Modeling circulation patterns induced by spatial cross-shore wind variability in a small-size coastal embayment

This contribution shows the importance of the cross-shore spatial wind variability in the water circulation in a small-sized micro-tidal bay. The hydrodynamic wind response at Alfacs Bay (Ebro River delta, NW Mediterranean Sea) is investigated with a numerical model (ROMS) supported by in situ observations. The wind variability observed in meteorological measurements is characterized with meteorological model (WRF) outputs. From the hydrodynamic simulations of the bay, the water circulation response is affected by the cross-shore wind variability, leading to water current structures not observed in the homogeneous-wind case. If the wind heterogeneity response is considered, the water exchange in the longitudinal direction increases significantly, reducing the water exchange time by around 20%. Wind resolutions half the size of the bay (in our case around 9 km) inhibit cross-shore wind variability, which significantly affects the resultant circulation pattern. The characteristic response is also investigated using idealized test cases. These results show how the wind curl contributes to the hydrodynamic response in shallow areas and promotes the exchange between the bay and the open sea. Negative wind curl is related to the formation of an anti-cyclonic gyre at the bay's mouth. Our results highlight the importance of considering appropriate wind resolution even in small-scale domains (such as bays or harbors) to characterize the hydrodynamics, with relevant implications in the water exchange time and the consequent water quality and ecological parameters.Peer ReviewedPostprint (author's final draft

The performance of polyurethane grout to stabilise hemic peat

Peat has always considered as a challenging ground for any form of construction due to its engineering characteristics such as high short-term settlement, prolonged long�term post construction settlement and high natural moisture content exceedingly more than 100%. Numerous construction materials and methods have been developed in recent years for sustainable construction on peat. The polyurethane (PU) grouting as an option is similar to the cement base grouting application widely used for ground improvement. However, the PU grouting is a strong lightweight material with very short curing time. The Parit Nipah hemic peat has high natural moisture content (> 500%) with high initial void ratio (6.72-10.11) and compression index, cc between 3.17 to 4.57. Optimum mixing ratio for PU of 1:2 (polyol:isocyanate) was established to be used for PU grouting based on its compressive strength (>200 kPa) and curing time (<7 minutes). Numerical analysis was conducted by using PLAXIS 3D Foundation software to determine the boundary for laboratory and field models, as well to determine the grouting depth for PU. The depth of grouting for laboratory scale models were determined at 100 mm and 200 mm, while for the field scale models was at 1 m and 2 m deep. The settlement for natural and treated peat under embankment constructed in stages were monitored. The results of laboratory physical scale models and field models displayed similar settlement pattern. The PU grouted peat showed improvement in term of ground settlement compared to natural peat. PU grouting managed to reduce the settlement of peat up to 30% compared to natural peat. For the PU grouted peat, the increment in term of depth of grouting displayed better settlement improvement. Results showed that PU grouting has good potential to reduce the settlement of hemic peat

Computational techniques for flows with finite-rate condensation

A computational method to simulate the inviscid two-dimensional flow of a two-phase fluid was developed. This computational technique treats the gas phase and each of a prescribed number of particle sizes as separate fluids which are allowed to interact with one another. Thus, each particle-size class is allowed to move through the fluid at its own velocity at each point in the flow field. Mass, momentum, and energy are exchanged between each particle class and the gas phase. It is assumed that the particles do not collide with one another, so that there is no inter-particle exchange of momentum and energy. However, the particles are allowed to grow, and therefore, they may change from one size class to another. Appropriate rates of mass, momentum, and energy exchange between the gas and particle phases and between the different particle classes were developed. A numerical method was developed for use with this equation set. Several test cases were computed and show qualitative agreement with previous calculations

The hydrodynamics of the southern basin of Tauranga Harbour

The circulation of the southern basin of Tauranga Harbour was simulated using a 3-D hydrodynamic model ELCOM. A 9-day field campaign in 1999 provided data on current velocity, temperature and salinity profiles at three stations within the main basin. The tidal wave changed most in amplitude and speed in the constricted entrances to channels, for example the M2 tide attenuated by 10% over 500 m at the main entrance, and only an additional 17% over the 15 km to the top of the southern basin. The modelled temperature was sensitive to wind mixing, particularly in tidal flat regions. Residence times ranged from 3 to 8 days, with higher residence times occurring in sub-estuaries with constricted mouths. The typical annual storm events were predicted to reduce the residence times by 24%–39% depending on season. Model scenarios of storm discharge events in the Wairoa River varying from 41.69 m3/s to 175.9 m3/s show that these events can cause salinity gradients across the harbour of up to 4 PSU

Encapsulation kinetics and dynamics of carbon monoxide in clathrate hydrate.

