Optimal Vibration Control Strategy for Offshore Platforms Accounting for AMD Constraints

2004 ◽  
Author(s):  
Chunyan Ji ◽  
Qingmin Meng
Keyword(s):  
Control Algorithm ◽  
Feedback Gain ◽  
Offshore Platforms ◽  
Control Force ◽  
Wave Loading ◽  
Offshore Structure ◽  
H2 Control ◽  
Input Control ◽  
The Mathematical Model ◽  
H2 Optimization

In order to control the excessive vibration of offshore platforms under wave excitations, an H2 control algorithm was presented in this paper. In the present study, noise terms for generating filtered wave loading and accounting for model uncertainty are separated. In addition, in H2 optimization problem, AMD’s capacities are considered by setting the limits of AMD stroke and maximum input control force. And the formulations of such algorithm are described. In order to investigate the feasibility and effectiveness of the proposed method, a numerical example applied to an offshore platform is presented in this paper. The numerical results demonstrate that the proposed algorithm is effective in reducing the vibration of offshore structure when there are some uncertainties in building the mathematical model of the structure. In addition, AMD designed by the proposed method can keep its operation by choosing appropriate feedback gain among several gain candidates based on the AMD limits.

Analysis of Offshore Structures Subjected to Various Types of Sea Wave

2004 ◽  
Author(s):  
K. Kuntiyawichai ◽  
S. Chucheepsakul ◽  
M. M. K. Lee
Keyword(s):  
Finite Element ◽  
Wavelet Analysis ◽  
Dynamic Behaviour ◽  
Time History ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Wave Loading ◽  
Offshore Structure ◽  
Finite Element Software ◽  
Jacket Structures

The principal aim of this paper is to study the dynamic behaviour of offshore platforms subjected to wave loading. A general review of offshore structure, wave loading and their effects on offshore structures are presented. A brief review on the basics of Wavelet analysis is also mentioned in this study. The techniques for modeling wave loading in finite element analyses are described and discussed in detail. A series of 3D analyses were carried out using the ABAQUS finite element software to study the effects on the dynamic response of the change in support conditions at the seabed. The effects of wave height, wave period and wave velocity on platform behaviour were studied. The results from time history analysis are characterized using Wavelet Analysis in order to obtain the response pattern due to wave loading. These analyses allow the frequency response of the jacket structures to be described in the time domain. These results give a clear view on the response of jacket structure. The important parameters on offshore modeling have also been identified and discussed in this paper. The results presented in this study can be used as a guidance for engineer in order to understand the dynamic behaviour of jacket structures subjected to wave loading.

State Estimator of Flow as an Integrated Computational Method With the Feedback of Online Experimental Measurement

1997 ◽  
Vol 119 (4) ◽  
pp. 814-822 ◽  
Author(s):  
Toshiyuki Hayase ◽  
Satoru Hayashi
Keyword(s):  
Mathematical Model ◽  
Turbulent Flows ◽  
Experimental Measurement ◽  
Flow Simulation ◽  
Computational Method ◽  
Feedback Gain ◽  
State Estimator ◽  
Output Measurement ◽  
Real Flow ◽  
The Mathematical Model

This paper deals with a state estimator or simply an observer of flow field. The observer, being a fundamental concept in the control system theory, also has a potential in the analysis of flow related problems as an integrated computational method with the aid of experiment. In the framework of the observer, the state of physical flow is estimated from the mathematical model with the feedback of on-line experimental measurement. A SIMPLER based flow simulation algorithm is used as the mathematical model of the real flow and partial experimental measurement of flow is fed back to the boundary condition through the feedback controller. The existence of the feedback-loop essentially distinguishes the observer from ordinary flow simulations. Time variation of the computational result of the observer is expected to converge exactly to that of the physical flow in the whole flow domain even for unstable turbulent flows. A numerical experiment has been performed to confirm the validity of the proposed observer for a turbulent flow through a duct of square cross section. The physical flow to be estimated is modeled by a numerical solution. Appropriate choice for the proportional feedback gain of the observer results in accelerated convergence of the simulation by a factor of 0.012 and reduced error in estimation of the perturbation velocity by a factor of 0.6 in the whole domain or a factor of 0.3 behind the output measurement plane in comparison with the ordinary flow simulation without feedback.

Increasing the mobility of a high-speed tracked vehicle based on a controlled skid algorithm

2020 ◽  
pp. 29-33
Author(s):  
S. V. Kondakov ◽  
O.O. Pavlovskaya ◽  
I.D. Ivanov ◽  
A.R. Ishbulatov
Keyword(s):  
Mathematical Model ◽  
Dynamic Stability ◽  
Simulation Modeling ◽  
Automatic System ◽  
High Speed ◽  
Control Algorithm ◽  
Loss Of Stability ◽  
Tracked Vehicle ◽  
Hydrostatic Transmission ◽  
The Mathematical Model

A method for controlling the curvilinear movement of a high-speed tracked vehicle in a skid without loss of stability is proposed. The mathematical model of the vehicle is refined. With the help of simulation modeling, a control algorithm is worked out when driving in a skid. The effectiveness of vehicle steering at high speed outside the skid is shown. Keywords: controlled skid, dynamic stability, steering pole displacement, hydrostatic transmission, automatic system, fuel supply. [email protected]

