Transit Draft Heave and Pitch Motion Analysis of the Mobile Offshore Base (MOB) Using Reverse MI/SO Techniques

2002 ◽  
Author(s):  
Jeffrey Falzarano ◽  
Jun Cheng ◽  
William Rodrigues
Keyword(s):  
System Modeling ◽  
Design Feature ◽  
Statistical Signal Processing ◽  
Time Frame ◽  
Static Stability ◽  
Green Water ◽  
Naval Research ◽  
Non Linear ◽  
Mobile Offshore Base ◽  
Non Linear System

A major design feature of the Mobile Offshore Base (MOB) is its ability to transit anywhere in the world in the required time frame. This means that the MOB must be able to transit in severe environmental conditions. In these extreme sea conditions, a primary cause for concern is the large accelerations that the vessel motions might experience due to the high static stability of the MOB at Transit Draft. Furthermore, since the vessel has minimum freeboard in this condition, it is exposed to green water over the pontoon tops. The submergence of the pontoon deck causes a considerable loss in the vessel’s restoring moment. These concerns have warranted a study by the Office of Naval Research into the Transit Draft Dynamics of the MOB. A part of the research in progress involves the development of a non-linear system modeling and optimization tool utilizing Reverse MI/SO (Multiple-Input/Single Output) techniques. Reverse MI/SO is based on the statistical signal processing of the recorded time histories of the excitation and response of the non-linear multi-degree-of-freedom system. This method of analysis is functional and reliable in identifying an ideal representation of the linear and non-linear terms of the system under consideration. Reverse MI/SO is a frequency domain analysis technique that also provides coherence functions for each of the terms in the model enabling an evaluation of the correctness of the proposed integro-diffrential equation of motion representing the system.

System Identification of Nonlinear Coupled Ship/Offshore Platform Dynamics in Beam Seas

2003 ◽  
Author(s):  
Jun Cheng ◽  
Jeffrey M. Falzarano
Keyword(s):  
System Modeling ◽  
Statistical Signal Processing ◽  
Time Frame ◽  
Static Stability ◽  
Green Water ◽  
Naval Research ◽  
Strong Nonlinearity ◽  
Nonlinear System Modeling ◽  
Beam Seas ◽  
Non Linear

The Mobile Offshore Base (MOB) is designed to transit to anywhere in the world in the required time frame. This means that the MOB must be able to transit in severe environmental conditions. In these extreme sea conditions, a primary cause for concern is the large accelerations that the vessel motions might experience due to the high static stability of the MOB at Transit Draft. Furthermore, since the vessel has minimum freeboard in this condition, it is exposed to green water over the pontoon tops. The submergence of the pontoon deck causes a considerable loss in the vessel’s restoring moment. These concerns have warranted a study by the Office of Naval Research into the Transit Draft Dynamics of the MOB. During the research of MOB dynamical properties, a nonlinear system modeling and optimization tool utilizing Reverse MI/SO (Multiple-Input / Single Output) techniques was developed and applied to different aspects of MOB dynamics analysis. MISO is based on statistical signal processing of the recorded time histories of the excitation and response of the non-linear multi-degree-of-freedom system. This method of analysis is functional and reliable in identifying an optimum representation of the linear and non-linear parameters of the system under consideration. In this paper, we analyze the model testing data in beam seas using the Reverse MISO technique. We expected to identify significant nonlinear roll damping for the nonlinear integro-differential equation as is the case with ships. Instead, a significant nonlinear heave damping related with the nonlinear relative heave velocity has been found during the analysis. This reminds us again that due to the strong nonlinearity of MOB motions in the severe sea ways, nonlinear analysis methods such as Reverse MISO are important and need to be applyed in order to fully identify the dynamics of the MOB motion.

