Generation of Velocity Profiles with Speed Limit of Each Axis for High-Speed Machining using Look-Ahead Buffer

이철수 한국정밀공학회 2010 International Journal of Precision Engineering and Vol. No.

An efficient look-ahead algorithm to generate velocity profiles is presented in this paper. Algorithm allows for a nonzero starting point velocity and end point velocity of every line segment to increase machining productivity. The paper considers the intelligence of look-ahead to achieve faster machining speed, along with required accuracy. Speed limitation of a specific axis and the direction change of an axis are newly added to the constraints of the velocity profile problem. This paper solves graphically the problem of generating velocity profiles and derives the equations for representing the velocity profile. A method to manage the look-ahead buffer is also proposed. To generate velocity profiles using the look-ahead buffer, three phases are proposed. Phase 1determines the velocity conditions such as the maximum velocity, starting point velocity and end point velocity. In phase 2, velocity profiles are generated independently. Phase 3 handles the change of the start or end point velocity. This phase 3 is repeated until all adjacent point velocities are the same. The proposed method was utilized in the manufacturing field to engrave aluminum tire molds. It was demonstrated that this method contributes to an increase of the machining accuracy and a reduction of the production time.

A summertime near-ground velocity profile of the Bora wind

Petra Lepri,Hrvoje Kozmar,Željko Večenaj,Branko Grisogono 한국풍공학회 2014 Wind and Structures, An International Journal (WAS Vol.19 No.5

While effects of the atmospheric boundary layer flow on engineering infrastructure are more or less known, some local transient winds create difficulties for structures, traffic and human activities. Hence, further research is required to fully elucidate flow characteristics of some of those very unique local winds. In this study, important characteristics of observed vertical velocity profiles along the main wind direction for the gusty Bora wind blowing along the eastern Adriatic coast are presented. Commonly used empirical power-law and the logarithmic-law profiles are compared against unique 3-level high-frequency Bora measurements. The experimental data agree well with the power-law and logarithmic-law approximations. An interesting feature observed is a decrease in the power-law exponent and aerodynamic surface roughness length, and an increase in friction velocity with increasing Bora wind velocity. This indicates an urban-like velocity profile for smaller wind velocities and rural-like velocity profile for larger wind velocities, which is due to a stronger increase in absolute velocity at each of the heights observed as compared to the respective velocity gradient (difference in average velocity among two different heights). The trends observed are similar during both the day and night. The thermal stratification is near neutral due to a strong mechanical mixing. The differences in aerodynamic surface roughness length are negligible for different time averaging periods when using the median. For the friction velocity, the arithmetic mean proved to be independent of the time record length, while for the power-law exponent both the arithmetic mean and the median are not influenced by the time averaging period. Another issue is a large difference in aerodynamic surface roughness length when calculating using the arithmetic mean and the median. This indicates that the more robust median is a more suitable parameter to determine the aerodynamic surface roughness length than the arithmetic mean value. Variations in velocity profiles at the same site during different wind periods are interesting because, in the engineering community, it has been commonly accepted that the aerodynamic characteristics at a particular site remain the same during various wind regimes.

A summertime near-ground velocity profile of the Bora wind

Lepri, Petra,Kozmar, Hrvoje,Vecenaj, Zeljko,Grisogono, Branko Techno-Press 2014 Wind and Structures, An International Journal (WAS Vol.19 No.5

