The optimization of ejector geometry for mixing NaOH powders with water in on-board carbon solidification system

Owing to increasing requirement of greenhouse gas emissions reductions, researchers all over the world has been investigating and developing technology applying to all different sectors. According to the report from International Maritime Organization (IMO), the international shipping has contributed 2.2% of global carbon emissions in 2012. To mitigate this situation, organizations, researchers and engineers are striving to reduce the emissions by increasing the energy efficiency or applying emission reduction regulations and techniques. Authors has investigated a chemical absorption method to absorb and solidify the carbon content in the exhaust gases from ships. In the chemical absorption method, to absorb the carbon dioxide from exhaust gases, sodium hydroxide (NaOH) solution is applied as absorbent. However, the storage of NaOH solution may cause stability and corrosion problems on ships. To eliminate these problem, this paper introduce the ejector technology to mix NaOH powders with water to supply and replenish absorbent to the system which will reduce the storage of NaOH solution and instead only NaOH powders should be stored on board. This paper also investigates the impact of swapping fluid inlets to determine a preferred design. With the application of design of experiment and computing fluid dynamic, the optimization of the preferred design is also carried out in order to determine an optimal design of the ejector geometry

The drop keel concept : a semi-submersible-spar foundation adpated for ease of assembly for the floating offshore wind turbine market

This paper provides an overview of the analysis methods, results and conclusions reached during an Innovate UK funded research program into a novel 10MW wind turbine floating foundation structure. Current foundation designs are developments of concepts established in the offshore oil and gas sector: semi-submersible, spar and tension leg platforms. Each have their own particular technical and operational drawbacks. The project set out to develop an alternative hybrid solution to take advantage of the benefits of the semi-submersible and spar designs while removing their disadvantages. The concept considered is referred to as the Drop Keel and applied a solid ballasted keel elevated in the launch and transit conditions and deployed to depth in the operation condition. Thus, the hybrid would exhibit the semi-submersible advantages of assembly and launch at a quayside location while possessing the spar advantage of a low centre of gravity in operation. Results from independent numerical and wave tank tests provided consistent results that proved the concept exhibited stable operating performance for the simulated offshore wind and wave conditions. However, the initial Drop Keel concept lacked commercial appeal due to a high steel and ballast weight estimate, complex assembly method, dependency on deep draft submersible barge for assembly and launch, and use of multiple mechanical lift devices that presented logistical challenges for removal during installation. Fortunately, identification of these drawbacks provided a basis for design improvement and led to a final design outcome that resolved all of these disadvantages and improved the design’s commercial appeal

Investigation on the hydrodynamic scaling effect of an OWC type wave energy device using experiment and CFD simulation

This paper presents a study of the effect of model scale on the performance of a fixed Oscillating Water Column (OWC) type Wave Energy Converter (WEC). Tank tests at two different scales, including the effect of scaling of the test tanks to minimise the bias introduced by different wave blockage effects. CFD simulations based on Reynolds Average Navier Stokes (RANS) method were then carried out for both scaled OWCs to investigate whether CFD simulation is able to reproduce the scale effect. Comparison between the tank test results and the CFD simulation results suggests that CFD simulation is capable of reproducing the hydrodynamic scaling effect with a good accuracy. Results also suggest that the hydrodynamic scaling effect is mainly introduced by the Reynolds number effect for cases investigated in the current study

An experimental and CFD study of the extreme waves impact on OC3-Hywind Spar Floating offshore wind turbine

