Vessel Heave Motion Research Articles

NMPC-PID control of secondary regulated active heave compensation system for offshore crane

In this paper, an offshore crane driven by a secondary controlled unit (SCU) which offers advantages in terms of high dynamic behavior and energy efficiency is investigated. To counteract the negative impact of the support vessel's heave motion on the station-keeping and trajectory tracking performance of heavy payload, an adaptive robust control scheme for the secondary regulated active heave compensation (AHC) system is proposed based on the combination of a nonlinear model predictive control (NMPC) strategy, a conventional proportional-integral-derivative (PID) control scheme and a vessel heave motion prediction algorithm. The motivation of utilizing the PID-based control structure is given by the excellent resistance against irregular external disturbances and robust capability to eliminate the uncertainties, with real-time tuning gains provided by the NMPC synthesized with the autoregressive integrated moving average (ARIMA) model to ensure optimal evolution that satisfies state and input constraints while accounting for model nonlinearities. Comparative simulation studies in the practical Simulink-based mechanical-electrical-hydraulic research system demonstrate the superior tracking and heave compensation performance, strong robustness, constraint satisfaction, and energy efficiency of the proposal.

Prediction about the vessel’s heave motion under different sea states based on hybrid PSO_ARMA model

In order to solve the problem of control performance degradation caused by time delay in the wave compensation control system, the vessel heave motion displacement needs multi-step predictability because different wave compensation control systems have different delay response times. Inspired by the flexible and powerful optimization capability of the Particle Swarm Optimization (PSO) algorithm, this paper proposes a hybrid model of PSO algorithm and autoregressive moving average (ARMA) model to predict the vessel heave motion at different sea states. The fitness function for the ARMA model parameter optimization problem is formulated through the error function created by residuals squares sum, and the optimization of the ARMA prediction model parameter value is carried out with an effective global search technique based on the PSO algorithm. Simulations are performed with filed data, the results show that the PSO algorithm optimizing the ARMA model parameters to predict vessel heave motion is effective and it can get satisfying precision. In addition, the PSO_ARMA prediction model has excellent robustness, it can not only adapt to the prediction of vessel heave motion under certain conditions but also adapt to the prediction of various sea states.

Dynamic behavior of lifting pipe with equivalent model under mining vessel heave motion

Dynamic behavior of lifting pipe with equivalent model under mining vessel heave motion

Hierarchical NMPC–ISMC of active heave motion compensation system for TMS–ROV recovery

This study reveals the operating risk of cable breaking when the TMS–ROV recovery is carried out beneath rough ocean waves. To release the negative impact of the support vessels vertical heave motion on the station-keeping and position tracking performance of TMS, a robust hierarchical control scheme for a hydraulic-driven winch-based active heave compensation (AHC) system is proposed based on the combination of a nonlinear model predictive control (NMPC) strategy, an integral sliding mode control (ISMC) scheme and a vessel heave motion prediction algorithm. The motivation of utilizing the ISMC-based internal level combined with the integral state transformation technique is given by the robust capability to eliminate the uncertainties, which provides the nominal model for NMPC-based external level to guarantee the optimal evolution satisfying the state and input constraints and resisting the dynamical hysteresis caused by the employed extremely long cable length for deep-sea operation. Comparative simulation studies contribute to the analysis of the surge in cable tension during the TMS–ROV recovery and demonstrate the superior tracking and heave compensation performance, strong robustness and constraint satisfaction of the proposal.

Short-Term Prediction in Vessel Heave Motion Based on Improved LSTM Model

In order to solve the problem of control performance degradation caused by time delay in wave compensation control system, predicting vessel heave motion can be the input vector of the control system to alleviate time delay problem. The vessel heave motion belongs to the problem of time series, this paper proposes an improved Long Short-Term Memory (LSTM) model with a random deactivation layer (dropout), which can deal with the time series problem very well. In order to obtain the vessel heave motion, this paper establishes a wave model suitable for marine operation, and solves the vessel heave motion through the mathematical model of vessel motion. Finally, the paper predicts the vessel heave motion in a short predicted time series. In the process of obtaining the prediction effect of vessel heave motion, the Back Propagation (BP) neural network and the standard LSTM neural network are used to compare with the improved LSTM neural network. While the predicted time series is 0.1 s at sea state 3, the mean absolute percentage (MAPE) errors of BP neural network in the prediction of vessel heave motion is $1.06\times 10^{-2}\%$ , the standard LSTM in the prediction of heave motion is $1.43\times 10^{-4}\%$ , the improved LSTM in the prediction of heave motion is $7.51\times 10^{-6}\%$ . The improved LSTM improves MAPE by $1.05\times 10^{-2}\%$ compared with the BP and $1.42\times 10^{-4}\%$ compared with the standard LSTM. The prediction results show that the improved LSTM has a strong prediction capability with not easily overfitted in vessel heave motion prediction. The results show that the improved LSTM provides a new idea for vessel motion prediction and solves the problem of time delay, which is useful for the study of stability in marine operations.

