This paper models the large periodic plate structure as Kirchhoff-Love plates and introduces a novel implementation of asymptotic homogenization (NIAH) to enable an efficient calculation of the structural stiffness. Compared to full finite element models, applying NIAH to a unit-cell model greatly reduces computational costs. This paper systematically presents the derivation and finite element formulation of asymptotic homogenization (AH), and the development of NIAH. Benchmark cases, including solid, thin-walled, multi-material plates, and a plate with octagonal holes, are used to validate the NIAH implementation. A series of representative fish cage designs are analyzed to investigate the influence of pontoon components, structural layouts, and material distribution on structural stiffness. To ensure the reliability of the calculations, the choice of unit-cell model and the sensitivity of the results to mesh density and unit-cell size are also discussed.
Large and remote offshore wind farms (OWFs) usually use voltage source converter (VSC) systems to transmit electrical power to the main network. Submarine high-voltage direct current (HVDC) cables are commonly used as transmission links. As they are liable to insulation breakdown, fault location in the HVDC cables is a major issue in these systems. Exact fault location can significantly reduce the high cost of submarine HVDC cable repair in multi-terminal networks. In this paper, a novel method is presented to find the exact location of the DC faults. The fault location is calculated using extraction of new features from voltage signals of cables' sheaths and a trained artificial neural network (ANN). The results obtained from a simulation of a three-terminal HVDC system in power systems computer-aided design (PSCAD) environment show that the maximum percentage error of the proposed method is less than 1%.
The offshore de-oiling process is a vital part of current oil recovery, as it separates the profitable oil from water and ensures that the discharged water contains as little of the polluting oil as possible. With the passage of time, there is an increase in the water fraction in reservoirs that adds to the strain put on these facilities, and thus larger quantities of oil are being discharged into the oceans, which has in many studies been linked to negative effects on marine life. In many cases, such installations are controlled using non-cooperative single objective controllers which are inefficient in handling fluctuating inflows or complicated operating conditions. This work introduces a model-based robust H ∞ control solution that handles the entire de-oiling system and improves the system’s robustness towards fluctuating flow thereby improving the oil recovery and reducing the environmental impacts of the discharge. The robust H ∞ control solution was compared to a benchmark Proportional-Integral-Derivative (PID) control solution and evaluated through simulation and experiments performed on a pilot plant. This study found that the robust H ∞ control solution greatly improved the performance of the de-oiling process.
Floating breakwaters (FBs) are frequently used to protect marinas, fisheries, or other bodies of water subject to wave attacks of moderate intensity. New forms of FBs are frequently introduced and investigated in the literature as a consequence of technological advancements. In particular, a new possibility is offered by High-Density Polyethylene (HDPE) by extruding pipes of large diameters (e.g., 2.5 m in diameter) and with virtually no limit in length (hundreds of meters). By connecting two or three such pipes in a vertical layout, a novel low-cost floating breakwater with deep draft is devised. This note investigates numerically and experimentally the efficiency of this type of multi-cylindrical FBs in evaluating different geometries and aims at finding design guidelines. Due to the extraordinary length of the breakwater, the investigation is carried out in two dimensions. The 2D numerical model is based on the solution of the rigid body motion in the frequency domain, where the hydrodynamic forces are evaluated (thanks to a linear potential flow model), and the mooring forces do not include dynamic effects nor drag on the lines. The numerical predictions are compared to the results of a 1:10 scale experimental investigation. An atypical shape of the wave transmission (𝑘𝑡) curve is found, with a very low minimum in correspondence with the heave resonance frequency. The results essentially point out the influence of the position of the gravity center, the stiffness, and the mutual distance among cylinders on 𝑘𝑡.
The share of renewables in the power system is increasing rapidly. Large offshore wind power plants (OWPPs) are developed at a high pace and conventional fossil fuel-based plants are decommissioned. Consequently, there will be a risk of insufficient amount of power plants providing black start functionality for system restoration after a black out. This paper proposes a STATCOM with a battery energy storage that is located at the point of common connection to an OWPP that together can provide a reliable black start service to the power grid. The concept is demonstrated by using time domain simulations in PSCAD. The STATCOM functionality provides fast and dynamic reactive power management and the battery unit provides active power balancing capability to maintain the frequency within a tolerable range specified by the system operator. The simulation results fulfill the success criteria for the black start and confirm its feasibility for practical implementation.