Transit Draft Heave and Pitch Motion Analysis of the Mobile Offshore Base (MOB) Using Reverse MI/SO Techniques

2004 ◽  
Vol 126 (1) ◽  
pp. 16-25 ◽  
Author(s):  
Jeffrey Falzarano ◽  
Jun Cheng ◽  
William Rodrigues
Keyword(s):  
Large Amplitude ◽  
System Modeling ◽  
Design Feature ◽  
Statistical Signal Processing ◽  
Time Frame ◽  
Green Water ◽  
Ship Motions ◽  
Naval Research ◽  
Pitch Motion ◽  
Mobile Offshore Base

A major design feature of the Mobile Offshore Base (MOB) is its ability to transit anywhere in the world in the required time frame. This means that the Single Base Units (SBU’s) of the MOB must be able to transit in severe environmental conditions. In these extreme sea conditions, a primary cause for concern is the large accelerations that the vessel motions might experience due to the high static stability of the MOB at Transit Draft. Furthermore, since the vessel has minimum freeboard in this condition, it is exposed to green water over the pontoon tops. The submergence of the pontoon deck causes a considerable loss in the vessel’s restoring moment. These concerns have warranted a study by the Office of Naval Research into the Transit Draft Dynamics of the MOB. A part of the research in progress involves the development of a nonlinear system modeling and optimization tool utilizing Reverse MI/SO (Multiple-Input/Single Output) techniques. Reverse MI/SO is based on the statistical signal processing of the recorded time histories of the excitation and response of the nonlinear multi-degree-of-freedom system. This method of analysis is functional and reliable in identifying an ideal representation of the linear and nonlinear terms of the system under consideration. Reverse MI/SO is a frequency domain analysis technique that also provides coherence functions for each of the terms in the model enabling an evaluation of the correctness of the proposed integro-diffrential equation of motion representing the system. In this paper we analyze the large amplitude heave and pitch motion of the MOB. It is a well-known fact in linear ship motions theory that for a symmetric ship with zero forward speed the cross-coupling added mass and damping coefficients are zero [1]. However, for large amplitude (nonlinear) motions of the MOB, we find these linear coefficients to be non-zero.

scholarly journals Non-linear system modeling using LSTM neural networks

2018 ◽  
Vol 51 (13) ◽  
pp. 485-489 ◽  
Author(s):  
Jesús Gonzalez ◽  
Wen Yu
Keyword(s):  
Neural Networks ◽  
Linear System ◽  
System Modeling ◽  
Non Linear ◽  
Non Linear System

A novel LSSVM-L Hammerstein model structure for system identification and nonlinear model predictive control of CSTR servo and regulatory control

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Akshaykumar Naregalkar ◽  
Subbulekshmi Durairaj
Keyword(s):  
Linear System ◽  
Regulatory Control ◽  
Hammerstein Model ◽  
Support Vector ◽  
Model Structure ◽  
Linear Dynamics ◽  
Vector Machines ◽  
Non Linear ◽  
Laguerre Filters ◽  
Non Linear System

Abstract A continuous stirred tank reactor (CSTR) servo and the regulatory control problem are challenging because of their highly non-linear nature, frequent changes in operating points, and frequent disturbances. System identification is one of the important steps in the CSTR model-based control design. In earlier work, a non-linear system model comprises a linear subsystem followed by static nonlinearities and represented with Laguerre filters followed by the LSSVM (least squares support vector machines). This model structure solves linear dynamics first and then associated nonlinearities. Unlike earlier works, the proposed LSSVM-L (least squares support vector machines and Laguerre filters) Hammerstein model structure solves the nonlinearities associated with the non-linear system first and then linear dynamics. Thus, the proposed Hammerstein’s model structure deals with the nonlinearities before affecting the entire system, decreasing the model complexity and providing a simple model structure. This new Hammerstein model is stable, precise, and simple to implement and provides the CSTR model with a good model fit%. Simulation studies illustrate the benefit and effectiveness of the proposed LSSVM-L Hammerstein model and its efficacy as a non-linear model predictive controller for the servo and regulatory control problem.

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