• Title/Summary/Keyword: SA오차

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Analysis of Dynamic Positioning System Based on Self-Tuning Control (자기동조 제어기를 이용한 위치확보 시스템에 관한 연구)

  • Sang-M.,Lee;Pan-M.,Lee;Sa-Y.,Hong
    • Bulletin of the Society of Naval Architects of Korea
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    • v.26 no.2
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    • pp.32-40
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    • 1989
  • Dynamic ship positioning(DP) system is used to keep the position and heading of a ship, or a floating platform, above a pre-selected site on the seabed by using thrusters. This paper presents a control system based on filtering technique and optimal control theory. The planar motions of a vessel are assumed to consist of low frequency(LF) component and high frequency(HF) one. The former is mainly due to thrusters, current, wind and second order wave forces, while the latter is mainly due to first order oscillatory component of the wave force. Furthermore position measurement signals include the noise. By means of self-tuning filter and Kalman filter techniques, LF motion estimates and HF ones are seperately achieved from the position measurements of the vessel. The estimated LF motions are used as input to the feedback loops. The total thruster power is minimized using the Linear Quadratic Gaussian control theory. The performance of the vessel with the DP system is investigated by computer simulation.

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A Study on the Fracture Behavior of Composite Laminated T-Joints Using AE (AE를 이용한 복합재료 T 조인트부의 파괴거동에 관한 연구)

  • Kim, J.H.;Ahn, B.W.;Sa, J.W.;Park, B.J.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.19 no.4
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    • pp.277-287
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    • 1999
  • Quasi-static tests such as monotonic tension and loading/unloading tension were performed to investigate the bond characteristics and the failure processes for the T-joint specimens made from fiber/epoxy composite material. Two types of specimens, each consists of two components, e. g. skin and frame. were manufactured by co-curing and secondary bonding. During the monotonic tension test, AE instrument was used to predict AE signal at the initial and middle stage of the damage propagation. The damage initiation and progression were monitored optically using m (Charge Coupled Device) camera. And the internal crack front profile was examined using ultrasonic C-scan. The results indicate that the loads representing the abrupt increase of the AE signal are within the error range of 5 percent comparing to the loads shown in the load-time curve. Also it is shown that the initiation of crack occurred in the noodle region for both co-cured and secondarily bonded specimen. The final failure occurred in the noodle region for the co-cured specimen. but at the skin/frame termination point for the secondarily bonded specimen. Based on the results, it was found that two kinds of specimen show different failure modes depending on the manufacturing methods.

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Derivation of Basal Area Projection Function for Forest Plantation Using Medium (3-5years) Measurement Cycles (중간(中間) 측정(測定) 주기(週期) (3-5년)를 이용(利用)한 인공림(人工林)의 흉고단면적(胸高斷面績) 추정(推定) 함수(函數)의 유도(誘導))

  • Lee, Sang-Hyun
    • Journal of Korean Society of Forest Science
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    • v.89 no.4
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    • pp.463-469
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    • 2000
  • Douglas-fir (Pseudotsuga menziesd Mirb. Franco) is highly regarded as a commercial timber species throughout the world in part due to its fast growth relative to many other species. In this study, basal area per hectare equation for Douglas-fir plantations in Southland of New Zealand has been developed based on medium measurement cycles of permanent sample plots data set. The function was developed using the algebraic difference equation method, and various sigmoid-shaped projection equations were used. Parameter estimation was obtained by non-linear routine of the SAS. As a result, of the functions tested a variant of the Schumacher polymorphic function including site index and thinning term as predictor variables showed the higher precision of the fitting. The results indicate that site index is positively correlated with basal area growth. And the thinning term was found to be useful to increase precision of the model.

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Analysis of Influences due to Navigation Message Error of GPS Signals on Receiver (GPS 항법메시지 이상이 수신기에 미치는 영향 분석)

  • Kang, Hee-Won;Cho, Deuk-Jae;Park, Sang-Hyun
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.14 no.10
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    • pp.2223-2229
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    • 2010
  • The integrity monitoring of anomalous GPS signal have been researched because of the degradation of GPS satellite performance. It is known that anomalous GPS signal can occur by failure of GPS satellite, sudden increase of ionosphere delay error, SA, wrong modeling for navigation parameters from control segment, and an electromagnetic wave interference, etc. In case of GPS anomaly by satellites can arise from carrier frequency, code and navigation message. In this paper, the scenarios with navigation message errors were made by using GPS simulator, and the influences of GPS navigation message error to receiver were analysed. The anomalies of preamble, bits related TOW count message, subframe ID in HOW, bits related satellite healthy, and the other navigation message errors were described and simulated. Also, the number of satellites, DOP and pseudorange are analyzed to know how the anomalous signal can affect on GPS receiver.

Experimental Study of the End-plate Gap Effect on the Performance of Extended End-plate Type Splice (이음면 이격이 확장형 단부판 이음부 성능에 미치는 영향에 대한 실험적 연구)

  • Kim, Cheol Hwan;Lee, Myung Jae;Kim, Hee Dong;Kim, Sa Bin
    • Journal of Korean Society of Steel Construction
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    • v.28 no.6
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    • pp.427-438
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    • 2016
  • This study is experimental research for the effect of gap at the end plate on the performance of extended end-plate type splice. For this research, simple beam type specimens by using extended end-plate type splice are planned. Main variables are the initial gap between end-plates, the installation of finger shim plate before the installation of high tension bolts, the final gap between end-plates, and the installation of finger shim plate after the installation of high tension bolts. The static loading tests results show that the maximum bending strength of splice is not dependent on the gap, but the vertical displacement, initial stiffness and elastic stiffness are affected by the gap. In addition to that, the possibility of brittle fracture is increased when the torque of high tension bolt is used to control the gap. Thus, careful consideration is needed in this case.