Extreme Response Prediction for Fixed Offshore Structures by Monte Carlo Time Simulation Technique

2016 ◽  
Author(s):  
M. K. Abu Husain ◽  
N. I. Mohd Zaki ◽  
M. B. Johari ◽  
G. Najafian
Keyword(s):  
Monte Carlo ◽  
Statistical Properties ◽  
Simulation Technique ◽  
Random Wave ◽  
Wave Loading ◽  
Offshore Structure ◽  
Sampling Variability ◽  
Time Simulation ◽  
Wide Range ◽  
Extreme Response

For an offshore structure, wind, wave, current, tide, ice and gravitational forces are all important sources of loading which exhibit a high degree of statistical uncertainty. The capability to predict the probability distribution of the response extreme values during the service life of the structure is essential for safe and economical design of these structures. Many different techniques have been introduced for evaluation of statistical properties of response. In each case, sea-states are characterised by an appropriate water surface elevation spectrum, covering a wide range of frequencies. In reality, the most versatile and reliable technique for predicting the statistical properties of the response of an offshore structure to random wave loading is the time domain simulation technique. To this end, conventional time simulation (CTS) procedure or commonly called Monte Carlo time simulation method is the best known technique for predicting the short-term and long-term statistical properties of the response of an offshore structure to random wave loading due to its capability of accounting for various nonlinearities. However, this technique requires very long simulations in order to reduce the sampling variability to acceptable levels. In this paper, the effect of sampling variability of a Monte Carlo technique is investigated.

scholarly journals Vibration Reduction of the Nonlinearly Tufted Carpet Yarn by a Modified Sliding Mode Control Method

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Shuang Huang ◽  
Xin Wu ◽  
Peixing Li
Keyword(s):  
Sliding Mode Control ◽  
High Frequency ◽  
Control Algorithm ◽  
Control Method ◽  
Sliding Mode ◽  
Control Law ◽  
Control Force ◽  
Fuzzy Sliding Mode Control ◽  
Mode Control ◽  
Fuzzy Sliding Mode

The yarn vibration causes the yarn tension value to fluctuate, causing a change in the amount of yarn feed, thus causing a deviation of the carpet pile height from the predetermined value. To solve this problem, the sliding mode control algorithm is used to design the sliding mode function and the sliding mode control law. And four variables in the yarn vibration system are controlled by the MATLAB software. For solving the chattering problem of the control law, the sliding mode control law is improved. The fuzzy sliding mode control algorithm based on the quasisliding mode is adopted. The results show that the sliding mode control algorithm is effective, but the sliding mode control force needs to be switched at high frequency and there is severe chattering. The fuzzy sliding mode control algorithm based on quasisliding mode is adopted to achieve better control effect with a smaller force. In addition, the control force does not have high-frequency switching, and the change is relatively stable, which reduces the chattering phenomenon of sliding mode control.

scholarly journals NON-LINEAR DYNAMIC ANALYSIS OF COUPLED SPAR PLATFORM

2013 ◽  
Vol 19 (4) ◽  
pp. 476-491 ◽  
Author(s):  
Mohammed Jameel ◽  
Suhail Ahmad ◽  
A. B. M. Saiful Islam ◽  
Mohd Zamin Zummat
Keyword(s):  
Dynamic Analysis ◽  
Wave Frequency ◽  
Mooring Line ◽  
Wave Loading ◽  
Structural Behaviour ◽  
Offshore Structure ◽  
Spar Platform ◽  
Linear Dynamic ◽  
Long Duration ◽  
Non Linear

Spar platforms are treated as cost-effective and resourceful type of offshore structure in deep water. With increasing depth there are significant changes in its structural behaviour due to coupling of spar hull-mooring line along with radical influence of mooring line damping. So these phenomena should be precisely counted for accurate motion analysis of spar mooring system. In present study, spar platform are configured as a single fully coupled integrated model in ABAQUS/AQUA. Non-linear dynamic analysis in time domain is performed adopting Newmark-β automatic time incrementation technique. Non-linearities due to geometric, loading and boundary conditions are duly considered. Displacement and rotational responses of spar and mooring tensions are obtained during long-duration storm. spar responses get significantly modified and mean position of oscillations gets shifted after longer wave loading. The surge, heave and pitch responses are predominantly excited respectively. The energy contents of PSDs of these responses reduce considerably after long wave loading. Mooring tension responses are significantly different reflecting the damping effect of mooring lines. The pitch response is fairly sensitive to the wave loading duration. After long duration of storm the wave frequency response increases. However, low frequency and wave frequency responses may simultaneously occur due to synchronising sea states.