Carbon monoxide clathrate hydrate is a potentially important constituent in the solar system. In contrast to the well-established relation between the size of gaseous molecule and hydrate structure, previous work showed that carbon monoxide molecules preferentially form structure-I rather than structure-II gas hydrate. Resolving this discrepancy is fundamentally important to understanding clathrate formation, structure stabilization and the role the dipole moment/molecular polarizability plays in these processes. Here we report the synthesis of structure-II carbon monoxide hydrate under moderate high-pressure/low-temperature conditions. We demonstrate that the relative stability between structure-I and structure-II hydrates is primarily determined by kinetically controlled cage filling and associated binding energies. Within hexakaidecahedral cage, molecular dynamic simulations of density distributions reveal eight low-energy wells forming a cubic geometry in favour of the occupancy of carbon monoxide molecules, suggesting that the carbon monoxide-water and carbon monoxide-carbon monoxide interactions with adjacent cages provide a significant source of stability for the structure-II clathrate framework

Tidal Downsizing model. I. Numerical methods: saving giant planets from tidal disruptions

Tidal Downsizing (TD) is a recently developed planet formation theory that supplements the classical Gravitational disc Instability (GI) model with planet migration inward and tidal disruptions of GI fragments in the inner regions of the disc. Numerical methods for a detailed population synthesis of TD planets are presented here. As an example application, the conditions under which GI fragments collapse faster than they migrate into the inner $a\sim$ few AU disc are considered. It is found that most gas fragments are tidally or thermally disrupted unless (a) their opacity is $\sim 3$ orders of magnitude less than the interstellar dust opacity at metallicities typical of the observed giant planets, or (b) the opacity is high but the fragments accrete large dust grains (pebbles) from the disc. Case (a) models produce very low mass solid cores ($M_{\rm core} < 0.1$ Earth masses) and follow a negative correlation of giant planet frequency with host star metallicity. In contrast, case (b) models produce massive solid cores, correlate positively with host metallicity and explain naturally while giant gas planets are over-abundant in metals.Comment: Submitted to MNRAS November 19 2014. Comments welcom

Dimensionality and morphology of particle and bubble clusters in turbulent flow

We conduct numerical experiments to investigate the spatial clustering of particles and bubbles in simulations of homogeneous and isotropic turbulence. Varying the Stokes parameter and the densities, striking differences in the clustering of the particles can be observed. To quantify these visual findings we use the Kaplan--Yorke dimension. This local scaling analysis shows a dimension of approximately 1.4 for the light bubble distribution, whereas the distribution of very heavy particles shows a dimension of approximately 2.4. However, clearly separate parameter combinations yield the same dimensions. To overcome this degeneracy and to further develop the understanding of clustering, we perform a morphological (geometrical and topological) analysis of the particle distribution. For such an analysis, Minkowski functionals have been successfully employed in cosmology, in order to quantify the global geometry and topology of the large-scale distribution of galaxies. In the context of dispersed multiphase flow, these Minkowski functionals -- being morphological order parameters -- allow us to discern the filamentary structure of the light particle distribution from the wall-like distribution of heavy particles around empty interconnected tunnels.Comment: 12 pages, 8 figure

Potential and analysis of an osmotic power plant in the Magdalena River using experimental field-data

Producción CientíficaThe Magdalena River mouth in Colombia is studied as a candidate site for a renewable power plant via osmotic energy technology, using pressure retarded osmosis. This power generation plant would operate through the controlled mix of two flows with different salinities (river water and seawater in this case study). A preliminary design of a pressure retarded osmosis power plant is proposed here by means of experimental data acquisition on-site at the river mouth. The obtained net power production is shown to reach 6 MW, with adequate membrane power densities above 5 W/m2. These promising results consider energetic losses involved in the process, which have been further analysed to propose improvement targets in pretreatment processes and membrane permeability.Spanish Ministry of Economy through the project DPI2014-54530-R and the predoctoral grant BES-2015-073871, by the Junta de Castilla y León and European Regional Development Fund, UIC 233, and by the Banco Santander Iberoamérica Research Grants program. Field data acquisition was funded by COLCIENCIAS -Department of Science, Technology and Innovation of Colombia- by the project: 121571451074, resolution 881 – 2015

Three-dimensional numerical simulations on wind- and tide-induced currents: The case of Augusta Harbour (Italy)

The hydrodynamic circulation in the coastal area of the Augusta Bay (Italy), located in the eastern part of Sicily, is analysed. Due to the heavy contamination generated by the several chemical and petrochemical industries active in the zone, the harbour was declared a Contaminated Site of National Interest. To mitigate the risks connected with the industrial activities located near the harbour, it is important to analyse the hydrodynamic circulation in the coastal area. To perform such analysis, a parallel 3D numerical model is used to solve the Reynolds-averaged momentum and mass balance, employing the k-? turbulence model for the Reynolds stresses. The numerical model is parallelized using the programing technology - Message Passing Interface (MPI) and applying the domain decomposition procedure.The Augusta Bay circulation is mainly due to the relative contribution of the wind force acting over the free surface and the tidal motion through the mouths. Due to the geometric complexity of the domain and the presence of several piers along the coast, a curvilinear boundary-fitted computational grid was used, where cells corresponding to land areas or to wharfs were excluded from the computation. Comparisons between numerical results and field measurements were performed. Three different simulations were performed to selectively isolate the effect of each force, wind and tide, acting in the considered domain. The current in the basin was successfully estimated on the basis of the numerical results, demonstrating the specific role of wind and tidal oscillation in the hydrodynamic circulation inside the harbour