Academic literature on the topic 'Spherical point absorber with asymmetric mass'

The development and utilization of wave energy have great potentiality to alleviate the urgent problem of global energy shortage. Spherical bodies can be used as point absorbers to extract wave energy, and much attention has been paid to the performance of spherical absorbers in an open water domain. This study focuses on the hydrodynamic performance and energy absorption of multiple spherical absorbers in front of a straight coast. The coast is assumed to be a fully reflecting vertical wall, and all the absorbers are restricted to only heave motion. An analytical solution based on linear potential flow theory is developed for the problem of wave diffraction and radiation by multiple absorbers. In the solution procedure, the hydrodynamic problem is transformed into an equivalent problem in an open water domain by applying the image principle. The velocity potential of the fluid motion is solved using the method of multipole expansions combined with the shift of local spherical coordinate systems. Then, the wave excitation force, added mass coefficient, radiation damping coefficient, and energy extraction performance of the absorbers are calculated. Case studies are presented to analyze the effects of the coastal reflection and hydrodynamic interaction among absorbers on the energy extraction performance of the wave energy converter (WEC) system. The effects of wave frequency, incident angle, spacing between the absorber and coast, submergence depth, absorber number, and plane layout are also clarified. The results suggest that the energy extraction performance of an isolated absorber is significantly improved when the motions of the waves and absorber are in resonance, and the coastal reflection can enhance the overall energy extraction performance for a WEC system with multiple absorbers. In addition, when the number of absorbers increases, the effects of the coastal reflection and hydrodynamic interaction become more complicated.

Since its introduction, the Triangulation number has been the most successful and ubiquitous scheme for classifying spherical viruses. However, despite its many successes, it fails to describe the relative angular orientations of proteins, as well as their radial mass distribution within the capsid. It also fails to provide any critical insight into sites of stability, modifications or possible mutations. We show how classifying spherical viruses using icosahedral point arrays, introduced by Keef and Twarock, unveils new geometric rules and constraints for understanding virus stability and key locations for exterior and interior modifications. We present a modified fitness measure which classifies viruses in an unambiguous and rigorous manner, irrespective of local surface chemistry, steric hinderance, solvent accessibility or Triangulation number. We then use these point arrays to explain the immutable surface loops of bacteriophage MS2, the relative reactivity of surface lysine residues in CPMV and the non-quasi-equivalent flexibility of the HBV dimers. We then explain how point arrays can be used as a predictive tool for site-directed modifications of capsids. This success builds on our previous work showing that viruses place their protruding features along the great circles of the asymmetric unit, demonstrating that viruses indeed adhere to these geometric constraints.

In this paper, we investigated how the added mass, the hydrodynamic damping and the drag coefficient of a Wave Energy Converter (WEC) can be calculated using DualSPHysics. DualSPHysics is a software application that applies the Smoothed Particle Hydrodynamics (SPH) method, a Lagrangian meshless method used in a growing range of applications within the field of Computational Fluid Dynamics (CFD). Furthermore, the effect of the drag force on the WEC’s motion and average absorbed power is analyzed. Particularly under controlled conditions and in the resonance region, the drag force becomes significant and can greatly reduce the average absorbed power of a heaving point absorber. Once the drag coefficient has been determined, it is used in a modified equation of motion in the frequency domain, taking into account the effect of the drag force. Three different methods were compared for the calculation of the average absorbed power: linear potential flow theory, linear potential flow theory modified to take the drag force into account and DualSPHysics. This comparison showed the considerable effect of the drag force in the resonance region. Calculations of the drag coefficient were carried out for three point absorber WECs: one spherical WEC and two cylindrical WECs. Simulations in regular waves were performed for one cylindrical WEC with two different power take-off (PTO) systems: a linear damping and a Coulomb damping PTO system. The Coulomb damping PTO system was added in the numerical coupling between DualSPHysics and Project Chrono. Furthermore, we considered the optimal PTO system damping coefficient taking the effect of the drag force into account.