Influence of Vehicle Model Complexity in Autonomous Emergency Manoeuvre Planning

2008 ◽  
Author(s):  
Daniele Bortoluzzi ◽  
Francesco Biral ◽  
Enrico Bertolazzi ◽  
Paolo Bosetti ◽  
Fabrizio Zendri
Keyword(s):  
Control Algorithm ◽  
Computational Cost ◽  
Model Complexity ◽  
Critical Conditions ◽  
Vehicle Model ◽  
Reduced Order ◽  
Evasive Manoeuvre ◽  
Horizon Planning ◽  
The Mathematical Model

In this paper the effectiveness of an optimal reference manoeuvre is analysed w.r.t. the complexity of the vehicle model used within the optimal control algorithm. The optimal reference manoeuvre is computed by means of a Nonlinear Receding Horizon planning (NRHP) strategy which is based on a simplified vehicle model. The reference manoeuvre is tracked by a controller implemented on a low level faster loop. The system is able to perform autonomously lane change and obstacle avoidance manoeuvres by tracking the computed reference one. The quality of the performed manoeuvres depends on the reference manoeuvre and consequently on the vehicle model used by the NRHP. For manoeuvres with low or mild lateral accelerations reduced order models might yield realistic and reliable reference manoeuvres. However, critical conditions (e.g. evasive manoeuvre) require a manoeuvre planner able to catch highly non-linear vehicle dynamics that characterizes such situations. On the other hand, being the NRHP computational cost generally high and related to the number of equations of the mathematical model, a trade-off between computational efficiency and model complexity is required. The work analyses the reference manoeuvres produced by two vehicle models of increasing complexity used as reference within the NRHP. Optimal planner performance evaluation on evasive manoeuvre in critical conditions will be presented with simulations results.

Integrity Management System for Fixed Offshore Structures Inspection Strategy

2004 ◽  
Author(s):  
Mohamed A. El-Reedy
Keyword(s):  
Management System ◽  
Offshore Structures ◽  
Assessment Method ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Structure Comparison ◽  
Actual Structure ◽  
Existing Structures ◽  
Integrity Management

The GUPCO offshore structure management system was developed as a part of an integrated infrastructure management system. This paper presents a case study of providing an integrity management system for inspection, evaluation and repair of the fixed offshore platforms in Gulf of Suez. The management system procedure is presented focusing on the first step for defining the highly risky weight to the lower risky weight structure based on API criteria for assessment of the existing structures. The risk analysis methodology for developing design and assessment criteria for fixed offshore structure based on consequence of failure is illustrated. In our case study the assessment method is applied for a number of fixed offshore structures. The above methodology is performed after theoretical assessment and then verifying by using ROV subsea inspection for the fixed offshore structure. Comparison between the actual structure performance and the predicting risk assessment for the structure from the model will be studied. The overall management system will be illustrated in scope of predictive maintenance philosophy and reliability for all offshore structures.

On Selection of Control Parameters for H∞ Output Feedback

2005 ◽  
Author(s):  
Chang-Ching Chang ◽  
Chi-Chang Lin
Keyword(s):  
Control System ◽  
Feedback Control ◽  
Output Feedback ◽  
Delay Time ◽  
Output Feedback Control ◽  
Feedback Gain ◽  
Control Force ◽  
Control Parameters ◽  
Structural Responses ◽  
Control Forces

In this paper, an H∞ direct output feedback control algorithm through minimizing the entropy, a performance index measuring the tradeoff between H∞ optimality and H2 optimality, is employed to design the control system in reducing structural responses due to dynamic loads such as earthquakes. The control forces are obtained from the multiplication of direct output measurements by a pre-calculated time-invariant feedback gain matrix. To achieve optimal control performance, the strategy to select both control parameters γ and α is extensively investigated. The decrease of γ or increase of α results in better control effectiveness, but larger control force requirement. For a single degree-of-freedom (SDOF) damped structure, exact solutions of output feedback gains and control parameters are derived. It can be proved analytically that the LQR control is a special case of the proposed H∞ control. Direct velocity feedback control is effective in reducing structural responses with very small number of sensors and controllers compared with the DOFs of the structure. In active control of a real structure, control force execution time delay cannot be avoided. Relatively small delay time not only can render the control ineffective, but also may cause system instability. In this study, explicit formulas to calculate maximum allowable delay time and critical control parameters are derived for the design of a stable control system. Some solutions are also proposed to increase the maximum allowable delay time.

An investigation of fuzzy logic control of flexible robots

Robotica ◽  
1993 ◽  
Vol 11 (4) ◽  
pp. 363-372 ◽  
Author(s):  
Yueh-Jaw Lin ◽  
Tian-Soon Lee
Keyword(s):  
Fuzzy Logic ◽  
Control Algorithm ◽  
Fuzzy Logic Controller ◽  
Robot Manipulator ◽  
Nonlinear Effects ◽  
Control Law ◽  
Flexible Robot ◽  
Control Rules ◽  
Logic Control ◽  
The Mathematical Model

SUMMARYIn this paper a control law, which consists of a fuzzy logic controller plus a nonlinear effects negotiator for a flexible robot manipulator, is presented. The nonlinear effects negotiator is used to enhence the control system's ability in dealing with the uncertainty of the mathematical model. The control algorithm is simple and easy to tune as opposed to conventional control law which requires time consuming gains selections. To obtain fuzzy control rules, an error response plane method is proposed.

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