• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.78-78
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• 2017

강우레이더 관측의 정확도는, 호우의 강도나 형태와 같은 기상학적 조건(변동 오차 요소) 외에도, 관측 지점의 레이더로부터의 거리, 고도, 관측유역의 형태나 크기 등 다양한 관측환경 조건(고정 오차 요소)에 의해서도 달라질 수 있기 때문에, 강우레이더 관측의 오차 성분을 정량화할 필요가 있다. 본 연구에서는 거리와 고도에 의한 오차 특성을 이중편파 변수의 특성을 이용하여 실증적으로 분석하였고, 이를 통해 감쇠의 영향과 산지효과(또는 지형효과)로 인한 오차 규모를 정량적으로 산정 비교하였다. 거리가 멀어짐에 따라 고도도 높아지기 때문에 QPE 불확실도의 거리와 고도에 따른 성분을 구분하는 것은 매우 어려운데, 거리에 대한 불확실도 성분이 매우 작은 R(KDP)를 이용한다면 효과적으로 분리가 가능하다. 이러한 원리를 이용하여, 관측 거리에 따른 오차가 매우 작은 R(KDP)를 기준으로 관측 거리에 따른 오차와 고도에 따른 오차를 분리하여 표준화[Z-score] 하였다. R(Z)의 경우는 관측 고도와 거리에 따른 오차가 중첩되어 나타나나, R(KDP)는 거리에 따른 오차는 거의 나타나지 않으므로 이를 기본 가정으로 하여 R(Z)와 R(KDP) 관계로부터 관측 고도에 따른 오차 성분만 분리하였다. 분리 결과, 관측 거리에 따른 표준 오차의 경우 100km 까지는 대략 10%(0.1) 이하로 나타났으나, 150km 이상에서는 30%(0.3)를 초과하는 것으로 나타났다. 관측 고도에 따른 표준 오차의 경우 2~3번째 고도각 까지는 대략10%(0.1) 이하로 나타났으나, 3번째 고도각 이상에서는 20%(0.2), 4번째 고도각 이상에서는 50%(0.5)를 초과하는 것으로 나타나, 고도에 의한 영향이 거리에 의한 영향보다 민감하게 나타났다. 1번째 고도각에서는, 100km 이내 근거리에서 관측 거리가 가까워질수록 오차가 증가하는 경향을 보이는데, 이는 저고도 빔 간섭(빔 차폐) 등의 영향으로 추정되었다.

• Proceedings of the KIEE Conference
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• 1997.07b
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• pp.571-574
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• 1997

항법장치의 핵심요소인 가속도센서와 자이로센서는 선형거리추측(Linear position estimation)과 각 변위 추측(orientation estimation)시 출력 데이터에 포함된 오차성분의 적분에 의하여 시간이 증가함에 따라 선형거리 오차와 각 변위 오차가 누적된다. 이에 따라 본 논문에서는 정밀한 항법을 위한 저가의 IMU (Inertial Measurement Unit)를 설계하고, 오차성분의 사전해석을 통하여 정확한 오차모델을 찾는데 그 목적이 있다.

• Journal of Korea Water Resources Association
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• v.43 no.2
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• pp.153-165
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• 2010

Large-Scale Particle Image Velocimetry (LSPIV) is an extension of particle image velocimetry (PIV) for measurement of flows spanning large areas in laboratory or field conditions. LSPIV is composed of six elements - seeding, illumination, recording, image transformation, image processing, postprocessing - based on PIV. Possible error elements at each step of Mobile LSPIV (MLSPIV), which is a mobile version of LSPIV, in field applications are identified and summarized the effect of the errors which were quantified in the previous studies. The total number of elemental errors is 27, and five error sources were evaluated previously, seven elemental errors are not effective to the current MLSPIV system. Among 15 elemental errors, four errors - sampling time, image resolution, tracer, and wind - are investigated through an experiment at a laboratory to figure out how those errors affect to velocity calculation. The analysis to figure out the effect of the number of images used for image processing on the velocity calculation error shows that if over 50 images or more are used, the error due to it goes below 1 %. The effect of the image resolution on velocity calculation was investigated through various image resolution using digital camera. Low resolution image set made 3 % of velocity calculation error comparing with high resolution image set as a reference. For the effect of tracers and wind, the wind effect on tracer is decreasing remarkably with increasing the flume bulk velocity. To minimize the velocity evaluation error due to wind, tracers with high specific gravity is favorable.

