Collin Howe Hing Tang

Neural-network prediction of riser top tension for vortex induced vibration suppression

Vortex induced vibration (VIV) of marine riser is a significant challenge for the offshore oil and gas industry. Traditional passive suppression devices which are commonly used in permanent production risers to reduce the risks of collision caused by VIV are less practical to be utilized in short-term drilling operation due to expensive overhead cost and installation time factors. This paper studied active control of riser VIV by tuning the tensioner output force (pretension) so that this method can be utilized in short-term operation, such as drilling, without adding additional high-cost systems. A novel active control method by using neural network in tuning top tension of marine riser was studied to examine the effectiveness of VIV suppression. A response surface was derived from VIV experimental data and used to predict the targeted riser top tension to be exerted by the tensioner under different conditions. Reduction of VIV amplitude has been identified for the range of applicability. The findings of this paper have identified the practical scope of active control for riser top tension tuning to suppress VIV.

Prediction on parametric resonance of offshore crane cable for lowering subsea structures

Parametric resonance of offshore crane cable was predicted by using Mathieu equation to provide structural safety prediction during subsea lowering operation. This paper studied the predicting method of offshore crane cable to complement the safety management during subsea lowering operation. The offshore crane cable was modeled as a tensioned long cylindrical structure and Mathieu instability coefficients were utilized to predict the dynamic instability of the structure. Numerical analyses were conducted to predict the parametric resonance of cable and evaluate the sensitivity effective submerged length, dynamic tension variation. Dynamic instability at sub-harmonic 2∶1 unstable region of Mathieu stability diagram potentially creates high risk for lowering operation if the damping coefficient is low. Dynamic tension variation can cause instability of offshore crane cable during passing through wave splash zone and landing subsea payload. The reduction of axial tension variation can stabilize the dynamic of offshore crane cable. Parametric resonance of cable is also sensitive to the total payload. The findings of this paper can enhance structural integrity prediction of offshore crane cable and complement to safety management during subsea lowering operation.

Winch driven active heave compensation for load transfer in overhead crane system

Ocean wave induced vessel heave motion is one of the most important issues in marine operation, especially in the load transfer using overhead crane system. The control of marine overhead crane system aims to regulate the positioning of the cart and the payload continuously, irrespective of the vessel heave motion. This paper presented an integrated motion controller by incorporating the active heave compensator into the winch classical PID motion controller. Through active heave compensator, the gap between the payload and the vessel main deck was continuously monitored and regulated to avoid hammering of the payload into the intended mating object. From the simulation results, the performance of the overhead crane system, assisted by the integrated winch PID motion controller and active heave compensation mechanism, can be significantly improved, even in the presence of ocean wave induced vessel heave motion, with distinctively small payload sway angle and displacement errors.

Underwater Target Tracking of Offshore Crane System in Subsea Operations

Accurate underwater target tracking during subsea lowering is a complex technological problem in offshore installation and deep ocean mining. It involves the real-time motion compensation of both combined effects from flow-induced vibration on the cable-payload and wave-induced motions on the host vessel. A target tracking mechanism for a planar motion was theoretically derived and simulated in this paper under both regular and irregular wave motions. The simulation results have shown that the proposed target tracking system, by using PID controller integrated with hydrodynamic effects of both surface vessel and subsea payload, has followed the movable subsea target with small vicinity. The findings of this paper can be further implemented in the development of automatizing the subsea operations of the offshore crane system.

Position Control of Hydraulic Actuators Using Fuzzy Pulse Width Modulation (PWM)

Hydraulic actuators are widely employed for industrial automation for its high power over weight ratio, functionality in tough operating conditions and low cost. However, the dynamics of hydraulic systems are non-linear and the system subjected to non-smooth and discontinuous non-linearities due to directional change of valve opening, friction, valve overlap and changes of hydraulic pressure acted on valve spool. Taking into account the effect of nonlinear parameter variations such as bulk modulus, compressibility of oil or viscosity of oil, fuzzy logic approach is chosen. Fuzzy control can adapt the inconstant working condition and non-linear system alongside of its robustness. For PWM controlled hydraulic component such as solenoid valve, effective approximation of the flow properties in a solenoid valve is essential. In this paper, the effect of fuzzy logic approach incorporated on pulse width modulation (PWM) controlled hydraulic system is to be investigated and experimentally verified.

Periodic Cubic Spline on Motion of Five-Link Human Bipedal Model Using Nonlinear Predictive Control

This paper studies about the performance of periodic cubic spline applied on the nonlinear predictive control (NPC) based on receding-horizon cost function optimization. The five-link human bipedal model includes a torso and two legs which has a thigh and a shank in every leg. The periodic cubic spline is used to achieve smooth walking trajectories of every joint in the bipedal model in the sagittal plane. The results show that the tracking error after using periodic cubic spline is smaller than the tracking error before using periodic cubic spline.

Robust active heave compensated winch-driven overhead crane system for load transfer in marine operation

Active heave compensation (AHC) is important for load transfer in marine operation using the overhead crane system (OCS). The control of marine OCS aims to continuously regulate the displacement of the cart and the payload sway angle, whilst at the same time, maintaining the gap between the payload and the vessel main deck at a desirable and safe distance. As the marine OHC system is to be operated in a continuously changing environment, with plenty inevitable disturbances and undesirable loads, a robust controller, i.e., active force control (AFC) is thus greatly needed to promote accuracy and robustness features into the controllability of OCS in rough working environment. This paper highlights a novel method for controlling the payload in an OCS based on the combination of both AFC and AHC. Results from the simulation study clearly indicate that the performance of OCS can be greatly improved by the proposed robust AFC controller, as compared with the classical PID controller scheme.