• Title/Summary/Keyword: Resolution Schemes

Search Result 162, Processing Time 0.022 seconds

AN IMPROVED ALTERNATIVE WENO SCHEMES WITH PERTURBATIONAL TERMS FOR THE HYPERBOLIC CONSERVATION LAWS

  • KUNMIN SUNG;YOUNGSOO HA;MYUNGJOO KANG
    • Journal of the Korean Society for Industrial and Applied Mathematics
    • /
    • v.27 no.4
    • /
    • pp.207-231
    • /
    • 2023
  • This paper aims to improve the alternative formulation of the fifth- and sixth-order accurate weighted essentially non-oscillatory (AWENO) finite difference schemes. The first is to derive the AWENO scheme with sixth-order accuracy in the smooth region of the solution. Second, a new weighted polynomial functions combining the perturbed forms with conserved variable to the AWENO is constructed; the new form of tunable functions are invented to maintain non-oscillatory property. Detailed numerical experiments are presented to illustrate the behavior of the new perturbational AWENO schemes. The performance of the present scheme is evaluated in terms of accuracy and resolution of discontinuities using a variety of one and two-dimensional test cases. We show that the resulted perturbational AWENO schemes can achieve fifth- and sixth-order accuracy in smooth regions while reducing numerical dissipation significantly near singularities.

Numerical Dispersive Characteristics and Stability Condition of the Multi-Resolution Time Domain(MRTD) Method (다해상도 시간영역법의 수치적 분산특성과 안정조건)

  • 홍익표;유태훈;윤영중;박한규
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
    • /
    • v.7 no.4
    • /
    • pp.328-335
    • /
    • 1996
  • The numerical dispersive characteristics and the numerical stability confition of the Multi-Resolution Time-Domain(MRTD) method are calculated. A dispersion analysis of the MRTD schemes including a comparison to Yee's Finite-Difference Time-Domain(FDTD) method is given. The superiority of the MRTD method to the spatial discretization is shown. The required computational memory can be reduced by using the MRTD method. We expect that the MRTD method will be very useful method for numerical modelling of electromagnetics.

  • PDF

On the Ultra-Wideband Ambiguity Function (초광대역 Ambiguity Function에 관한 연구)

  • 이준용
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.29 no.3C
    • /
    • pp.368-373
    • /
    • 2004
  • Extremely fine tine resolution of ultra-wideband (UWB) signal poses a new problems to the system designer. A reasonable accuracy of the system clock is necessary to process signals with such a high space resolution. A useful way of illustrating the time resolution of a signal is to evaluate the ambiguity function. The ambiguity function for carrierless UWB defined using the time mismatch and time scaling factor as its two parameters. The UWB ambiguity function is evaluated for various signaling schemes of impulse radio.

Energy-efficient mmWave cell-free massive MIMO downlink transmission with low-resolution DACs and phase shifters

  • Seung-Eun Hong;Jee-Hyeon Na
    • ETRI Journal
    • /
    • v.44 no.6
    • /
    • pp.885-902
    • /
    • 2022
  • The mmWave cell-free massive MIMO (CFmMIMO), combining the advantages of wide bandwidth in the mmWave frequency band and the high- and uniform-spectral efficiency of CFmMIMO, has recently emerged as one of the enabling technologies for 6G. In this paper, we propose a novel framework for energy-efficient mmWave CFmMIMO systems that uses low-resolution digital-analog converters (DACs) and phase shifters (PSs) to introduce lowcomplexity hybrid precoding. Additionally, we propose a heuristic pilot allocation scheme that makes the best effort to slash some interference from copilot users. The simulation results show that the proposed hybrid precoding and pilot allocation scheme outperforms the existing schemes. Furthermore, we reveal the relationship between the energy and spectral efficiencies for the proposed mmWave CFmMIMO system by modeling the whole network power consumption and observe that the introduction of low-resolution DACs and PSs is effective in increasing the energy efficiency by compromising the spectral efficiency and the network power consumption.

