Critical speed of high-speed trains considering wheel-rail contact

최연선,신범식 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.11

The maximum speed of a high-speed train is limited to its critical speed. In this study, the definition of critical speed is reviewed. Therelationship between creepage and creep force and the effects of the parameters of the first and second suspension systems are also studiedusing a bogie model to increase the critical speed. Kalker’s linear creep theory and its modification of Wormey’s saturation constantare reviewed. The nonlinear creep force of Vermeulen’s creep theory, Polach’s calculation, and the newly calculated longitudinal andlateral creep forces using strip theory from wheel-rail contact pressure are investigated for the critical speed. Flange contact is also consideredwhen lateral displacement exceeds the dead band between wheel flange and rail. Direct numerical integration and a shootingalgorithm are devised to calculate the response, especially for the limit cycle. Results show that as speed increases, the equilibrium pointbecomes unstable and creates a limit cycle through a Hopf bifurcation. The unstable fixed point can be a critical speed. The critical speedincreases as the creep curve becomes stiff before saturation, which is more effective than the variation in suspension parameters. Theconsideration of flange contact can also increase the critical speed.

초고속 주행환경에서의 종단경사 설계기준에 관한 기초연구

송민태,강호근,김흥래,이의준,신준수,김종원 한국도로학회 2013 한국도로학회논문집 Vol.15 No.4

PURPOSES: The purpose of this study theoretically reviews vertical grade deriving process in super high speed environment and compares overseas design criteria with Domestic Standardization also draws suitable vertical grade design criteria of high standard for Domestic Circumstances in Korea. METHODS : By researching domestic vehicle registration status, calculating typical vehicle, using Vissim which is traffic simulation program, Speed-distance curve of the vehicle is derived under each design speed condition. Through Speed-distance curve, estimating critical length of grade and considering critical length of grade, maximum longitudinal incline is proposed. RESULTS : The result of domestic vehicle registration status, the typical vehicle for deriving vertical grade is calculated based on gravity horsepower ratio 200 lb/hp. For calculating critical length of grade, according to change speed of uphill entry, speed-distance curve is derived by using Vissim. Critical length of grade is calculated based on design speed 20 km/h criteria which is point of retardation. Estimated critical length of grade is 808 m and based on this result, maximum longitudinal incline was confirmed in the design speed between 130km/h to 140km/h. CONCLUSIONS: The case of the typical vehicle(truck) which is gravity horsepower ratio 200 lb/hp, maximum longitudinal incline 2% is desirable at the super high speed environment in the design speed between 130km/h to 140km/h.

DDM Rotordynamic Design Sensitivity Analysis of an APU Turbogenerator Having a Spline Shaft Connection

Lee, An-Sung,Ha, Jin-Woong The Korean Society of Mechanical Engineers 2003 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.17 No.1

An eigenvalue design sensitivity formulation of a general nonsymmetric-matrix rotor-bearing system is devised. using the DDM (direct differential method). Then, investigations on the design sensitivities of critical speeds are carried out for an APU turbogenerator with a spline shaft connection. Results show that the dependence of the rate of change of the critical speed on the stiffness changes of bearing models of spline shaft connection points is negligible, and thereby their modeling uncertainty does not present any problem. And the passing critical speeds up to the 4th critical speed are not sensitive to the design stiffness coefficients of four main bearings. Further, the dependence of the rate of change of the critical speed on the shaft-element length changes shows quantitatively that the spline shaft has some limited influence on the 4th critical speed but no influence on the 1st to 3rd critical speeds. With no adverse effect from the spline shaft, the APU system achieves a critical speed separation margin of more than 40% at a rated speed of 60,000 rpm.

프로세스 대형 모터-발전기의 저어널 베어링 설계 개선

이안성(An Sung Lee) 한국트라이볼로지학회 2012 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.28 No.6

