scholarly journals Study on determination method of hydrodynamic coefficient of Marine pile foundation

2020 ◽  
Vol 143 ◽  
pp. 01021
Author(s):  
Jiang Zongnan
Keyword(s):  
Fourier Analysis ◽  
Time History ◽  
Least Square Method ◽  
Wave Force ◽  
Least Square ◽  
Irregular Waves ◽  
Hydrodynamic Coefficient ◽  
Irregular Wave ◽  
Advantages And Disadvantages ◽  
The Moment

The irregular waves are simulated by using standard spectrum. Instantaneous value method, Fourier analysis method, least square method and "harbour hydrological code" are used to determine the moment force of coefficient CM and drag coefficient CD. Then CM and CD that linearized by Borgman L.E. equation are substituted into Morison equation. The time history curve of the wave force on the pile is calculated and compared with the measured wave force data under the action of irregular wave to analyze the advantages and disadvantages of several methods to determine CM and CD. The results show that the comparison between CM and CD determined by Fourier analysis and least square method is practical.

A Study for Statistical Characteristics of Riser Response in Global Dynamic Analysis With Irregular Wave

2014 ◽  
Author(s):  
Yanqiu Zhang ◽  
Zhimin Tan ◽  
Yucheng Hou ◽  
Jiabei Yuan
Keyword(s):  
Dynamic Simulation ◽  
Wave Train ◽  
Time History ◽  
Irregular Waves ◽  
Statistical Characteristics ◽  
Normal Process ◽  
Autocorrelation Functions ◽  
Irregular Wave ◽  
Global Dynamic ◽  
Time Histories

A study was conducted to have a deeper understanding to the statistical characteristics of response of flexible riser in global dynamic simulation with irregular wave. If consider the numerical simulation model as a system and the input wave train as an excitation to it, the time histories of riser load should be the response of the system to the excitation. In order to look the effect of riser configuration and water depth, the study was conducted with three kinds of configuration: Free-Hanging, Lazy-S and Tethered-Wave, which were in different water depths. In order to examine the stationarity and ergodicity of riser response, 100 simulations were performed. Each simulation was performed with a 3-hours-long storm. Except the seeds used to generate the random phases to the wave components, the 100 irregular wave processes for each riser are completely the same. When the number of wave components is enough large, the input irregular wave train should be a stationary normal process. Since the software used for the dynamic simulation is high nonlinear, however, the time history of riser response may not be perfectly stationary normal process. Then different probability distribution theories were applied to fit these time histories and the most fitting one was found out for different riser responses and for different riser configurations. The ensemble autocorrelation functions and the time autocorrelation functions were also examined for both irregular waves and the riser responses. Then the study indicated that both irregular waves and riser responses as random processes should be ergodic stationary. Finally the cross correlations between the irregular waves and riser responses were also examined and it was found that the irregular wave for each riser should be jointly stationary with each response of the riser.

Study on Detection of Epileptic Discharges Based on a Duffing Oscillator Model

2014 ◽  
Author(s):  
Takahiro Murakami ◽  
Yasumi Ukida ◽  
Masami Fujii ◽  
Michiyasu Suzuki ◽  
Takashi Saito
Keyword(s):  
Duffing Oscillator ◽  
Time History ◽  
Least Square Method ◽  
Least Square ◽  
Quantitative Detection ◽  
Model Parameters ◽  
Appearance Time ◽  
Epileptic Discharges ◽  
History Of ◽  
Electrocorticogram Ecog

In order to establish a quantitative detection method for appearance in epileptic discharges (EDs), we propose using the model parameters in a Duffing oscillator, which is a nonlinear mathematical model. Extracting four frequency bands of delta, theta, alpha and beta waves from the time history of the electrocorticogram (ECoG) obtained from rats with induced EDs, we applied a sweep window to the time history for each band. So as to fit the equation for the Duffing oscillator to the time history of the ECoG, we used the least square method to determine the model parameters expressing characteristics of ECoG. The Duffing oscillator has three kinds of vibrational parameters and four kinds of parameters about the amplitude for the driving force with two predominant frequencies contained in ECoG. In order to examine the appearance time of the EDs and the change of ECoG characteristics, we determined the model parameters for each sweep window. When epilepsy occurs, we found that the amount of the parameters related to “conservation”, “dissipation” and “input quantities” increases. On the other hand, the parameter value corresponding to nonlinearity tends to decrease. It is found that the proposed method by the model parameters of the Duffing oscillator can be used in quantitative detection for EDs.

scholarly journals Semi-submersible Offshore Coupled Motion in Irregular Waves

2020 ◽  
Vol 2 (2) ◽  
Author(s):  
Baoji Zhang ◽  
Ying Wang
Keyword(s):  
Return Period ◽  
Simple Algorithm ◽  
Wave Force ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Offshore Platforms ◽  
Wave Direction ◽  
Motion Response ◽  
Irregular Wave ◽  
Control Equation