Objective: To promote the physical and mental health of employees in a maritime setting and provide knowledge and tools to assist seafarers in managing daily challenges.
Materials and methods: The intervention drew on a goal-based approach, including workshops, coaching,health checks, interviews, and questionnaires.
Results: A process evaluation was used to explore intervention challenges and barriers. Results show that an intervention at sea is complex and needs flexibility. Findings varied, and the main challenges were low participation in one group and lack of continuity due to Covid-19. Data showed a significant positive shift in how the crew rated perceived stress and a statistically significant increase in intake of salad, fish, and vegetarian food.
Conclusions: Workplace interventions in poor health status settings are complex, necessary, and possible, and management’s participation is crucial. Increased awareness was achieved. Learning outcomes: The results showed some positive changes, such as lower stress levels and more intake of salad, fish, and vegetarian food. Flexibility is important for workplace interventions. Work place interventions contribute to health and wellbeing with appropriate management support.
The project "IEA OES Task 10 Phase III - WEC Modelling" is a publicly-funded research project under the Danish Energy Agency EUDP grant with Journal no. 134232-510153. As part of the initial period of the project, a selection of three test cases has been defined under WP2. The present report forms the deliverable for Milestone "M1: Case studies defined".
The paper presents incompressible Navier-Stokes simulations of the dynamics of a floating wave energy converter (WEC) coupled to a high-order finite element solver for cable dynamics. The coupled model has very few limiting assumptions and is capable of capturing the effects of breaking waves, green water loads on the WEC as well as non-linear mooring forces and snap loads, all of which are crucial for correct estimates of the extreme loads acting on the system in violent seas. The cable dynamics model has been developed as a stand-alone library that can be coupled to any body motion solver. In this study the open-source CFD package OpenFOAM has been employed. Preliminary test cases using incident regular Stoke's 5th order waves are presented, both for wave heights corresponding to operational conditions of the WEC as for a more severe condition in survival mode. It is illustrated that the coupled model is able to capture the complicated force propagation in the mooring cables.
A generic point-absorbing wave energy converter is modeled in CFD as a vertical cylinder, moored with a single catenary chain that is fully coupled through a dynamic mooring code. The method of choice is very complete and takes much of the non-linearities in the highly coupled system of the moored body into account. The paper presents numerical results compared with experimental data for surge, heave and pitch motion in both decay tests and regular waves. Further, the wave motion response of the cylinder is computed using both a viscous and a non-viscous formulation as a first attempt to quantify viscous effects. Results show a good match between numerical and experimental results in heave, while the surge and pitch motion are more difficult to reproduce. The mooring load cycle appearance compares well with the experiments in shape but gives higher peak values. Although made at low Keulegan-Carpenter numbers, the simulations show vortical structures due to the heave motion, and the resulting motions are clearly affected by the inclusion or exclusion of viscosity. More test-cases and detailed experimental results are needed for further quantification of the viscous impact on floating point absorbers.
Offshore de-oiling installations are facing an increasing challenge with regards to removing oil residuals from produced water prior to discharge into the ocean. The de-oiling of produced water is initially achieved in the primary separation processes using gravity-based multi-phase separators, which can effectively handle large amounts of oil-well fluids but may struggle with the efficient separation of small dispersed oil particles. Thereby hydrocyclone systems are commonly employed in the downstream Produced Water Treatment (PWT) process for further reducing the oil concentration in the produced water before it can be discharged into the ocean. The popularity of hydrocyclone technology in the offshore oil and gas industry is mainly due to its rugged design and low maintenance requirements. However, to operate and control this type of system in an efficient way is far less simple, and alternatively this task imposes a number of key control challenges. Specifically, there is much research to be performed in the direction of dynamic modeling and control of de-oiling hydrocyclone systems. The current solutions rely heavily on empirical trial-and-error approaches. This paper gives a brief review of current hydrocyclone control solutions and the remaining challenges and includes some of our recent work in this topic and ends with a motivation for future work.