• The Journal of Korean Institute for Practical Engineering Education
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• v.3 no.1
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• pp.45-50
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• 2011

Despite the highly sophisticated development of finite element analysis, a finite element model for structural dynamic analysis can be inaccurate or even incorrect due to the difficulties of correct modelling, uncertainties on the finite element input data and geometrical oversimplification, while the modal data extracted from measurement are supposed to be correct, even though incomplete. The assumption that the test results represent the true dynamic behaviour of the structure, however, may not be correct because of various measurement errors. The measurement errors are investigated and their effects on estimated frequency response functions(FRFs) are also investigated.

• Computational Structural Engineering
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• v.11 no.1
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• pp.261-274
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• 1998

In this paper, local and global error estimates for the element-free Galerkin (EFG) method are proposed. The essence of proposed error estimates is to use the difference between the values of the projected stress and these given directly by the EFG solution. The stress projection can be obtained simply by taking product of shape function based on a different domain of influence with the stresses at nodes. In this study, it was found that the effectivity index is optimized if the domain of influence in stress projection procedure is the smallest that retains regularity of the matrices in EFG. Numerical tests are shown for various 1D and 2D examples illustrating the good effectiveness of the proposed error estimator in the global energy norm and in the local error estimates.

• Korean Journal of Optics and Photonics
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• v.17 no.4
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• pp.359-365
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• 2006

Wave-front error(WFE) is the main parameter that determines the optical performance of the opto-mechanical system. In the development of opto-mechanics, WFE due to the main loading conditions are set to the important specifications. The deformation of the optical surface can be exactly calculated thanks to the evolution of numerical methods such as the finite element method(FEM). To calculate WFE from the deformation results of FEM, another approximation of the optical surface deformation is required. It needs to construct additional grid or element mesh. To construct additional mesh is troublesomeand leads to transformation error. In this work, the moving least-squares approximation is used to reconstruct wave front error It has the advantage of accurate approximation with only nodal data. There is no need to construct additional mesh for approximation. The proposed method is applied to the examples of GOCI scan mirror in various loading conditions. The validity is demonstrated through examples.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.672-675
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• 2000

There are many sources of errors in the parallel device. This study investigates the effect of a clearance error at a U-joint on the position and orientation errors of the platform of a new parallel device, cubic parallel manipulator. In this study, the limits of errors can be estimated for given conditions.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.789-794
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• 2000

This study proposes an error analysis for a cubic parallel device. There are many sources of errors in the device. An error analysis is presented based on an error model formed from the relation between the universal joint error of the cubic parallel manipulator and the end effector accuracy. The analysis shows that the method can be used in evaluating the accuracy of a parallel device.

• Proceedings of the Korea Contents Association Conference
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• 2013.05a
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• pp.211-212
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• 2013

방사선 치료를 받는 모든 환자의 경우 먼저 모의 치료를 시행한 후에 동일한 자세로 방사선 치료를 실시한다. 이 때 무엇보다도 중요한 사항은 정확한 자세의 재현성이다. 직장암 환자의 방사선 치료를 시행하는 경우에도 모의 치료와 동일한 자세 유지가 요구되어진다. 하지만 호흡 및 환자의 여러 가지 요소에 의해 자세의 오차가 발생할 수 있다. 이에 본 논문은 직장암 환자의 방사선 치료를 시행하는 경우 오차가 발생할 수 있는 요소 중에 환자의 체지량 지수 차이에 의한 자세 재현성에 대해 알아보고 향후 자세 오차를 줄일 수 있는 방법을 모색하고자 한다.

• Journal of the Korean Chemical Society
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• v.39 no.12
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• pp.925-931
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• 1995

Urea sensors, prepared by immobilizing urease on ammonium-selective membrane electrodes doped with nonactin, can show interference from several ionic species present in blood samples (e.g., sodium, potassium, and endogenous ammonium ions). This interference problem does not arise from the immobilized biocatalytic reaction but rather from the innate response of the base transducer to ionic species in the sample. In this work, the use of calibrators containing adequate amounts of ionic species is examined to reduce errors caused by endogenous ionic interferences with blood urea measurements. Simultaneous measurements of the interfering species with additional sensors and subsequent substractions of these values from the urea electrode signals are also described. It is shown that the use of a potassium-selective electrode with an adequate calibrator system greatly enhances the accuracy of the urea sensor measurements.