Dynamic Tilt Correction Using Direct Rotational Motion Measurements

2020 ◽  
Vol 91 (5) ◽  
pp. 2872-2880 ◽  
Author(s):  
Felix Bernauer ◽  
Joachim Wassermann ◽  
Heiner Igel
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Ground Deformation ◽  
Time Domain Method ◽  
Caldera Collapse ◽  
Frequency Domain Method ◽  
Test Cases ◽  
Ground Acceleration ◽  
Data Set ◽  
Domain Method

Abstract Inertial sensors like seismometers or accelerometers are sensitive to tilt motions. In general, from pure acceleration measurements, it is not possible to separate the tilt acceleration from the translational ground acceleration. This can lead to severe misinterpretation of seismograms. Here, we present three different methods that can help solving this problem by correcting translational records for dynamic tilt induced by ground deformation with direct measurements of rotational motions: (1) a simple time-domain method, (2) a frequency-domain method proposed by Crawford and Webb (2000) using a coherence-weighted transfer function between rotation and acceleration, and (3) an adapted frequency-domain method that corrects only those parts of the spectrum with coherence between translational acceleration and rotation angle higher than 0.5. These three methods are discussed in three different experimental settings: (1) a reproducible and precisely known laboratory test using a high-precision tilt table, (2) a synthetic test with a simulated volcanic very-long-period event, and (3) a real data set recorded during the 2018 Mt. Kīlauea caldera collapse. All the three test cases show severe influence of tilt motion on the acceleration measurements. The time-domain method and the adapted frequency-domain method show very similar performance in all three test cases. Those two methods are able to remove the tilt component reliably from the acceleration record.

A New Time Domain Analysis of the Wave Power

2012 ◽  
Vol 253-255 ◽  
pp. 720-723
Author(s):  
Mao Xing Wei ◽  
Zhi Gang Bai
Keyword(s):  
Frequency Domain ◽  
Incident Wave ◽  
Time Domain ◽  
Time Domain Method ◽  
Frequency Domain Method ◽  
Wave Power ◽  
Alternative Measure ◽  
Data Set ◽  
Domain Method ◽  
The Time Domain

The present frequency domain method of calculating wave power may not be accurate enough for calculating the incident wave power of a specific site, which is primary measurement for evaluating the efficiency of wave energy converters (WECs) and an alternative measure, the time domain method, is proposed. Three sites including two nearshore sites and one deepwater site at Chengshantou sea area were selected, and a sample wave parameters data set was obtained from wave model SWASH to demonstrate the application of these two methods. A comparison of the results of each method was also performed and two influential parameters used in calculation were analyzed. The results show that frequency domain method is very likely to overestimate the wave power at both deepwater and nearshore site. The time domain method proposed in this paper is believed to be more superior in calculating the incident wave power during a short term.

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.

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.

Estimating interannual variability arising from weather events

2001 ◽  
Vol 38 (A) ◽  
pp. 274-288 ◽  
Author(s):  
Xiaogu Zheng ◽  
James Renwick
Keyword(s):  
Frequency Domain ◽  
Interannual Variability ◽  
Time Domain ◽  
Synthetic Data ◽  
Estimation Procedure ◽  
Frequency Domain Method ◽  
Domain Method ◽  
Weather Events ◽  
Long Time ◽  
The Time Domain

The advantages and limitations of frequency domain and time domain methods for estimating the interannual variability arising from day-to-day weather events are summarized. A modification of the time domain method is developed and its application in examining a precondition for the frequency domain method is demonstrated. A combined estimation procedure is proposed: it takes advantage of the strengths of both methods. The estimation procedures are tested with sets of synthetic data and are applied to long time series of three meteorological parameters. The impacts of the different methods on tests of potential long-range predictability for seasonal means are also discussed.

scholarly journals The Comparison of the Effect of Haimming Window and Blackman Window in the Time-Scaling and Pitch-Shifting Algorithms

2011 ◽  
Vol 1 ◽  
pp. 221-225
Author(s):  
Zhi Wei Lin ◽  
Li Da ◽  
Hao Wang ◽  
Wei Han ◽  
Fan Lin
Keyword(s):  
Fourier Transform ◽  
Frequency Domain ◽  
Time Domain ◽  
Frequency Domain Method ◽  
Domain Type ◽  
Domain Method ◽  
Time Scaling ◽  
Window Functions ◽  
Inherent Frequency ◽  
The Time Domain

The real-time pitch shifting process is widely used in various types of music production. The pitch shifting technology can be divided into two major types, the time domain type and the frequency domain type. Compared with the time domain method, the frequency domain method has the advantage of large shifting scale, low total cost of computing and the more flexibility of the algorithm. However, the use of Fourier Transform in frequency domain processing leads to the inevitable inherent frequency leakage effects which decrease the accuracy of the pitch shifting effect. In order to restrain the side effect of Fourier Transform, window functions are used to fall down the spectrum-aliasing. In practical processing, Haimming Window and Blackman Window are frequently used. In this paper, we compare both the effect of the two window functions in the restraint of frequency leakage and the performance and accuracy in subjective based on the traditional phase vocoder[1]. Experiment shows that Haimming Window is generally better than Blackman Window in pitch shifting process.