While effects of the atmospheric boundary layer flow on engineering infrastructure are more or less known, some local transient winds create difficulties for structures, traffic and human activities. Hence, further research is required to fully elucidate flow characteristics of some of those very unique local winds. In this study, important characteristics of observed vertical velocity profiles along the main wind direction for the gusty Bora wind blowing along the eastern Adriatic coast are presented. Commonly used empirical power-law and the logarithmic-law profiles are compared against unique 3-level high-frequency Bora measurements. The experimental data agree well with the power-law and logarithmic-law approximations. An interesting feature observed is a decrease in the power-law exponent and aerodynamic surface roughness length, and an increase in friction velocity with increasing Bora wind velocity. This indicates an urban-like velocity profile for smaller wind velocities and rural-like velocity profile for larger wind velocities, which is due to a stronger increase in absolute velocity at each of the heights observed as compared to the respective velocity gradient (difference in average velocity among two different heights). The trends observed are similar during both the day and night. The thermal stratification is near neutral due to a strong mechanical mixing. The differences in aerodynamic surface roughness length are negligible for different time averaging periods when using the median. For the friction velocity, the arithmetic mean proved to be independent of the time record length, while for the power-law exponent both the arithmetic mean and the median are not influenced by the time averaging period. Another issue is a large difference in aerodynamic surface roughness length when calculating using the arithmetic mean and the median. This indicates that the more robust median is a more suitable parameter to determine the aerodynamic surface roughness length than the arithmetic mean value. Variations in velocity profiles at the same site during different wind periods are interesting because, in the engineering community, it has been commonly accepted that the aerodynamic characteristics at a particular site remain the same during various wind regimes.

수분 함유량이 콘크리트의 종파 속도에 미치는 영향에 관한 연구

김동수,이광명,이회근,김지상 韓國非破壞檢査學會 1999 한국비파괴검사학회지 Vol.19 No.4

최근 초음파 속도법과 충격반향기법 등과 같이 탄성파를 이용한 비파괴검사 방법이 콘크리트의 강도나 탄성계수를 결정하는데 유용하게 사용되고 있다. 하지만 탄성과 속도에 영향을 미치는 다양한 인자들이 고려되지 않은 상태에서 비파괴검사가 행해지고 있어 실제로 만족할 만한 결과를 주지 못하고 있다. 이 연구에서는 다양한 영향인자들 중에서 특히 콘크리트의 수분함유량이 종파 속도에 미치는 영향정도를 실험을 통해 조사하였다. 콘크리트 내부의 수분함유량이 감소하면, 즉 콘크리트가 건조해지면 종파 속도는 점점 감소하며, 충격반향기법에 의해 측정된 막대파 속도가 초음파 속도보다 수분의 영향을 더 많이 받는 것으로 나타났다. 또한 기건양생하에서는 재령이 증가함에 따라 수분함량이 감소하게 되어 콘크리트의 종파 속도는 거의 증가하지 않는 반면에 강도는 점차적으로 증가하는 경향을 보이기 때문에 종파 속도와 콘크리트 강도의 상관관계 설정시 이를 반드시 고려해야 할 것으로 판단된다. Elastic wave velocity measurement technique such as impact-echo method and ultrasonic pulse velocity method has been successfully used to evaluate the moduli and strength of concrete. However, estimation results obtained by the NDT methods do not agree well with real things because longitudinal wave velocity is influenced by various factors. In this paper, among several factors influencing P-wave velocity, the influence of moisture content in concrete was investigated through the experiment. Test results show that longitudinal verve velocity is significantly affected by the moisture content of concrete, i.e., the lower moisture content, the lower velocity. Moisture content influences rod-wave velocity measured by impact-echo method stronger than ultrasonic pulse velocity measured by transmission method. During drying process with ages, the difference of increasing rate between longitudinal wave velocity and compressive strength of concrete is gradually increased. Therefore, to establish more accurate relationship between longitudinal wave velocity and strength, the difference of the increasing rate should be considered

부두 설계 접안에너지를 고려한 선박 규모별 허용접안속도에 대한 분석

강은지(Eun-Ji Kang),이형탁(Hyeong-Tak Lee),조익순(Ik-Soon Cho) 한국연안방재학회 2021 한국연안방재학회지 Vol.8 No.4

