Pollutant dispersion in the nearshore region: modelling and measurements

1995 ◽  
Vol 32 (9-10) ◽  
pp. 169-178 ◽  
Author(s):  
A. Rodriguez ◽  
A. Sánchez-Arcilla ◽  
J. M. Redondo ◽  
E. Bahia ◽  
J. P. Sierra

Some results on pollutant dispersion modelling and tracer measurements for the Mediterranean Spanish coast are presented. Two hydrodynamic models have been used to simulate wind and wave induced circulation in the nearshore and surf zones respectively. A “near field” model has been used in order to simulate the initial conditions for the local “far field” dispersion model. Two study cases are presented: The first one shows the mixing of conservative tracers in a Mediterranean surf zone from an experimental and numerical models used to predict bacterial dispersion from the main sea outfalls of Barcelona City. The comparison between dye dispersion experiments and model in the surf zone is good, while the outfall predictions show the importance of accurately modelling the effects of buoyancy on the plume.

1996 ◽  
Vol 118 (1) ◽  
pp. 37-44 ◽  
Author(s):  
G. A. Eghneim ◽  
S. J. Kleis

A combined experimental and numerical study was conducted to support the development of a new gradient maintenance technique for salt-gradient solar ponds. Two numerical models were developed and verified by laboratory experiments. The first is an axisymmetric (near-field) model which determines mixing and entrainment in the near-field of the injecting diffuser by solving the conservation equations of mass, momentum, energy, and salt. The model assumes variable properties and uses a simple turbulence model based on the mixing length hypothesis to account for the turbulence effects. A series of experimental measurements were conducted in the laboratory for the initial adjustment of the turbulence model and verification of the code. The second model is a one-dimensional far-field model which determines the change of the salt distribution in the pond gradient zone as a result of injection by coupling the near-field injection conditions to the pond geometry. This is implemented by distributing the volume fluxes obtained at the domain boundary of the near-field model, to the gradient layers of the same densities. The numerical predictions obtained by the two-region model was found to be in reasonable agreement with the experimental data.


2010 ◽  
Vol 18 (4) ◽  
pp. 288-295 ◽  
Author(s):  
Liliana Rusu

The last decades continuously increasing of the economical activities in the coastal environment of the Black Sea is obviously leading to the enhancement of the pollution risks due to accidental oil spillages. Starting from the fact that most accidents were generated by an inadequate forecast of the wave conditions, the aim of the present work is to develop a methodology based on spectral phase–averaging wave models able to predict the wave propagation in the coastal environment. The wave induced currents that may be a key factor in driving the pollution are also assessed. This implies both the Stokes drift and the wave induced nearshore currents. The surface streaming effect due to the molecular viscosity was also accounted for. In the nearshore, close to the surf zone, the pollution is usually spread along the coast due to the longshore currents. In this connection, the results of a simple but effective model system called ISSM are also presented. As an alternative simulations with the SHORECIRC model system are also performed. Finally, as a case study, the propagation of the pollution towards the Romanian coast generated by a hypothetic accident at the Gloria drilling platform was assessed. Santrauka Per pastaruosius dešimtmečius pletojant pramone Juodosios jūros priekrantes zonoje, del atsitiktiniu naftos išsiliejimu padidejo taršos rizika. Viena iš priežasčiu, del kuriu ivyksta tokios avarijos, yra netikslios bangu būkles prognozes. Darbo tikslas – remiantis spektriniu fazes vidurkiu apskaičiavimu modeliais, sukurti metodologija, kuri leistu numatyti bangu sklidima priekrantes zonoje. Taip pat ivertinamos bangos sukeltos sroves. Jos gali būti vienas iš pagrindiniu veiksniu, turinčiu itakos teršalu sklidimui jūroje. I skaičiavimus itraukiama Stokso tekme bei bangos sukeltos pakrantes sroves, išreiškiamas paviršiaus sroviu efektas pagal molekuline klampa. Del ilguju pakrantes sroviu prie kranto iš arčiau pavir‐šiaus zonos esančio šaltinio tarša dažniausiai sklinda palei pakrante, todel rezultatai pristatomi taikant modeliavimo siste‐mas ISSM ir SHORECIRC. Modeliuojant remtasi studija, kurioje vertinamas taršos sklidimas ties Rumunijos pakrante del spejamai ivykusios avarijos Glorijos grežinio platformoje. Резюме Постоянно увеличивающаяся в последние десятилетия экономическая активность в прибрежной зоне Чѐрного моря ведѐт к бóльшему риску загрязнения из-за случайных разливов нефти. В связи с тем, что большая часть случаев разлива была связана с неадекватным прогнозом волнения, целью настоящей работы было разработать методологию, основанную на спектральных моделях волнения с усреднением фазы, способную предсказывать распространение волн в прибрежной зоне. Было оценено также течение, вызванное волнением, которое может стать решающим фактором в распространении загрязнения. Оно включает в себя стоксово дрейфовое течение и прибрежное течение. Учтено также поверхностное течение, вызываемое ветром через касательные напряжения. В качестве примера рассмотрено распространение в направлении румынского берега загрязнения, вызванного гипотетической аварией на буровой платформе Глория.


1992 ◽  
Vol 25 (9) ◽  
pp. 225-234 ◽  
Author(s):  
T. Larsen ◽  
R. Burrows ◽  
L. Engedahl

The internal hydraulics of the multiport diffuser section in long sea outfalls has been studied by laboratory experiments and numerical modelling. The study has run for five years as a coordinated effort at both the University of Liverpool and the University of Aalborg. The investigations have covered such phenomena as saline intrusion, wave influence and unsteady flow caused by pump operation. Results show that numerous flow regimes exist depending on the boundary conditions. Numerical models have been developed to simulate the flow field in the diffuser section and some of the most interesting phenomena, in particular the wave induced saline intrusion, can now be modelled satisfactorily. Some aspects of the behaviour relating to very low fresh water discharges, e.g. unsteady flow when saline wedges are present, are still not very well described.


