scholarly journals Detection Line Spectrum of Ship Radiated Noise Based on a New 3D Chaotic System

Sensors ◽  
2021 ◽  
Vol 21 (5) ◽  
pp. 1610
Author(s):  
Gang Hu ◽  
Kejun Wang ◽  
Liangliang Liu
Keyword(s):  
Chaotic System ◽  
Analysis Tool ◽  
Weak Signal ◽  
Acoustic Detection ◽  
Third Order ◽  
Radiated Noise ◽  
Detection Model ◽  
The Time Domain ◽  
C0 Complexity ◽  
Complexity Algorithm

This paper proposes a new detection model of a weak signal based on a third-order chaotic system. Using a dynamic analysis tool, such as the Lyapunov exponent and the bifurcation diagram, variations of dynamic behavior can be observed, and the weak signal underwater can be picked up. In order to improve the observability of detection signals in the time domain and frequency domain, the spectral entropy complexity algorithm (SE) and C0 complexity algorithms are used to analyze and extract the weak signal. The experimental results show that the spectrum extraction based on the complexity algorithm can accurately reflect the dynamic characteristics of the detected signal. It provides the theoretical direction and experimental data support for the application of the chaotic system in the field of acoustic detection.

scholarly journals On the nature of rainfall intermittency as revealed by different metrics and sampling approaches

2013 ◽  
Vol 17 (1) ◽  
pp. 355-369 ◽  
Author(s):  
G. Mascaro ◽  
R. Deidda ◽  
M. Hellies
Keyword(s):  
Scale Invariance ◽  
Weather Forecasting ◽  
Rainfall Variability ◽  
Analysis Tool ◽  
Systematic Analysis ◽  
Local Climate ◽  
Rainfall Occurrence ◽  
Frontal Systems ◽  
Intensity Fluctuations ◽  
The Time Domain

Abstract. A general consensus on the concept of rainfall intermittency has not yet been reached, and intermittency is often attributed to different aspects of rainfall variability, including the fragmentation of the rainfall support (i.e., the alternation of wet and dry intervals) and the strength of intensity fluctuations and bursts. To explore these different aspects, a systematic analysis of rainfall intermittency properties in the time domain is presented using high-resolution (1-min) data recorded by a network of 201 tipping-bucket gauges covering the entire island of Sardinia (Italy). Four techniques, including spectral and scale invariance analysis, and computation of clustering and intermittency exponents, are applied to quantify the contribution of the alternation of dry and wet intervals (i.e., the rainfall support fragmentation), and the fluctuations of intensity amplitudes, to the overall intermittency of the rainfall process. The presence of three ranges of scaling regimes between 1 min to ~ 45 days is first demonstrated. In accordance with past studies, these regimes can be associated with a range dominated by single storms, a regime typical of frontal systems, and a transition zone. The positions of the breaking points separating these regimes change with the applied technique, suggesting that different tools explain different aspects of rainfall variability. Results indicate that the intermittency properties of rainfall support are fairly similar across the island, while metrics related to rainfall intensity fluctuations are characterized by significant spatial variability, implying that the local climate has a significant effect on the amplitude of rainfall fluctuations and minimal influence on the process of rainfall occurrence. In addition, for each analysis tool, evidence is shown of spatial patterns of the scaling exponents computed in the range of frontal systems. These patterns resemble the main pluviometric regimes observed on the island and, thus, can be associated with the corresponding synoptic circulation patterns. Last but not least, we demonstrate how the methodology adopted to sample the rainfall signal from the records of the tipping instants can significantly affect the intermittency analysis, especially at smaller scales. The multifractal scale invariance analysis is the only tool that is insensitive to the sampling approach. Results of this work may be useful to improve the calibration of stochastic algorithms used to downscale coarse rainfall predictions of climate and weather forecasting models, as well as the parameterization of intensity-duration-frequency curves, adopted for land planning and design of civil infrastructures.

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.

