Active Control of a Very Large Floating Beam Structure

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Jia Sheng Yang ◽  
Rui Ping Gao
Keyword(s):  
Control Method ◽  
Direct Method ◽  
Vertical Vibration ◽  
Distributed Parameter ◽  
Bending Rigidity ◽  
Parameter System ◽  
Regular Waves ◽  
Floating Structure ◽  
Boundary Control Method ◽  
Hydroelastic Response

In this paper, a novel boundary control method is investigated to suppress the vertical vibration of a very large floating structure (VLFS) with regular waves. The VLFS can be described as a distributed parameter system with partial differential equation (PDE). The proposed boundary controllers are developed based on Lyapunov's direct method to act on the upstream and downstream ends of the VLFS, respectively. Along with the suitable choice of control parameters, the proposed controllers could stabilize the vertical vibration of the VLFS subjected to regular waves. This study verifies the effectiveness of the proposed control methods to the VLFS. Then, the effects of wave amplitude and bending rigidity on the hydroelastic response of the VLFS are investigated.

The Effect of Bending Stiffness on Hydroelastic Response of VLFS

2014 ◽  
Author(s):  
Wei Wei ◽  
Shixiao Fu ◽  
Fei Guo ◽  
Yuanhua Liang ◽  
Shuhong Chai
Keyword(s):  
Rigid Body ◽  
Traditional Method ◽  
Three Dimensional ◽  
Bending Moment ◽  
Bending Stiffness ◽  
Wave Frequency ◽  
Regular Waves ◽  
Floating Structure ◽  
Hydroelastic Response ◽  
Complex Influence

Owing to the flexibility of ocean structures with large dimension, the hydroelastic theory is more applicable than traditional method of treating the floating structure as a rigid body. To study the factors that influence the hydroelastic responses, a very large floating structure (namely, VLFS) model is chosen to conduct numerical calculations in regular waves with the aid of three dimensional linear hydroelastic code concerning varied bending stiffness and wave frequency. It is found that bending stiffness and wave frequency have a critical but complex influence on relevant hydroelastic results, including generalized displacement, vertical response amplitude and bending moment. More specifically, the effect of bending stiffness on hydroelastic parameters above can be categorized into different phases, and quite different tendencies are observed in each phase.

Vibration Reduction by Active Control of Flexible Marine Riser Angle Subjected to Time-Varying Distributed Force

2016 ◽  
Author(s):  
F. Bakhtiari-Nejad ◽  
A. Azimi
Keyword(s):  
Boundary Control ◽  
Closed Loop ◽  
Direct Method ◽  
Surface Current ◽  
Ocean Surface ◽  
Distributed Parameter ◽  
Time Varying ◽  
Parameter System ◽  
Closed Loop System ◽  
Ocean Surface Current

In this research, boundary control is developed at the upper end of the riser based on the Lyapanuv’s direct method to reduce top angle and transverse vibration of the riser subjected to time-varying disturbance. First, ocean surface current is assumed to be linearly declined to zero from the ocean surface to the ocean floor and then it is assumed to be exponentially declined to zero. The riser is modeled as a distributed parameter system with one partial differential equation (PDE) coupled with boundary conditions (ODE). Since all of the control signals can be measured by sensors or can be calculated by a backwards difference algorithm, so the boundary control is practical and implementable with existing instrumentation. The Lyapunov’s direct method is applied to stability analysis of the closed-loop system. Finally, efficiency of the controller is verified and results of linear and exponential profiles are compared to each other.

scholarly journals Application of Genetic Algorithm Elements to Modelling of Rotation Processes in Motion Transmission Including a Long Shaft

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 115
Author(s):  
Andriy Chaban ◽  
Marek Lis ◽  
Andrzej Szafraniec ◽  
Radoslaw Jedynak
Keyword(s):  
Genetic Algorithm ◽  
Genetic Algorithms ◽  
Fitness Function ◽  
Least Square ◽  
Distributed Parameter ◽  
Parameter Method ◽  
Analytical Mechanics ◽  
Parameter System ◽  
Rotational Systems ◽  
Elastic Elements

