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A thrust allocation method was proposed based on a hybrid optimization algorithm to efficiently and dynamically position a semisubmersible drilling rig. That is, the thrust allocation was optimized to produce the generalized forces and moment required while at the same time minimizing the total power consumption under the premise that forbidden zon...
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... Improper allocation may lead to degraded control performance, lower energy efficiency and the increased wear and tear of the actuators. There is a rich literature regarding control allocation for marine surface vessels, commonly referred to as thrust allocation [106][107][108][109][110][111][112][113][114][115][116][117][118][119][120]. In-depth reviews of the literature are given in [121,122]. ...
The main goal of the research is to design an efficient controller for a dynamic positioning system for autonomous surface ships using the backstepping technique for the case of full-state feedback in the presence of unknown external disturbances. The obtained control commands are distributed to each actuator of the overactuated vessel via unconstrained control allocation. The numerical hydrodynamic model of CyberShip I and the model of environmental disturbances are applied to simulate the operation of the ship control system using the time domain analysis. Simulation studies are presented to illustrate the effectiveness of the proposed controller and its robustness to external disturbances.
... As a consequence of sustained interest in the development of underground space, tunnels played a more and more important role in human production activities and life. Hence, drill rigs had been widely used in various construction occasions because of the high automatic and working efficiency [1,2]. ...
In order to improve the performance of slip and reduce the extrusion damage of the drill pipe in the drill rig, the optimization of structural parameters and teeth shape of the slip while clamping the drill pipe had been researched in this article. On the macroscale, the structural parameters of the slip had been optimized with response surface method (RSM) and Multiobjective Genetic Algorithm (MOGA). The optimized result showed that the single weight of the slip had been reduced from 3.99 kg to 2.91 kg and the maximum deformation of the drill pipe was reduced from 3.75 mm on both sides to 2.56 mm on both sides. On the microscale, a mathematical model for the single slip teeth while clamping the drill pipe had been established to give a detailed description to calculate the equivalent coefficient of friction and provide the relationship between the frictional torque with the allowable compression strength. In addition, the finite element model that had been set up by ABAQUS was used to verify the mathematical model, and the comparison of results had shown the accuracy of the mathematical model of the slip teeth while clamping the drill pipe. According to the mathematical model of the slip teeth in the drill rig, while clamping the drill pipe, the optimal shape of the slip teeth in the drill rig was achieved under the following condition: the slope of the slip teeth θ is 60°, the top width of the slip teeth wh is 1.5 mm, and the depth of the slip teeth clamping the drill pipe d is 0.5 mm. The equivalent coefficient of friction fv can be increased from 1.73 to 2.06, and the optimal result fv increases 11.3%.
... However, the search method combining the mutation operator in differential evolution (DE) with the social cognitive function of particle swarm optimization (PSO) is not perfect, and the control parameters need to be tested repeatedly. Hybrid algorithm based on the genetic algorithm (GA) and SQP was proposed by Zhao [15]. Guo proposed a new algorithm combining the biogeography-based optimization (BBO) and PSO [16]. ...
The azimuth thruster is widely used in electric propulsion ships due to its excellent performance. The thrust allocation (TA) method of multi-azimuth thruster is the key technology in ship motion control. The purpose of TA is to accurately distribute the thrust and angle of each thruster to provide the vessel the required force and moment. A TA strategy based on the improved non-dominated sorting genetic algorithm II (INSGA-II) is developed in this study. The algorithm introduces the differential mutation operator in the differential evolution (DE) to replace the polynomial variation in NSGA-II, which improves the local optimization ability of the algorithm. The effectiveness of the TA strategy based on INSGA-II algorithm is illustrated by simulations.
... So the propeller system equipped with multiple propellers constitutes a redundant system, there are multiple combinations of thrust and direction that can meet the force and yaw moment required by ship motion. Then how to select a set of optimal values from these combinations of thrust and direction is the thrust allocation optimization problem of the propeller system [2]. Scholars have proposed various thrust allocation methods for DPS. ...
The pseudo inverse method can not optimize the angle and needs to give the azimuth angle artificially, therefore, when the dynamic positioning system has variable vector propellers and rudder, the pseudo inverse method can not be applied to the full automatic control and cannot realize the optimal exactly. In view of the above problems, considering the propeller and the environment load conditions, a thrust allocation scheme based on the pseudo inverse algorithm with weight is proposed for minimizing the energy consumption in this paper. The thrust allocation scheme distributes the thrust after optimizing the angle. It combines the full-revolving propulsion angle optimization with the thrust optimization to realize the ship thrust allocation reasonably and efficiently, and achieves the minimum energy consumption and wear. Finally, experimental results verify the effectiveness of the proposed method.
