• 한국항공우주학회지
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• 제50권8호
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• pp.531-540
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• 2022

본 논문에서는 IMM 필터 기반으로 장사정포의 탄종을 식별하고 탄착점을 신속하게 예측하는 알고리즘을 제시한다. 탄도궤적 방정식을 시스템 모델로 사용하고, 각각 다른 탄도계수 값을 갖는 3가지 모델을 IMM 필터에 적용한다. 가속도를 중력, 공기저항, 양력에 의한 3가지 성분으로 나누고 양력가속도를 새로운 상태변수로 추가하여 추정한다. 속도벡터와 양력가속도가 수직이라는 운동학 조건을 유사 측정값으로 추가한 측정방정식을 다룬다. IMM 필터를 통해 추정된 상태변수와 모드 확률이 가장 높은 모델의 탄도계수를 기반으로 탄착점을 예측한다. 탄착점 예측을 위해 일반적으로 사용되는 룽게-쿠타 수치적분 대신, 준해석적인 방법을 사용하여 적은 계산량으로 탄착점을 예측할 수 있음을 설명한다. 마지막으로 최소제곱법을 이용한 상태변수 초기화 방법에 대해 제안하고 성능을 확인하였다. 탄종식별, 탄착점 예측 및 초기화를 포함한 통합 알고리즘을 제시하고 시뮬레이션을 통해 제안한 방법의 타당성을 검증하였다.

• 한국운동역학회지
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• 제15권1호
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• pp.237-257
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• 2005

It was to study as a following-research of "A Case Study on Center of Gravity(COG) Analysis when Performing Uchimata(inner thigh reaping throw) by Posture and Voluntary Resistance Levels(VRL) of Uke in Judo[I]". The purpose of this study was to analyze the COG variables when performing uchimata(inner thigh reaping throw) by two postures and voluntary resistance levels(VRL) of uke(reciver) in Judo. The subjects, who were one male judoka(YH) for 1992 Barcelona Olympic Games Olympian(silver medalist), and one male trainee; Y.I.University representative member (SDK), and were filmed on two S-VHS 16mm video cameras(60fields/sec.) through 3-dimensional motion analysis methods, that postures of uke were shizenhontai (straight natural posture) and jigohontai(straight defensive posture), VRL of uke were 0% and 100%, respectively. The kinematical variable was COG variable, distance of COG, and distance of resultant COG between uke and tori(the thrower), velocity and acceleration of COG. The data of this study collection were digitized by SIMI Motion Program computed the mean values and the standard deviation calculated for each variables. When performing uchinmata according to each posture and VRL of uke and classifying. From the data analysis and discussion, the conclusions were as follows : 1. Displacement of COG Subject YH, COG was the highest in kuzushi(balance -breaking), vertical COG was low when following in tsukuri(positioning; set-up), kake(application; execution), and COG was pattern of same character each postures and resistance, respectively. Subject SDK, COG was low from kumikata(engagement positioning) to kake, and COG was that each postures and resistance were same patterns, respectively. Subject YH, SDK, each individual, postures and resistance, vertical COG was the lowest in kake phase, when performing. 2. Distance of COG between uke and tori The distance of COG between uke and tori when performing, subject YH was $0.64{\sim}0.70cm$ in kumikata, $0.19{\sim}0.28cm$ in kake, and SDK was $0.68{\sim}0.72cm$ in kumikata, $0.30{\sim}0.42\;cm$ in kake. SDK was wider than YH. 3. Distance of resultant COG between uke and tori The distance of resultant COG between uke and tori when performing, subject YH was $0.27{\sim}0.73cm$ from kumikata to kake. and SDK was $0.14{\sim}0.34cm$ in kumikata, $0.28{\sim}0.65cm$ in kake. Jigohontai(YH:$0.43{\sim}0.73cm$,SDK:$0.59{\sim}0.65cm$) was more moved than shizenhontai(YH:$0.27{\sim}0.53cm$, SDK: $0.28{\sim}\;0.34cm$). 4. Velocity of COG The velocity of COG when performing uchimata, subject YH was fast anterior-posterior direction in kuzushi, ant.-post. and vertical direction fast in tsukuri and kake. SDK was lateral, ant.-post. and vertical direction in kuzushi, ant.-post. and vertical direction in tsukuri and ant.-post. direction in take, respectively. 5. Acceleration of COG The acceleration of COG when performing uchimata, The trend of subject YH was showed fast vertical direction in kuzushi and tsukuri, ant.-post. and vertical direction fast in kake. The trends of SDK showed lateral direction in kuzushi, lateral and ant.-post. direction in tsukuri and ant.-post. direction in kake, respectively.