Genetic algorithms are used to parameter identification of the model of oscillatory processes in complicated motion transmission of electric drives containing long elastic shafts as systems of distributed mechanical parameters. Shaft equations are generated on the basis of a modified Hamilton–Ostrogradski principle, which serves as the foundation to analyse the lumped parameter system and distributed parameter system. They serve to compute basic functions of analytical mechanics of velocity continuum and rotational angles of shaft elements. It is demonstrated that the application of the distributed parameter method to multi-mass rotational systems, that contain long elastic elements and complicated control systems, is not always possible. The genetic algorithm is applied to determine the coefficients of approximation the system of Rotational Transmission with Elastic Shaft by equivalent differential equations. The fitness function is determined as least-square error. The obtained results confirm that application of the genetic algorithms allow one to replace the use of a complicated distributed parameter model of mechanical system by a considerably simpler model, and to eliminate sophisticated calculation procedures and identification of boundary conditions for wave motion equations of long elastic elements.

scholarly journals Research on Hydroelastic Response of an FMRC Hexagon Enclosed Platform

Symmetry ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1110
Author(s):  
Wei-Qin Liu ◽  
Luo-Nan Xiong ◽  
Guo-Wei Zhang ◽  
Meng Yang ◽  
Wei-Guo Wu ◽  
...  
Keyword(s):  
Time Domain ◽  
Numerical Models ◽  
Structural Response ◽  
Deep Ocean ◽  
Surface Model ◽  
Large Area ◽  
Floating Structure ◽  
Small Depth ◽  
Response Amplitude Operators ◽  
Hydroelastic Response

The numerical hydroelastic method is used to study the structural response of a hexagon enclosed platform (HEP) of flexible module rigid connector (FMRC) structure that can provide life accommodation, ship berthing and marine supply for ships sailing in the deep ocean. Six trapezoidal floating structures constitute the HEP structure so that it is a symmetrical very large floating structure (VLFS). The HEP has the characteristics of large area and small depth, so its hydroelastic response is significant. Therefore, this paper studies the structural responses of a hexagon enclosed platform of FMRC structure in waves by means of a 3D potential-flow hydroelastic method based on modal superposition. Numerical models, including the hydrodynamic model, wet surface model and finite element method (FEM) model, are established, a rigid connection is simulated by many-point-contraction (MPC) and the number of wave cases is determined. The load and structural response of HEP are obtained and analyzed in all wave cases, and frequency-domain hydroelastic calculation and time-domain hydroelastic calculation are carried out. After obtaining a number of response amplitude operators (RAOs) for stress and time-domain stress histories, the mechanism of the HEP structure is compared and analyzed. This study is used to guide engineering design for enclosed-type ocean platforms.

Application of the Mode-Acceleration Technique to the Solution of the Moving Oscillator Problem

1999 ◽  
Author(s):  
Alexander V. Pesterev ◽  
Lawrence A. Bergman
Keyword(s):  
Shear Force ◽  
Series Representation ◽  
Bending Moment ◽  
Static Solution ◽  
Distributed Parameter ◽  
Distributed Parameter System ◽  
Parameter System ◽  
One Dimensional ◽  
Acceleration Technique ◽  
Moving Oscillator

Abstract The problem of calculating the dynamic response of a one-dimensional distributed parameter system excited by an oscillator traversing the system with an arbitrarily varying speed is investigated. An improved series representation for the solution is derived that takes into account the jump in the shear force at the point of the attachment of the oscillator, which makes it possible to efficiently calculate the distributed shear force and, where applicable, bending moment. The improvement is achieved through the introduction of the “quasi-static” solution, an approximation to the desired one, which makes it possible to apply to the moving oscillator problem the “mode-acceleration” technique conventionally used for acceleration of series in problems related to the steady-state vibration of distributed systems. Numerical results illustrating the efficiency of the method are presented.

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