The berthing velocity is the factor that has the greatest influence on the berthing energy. For the vessel to berth safely, it should not exceed the appropriate berthing velocity. In addition, when the vessel is berthing, it should be berthed with berthing energy smaller than the energy absorption of the fender. This study intends to derive the allowable berthing velocity by ship size considering the berthing capacity. When a small vessel berth, the allowable berthing velocity is greater than when a relatively large vessel berths. In this study, the extrapolated velocity is defined as the relative value of the ship’s berthing velocity when considering the ship s size and the berthing capacity. A regression equation for the allowable berthing velocity by ship size was derived by calculating the designed berthing energy for each fender performance. It was also verified whether any ships were exceeding the allowable berthing velocity by comparing it with the measured data for each jetty. In addition, the extrapolated velocity was proposed using the regression equation, and as a result of applying the measured data, 11 ships exceeded the designed velocity in jetty 1, but it was confirmed that all ships were safely berthed in jetty 2,3. Therefore, the target pier of this study was evaluated as a pier where ships can be berthed safely. A safer berthing velocity operation guideline can be suggested if the allowable berthing velocity by ship size is analyzed and utilized at various piers. Extrapolated velocity can also be used for risk analysis of berthing.

Laboratory/In situ Sound Velocities of Shelf Sediments in the South Sea of Korea

Kim, Dae-Choul,Kim, Gil-Young,Jung, Ja-Hun,Seo, Young-Kyo,Wilkens, Roy H.,Yoo, Dong-Geun,Lee, Gwang-Hoon,Kim, Jeong-Chang,Yi, Hi-Il,Cifci, Gunay The Korean Society of Fisheries and Aquatic Scienc 2008 Fisheries and Aquatic Sciences Vol.11 No.2

Compressional sound velocities of shelf sediments in the South Sea of Korea, were measured in situ and in the laboratory for six cores. In situ sound velocity was measured using the Acoustic Lance (frequency of 7.5-15 kHz), while laboratory velocity was measured by the pulse transmission technique (frequency of 1MHz). Physical properties were relatively uniform with sediment depth, suggesting little effect of sediment compaction and/or consolidation. Average in situ velocity at each core site ranged from 1,457 to 1,488 m/s, which was less than the laboratory velocity of 1,503 and 1,604m/s. In muddy sediments the laboratory velocity was 39-47 m/s higher than in situ velocity. In sandy sediments, the difference was greater by an average of 116 m/s. Although the velocity data were corrected by the velocity ratio method based on bottom water temperature, the laboratory velocity was still higher than the in situ velocity (11-21 m/s in muddy sediments and 91 m/s in sandy sediments). This discrepancy may be caused by sediment disturbance during core collection and/or by the pressure of Acoustic Lance insertion, but it was most likely due to the frequency difference between in situ and laboratory measurement systems. Thus, when correcting laboratory velocity to in situ velocity, it is important to consider both temperature and frequency.

