• 로봇학회논문지
• /
• 제7권4호
• /
• pp.231-242
• /
• 2012

This paper proposes particle filter(PF) method using acoustic signal for localization of an underwater robot. The method uses time of arrival(TOA) or time difference of arrival(TDOA) of acoustic signals from beacons whose locations are known. An experiment in towing tank uses TOA information. Simulation uses TDOA information and it reveals dependency of the localization performance on the uncertainty of robot motion and senor data. Also, comparison of the PF method with the least squares method of spherical interpolation(SI) and spherical intersection(SX) is provided. Since PF uses TOA or TDOA which comes from measurement of external information as well as internal motion information, its estimation is more accurate and robust to the sensor and motion uncertainty than the least squares methods.

• 한국전자파학회:학술대회논문집
• /
• 한국전자파학회 2000년도 종합학술발표회 논문집 Vol.10 No.1
• /
• pp.29-33
• /
• 2000

Stripmap SAR 시스템에서 레이더는 Slant range-domain에서 고정된 Strip상에 Data acquisition period 동안 계속해서 같은 Broadside 방사 패턴을 유지하며, Range domain에서 고정돈 Strip내의 지형의 지도를 제공하는 SAR 영상 시스템이다. Stripmap SAR를 위한 고전적인 영상 복원을 Synthetic aperture (slow-time) domain에서 Deramping 또는 Chirp deconvolution을 이용하는 Fresnel approximaptio에 의존하였다. 또 다른 Stripmap SAR 영상화의 접근방법으로 SAR wavefront reconstruction이론과 레이더 방사형태에 대한 spherical wave Fourier decomposition을 통하여 slow-time domain에서의 SAR 신호의 분석에 기본을 두고 있다. 본 논문에서는 컴퓨터 모의 실험을 통해 생성된 Stripmap SAR 데이터를 이용하여 Fresnel approximation 기법과 Wavefront Reconstruction 기법을 비교 분석한다.

• 한국측량학회지
• /
• 제3권2호
• /
• pp.11-17
• /
• 1985

지오이드와 기준타원분 사이의 거리, 즉, 지오이드고의 결정은 측지학에서 매우 중요한 문제로 취급되어왔다. 본 논문에서는 곡면다항식(Spherical Surface - Polynomial)에 의한 보간으로 우리나라의 천문지오이드고(Astro - Geodetic Ceoid)를 결정하고자 하였으며, 그 결과로부터 우리나라의 측지강이 동경원점(Too Datum)의 영향을 받고 있음이 확인되었다.

• 지구물리와물리탐사
• /
• 제15권4호
• /
• pp.245-248
• /
• 2012

일정고도에서 얻어진 중력 혹은 자력탐사자료에 대하여 보다 높은 고도에서의 값으로 연속하여 구하는 방법, 즉 상향연속의 경우 2차원 푸리에변환을 사용할 수 있다. 기존의 상향연속 방법에서는 지구의 곡률이 고려되지 않았으나, 지역이 수백킬로미터 이상으로 넓은 경우 곡률이 고려됨이 바람직하다. 본 연구에서는 지구의 곡률효과를 산정하는 중/자력 마당의 새로운 상향연속방법을 계발하였다.

• 천문학회보
• /
• 제39권1호
• /
• pp.57.2-57.2
• /
• 2014

Protostellar jets and outflows are signatures of star formation and promising mechanisms for driving supersonic turbulence in molecular clouds. We quantify outflow-driven turbulence through three-dimensional numerical simulations using an isothermal version of the total variation diminishing code. We drive turbulence in real space using a simplified spherical outflow model, analyze the data through density probability distribution functions (PDFs), and investigate density and velocity power spectra. The real-space turbulence-driving method produces a negatively skewed density PDF possessing an enhanced tail on the low-density side. It deviates from the log-normal distributions typically obtained from Fourier-space turbulence driving at low densities, but can provide a good fit at high densities, particularly in terms of mass-weighted rather than volume-weighted density PDF. We find shallow density power-spectra of -1.2. It is attributed to spherical shocks of outflows themselves or shocks formed by the interaction of outflows. The total velocity power-spectrum is found to be -2.0, representative of the shock dominated Burger's turbulence model. Our density weighted velocity power spectrum is measured as -1.6, slightly less that the Kolmogorov scaling values found in previous works.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.132-137
• /
• 2004

