CCP-WSI Blind Test Series 3: OpenFOAM Simulation of Focused Wave Interaction with a Simplified Wave Energy Converter

This paper presents a numerical study of a simplified wave energy converter (WEC) with and without a moon-pool under focused wave conditions and the work presented corresponds to a contribution to the CCP-WSI Blind Test Series 3. The numerical model applies the overset mesh technique in order to deal with large amplitude motions induced by the focused wave groups. The generation of the incident wave group is first examined through a mesh convergence test and by comparing with the experimental data. Simulations are then carried out with the presence of the WEC. In total three wave conditions are considered, each with the same wave period but different wave height. Non-linear effects on the WEC motion are clearly shown when the wave steepness increases and wave over-topping occurs. Furthermore, the effects of the moon pool on the dynamics and kinematics of the WEC including the damping effects on pitch response are also discussed, where the WEC motion is compared for the case with and without a moon-pool under the same wave conditions

Development of a 3D fully nonlinear potential flow wave tank in framework of OpenFOAM

A 3-Dimensional numerical wave tank based on the fully nonlinear potential flow theory has been developed in OpenFOAM, where the Laplace equation of velocity potential is discretized by Finite Volume Method. The water surface is tracked by the semi-Eulerian-Lagrangian method, where water particles on the free surface are allowed to move vertically only. The incident wave is generated by specifying velocity profiles at inlet boundary with a ramp function at the beginning of simulation to prevent initial transient disturbance. Additionally, an artificial damping zone is located at the end of wave tank to sufficiently absorb the outgoing waves before reaching downstream boundary. A five-point smoothing technique is applied at the free surface to eliminate the saw-tooth instability. The proposed wave model is validated against theoretical results and experimental data. The developed solver could be coupled with multiphase Navier-Stokes solvers in OpenFOAM in the future to establish an integrated versatile numerical wave tank for studying efficiently wave structure interaction problems

Investigation of nonlinear wave-induced seabed response around mono-pile foundation

YesStability and safety of offshore wind turbines with mono-pile foundations, affected by nonlinear wave effect and dynamic seabed response, are the primary concerns in offshore foundation design. In order to address these problems, the nonlinear wave effect on dynamic seabed response in the vicinity of mono-pile foundation is investigated using an integrated model, developed using OpenFOAM, which incorporates both wave model (waves2Foam) and Biot’s poro-elastic model. The present model was validated against several laboratory experiments and promising agreements were obtained. Special attention was paid to the systematic analysis of pore water pressure as well as the momentary liquefaction in the proximity of mono-pile induced by nonlinear wave effects. Various embedment depths of mono-pile relevant for practical engineering design were studied in order to attain the insights into nonlinear wave effect around and underneath the mono-pile foundation. By comparing time-series of water surface elevation, inline force, and wave-induced pore water pressure at the front, lateral, and lee side of mono-pile, the distinct nonlinear wave effect on pore water pressure was shown. Simulated results confirmed that the presence of mono-pile foundation in a porous seabed had evident blocking effect on the vertical and horizontal development of pore water pressure. Increasing embedment depth enhances the blockage of vertical pore pressure development and hence results in somewhat reduced momentary liquefaction depth of the soil around the mono-pile foundation.Energy Technology Partnership (ETP), Wood Group Kenny, and University of Aberdeen; the National Science Fund for Distinguished Young Scholars (51425901) and the 111 project (B12032)

Oblique focused wave group generation and interaction with a fixed FPSO-shaped body: 3D CFD simulations and comparison with experiments

© 2019 Elsevier Ltd This paper presents a numerical study of oblique focused wave group generation and interaction with a fixed FPSO-shaped body, with thorough validations against available experimental data. The 3D numerical model is based on the open-source toolbox OpenFOAM®, where the oblique waves are generated using multiple virtual segmented wave paddles. The surface elevation and velocity profiles on each paddle are derived based on the snake principle, which mimics the behaviour of wave paddles in the physical wave tank. Numerical tests are firstly conducted for focused wave groups propagating obliquely in an empty wave tank using the proposed scheme. By analysis of the surface elevation, it is found that reasonably good quality of oblique wave fields can be generated in the central area of the wave basin. Furthermore, investigations are carried out on the effects of wave angles on the harmonic structures of the wave groups using the phase-inversion method. It is shown that while the wave angle has minor effects on the linear and second order harmonics, the third order harmonic is altered by the wave angles, albeit its magnitude is very small. Finally, to show the effectiveness of the numerical oblique wave generation method and the importance of the angle effects in the wave-structure interaction process, simulations are carried out for the oblique focused wave group interacting with a fixed FPSO-shaped body. The effects of the wave incidence angle are clearly shown from the comparison of the integrated wave forces between the cases with different wave propagating angles

Focused wave interactions with floating structures: A blind comparative study

The paper presents results from the Collaborative Computational Project in Wave Structure Interaction (CCP-WSI) Blind Test Series 2. Without prior access to the physical data, participants, with numerical methods ranging from low-fidelity linear models to fully non-linear Navier−Stokes (NS) solvers, simulate the interaction between focused wave events and two separate, taut-moored, floating structures: a hemispherical-bottomed cylinder and a cylinder with a moonpool. The ‘blind’ numerical predictions for heave, surge, pitch and mooring load, are compared against physical measurements. Dynamic time warping is used to quantify the predictive capability of participating methods. In general, NS solvers and hybrid methods give more accurate predictions; however, heave amplitude is predicted reasonably well by all methods; and a WEC-Sim implementation, with CFD-informed viscous terms, demonstrates comparable predictive capability to even the stronger NS solvers. Large variations in the solutions are observed (even among similar methods), highlighting a need for standardisation in the numerical modelling of WSI problems