Non-Linear Time and Frequency Domain Methods for Multi-Row Aeromechanical Analysis

2012 ◽  
Author(s):  
M. T. Rahmati ◽  
L. He ◽  
D. X. Wang ◽  
Y. S. Li ◽  
R. G. Wells ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Computational Models ◽  
Linear Time ◽  
Navier Stokes ◽  
Frequency Domain Method ◽  
Domain Method ◽  
Frequency Domain Methods ◽  
Blade Row ◽  
Nonlinear Time Domain

An unsteady Navier-Stokes solution system for aeromechanical analysis of multiple blade row configurations is presented. A distinctive feature of the solver is that unified numerical methods and boundary condition treatments are consistently used for both a nonlinear time-domain solution mode and a frequency-domain one. This not only enables a wider range of physical aeromechanical problems to be tackled, but also provides a consistent basis for validating different computational models, identifying and understanding their relative merits and adequate working ranges. An emphasis of the present work is on a highly efficient frequency-domain method for multi-row aeromechanic analysis. With a new interface treatment, propagations and reflections of pressure waves between adjacent blade rows are modeled within a domain consisting of only a single passage in each blade row. The computational model and methods are firstly described. Then, extensive validations of the frequency-domain method against both experimental data and the nonlinear time-domain solutions are described. Finally the computational analysis and demonstration of the intra-row reflection effects on the rotor aerodynamic damping are presented.

3D marine magnetotelluric modeling and inversion with the finite-difference time-domain method

Geophysics ◽  
2014 ◽  
Vol 79 (6) ◽  
pp. E269-E286 ◽  
Author(s):  
Sébastien de la Kethulle de Ryhove ◽  
Rune Mittet
Keyword(s):  
Finite Difference ◽  
Frequency Domain ◽  
Time Domain ◽  
Finite Difference Time Domain ◽  
Linear Equations ◽  
Time Domain Method ◽  
Domain Method ◽  
Frequency Domain Methods ◽  
Starting Point ◽  
Difference Time

Frequency-domain methods, which are typically applied to 3D magnetotelluric (MT) modeling, require solving a system of linear equations for every frequency of interest. This is memory and computationally intensive. We developed a finite-difference time-domain algorithm to perform 3D MT modeling in a marine environment in which Maxwell’s equations are solved in a so-called fictitious-wave domain. Boundary conditions are efficiently treated via convolutional perfectly matched layers, for which we evaluated optimized parameter values obtained by testing over a large number of models. In comparison to the typically applied frequency-domain methods, two advantages of the finite-difference time-domain method are (1) that it is an explicit, low-memory method that entirely avoids the solution of systems of linear equations and (2) that it allows the computation of the electromagnetic field unknowns at all frequencies of interest in a single simulation. We derive a design criterion for vertical node spacing in a nonuniform grid using dispersion analysis as a starting point. Modeling results obtained using our finite-difference time-domain algorithm are compared with results obtained using an integral equation method. The agreement was found to be very good. We also discuss a real data inversion example in which MT modeling was done with our algorithm.

Improved Hybrid Frequency-Time Domain Method for Nonlinear Analysis of Frictionally Damped Blade Systems

2016 ◽  
Author(s):  
Yalin Liu ◽  
Shangguan Bo ◽  
Zili Xu
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Computation Time ◽  
Time Domain Method ◽  
Friction Contact ◽  
Improved Method ◽  
Computation Efficiency ◽  
Hybrid Frequency ◽  
Domain Method ◽  
Domain Transformation

An improved hybrid frequency-time domain method is proposed to efficiently study the nonlinear response of blade systems subject to dry friction damping. In this method, the friction force is calculated in time domain by tracing the motion trajectory of friction contact pairs. The Newton iterative algorithm is used to solve the algebraic equations of blade system in frequency domain. The parabolic-interpolation fast Fourier transform is used in time-frequency domain transformation. It can improve computation accuracy and enlarge spectral analysis range of the original alternating frequency/time domain (AFT) method. The multi-modal analysis technique is employed to reduce linear degree of freedoms (DOFs), and only the nonlinear DOFs are brought in iterative procedure. It can significantly reduce computation time. The improved method combined with three dimensional friction contact model is used to predict the vibration response of a shrouded blade with nonlinear friction contact. The effect of parameters on resonant frequency and response is investigated and discussed. The computation time of the improved method is only 42.25 percent of the original AFT method, while the relative difference between the results of the two methods is no more than 0.01%. The improved method is shown to be superior to the original AFT method in computation efficiency and accuracy, and it can be used in analyzing dynamic characteristics of complex frictionally damped blade systems.

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