The evaporation and combustion of a single-component fuel droplet which is moving slowly in a hot oxidant atmosphere have been analysed using perturbation methods. Results for the flow field, temperature and species distributions in each phase, inter-facial heat and mass transfer, and the enhancement of the mass burning rate due to the presence of convection have all been developed correct to second order in the translational Reynolds number. This represents an advance over a previous study which analysed the problem to first order in the perturbation parameter. The primary motivation for the development of detailed analytical/numerical solutions correct to second order arises from the need for such a higher-order theory in order to investigate fuel droplet ignition and extinction characteristics in the presence of convective flow. Explanations for such a need, based on order of magnitude arguments, are included in this article. With a moving droplet, the shear at the interface causes circulatory motion inside the droplet. Owing to the large evaporation velocities at the droplet surface that usually accompany drop vaporization and burning, the entire flow field is not in the Stokes regime even for low translational Reynolds numbers. In view of this, the formulation for the continuous phase is developed by imposing slow translatory motion of the droplet as a perturbation to uniform radial flow associated with vigorous evaporation at the surface. Combustion is modelled by the inclusion of a fast chemical reaction in a thin reaction zone represented by the Burke–Schumann flame front. The complete solution for the problem correct to second order is obtained by simultaneously solving a coupled formulation for the dispersed and continuous phases. A noteworthy feature of the higher-order formulation is that both the flow field and transport equations require analysis by coupled singular perturbation procedures. The higher-order theory shows that, for identical conditions, compared with the first-order theory both the flame and the front stagnation point are closer to the surface of the drop, the evaporation is more vigorous, the droplet lifetime is shorter, and the internal vortical motion is asymmetric about the drop equatorial plane. These features are significant for ignition/extinction analyses since the prediction of the location of the point of ignition/extinction will depend upon such details. This article is the first of a two-part study; in the second part, analytical expressions and results obtained here will be incorporated into a detailed investigation of fuel droplet ignition and extinction. In view of the general nature of the formulation considered here, results presented have wider applicability in the general areas of interfacial fluid mechanics and heat/material transport. They are particularly useful in microgravity studies, in atmospheric sciences, in aerosol sciences, and in the prediction of material depletion from spherical particles.

The adoption of renewable energy has long been regarded as an effective solution to fulfil the growing demand for electricity and reduce greenhouse gas emissions. Ocean wave energy is a promising and reliable resource in the renewable energy mix, which exhibits higher power density and continuity than solar and wind energy. Furthermore, the overall potential of ocean wave energy is estimated as being much as 3.7 terawatts, which is double the current global demand for electricity. Although the first wave energy converter (WEC) design appeared as early as 1790, the technology of wave energy conversion is still at an early stage of commercialisation. Compared with solar and wind energy plants, the existing WEC systems have relatively small power generation capacity and exhibit greater costs associated with investment, infrastructure and maintenance. Consequently, wave energy conversion is currently at an economic disadvantage in the renewable energy mix. This thesis studies the efficiency improvement of a single-tether submerged spherical point absorbing wave energy converter by utilising an asymmetric mass distributed buoy. The spherical point absorber with asymmetric mass distribution is referred to as SPAMD in the thesis. The main contribution lies in frequency-domain modal analysis, parametric optimisation and high-fidelity modelling of the system. This Ph.D. research answers three questions: (i) What effect does mass distribution have on the dynamics of a submerged spherical buoy; (ii) how does the mass distribution of the buoy affect the power output of the SPAMD in irregular waves; and (iii) do the nonlinear hydrodynamic effects compromise the performance of the SPAMD? To understand the working principle and evaluate the efficiency improvement of the SPAMD, a frequency-domain modal analysis is conducted over typical wave frequencies. The influence of a power take-off device on the performance of the SPAMD is discussed on the basis of a modal analysis. The efficiency improvement over a generic point absorber for regular waves is assessed over different frequency regimes. Recommendations pertaining to the application of an asymmetric mass distributed buoy in wave energy harvesting are provided. The design considerations of the mass distribution of the buoy are also investigated under irregular waves characterised by the Pierson-Moskowitz spectrum. A spectral-domain model, including viscous drag effects, is developed to evaluate the performance of the SPAMD efficiently. Attention is given to the power absorption bandwidth, the mean power output and the dynamic mooring loading caused by the configuration of mass distribution. Suggestions regarding the configuration of the mass distribution of the buoy are provided according to the facility cost and the system performance. The final part of this thesis explores the trajectory and power analysis of the SPAMD in a high-fidelity simulation. A numerical wave tank has been developed from the Navier-Stokes equations, to simulate the fluid-structure interface during the operation of the SPAMD. It was found that the nonlinear hydrodynamics significantly modify the trajectory of the device as the wave height grows. The large change in the motion trajectory of the buoy decreases the efficiency of the converter in terms of wave energy harvesting. The efficiency improvement of the SPAMD in comparison with the generic point absorber is demonstrated in the numerical wave tank experiment.
Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2020