The incomplete reception error in acoustic analogy integral with source time domain algorithm

2019 ◽  
Vol 18 (8) ◽  
pp. 780-797
Author(s):  
Yongfei Mu ◽  
Jie Li
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Acoustic Signal ◽  
Processing Method ◽  
Acoustic Analogy ◽  
Time Step ◽  
Retarded Time ◽  
Comparison Results ◽  
Numerical Oscillations ◽  
The Difference

There are two algorithms to solve the retarded time equation in the acoustic analogy. One is the classic retarded time method, and the other is the source time domain algorithm or the advanced time approach. The latter is more effective and simple than the former. However, difficulties may arise in the reconstruction of the acoustic signal in the observer time domain. The signal interpolation in every observer time step and a completeness check at the end are necessary for the reconstruction. In addition, two error regions which cannot to be ignored in frequency domain are generated by the latter. They are called the incomplete reception error. It is the main purpose of present work to analyze the formation process and characteristics of the incomplete reception error. Then the analysis is tested with a simplified model and the numerical results show that there are some spurious numerical oscillations in frequency domain if the incomplete reception regions are not removed. Finally, the difference between the method of directly removing the incomplete reception regions and the standard acoustic signal post-processing method is compared. The comparison results show that the method of removing incomplete reception regions directly is better.

A Novel Solution to Compute Stress Time Series in Nonlinear Hydro-Structure Simulations

2015 ◽  
Author(s):  
Fabien Bigot ◽  
François-Xavier Sireta ◽  
Eric Baudin ◽  
Quentin Derbanne ◽  
Etienne Tiphine ◽  
...  
Keyword(s):  
Time Series ◽  
Frequency Domain ◽  
Time Domain ◽  
Hot Spot ◽  
Structural Response ◽  
Container Ship ◽  
Time Step ◽  
Computation Cost ◽  
Hull Girder ◽  
Non Linear

Ship transport is growing up rapidly, leading to ships size increase, and particularly for container ships. The last generation of Container Ship is now called Ultra Large Container Ship (ULCS). Due to their increasing sizes they are more flexible and more prone to wave induced vibrations of their hull girder: springing and whipping. The subsequent increase of the structure fatigue damage needs to be evaluated at the design stage, thus pushing the development of hydro-elastic simulation models. Spectral fatigue analysis including the first order springing can be done at a reasonable computational cost since the coupling between the sea-keeping and the Finite Element Method (FEM) structural analysis is performed in frequency domain. On the opposite, the simulation of non-linear phenomena (Non linear springing, whipping) has to be done in time domain, which dramatically increases the computation cost. In the context of ULCS, because of hull girder torsion and structural discontinuities, the hot spot stress time series that are required for fatigue analysis cannot be simply obtained from the hull girder loads in way of the detail. On the other hand, the computation cost to perform a FEM analysis at each time step is too high, so alternative solutions are necessary. In this paper a new solution is proposed, that is derived from a method for the efficient conversion of full scale strain measurements into internal loads. In this context, the process is reversed so that the stresses in the structural details are derived from the internal loads computed by the sea-keeping program. First, a base of distortion modes is built using a structural model of the ship. An original method to build this base using the structural response to wave loading is proposed. Then a conversion matrix is used to project the computed internal loads values on the distortion modes base, and the hot spot stresses are obtained by recombination of their modal values. The Moore-Penrose pseudo-inverse is used to minimize the error. In a first step, the conversion procedure is established and validated using the frequency domain hydro-structure model of a ULCS. Then the method is applied to a non-linear time domain simulation for which the structural response has actually been computed at each time step in order to have a reference stress signal, in order to prove its efficiency.

