Parameterization for Nonlinearity of Random Waves Over Slopes

2013 ◽  
Author(s):  
Hongzhou Chen ◽  
Guohai Dong ◽  
Yuxiang Ma
Keyword(s):  
Coastal Region ◽  
Least Square Method ◽  
Peak Frequency ◽  
Least Square ◽  
Wave Transformation ◽  
Random Wave ◽  
Random Waves ◽  
Nonlinear Characteristics ◽  
Wave Flume ◽  
Physical Experiments

Nonlinearity of gravity waves in coastal region plays crucial role in the wave evolution and the sediment transport. Parameterization of the nonlinear characteristics of random waves is an efficient and important way to descript the wave process. It is well known that coastal topography has a key effect on the wave transformation. However, the related previous studies have ignored the slope effects. It is the primary motivation of the research. To implement this aim, physical experiments of random waves propagating over three slopes (1/15, 1/30, 1/45) were carried out in a wave flume with 50m long, 3m wide and used with a water depth of 0.52m. About 20 random wave simulations based on JONSWAP spectra with varying wave height and peak frequency were considered. The wavelet based bispectrum is adopted to obtain the nonlinear parameters, bicoherence, biphase, skewness and asymmetry. On each slope bottoms, several empirical relationships between these parameters and the local Ursell number are derived using the least square method. The results indicate that the bicoherence and the asymmetry of waves relate to the slope. However, the slopes have negligible effect on the formulae of the skewness. Then, the empirical formulae on the bicoherence and asymmetry combining with the bottom slope are constructed.

A Least Square Method for Measurement and Optimisation in Selected Physical Experiments

2005 ◽  
Vol 295-296 ◽  
pp. 681-686 ◽  
Author(s):  
I. Frollo ◽  
P. Andris ◽  
I. Strolka ◽  
L. Bačiak
Keyword(s):  
Magnetic Field ◽  
Input Parameter ◽  
Target Function ◽  
Least Square Method ◽  
Least Square ◽  
Physical Experiments ◽  
Magnetic Field Homogeneity ◽  
Field Homogeneity ◽  
Basic Parameters ◽  
Shim Coils

The scope of this paper is to demonstrate a least square method for optimisation of basic parameters for selected physical experiment design where large input parameter measurement and adjustment is needed. The speed of calculation and experimentally verified results are promising to use this method in many physical projects. We have demonstrated this method for computation of feeding currents of correcting coils for stationary magnetic field used in NMR imaging. A set of linear equation definition and determination of a target function and optimisation computations are presented with procedures that provide optimal values of currents for shim coils. The proposed method, because of its simplicity and speed of computation, is convenient for basic adjustment of the magnetic field homogeneity by the first magnet installation. It is also suitable for periodic testing and magnet inhomogeneity correction for MRI magnets.

Optimization of Hydraulic Efficiency of a Free Surface Semicircular Breakwater Using Wave Screens

2015 ◽  
Author(s):  
Hee Min Teh ◽  
Vengatesan Venugopal
Keyword(s):  
Free Surface ◽  
Wave Climate ◽  
Wave Transmission ◽  
Hydrodynamic Performance ◽  
Wave Transformation ◽  
Random Waves ◽  
Wave Flume ◽  
Wave Measurements ◽  
Test Models ◽  
Semicircular Breakwater

A free surface semicircular breakwater (SCB) with rectangular perforations has been developed to serve as a wave defence structure. Hydrodynamic performance of the breakwaters of various perforations has been thoroughly investigated through wave measurements in a wave flume under random waves. The SCBs were experimentally confirmed to be good anti-reflection wave structures; however, the level of wave transmission at the leeside of the SCBs was rather high particularly when immersed in limited depth and confronted by waves of longer period. This study aims at optimizing the hydraulic characteristics of the SCB by extending its draft by means of wave screens. Three test configurations have been identified in this study, namely (1) the SCB with front screen, (2) the SCB with rear screen, and (3) the SCB with double screens. For each wave screen, three porosities (i.e. 25, 40 and 50%) have been considered in the experiments. The models of shallow immersion depths have been tested in random waves of different characteristics in a wave flume. Wave transformation at different locations upstream and downstream of the test models has been recorded by wave probes. The hydraulic performance of the breakwater are quantified by the coefficients of wave transmission, reflection and energy dissipation, and the wave climate in the vicinity of the breakwater are presented in the form of a ratio relative to the incident wave height. The optimum design of SCB supplemented by truncated wave screen(s) is proposed at the end of the study.