An Experimental Study of the Synthetic Sinc Wave in Ultrasonic Imaging (초음파 의료 영상에서 합성 Sinc 음장 집속방법의 실험적 고찰)

  • 이광주;정목근
    • Journal of Biomedical Engineering Research
    • /
    • v.23 no.3
    • /
    • pp.243-251
    • /
    • 2002
  • Synthetic zinc wave employs Pulsed plane wave as transmit beam with linear time delay curve. The received echoes in different transmit directions at different transmit times are superposed at imaging Points with Proper time delay compensation using synthetic focusing scheme. This scheme. which uses full aperture in transmit, obtains a high SNR image, and also features high lateral resolution by using two way dynamic focusing at all imaging depths. In this Paper, we consider the Problems in realization of synthetic zinc wave. Also. we have applied the scheme to obtain phantom and in-vivo images using a linear array of 5 MHz. In phantom test. experimental images show high resolution over a more extended imaging depth than conventional fixed Point transmit and receive dynamic focusing schemes In-vivo images show that the resolution could not overcome conventional focusing systems because of motion blurring and(or) aberration of tissue. but the frame rate tan be increased by a factor of more than 5 compared to conventional focusing schemes. with competitive resolution at all imaging depths .

Study on the Improvement of the Convective Differencing Scheme for the High-Accuracy and Stable Resolution of the Numerical Solution (수치해의 정확성과 안정성이 보장되는 대류항 미분법 개선에 관한 연구)

  • 신종근;최영돈
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.16 no.6
    • /
    • pp.1179-1194
    • /
    • 1992
  • QUICKER scheme has several attractive properties. However, under highly convective conditions, it produces overshoots and possibly some oscillations on each side of steps in the dependent variable when the flow is convected at an angle oblique to the grid line. Fortunately, it is possible to modify the QUICKER scheme using non-linear and linear functional relationship. Details of the development of polynomial upwinding scheme are given in this paper, where it is seen that this non-linear scheme has also third order accuracy. This polynomial upwinding scheme is used as the basis for the SHARPER and SMARTER schemes. Another revised scheme was developed by partial modification of QUICKER scheme using CDS and UPWIND schemes(QUICKUP). These revised schemes are tested at the well known bench mark flows, Two-Dimensional Pure Convection Flows in Oblique-Step, Lid Driven Cavity Flows and Buoyancy Driven Cavity Flows. For pure convection oblique step flow test problem, QUICKUP, SMARTER and SHARPER schemes remain absolutely monotonic without overshoot and oscillation. QUICKUP scheme is more accurate than any other scheme in their relative accuracy. In high Reynolds number Lid Driven Cavity Flow, SMARTER and SHARPER schemes retain lower computational cost than QUICKER and QUICKUP schemes, but computed velocity values in the revised schemes produced less predicted values than QUICKER scheme which is strongly effected by overshoot and undershoot values. Also, in Buoyancy Driven Cavity Flow, SMARTER, SHARPER and QUICKUP schemes give acceptable results.

Study on planetary boundary layer schemes suitable for simulation of sea surface wind in the southeastern coastal area, Korea (한반도 남동해안 해상풍 모의에 적합한 경계층 물리방안 연구)

  • Kim Yoo-Keun;Jeong Ju-Hee;Bae Joo-Hyun;Song Sang-Keun;Seo Jang-Won
    • Journal of Environmental Science International
    • /
    • v.14 no.11
    • /
    • pp.1015-1026
    • /
    • 2005
  • The southeastern coastal area of the Korean peninsula has a complex terrain including an irregular coastline and moderately high mountains. This implies that mesoscale circulations such as mountain-valley breeze and land-sea breeze can play an important role in wind field and ocean forcing. In this study, to improve the accuracy of complex coastal rind field(surface wind and sea surface wind), we carried out the sensitivity experiments based on PBL schemes in PSU/NCAR Mesoscale Model (MM5), which is being used in the operational system at Korea Meteorological Administration. Four widely used PBL parameterization schemes in sensitivity experiments were chosen: Medium-Range Forecast (MRF), High-resolution Blackadar, Eta, and Gayno-Seaman scheme. Thereafter, case(2004. 8. 26 - 8. 27) of weak-gradient flows was simulated, and the time series and the vertical profiles of the simulated wind speed and wind direction were compared with those of hourly surface observations (AWS, BUOY) and QuikSCAT data. In the simulated results, the strength of rind speed of all schemes was overestimated in complex coastal regions, while that of about four different schemes was underestimated in islands and over the sea. Sea surface wind using the Eta scheme showed the highest wind speed over the sea and its distribution was similar to the observational data. Horizontal distribution of the simulated wind direction was very similar to that of real observational data in case of all schemes. Simulated and observed vertical distribution of wind field was also similar under boundary layer(about 1 km), however the simulated wind speed was underestimated in upper layer.