드론을 이용한 홍수기 유량측정방법 개발(II) - 전자파표면유속계 적용

이태희,강종완,이기성,이신재 한국수자원학회 2021 한국수자원학회논문집 Vol.54 No.11

In the flood season, the measurement of the river discharge has many restrictions due to reasons such as budget, manpower, safety, convenience in measurement and so on. In particular, when heavy rain events occur due to typhoons, etc., it is difficult to measure the amount of flood due to the above problems. In order to improve this problem, in this study, a method was developed that can measure the river discharge in a flood season simply and safely in a short time with minimal manpower by combining the functions of a drone and a surface velocity doppler radar. To overcome the mechanical limitations of drones caused by weather issues such as wind and rainfall derived from the measurement of the river discharge using the conventional drone, we developed a drone with P56 grade dustproof and waterproof performance, stable flight capability at a wind speed of up to 36 km/h, and a payload weight of up to 10 kg. Further, to eliminate vibration which is the most important constraint factor in the measurement with a surface velocity doppler radar, a damper plate was developed as a device that combines a drone and a surface velocity Doppler radar. The velocity meter DSVM (Dron and Surface Veloctity Meter using doppler radar) that combines the flight equipment with the velocity meter was produced. The error of ±3.5% occurred as a result of measuring the river discharge using DSVM at the point of Geumsan-gun (Hwangpunggyo) located at Bonghwang stream (the first tributary stream of the Geum River). In addition, when calculating the mean velocity from the measured surface velocity, the measurement was performed using ADCP simultaneously to improve accuracy, and the mean velocity conversion factor (0.92) was calculated by comparing the mean velocity. In this study, the discharge measured by combining a drone and a surface velocity meter was compared with the discharge measured using ADCP and floats, so that the application and utility of DSVM was confirmed. 홍수기 하천에서 유량측정은 예산, 인력, 안전 및 측정 시 편의성 등의 이유로 측정에 제한이 많다. 특히, 태풍 등으로 인한 호우사상 발생 시 위와 같은 문제로 홍수량 측정에 어려움이 따른다. 이러한 문제점을 개선하기 위해 본 연구에서는 드론(Drone)과 전자파표면유속계(Surface velocity doppler radar)의 기능을 조합하여 최소 인력으로 짧은 시간에 간편하고, 안전하게 홍수기에 하천유량을 측정할 수 있는 방법을 개발하였다. 기존 드론을 이용한 유량측정 연구에서 도출된 바람, 강우 등 기상 요인에 의한 드론의 기계적인 한계를 극복하기 위해 본 연구에서는 IP56 등급의 방진·방수 성능, 최대 36 km/h의 풍속에서 안정적인 비행능력과 최대 10 kg을 탑재할 수 있는 드론을 개발하였다. 또한 전자파표면유속계 측정에 있어서 주요 제약 요소인 진동을 제거하기 위해 드론과 전자파표면유속계를 결합하는 댐퍼플레이트를 개발하였다. 이들 비행장비와 유속계를 결합시킨 유속계 DSVM (Dron and Surface Veloctity Meter using doppler radar)을 제작하였으며, 봉황천(금강 제1지류)에 위치한 금산군(황풍교)지점에서 DSVM을 운용하여 홍수량을 측정한 결과 ±3.5%의 오차가 발생하였다. 또한 측정된 표면유속으로부터 평균유속을 산정할 때 정확도 향상을 위해 ADCP를 이용하여 동시 측정하고, 평균유속을 비교하여 평균유속환산계수(0.92)를 산정하였다. 본 연구에서는 드론과 전자파표면유속계를 결합해 측정한 유량과 ADCP 및 봉부자를 이용해 측정한 유량을 비교하고, DSVM의 적용 및 활용 가능성을 확인하였다.

저속 충돌제트에 의해 형성되는 액막의 속도 분포에 관한 연구

추연준 ( Yeon Jun Choo ),강보선 ( Bo Seon Kang ) 한국액체미립화학회 2000 한국액체미립화학회지 Vol.5 No.1

In this research, the velocity distribution of the liquid sheet formed by two impinging jets at low velocities are measured using LDV. The spatial distribution of the sheet velocity as well as the effects of impinging anlge and jet velocity on the sheet velocity are examined. The sheet velocity is highest along the sheet axis and it decreases with the increase of the azimuthal angle. With the increase of the impinging angle, the average sheet velocity is decreased due to the increased impact momentum. The average sheet velocity is proportional to the jet velocity but it is always higher than the jet velocity. This result is against the fact that the sheet velocity can be assumed to be equal to the jet velocity in the previous researches.

