Flexible Marine Riser Research Articles

Global stabilization of three-dimensional flexible marine risers by boundary control

A method to design a boundary controller for global stabilization of three-dimensional nonlinear dynamics of flexible marine risers is presented in this paper. Equations of motion of the risers are first developed in a vector form. The boundary controller at the top end of the risers is then designed based on Lyapunov's direct method. Proof of existence and uniqueness of the solutions of the closed loop control system is carried out by using the Galerkin approximation method. It is shown that when there are no environmental disturbances, the proposed boundary controller is able to force the riser to be globally exponentially stable at its equilibrium position. When there are environmental disturbances, the riser is stabilized in the neighborhood of its equilibrium position by the proposed boundary controller.

Robust adaptive boundary control of a flexible marine riser with vessel dynamics

In this paper, robust adaptive boundary control for a flexible marine riser with vessel dynamics is developed to suppress the riser’s vibration. To provide an accurate and concise representation of the riser’s dynamic behavior, the flexible marine riser with vessel dynamics is described by a distributed parameter system with a partial differential equation (PDE) and four ordinary differential equations (ODEs). Boundary control is proposed at the top boundary of the riser based on Lyapunov’s direct method to regulate the riser’s vibration. Adaptive control is designed when the system parametric uncertainty exists. With the proposed robust adaptive boundary control, uniform boundedness under the ocean current disturbance can be achieved. The proposed control is implementable with actual instrumentation since all the required signals in the control can be measured by sensors or calculated by a backward difference algorithm. The state of the system is proven to converge to a small neighborhood of zero by appropriately choosing design parameters. Simulations are provided to illustrate the applicability and effectiveness of the proposed control.

Boundary Control of a Coupled Nonlinear Flexible Marine Riser

In this paper, boundary control for a coupled nonlinear flexible marine riser with two actuators in transverse and longitudinal directions is developed to reduce the riser's vibrations. The dynamic behavior of the flexible riser is represented by a distributed parameter system with partial differential equations (PDEs) and the control is applied at the top boundary of the riser based on Lyapunov's direct method to regulate the riser's vibrations. With the proposed boundary control, uniform boundedness under ocean current disturbance, and exponential stability under free vibration condition can be achieved. The proposed control is independent of system parameters, which ensures the robustness of the system to variations in parameters. Numerical simulations for demonstrating the effectiveness of the proposed control are presented.

Active control of flexible marine risers

In this article, active control of flexible marine riser angle and the reduction of forced vibration under a time-varying distributed load are considered using boundary control approach. A torque actuator is introduced in the upper riser package and a boundary control law is designed to generate the required signal for riser angle control and vibration reduction with guaranteed closed-loop stability. Exponential stability can be achieved under the free vibration condition. The proposed control is simple, implementable with actual instrumentation, and is independent of system parameters, thus possessing stability robustness to variations in parameters. The design is based on the partial differential equations of the system, thus avoiding some drawbacks associated with the traditional truncated-model-based design approaches. Numerical simulations are provided to verify the effectiveness of the approach presented.

Boundary control of transverse motion of marine risers with actuator dynamics

This paper presents a boundary controller to reduce transverse motion of flexible marine risers driven by a hydraulic system at the top end of the risers under environmental disturbances induced by waves, wind, and ocean currents. The boundary controller is designed based on Lyapunov's direct method and the backstepping technique. Proof of existence and uniqueness of the solutions of the closed-loop control system is carried out by using the Galerkin approximation method. Simulation results illustrate the effectiveness of the proposed boundary controller.

Boundary Control of flexible marine risers

Abstract A method to design a boundary controller for global stabilization of three-dimensional nonlinear dynamics of flexible marine risers is presented. Equations of motion of the risers are first developed in a vector form. The boundary controller at the top end of the risers is then designed based on Lyapunov's direct method. It is shown that when there are no environmental disturbances, the proposed boundary controller is able to force the riser to be globally exponentially stable at its equilibrium position. When there are environmental disturbances, the riser is stabilized in the neighborhood of its equilibrium position by the proposed boundary controller.

