Analysis of Power Performance and Mooring Fatigue Damage for Wave Energy Parks

Wave energy has been recognized as a promising alternative to traditional energy sources due to its cleanliness and sustainability. To harness this energy, wave energy converters (WECs) are utilized. These WECs operate using a variety of working principles and are typically deployed in large numbers in the form of wave energy parks to generate electricity with high efficiency and low levelized cost of energy (LCOE). However, the interaction effects between multiple WECs can positively or negatively impact power performance and mooring fatigue damage, highlighting the importance of numerical methodologies to evaluate such effects and facilitate agile wave energy park design processes.The primary objective of this thesis was to develop numerical methodologies and data post-processing techniques to effectively access single WECs and wave energy parks consisting of two different WEC concepts belonging to the point absorber group: WaveEL and NoviOcean. Specifically, two methodologies were built based on the potential theory and a computational fluid dynamics (CFD) method, for which the boundary element method (BEM) and direct numerical simulation (DNS) with volume of fluid (VOF) modelling were adopted, respectively. These methods were implemented using the software, DNV SESAM and STAR-CCM+. The WEC concepts were evaluated in terms of the performance and mooring fatigue damages of each WEC concept with varying WEC generations, wave conditions, wave incoming directions and wave park layouts. This thesis contributes to a better understanding of WEC system modelling, power performance and mooring fatigue damage estimation. Ultimately, these findings are anticipated to facilitate the development of optimized wave energy park layouts in the future

The closest isotropic, cubic and transversely isotropic stiffness and compliance tensor to an arbitrary anisotropic material

The aim of this paper is to provide, in the framework of Green elasticity, the closest or nearest fourthorder isotropic, cubic and transversely isotropic elasticity tensors with higher symmetries for a general anisotropic elasticity tensor or any other tensors with lower symmetry. Using a gauge parameter, the procedure is done on a dimensionless form based on different generalized Euclidean distances, namely conventional, log-, and power-Euclidean distance functions. In the case of power-Euclidean distance functions, results are presented for powers of 0.5, 1 and 2. Except for the conventional distance function, the different generalized distance functions adopted in this paper preserve the property of invariance by inversion, meaning that the results for the closest stiffness tensor are also valid for the compliance tensor. Explicit formulations are given for determining the closest isotropic and cubic tensors, where the multiplication tables of the bases are diagonal. More involved coupled equations are given for the coefficients of the closest transversely isotropic elasticity tensors, which can be solved numerically. Two different material cases are studied in the numerical examples, which i llustrate the material coefficients and error measures based on the present methods, including the influence from the gauge parameter

A comparison of two wave energy converters’ power performance and mooring fatigue characteristics – One WEC vs many WECs in a wave park with interaction effects

The production of renewable energy is key to satisfying the increasing demand for energy without further increasing pollution. Harnessing ocean energy from waves has attracted attention due to its high energy density. This study compares two generations of floating heaving point absorber WEC, WaveEL 3.0 and WaveEL 4.0, regarding their power performance and mooring line fatigue characteristics, which are essential in, e.g., LCoE calculations. The main differences between the two WECs are the principal dimensions and minor differences in their geometries. The DNV software SESAM was used for simulations and analyses of these WECs in terms of buoy heave motion resonances for maximising energy harvesting, motion characteristics, mooring line forces, fatigue of mooring lines, and hydrodynamic power production. The first part of the study presents results from simulations of unit WEC in the frequency domain and in the time domain for regular wave and irregular sea state conditions. A verification of the two WECs’ motion responses and axial mooring line forces is made against measurement data from a full-scale installation. In the second part of the study, the influence of interaction effects is investigated when the WECs are installed in wave parks. The wave park simulations used a fully-coupled non-linear method in SESAM that calculates the motions of the WECs and the mooring line forces simultaneously in the time domain. The amount of fatigue damage accumulated in the mooring lines was calculated using a relative tension-based fatigue analysis method and the rainflow counting method. Several factors that influence the power performance of the wave park and the accumulated fatigue damage of the mooring lines, for example, the WEC distance of the wave park, the sea state conditions, and the direction of incoming waves, are simulated and discussed. The study\u27s main conclusion is that WaveEL 4.0, which has a longer tube than WaveEL 3.0, absorbs more hydrodynamic energy due to larger heave motions and more efficient power production. At the same time, the accumulated fatigue damage in the moorings is lower compared to WaveEL 3.0 if the distance between the WECs in the wave park is not too short. Its motions in the horizontal plane are larger, which may require a larger distance between the WEC units in a wave park to avoid losing efficiency due to hydrodynamic interaction effects

