Total wave power absorption by a multi-float wave energy converter and a semi-submersible wind platform with a fast far field model for arrays

Wave energy converters absorb wave power by mechanical damping for conversion into electricity and multi-float systems may have high capture widths. The kinetic energy of the floats causes waves to be radiated, generating radiation damping. The total wave power absorbed is thus due to mechanical and radiation damping. A floating offshore wind turbine platform also responds dynamically and damping plates are generally employed on semi-submersible configurations to reduce motion, generating substantial drag which absorbs additional wave power. Total wave power absorption is analysed here by linear wave diffraction–radiation–drag models for a multi-float wave energy converter and an idealised wind turbine platform, with response and mechanical power in the wave energy case compared with wave basin experiments, including some directional spread wave cases, and accelerations compared in the wind platform case. The total power absorption defined by capture width is input into a far field array model with directional wave spreading. Wave power transmission due a typical wind turbine array is only reduced slightly (less than 5% for a 10 × 10 platform array) but may be reduced significantly by rows of wave energy converters (by up to about 50%).

Laboratory Quantification of the Relative Contribution of Staghorn Coral Skeletons to the Total Wave-Energy Dissipation Provided by an Artificial Coral Reef

Coral reefs function as submerged breakwaters providing wave mitigation and flood-reduction benefits for coastal communities. Although the wave-reducing capacity of reefs has been associated with wave breaking and friction, studies quantifying the relative contribution by corals are lacking. To fill this gap, a series of experiments was conducted on a trapezoidal artificial reef model with and without fragments of staghorn coral skeletons attached. The experiments were performed at the University of Miami’s Surge-Structure-Atmosphere-Interaction (SUSTAIN) Facility, a large-scale wind/wave tank, where the influence of coral skeletons on wave reduction under different wave and depth conditions was quantified through water level and wave measurements before and after the reef model. Coral skeletons reduce wave transmission and increase wave-energy dissipation, with the amount depending on the hydrodynamic conditions and relative geometrical characteristics of the reef. The trapezoidal artificial coral reef model was found to reduce up to 98% of the wave energy with the coral contribution estimated to be up to 56% of the total wave-energy dissipation. Depending on the conditions, coral skeletons can thus enhance significantly, through friction, the wave-reducing capability of a reef.

Refined karst feature and fault identification through integrated wave field separation and imaging of Diffraction energy

In this abstract, a case study from offshore Indonesia is showcased with examples emphasizing integrated wave field separation methods with the objective of diffraction imaging towards refined karst feature and fault identification. For imaging optimally all diffraction energy, pre-migration and post-migration methods have been integrated. The dataset and examples in this abstract are in a complex geological setting in a very shallow water environment, with a subsurface that is characterized by large carbonate pinnacles containing large amount of karst features with thinning and thickening carbonate layers. For the purpose of refined imaging of diffraction energy only, the total wave field has been separated into specular reflections and diffractions prior to migration and these have been integrated with existing post-migration wave field separation methods. Both the pre-migration and post-migration wave field separation methods have their advantages and disadvantages and is discussed later in this abstract. Diffraction energy, in general is much lower in amplitude than the specular reflections and separately imaging these, unveils higher resolution small scale geological features such as karst features and faults complementing the total wave field PSDM data. With existing industry available methods applying wave field separation in either pre-migration or post-migration stage, limitations have been observed, and therefore we propose in this abstract to integrate both methods and take advantage of the improvements showcased with examples throughout the abstract.

Numerical Study on Wave Attenuation of Tsunami-Like Wave by Emergent Rigid Vegetation

The extreme surges and waves generated in tsunamis can cause devastating damages to coastal infrastructures and threaten the intactness of coastal communities. After the 2004 Indian Ocean tsunami, extensive physical experiments and numerical simulations have been conducted to understand the wave attenuation of tsunami waves due to coastal forests. Nearly all prior works used solitary waves as the tsunami wave model, but the spatial-temporal scales of realistic tsunamis differ drastically from that of solitary waves in both wave period and wavelength. More recent work has questioned the applicability of solitary waves and been looking towards more realistic tsunami wave models. Therefore, aiming to achieve more realistic and accurate results, this study will use a parameterized tsunami-like wave based on wave observations during the 2011 Japan tsunami to study the wave attenuation of a tsunami wave by emergent rigid vegetation. This study uses a high-resolution numerical wave tank based on the non-hydrostatic wave model (NHWAVE). This work examines effects of prominent factors, such as wave height, water depth, vegetation density and width, on the wave attenuation efficiency of emergent rigid vegetation. Results indicate that the vegetation patch can dissipate a considerable amount of the total wave energy of the tsunami-like wave. However, the tsunami-like wave has a higher total wave energy, but also a lower wave energy dissipation rate. Results show that using a solitary instead of a tsunami-like wave profile can overestimate the wave attenuation efficiency of the coastal forest.

