Identification of the Dynamic Characteristics of Long Annular Seals Using a Time Domain Technique

1998 ◽  
Vol 120 (3) ◽  
pp. 705-712 ◽  
Author(s):  
M. Ismail ◽  
R. D. Brown
Keyword(s):  
Dynamic Characteristics ◽  
Time Domain ◽  
Theoretical Models ◽  
Rotational Frequency ◽  
Singular Value Decomposition Method ◽  
Damping Coefficients ◽  
Theoretical Predictions ◽  
The Time Domain ◽  
Value Decomposition ◽  
Annular Seals

This paper describes experimental results from a research program aimed at a study of the static and dynamic characteristics of liquid long annular seals. A seal test rig permits the identification in the time domain of mass, stiffness, and damping coefficients using a least-squares technique based on the singular value decomposition method. The experimental method relies on the forced excitation of a flexibly supported stator by two hydraulic shakers. The forcing signal is composed from a small number of frequencies which are not related to the rotational frequency of the rigid shaft rotating inside the stator. The test data consisting of two inertia, four stiffness, and four damping coefficients is compared with theoretical predictions based on two theoretical models: (i) the model of Black et al. (1971 and 1981) and (ii) the model of Childs and Kim (1985).

The Effect of Inlet Grooves and Swirl on the Dynamics of Long Annular Seals in Centrifugal Pumps

1993 ◽  
Author(s):  
Mohamed Ismail ◽  
R. David Brown ◽  
David France
Keyword(s):  
Rolling Element Bearings ◽  
Rigid Rotor ◽  
Centrifugal Pumps ◽  
Test Rig ◽  
Singular Value Decomposition Method ◽  
Forcing Function ◽  
Rolling Element ◽  
The Time Domain ◽  
Value Decomposition ◽  
Annular Seals

Abstract This paper describes additional results from a continuing research program which aims to identify the dynamics of long annular seals in centrifugal pumps. A seal test rig designed to experimentally identify dynamic coefficients using a least-squares technique based on the singular value decomposition method. The analysis is carried out in the time domain using a multifrequency forcing function. The experimental method relies on the forced excitation of a flexibly supported stator by two hydraulic shakers. A rigid rotor supported in rolling element bearings runs through the stator. The only physical connection between shaft and stator is a pair of annular gaps filled with pressurised water discharged axially. The experimental coefficients obtained from the tests are compared with theoretical values.

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.

scholarly journals A Through-the-Wall Imaging Approach Based on a TSVD/Variable-Exponent Lebesgue-Space Method

2021 ◽  
Vol 13 (11) ◽  
pp. 2028
Author(s):  
Andrea Randazzo ◽  
Cristina Ponti ◽  
Alessandro Fedeli ◽  
Claudio Estatico ◽  
Paolo D’Atanasio ◽  
...  
Keyword(s):  
Variable Exponent ◽  
Scattering Problem ◽  
Inverse Scattering Problem ◽  
Source Spectrum ◽  
Computationally Efficient ◽  
Geometrical Properties ◽  
Singular Value Decomposition Method ◽  
The Time Domain ◽  
Value Decomposition ◽  
Wall Imaging

A hybrid inversion scheme for through-the-wall imaging is proposed in this paper. The approach is based on a linearized model of the inverse-scattering problem, employing the Green’s function developed for a layered background. The reconstruction is obtained by means of a Landweber-like iterative method performing a regularization in the framework of variable-exponent Lebesgue spaces. Thanks to the non-conventional geometrical properties of such spaces, it is possible to enhance the reconstruction capabilities, e.g., by promoting sparseness and reducing over-smoothing. The exponent function defining the specific space adopted in the inversion procedure is adaptively obtained directly from the measured data, through a truncated-singular value decomposition method. In this way, it is possible to precompute and reuse in both steps, for a given scenario, all the matrices necessary in the inversion process, thus leading to a computationally efficient solving strategy. The effectiveness of the approach is evaluated by using experimental data obtained with a commercial GPR apparatus employing a pulsed source field. A fast Fourier transform is applied to the time-domain measurements to extract frequency-domain data at a set of frequencies in the source spectrum, which are fed in input to the imaging scheme. Very good reconstruction capabilities are obtained both with a single metallic target, as well as in a challenging two targets layout including both a metallic object and a low-permittivity target.

In Situ Estimation of the Dynamic Characteristics of an Uncavitated Squeeze-Film Damper

1988 ◽  
Vol 110 (1) ◽  
pp. 162-166
Author(s):  
C. R. Burrows ◽  
M. N. Sahinkaya ◽  
N. C. Kucuk ◽  
M. L. Tong
Keyword(s):  
Frequency Domain ◽  
Dynamic Characteristics ◽  
Estimation Algorithm ◽  
Squeeze Film ◽  
Oil Film ◽  
Squeeze Film Damper ◽  
Damping Coefficients ◽  
Theoretical Predictions

A modified form of the author’s frequency-domain estimation algorithm has been applied to estimate the inertia and damping coefficients of an uncavitated squeeze-film bearing. These estimates are obtained in situ from measurements on a specially designed rig. The experiments provided further evidence that oil-film inertia coefficients may be significant and showed that theoretical predictions are inadequate.