• 대한통합의학회지
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• 제8권3호
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• pp.33-41
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• 2020

Purpose : Conventional Balance Measurement can only measure the center of gravity and the shaking movement of the body. As a result, it has the disadvantages of not responding to visual changes and blocking functions of variables. This study was carried out to evaluate the performance of new equipment that measures the balance of the body using changes in body segment and pressure using the acceleration sensor to compensate for the disadvantages of the existing equipment. Methods : To this end, balance ability was measured in 43 healthy male/female adults without orthopedic injuries and nervous system damage in the last 6 months. in a situation where the visual information was restricted by Virtual Reality (VR) gear, all subjects measured and evaluated the balance ability utilizing the new equipment. Balance measurement (Prime Medilab, Korea) and Wii fit (Nintendo, Japan) were used to measure the balance ability of the subjects, and the balance ability test was performed in 4 postures using each device for data acquisition. The test duration for each posture was 30 seconds. For data acquisition, the average value of three experiments measured using each equipment was analyzed, and the statistical test was performed using the independent sample and the corresponding sample t-test, and the significance level was set to α=.05. Results : As a result of measuring the balance ability using individual equipment, blocking visual information using VR gear, the average speed, maximum speed, and moving area of the COP increased equally. It was found that the obtained absolute size of the result in Wii was somewhat larger than that of BM. Conclusion : It is considered that in the future research, it is necessary to measure changes in the body's center of gravity through image analysis, etc., to make clear comparison and evaluation of the usability.

• 한국항공우주학회지
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• 제44권11호
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• pp.965-972
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• 2016

유도형 탄약은 비행속도 증가를 이용한 기존의 사거리 증가 방식과 다르게 정밀 유도제어를 사거리 연장 및 정밀 타격하는 기술을 기반으로 한다. 고회전으로 상승하는 탄은 탄도 정점에서 후미 날개를 전개하여 회전을 감소하고, 최종적으로 회전을 제거한 후 비행하게 된다. 주 날개 전개 전 탄체 뒤집힘 감지를 위하여 자세 추정이 요구되는데, 회전 감속 중에서는 일정한 회전을 가정한 기존의 유도무기 자세 추정 기법을 사용할 수 없다. 또한, 비행 시에는 횡축 가속도를 제어하기 때문에 중력 가속도 성분을 기반으로 하는 일반적인 무인기의 자세 추정 기법은 큰 오차를 발생한다. 이러한 문제를 해결하기 위해 본 논문에서는 저속 회전 및 비행 중 자세추정기법을 제시하고, 무인기에 탑재하여 비행 실험을 통해 검증하였다. 저속 회전 중 자세 추정 기법은 롤 각을 상태변수로 갖는 칼만 필터 형태로 구성하였다. 비행 시 자세 추정 기법은 사원수를 이용한 곱연산 확장형 칼만 필터를 기반으로 하며, 가속도 측정치가 중력 가속도뿐만 아니라 선회에 의한 구심력을 포함하도록 측정 모델을 개선하였다.

• 대한원격탐사학회지
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• 제37권5_1호
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• pp.927-938
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• 2021