In this work, effects of hyper-elastic rubber material properties on the indentation load-deflection curve and subindenter deformation are first examined via [mite element (FE) analyses. An optimal data acquisition spot is selected, which features maximum strain energy density and negligible frictional effect. We then contrive two normalized functions. which map an indentation load vs. deflection curve into a strain energy density vs. first invariant curve. From the strain energy density vs. first invariant curve, we can extract the rubber material properties. This new spherical indentation approach produces the rubber material properties in a manner more effective than the common uniaxial tensile/compression tests. The indentation approach successfully measures the rubber material properties and the corresponding nominal stress.strain curve with an average error less than 3%.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 2002년도 추계학술대회 논문집
• /
• pp.474-480
• /
• 2002

Aspheric optical lenses and mirrors are widely used in recent. It is more difficult to manufacture and measure the aspherical optics compared to conventional spherical ones. The interferometric optical test is common for the measurement of spherical optical surface. But the application of the interferometry to the measurement of aspheric surface is difficult because it needs a precise null corrector and very careful environmental conditions such as keeping constant temperature, humidity, atmospheric pressure and vibrations. To enhance productivity of optics manufacturing on-machine measurement and correction has been developed in this study. For practical applications, robustness of the measurement method to environments is more important. For the purpose an optical OMM(On-Machine Measurement) system has been developed using Shack-Hartmann test which has robustness to the environment. The wavefront has been reconstructed from the measured data using the primary aberration polynomial function by least square fitting. The measured result of the developed only system gives the maximum deviation only in 200 nm from the result measured by a commercial Fizeau interferometer Wyko 6000.

• 한국분말재료학회지
• /
• 제8권1호
• /
• pp.61-69
• /
• 2001

Spark-Plasma Sintering(SPS) is one of the new sintering methods which takes advantages both inconventional pressure sintering and electric current sintering. It is known that SPS is very effective for the densification of hard-to-sinter materials like refractory metals, intermetallic compounds, glass and ceramics without grain growth. However, a clear explanation for sintering mechanism and an experimental evidence for the formation of weak plasma during SPS are not given yet. In this study, fundamental study on sintering behavior and mechanism of SPS was investiged. For this study, various spherical Fe powders were prepared such as as-received, as-reduced, and as-oxidized and then sintered by SPS facility. In order to confirm the surface cleaning effect during SPS neck region and fracture surface of sintered body was observed and analyzed by SEM/EPMA. Densification behavior was analyzed from the data of deflection along the pressure axis. Some specimens were additionally produced by Hot Pressing and the results were compared with those of SPS.

• International Journal of Quality Innovation
• /
• 제6권1호
• /
• pp.109-118
• /
• 2005

The parameter design is the most emphasized measure by researchers for a new products development. It is critical for makers to achieve simultaneously in both the time-to-market production and the quality enhancement. However, there are difficulties in practical application, such as (1) complexity and nonlinear relationships co-existed among the system's inputs, outputs and control parameters, (2) interactions occurred among parameters, (3) where the adjustment factors of Taguchi's two-phase optimization procedure cannot be sure to exist in practice, and (4) for some reasons, the data became lost or were never available. For these incomplete data, the Taguchi methods cannot treat them well. Neural networks have a learning capability of fault tolerance and model free characteristics. These characteristics support the neural networks as a competitive tool in processing multivariable input-output implementation. The successful fields include diagnostics, robotics, scheduling, decision-making, prediction, etc. This research is a case study of spherical annealing model. In the beginning, an original model is used to pre-fix a model of parameter design. Then neural networks are introduced to achieve another model. Study results showed both of them could perform the highest spherical level of quality.

• Journal of Information Processing Systems
• /
• 제10권1호
• /
• pp.23-35
• /
• 2014

Recently, novel application areas in digital geometry processing, such as simulation, dynamics, and medical surgery simulations, have necessitated the representation of not only the surface data but also the interior volume data of a given 3D object. In this paper, we present an efficient framework for the shape approximations of spherical solid objects based on trivariate B-splines. To do this, we first constructed a smooth correspondence between a given object and a unit solid cube by computing their harmonic mapping. We set the unit solid cube as a rectilinear parametric domain for trivariate B-splines and utilized the mapping to approximate the given object with B-splines in a coarse-to-fine manner. Specifically, our framework provides user-controllability of shape approximations, based on the control of the boundary condition of the harmonic parameterization and the level of B-spline fitting. Experimental results showed that our method is efficient enough to compute trivariate B-splines for several models, each of whose topology is identical to a solid sphere.