Near-wall modeling of forests for atmosphere boundary layers using lattice Boltzmann method on GPU

In this paper, the simulation and modeling of the turbulent atmospheric boundary layers (ABLs) in the presence of forests are studied using a lattice Boltzmann method with large eddy simulation, which was implemented in the open-source program GASCANS with the use of Graphic Processing Units (GPU). A method of modeling forests in the form of body forces injected near the wall is revisited, while the effects of leaf area density (LAD) on the model accuracy is further addressed. Since a uniform cell size is applied throughout the computational domain, the wall-normal height of the near-wall cells is very large, theoretically requiring a wall function to model the boundary layer. However, the wall function is disregarded here when the forest is modeled. This approximation is validated based on the comparison with previous experimental and numerical data. It concludes that for the ABL conditions specified in this study as well as a large body of literature, the forest forces overwhelm the wall friction so that the modeling of the latter effect is trivial. Constant and varying LAD profiles across the forest zone are defined with the same total leaf area despite the varying one being studied previously. It is found that the two LAD profiles provide consistent predictions. The present forest modeling can therefore be simplified with the use of the constant LAD without degrading the model accuracy remarkably

Interleukin 35 Delays Hindlimb Ischemia-Induced Angiogenesis Through Regulating ROS-Extracellular Matrix but Spares Later Regenerative Angiogenesis.

Interleukin (IL) 35 is a novel immunosuppressive heterodimeric cytokine in IL-12 family. Whether and how IL-35 regulates ischemia-induced angiogenesis in peripheral artery diseases are unrevealed. To fill this important knowledge gap, we used loss-of-function, gain-of-function, omics data analysis, RNA-Seq, in vivo and in vitro experiments, and we have made the following significant findings: i) IL-35 and its receptor subunit IL-12RB2, but not IL-6ST, are induced in the muscle after hindlimb ischemia (HLI); ii) HLI-induced angiogenesis is improved in Il12rb2-/- mice, in ApoE-/-/Il12rb2-/- mice compared to WT and ApoE-/- controls, respectively, where hyperlipidemia inhibits angiogenesis in vivo and in vitro; iii) IL-35 cytokine injection as a gain-of-function approach delays blood perfusion recovery at day 14 after HLI; iv) IL-35 spares regenerative angiogenesis at the late phase of HLI recovery after day 14 of HLI; v) Transcriptome analysis of endothelial cells (ECs) at 14 days post-HLI reveals a disturbed extracellular matrix re-organization in IL-35-injected mice; vi) IL-35 downregulates three reactive oxygen species (ROS) promoters and upregulates one ROS attenuator, which may functionally mediate IL-35 upregulation of anti-angiogenic extracellular matrix proteins in ECs; and vii) IL-35 inhibits human microvascular EC migration and tube formation in vitro mainly through upregulating anti-angiogenic extracellular matrix-remodeling proteins. These findings provide a novel insight on the future therapeutic potential of IL-35 in suppressing ischemia/inflammation-triggered inflammatory angiogenesis at early phase but sparing regenerative angiogenesis at late phase

“Other” and Nature: A Postcolonial Ecocritical Reading of “Yoneko’s Earthquake”

“Yoneko’s Earthquake” is a masterpiece among the short stories by Japanese American writer Hisaye Yamamoto, and it reflects the plight and tragedy of Japanese American women. The plot of the short story is seemingly simple but profound, especially the design of the underlying text, which is full of ingenuity. From the perspective of postcolonial ecocriticism, Hisaye Yamamoto’s “Yoneko’s Earthquake” reflects the complicity of colonialism and ecologism in many aspects. Take a close look at the natural images (the dog, the field and the earthquake) in the short story. This paper tries to find an interconnected identity between the “other” and nature. The dog and the animalized human are both put in the position of the “other” under the colonial discourse; the field as a domain of colonization also nurtures the power of resistance from the “other”,; and the subversive nature of the earthquake makes the identity of “self” and “other” briefly displaced. The theory of postcolonial ecocriticism injects new vitality into this short story; meanwhile, it helps to provoke new thinking about racism and speciesism

Fatigue of mooring lines in wave energy parks

This study analyzes the amount of fatigue damage accumulated by polyester mooring lines in different wave parks for six heaving point absorber wave energy converters (WECs). The wave park simulation uses a coupled non-linear method that calculates the motion of the WECs and the mooring line forces simultaneously in the time domain. The amount of fatigue damage accumulated by the mooring lines is calculated using a relative tension-based fatigue analysis method. Several factors that influence the fatigue life of the mooring lines, for example, the WEC distance of the wave park, the sea state conditions, and the direction of incoming waves, are discussed in detail