scholarly journals The Use of Frequency Analysis as a Complementary and Explanatory Element for Time Domain Analysis in Measurements of the Ability to Maintain Balance

2021 ◽  
Vol 76 (1) ◽  
pp. 117-129
Author(s):  
Jacek Jurkojć ◽  
Piotr Wodarski ◽  
Robert Michnik ◽  
Wojciech Marszałek ◽  
Kajetan J. Słomka ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Sagittal Plane ◽  
Three Dimensional ◽  
Time Domain Analysis ◽  
Sensory Conflict ◽  
Cyclical Component ◽  
Human Balance ◽  
Analysis Of Results ◽  
The Time Domain

Abstract Assessment of human balance is one of the most common diagnostic tests, both in medical applications and during sports training. Many new methods of measuring are introduced in these studies; however, the analysis of results is still carried out mainly based on the values determined in the time domain – the average COP speed or the ellipse field of the prediction. The aim of the current work is to present the possibilities for the practical application of frequency analyses in assessment of the ability to maintain body balance as a method supplementing standard analyses. As part of the study, measurements of the ability to maintain balance in sensory conflict conditions introduced in the form of an oscillating, three-dimensional, virtual scenery were carried out. 27 healthy volunteers (13 women and 14 men) took part in the study. The three-dimensional scenery, presented by means of the Oculus system, oscillated in the sagittal plane with frequencies equal to 0.7 Hz and 1.4 Hz. The frequency value during the measurement was constant or changed in the middle of the test. Measurements were conducted on the FDM Zebris platform. The results were analyzed using developed coefficients determined on the basis of the Short-time Fourier transform (STFT). The use of frequency-domain analyses confirmed that in the COP movement, one can observe a cyclical component corresponding to following the scenery, as well as the appearance of other cyclical components whose observation is important in terms of assessing the ability to maintain balance. It has been shown that the changes in the average COP speed that occur during the measurement can result from changes related to the movement of following the scenery as well as additional body movements indicating a greater or lesser loss of balance. It has been shown that there are differences in the COP movement provoked by the movement of the surrounding scenery, which depend on the parameters of the introduced disturbances – something that can only be observed in results obtained in the frequency domain. The conducted research shows that in measurements involving the ability to maintain one’s balance conducted in sensory conflict conditions, standard time-domain analyses should be supplemented with other types of data analysis, e.g. frequency domain analyses.

Numerical Simulation on Mooring Performance of LNG-FPSO System in Realistic Seas

2005 ◽  
Author(s):  
Yoshiyuki Inoue ◽  
Md. Kamruzzaman
Keyword(s):  
Time Domain ◽  
Oil And Gas ◽  
Three Dimensional ◽  
Time Domain Analysis ◽  
Analysis Tool ◽  
Motion Response ◽  
Non Linear ◽  
Floating System ◽  
Exciting Forces ◽  
The Time Domain

The LNG-FPSO concept is receiving much attention in recent years, due to its active usage to exploit oil and gas resources. The FPSO offloads LNG to an LNG carrier that is located close to the FPSO, and during this transfer process two large vessels are in close proximity to each other for daylong periods of time. Due to the presence of neighboring vessel, the motion response of both the vessels will be affected significantly. Hydrodynamic interactions related to wave effects may result in unfavorable responses or the risk of collisions in a multi-body floating system. Not only the motion behavior but also the second order drift forces are influenced by the neighboring structures due to interactions of the waves among the structures. A study is made on the time domain analysis to assess the behavior and the operational capability of the FPSO system moored in the sea having an LNG carrier alongside under environmental conditions such as waves, wind and currents. This paper presents an analysis tool to predict the dynamic motion response and non-linear connecting and mooring forces on a parallel-connected LNG-FPSO system due to non-linear exciting forces of wave, wind and current. Simulation for the mooring performance is also investigated. The three-dimensional source-sink technique has been applied to obtain the radiation forces and the transfer function of wave exciting forces on floating multi-bodies. The hydrodynamic interaction effect between the FPSO and the LNG carrier is included to calculate the hydrodynamic forces. For the simulation of a random sea and also for the generation of time depended wind velocity, a fully probabilistic simulation technique has been applied. Wind and current loads are estimated according to OCIMF. The effects of variations in wave, wind and current loads and direction on the slowly varying oscillations of the LNG and FPSO are also investigated in this paper. Finally, some conclusions are drawn based on the numerical results obtained from the present time domain simulations.