大水深ライザー管のゲインスケジューリング制御によるリエントリー実験について

大水深ライザー管のゲインスケジューリング制御によるリエントリー実験について

速度変動に伴う流体抗力の影響を考慮した大水深ライザー管のゲインスケジューリング制御

In the entry/reentry operation of the flexible marine riser, the operators are required to connect its lower end to the blowout preventer at the seabed quickly with both its top connected angle and its deformation controlled. Because of the hydrodynamical force and the flexibility of the riser, it is very difficult for them to operate it correctly. In the paper, we consider the entry/reentry control problem of the flexible marine riser. Firstly, the governing equation of the flexible marine riser is formulated and transformed to the finite dimensional equation by the mode expansion method. Secondly, for the control problem, we apply LPV (Linear Parameter Varying) technique taking the varying parameter as its upper end velocity which determines the hydrodynamical damping force. Finally, the effectiveness of the LPV technique is shown by numerical simulations, compared with the results by the LTI (Linear Time Invariant) H∞ control

Three-Dimensional Dynamics of a Flexible Marine Riser Undergoing Large Elastic Deformations

The equations of the three dimensional motion of a marine riser undergoinglarge elastic deformations are formulated using Kane's formalism. The riseris modeled using lumped masses connected by extensional and rotationalsprings including structural damping. Surface waves are described by Stokes'second-order wave theory. Fluid-structure coupling is achieved byapplication of the hydrodynamic loads via Morison's equation and added-masscoefficients using the instantaneous relative velocities and accelerationsbetween the fluid field and the riser segments. In the same way, a model forincorporating the effects of vortex-induced lift forces is included. Theeffect of internal flow is included in the model. The detailed algorithm ispresented and the equations are solved using a robust implementation of theRunge–Kutta method provided in MATLAB. The mathematical model and associatedalgorithm are validated by comparing the steady-state equilibriumconfiguration of the riser with special cases of an elastic catenary mooringline and large deflection statics of a cantilever beam. The results ofsample simulations are presented.

Study on Initial Design Method of Underwater Line Structures (2nd Report)

In the previous report, we derived extensible catenary equations and discussed the fundamental characteristics of catenary. We also descrived the ways to solve the equations under various boundary conditions.In this paper, we introduce a program package based on the extensible catenary theory. Next, a simplified dynamic analysis method is shown. The accuracy of calculation by the program package is verified by comparing with the results of tank tests or calculations with other programs. Finally, initial design method of underwater line structures using the program package is shown and typical line structures such as mooring lines, towing lines and flexible marine risers are designed easily applying this method.

A simple and efficient algorithm for the static and dynamic analysis of flexible marine risers

The lumped mass discretization method is used to derive the equations of motion of flexible risers in three dimensional space. Nodal shear forces and bending moments are included in the formulations and fluid loading on the structure is calculated using the Morison equation. A simple model of the sea bed contact for catenary risers is given and tested. Nonlinear equations describing the riser motions are solved in the time domain using the tangent stiffness incremental approach combined with the Wilson-theta numerical integration algorithm. Computational efficiency is improved via a compact ‘profile storage’ technique, used for the assembly of element matrices, given by Taylor [Computer procedures for finite element analysis, in The Finite Element Method (Edited by O.C. Zienkiewicz), 3rd Edn. McGraw-Hill, New York (1977)]. Consideration is also given to natural periods and mode shapes for small oscillations about the static equilibrium position of the riser. Comparison of results with experimental values, analytical solutions and independent results from the published literature show very good agreement.

A Mathematical Model for Dynamic Analysis of a Flexible Marine Riser Connected to a Floating Vessel

A Mathematical Model for Dynamic Analysis of a Flexible Marine Riser Connected to a Floating Vessel