The study presents a combined wave tank experiment and Computational Fluid Dynamics(CFD) study on the OC3-Hywind Spar Floating [1] offshore wind turbine under extreme wave conditions. Focused wave is adopted in the present study as one of the effective ways to model the extreme wave. The main objectives of this study are to demonstrate how the focused waves could represent the extreme waves and the difference of focused waves approach and other wave types to model extreme waves, i.e., irregular waves. The experimental tank test was carried out with a 1/74 scale model both in irregular and focused wave conditions in Kelvin Hydrodynamics Laboratory at the University of Strathclyde. The irregular waves are designed by using identical wave spectrum with focused waves in the wave tank, and it will be helpful to determine the viability of using different wave types to represent high amplitude waves. The study provides a comparison of the dynamic responses, motion RAOs of the floater between focused waves and irregular waves. In addition, an in-house CFD code[2][3][4] based on an open-source CFD framework OpenFOAM [5] is adopted to simulate the fluid flow around the Spar-FOWT in a numerical wave tank under regular and focused wave conditions. Firstly, for code validation, the dynamic response of the Spar-FOWT is simulated under regular waves and the results are compared with the existing research [6]. Next, the focused wave with the identical wave spectrum provided by the experimental test is generated in our numerical wave tank without the floating structure. After the validation of the focused wave generation, the wave-structure interaction and the dynamic response of the Spar-FOWT is investigated under the focused wave. The results show good agreement with the tank test which demonstrates the capacity and the fidelity of our CFD tools

An experimental study of a quasi-impulsive backwards wave force associated with secondary load cycle on a vertical cylinder

Steep wave breaking on vertical cylinder (a typical foundation supporting offshore wind turbines) will induce slam loads. Many questions on the important violent wave loading and the associated secondary load cycle still remain unanswered. We use laboratory experiments with unidirectional waves to investigate the fluid loading on vertical cylinders. We use a novel three-phase decomposition approach which allows us to separate different types of non-linearity. Our findings reveal the existence of an additional quasiimpulsive loading component that is associated with the secondary load cycle and occurs in the backwards direction against that of the incoming waves. This quasi-impulsive force occurs at the end of the secondary load cycle and close to the passage of the downward zero-crossing point of the undisturbed wave. Wavelet analysis showed that the impulsive force exhibits superficially similar behaviour to a typical wave-slamming event but in the reverse direction. To monitor the scattered wave field and extract run-up on the cylinder, we installed a four-camera synchronized video system and found a strong temporal correlation between the arrival time of the Type-II scattered wave onto the cylinder and the occurrence of this quasi-impulsive force. The temporal characteristics of this quasi-impulsive force can be approximated by the Goda wave impact model, taking the collision of the Type-II scattered waves at the rear stagnation point as the impact source

Experimental investigation on stability of intact and damaged combatant ship in beam sea

The stability of the damaged ship is influenced by several factors including the encountered waves and its response to them, the floodwater behaviour and its interaction with the ship’s motions. The behaviour of floodwater is highly nonlinear and therefore the model testing is one of the best ways to assess the actual behaviour of the damaged ship. The present study addresses mainly the experimental study of the stability in intact and damage condition of a combatant vessel in beam waves. The tests were carried out at the Kelvin Hydrodynamics Laboratory of the University of Strathclyde, using a model of the well-known DTMB 5415, equipped with a double bottom. A 1/51-scale model was used. Free rolling decay tests with and without restricted constraint were implemented in calm water, with the model restrained at the bow and stern during the wave excited oscillation tests. In order to investigate the performance of the damaged ship, an opening was made at the starboard side near the midship through which two internal compartments were flooded. The obtained results show how in the damage condition and the floodwater dynamics the compartments impact on the motion responses of the ship and forces acting on the ship’s hull. Nonlinear behaviour of the RAOs of all tests are given to provide the benchmark results for prediction with CFD methods further

Rapid validation of water wave metamaterials in a desktop-scale wave measurement system

Metamaterials have a unique ability to manipulate wave phenomena beyond their natural capabilities, and they have shown great promise in electromagnetic and acoustic wave control. However, their exploration in hydrodynamics remains limited. This article introduces a novel desktop-scale wave measurement system, specifically designed for the rapid prototyping and validation of water wave metamaterials. By utilizing 3D printing, the system accelerates the transition from theoretical designs to practical testing, offering a versatile and user-friendly platform. This is further enhanced by a synchronized stereo-camera setup and advanced data processing algorithms, enabling precise measurement and reconstruction of water wave behavior. Our experimental results demonstrate the system’s effectiveness in capturing intricate interactions between engineered structures and water waves. This significantly advances rapid prototyping for water wave metamaterial research, underscoring the system’s potential to catalyze further innovation in this emerging field