A Frequency Domain Analysis of Learning Control

1994 ◽  
Vol 116 (4) ◽  
pp. 781-786 ◽  
Author(s):  
C. J. Goh
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Linear Time ◽  
Planning Horizon ◽  
Time Domain Analysis ◽  
Learning Control ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Convergence Criterion ◽  
The Time Domain

The convergence of learning control is traditionally analyzed in the time domain. This is because a finite planning horizon is often assumed and the analysis in time domain can be extended to time-varying and nonlinear systems. For linear time-invariant (LTI) systems with infinite planning horizon, however, we show that simple frequency domain techniques can be used to quickly derive several interesting results not amenable to time-domain analysis, such as predicting the rate of convergence or the design of optimum learning control law. We explain a paradox arising from applying the finite time convergence criterion to the infinite time learning control problem, and propose the use of current error feedback for controlling possibly unstable systems.

scholarly journals Effect of Wave-Current Interaction on Structural Responses of a Very Long and Side-Anchored Floating Bridge

2020 ◽  
Author(s):  
Jian Dai ◽  
Bjørn Christian Abrahamsen ◽  
Bernt Johan Leira
Keyword(s):  
Time Domain ◽  
Transfer Functions ◽  
Computational Study ◽  
Three Dimensional ◽  
Time Domain Analysis ◽  
Bridge Model ◽  
Structural Responses ◽  
Floating Bridge ◽  
Current Interaction ◽  
The Time Domain

Abstract This paper is concerned with a computational study on the hydroelastic response of a long, straight and side-anchored fjord-crossing floating bridge accounting for the wave-current interaction. The effect of this interaction on a single bridge pontoon is investigated by using the three-dimensional potential solver VERES3D. The frequency-dependent hydrodynamic coefficients and excitation force transfer functions are presented and compared with WAMIT results where the current effect is ignored. Based on the frequency domain results, an approach to account for the wave-current interaction in time domain analysis is proposed. Next, a generic straight and side-anchored floating bridge model is put forward to examine the stochastic structural responses in the time domain. For the purpose of comparison, the bridge responses under waves and current without interaction are also investigated. This study attempts to quantify the wave-current interaction effect on the structural responses of a floating bridge and provide useful recommendations and suggestions to researchers and engineers for their study of similar structures.

Comparison of Time and Frequency Domain Analysis With Full Scale Data for the Horn Mountain Spar During Hurricane Isidore

2006 ◽  
Author(s):  
Arcandra Tahar ◽  
John Halkyard ◽  
Mehernosh Irani
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Full Scale ◽  
Frequency Domain Method ◽  
Drag Forces ◽  
The Time Domain ◽  
Scale Data

The Horn Mountain Spar is located in 1,654 m of water about 135 km from Venice, Louisiana in the Gulf of Mexico. The facility was instrumented extensively to measure key spar and riser response parameters (Edwards et. al. 2003). Halkyard et. al. (2004) and Tahar et. al. (2005) have compared measured spar responses such as motion and mooring line tensions with numerical predictions. This paper extends the work done on comparison of the full scale data during hurricane Isidore. All previous numerical simulations were based on a time domain analysis procedure. One concern related to this method is that it is computationally intensive and time consuming. In the initial stages of a project, a frequency domain solution may be an effective tool compared with a fully coupled time domain analysis. The present paper compares results of time domain and frequency domain simulations with field measurements. Particular attention has been placed on the importance of the phase relationship between motion and excitation force. In the time domain analysis, nonlinear drag forces are applied at the instantaneous position. Whereas in the frequency domain analysis, nonlinear drag forces are stochastically linearized and solutions are obtained by an iterative procedure. The time domain analysis has better agreement with the field data compared to the frequency domain. Overall, however, the frequency domain method is still promising for a quick and approximate estimation of relevant statistics. With advantages in terms of CPU time, the frequency domain method can be recommended as a tool in pre-front end engineering design or in a phase where an iterative nature of design of an offshore structure takes place.