In order to predict the hydrodynamic performance of semi-submersible offshore platform accurately, based on CFD theory, continuous equation and N-S equation as the control equation, RNG type k-ε model as turbulence model, using the finite difference method to discretize the control equation，using the Semi-Implicit Method for Pressure Linked Equation (SIMPLE) algorithm to solve the control equation，using the VOF method to capture the free surface. The numerical wave tank of irregular wave is established, and the wave force and motion response of the semi-submersible platform under irregular wave are studied. Based on the Jonswap spectrum density function, for a certain area of two irregular waves (South China sea, a-ten-year return period, a-hundred-year return period) sea condition, five wave direction Angle (0 °, 30 °, 45 °, 60 °, 90 °), a total of 10 kinds of conditions of the motion response of semi-submersible platform are simulated, through analysis and comparison of simulation results, the influence law of wave angle, wave period and wave height on platform motion is obtained. Compared with the experimental values, the results of heave and pitch are close to the experimental data under the sea condition of 2, 0 degree wave angles. The research results in this paper can provide reference for the design and motion response prediction of practical semi-submersible offshore platforms.

scholarly journals Optimal attitude determination method in presence of noise and bias on different star sensors

2014 ◽  
Vol 3 (2) ◽  
pp. 155 ◽  
Author(s):  
Amir Moghtadaei Rad
Keyword(s):  
Attitude Determination ◽  
Least Square Method ◽  
Least Square ◽  
Optimal Method ◽  
Input Noise ◽  
Advantages And Disadvantages ◽  
Celestial Navigation ◽  
Stochastic Characteristic ◽  
Determination Methods ◽  
N Vector

There are different attitude determination methods which have been used in satellite and spacecraft by star tracker. Each of these methods have its own advantages and disadvantages depending on their application, stochastic characteristic of noise on sensors (bias or noise), and weight of noise falling on different sensors. The present study has thus explored the major methods from two perspectives: the effect of input noise or bias on each star sensor and the corresponding weight of each noise or bias falling on each sensor. These aspects are compared in each method and the optimal method according to each condition is introduced. N Vector, Triad, Quest, Q method and least square method are the methods studied and simulated in this article. Finally, a comparison is made between the methods and the optimal method is introduced theoretically and practically. Keywords: Attitude Determination, Celestial Navigation, Triad, Quest, Least Square, Satellite.

scholarly journals STUDY OF STATISTICAL CHARACTERISTICS OF IRREGULAR WAVE PRESSURE ON A COMPOSITE BREAKWATER

1986 ◽  
Vol 1 (20) ◽  
pp. 131
Author(s):  
Chien-Kee Chang ◽  
Ching-Her Hwang
Keyword(s):  
Pressure Distribution ◽  
Wave Height ◽  
Wave Force ◽  
Shock Pressure ◽  
Irregular Waves ◽  
Statistical Characteristics ◽  
Wave Forces ◽  
Incoming Wave ◽  
Wave Pressure ◽  
Irregular Wave

Wave pressure is the most important external force for the design of breakwater. During recent years, there has been considerable development in the technology of vertical face breakwater; however, there is no reliable method to compute wave forces induced by irregular waves. The purpose of this study is to obtain statistical characteristics of irregular wave pressure distribution from the data of model tests. The results of this study shown that vertical face breakwater under the action of irregular waves, some waves are reflected, so that the next wave breaks a critical distance resulting in a rapidly rising shock pressure on the breakwater. On the average, the wave pressure increase with incoming wave height, but the maximum wave force does not necessarily occur for the largest wave height. It can be occurred for serval larger wave group in an appropiate phase composition. The irregular wave pressure distribution on the breakwater is quite uniform; the ratio of tested and calculated wave pressures decreases with the reduction of relative crest height of breakwater. Coda formula can predict the total horizontal force of the upper part of breakwater quite well except exetreme shock pressure occurred by non-breaking waves. Wave forces calculated by Miche-Rundgren and Nagai wave force formula are about 10% cummulated exceeding percentage of wave force obtained from model test.

Dynamic Analysis of Aquaculture Fish Cages in Irregular Waves

2013 ◽  
Author(s):  
Li Li ◽  
Shixiao Fu ◽  
Runpei Li
Keyword(s):  
Time History ◽  
Irregular Waves ◽  
Structural Deformation ◽  
Random Waves ◽  
Irregular Wave ◽  
Beam Elements ◽  
Open Sea ◽  
Structural Deformations ◽  
Aquaculture Fish ◽  
Fish Cages

The aquaculture fish cage encounters random waves in the open sea. Understandings of their dynamic behaviors are important for design of the deepwater fish cages. In this paper, the hydrodynamic responses of a gravity-typed fish cage in irregular waves are studied based on FEM and Morison equations. The floating collar and the bottom ring are modeled by beam elements. Net lines are modeled by truss elements. Hydrodynamic forces are calculated by a modified Morison equation taking the relative motion between the fluid and structure members into account. The displacement responses characters (time history and spectrum) of the fish cage floating collar in random waves are investigated. The response results show some similarities between fish cage in regular waves and irregular waves. Both rigid body motions and flexible structural deformations can be seen of the floating collar and the whole fish cage. The net volume changes with time in irregular wave and also high frequency responses caused by the structural deformation are observed.