Parametric Studies on Moving Axle Load Identification

2001 ◽  
Author(s):  
Ling Yu ◽  
Tommy H. T. Chan
Keyword(s):  
Time Domain ◽  
Time Domain Method ◽  
Identification Accuracy ◽  
Load Identification ◽  
System Parameters ◽  
Domain Method ◽  
Parametric Studies ◽  
The Time Domain ◽  
Value Decomposition ◽  
Pseudo Inverse

Abstract This study addresses the effects of various parameters on moving axle load identification when vehicles move across a bridge. Main emphases are placed on evaluation of two solutions, pseudo-inverse (PI) and Singular value decomposition (SVD) solutions, to an over-determined set of equations established under the time domain method (TDM) and frequency-time domain method (FTDM). The effects of vehicle-bridge system parameters and of measurement system parameters on the TDM and FTDM are also investigated. Assessment results based on experiments in laboratory show that the TDM is a better and non-sensitive method. The SVD technique can effectively improve identification accuracy when using TDM and FTDM particularly in the case of the FTDM.

scholarly journals Variability in Active Galactic Nuclei

2011 ◽  
Vol 7 (S285) ◽  
pp. 109-110
Author(s):  
Erin Wells Bonning
Keyword(s):  
Active Galactic Nuclei ◽  
Time Domain ◽  
Galactic Nuclei ◽  
Periodic Oscillation ◽  
Theoretical Models ◽  
Quasi Periodic Oscillation ◽  
Complex Processes ◽  
Central Engine ◽  
The Rich ◽  
The Time Domain

AbstractThis talk explored variability in active galactic nuclei (AGN) for a variety of scales across the time domain. From billion-year-scale intermittency to a quasi-periodic oscillation signal with a period of one hour, time-varying signals offer insights into a myriad of complex processes driven by the AGN central engine. Athough the era of time-domain observations of AGN across the spectrum has but just begun, already observations reveal the rich detail of phenomena associated with actively accreting black holes which challenge theoretical models.

Experimental Modal Analysis of Motorized Spindle Based on Stochastic Subspace Identification

2011 ◽  
Vol 103 ◽  
pp. 469-474
Author(s):  
Jie Meng ◽  
Xiao An Chen
Keyword(s):  
Modal Analysis ◽  
Dynamic Characteristics ◽  
Time Domain ◽  
Experimental Modal Analysis ◽  
Modal Parameters ◽  
Vibration Velocity ◽  
Subspace Identification ◽  
Motorized Spindle ◽  
Stochastic Subspace Identification ◽  
The Time Domain

Experimental modal analysis is done to the grinding motorized spindle under 36000r/min. The corresponding theory and experimental plan are introduced. The time domain waveform is gained and the maximum vibration velocity is worked out. Stochastic Subspace Identification (SSI) is applied to study dynamic characteristics of motorized spindle which is running idle, then modal parameters are extracted. The correctness of the experimental method is validated, which has certain referential importance.

scholarly journals Robust and Blind Audio Watermarking Algorithm in Dual Domain for Overcoming Synchronization Attacks

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Qiuling Wu ◽  
Aiyan Qu ◽  
Dandan Huang
Keyword(s):  
Time Domain ◽  
Audio Watermarking ◽  
Transform Domain ◽  
Quantization Step ◽  
Blind Audio Watermarking ◽  
Synchronization Mechanism ◽  
The Time Domain ◽  
Value Decomposition ◽  
Dual Domain ◽  
Conventional Signal

How to effectively resist synchronization attacks is the most challenging topic in the research of robust watermarking algorithms. A robust and blind audio watermarking algorithm for overcoming synchronization attacks is proposed in dual domain by considering time domain and transform domain. Based on analysing the characteristics of synchronization attacks, an implicit synchronization mechanism (ISM) is developed in the time domain, which can effectively track the appropriate region for embedding and extracting watermarks. The data in this region will be subjected to discrete cosine transform (DCT) and singular value decomposition (SVD) in turn to obtain the eigenvalue that can be utilized to carry watermarks. In order to extract the watermark blindly, the eigenvalue will be quantized. Genetic algorithm (GA) is utilized to optimize the quantization step to balance both transparency and robustness. The experimental results confirm that the proposed algorithm not only withstands various conventional signal processing operations but also resists malicious synchronization attacks, such as time scale modification (TSM), pitch-shifting modification (PSM), jittering, and random cropping. Especially, it can overcome TSM with strength from −30% to +30%, which is much higher than the standard of the International Federation of the Phonographic Industry (IFPI) and far superior to the other algorithms in related papers.

Apodisation in the time domain

1992 ◽  
Vol 2 (4) ◽  
pp. 615-620
Author(s):  
G. W. Series
Keyword(s):  
Time Domain ◽  
The Time Domain
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