케미컬루핑 연소를 위한 산소전달입자의 최소유동화속도 및 고속유동층 전이유속에 미치는 압력의 영향

김정환,배달희,백점인,박영성,류호정 한국수소및신에너지학회 2017 한국수소 및 신에너지학회논문집 Vol.28 No.1

To develop a pressurized chemical looping combustor, effect of pressure on minimum fluidization velocity and transition velocity to fast fluidization was investigated in a two-interconnected pressurized fluidized bed system using oxygen carrier particle. The minimum fluidization velocity was measured by bed pressure drop measurement with variation of gas velocity. The measured minimum fluidization velocity decreased as the pressure increased. The transition velocity to fast fluidization was measured by emptying time method and decreased as the pressure increased. Gas velocity in the fuel reactor should be greater than the minimum fluidization velocity and gas velocity in the air reactor should be greater than the transition velocity to fast fluidization to ensure proper operation of two interconnected fluidized bed system.

만성 편마비 장애인의 보행속도와 동맥경직도와의 관련성

이용희 ( Yong Hee Lee ),박수현 ( Soo Hyun Park ),윤은선 ( Eun Sun Yoon ),제세영 ( Sae Young Jae ) 한국특수체육학회 2012 한국특수체육학회지 Vol.20 No.1

동맥경직도의 증가는 심혈관계 질환의 위험성 증가와 관련이 높으며, 보행속도 또한 혈관의 죽상경화와 같은 심혈관계 질환의 위험요인과 관계한다. 최근 선행연구에서는 이와 같은 동맥경직도와 보행속도와의 관련성을 보고하고 있으나 동맥경직도가 높아져 있고, 보행에 문제가 있는 편마비 장애인을 대상으로 한 연구는 없다. 따라서 본 연구는 편마비 장애인을 대상으로 보행속도와 동맥경직도와의 관련성을 알아보는데 목적이 있다. 본 연구에서는 편마비 장애인 94명(남 68명, 여 26명, 평균 61세)을 대상으로 하였고, 보행속도는 10m 보행과 6분걷기 검사로 측정하였으며 동맥경직도의 지표로서 경동맥-대퇴동맥 맥파전파속도를 측정하였다. 그 결과 10m보행속도와 동맥경직도간에는 유의한 역 상관관계를 보였으며(r =-.34, p=.001), 6분 걷기에서도 역 상관관계가 나타났다(r =-.45, p=.001). 그리고 나이, 성별, 체질량지수, 체중, 유병기간, 혈압, 심박수, 약물복용을 보정한 후에도 보행속도는 동맥경직도와 관계하는 것으로 나타났다(10m 보행속도 β =-.19, p=.025; 6분 걷기 보행속도 β =-.27, p=.004). 또한 보행속도가 빠른 그룹이 느린 그룹에 비해 동맥경직도가 더 낮은 것으로 나타났다(8.6m/s vs. 11.4m/s, p=.001). 따라서 빠른 보행속도는 낮은 동맥경직도와 관계하는 것으로 사료된다. Increased arterial stiffness is a strong predictor of future cardiovascular events. Several studies have shown that gait velocity is associated with arterial stiffness, but it is unclear in individuals with chronic hemiplegia. We investigated the relationship between gait velocity and arterial stiffness in individuals with chronic hemiplegia. Ninety four patients with stroke(68 male , 26 female, mean age 61) were recruited in the study. We measured the 10 meter gait test and the six minutes walk test(6MWT) as indices of gait velocity. Arterial stiffness was assessed by carotid-femoral pulse wave velocity using applanation tonometry. There was a significant inversely association between gait velocity and pulse wave velocity(10m gait test r=-.34, p=.001; 6MWT r=-.45, p=.001). In separate multivariable linear regression models that adjusted for age, gender, body mass index, duration of stroke, systolic blood pressure, heart rate, and medication, gait velocity was an independent associated with pulse wave velocity(10m gait test β=-.19, p=.025; 6MWT β=-.27, p=.004). Subjects with fast gait velocity had significantly lower pulse wave velocity than subjects with low gait velocity(8.6m/s vs. 11.4m/s, p=.001). These findings demonstrate that high gait velocity was associated with low arterial stiffness independent of risk factors in individuals with chronic hemiplegia