편대 비행하는 저궤도위성에는 비슷한 크기의 비중력 섭동이 일정한 시간 차이를 두고 가해진다. 이러한 시간상관관계를 이용하면 한 개 위성의 가속도계에서 측정된 가속도 값으로 다른 편대비행 저궤도위성의 비중력가속도를 추정할 수 있다. 편대비행 저궤도위성인 GRACE 및 GRACE-FO 위성에서 한 개 위성의 가속도계 데이터를 사용할 수 없는 기간이 존재하는데, 앞서 기술된 시간 이식 기법이 JPL (Jet Propulsion Laboratory)에서 공식적으로 가속도계 데이터 복원 시 사용되고 있다. 본 논문에서는 기존의 시간 이식 기법의 가속도계 추정 정확도를 개선하기 위하여 신경망 (neural network; NN) 모델 기반 편대비행 저궤도위성 가속도계 데이터 추정 방법을 제안하였다. 시간 이식 기법은 위성의 위치 및 우주환경요소 등을 반영할 수 없지만, NN 모델은 이를 모델 입력으로 사용할 수 있으므로 예측 정확도를 높일 수 있다. 1개월간 NN 모델을 사용하여 가속도계 예측 시험을 수행하고 시간 이식 기법과 예측 정확도를 비교하였다. 그 결과 along-track 및 radial 방향에서 NN모델의 가속도계 데이터의 예측 오차는 시간 이식 기법에 비해 각각 55.0%, 40.1% 감소하였다.

• 드라이브 ㆍ 컨트롤
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• 제13권2호
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• pp.10-18
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• 2016

A front-end loader (FEL) mounted on an agricultural tractor is one of the most commonly used implements to mechanize routine agricultural tasks. When the FEL is used with a loaded bucket, careful operation is required to maintain safety and avoid spillage when the tractor passes a bump because a change in the gravity center of the tractor due to varied loadings can affect the stability of the tractor. Use of a boom suspension system consisting of accumulators and orifice dampers can be instrumental in reducing pitching vibrations while increasing the handling performance of the FEL-mounted tractor. The objective of this research was to reduce bump shocks by adding an orifice and a flow control valve to the original hydraulic circuit composed solely of accumulators. A simulation study was performed using the SimulationX program to investigate the effects of an accumulator and an orifice-throttle damper on bump shocks. Results showed that the peak pressure on a boom cylinder and the vertical acceleration of a bucket were significantly affected by use of both an accumulator and an orifice damper. In a field test conducted with a 75-kW tractor, the peak pressure of the boom cylinder, and the root mean square (RMS) vertical acceleration of the bucket and seat were reduced by on average, 23.0, 42.2, and 44.9% respectively, as compared to those measured with the original accumulator system, showing that an improved design for the accumulator hydraulic circuit can reduce bump shocks. Further studies are needed to design a tractor suspension system that includes the effects of cabin suspension and tires as well as dynamic analysis.

• 물과 미래
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• 제27권4호
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• pp.123-133
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• 1994

하천 흐름해석에서 단순화된 운동방정식을 사용한 kinematic 모델과 diffusion 모델이 full dynamic 모델에 비하여 여러 장점을 지니고 있기 때문에 수치모의에 종종 사용된다. 본 논문에서는 kinematic 모델과 diffusion 모델의 적용범위에 대하여 보다 폭넓게 사용될 수 있는 적용한계를 하천의 수로경사 $S_{02}$, 무차원의 상류측 수심증가 수 Gw 및 Froude수 Fr등 3개의 주요한 인자를 기준으로 하여 연구하였다. 이 때 적용범위는 full dynamic 방정식의 시간 가속도항, 공간 가속도항, 압력항, 중력항 및 마찰항의 상대적 크기의 비교를 통하여 도출되었다. 실험모의중에 Courant수는 0.5로 한정되었으며, 하천의 하상경사는 0.00001부터 0.05까지 변하였다. 또한, 0.1, 0.5 및 0.9의 Froude 수가 사용되었다. 본 논문에서는 kinematic 모델의 적용범위는 Froude 수가 증가함에 따라 증가하는 것으로 나타났으나, diffusion 모델의 적용범위는 Froude 수가 증가함에 따라 감소하였다. 최종적으로 kinematic 모델과 diffusion 모델의 적용을 위한 지침으로 사용할 수 있는 9개의 그림이 제안되었으며 이 제안된 그림을 적절하게 활용할 때 하천이나 강에 흐름모의가 보다 효율적으로 이루어질 수 있을 것이다.

