Hybrid/sup (3)/: combining the time-domain method of moments, the time-domain geometrical theory of diffraction and the FDTD

2005 ◽  
Author(s):  
A. Becker ◽  
V. Hansen
Keyword(s):  
Method Of Moments ◽  
Time Domain ◽  
Time Domain Method ◽  
Geometrical Theory ◽  
Domain Method ◽  
Geometrical Theory Of Diffraction ◽  
The Time Domain

scholarly journals A hybrid method combining the Time-Domain Method of Moments, the Time-Domain Uniform Theory of Diffraction and the FDTD

2007 ◽  
Vol 5 ◽  
pp. 107-113
Author(s):  
A. Becker ◽  
V. Hansen
Keyword(s):  
Method Of Moments ◽  
Hybrid Method ◽  
Time Domain ◽  
Time Domain Method ◽  
Thin Wire ◽  
Uniform Theory Of Diffraction ◽  
Domain Method ◽  
Inhomogeneous Bodies ◽  
Wire Antennas ◽  
The Time Domain

Abstract. In this paper a hybrid method combining the Time-Domain Method of Moments (TD-MoM), the Time-Domain Uniform Theory of Diffraction (TD-UTD) and the Finite-Difference Time-Domain Method (FDTD) is presented. When applying this new hybrid method, thin-wire antennas are modeled with the TD-MoM, inhomogeneous bodies are modelled with the FDTD and large perfectly conducting plates are modelled with the TD-UTD. All inhomogeneous bodies are enclosed in a so-called FDTD-volume and the thin-wire antennas can be embedded into this volume or can lie outside. The latter avoids the simulation of white space between antennas and inhomogeneous bodies. If the antennas are positioned into the FDTD-volume, their discretization does not need to agree with the grid of the FDTD. By using the TD-UTD large perfectly conducting plates can be considered efficiently in the solution-procedure. Thus this hybrid method allows time-domain simulations of problems including very different classes of objects, applying the respective most appropriate numerical techniques to every object.

Effects of blood volume changes on characteristic impedance of the pulmonary artery

1982 ◽  
Vol 242 (2) ◽  
pp. H197-H202 ◽  
Author(s):  
J. P. Dujardin ◽  
D. N. Stone ◽  
C. D. Forcino ◽  
L. T. Paul ◽  
H. P. Pieper
Keyword(s):  
Pulmonary Artery ◽  
Blood Volume ◽  
Time Domain ◽  
Volume Expansion ◽  
Characteristic Impedance ◽  
Main Pulmonary Artery ◽  
Time Domain Method ◽  
Frequency Domain Method ◽  
Domain Method ◽  
The Time Domain

Experiments were performed on eight anesthetized dogs to study the response of the characteristic impedance (Zc) of the main pulmonary artery to changes in circulating blood volume. Pressure and flow were measured in the proximal main pulmonary artery under control conditions, after hemorrhage (-15% of the estimated blood volume), again under control conditions, and finally after volume expansion (+30% of the estimated blood volume). Two different methods were used to determine Zc from these recordings. With the frequency-domain method values for Zc were obtained by averaging the input impedance moduli between 2 and 15 Hz. With the time-domain method Zc was derived as the slope of the early ejection pressure-flow relationship. The values for Zc obtained with the two methods were not statistically different. In the time-domain method the average increase in Zc with hemorrhage was 30.7 +/- 7.4 (SE) %, and the average decrease with volume expansion was -21.1 +/- 5.0 (SE) %. Because the time-domain method allowed the values of Zc during control conditions and after hemorrhage to be obtained in the same pressure range, it was concluded that the observed changes were caused by a change in the activity of the smooth muscle in the pulmonary arterial wall. Similarly, it was concluded that the decrease in Zc after volume expansion was active in nature.