Data Informed Model Test Design With Machine Learning – An Example in Nonlinear Wave Load on a Vertical Cylinder

Model testing is common in coastal and offshore engineering. The design of such model tests is important such that the maximal information of the underlying physics can be extrapolated with a limited amount of test cases. The design of experiments also requires considering the previous similar experimental results and the typical sea-states of the ocean environments. In this study, we develop a model test design strategy based on Bayesian sampling for a classic problem in ocean engineering—nonlinear wave loading on a vertical cylinder. The new experimental design strategy is achieved through a GP-based surrogate model, which considers the previous experimental data as the prior information. The metocean data are further incorporated into the experimental design through a modified acquisition function. We perform a new experiment, which is mainly designed by data-driven methods, including several critical parameters such as the size of the cylinder and all the wave conditions. We examine the performance of such a method when compared to traditional experimental design based on manual decisions. This method is a step forward to a more systematic way of approaching test designs with marginally better performance in capturing the higher-order force coefficients. The current surrogate model also made several “interpretable” decisions which can be explained with physical insights

Wave energy conversion by an array of oscillating water columns deployed along a long-flexible floating breakwater

Large-scale spatial configurations combining Wave Energy Converters (WECs) and coastal attenuating-wave facilities have the potential to exploit marine renewable energy sustainably. In this study, an integrated concept of multiple Oscillating Water Columns (OWCs) and a very long floating breakwater is introduced. Associated energy extraction, gap resonance and hydroelastic interaction problems are examined. A coupled numerical simulation methodology consisting of a Finite Volume Method (FVM)based solver and a Finite Element Method (FEM) solver, is developed to investigate the strong fluid and structure coupled problem. The fluid-structure information is matched in real-time and the flexible modes of the floating breakwater are obtained by imposing a restrained beam inside the pontoon. The accurate time-domain model is validated against both simulated and measured data. Extensive parametric studies indicate that the energy conversion has a conflict with the wave attenuation in terms of determining the along-shore number of OWCs. The highest energy conversion in medium-period and long-period waves are observed in the OWCs near the end and middle locations, respectively. Besides, the constructive resonant gap effect between OWCs and the breakwater can amplify the peaks of energy conversion efficiency, leads to a sudden collapse in transmission coefficient curves. With an increased sidewall draft, OWCs closer to oblique incident direction generate stronger piston-type and sloshing oscillations. Additionally, compared with a rigid breakwater, the elastic deformation of the breakwater plays a destructive role in wave energy conversion, which is attributed to the out-of-phase interference of multi-mode radiated waves

An investigation of high-order harmonics in the pressure field around a vertical cylinder in steep wave conditions

Offshore structures, encompassing foundations for offshore wind turbines, supports for marine renewable energy devices, bridge piers, and floating vessels, are consistently subjected to severe environmental loads. These loads often dictate the design criteria. Understanding the physics and statistics of wave-structure interaction, especially under non-linear loads experienced in extreme conditions, remains a complex and partially unresolved challenge. Notably, secondary load cycles significantly contribute to the ’ringing’ responses in cylindrical structures, as discussed in previous studies (e.g., Grue et al. (1993), Chaplin et al. (1997)). This paper focuses on analysing loads in focused wave groups, representing short-term extreme wave conditions, on bottom-mounted vertical cylinders relevant to fixed offshore wind turbines. Pressure contour plots over the cylinder’s surface were previously examined by Ghadirian & Bredmose (2020) while studying secondary load cycles. In this research, we adopt the phase-based harmonic separation method for wave forces (Fitzgerald et al. (2014)) to analyse the pressure contour plots. This method effectively isolates harmonic pressure components from the total pressures, enabling a novel exploration of the mechanisms behind secondary load cycles from the perspective of high-order harmonics on the cylinder surface