• Title/Summary/Keyword: Hunting phenomenon

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Analysis of the Critical Speed and Hunting Phenomenon of a High Speed Train (고속전철의 임계속도와 헌팅현상 해석)

  • Song, Ki-Seok;Koo, Ja-Choon;Choi, Yeon-Sun
    • Journal of the Korean Society for Railway
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    • v.17 no.5
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    • pp.342-348
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    • 2014
  • Contact between wheel and rail leads to the creep phenomenon. Linear creep theory, assuming linear increase in the creep force vs creep, results in a critical speed at which the vibration of a railway vehicle goes to infinity. However, the actual creep force converges to a limited value, so that the vibration of a railway vehicle cannot increase indefinitely. In this study, the dynamics of a railway vehicle is investigated with a 6 DOF bogie model includingthe nonlinear creep curves of Vermeulen, Polach, and a newly calculated creep curve with strip theory. Strip theory considers the profiles of the wheel and rail. The results show that the vibration of a railway vehicle results in a limit-cycle over a specific running speed, and this limit-cycle becomes smaller as the slope of the creep-curve steepens. Moreover, a hunting phenomenon is caused due to flange contact, which restricts the magnitude of the limit-cycle.

An Experimental Study on Validation of Nonlinear Critical Speed (비선형 임계속도 검증을 위한 실험적 연구)

  • 정우진;김성원
    • Journal of the Korean Society for Railway
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    • v.3 no.1
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    • pp.12-18
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    • 2000
  • This paper addresses the experimental study on the nonlinear critical speed and the validity of simple prediction formulation. The experiment on nonlinear critical speed is carried out using roller rigs, which has been impossible on track because of a possibility of an accident. In addition, experiment for a bogie is performed to check the difference in modeling a full railway vehicle and a bogie. It is found that nonlinear critical speed proves to be an inherent phenomenon of a railway vehicle itself and the difference of test results between a full railway vehicle and a bogie is comparatively negligible. Finally. the accuracy of simple prediction formulation for outbreak velocity and response frequency in hunting is investigated.

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A Study on the Eigenmode Characteristics by Changing Damping Parameters of Secondary Suspension (Damper) on Railway Vehicles (철도차량 이차현가장치 댐퍼 매개변수 변화에 따른 고유모드 특성에 대한 연구)

  • Shin, Yu-Jeong;You, Won-Hee;Park, Joon-Hyuk;Hur, Hyun-Moo
    • Journal of the Korean Society for Precision Engineering
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    • v.28 no.7
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    • pp.796-804
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    • 2011
  • Railway vehicles are capable of indicating several types of instability. This phenomenon, which is called hunting motion, is a self excited lateral oscillation that is caused by the running velocity of the vehicle and wheel frail interactive forces. The interactive forces act to change effectively the damping characteristics of railway vehicle systems. This paper will show the impact of instability on the transfer function behavior using damping characteristics of secondary suspension. The vehicle dynamics are modeled using a 17 degree of freedom considering linear wheel/rail contact. The paper deals with certain condition of the damper characteristics that one is about various damping coefficient and another is equipped damper direction.

An Exploratory Analysis on the Employment Preparation Process of Young Job-Seekers (청년구직자의 취업준비 과정에 대한 탐색적 분석)

  • Kong, Su-Youn;Yang, Sung-Eun
    • Journal of Families and Better Life
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    • v.30 no.2
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    • pp.47-64
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    • 2012
  • Purpose of this research is to analyze young job-seekers' preparation for employment process. Participants for the present research include 30 unmarried single males and females in their 20s, who are preparing for employment after graduating four-year colleges. To follow the rule of data triangulation, data includes in-depth personal interviews, field notes, memorandums, coding books, and additional questionnaires. There are 556 abstracted meaning units, 15 subcategories, 11 main categories, and final 5 themes from the data analysis. The result showed that young job-seekers were experiencing a typical cycle of preparation, attempt, failure, slump, and downgrade in job seeking standard. It is also observed that youth unemployment was a persistent phenomenon of vicious circle not easy to overcome. Especially, young job seekers were reported to restructure the perception on employment as they struggle for seeking a job, in particular, at times of experiencing hardship during the job hunting process. The interviewees responded that the possibility of getting a job declines as the job hunting period drags on eventually ending up with applying for a job of lower qualification standard.