Statistical Analysis in Time and Frequency Domain of the Last Decades Earth Data

DIALOGO ◽  
2021 ◽  
Vol 8 (1) ◽  
pp. 67-76
Author(s):  
Catalin Nutu
Keyword(s):  
Statistical Analysis ◽  
Frequency Domain ◽  
Time Domain ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Spectral Domain ◽  
Future Evolution ◽  
The Time Domain

This paper analyses data available from the last fifty years, with regard to Earth and it has the purpose to analyze them from both perspectives: the time domain analysis and spectral-domain analysis. Following this analysis, one can conclude about the correlations within the analyzed data or about forecasted future evolution and necessary measures to be taken in order to reduce the dangers.

scholarly journals Cyclicality of industrial production in the context of time and frequency domain

2010 ◽  
Vol 58 (6) ◽  
pp. 355-368
Author(s):  
Jitka Poměnková
Keyword(s):  
Czech Republic ◽  
Frequency Domain ◽  
Time Domain ◽  
Industrial Production ◽  
Autoregressive Process ◽  
Time Domain Analysis ◽  
The Czech Republic ◽  
Dating Method ◽  
Cyclical Behaviour ◽  
The Time Domain

Presented paper is focused on evaluation of cyclical behaviour of industrial production of the Czech Republic in time and frequency domain. Analyses in both domains are done in the context of commonly used detrending techniques necessary for obtaining growth business cycle. In the case of time domain analysis, the length of existing cycles is calculated on the basis of dating method application, i.e. right and left version of naive rules as well as Bry–Boschan algorithm. In the case of frequency domain, estimate of the spectra using periodogram and autoregressive process with optimum lag are used. In the time domain evaluation of the unity of the results of detrending techniques from the turning points identification is done as well. All analysis are done on the data of industrial production in the Czech Republic in 1996/Q1–2008/Q4.

scholarly journals   Time and frequency domain in the business cycle structure

2012 ◽  
Vol 58 (No. 7) ◽  
pp. 332-346 ◽  
Author(s):  
J. Poměnková ◽  
R. Maršálek
Keyword(s):  
Business Cycle ◽  
Frequency Domain ◽  
Time Domain ◽  
Autoregressive Process ◽  
Time Domain Analysis ◽  
Structure Identification ◽  
Regression Curves ◽  
Unobserved Component ◽  
The Time Domain ◽  
The Right

 The presented paper deals with the identification of cyclical behaviour of business cycle from the time and frequency domain perspective. Herewith, methods for obtaining the growth business cycle are investigated – the first order difference, the unobserved component models, the regression curves and filtration using the Baxter-King, Christiano-Fitzgerald and Hodrick-Prescott filter. In the case of the time domain, the analysis identification of cycle lengths is based on the dating process of the growth business cycle. Thus, the right and left variant of the naive techniques and the Bry-Boschan algorithm are applied. In the case of the frequency domain, the analysis of the cyclical structure trough spectrum estimate via the periodogram and the autoregressive process are suggested. Results from both domain approaches are compared. On their bases, recommendations for the cyclical structure identification of the growth business cycle of the Czech Republic are formulated. In the time domain analysis, the evaluation of the unity results of detrending techniques from the identification turning point points of view is attached. The analyses are done on the quarterly data of the GDP, the total industry excluding construction, the gross capital formation in 1996–2008 and on the final consumption expenditure in 1995–2008.    

Investigation on the Use of Different Approaches to Mooring Analysis and Appropriate Safety Factors

2012 ◽  
Author(s):  
Sojan Vasudevan ◽  
Paul Westlake
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Line Tension ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Mooring Line ◽  
Mooring System ◽  
Safety Factors ◽  
Dynamic Time ◽  
The Time Domain

This paper presents the results of the analyses of a twelve line catenary mooring system using a quasi-static method in the frequency domain, and uncoupled and coupled dynamic methods in the time domain. The latter is found to produce significantly higher tensions. The reasons for these differences are investigated. The minimum line tension safety factors required by design codes do not distinguish between uncoupled and coupled dynamic analyses and some codes use the same factors even for quasi-static analyses. Consequently, the present mooring system passes the acceptance criteria based on quasistatic frequency domain and uncoupled dynamic time domain analyses but does not meet the same criteria when a coupled dynamic time domain analysis is employed. It is understood that because the coupled time domain analysis determines the vessel motions using all forces the accuracy of mooring line tension estimation will be improved over other methods. Hence the application of less conservative safety factors is proposed.