Servo System Identification Using Relay Feedback: A Time-Domain Approach

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Jia Liu ◽  
Jianhua Wu ◽  
Zhenhua Xiong ◽  
Xiangyang Zhu
Keyword(s):  
System Identification ◽  
Dynamic Characteristics ◽  
Time Domain ◽  
Oscillation Amplitude ◽  
Servo System ◽  
Time Domain Method ◽  
Relay Feedback ◽  
Servo Systems ◽  
Domain Method ◽  
The Time Domain

In servo systems, the dynamic characteristics may not only differ between axes but may also vary with moving directions for a single axis. The direction dependent characteristics would result in additional tracking or positioning error and degrade the performance of the system. In this paper, relay feedback tests are successfully applied to identify the dynamic characteristics in servo systems. A time-domain method is used to analyze the relay feedback other than the conventional describing function (DF) method. The time-domain method utilizes the same oscillation parameters (oscillation amplitude and half period) as the DF method for system identification. However, the time-domain method takes several advantages: First, the direction dependent characteristics of the system can be properly revealed; second, no approximation is made in this method, so that the exact expressions of the amplitudes and the periods of the limit cycles under relay feedback can be derived. A feedforward compensator is then designed using the estimated values of the system parameters. Simulation results show that the identification results through the time-domain method are more accurate than the DF method and are more robust under different relay parameters. Real time experiments show that the feedforward compensator designed by the proposed method compensates disturbances related to the direction and hence improves the tracking and positioning performance of the servo system.

Research on the Identification Methods of Friction in Kinematical Joints of Mechanical Systems

2005 ◽  
Author(s):  
Ziying Wu ◽  
Hongzhao Liu ◽  
Lilan Liu ◽  
Pengfei Li ◽  
Daning Yuan
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Time Domain Method ◽  
Estimation Accuracy ◽  
Frequency Domain Method ◽  
Linkage Mechanism ◽  
Identification Methods ◽  
Low Snr ◽  
Domain Method ◽  
The Time Domain

This paper describes two approaches for the simultaneous identification of the coulomb and viscous parameters in kinematical joints. One is a time-domain method (TDM) and the other is a frequency-domain method (FDM). Simulation shows that both of the two methods have good performances in identifying friction at high SNR (90dB). But at low SNR (20dB), the estimation accuracy of the frequency-domain method is higher than that of the time-domain method. A field experiment employing a linkage mechanism driven by motor is also carried out. The experimental results obtained by the two approaches are almost identical under different experiment conditions. It has been concluded that the presented identification methods of friction in kinematical joints are correct and applicable.

Separating Cloud and Drizzle Signals in Radar Doppler Spectra Using a Parametric Time Domain Method

2020 ◽  
Vol 37 (9) ◽  
pp. 1669-1680
Author(s):  
Shashank S. Joshil ◽  
Cuong M. Nguyen ◽  
V. Chandrasekar ◽  
J. Christine Chiu ◽  
Yann Blanchard
Keyword(s):  
Remote Sensing ◽  
Time Domain ◽  
Marine Boundary Layer ◽  
Time Domain Method ◽  
Radar Signal ◽  
Liquid Water Path ◽  
Microphysical Properties ◽  
Observation Volume ◽  
Domain Method ◽  
The Time Domain

AbstractThe ability to separate cloud and drizzle returns in active remote sensing observations is important for understanding the microphysics of clouds and precipitation. Yet, robust separations remain challenging in radar remote sensing. Prior methods for cloud and drizzle separation for radar observations use the properties of the Doppler spectra such as skewness. However, these methods have challenges when the drizzle becomes dominant in the observation volume. This paper presents a parametric time domain method (PTDM) that separates cloud and drizzle using the Doppler spectra measurements without assuming any prior properties of cloud and drizzle. The advantage of PTDM is that it can estimate the signal properties in the time domain and can obtain the cloud and drizzle estimates simultaneously. Based on our radar signal simulations, the uncertainty in estimated power and velocity from PTDM are within 2 dB and 0.02 m s−1, respectively. We have also evaluated the PTDM algorithm using observations from the Atmospheric Radiation Measurement (ARM) Program W-band cloud radar in the Clouds, Aerosols, and Precipitation in the Marine Boundary Layer (CAP-MBL) campaign at the Azores in 2009–10. Two cases corresponding to light and moderate drizzling conditions are considered for the study. The statistics of the estimates obtained show that the PTDM method performs well in separating the cloud and drizzle returns. Finally, the estimated cloud and drizzle reflectivity from PTDM were used to retrieve their corresponding microphysical properties, showing that the retrieved liquid water path agrees to 25 g m−2 with the benchmark microwave method.

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