• Title/Summary/Keyword: Roll-coefficient

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A Study for Roll characteristic of Railway Vehicle (철도차량의 Roll 특성에 관한 연구)

  • Yang, Hee-Joo;Lee, Kang-Wun;Park, Kil-Bae;Seong, Jae-Ho
    • Proceedings of the KSR Conference
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    • 2006.11b
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    • pp.1184-1189
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    • 2006
  • Railway vehicle have three translational motions-longitudinal, vertical and lateral, and three rotational motions-rolling, pitching and yawing caused by track irregularity, wheel and rail characteristic, dynamic behaviors etc. The rolling motion in vehicle mainly happens in cases of the vehicles stationary and running on canted track. When the vehicle positioned in stationary on canted track, vehicle is inclined toward inside of installed cant due to gravity component. When the vehicle has running on a track with cant deficiency, vehicle is inclined toward outside of installed cant due to centrifugal force. The roll coefficient(s) is defined as the ratio between the angle of inclination of the vehicle($\eta$) and the angle of the rail level($\alpha$). This paper has noted the test method, test result and analysis result to calculate the roll coefficient according to UIC505-5, international standard

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Optimal Number of Filter Coefficient and Tabs for FTN Transmission Method (FTN 전송기법에서 최적의 필터 roll-off 값 및 탭수 설정)

  • Jung, Ji-Won
    • The Journal of Korea Institute of Information, Electronics, and Communication Technology
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    • v.8 no.2
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    • pp.101-106
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    • 2015
  • In this paper, to increase the throughput for wireless communication, FTN methods that is faster than Nyquist rate are used recently. To improve performance, turbo equalization algorithms that iteratively exchange probabilistic information between soft Viterbi equalizer and LDPC decoder to minimize ISI are applied in this paper. In FTN transmission, the performance depends on roll-off value and number of tabs of SRRC(Square Root Raised Cosine) filter. Therefore, Based on simulation, this paper present optimal number of filter coefficient and tab for various ISI factor of ${\tau}$.

Experimental Study to Examine Wear Characteristics and Determine the Wear Coefficient of Ductile Cast Iron (DCI) Roll (Ductile Cast Iron (DCI) 롤의 마모 특성 고찰 및 마모계수 도출을 위한 실험적 연구)

  • Byon, Sang-Min
    • Tribology and Lubricants
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    • v.33 no.3
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    • pp.98-105
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    • 2017
  • A pin-on-disk test is performed to measure the wear volume of a ductile cast iron (DCI) roll when it wears down using a high carbon steel and two alloy steels at different sliding velocities between the roll and the material (steel). Normal pressure is set as constant and test temperatures are 400, 500 and $600^{\circ}C$. In addition, thermal softening behavior of the DCI roll is examined using a high-temperature micro-hardness tester and the surface hardness variation of the DCI roll is expressed in terms of temperature and heating time. Based on experimental data, a wear coefficient used in Archard's wear model for each material is obtained. The wear volume is clearly observed when the test temperature is $400^{\circ}C$ and sliding velocity varies. However, it is not measured at temperatures of $500^{\circ}C$ and $600^{\circ}C$ even with variations in sliding velocity. From the optical photographs of the pin and disk, the abrasive wear is observed at $400^{\circ}C$ clearly, but no at $500^{\circ}C$ and $600^{\circ}C$. At higher temperatures, the pin surface is not smooth and has many tiny caves distributed on it. It is found that wear volume is dependent on the carbon contents rather than alloy contents. Results also reveal that the variations of wear coefficients are almost linearly proportional to the carbon contents of the material.

Thermal Analysis on Twin-Roll Type Strip Continuous Casting Process Considering Contact Thermal Resistance between Molten Metal and Cooling Roll (쌍롤식 박판 연속주조공정에 있어서 용탕과 냉각롤의 접촉 열저항을 고려한 전열해석)

  • Kim, Y.D;Kim, C.G
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.1
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    • pp.189-205
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    • 1996
  • The twin-roll type strip continuous casting process(or direct rolling process) of steel materials is characterized by two rotating water cooled rolls receiving a steady supply of molten metal which solidifies onto the rolls. A solidification analysis of molten metal considering phase transformation and thermofluid is performed using finite diffefence method with curvilinear coordinate to reduce computing time and molten region analysis with arbitrary shape. An enthalpy-specific heat method is used to determine the temperatures inthe roll and the steel. The temperature distribution of cooling roll is calculated using two dimensional finite element method, because of complex roll shape due to cooling hole in rolls and improvemnt accuracy of calculation result. The energy equaiton of cooling roll is solved simultanuously with the conservation equaiton of molten metal in order to consider heat transfer through the cooling roll. The calculated roll temperature is compared to experimental results and the heat transfer coefficient between cooling roll surface and rolling material(steel) is also determined from comparison of measured roll temperature and calculated temperature.

A Study of Aerodynamic Modelling for Fin Unfolding Motion Analysis (공력면 전개 모사를 위한 공력 모델링 연구)

  • Jung, Suk-Young;Yoon, Sung-Joon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.5
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    • pp.420-427
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    • 2008
  • For simulation of a fin unfolding motion for the various aerodynamic conditions, equations and moments applying to the unfolding fin were modelled. Aerodynamic roll moment consists of the static roll moment and the damping moment, which were obtained through wind tunnel tests and numerical analyses respectively. Panel method was used to compute the roll damping coefficient with deflected fin, whose angle was equivalent to angle of attack due to the deployment motion. Roll damping coefficient is a function of angle of attack, sideslip angle, and deployment angle but not of angular velocity of deployment. Simulation with aerodynamic damping model gave more similar deployment time compared to fin deployment test results.