scholarly journals Modelling of the Automatic Depth Control Electrohydraulic System Using RBF Neural Network and Genetic Algorithm

2010 ◽  
Vol 2010 ◽  
pp. 1-16 ◽  
Author(s):  
Xing Zong-yi ◽  
Qin Yong ◽  
Pang Xue-miao ◽  
Jia Li-min ◽  
Zhang Yuan
Keyword(s):  
Neural Network ◽  
Genetic Algorithm ◽  
Distance Measure ◽  
Rbf Neural Network ◽  
Least Square Method ◽  
Least Square ◽  
Nonlinear Characteristics ◽  
Electrohydraulic System ◽  
Comparison Results ◽  
Depth Control

The automatic depth control electrohydraulic system of a certain minesweeping tank is complex nonlinear system, and it is difficult for the linear model obtained by first principle method to represent the intrinsic nonlinear characteristics of such complex system. This paper proposes an approach to construct accurate model of the electrohydraulic system with RBF neural network trained by genetic algorithm-based technique. In order to improve accuracy of the designed model, a genetic algorithm is used to optimize centers of RBF neural network. The maximum distance measure is adopted to determine widths of radial basis functions, and the least square method is utilized to calculate weights of RBF neural network; thus, computational burden of the proposed technique is relieved. The proposed technique is applied to the modelling of the electrohydraulic system, and the results clearly indicate that the obtained RBF neural network can emulate the complex dynamic characteristics of the electrohydraulic system satisfactorily. The comparison results also show that the proposed algorithm performs better than the traditional clustering-based method.

scholarly journals THE DYNAMIC RESPONSE OF SHINGLE BEACHES TO RANDOM WAVES

1988 ◽  
Vol 1 (21) ◽  
pp. 130 ◽  
Author(s):  
K.A. Powell
Keyword(s):  
Field Data ◽  
Wave Reflection ◽  
Relative Magnitude ◽  
Random Wave ◽  
Random Waves ◽  
Wave Flume ◽  
Probabilistic Distribution ◽  
Laboratory Results ◽  
Run Up ◽  
Reflection Characteristics

An extensive laboratory investigation into the behaviour of shingle beaches has been undertaken using a large random wave flume. The study utilised a lightweight material scaled to reproduce the correct permeability of the beach, and the correct threshold and relative magnitude of the onshore/offshore movement. Results are presented describing both the wave reflection characteristics of the beach and the probabilistic distribution of wave run-up crests on the foreshore. Where possible the laboratory results are validated against field data.

Reconstruction and Analysis of Freak Waves Generated From Unidirectional Random Waves

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Yuxiang Ma ◽  
Changfu Yuan ◽  
Congfang Ai ◽  
Guohai Dong
Keyword(s):  
Time Series ◽  
Extreme Event ◽  
Wave Model ◽  
Rogue Waves ◽  
Random Wave ◽  
Random Waves ◽  
Long Distance ◽  
Freak Waves ◽  
Freak Wave ◽  
Wave Flume