Design of Flight Control System for a Novel Tilt-Rotor UAV

This paper presents the control system design process of a novel tilt-rotor unmanned aerial vehicle (TRUAV). First, a new configuration scheme with the tilting rotors is designed. Then, the detailed nonlinear mathematical model is established, and the parameters are acquired from designed experiments and numerical analyses. For control design purposes, the dynamics equation is linearized around the hovering equilibrium point, and a control allocation method based on trim calculation is developed. To deal with the actuator saturation and uncertain disturbance problems for the novel TRUAV, an improved flight control law based on the combination of the robust servo linear quadratic regulator (RSLQR) optimal control and the extended state observer (ESO) is proposed. The designed flight control law has a simple structure with a high reliability in engineering. Simulations and hovering flight tests are carried out to verify the effectiveness of the mathematical model and the proposed control strategy

CFD Simulation of Wave Energy Converters in Focused Wave Groups Using Overset Mesh

This paper presents the numerical modelling of two point absorber wave energy converters (WECs) with and without a moonpool under focused wave conditions. The numerical model applies the overset mesh technique in order for the mesh to conform with the large-amplitude WEC motion induced by the focused wave groups. The incident wave group is first examined by a mesh convergence test and by comparing with the experimental data. The simulations are then carried out with the presence of the WEC. In total, three wave conditions are considered, each with the same wave period but with different wave heights. Nonlinear effects on the WEC motion are clearly exhibited when the wave steepness increases. The accuracy of the numerical results is carefully assessed against experimental data. Furthermore, the effects of the moonpool on the dynamics of the WEC are also discussed, where the WEC motion is compared for the case with and without a moonpool under the same wave conditions

Swash-flow induced forces on human body standing on a smooth and impermeable slope: A numerical study with experimental validations

ABSTRACTSwash flow poses a significant hazard to pedestrians standing on the slope of the seawall. Unlike the forces of overtopping flow or open channel flow on the human body, which have been studied before, swash flow has two distinct cycles within one wave period: onshore flow and offshore flow. Both cycles can risk human safety by exerting hydrodynamic forces on the body. This paper presents a numerical study to examine the hydrodynamic forces exerted on the human body when subjected to swash flow on a smooth and impermeable slope. A Reynolds-averaged Navier-Stokes (RANS) model is set up in OpenFOAM, where the numerical results are compared with experimental data obtained from wave tank tests. Reasonable agreement has been achieved, which validates the numerical model. We examine the kinematics of swash flow generated by plunging and surging breakers. In the case of a plunging breaker, we observe that the instantaneous runup height exhibited asymmetry, whereas it is nearly symmetric for a surging breaker. The velocity profile is then used to compute the momentum flux of the swash flow, which is shown to be associated with the inline forces exerted on the human body. We have defined an instability index to assess the risk of pedestrian mobilisation by swash flow, demonstrating its dependence on the Iribarren number and the body's position. The analysis reveals that the associated risk is substantially reduced as the Iribarren number increases and when the body moves towards the shoreline

Effects of purified zearalenone on selected immunological and histopathologic measurements of spleen in post-weanling gilts

The present study was aimed at investigating the adverse effects of dietary zearalenone (ZEA) on the lymphocyte proliferation rate (LPR), interleukin-2 (IL-2), mRNA expressions of pro-inflammatory cytokines, and histopathologic changes of spleen in post-weanling gilts. A total of 20 crossbred piglets (Yorkshire × Landrace × Duroc) with an initial BW of 10.36 ± 1.21 kg (21 d of age) were used in the study. Piglets were fed a basal diet with an addition of 0, 1.1, 2.0, or 3.2 mg/kg purified ZEA for 18 d ad libitum. The results showed that LPR and IL-2 production of spleen decreased linearly (P < 0.05) as dietary ZEA increased. Splenic mRNA expressions of interleukin-1β (IL-1β) and interleukin-6 (IL-6) were linearly up-regulated (P < 0.05) as dietary ZEA increased. On the contrary, linear down-regulation (P < 0.05) of mRNA expression of interferon-γ (IFN-γ) was observed as dietary ZEA increased. Swelling splenocyte in 1.1 mg/kg ZEA treatments, atrophy of white pulp and swelling of red pulp in 2.0 and 3.2 mg/kg ZEA treatments were observed. The cytoplasmic edema in 1.1 mg/kg ZEA treatments, significant chromatin deformation in 2.0 mg/kg ZEA treatment and phagocytosis in 3.2 mg/kg ZEA treatment were observed. Results suggested that dietary ZEA at 1.1 to 3.2 mg/kg can induce splenic damages and negatively affect immune function of spleen in post-weanling gilts

Simulating focused wave impacts on point absorber wave energy converters

Abstract This work contributes to the CCP-WSI Blind Test Series 2 by numerically investigating the dynamic response of two simplified point absorber wave energy converters (a hemispherical-bottom cylinder and a cylinder with moon-pool) under the action of focused waves of varying steepness. The open source toolbox OpenFOAM along with its new overset grid functionality is applied and evaluated for the complex flow problem involving both large free surface deformations and large amplitude motions of floating objects. The quality of the numerically generated focused wave groups is first examined and validated against the experimental data. The effects of both wave steepness and the moon-pool on the dynamic responses and mooring loads of the simplified wave energy converters (WECs) are then analyze