A Broadband Array Signal Processing Method Based on Joint Sparsity of Signal Spatial Domain

2019 ◽  
Author(s):  
Daqian He ◽  
Dahai Zhang ◽  
Congying Wang ◽  
Xirui Peng
Keyword(s):  
Signal Processing ◽  
Frequency Domain ◽  
Acoustic Signal ◽  
Array Signal Processing ◽  
Doa Estimation ◽  
Spatial Domain ◽  
Processing Method ◽  
Arrival Angle ◽  
Joint Sparsity ◽  
Signal Processing Method

Abstract Broadband underwater acoustic signal direction of arrival (DOA) estimation method is an important part of underwater array signal processing. The commonly used array signal DOA estimation algorithms due to the restriction of algorithm principles, are unable to process broadband array signal effectively, at the case of the arriving signals have strong correlation, small sampling snapshots or small arrival angle. Therefore, we need a new efficient algorithm to meet the increasing demand of broadband under water acoustic signal processing method. This paper makes use of the broadband acoustic signal similarity of joint sparsity in signal spatial domain received by underwater sonar arrays, establishes the whole space grid covering all broadband frequency domain slices. On the basis, the global sparsity of each frequency domain slice is combined with sparse element extraction class algorithm. By integrating the energy of signal on each slice, the spatial sparsity of each slice is obtained, from which we can get the directions of the arriving broadband wave signals. Through the simulation analysis and experimental verification on lake, we can be see that: The SDJS algorithm improves the performance and signal processing capability of the algorithm compared with the traditional algorithms. Therefore SDJS algorithm has a widely range of research value and application space.

scholarly journals Sex Differences in Time-Domain and Frequency-Domain Heart Rate Variability Measures of Fatigued Drivers

2020 ◽  
Vol 17 (22) ◽  
pp. 8499
Author(s):  
Chao Zeng ◽  
Wenjun Wang ◽  
Chaoyang Chen ◽  
Chaofei Zhang ◽  
Bo Cheng
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Sex Differences ◽  
Frequency Domain ◽  
Time Domain ◽  
Mental States ◽  
Male And Female ◽  
Frequency Domain Methods ◽  
The Difference ◽  
Electrocardiogram Ecg

The effects of fatigue on a driver’s autonomic nervous system (ANS) were investigated through heart rate variability (HRV) measures considering the difference of sex. Electrocardiogram (ECG) data from 18 drivers were recorded during a simulator-based driving experiment. Thirteen short-term HRV measures were extracted through time-domain and frequency-domain methods. First, differences in HRV measures related to mental state (alert or fatigued) were analyzed in all subjects. Then, sex-specific changes between alert and fatigued states were investigated. Finally, sex differences between alert and fatigued states were compared. For all subjects, ten measures showed significant differences (Mann-Whitney U test, p < 0.01) between different mental states. In male and female drivers, eight and four measures, respectively, showed significant differences between different mental states. Six measures showed significant differences between males and females in an alert state, while ten measures showed significant sex differences in a fatigued state. In conclusion, fatigue impacts drivers’ ANS activity, and this impact differs by sex; more differences exist between male and female drivers’ ANS activity in a fatigued state than in an alert state.

NON LINEAR ANALYSIS OF SHIP MOTIONS AND LOADS IN LARGE AMPLITUDE WAVES

2021 ◽  
Vol 153 (A2) ◽  
Author(s):  
G Mortola ◽  
A Incecik ◽  
O Turan ◽  
S.E. Hirdaris
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Large Amplitude ◽  
Linear Time ◽  
Ship Motions ◽  
Wave Loads ◽  
Time Step ◽  
Strip Theory ◽  
Non Linear ◽  
The Time Domain

A non linear time domain formulation for ship motions and wave loads is presented and applied to the S175 containership. The paper describes the mathematical formulations and assumptions, with particular attention to the calculation of the hydrodynamic force in the time domain. In this formulation all the forces involved are non linear and time dependent. Hydrodynamic forces are calculated in the frequency domain and related to the time domain solution for each time step. Restoring and exciting forces are evaluated directly in time domain in a way of the hull wetted surface. The results are compared with linear strip theory and linear three dimensional Green function frequency domain seakeeping methodologies with the intent of validation. The comparison shows a satisfactory agreement in the range of small amplitude motions. A first approach to large amplitude motion analysis displays the importance of incorporating the non linear behaviour of motions and loads in the solution of the seakeeping problem.