The Effects of Flare and Overhangs on the Motions of a Yacht in Head Seas

1993 ◽  
Author(s):  
John C. Kuhn ◽  
Eric C. Schlageter
Keyword(s):  
Nonlinear Differential Equations ◽  
Equations Of Motion ◽  
Linear Equations ◽  
Order Effects ◽  
Third Order ◽  
Numerical Work ◽  
Strip Theory ◽  
Hull Forms ◽  
The Time Domain ◽  
The Impact

The coupled heave and pitch motions of hull forms with flare and overhangs are examined numerically. The presence of flare and overhangs is numerically modelled with nonlinear hydrostatic and Froude-Krylov forces based on integrals over the instantaneous wetted surface. Forces due to radiation and diffraction are computed with a linear strip-theory. These forces are combined in two coupled nonlinear differential equations of motion that are solved in the time domain with a fourth-order Runge-Kutta integration method. An assessment of the impact of flare and overhangs on motions is obtained by comparing these nonlinear solutions with solutions of the traditional linear equations of motion, which do not contain forces due to flare and overhangs. For an example based on an International America's Cup Class yacht design, it is found that the nonlinear heave and pitch motions are smaller than the linear motions. This is primarily due to reduced first-order response components, which are coupled with nonlinear response components. Comparisons of these results with towing tank data demonstrate that the nonlinear procedure improves prediction quality relative to linear results. In support of this numerical work, the hydrostatic and Froude­Krylov force integrals are expanded in Taylor series with respect to wave elevation. These results indicate how hydrostatic and Froude-Krylov forces change with changing flare and overhang angles, revealing that sectional slope has second and third-order effects on forces while sectional curvature and overhang angles produce third-order effects.

scholarly journals Research on a Tool Wear Monitoring Algorithm Based on Residual Dense Network

Symmetry ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 809 ◽  
Author(s):  
Yiting Li ◽  
Qingsheng Xie ◽  
Haisong Huang ◽  
Qipeng Chen
Keyword(s):  
Tool Wear ◽  
Cutting Tool ◽  
Detection Accuracy ◽  
Dense Network ◽  
Residual Network ◽  
Detection Model ◽  
Acceleration Sensors ◽  
Wear Monitoring ◽  
The Time Domain ◽  
Monitoring Algorithm

To accurately and efficiently detect tool wear values during production and processing activities, a new online detection model is proposed called the Residual Dense Network (RDN). The model is created with two main steps: Firstly, the time-domain signals for a cutting tool are obtained (e.g., using acceleration sensors); these signals are processed to denoise and segmented to provide a larger number of uniform samples. This processing helps to improve the robustness of the model. Secondly, a new deep convolutional neural network is proposed to extract features adaptively, by combining the idea of a recursive residual network and a dense network. Notably, this method is specifically tailored to the tool wear value detection problem. In this way, the limitations of traditional manual feature extraction steps can be avoided. The experimental results demonstrate that the proposed method is promising in terms of detection accuracy and speed; it provides a new way to detect tool wear values in practical industrial scenarios.

Multi-scroll fractional-order chaotic system and finite-time synchronization

2022 ◽  
Author(s):  
Shaohui Yan ◽  
Qiyu Wang ◽  
Ertong Wang ◽  
Xi Sun ◽  
Zhenlong Song
Keyword(s):  
Fractional Order ◽  
Chaotic System ◽  
Finite Time ◽  
Secure Communication ◽  
Analog Circuit ◽  
Time Synchronization ◽  
Hidden Attractor ◽  
Initial Values ◽  
Coexistence Of Attractors ◽  
The Time Domain

Abstract The definition of fractional calculus is introduced into the 5D chaotic system, and the 5D fractional-order chaotic system is obtained. The new 5D fractional-order chaotic system has no equilibrium, multi-scroll hidden attractor and multi-stability. By analyzing the time-domain waveform, phase diagram, bifurcation diagram and complexity, it is found that the system has no equilibrium but is very sensitive to parameters and initial values. With the variation of different parameters, the system can produce attractors of different scroll types accompanied by bursting oscillation. Secondly, the multi-stability of the hidden attractor is studied. Different initial values lead to the coexistence of attractors of different scroll number, which shows the advantages of the system. The correctness and realizability of the fractional-order chaotic system are proved by analog circuit and physical implement. Finally, because of the high security of multi-scroll attractor and hidden attractor, finite-time synchronization based on the fractional-order chaotic system is studied, which has a good application prospect in the field of secure communication.