• 콘크리트학회지
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• 제11권1호
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• pp.109-118
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• 1999

국내에서는 1988년부터 내진 규준이 시행되었으며, 따라서 그 이전에 지어진 저층 철근콘크리트 건물들은 내진 규준이 적용되지 않고 단지 축하중만을 고려하여 설계되었다. 그러므로 약한 지진이 발생하여도 이러한 건물들은 심한 피해를 입을 수 있다. 본 논문에서는, 내진 규준이 시행되기 이전에 지어진 비내진 저층 철근콘크리트 모멘트 저항 골조의 지진 발생시 거동과 피해를 알아보기 위하여, 실제 존재하는 비내진 건물 중 3층 철근콘크리트 라멘조 공공청사 건물의 외부 적합부를 교차보가 있는 것과 없는 것의 2종류를 1/2의 실물크기로 제작하고, 횡방향 변위 제어로 반복하중을 가하여 실험을 수행하였다. 비내진 접합부의 가장 큰 특징은 적합부내의 횡보강근이 없다는 것이다. 실험을 통하여 균열의 형태, 강도${\cdot}$강성의 저하, 에너지 소산 그리고 기둥과 보 부재의 철근 미끄러짐을 조사하였다. 국내에서 규정하고 있는 최대지반가속도인 0.12g크기의 횡방향 하중을 가력하였을 경우에는 균열이 발생하지 않았으나, 횡방향 하중을 0.12g이상으로 증가할수록 교차보가 없는 외부접합부에서 전단균열이 발생하였다.

• Earthquakes and Structures
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• 제15권5호
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• pp.453-462
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• 2018

Damages to buildings affected by a near-fault strong ground motion are largely attributed to the vertical component of the earthquake resulting in column failures, which could lead to disproportionate building catastrophic collapse in a progressive fashion. Recently, considerable interests are awakening to study effects of earthquake vertical components on structural responses. In this study, detailed modeling and time-history analyses of a 12-story code-conforming reinforced concrete moment frame building carrying the gravity loads, and exposed to once only the horizontal component of, and second time simultaneously the horizontal and vertical components of an ensemble of far-field and near-field earthquakes are conducted. Structural responses inclusive of tension, compression and its fluctuations in columns, the ratio of shear demand to capacity in columns and peak mid-span moment demand in beams are compared with and without the presence of the vertical component of earthquake records. The influences of the existence of earthquake vertical component in both exterior and interior spans are separately studied. Thereafter, the correlation between the increase of demands induced by the vertical component of the earthquake and the ratio of a set of earthquake record characteristic parameters is investigated. It is shown that uplift initiation and the magnitude of tensile forces developed in corner columns are relatively more critical. Presence of vertical component of earthquake leads to a drop in minimum compressive force and initiation of tension in columns. The magnitude of this reduction in the most critical case is recorded on average 84% under near-fault ground motions. Besides, the presence of earthquake vertical components increases the shear capacity required in columns, which is at most 31%. In the best case, a direct correlation of 95% between the increase of the maximum compressive force and the ratio of vertical to horizontal 'effective peak acceleration (EPA)' is observed.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권1호
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• pp.161-177
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• 2013

High-speed vessels require good resistance and seakeeping performance for safe operations in rough seas. The resistance and seakeeping performance of high-speed vessels varies significantly depending on their hull forms. In this study, three planing hulls that have almost the same displacement and principal dimension are designed and the hydrodynamic characteristics of those hulls are estimated by high-speed model tests. All model ships are deep-V type planing hulls. The bows of no.2 and no.3 model ships are designed to be advantageous for wave-piercing in rough water. No.2 and no.3 model ships have concave and straight forebody cross-sections, respectively. And length-to-beam ratios of no.2 and no.3 models are larger than that of no.1 model. In calm water tests, running attitude and resistance of model ships are measured at various speeds. And motion tests in regular waves are performed to measure the heave and pitch motion responses of the model ships. The required power of no.1 (VPS) model is smallest, but its vertical motion amplitudes in waves are the largest. No.2 (VWC) model shows the smallest motion amplitudes in waves, but needs the greatest power at high speed. The resistance and seakeeping performance of no.3 (VWS) model ship are the middle of three model ships, respectively. And in regular waves, no.1 model ship experiences 'fly over' phenomena around its resonant frequency. Vertical accelerations at specific locations such as F.P., center of gravity of model ships are measured at their resonant frequency. It is necessary to measure accelerations by accelerometers or other devices in model tests for the accurate prediction of vertical accelerations in real ships.