Quality Control of the UHF Wind Profiler Radar (UHF 윈드프로파일러 레이더 자료의 품질 개선)

  • Jo, Won-Gi;Kwon, Byung-Hyuk;Kim, Park-Sa;Kim, Min-Seong;Yoon, Hong-Joo
    • The Journal of the Korea institute of electronic communication sciences
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    • v.13 no.2
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    • pp.277-290
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    • 2018
  • Wind data observed by wind profiler provide wind vectors with the altitudes using PCL1300, wind computation program. As a result of application with parameters set in program currently, it is difficult to compute wind vectors in the upper air over 3 km. This id because a very strict criterion for parameters removes large amounts of data. In this study, therefore, we improve the methods of application by resetting parameters to expand data collection area of wind vectors and reduce underestimation. Although the acquisition rate of the wind vector increased from 72.2% to 92.2%, the RMSE of the wind speed maintained 1.5 m/s - 3.1 m/s, which is less than 15% of the error rate at each altitude.

Development of an Inverse Method Using Orthogonal Basis Functions for the Evaluation of Boundary Tractions on an Elastic Body (탄성체 경계 트랙션을 구하는 문제에서 상호 수직 기저 함수를 사용한 역문제 해석 방법의 개발)

  • Kim, Sa-Young;Kim, Hyun-Gyu
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.4
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    • pp.487-493
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    • 2010
  • Most structural analyses are concerned with the deformations and stresses in a body subjected to external loads. However, in many fields, inverse problems have to be interpreted to determine surface tractions or internal stresses from displacements measured on a remote surface. In this study, the inverse processes are studied by using the finite element method for the evaluation of internal stresses. Small errors in the measured displacements often result in a substantial loss of stability of an inverse system. In order to improve the stability of the inverse system, the displacements on a section near the region of the unknown tractions are predicted by using orthogonal basis functions. We use the Gram-Schmidt orthogonal technique to determine two bases for the displacements on a section near the region of the unknown tractions. Advantages over previous methods are discussed by using numerical examples.

Sensitivity Analysis of Vortical Hull Girder Vibration (선체 저차 상하고유진동 감도해석)

  • Dae-Seung Cho;Sa-Soo Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.35 no.3
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    • pp.54-61
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    • 1998
  • This paper presents a prediction method of natural frequencies of vertical hull girder vibration based on design sensitivity analysis in case of design modification and the variation of loading condition. The resented method premises the vibration analysis by the transfer matrix method. Governing sensitivity equation is derived from the direct differentiation of state vector and transfer matrix to parameters and its transfer over all the hull girder elements. Derivatives of natural frequencies and mode shapes are determined by two trial calculation of the governing equation. Using the derivatives, the changes of natural frequencies and mode shapes can be predicted when mass and stiffness parameter's are changed. As results, it is possible to optimize ship structure as well as to avoid troublesome calculation in hull girder vibration analysis rationally and efficiently. To verify the accuracy and efficiency of the resented method numerical results obtained by both the sensitivity analysis and the ordinary reanalysis far a real ore/bulk carrier in case of the change of mass and stiffness parameters are compared.

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A Study on the Effect of Temperature on the Elastic-Plastic Fracture Toughness $J_{IC}$ of Materials (I) - A Comparative Study of $J_{IC}$ Test Methods Recommended by ASTM and JSME - (재료의 탄소성 파괴인성치 $J_{IC}$의 온도 의존성에 관한 연구 I - AST과 JSME의 $J_{IC}$ 시험법에 관한 비교연구 -)

  • 석창성;최용식;양원호;김영진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.4
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    • pp.653-659
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    • 1989
  • Elastic-plastic fracture toughness J$_{IC}$ can be used as an effective design criterion in elastic plastic fracture mechanics. In the J$_{IC}$ test methods approved by ASTM and JSME, there are discrepancies such as the definition of J$_{IC}$, the slope of the blunting line, curve fitting method and the measurement of crack extension etc. The objective of this paper is to evaluate the effect of these discrepancies on the determination of J$_{IC}$ values. Fracture toughness tests were performed on A516, SA508 and SCM415 steels, and test results were analyzed according to ASTM E 813-81, ASTM E 813-87 and JSME S 001-1981. Results showed significant differences depending on the analysis methods. Therefore, a conversion equation between two ASTM methods was proposed, and the conversion error was within acceptable range(less then 8.5%)en 8.5%)

Analysis of Steady and Unsteady Flow Around a Ship Using a Higher-Order Boundary Element Method (고차경계요소법에 의한 선체주위 유동해석)

  • Sa-Y. Hong;Hang-S. Choi
    • Journal of the Society of Naval Architects of Korea
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    • v.32 no.1
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    • pp.42-57
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    • 1995
  • An efficient and accurate scheme has been constructed by taking advantages of the hi-quadratic spline scheme and the higher-order boundary element method selectively depending on computation domains. Boundary surfaces are represented by 8-node boundary elements to describe curved surfaces of a ship and its neighboring free surface more accurately. The variation of the velocity potential complies with the characteristics of the 8-node element on the body surface. But on the free surface, it is assumed to follow that of the hi-quadratic spline scheme. By which, the free surface solution is free from numerical damping and has better numerical dispersion property. As numerical examples, steady and unsteady Neumann-Kelvin problems are considered. Numerical results for a submerged spheroid, Series 60($C_B=0.6$) and a modified support the proposed method. Finally, a new upstream radiation condition is derived using a wave equation operator in order to deal with problems for subcritical reduced frequency. The relevance of this operator has been confirmed in the case of unsteady Kelvin source potential.

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