An Enhanced Broadcasting Algorithm in Wireless Ad hoc Networks (무선 ad hoc 네트워크를 위한 향상된 방송 알고리즘)

  • Kim, Kwan-Woong;Bae, Sung-Hwan;Kim, Dae-Ik
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.33 no.10A
    • /
    • pp.956-963
    • /
    • 2008
  • In a multi-hop wireless ad hoc network broadcasting is an elementary operation to support route discovery, address resolution and other application tasks. Broadcasting by flooding may cause serious redundancy, contention, and collision in the network which is referred to as the broadcast storm problem. Many broadcasting schemes have been proposed to give better performance than simple flooding in wireless ad hoc network. How to decide whether re-broadcast or not also poses a dilemma between reachability and efficiency under different host densities. In this paper, we propose enhanced broadcasting schemes, which can reduce re-broadcast packets without loss of reachability. Simulation results show that proposed schemes can offer better reachability as well as efficiency as compared to other previous schemes.

Sensitivity Evaluation of Wind Fields in Surface Layer by WRF-PBL and LSM Parameterizations (WRF 모델을 이용한 지표층 바람장의 대기경계층 모수화와 지면모델 민감도 평가)

  • Seo, Beom-Keun;Byon, Jae-Young;Choi, Young-Jean
    • Atmosphere
    • /
    • v.20 no.3
    • /
    • pp.319-332
    • /
    • 2010
  • Sensitivity experiments of WRF model using different planetary boundary layer (PBL) and land surface model (LSM) parameterizations are evaluated for prediction of wind fields within the surface layer. The experiments were performed with three PBL schemes (YSU, Pleim, MYJ) in combination with three land surface models (Noah, RUC, Pleim). The WRF model was conducted on a nested grid from 27-km to 1-km horizontal resolution. The simulations validated wind speed and direction at 10 m and 80 m above ground level at a 1-km spatial resolution over the South Korea. Statistical verification results indicate that Pleim and YSU PBL schemes are in good agreement with observations at 10 m above ground level, while the MYJ scheme produced predictions similar to the observed wind speed at 80 m above ground level. LSM comparisons indicate that the RUC model performs best in predicting 10-m and 80-m wind speed. It is found that MYJ (PBL) - RUC (LSM) simulations yielded the best results for wind field in the surface layer. The choice of PBL and LSM parameterization will contribute to more accurate wind predictions for air quality studies and wind power using WRF.

INFLUNCE OF THE TOPOGRAPHIC INTERPOLATION METHODS ON HIGH-RESOLUTION WIND FIELD SIMULATION WITH SRTM ELEVATION DATA OVER THE COASTAL AREA

  • Kim, Yoo-Keun;Lo, So-Young;Jeong, Ju-Hee
    • Proceedings of the KSRS Conference
    • /
    • 2008.10a
    • /
    • pp.297-300
    • /
    • 2008
  • High-resolution mesoscale meteorological modeling requires more accurate and higher resolution digital elevation model (DEM) data. Shuttle Radar Topographic Mission (SRTM) has created 90 m DEM for entire globe and that is freely available for meteorological modeling and environmental applications. In this research, the effects of the topographic interpolation methods on high-resolution wind field simulation in the coastal regions were quantitatively analyzed using Weather Research and Forecasting (WRF) model with SRTM data. Sensitivity experiments with three different interpolation schemes (four-point bilinear, sixteen-point overlapping parabolic and nearest neighbor interpolation methods) were preformed using SRTM. In WRF modeling with sixteen-point overlapping parabolic interpolation, the coastal line and some small islands show more clearly than other cases. The maximum height of inland is around 140 meters higher, while the minimum of sea height is about 80 meter lower. As it concerns the results of each scheme it seems that the sixteen-point overlapping parabolic scheme indicates the well agreement with observed surface wind data. Consequently, topographic changes due to interpolation methods can lead to the significant influence on mesoscale wind field simulation of WRF modeling.

  • PDF