Expansion Valves Characteristics for Development of Control System on Air Conditioning and Refrigeration Systems (공조.냉동장치의 제어시스템 개발을 위한 팽창밸브 특성)

  • Kim, J.D.;Jang, J.E.;Yoon, J.I.
    • Journal of Power System Engineering
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    • v.2 no.3
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    • pp.34-40
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    • 1998
  • Performance characteristics of a refrigeration systems with various expansion valves and superheat changes were investigated experimentally. Experimental data have been taken utilizing three different devices; a thermostatic expansion valve, a linear type electronic expansion valve and a solenoid type electronic expansion valve. The data taken from tile three types of expansion valves were discussed with the temperature distribution of each zone in the evaporator and the superheat changes of the evaporator outlet In each zone temperature distribution fluctuated larger with the thermostatic expansion valve than with the electronic expansion valves. The optimum superheat ranged from $5^{\circ}C\;to\;15^{\circ}C$, and the superheat with the thermostatic expansion valve showed hunting phenomenon, which affected the evaporating and condensing temperature.

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Study on an Adaptive Maximum Torque Per Amp Control Strategy for Induction Motor Drives

  • Kwon, Chun-Ki
    • Journal of Electrical Engineering and Technology
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    • v.8 no.1
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    • pp.110-117
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    • 2013
  • Maximum Torque Per Amp (MTPA) control for induction motor drives seeks to achieve a desired torque with the minimum possible stator current. This is favorable in terms of inverter operation and nearly optimal in terms of motor efficiency. However, rotor resistance variation can cause significant performance degradation. This work demonstrates that existing MTPA controls perform sub-optimally as temperature varies. An adaptive MTPA control strategy is proposed that always achieves optimal performance without exhibiting hunting phenomenon regardless of rotor temperature. The proposed control is experimentally shown to accurately achieve the desired torque.

Hydrochloric Acid Gas Removal from Iron and Steel Industry Using Micro-bubbles of a Dip Injection Wet Scrubber System (침액식 세정설비의 마이크로버블을 이용한 철강산업 공정의 산세조 발생 염화수소 제거)

  • Kim, Ye-Jin;Jung, Jae-Ouk;Jung, Yong-Jun
    • Journal of Wetlands Research
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    • v.17 no.1
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    • pp.75-79
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    • 2015
  • DIWS system was introduced to treat HCl gas from the scrubber of iron and steel industry according as the regulation of air quality is expected to be changed to 2ppm. pH of condensed water at stack was increased to 6.0. While 13.3ppm of inflow HCl was introduced to DIWS system, the average exhaust gas was 0.43ppm with 96.9% of removal efficiency. Compared with HCl data of TMS, the stable removal efficiency was shown in DIWS system, but the phenomenon of data hunting was also observed with different types of TMS apparatus.

Spatial Diffusion Process of Private Passenger Cars in Korea (우리나라 자가용 승용차의 공간적 확산과정)

  • 李種起;韓柱成
    • Journal of the Korean Geographical Society
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    • v.36 no.1
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    • pp.52-65
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    • 2001
  • Between 1985 and 1997 the diffusion of private passenger cars first occurred in major cities such as Seoul, Busan, Daegu and the satellite cities of the capital city that enjoyed high incomes and advanced service industries and then it gradually expanded to industrial and major provincial cities while posting a downturn in the major cities. Factor contrbuting to this phenomenon most significantly was the rate of employment in the financial insurance, real estate, and business service sectors in 1985 and 1990. The most ingluential factor in 1997 was the rate of employment in agriculture, hunting, forestry, and fishery. When measured against 1991 as a yardstick, the spatiotemporal ditribution rate of private passenger cars was highly between 1985 and 1990 in Seoul's satellite cities and major regional cities, showing a large inter-regional gap in terms of diffusion rate. The period from 1991 to 1997 showed a high rate of diffusion in cities within the capital region as well as in major regional cities, but inter-regional diffusion rate became similar. Key factors responsible for regional types of the diffusion were {1}the rate of employment in the service industrier and income in the major citier, and (2)the geogtaphic distamce between counties and Seoul plus the size of population in the county regions.

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Study on Medical Records In ${\ulcorner}$the Historical Records of the Three Kingdoms${\lrcorner}$ ("삼국사기(三國史記)"에 기록된 의약내용(醫藥內容) 분석)