Numerical Investigation of Nonlinear Fluid-Structure Interaction in Vibrating Compressor Blades

2000 ◽  
Author(s):  
Volker Carstens ◽  
Joachim Belz
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Transonic Flow ◽  
Fluid Structure Interaction ◽  
Time Step ◽  
Compressor Blades ◽  
Stability Boundaries ◽  
Structure Interaction ◽  
The Time Domain ◽  
Nonlinear Fluid

The aeroelastic behaviour of vibrating blade assemblies is usually investigated in the frequency domain where the determination of aeroelastic stability boundaries is separated from the computation of linearized unsteady aerodynamic forces. However, nonlinear fluid-structure interaction caused by oscillating shocks or strong flow separation may significantly influence the aerodynamic damping and hence effect a shift of stability boundaries. In order to investigate such aeroelastic phenomena, the governing equations of structural and fluid motion have to be simultaneously integrated in time. In this paper a technique is presented which analyzes the aeroelastic behaviour of an oscillating compressor cascade in the time domain. The structural part of the governing aeroelastic equations is time-integrated according to the algorithm of Newmark, while the unsteady airloads are computed at every time step by an Euler upwind code, The link between the two time integrations is an automatic grid generation in which the used mesh is dynamically deformed as such that it conforms with the deflected blades at every time step. The computed time series of the aeroelastic simulation of an assembly of twenty compressor blades performing torsional vibrations in transonic flow are presented. For subsonic flow, the differences between time domain and frequency domain results are of negligible order. For transonic flow, however, where vibrating shocks and a temporarily choked flow in the blade channel dominate the unsteady flow, the energy transfer between fluid and structure is no longer comparable to that of a linear system. It is demonstrated that the application of the time domain method leads to a significantly different aeroelastic behaviour of the blade assembly including a shift of the stability boundary.

Towards a Time-Domain Finite Element Analysis of Vortex Induced Vibrations

2011 ◽  
Author(s):  
Philippe Mainc¸on ◽  
Carl M. Larsen
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Laguerre Polynomials ◽  
Cross Flow ◽  
Domain Model ◽  
Time Step ◽  
Element Analysis ◽  
Vortex Induced Vibrations ◽  
Frequency Components ◽  
Chaotic Nature

Slender structures immersed in a cross flow can experience vibrations induced by vortex shedding (VIV), which cause fatigue damage and other problems. Engineering VIV models tend to operate in the frequency domain. A time domain model would allow to capture effects beyond the scope of today’s frequency domain empirical codes: interaction between in-line and cross-flow vibrations, higher order frequency components, structural non-linearities, simultaneous actions from other loads like waves and forced motions at boundaries. There is also the potential to capture the chaotic nature of VIV. Such a model was formulated in the present work: for each cross section and at each time step, the recent velocity history is described as a combination of Laguerre polynomials. The coefficients of that combination are used to enter an interpolation function to predict the instantaneous force, allowing to step the dynamic analysis. An offshore riser was modeled in this way: Some analyses provided an unusually fine level of realism, while in other analyses, the riser fell into an unphysical pattern of vibration. It is concluded that the concept is very promising, yet that more work is needed to understand trajectory stability and related issues, in order to further progress towards an engineering tool.

scholarly journals Dilemma and Solution of Traditional Feature Extraction Methods Based on Inertial Sensors

2018 ◽  
Vol 2018 ◽  
pp. 1-6
Author(s):  
Zhiqiang Peng ◽  
Yue Zhang
Keyword(s):  
Feature Extraction ◽  
Angular Velocity ◽  
Frequency Domain ◽  
Time Domain ◽  
Inertial Sensors ◽  
Extraction Methods ◽  
Feature Extraction Method ◽  
The Difference ◽  
The Time Domain ◽  
Almost All

Correctly identifying human activities is very significant in modern life. Almost all feature extraction methods are based directly on acceleration and angular velocity. However, we found that some activities have no difference in acceleration and angular velocity. Therefore, we believe that for these activities, any feature extraction method based on acceleration and angular velocity is difficult to achieve good results. After analyzing the difference of these indistinguishable movements, we propose several new features to improve accuracy of recognition. We compare the traditional features and our custom features. In addition, we examined whether the time-domain features and frequency-domain features based on acceleration and angular velocity are different. The results show that (1) our custom features significantly improve the precision of the activities that have no difference in acceleration and angular velocity; and (2) the combination of time-domain features and frequency-domain features does not significantly improve the recognition of different activities.