Transfer Function Development and Dynamic Analysis of a Heat Pipe Cooled Reactor

2021 ◽  
Author(s):  
Songmao Pu ◽  
Peiwei Sun ◽  
Xinyu Wei
Keyword(s):  
Transfer Function ◽  
Dynamic Analysis ◽  
Heat Pipe ◽  
Frequency Domain ◽  
Dynamic Model ◽  
Time Domain ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Reactor Power ◽  
The Time Domain

Abstract The heat pipe cooled reactor adopts the solid-state reactor design concept and the heat is passively transferred out of the core through heat pipes. It is characterized by high inherent safety and simple operation and has broad application prospects in deep space exploration and propulsion, sea submarine navigation and exploration. The design of heat pipe cooled reactor is unique, and its dynamics are different from traditional water-cooled reactors. Therefore, it is necessary to develop its dynamic model and perform dynamic analysis, and in this paper, the study object of the heat pipe cooled reactor is the 100kW nuclear silent thermoelectric reactor (NUSTER-100). A nonlinear dynamic model is derived from the conservation equations of mass, energy and momentum. Point reactor kinetics equations are adopted. The linear dynamic model is constructed by linearization of the nonlinear model based on the disturbance theory and the transfer function is further derived applying Laplace transform. Both models including the nonlinear model and transfer function model are established on the MATLAB & Simulink simulation platform. Dynamic characteristic analysis contains time domain analysis and frequency domain analysis. For the time domain analysis, by introducing a variety of boundary condition disturbances, the results were compared with those from transfer function. The results are consistent and can correctly reflect the dynamic characteristics of the heat pipe cooled reactor. Therefore, the transfer function model can be applied to the subsequent design of the heat pipe cooled reactor power control system. For the dynamic analysis, it is divided into time domain and frequency domain. The time domain is to observe the change of core power and sodium temperature by introducing reactivity disturbance. For the frequency domain, after drawing the Bode plot of the transfer function, the system’s characteristics at different frequencies are analyzed. In addition, it can provide a theoretical basis for the design of the heat pipe cooled reactor power control system.

Assessment of Wave Energy Extraction From Seas: Numerical Validation

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Wanan Sheng ◽  
Anthony Lewis
Keyword(s):  
Numerical Simulation ◽  
Frequency Domain ◽  
Wave Energy ◽  
Time Domain ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Energy Converter ◽  
Power Capture ◽  
Power Matrix ◽  
The Time Domain

In developing a wave energy converter (WEC), assessing and rating the device is a difficult, but important issue. Conventionally, a large scaled device (maybe large enough for accommodating a power takeoff (PTO) system) or prototype device is needed to be tested in wave tanks or in seas in different wave conditions so that a power matrix for the device can be defined using scaling or interpolation/extrapolation methods. Alternatively, a pure numerical simulation in time-domain may be used for assessing the power capture capacities of wave energy devices. For the former, it is convincing, but can be especially difficult in the early stages of development, when small scaled models are normally used; and for the latter, the pure numerical simulation may not be very reliable and convincing, especially when the dynamic problem is very complicated. In this paper, a method for assessing the captured wave power for a device from its power capture response is presented. In the proposed method, a measured or calculated linear power capture response of the device is combined with wave spectrum to compute the average captured power function. Once the average captured power function is obtained, the overall average captured power corresponding to the wave state can be easily calculated. If a linear power capture response is obtained from a model test, the power assessment based on this proposed method can be very convincing and reliable. To illustrate the application of the proposed method, an example of a fully linear dynamic system, including the linear hydrodynamics of the floating structure and a linear power takeoff, is considered. For such a system, the frequency-domain analysis can be employed to obtain the performance of the floating device under waves and the power takeoff system. The hydrodynamic performance of the wave energy converter is then used to define the power capture response and to calculate the average captured power functions in different sea states. Then, the captured power of the device in different sea states, i.e, the power matrix, can be calculated, and accordingly, the device can be assessed and rated. To validate the proposed method, a time-domain analysis is also performed for a cross-check. In the time-domain analysis, the hydrodynamic coefficients and responses are first assessed in frequency-domain, and then transformed into the relevant terms by means of impulse response functions for establishing the time-domain (TD) equation. By comparing the results from frequency-domain and time-domain analyses of irregular waves, it can be concluded that the proposed wave energy capture assessment method can be used in assessing or rating the device.

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