Abstract The generation of two freak waves in a broadband and a narrowband random series registered in the experiments of Li, J. X., Li, P. F., and Liu, S. X. (2013, “Observations of Freak Waves in Random Wave Field in 2D Experimental Wave Flume,” China Ocean Eng., 27(5), pp. 659–670) is precisely reconstructed using a fully non-hydrostatic water wave model. The simulation results indicate that even when the background spectral bandwidths are different, the evolution processes of the two freak waves are similar. Both freak waves emerge quickly during the transition from normal states to extreme events. The freak waves can persist over a long distance, i.e., approximately 5 peak wavelengths. The reconstructed time series in both the backward and forward locations at which the freak waves were recorded reveal that the largest freak wave crests were not captured in the experiment. The freak waves gradually emerged from an intense wave group. The waves developed quickly during the transition from a normal state to an extreme event. Very deep troughs were also formed in the evolution process. The two freak waves were actually generated via different spectral bandwidth processes, but the generation mechanisms of the rogue waves were similar. By analyzing the time series of the freak wave groups, the formation of the freak waves is found to result from the combined effect of the dispersive focusing, the third-order resonant wave interactions, and the higher harmonics.

The Study on the Battery Modeling through the Mathematical Modeling Techniques of High-Power Lithium-Polymer Battery for HEV

2012 ◽  
Vol 260-261 ◽  
pp. 543-547
Author(s):  
Dong Woo Seo ◽  
Ja Kyung Koo ◽  
Il Song Kim
Keyword(s):  
High Power ◽  
Least Square Method ◽  
State Equation ◽  
Least Square ◽  
Nonlinear Characteristics ◽  
Battery Modeling ◽  
Lithium Polymer Battery ◽  
Modeling Techniques ◽  
Electrical Vehicle ◽  
Polymer Battery

This paper proposes the battery mathematical for modeling HEV(Hybrid Electrical Vehicle) high-power lithium-polymer battery. The nonlinear characteristics of Lithium Battery are expressed by the state equation. The battery parameters are obtained by the least square method to minimize errors using charge and discharge driving cycle data. The proposed method is verified by the battery cycler.

Charging and Discharging Equalization with Improved Switching Matrix for Series-Connected Battery Pack in EV

2012 ◽  
Vol 260-261 ◽  
pp. 385-390
Author(s):  
Ya Jun Rong ◽  
Chun Yu Hua ◽  
Wen Bin Tang
Keyword(s):  
High Power ◽  
Lithium Battery ◽  
Least Square Method ◽  
State Equation ◽  
Least Square ◽  
Nonlinear Characteristics ◽  
Lithium Polymer Battery ◽  
Electrical Vehicle ◽  
Switching Matrix ◽  
Polymer Battery

This paper proposes the battery mathematical for modeling HEV(Hybrid Electrical Vehicle) high-power lithium-polymer battery. The nonlinear characteristics of Lithium Battery are expressed by the state equation. The battery parameters are obtained by the least square method to minimize errors using charge and discharge driving cycle data. The proposed method is verified by the battery cycler.

Random Extreme Wave Analysis of Deepwater Structures

1989 ◽  
Vol 111 (4) ◽  
pp. 331-336 ◽  
Author(s):  
C. Y. Chen ◽  
S. Armbrust ◽  
C. Llorente
Keyword(s):  
Second Harmonic ◽  
Response Spectrum ◽  
Wave Spectrum ◽  
Peak Frequency ◽  
Random Wave ◽  
Random Waves ◽  
Wave Analysis ◽  
Extreme Wave ◽  
Peak Response ◽  
Two Peaks

This paper reviews various wave analysis procedures for designing deepwater structures under an extreme seastate. The random wave analysis procedures suitable for fixed stiff platforms and compliant towers are discussed. The random wave analysis procedures are then applied to a 1350-ft water depth fixed platform. The reduction in design force levels due to random waves is indicated by comparing with the conventional regular wave analysis approach. The second harmonic effects due to waves can be easily identified through the dynamic response spectrum which has two peaks occurring at the peak frequency of the input wave spectrum and the natural frequency of the structure. The study also shows that the expected extreme value estimated based on the upcrossing approach agrees well with the snapshot peak response derived from a wave record containing an extreme wave height.

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