Analysis of Constraint Configurations in Mechanical Assembly via Screw Theory

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Leonard Rusli ◽  
Anthony Luscher ◽  
James Schmiedeler
Keyword(s):  
Degrees Of Freedom ◽  
Screw Theory ◽  
Analysis Tool ◽  
Mechanical Assembly ◽  
Third Order ◽  
Analysis Methodology ◽  
Assembly Features ◽  
Reaction Forces ◽  
Attachment Level

The essential function of a mechanical assembly is the removal of degrees of freedom (DOF) to enable the transfer of load between two bodies. Assembly constraint features serve to provide this DOF removal, so their locations and orientations greatly affect the quality of an assembly as measured by its ability to resist relative motion between the parts. This paper addresses attachment-level design in which design decisions are made to establish the types, locations, and orientations of assembly features. The analysis methodology in this paper models assembly features such as point, pin, line, and plane constraints with equivalent first, second, and third order wrench systems. The set of relative motions to be evaluated is generated by composing from among these constraints a five-system pivot wrench combination to which a freedom screw motion is reciprocal. The effectiveness of each constraint to resist these motions is calculated as the ratio of the reaction forces at each resisting constraint to the input wrench magnitude. Based on these resistance values, multiple rating metrics are calculated to rate the overall assembly’s performance in resisting the motion. This work represents the first tool available to analyze a constraint configuration’s effectiveness to resist motion with a quantitative metric. Case studies are presented to demonstrate the utility of the analysis tool.

Simulating Riser VIV in Current and Waves Using an Empirical Time Domain Model

2017 ◽  
Author(s):  
Mats J. Thorsen ◽  
Svein Sævik
Keyword(s):  
Frequency Domain ◽  
Vortex Shedding ◽  
Time Domain ◽  
Theoretical Background ◽  
Domain Model ◽  
Wave Period ◽  
Time Variability ◽  
Analysis Tool ◽  
Load Model ◽  
The Time Domain

The theoretical background of an empirical model for time domain simulation of VIV is reviewed. This model allows the surrounding flow to be time varying, which is in contrast to the traditional frequency domain tools. The hydrodynamic load model consists of Morison’s equation plus an additional term representing the oscillating effect of vortex shedding. The magnitude of the vortex shedding force is given by a dimensionless coefficient, and this force is assumed to act perpendicular to the relative velocity between the cylinder and the fluid. The time variability of the vortex shedding force is described by a synchronization model, which captures how the instantaneous frequency reacts to cylinder motion. The parameters in the time domain load model are calibrated against a commonly used frequency domain VIV analysis tool, VIVANA. To do this, a finite element model of a vertical tensioned riser is established, and the structure is exposed to a linearly sheared flow. Key results such as cross-flow displacements along the riser, frequency content, r.m.s. of bending stresses and mean in-line displacements are compared, and it is shown that the frequency and time domain methods are close to equivalent in this simple case with stationary flow. Finally, the time domain model is utilized to study VIV of a riser subjected to regular waves. The characteristics of wave induced VIV are discussed in light of the simulation results. It is seen that VIV is excited in the zone close to the surface, and the energy is transported downwards as traveling waves. The vibrations typically build up as the horizontal water particle velocity is high, and die out as the velocity decreases. The effect of varying the wave amplitude and period is investigated, and it is found that the dominating frequency, mode and r.m.s. stresses increase together with the wave height. The effect of the wave period is however more complicated. For example, reducing the wave period increases the dominating mode but decreases the displacements. Hence the stress may increase or decrease, depending on which of these effects are strongest.

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