  • Shin, Soon-Shik;Choi, Hwan-Soo
    • Journal of The Association for Neo Medicine
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    • v.2 no.1
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    • pp.35-54
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    • 1997
  • We tried to observe the features of ancient medical practice by analysing the records related to medicine in the book, ${\ulcorner}$the Historical Records of the Three Kingdom${\lrcorner}$ of which content includes the features of medicine in mythology, plague, delivery of twins, drugs, medical system, shamanism, constitutional medicine, psychiatry, forensic medicine, deformity, a spa, medical phrase, health and welfare work, religion, death. physiological anatomy, Taoist medicine, acupuncture, the occult af of transformation and etc. Our initial concern was about where to draw line as of medical field and we defined medicine in more broad meaning. The book ${\ulcorner}$the Historical Records of the Three Kingdoms${\lrcorner}$ describes the world of mythology by way of medicine which is not clearly a conventional one. There appears records of birth of multiple offsprings 7 times in which cases are of triplets or more. Delivering multiple offsprings were rare phenomenon though such fertility was highly admired. This shows one aspect of ancient country having more population meant more power of the nation. Of those medical records conveyed in that book includes stories of childbirth such as giving birth to a son after praying, giving birth to Kim Yoo-shin after 20 months after mother's dream of conception, and a song longing for getting a laudable child. Plagues were prevalent throughout winter to spring season and one can observe various symptoms of plagues in the record. Of these epidemic diseases, cold type might have been more common than the heat one. Appearance of epidemic diseases frequently coincided with that of natural disasters that this suggests a linkage between plague and underlying doctrine on five elements' motion and six kinds of natural factors. There exists only a few names of diseases such as epidemic disease, wind disease, and syndrome characterized by dyspnea. Otherwise there appeared only afflictions that were not specified therefore it remains cluless to keep track of certain diseases of prevalence. Since this ${\ulcorner}$Historical Records of the Three Kingdoms'${\lrcorner}$ wasn't any sort of medical book, words and terms used were not technical kind and most were the ones used generally among lay people. Therefore any mechanisms of the diseases were hardly mentioned. Some of medicinal substances such as Calculus Bovis, Radix Ginseng, Gaboderma Luciderm, magnetitum were also in use in those days. 53 kinds of dietary supplies appears in the records and some of these might have been used as medicinal purpose. Records concerning dicipline of one's body includes activities such as hunting, archery, horseback riding etc. In Shilla dynasty there were positions such as professor of medicine, Naekongbong(內供奉), Kongbong's doctor(供奉醫師), Kongbong's diviner(供奉卜師). As an educational facility, medical school was built at the first year of King Hyoso's reign and it's curricula included various subjects as ${\ulcorner}$Shin Nong's Herbal classic${\lrcorner}$, ${\ulcorner}$Kabeul classic of acupuncture and moxbustion${\lrcorner}$, ${\ulcorner}$The Plain Questions of the Yellow Emperor's Classic of Internal Medicine${\lrcorner}$, ${\ulcorner}$Classic of Acupuncturer${\lrcorner}$, ${\ulcorner}$The Pulse Classic${\lrcorner}$, ${\ulcorner}$Classic of Channels and Acupuncture Points${\lrcorner}$ and ${\ulcorner}$Difficult Classic${\lrcorner}$. There were 2 medical professors who were in charge of education. To establish pharmacopoeia, 2 Shaji(舍知), 6 Sha(史), 2 Jongshaji(從舍知) were appointed. In Baekje dynasty, Department of Herb was maintained. Doing praying for the sake of health, doing phrenology also can be extended to medical arena. Those who survived over 100 years of age appear 3 times in the record, while 98 appears once. The earliest psychiatrist Nokjin differentiated symptoms to apply either therapies using acupuncture and drug or psychotherapy. There appears a case of rape, a case of burying alive with the dead, 8 cases of suicide that can characterize a prototype of forensic medicine. Deformity-related records include phrases as follow: 'there seems protrudent bone behind the head', 'a body which has two heads, two trunks, four arms.', 'a body equipped with two heads' In those times spa can be said to be used as a place for he리ing, convalescence, and relaxation seeing the records describing a person pretended illness and went to spa to enjoy with his friends. Priest doctors and millitary surgeons were in charge of the medical sevice in the period of the Three Kingdoms by the record written by Mookhoja(墨胡子) and Hoonkyeom(訓謙). Poor diet and regimen makes people more vulnerable to diseases. So there existed charity services for those poor people who couldn't live with one's own capacity such as single parents, orphans, the aged people no one to take care and those who are ill. The cause of affliction was frequently coined with human relation. There appeared the phenomenon of releasing prisoners and allowing people to become priests at the time of king's suffering. Besides, as a healing procedure, sutra-chanting was peformed. There appears 10 cases of death related records which varies from death by drowning, or by freezing, death from animals, death from war, death from wightloss and killing oneself at the moment of spouse's death and etc. There also exist certain records which suggest the knowledge of physiology and anatomy in those times. Since the taoist books such as ${\ulcorner}$Book of the Way and Its Power(老子道德經)${\lrcorner}$ were introduced in the period of Three Kingdoms, it can be considered that medicine was also influenced by taoism. Records of higher level of acupuncture, records which links the medicine and occult art of transformation existed. Although limited, we could figure out the medical state of ancient society.

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