... A DP system is over-actuated when the number of available output is higher that the number of control inputs. In particular, for DP purposes, the number of available thrusters on board is over-estimated in order to allow the system to compensate extreme environmental disturbances, as reported in [8] and [16], as well as to manage failures. ...
Dynamic positioning systems are most commonly used in offshore operations. They provide an automated controlling of position and heading of the vessel using its own thrusters to compensate environmental disturbances. The allocation of total required force over the available actuators is a complex task, as DP-systems are over-actuated. Therefore, one of the main challenges faced by the industry is constantly seeking to improve the systems efficiency for both sustainability and economic reasons. Furthermore, it is important to evaluate the performance of a DP vessel under critical conditions. In this paper, the authors aim to compare different thrust allocation logics based on the optimisation of different objective functions. Using a simple validation tool, the authors were able to investigate the overall efficiency of a dynamic positioning propulsion system and its ability to operate when a failure occurs.
... , n), α i is the azimuth angle of i-th thruster, T i,max is the maximum thruster capacity of i-th thruster. Another constraint group is the thrust-variation rate that can be considered as the movable range of thrust per unit time, as in Equation (8). ...
This research, a new thrust-allocation algorithm based on penalty programming is developed to minimize the fuel consumption of offshore vessels/platforms with dynamic positioning system. The role of thrust allocation is to produce thruster commands satisfying required forces and moments for position-keeping, while fulfilling mechanical constraints of the control system. The developed thrust-allocation algorithm is mathematically formulated as an optimization problem for the given objects and constraints of a dynamic positioning system. Penalty programming can solve the optimization problems that have nonlinear object functions and constraints. The developed penalty-programming thrust-allocation method is implemented in the fully-coupled vessel–riser–mooring time-domain simulation code with dynamic positioning control. Its position-keeping and fuel-saving performance is evaluated by comparing with other conventional methods, such as pseudo-inverse, quadratic-programming, and genetic-algorithm methods. In this regard, the fully-coupled time-domain simulation method is applied to a turret-moored dynamic positioning assisted FPSO (floating production storage offloading). The optimal performance of the penalty programming in minimizing fuel consumption in both 100-year and 1-year storm conditions is demonstrated compared to pseudo-inverse and quadratic-programming methods.
Thrust allocation is of great importance for the application of Dynamic Positioning System (DPS). For dynamically positioned vessels, the thrust allocation is formulated as a nonlinear optimization problem, where the demanded forces and moments are distributed among the available thrusters. Both hydrodynamic interaction effects and physical limitations of thrusters affect the thrust generation. Therefore, the thrust allocation algorithm can be improved if these effects are considered. We propose a bivariate thrust efficiency function, dealing with both the forward thruster angle and the rear thruster angle, to describe the thrust loss. The thrust efficiency function is obtained from the model tests and approximated by the Radial Basis Function (RBF) neural network. The consequent thrust allocation problem is solved by the Sequential Quadratic Programming (SQP) algorithm with slack variables. The numerical simulations demonstrate a maximum power reduction of 16.03% compared with the forbidden zone algorithm. The proposed algorithm can also enhance system stability, highlighting the advantages of taking bivariate thrust efficiency function into account.
Application of ship Dynamic-Positioning systems strongly depends on physical ability of actuators (Thrusters) in providing commanded loads. This will consequently introduce some constraints and limitations to Thrust Allocation problem in design and control of such systems. However, there is a special case in which a simple explicit solution could be found by fixing orientation of azimuth thruster relative to vessel regarded as linear model. In this paper, three new alternative approaches based on linear model are introduced. Case study is a time domain simulation of Station-Keeping (instant Point-Tracking) operation for a supply vessel called Northern Clipper in North Sea with Beaufort number 6. As is evident by results, these approaches improve maneuvering performance and power consumption efficiency compared to the conventional linear model. Results show improved robustness of yaw control in Point-Tracking operation and decreased overall consumption of power compared to linear model. Furthermore, it is apparent from the results that these approaches are particularly efficient in tunnel thrusters compared to linear counterpart.
