Thesis
Control on multiple floating bodies
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2024
- Thesis identifier
- T16931
- Person Identifier (Local)
- 201977354
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Floating multi-body systems include different types of structures, such as arrays of wave energy converters (WECs) that extract energy from their interaction with the ocean waves, floating hybrid platforms requiring stabilisation of their main structure, and photovoltaics whose overall movement needs to be reduced for best energy capture. These systems exhibit sophisticated dynamics in sea conditions. The control of sucha system is a topic that has rarely been investigated in previous research. This thesis aims to address the challenge of controlling multiple floating bodies with mechanical connections by presenting the development and application of a novel optimal control strategy. The first objective is to overcome the challenge presented by the complex behaviour of multiple floating bodies in waves. In the dynamic equation, the wave-induced radiation force was described by a convolution term using Cummin’s impulse response function (IRF). Frequency domain identification (FDI) was adopted to estimate the convolution term with hydrodynamic parameters, as an expression of the linear representation. The mechanical connections within the system were coupled with the dynamic equation using constraint matrix method, and effectively reduced the degreesof freedom (DoFs) in the system. The state-space representation of dynamic equation provides a computationally efficient framework and benefits the integration of control forces into the system model. Upon establishing the dynamic equation of multiple floating bodies, the optimalcontrol strategy, based on Pontryagin’s Maximum Principle (PMP), can be applied to the system. This involves iterative optimisation of objective functions over a specified time horizon. A key component of the present approach is the implementation of declutching control, an effective method for exerting control force on multiple floating bodies. Its control force is a discrete function varying between 0 and a constant, typically generated by the damping effect of power take-off (PTO) system between bodies.The optimal declutching control method was adapted for different application scenarios, depending on the formulation of dynamic equation and the selection of objective functions. In the case of hinged boxes, the results in relative angle and heave motion at the hinge point are compared with published results. The good agreement of these results validated the accuracy of multiple floating bodies’ dynamic model. The efficiency of the control method was evident in its capacity to either minimise or maximiseselected objective function across a wide range of wave frequencies. Declutching control demonstrated good ability in tuning the phase between multiple floating bodies. Additionally, the control strategy showed robust adaptability to irregular waves and extendibility in systems including three or more bodies. In cases involving the control of floating platforms, the objective function was set as the minimisation of platform’s motion. An auxiliary structure was connected to the platform to construct the floating multi-body system. A crucial aspect of this system is the damping coefficient of the PTO between the bodies, which is instrumental inreducing the motion of the platform at a specific wave frequency. The present control methodology extends this capability, effectively reducing the platform’s motion over a broader range of wave frequencies and under irregular wave conditions. Furthermore, the mitigation of platform motion and the enhancement of PTO power output can be achieved simultaneously, which is described as “killing two birds with one stone”in this research. Subsequent analyses revealed that the initial mass of the auxiliary structure and the damping coefficient of the PTO are also critical factors influencing the efficiency of the control strategy. In cases of WECs, the objective function was set as the maximisation of power output from the PTO system. For multi-body WEC configurations, energy is absorbedthrough the relative motions between adjacent bodies. The control command adjusts the damping force, thereby influencing these relative motions between the bodies. The control effects of two objective functions: the power generated by wave (Pwave) and that absorbed by PTO system (PPTO), were compared in the analysis. The coupling of damping coefficient and relative motion poses a challenge for achieving convergence under the objective function PPTO. This can be potentially addressed by applying alternative optimisation algorithms. In conclusion, this research fills the gap in controlling floating multi-body systems and provides practical guides for their optimisation in various application scenarios.
- Advisor / supervisor
- Yuan, Zhiming
- Resource Type
- DOI
Beziehungen
Objekte
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PDF of thesis T16931 | 2024-05-21 | Öffentlich | Herunterladen |