Prediction of Vortex-Induced Vibration Response of Deep Sea Top-Tensioned Riser in Sheared Flow Considering Parametric Excitations

Abstract It is widely accepted that vortex-induced vibration (VIV) is a major concern in the design of deep sea top-tensioned risers, especially when the riser is subjected to axial parametric excitations. An improved time domain prediction model was proposed in this paper. The prediction model was based on classical van der Pol wake oscillator models, and the impacts of the riser in-line vibration and vessel heave motion were considered. The finite element, Newmark-β and Newton‒Raphson methods were adopted to solve the coupled nonlinear partial differential equations. The entire numerical solution process was realised by a self-developed program based on MATLAB. Comparisons between the numerical calculation and the published experimental test were conducted in this paper. The in-line and cross-flow VIV responses of a real size top-tensioned riser in linear sheared flow were analysed. The effects of the vessel heave amplitude and frequency on the riser VIV were also studied. The results show that the vibration displacements of the riser are larger than the case without vessel heave motion. The vibration modes and frequencies of the riser are also changed due to the vessel heave motion

Safety Assessment of Heave Compensator Using Multi-Body Dynamics

Heave Compensation system minimizes vessel heave motion during drilling operation of drillship. Heave compensator plays a role as damping form heave motion of drillship such as principle spring of car suspension system. The load transfers on the parts of heave compensator. Stress and deformation of all parts is evaluated to diagnose the stability of the compensator. This study makes a decision on the safety of structure by ANSYS 12.0v workbench.

Heave Motion Estimation of a Vessel Using Acceleration Measurements

AbstractOcean waves continuously disturb every vessel resulting in horizontal and vertical motions. Especially the vertical motion has a significant effect on certain marine applications like subsea lifting operations. Subsea lifts are required for underwater installations on the seabed. Since such operations are normally performed from vessels using offshore cranes, the vertical vessel motion results in excessive dynamic loads acting on the crane structure. Furthermore, an accurate positioning of the load on the seabed is nearly impossible during harsh sea conditions. To avoid these problems active heave compensation systems can be used. These systems actively compensate for the vessel's vertical motion and therefore reduce the dynamic loads acting on the crane structure and enable precise positioning of the load. However, active heave compensation systems always require the knowledge about a vessel's heave motion. This article presents an observer based method to estimate the heave motion of a vessel from accelerometer signals without requiring any vessel specific parameters. The observer model is formulated by a sum of periodic components that approximate the heave motion of a vessel. The parameters of these components are identified online. The identified model is used with an extended Kalman filter to estimate the heave motion with high accuracy. The proposed method is evaluated with simulation and measurement results from an experimental setup.

Basic Research on an Anti-Recoil System of a Deepsea Riser

When a drilling riser is operated, tension is applied to maintain configuration of the riser and protect it from collapse. In the emergency condition, for example drift off or drive off of drilling vessel, the riser is disconnected at top of the BOP which is placed on the sea floor. When disconnected, the riser starts to lift and recoil, and if the tension is not properly reduced the riser hits the vessel and destroy both the vessel and riser. If the tension is reduced too fast, riser can not reach the vessel and riser drops on to the sea floor and destroyed. An anti-recoil system is necessary to protect the riser and vessel from destruction and make the catching successful.In this research response prediction system of disconnected riser is developed considering coupled response of riser and dynamic response of internal and external fluid. Vessel heave motion prediction system is also developed. An algorithm is developed to search catching timing from the both predictions of riser motion and vessel heave motion. To achieve successful catching, the catching timing must satisfy catching condition of no relative displacement, velocity and acceleration. Once the catching timing is found, riser disconnection timing is determined from the predicted riser motion. Feedback control is employed at the final stage of catching to adjust and absorb modeling errors and prediction errors and secure successful catching. Effectiveness of the developed algorithm is verified by simulation calculation.

Active Heave Compensator for Heavy Hanging Body Suspended from Offshore Floating Unit

When a heavy facility or equipment is set on or picked up from the sea bed in deep sea area, it seems to be difficult to keep safety anytime throughout the long operation period, because of the risk of encountering rough sea conditions.Although conventional heave compensator using air spring mechanism has been already applied in such an operation, the compensation performance of such a passive system would not be sufficient against large heave motions in rough sea conditions, and dynamic hook load would come to dangerous level, especially in case of resonance condition of the air spring due to long period heave motions.In this research, it has been studied to stabilize the position of suspended heavy mass in sea water and reduce the dynamic hook load by adding active control force to the passive air spring mechanism.Simplified model tests and corresponding theoretical simulations have been performed and the results are shown in this paper.Tested model consists of vessel part, suspended mass part and heave compensation mechanism part. The responses of those were measured in various wave conditions. Heave compensation mechanism was simplified using AC servo motor controlled so as to simulate the performance of the ideal air spring and also to simulate hybrid mode together with active control force. The command of the active control force is derived from the signals of vertical accelerometer sensing vessel heave motion, and pulse generator sensing relative motion between the vessel and the suspended mass.The following conclusions have been derived by the model tests and corresponding theoretical simulations.(1) Variable hook load in hybrid mode (with active control force) has been reduced to about 1/10 compared with the case of fixed mode, and about 1/3 compared with the case of passive mode (using air spring only).(2) Theoretical simulations have shown good agreement with the tested model results.