Response of guyed tower to irregular waves for linear and nonlinear behaviour of mooring cables

1985 ◽  
Vol 12 (1) ◽  
pp. 200-212 ◽  
Author(s):  
Momen A. Wishahy ◽  
M. Arockiasamy
Keyword(s):  
Finite Element ◽  
Dynamic Response ◽  
Time History ◽  
Element Model ◽  
Irregular Waves ◽  
Wave Forces ◽  
Beam Model ◽  
Nonlinear Behaviour ◽  
Irregular Wave ◽  
Linear And Nonlinear

The dynamic response of a guyed tower to irregular waves has been studied by the finite element method. Hydrodynamic interaction is taken into account by the added water mass concept, and the fundamental frequencies are determined using (i) a lumped-parameter two-dimensional beam model and (ii) a three-dimensional truss finite element model. The effect of the mooring guy lines is simulated using one-dimensional boundary elements. The example structure analyzed is the Exxon test guyed tower erected in water of 89.3 m depth in the Gulf of Mexico. The measured wave height – time history reported by Exxon is used to determine the wave forces. Irregular wave forces are computed using the linearized Morison's equation. The nonlinearity of the mooring system is computed using an iterative technique in which the cable configuration is corrected using successive solutions. The tower response in terms of offset-time history to wave forces is determined for both linear and nonlinear cable behaviour. The computed frequencies and the responses agree reasonably well with the available measured values. Key words: guyed tower, irregular wave forces, linear and nonlinear mooring cable stiffness, dynamic response.

scholarly journals A NEW DESIGN METHOD OF RUBBLE MOUND STRUCTURES

1986 ◽  
Vol 1 (20) ◽  
pp. 161 ◽  
Author(s):  
Cheong-Ro Ryu ◽  
Toru Sawaragi
Keyword(s):  
Design Method ◽  
Wave Train ◽  
Wave Force ◽  
Irregular Waves ◽  
Wave Condition ◽  
Irregular Wave ◽  
The Mean ◽  
Rubble Mound ◽  
Run Up ◽  
Wave Control

A new design method of rubble mound structures with stability and wave control consideration is proposed, by which the reduction of wave reflection and run-up and increase in rubble stability are assured under the given wave conditions. Wave control and stability increasing functions due to change of the slope shape of rubble mound structures are discussed on the basis of the experimental results for regular and irregular waves. The new design formula developed here considered the allowable percentage of damage and the wave grouping effects on rubble stability using a new assumption of the mean run-sum as an index of the irregular wave force. The run-sum is defined as the energy sum of a run satisfying a critical wave condition and the mean run-sum is the mean of run-sum for a irregular wave train.

scholarly journals Replacing the observed object in a dynamic measuring system

2020 ◽  
Vol 16 (4) ◽  
pp. 415-422
Author(s):  
Mikhail V. Chashnikov ◽  
◽  
Valentina V. Chashnikova ◽  
Keyword(s):  
Time Moment ◽  
Sufficient Conditions ◽  
Least Square Method ◽  
Continuous Model ◽  
Least Square ◽  
Measuring System ◽  
Time Interval ◽  
Object State ◽  
Dynamic Measuring ◽  
The Moment

In this article the problem of an object state vector estimation is considered. This estimation is obtained by the treatment of measured parameters from several observed objects. In our case, we have two measured parameters that change their values over a certain time interval, but only one of them can be measured at each moment. The problem is to find the moment for switching the measurement from one object to another one in order to minimize the dispersion of one component of the state estimation vector. Previously, the Elfing problem was solved to repeatedly measure fixed parameters using this data in proportion to weight coefficients for processing with the least square method. Then, to change the measured values, a transfer from the discrete model to the continuous one was proposed. This made it possible to obtain an analytical expression dispersion that was dependent of the time moment on the switching. In this article, the estimation of the continuous model error is conducted and the sufficient conditions of using no more than one switching are proven. An example of this method’s application is shown to estimate the sea object coordinates using navigation satellites.

scholarly journals SIMULATION OF EXTREME WAVE INTERACTION WITH MONOPILE MOUNTS FOR OFFSHORE WIND TURBINES

2012 ◽  
Vol 1 (33) ◽  
pp. 22 ◽  
Author(s):  
Feng Gao ◽  
Clive Mingham ◽  
Derek Causon
Keyword(s):  
Wind Farm ◽  
Wave Interaction ◽  
Wave Force ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Offshore Wind Turbine ◽  
Wave Forces ◽  
Extreme Wave ◽  
Irregular Wave ◽  
Run Up

Extreme wave run-up and impacts on monopile foundations may cause unexpected damage to offshore wind farm facilities and platforms. To assess the forces due to wave run-up, the distribution of run-up around the pile and the maximum wave run-up height need to be known. This paper describes a numerical model AMAZON-3D study of wave run-up and wave forces on offshore wind turbine monopile foundations, including both regular and irregular waves. Numerical results of wave force for regular waves are in good agreement with experimental measurement and theoretical results, while the maximum run-up height are little higher than predicted by linear theory and some empirical formula. Some results for irregular wave simulation are also presented.

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