In the preceding Part I study, for improving the unbalance response vibration of a large PRT motorgenerator rotor fundamentally by design, a series of design analyses were carried out for bearing improvement by retrofitting from original plain partial journal bearings, applied for operation at a rated speed of 1,800 rpm, to final tilting pad journal bearings. To satisfy evenly key basic lubrication performances such as the minimum lift-off speed and maximum oil-film temperature, a design solution of 5-pad tilting pad journal bearings and maximizing the direct stiffness by about two times has been achieved. In this Part II study, a detailed rotordynamic analysis of the large PRT motor-generator rotor-bearing system will be performed, applying both the original plain partial journal bearings and the retrofitted tilting pad journal bearings, to confirm the effect of rotordynamic vibration improvement after retrofitting. The results show that the rotor unbalance response vibrations with the tilting pad journal bearings are greatly reduced by as much as about one ninth of those with the plain partial journal bearings. In addition, for the tilting pad journal bearings there exist no critical speed up to the rated speed and just one instance of a concerned critical speed around the rated speed, whereas for the plain partial journal bearings there exist one instance of a critical speed up to the rated speed and two instances of concerned critical speeds around the rated speed.

Influence of Thermal Expansion on Eccentricity and Critical Speed in Dry Submersible Induction Motors

Lv, Qiang,Bao, Xiaohua,He, Yigang The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.1

Rotor eccentricity is one of the major factors that directly influence the security of horizontal electrical machines, and the critical speed of the shaft has a close relationship with vibration. This paper deals with the influence of thermal expansion on the rotor eccentricity and critical speed in large dry submersible motors. The dynamic eccentricity (where the rotor is still turning around the stator bore centre but not its own centre) and critical speed of a three-phase squirrel-cage submersible induction motor are calculated via hybrid analytical/finite element method. Then the influence of thermal expansion is investigated by simulation. It is predicted from the study that the thermal expansion of the rotor and stator gives rise to a significant air-gap length decrement and an inconspicuous slower critical speed. The results show that the thermal expansion should be considered as an impact factor when designing the air gap length.

Influence of Thermal Expansion on Eccentricity and Critical Speed in Dry Submersible Induction Motors

Qiang Lv,Xiaohua Bao,Yigang He 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.1

Rotor eccentricity is one of the major factors that directly influence the security of horizontal electrical machines, and the critical speed of the shaft has a close relationship with vibration. This paper deals with the influence of thermal expansion on the rotor eccentricity and critical speed in large dry submersible motors. The dynamic eccentricity (where the rotor is still turning around the stator bore centre but not its own centre) and critical speed of a three-phase squirrelcage submersible induction motor are calculated via hybrid analytical/finite element method. Then the influence of thermal expansion is investigated by simulation. It is predicted from the study that the thermal expansion of the rotor and stator gives rise to a significant air-gap length decrement and an inconspicuous slower critical speed. The results show that the thermal expansion should be considered as an impact factor when designing the air gap length.

열차 증속에 따른 콘크리트 궤도 노반의 동적 응력 변화

이태희,최찬용,Ernest Nsabimana,정영훈 한국지반공학회 2013 한국지반공학회논문집 Vol.29 No.10

Societal interest on a faster transportation demands an increase of the train speed exceeding current operation speedof 350 km/h. To trace the pattern of variations in displacements and subsoil stresses in the concrete slab track system,finite element simulations were conducted. For a simple track-vehicle modeling, a mass-point system representing themoving train load was developed. Dynamic responses with various train speeds from 100 to 700 km/h were investigated. As train speeds increase the displacement at rail and subsoil increases nonlinearly, whereas significant dynamicamplification at the critical velocity has not been found. At low train speed, the velocity of elastic wave carrying elasticenergy is faster than the train speed. At high train speed exceeding 400 km/h, however, the train speed is approximatelyidentical to the elastic wave velocity. Nonlinearity in the stress history in subsoil is amplified with increasing train speeds,which may cause significant plastic strains in path-dependent subsoil materials.

Development of high speed continuous transport critical current measurement system for long piece of HTS conductor

Kim, S.,Park, M.,Yu, I.K.,Kim, G.H.,Ha, H.S.,Sim, K.,Oh, S.S.,Moon, S.H. North-Holland 2013 Physica. C, Superconductivity Vol.484 No.-

In case of long pieces of HTS conductor, their critical current measurement is an important process for the conductor manufacturer and the customer, however, it is very time consuming process. Conventional critical current measurement is carried out by 'four probe method', which increase the transport current and measure the voltage between the fixed voltage taps. Therefore, it consists of conductor moving and measuring process. To speed up the measuring process, longer distance between voltage taps is required. In this case, the measured critical current is averaged and small defects, which can be very crucial for thermal stability, cannot be found. Therefore, the limitation of the voltage tap length should be carefully decided considering the cooling environment. Another non-contact or indirect method is to measure the screening effect of magnetic field and converting the field signal to the critical current, which is called as hall probe method. This process is known as a very efficient way to find local defects and estimate the distribution of the critical current, however, it contains inevitable error and noise because it should measure the small magnetic field signals. This paper describes a new critical current measurement system, which have similar hardware structure of conventional 'four probe method'. However, it is much faster than other systems using fast feedback control of the transport current while the conductor is continuously moving with high speed. The measured results are compared with the conventional method and hall probe method.