Estimation of Roll Related Coefficients of a Ship by Using the System Identification Method (시스템 식별법을 이용한 선박의 횡동요 계수 추정)

  • 윤현규;손남선
    • Journal of the Society of Naval Architects of Korea
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    • v.41 no.4
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    • pp.53-58
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    • 2004
  • When a fast container ship or a naval vessel is turning, comparable roll motions occur. Therefore, roll effect has to be considered in the horizontal equations of motion of the ship to predict the maneuverability well. In this thesis, a new method to determine a roll model structure and estimate its coefficients by applying the system identification technique to the data of sea trial tests was proposed. The simulation results from the estimated roll model were well consistent with the true one in spite of the difference between the estimated and the true model structures of roll hydrodynamic moment.

Numerical Investigation of Motion Response of the Tanker at Varying Vertical Center of Gravities

  • Van Thuan Mai;Thi Loan Mai;Hyeon Kyu Yoon
    • Journal of Ocean Engineering and Technology
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    • v.38 no.1
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    • pp.1-9
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    • 2024
  • The vertical center of gravity (VCG) has a significant impact on the roll motion response of a surface ship, particularly oil tankers based on the oil level in the tanker after discharging oil at several stations or positional changes, such as changes in the superstructure and deck structure. This study examined the motion response of the Korea very large crude carrier 2 (KVLCC2) at various VCGs, especially roll motion when the VCG changed. The potential theory in the Ansys AQWA program was used as a numerical simulation method to calculate the motion response. On the other hand, the calculations obtained through potential theory overestimated the roll amplitudes during resonance and lacked precision. Therefore, roll damping is a necessary parameter that accounts for the viscosity effect by performing an experimental roll decay. The roll decay test estimated the roll damping coefficients for various VCGs using Froude's method. The motion response of the ship in regular waves was evaluated for various VCGs using the estimated roll-damping coefficients. In addition, the reliability of the numerical simulation in motion response was verified with those of the experiment method reported elsewhere. The simulation results showed that the responses of the surge, sway, heave, pitch, and yaw motion were not affected by changing the VCG, but the natural frequency and magnitude of the peak value of the roll motion response varied with the VCG.

A study for roll damping performance of a platform supply vessel with or without bilge keel using CFD (전산유체역학을 이용한 해양작업지원선의 빌지킬 유무에 따른 횡동요 성능에 관한 연구)

  • Seok, Jun;Kim, Sung-Yong;Yang, Young-Jun;Jin, Song-Han;Park, Jong-Chun
    • Journal of Advanced Marine Engineering and Technology
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    • v.40 no.9
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    • pp.791-798
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    • 2016
  • In this study, numerical simulations on the effects of bilge keel on roll motion were conducted. The numerical simulations were performed on a 110 m class PSV using the commercial viscous flow analysis software Star-CCM+. Before conducting the study on the 110 m class PSV, an additional simulation of DTMB 5512 was performed and compared with the experimental results to validate the feasibility of the numerical simulation. In the simulation on PSV, a nondimensional damping coefficient was calculated using a free roll decay simulation, and the response amplitude operator (RAO) for the roll motion was calculated with a nondimensional damping coefficient at two conditions (with/without bilge keel).

The Effect of friction between Roll and STS the Roll Cladding Behavior of STS/Al/STS Sandwich Sheet (압연에 의한 STS/AI/STS 클래드판재 제조시 롤과 STS 사이의 마찰의 영향)

  • 정영훈;지광구;서진유;신명철
    • Transactions of Materials Processing
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    • v.11 no.6
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    • pp.482-486
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    • 2002
  • Sandwich sheets composed of stainless steel/aluminum/stainless steel were produced by roll cladding. In order to investigate the effect of the friction between roll and cladding sample, the lubrication condition of the roll surface was varied. Clad rolling without lubrication gave rise to a small increment of the normal strain of aluminum in the rolling direction. This experimental result was confirmed by FEM modeling. Through-thickness hardness gradients in the mid aluminum layer was successfully explained by variations of the strain state through thickness layers. FEM modeling implied that cladding without lubrication led to a large shear strain variation at the surface of aluminum layer.

Experimental Study on Free Roll Decay Motions of a Damaged Ship for CFD Validation Database (CFD 검증용 데이터베이스 구축을 위한 손상 선박의 횡동요 감쇠 운동에 대한 실험적 연구)

  • Lee, Sung-Kyun;You, Ji-Myoung;Lee, Hyun-Ho;Rhee, Shin-Hyung;Rhee, Key-Pyo
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.1
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    • pp.52-59
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    • 2012
  • Among many factors to be considered for higher safety level requirements, the hull stability in intact and damaged conditions in seaways is of utmost importance. Since the assessment of a damaged ship is complicated due to the highly non-linear behavior, it is widely acknowledged that computational fluid dynamics (CFD) methods are one of the most feasible approaches. Although many research activities are being reported on the damaged ship stability recently, most of them are not designed for validation of CFD studies. In this study, well-designed model tests were performed to build a CFD validation database, which is essential in developing better CFD methods for the damage stability assessment. The geometry of the damaged compartment and test conditions were determined based on preliminary CFD simulations. Free roll decay tests in calm water with both intact and damaged ships were performed and the roll motion characteristics were compared. The damaged ship showed a larger roll damping coefficient and more rapid decrease of roll amplitude than the intact ship. The primary reason of these efforts can be explained by the movement of the flooded water.