Frequency Domain Methods for Analysis and Design

1995 ◽  
pp. 153-191
Author(s):  
Sigurd Skogestad
Keyword(s):  
Frequency Domain ◽  
Analysis And Design ◽  
Frequency Domain Methods

scholarly journals An Application of the Individual Channel Analysis and Design Approach to Control of a Two-input Two-output Coupled-tanks System

10.14311/1618 ◽  
2012 ◽  
Vol 52 (4) ◽  
Author(s):  
David J. Murray-Smith
Keyword(s):  
Feedback Control ◽  
Frequency Domain ◽  
Control Systems ◽  
Experimental Testing ◽  
Level Control ◽  
Nonlinear Dynamic Model ◽  
Analysis And Design ◽  
Frequency Domain Methods ◽  
Feedback Control Systems ◽  
Channel Analysis

Frequency-domain methods have provided an established approach to the analysis and design of single-loop feedback control systems in many application areas for many years. Individual Channel Analysis and Design (ICAD) is a more recent development that allows neo-classical frequency-domain analysis and design methods to be applied to multi-input multi-output control problems. This paper provides a case study illustrating the use of the ICAD methodology for an application involving liquid-level control for a system based on two coupled tanks. The complete nonlinear dynamic model of the plant is presented for a case involving two input flows of liquid and two output variables, which are the depths of liquid in the two tanks. Linear continuous proportional plus integral controllers are designed on the basis of linearised plant models to meet a given set of performance specifications for this two-input two-output multivariable control system and a computer simulation of the nonlinear model and the controllers is then used to demonstrate that the overall closed-loop performance meets the given requirements. The resulting system has been implemented in hardware and the paper includes experimental results which demonstrate good agreement with simulation predictions. The performance is satisfactory in terms of steady-state behaviour, transient responses, interaction between the controlled variables, disturbance rejection and robustness to changes within the plant. Further simulation results, some of which involve investigations that could not be carried out in a readily repeatable fashion by experimental testing, give support to the conclusion that this neo-classical ICAD framework can provide additional insight within the analysis and design processes for multi-input multi-output feedback control systems.

An investigation of bridge influence line identification using time-domain and frequency-domain methods

Structures ◽  
2021 ◽  
Vol 33 ◽  
pp. 2061-2065
Author(s):  
Samim Mustafa ◽  
Ikumasa Yoshida ◽  
Hidehiko Sekiya
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Influence Line ◽  
Line Identification ◽  
Frequency Domain Methods

Evaluating jack-up dynamic response using frequency domain methods and the inertial load set technique

1996 ◽  
Vol 9 (1) ◽  
pp. 101-128 ◽  
Author(s):  
E.J. Greeves ◽  
B.H. Jukui ◽  
P.G.F. Sliggers
Keyword(s):  
Dynamic Response ◽  
Frequency Domain ◽  
Inertial Load ◽  
Frequency Domain Methods ◽  
Jack Up

scholarly journals Comparison of Common Methods in Dynamic Response Predictions of Rotor Systems with Malfunctions

2014 ◽  
Vol 2014 ◽  
pp. 1-8
Author(s):  
Hongliang Yao ◽  
Qian Zhao ◽  
Qi Xu ◽  
Bangchun Wen
Keyword(s):  
Frequency Domain ◽  
Harmonic Balance ◽  
Harmonic Balance Method ◽  
Balance Method ◽  
Newmark Method ◽  
Incremental Harmonic Balance Method ◽  
Rotor Systems ◽  
Double Frequency ◽  
Frequency Domain Methods ◽  
Incremental Harmonic Balance

The efficiency and accuracy of common time and frequency domain methods that are used to simulate the response of a rotor system with malfunctions are compared and analyzed. The Newmark method and the incremental harmonic balance method are selected as typical representatives of time and frequency domain methods, respectively. To improve the simulation efficiency, the fixed interface component mode synthesis approach is combined with the Newmark method and the receptance approach is combined with the incremental harmonic balance method. Numerical simulations are performed for rotor systems with single and double frequency excitations. The inherent characteristic that determines the efficiency of the two methods is analyzed. The results of the analysis indicated that frequency domain methods are suitable single and double frequency excitation rotor systems, whereas time domain methods are more suitable for multifrequency excitation rotor systems.