7톤급 액체로켓엔진 산화제펌프 임계속도 해석

전성민,윤석환,최창호,Jeon, Seong Min,Yoon, Suk-Hwan,Choi, Chang-Ho 항공우주시스템공학회 2015 항공우주시스템공학회지 Vol.9 No.1

A critical speed analysis of oxidizer pump was peformed for a 7 ton class liquid rocket engine as the third stage engine of the Korea Space Launch Vehicle II. Based on the previously developed experimental 30 ton class turbopump and presently developing 75 ton class turbopump for the first and second stage rocket engine of Korea Space Launch Vehicle II, a layout and configuration of the 7 ton class turbopump rotor assembly are determined. A ball bearing stiffness analysis and rotordynamic analysis are performed for both of the bearing unloaded condition and loaded condition. Structural flexibility of the oxidizer pump casing is also included to predict critical speeds. From the numerical analysis, it is confirmed that the rotor system acquires sufficient separate margin of critical speed as a sub-critical rotor even though decrease of critical speed due to the casing structural flexibility.

고속열차 객차의 임계속도 향상에 관한 연구

전창성(Chang-Sung Jeon) 한국산학기술학회 2016 한국산학기술학회논문지 Vol.17 No.12

국내에 고속열차가 도입된 지 12년이 지났고, 국내기술로 개발된 KTX-산천도 운행한지 6년 정도 되었다. 호남선 고속철도의 개통으로 현재 국내 고속선로의 수송용량은 거의 포화상태가 되었고, 이에 따라 수송용량을 증대하기 위하여 열차의 운행속도를 높이는 연구 등 다양한 연구가 수행되고 있다. 본 연구는 그 중 일부로 KTX-산천 고속열차의 운행속도를 350km/h로 높이기 위하여 열차의 임계속도를 향상시키기 위해 수행되었다. KTX와 KTX-산천 영업운행 차량에서 측정된 차륜마모 데이터를 이용하여 KTX-산천 편성 모델에 대한 동역학해석을 수행하였고, KTX-산천 영업차량에서 측정된 진동가속도 측정결과와의 비교를 통하여 해석결과의 타당성을 검증하였다. 고속열차의 운행속도 향상을 위하여 열차의 임계속도 향상을 목표로 대차 주요 현가장치 파라미터에 대한 최적화 연구를 수행하였다. 민감도 분석을 통해 최적화를 위한 주요 현가장치 파라미터를 선정하였고, 반응표면분석법에 의해 2차 회귀 모형 함수를 추정하였다. 2차의 목적함수를 최소화시키는데 있어서 효율적인 성능을 발휘하는 SQP 방법을 사용하여 최적화를 수행한 결과 KTX-산천의 임계속도가 9.4%정도 증가함을 확인하였다. 최적화된 현가장치 파라미터는 KTX-산천 영업속도를 300km/h에서 350km/h로 향상시키기 위한 신규대차 설계시 반영될 예정이다. Over 12 years have passed since the first commercial operation of a Korean high-speed train. Since then, the transport capacity of the high-speed lines has become almost saturated. Therefore, studies have been carried out to increase the operating speed of the trains in order to increase their transportation capacity. This study was carried out to improve the critical speed of the KTX-Sancheon, Korean high-speed train, in order to increase its operating speed. A dynamic analysis of the KTX-Sancheon train was performed using the contact data obtained from the wheel wear profiles that were measured from a KTX-Sancheon train in commercial operation. The analysis results were verified by comparing them with the measurement acceleration data obtained from KTX-Sancheon. The suspension parameters were optimized to improve the operation speed. The critical speed of KTX-Sancheon was increased by 9.4% after the optimization by the response surface method. The optimized suspension parameters are expected to be used for the new bogie design to increase the operating speed of KTX-Sancheon from 300km/h to 350km/h.