Modern State of the Pauli Exclusion Principle and the Problems of Its Theoretical Foundation

The Pauli exclusion principle (PEP) can be considered from two aspects. First, it asserts that particles that have half-integer spin (fermions) are described by antisymmetric wave functions, and particles that have integer spin (bosons) are described by symmetric wave functions. It is called spin-statistics connection (SSC). The physical reasons why SSC exists are still unknown. On the other hand, PEP is not reduced to SSC and can be consider from another aspect, according to it, the permutation symmetry of the total wave function can be only of two types: symmetric or antisymmetric. They both belong to one-dimensional representations of the permutation group, while other types of permutation symmetry are forbidden. However, the solution of the Schrödinger equation may have any permutation symmetry. We analyze this second aspect of PEP and demonstrate that proofs of PEP in some wide-spread textbooks on quantum mechanics, basing on the indistinguishability principle, are incorrect. The indistinguishability principle is insensitive to the permutation symmetry of wave function. So, it cannot be used as a criterion for the PEP verification. However, as follows from our analysis of possible scenarios, the permission of states with permutation symmetry more general than symmetric and antisymmetric leads to contradictions with the concepts of particle identity and their independence. Thus, the existence in our Nature particles only in symmetric and antisymmetric permutation states is not accidental, since all symmetry options for the total wave function, except the antisymmetric and symmetric, cannot be realized. From this an important conclusion follows, we may not expect that in future some unknown elementary particles that are not fermions or bosons can be discovered.

EarthCARE’s Broadband Radiometer: Uncertainties Associated with Cloudy Atmospheres

The Earth Clouds, Aerosol and Radiation Explorer (EarthCARE) satellite’s Broadband Radiometer (BBR) consists of three telescopes and a rotating chopper drum (CD). Together they yield alternating measurements of total wave (TW; 0.25 to >50 μm) and shortwave (SW; 0.25–4 μm) radiances with point spread functions that translate to 0.6-km-diameter pixels. The mission requires that SW and TW radiances be averaged over 100-km2 domains. Correspondingly, the average longwave (LW) radiances are the differences between TW and SW averages. It is shown that impacts on domain-average nadir radiances resulting from alternating samples of TW and SW signals for realistic cloudy atmospheres are sensitive to the variance of cloudy-sky radiances, CD rotation rate, and along-track length of averaging domains. Over domains measuring 5 × 21 km2 and at a 50% rotation rate, uncertainties reached up to 3.2 and 4.1 W m−2 sr−1 for SW and TW radiances, respectively. The BBR’s design allows for in-flight alteration of the CD rate. An approximate method is provided for estimating SW and LW uncertainties resulting from the CD rate. While the nominal rotation rate meets EarthCARE’s mission requirements, reducing below 75% of that rate will lead to uncertainties for domain-average LW radiances that will often exceed mission requirements. This could be mitigated by increasing the size of averaging domains but that would compromise the BBR’s role in EarthCARE’s radiative closure assessment program. Uncertainties for off-nadir radiances are largely free of impacts arising from changes to the CD rotation rate.

Mooring of Semi Submersibles in Extreme Sea States: Simplified Models for Wave Drift Forces and Low Frequency Damping

This paper presents results from extensive small-scale model testing of three semi submersibles together with an overview of damping contributions of low frequency motions. The objectives of the model tests were to verify empirical correction formulas for viscous wave drift forces and to recommend and validate theoretical low frequency damping models. The main parameters of the semis such as displacement, number of columns and diameter of columns were intentionally varied in order to assess the effects on total wave drift forces and corresponding damping. The results show that viscous effects significantly increase the total wave drift forces in extreme sea states. The presence of current increases the effect. As expected, the viscous contribution to wave drift is especially important for semis with slender columns. A revised empirical correction formula for wave drift forces is proposed based on model test results. An overview of the different low frequency damping effects is given. Damping from viscous forces on the hull and damping from the mooring system are the most important sources of damping for the moored semis. A simplified model to calculate mooring system damping is proposed. For accurate prediction of low frequency motions of moored semi submersibles in extreme sea states, a damping level in the range 40–70% of critical damping should be applied for surge and sway when the empirical correction formulas for wave drift forces are applied.