance of surface-piercing marine vehicles, such as tankers and container ships. However, it is rarely applied to evaluate the maneuvering performance of underwater vehicles such as gliders. This paper presents numerical studies for typical experiments such as static drift and Planar Motion Mechanism (PMM) to estimate the hydrodynamic maneuvering derivatives for a Ray-type Underwater Glider (RUG). A validation study was first performed on a manta-type Unmanned Undersea Vehicle (UUV), and the Computational Fluid Dynamics (CFD) results were compared with a model test that was conducted at the Circular Water Channel (CWC) in Korea Maritime and Ocean University. Two different RANS solvers were used (Star-CCM+ and OpenFOAM), and the results were compared. The RUG's derivatives with both static drift and dynamic PMM (pure heave and pure pitch) are presented.

초기설계 단계에서의 스트럿 설계 고찰 (Study on the Shaft-Strut Design in the Initial Design Stage)

  • 이화준;장학수;전호환
    • 대한조선학회논문집
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    • 제41권6호
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    • pp.114-119
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    • 2004
  • For passenger vessels, twin shaft types in propulsion system is generally adopted to provide a high-speed performance in low draught due to restricted operating condition in harbors or water channels. Struts of twin open shaft type support the shafts, bearings, and propellers. Therefore, strut design is needed to consider not only hydrodynamic performance but also structural and noise/vibration performance, In this paper, considerations in strut design at the initial design stage have been discussed based on existing references, numerical calculations, and their comparisons. Also, the strut design of a RoPax ferry has been carried out at the initial design stage, for an example.

고속 활주선의 선형에 따른 저항 성능 및 규칙파 중 운동 성능 고찰 (Effects of Hull Form Variations on Resistance and Seakeeping Performance of Planing Hulls with and without Incoming Regular Waves)

  • 김동진;김선영;김성환;서정화;이신형
    • 대한조선학회논문집
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    • 제51권5호
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    • pp.369-379
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    • 2014
  • Planing hull forms have significant influences on those hydrodynamic performances in calm water and in waves. Therefore, the hydrodynamic performance of a planing vessel should be predicted by model tests or theoretical calculations, and be confirmed whether it shows the performance requirements at the design stage. In this study, four planing hull forms are designed with the goal of the improvement of resistance and seakeeping performance, and 1/6.5 scale model tests are carried out in Seoul National University towing tank. The effects of design parameters such as length-to-beam ratio, deadrise angle and forebody shape on the hydrodynamic performance are investigated, based on model test results. Running attitude and resistance of model ships in calm water are also estimated by empirical formulae proposed by Savitsky (1964; 2007; 2012), and compared with the model test results. It is shown that calm water performance of non-prismatic planing hulls can be predicted well by Savitsky (2012)'s formula which improves the original Savitsky(1964/2007)'s formula by taking into account the variations of deadrise angles, and the actual angles between the hull bottom and the free surface.

전가동타와 비대칭타의 유체동역학적 특성 및 속도성능 (Hydrodynamic Characteristics and Speed Performance of a Full Spade and a Twisted Rudder)

  • 최정은;김정훈;이홍기;박동우
    • 대한조선학회논문집
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    • 제47권2호
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    • pp.163-177
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    • 2010
  • This article examines hydrodynamic characteristics and speed performances of a ship attached with a full spade and a twisted rudder based on a computational method. For this study, a 13,100 TEU container carrier is selected. The turbulent flows around a ship are analyzed by solving the Reynolds-averaged Navier-Stokes equation together with the application of Reynolds stress turbulence model. The computations are carried out at the conditions of rudder, bare hull, hull-rudder and hull-propeller-rudder. An asymmetric body-force propeller is applied. The speed performance is predicted by the model-ship performance analysis method of the revised ITTC'78 method. The hydrodynamic forces are compared in both rudder-open-water and self-propulsion conditions. The flow characteristics, the speed performance including propulsion factors and the rudder-cavitation performance are also compared. The model tests are conducted at a deep-water towing tank to validate the computational predictions. The computational predictions show that the twisted rudder is superior to the full spade rudder in the respect of the speed and the cavitation performances.