Numerical Investigation of Nonlinear Fluid-Structure Interaction in Vibrating Compressor Blades

2000 ◽  
Vol 123 (2) ◽  
pp. 402-408 ◽  
Author(s):  
Volker Carstens ◽  
Joachim Belz
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Transonic Flow ◽  
Fluid Structure Interaction ◽  
Time Step ◽  
Compressor Blades ◽  
Stability Boundaries ◽  
Structure Interaction ◽  
The Time Domain ◽  
Nonlinear Fluid

The aeroelastic behavior of vibrating blade assemblies is usually investigated in the frequency domain where the determination of aeroelastic stability boundaries is separated from the computation of linearized unsteady aerodynamic forces. However, nonlinear fluid-structure interaction caused by oscillating shocks or strong flow separation may significantly influence the aerodynamic damping and hence effect a shift of stability boundaries. In order to investigate such aeroelastic phenomena, the governing equations of structural and fluid motion have to be simultaneously integrated in time. In this paper a technique is presented which analyzes the aeroelastic behavior of an oscillating compressor cascade in the time domain. The structural part of the governing aeroelastic equations is time-integrated according to the algorithm of Newmark, while the unsteady airloads are computed at every time step by an Euler upwind code. The link between the two time integrations is an automatic grid generation in which the used mesh is dynamically deformed as such that it conforms with the deflected blades at every time step. The computed time series of the aeroelastic simulation of an assembly of twenty compressor blades performing torsional vibrations in transonic flow are presented. For subsonic flow, the differences between time domain and frequency domain results are of negligible order. For transonic flow, however, where vibrating shocks and a temporarily choked flow in the blade channel dominate the unsteady flow, the energy transfer between fluid and structure is no longer comparable to that of a linear system. It is demonstrated that the application of the time domain method leads to a significantly different aeroelastic behavior of the blade assembly including a shift of the stability boundary.

Application of Acoustic Fourier Domain Imaging for the Evaluation of Advanced Micro Electronic Packages

2002 ◽  
Author(s):  
Janet E. Semmens ◽  
Lawrence W. Kessler
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Acoustic Signal ◽  
Fourier Transforms ◽  
Fourier Domain ◽  
Electronic Packages ◽  
Internal Defects ◽  
End Products ◽  
Resolution Limits ◽  
The Time Domain

Abstract Acoustic Micro Imaging (AMI) has been used for years to evaluate microelectronic packages for the presence of internal defects. The drive in micro electronic packaging is to reduce the size of the components as much as possible to keep pace with the shrinking size of the end products. This leads to smaller/thinner packages with internal features and possibly defects that are approaching the resolution limits for conventional AMI. Recently AMI has been combined with Fourier transforms of the acoustic signal to produce frequency domain images. Previously features that were at or below the accepted resolution limits for a given frequency were not detected in the time domain images, however these features are revealed in the frequency domain images.

scholarly journals Non-linearity Analysis of Ship Roll Gyro-stabilizer Control System

2021 ◽  
Vol 3 (1) ◽  
Author(s):  
Sathit P. ◽  
Chatchapol C ◽  
Phansak I.
Keyword(s):  
Control System ◽  
Frequency Domain ◽  
Linear Model ◽  
Time Domain ◽  
Loop Model ◽  
System Use ◽  
Non Linear ◽  
Ship Roll ◽  
The Difference ◽  
Marine Vessels

A gyro-stabilizer is the interesting system that it can apply to marine vessels for diminishes roll motion. Today it has potentially light weight with no hydrodynamics drag and effective at zero forward speed. The twin-gyroscope was chosen. Almost, the modelling for designing the system use linear model that it might not comprehensive mission requirement such as high sea condition. The non-linearity analysis was proved by comparison the results between linear and non-linear model of gyro-stabilizer throughout frequency domain also same wave input, constrains and limitations. Moreover, they were cross checked by simulating in time domain. The comparison of interested of linear and non-linear close loop model in frequency domain has demonstrated the similar characteristics but gave different values at same frequency obviously. The results were confirmed again by simulation in irregular beam sea on time domain and they demonstrate the difference of behavior of both systems while the gyro-stabilizers are switching on and off. From the resulting analysis, the non-linear gyro-stabilizer model gives more real results that correspond to more accuracy in a designing gyro-stabilizer control system for various amplitudes and frequencies operating condition especially high sea condition.

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