A Comparative Study on the Hydrodynamic-Energy Loss Characteristics between a Ducted Turbine and a Shaftless Ducted Turbine

The shaftless ducted turbine (abbreviated as SDT), as an extraordinary innovation in tidal current power generation applications, has many advantages, and a wide application prospect. The structure of an SDT resembles a ducted turbine (abbreviated as DT), as both contain blades and a duct. However, there are some structural differences between a DT and a SDT, which can cause significant discrepancy in the hydrodynamic characteristics and flow features. The present work compares the detailed hydrodynamic-energy loss characteristics of a DT and a SDT by means of computational fluid dynamics (CFD), performed by solving the 3D steady incompressible Reynolds-averaged Navier-Stokes (RANS) equations in combination with the Menter’s Shear Stress Transport (SST k−ω) turbulence model and entropy production model. The results show the SDT features a higher power level at low tip speed ratio (TSR) and a potential reduction in potential flow resistance and disturbance with respect to the DT. Moreover, a detail entropy production analysis shows the energy loss is closely related to the flow separation and the reverse flow, and other negative flow factors. The entropy production of the SDT is lessened than that of the DT at different TSR. Unlike the DT, the SDT allows a large mass flow of water to leak through the open-center structure, which plays an important role in improving the wake structure and avoiding the negative flow along the central axis.

A Numerical Study on Hydrodynamic Energy Conversions of OWC-WEC with the Linear Decomposition Method under Irregular Waves

A numerical study was performed to investigate the applicability of the linear decomposition method for the hydrodynamic energy conversion of an oscillating-water-column type wave energy converter (OWC-WEC). Hydrodynamic problems of the OWC chamber were decomposed into the excitation and radiation problems with the time-domain numerical method based on the linear potential theory. A finite element method was applied to solve the potential flow in the entire fluid domain including OWC chamber structure. The validity of the linear decomposition method was examined by comparing with the direct interaction method for the turbine–chamber interaction based on the linear pressure drop characteristics. In order to estimate the hydrodynamic energy conversion performance under the irregular waves, the response spectrum method was applied with the transfer function based on the linear decomposition method. Under the various irregular wave conditions, the pneumatic power of OWC-WEC calculated by the response spectrum based on the linear decomposition method agreed well with the direct irregular wave simulation results.

Analyzing Hydrodynamic Energy Consumption to Predict Carrying Capacity Index

Summary Implementing efficient fluid-carrying capacity of drilled cuttings is an essential process for a good drilling program, either for a better rate of penetration (ROP) or a safer drilling operation. In this paper, I present a methodology that is based on the transfer function representation, which can be used to analyze the consumed fluid energy used in lifting the drilled cuttings in vertical wells to estimate the maximum carrying capacity index (CCI), which leads to performance at the desired ROP. The consumed hydrodynamic energy equation has been formulated using a second-order differential equation as a function of the drilling fluid, cuttings properties, and drilling operating parameters. Therefore, it allows an accurate quantitative monitoring of the fluid's CCI, which is the best alternative method to the currently empirical model. Moreover, it determines the perfect hydrodynamic energy required for any designed ROP to prevent excessive or poor hole-cleaning performance.

Macro-plastic weathering in a coastal environment: field experiment in Chesapeake Bay, Maryland

<p>It is now widely recognized that marine plastics, which are strongly resistant to chemical and biological degradation, have become a widespread and massive pollutant in the world’s oceans. Despite this resistance, in the environment, larger plastic items fragment and degrade into secondary microplastics which are ingestible by some marine organisms and are therefore a potential threat to aquatic foodwebs. The present study aims to better understand factors that contribute to the weathering of plastics in a coastal marine environment, where most microplastics appear to be generated. </p><p>Here we performed a field experiment to test the influence of different coastal conditions on macro-plastic weathering. Strips of commercial grade high-density polyethylene (HDPE) and polystyrene (PS) were mounted in replicate on racks (similar in appearance to keys on a glockenspiel, though all of the same length) and deployed at different treatment depths (subtidal versus intertidal) and different treatment hydrodynamic intensity zones (erosional versus depositional) in a sub-estuary of Chesapeake Bay (Maryland, USA). Strips were collected after environmental exposure of 4, 8 and 43 weeks and were analyzed for mass loss, surface chlorophyll accumulation, and surface appearance via SEM imaging.</p><p>We observed the PS strips degraded more quickly than the HDPE strips. The results show minor mass variation, in some samples even a slight mass increase, contrary to expectation. This was probably due to the deposition of clay and the presence of microorganisms into the microstructure of the strips, as observed by SEM. Moreover, the SEM images show different kind of fragmentation, with holes or with desquamations. The fragmentation was most marked for the PS strips located at intertidal depths caused by a more intense hydrodynamic energy. Finally, an increase over time was observed in the concentration of chlorophyll in both subtidal depositional PS strips and in subtidal erosional HDPE strips, associated with a lower hydrodynamic energy compared to the intertidal zones. This appears to confer a greater protection of the plastic which therefore undergoes less weathering.</p>

Cumulative charging behavior of water droplet driven freestanding triboelectric nanogenerators toward hydrodynamic energy harvesting

A maximum power density of 1.838 W m−2 is achieved and 30 LEDs can be lighted up by the cumulative water droplets driven freestanding triboelectric nanogenerator demonstrating the great potential for hydrodynamic energy harvesting from rain.

Lateral variability of ichnological content in muddy contourites: Weak bottom currents affecting organisms’ behavior

Although bioturbation is commonly recognized in contourites, only a few studies have analyzed the ichnological content of these deposits in detail. These studies have mainly focused on meso-scale bigradational sequence (a coarsening upward followed by a fining-upward sequence resulting from variations in current velocity). Here we present data from gravitational cores collected along the NW Iberian Margin showing systematic variation in ichnological content across proximal to distal depocenters within a large-scale elongated contourite drift. Data demonstrate that tracemakers’ behavior varies depending on the distance relative to the bottom current core. Trace fossils are already known to be a useful tool for studying of contouritic deposits and are even used as criterion for differentiating associated facies (e.g., turbidites, debrites), though not without controversy. We propose a mechanism by which the distance to the bottom current core exerts tangible influence on specific macro-benthic tracemaker communities in contourite deposits. This parameter itself reflects other bottom current features, such as hydrodynamic energy, grain size, nutrient transport, etc. Ichnological analysis can thus resolve cryptic features of contourite drift depositional settings.