scholarly journals The relevance of non-stationarities and non-Gaussianities in vibration fatigue

2018 ◽  
Vol 165 ◽  
pp. 10011 ◽  
Author(s):  
Martin Česnik ◽  
Janko Slavič ◽  
Lorenzo Capponi ◽  
Massimiliano Palmieri ◽  
Filippo Cianetti ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Dynamic Loading ◽  
Amplitude Modulation ◽  
Time History ◽  
Power Density Spectrum ◽  
Time To Failure ◽  
Density Spectrum ◽  
Frequency Domain Methods ◽  
Vibration Fatigue ◽  
Non Gaussian

In classical fatigue of materials, the frequency contents of dynamic loading are well below the natural frequencies of the observed structure or test specimen. However, when dealing with vibration fatigue the frequency contents of dynamic loading and structure's dynamic response overlap, resulting in amplified stress loads of the structure. For such cases, frequency counting methods are especially convenient. Gaussianity and stationarity assumptions are applied in frequency-domain methods for obtaining dynamic structure's response and frequency-domain methods for calculating damage accumulation rate. Since it is common in real environments for the structure to be excited with non-Gaussian and non-stationary loads, this study addresses the effects of such dynamic excitation to experimental time-to-failure of a structure. Initially, the influence of non-Gaussian stationary excitation is experimentally studied via excitation signals with equal power density spectrum and different values of kurtosis. Since no relevant changes of structure's time-to-failure were observed, the study focused on non-stationary excitation signals that are also inherently non-Gaussian. The non-stationarity of excitation was achieved by amplitude modulation and significantly shorter times-to-failure were observed when compared to experiments with stationary non-Gaussian excitation. Additionally, the structure's time-to-failure varied with the rate of the amplitude modulation. To oversee this phenomenon the presented study proposes a non-stationarity index which can be obtained from the excitation time history. The non-stationarity index was experimentally confirmed as a reliable estimator for severity of non-stationary excitation. The non-stationarity index is used to determine if the frequencydomain methods can safely be applied for time-to-failure calculation.

On the Simulation and Spectral Analysis of Unsteady Turbulence and Transition Effects in a Multistage Low Pressure Turbine

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Georg Geiser ◽  
Jens Wellner ◽  
Edmund Kügeler ◽  
Anton Weber ◽  
Anselm Moors
Keyword(s):  
Frequency Domain ◽  
Large Scale ◽  
Separation Bubble ◽  
Pressure Fluctuations ◽  
Low Pressure ◽  
Transition Flow ◽  
Low Pressure Turbine ◽  
Wall Pressure Fluctuations ◽  
Frequency Domain Methods ◽  
Transition Effects

A nonlinear full-wheel time-domain simulation of a two-stage low pressure turbine is presented, analyzed, and compared with the available experimental data. Recent improvements to the computational fluid dynamics (CFD) solver TRACE that lead to significantly reduced wall-clock times for such large scale simulations are described in brief. Since the configuration is characterized by significant unsteady turbulence and transition effects, it is well suited for the validation and benchmarking of frequency-domain methods. Transition, flow separation and wall pressure fluctuations on the stator blades of the second stage are analyzed in detail. A strong azimuthal π-periodicity is observed, manifesting in a significantly varying stability of the midspan trailing edge flow with a quasi-steady closed separation bubble on certain blades and highly dynamic partially open separation bubbles with recurring transition and turbulent reattachment on other blades. The energy spectrum of fluctuating wall quantities in that regime shows a high bandwidth and considerable disharmonic content, which is challenging for frequency-domain-based simulation methods.

Sign in / Sign up

Export Citation Format

Share Document