2015 ◽  
Vol 17 (1) ◽  
pp. 62-73 ◽  
Author(s):  
A. J. Koivisto ◽  
A. C. Ø. Jensen ◽  
M. Levin ◽  
K. I. Kling ◽  
M. Dal Maso ◽  
...  

Here we tested how well a NF/FF dispersion model predicts particulate matter concentrations when source emission potency was estimated using a material dustiness index.


1998 ◽  
Vol 38 (10) ◽  
pp. 323-330
Author(s):  
Philip J. W. Roberts

The results of far field modeling of the wastefield formed by the Sand Island, Honolulu, ocean outfall are presented. A far field model, FRFIELD, was coupled to a near field model, NRFIELD. The input data for the models were long time series of oceanographic observations over the whole water column including currents measured by Acoustic Doppler Current Profilers and density stratification measured by thermistor strings. Thousands of simulations were made to predict the statistical variation of wastefield properties around the diffuser. It was shown that the visitation frequency of the wastefield decreases rapidly with distance from the diffuser. The spatial variation of minimum and harmonic average dilutions was also predicted. Average dilution increases rapidly with distance. It is concluded that any impact of the discharge will be confined to a relatively small area around the diffuser and beach impacts are not likely to be significant.


2021 ◽  
Vol 11 (9) ◽  
pp. 4136
Author(s):  
Rosario Pecora

Oleo-pneumatic landing gear is a complex mechanical system conceived to efficiently absorb and dissipate an aircraft’s kinetic energy at touchdown, thus reducing the impact load and acceleration transmitted to the airframe. Due to its significant influence on ground loads, this system is generally designed in parallel with the main structural components of the aircraft, such as the fuselage and wings. Robust numerical models for simulating landing gear impact dynamics are essential from the preliminary design stage in order to properly assess aircraft configuration and structural arrangements. Finite element (FE) analysis is a viable solution for supporting the design. However, regarding the oleo-pneumatic struts, FE-based simulation may become unpractical, since detailed models are required to obtain reliable results. Moreover, FE models could not be very versatile for accommodating the many design updates that usually occur at the beginning of the landing gear project or during the layout optimization process. In this work, a numerical method for simulating oleo-pneumatic landing gear drop dynamics is presented. To effectively support both the preliminary and advanced design of landing gear units, the proposed simulation approach rationally balances the level of sophistication of the adopted model with the need for accurate results. Although based on a formulation assuming only four state variables for the description of landing gear dynamics, the approach successfully accounts for all the relevant forces that arise during the drop and their influence on landing gear motion. A set of intercommunicating routines was implemented in MATLAB® environment to integrate the dynamic impact equations, starting from user-defined initial conditions and general parameters related to the geometric and structural configuration of the landing gear. The tool was then used to simulate a drop test of a reference landing gear, and the obtained results were successfully validated against available experimental data.


2020 ◽  
Vol 4 (1) ◽  
pp. 17
Author(s):  
Saisantosh Vamshi Harsha Madiraju ◽  
Ashok Kumar

Transportation sources are a major contributor to air pollution in urban areas. The role of air quality modeling is vital in the formulation of air pollution control and management strategies. Many models have appeared in the literature to estimate near-field ground level concentrations from mobile sources moving on a highway. However, current models do not account explicitly for the effect of wind shear (magnitude) near the ground while computing the ground level concentrations near highways from mobile sources. This study presents an analytical model based on the solution of the convective-diffusion equation by incorporating the wind shear near the ground for gaseous pollutants. The model input includes emission rate, wind speed, wind direction, turbulence, and terrain features. The dispersion coefficients are based on the near field parameterization. The sensitivity of the model to compute ground level concentrations for different inputs is presented for three different downwind distances. In general, the model shows Type III sensitivity (i.e., the errors in the input will show a corresponding change in the computed ground level concentrations) for most of the input variables. However, the model equations should be re-examined for three input variables (wind velocity at the reference height and two variables related to the vertical spread of the plume) to make sure that that the model is valid for computing ground level concentrations.


2021 ◽  
Vol 217 (3) ◽  
Author(s):  
E. M. Rossi ◽  
N. C. Stone ◽  
J. A. P. Law-Smith ◽  
M. Macleod ◽  
G. Lodato ◽  
...  

AbstractTidal disruption events (TDEs) are among the brightest transients in the optical, ultraviolet, and X-ray sky. These flares are set into motion when a star is torn apart by the tidal field of a massive black hole, triggering a chain of events which is – so far – incompletely understood. However, the disruption process has been studied extensively for almost half a century, and unlike the later stages of a TDE, our understanding of the disruption itself is reasonably well converged. In this Chapter, we review both analytical and numerical models for stellar tidal disruption. Starting with relatively simple, order-of-magnitude physics, we review models of increasing sophistication, the semi-analytic “affine formalism,” hydrodynamic simulations of the disruption of polytropic stars, and the most recent hydrodynamic results concerning the disruption of realistic stellar models. Our review surveys the immediate aftermath of disruption in both typical and more unusual TDEs, exploring how the fate of the tidal debris changes if one considers non-main sequence stars, deeply penetrating tidal encounters, binary star systems, and sub-parabolic orbits. The stellar tidal disruption process provides the initial conditions needed to model the formation of accretion flows around quiescent massive black holes, and in some cases may also lead to directly observable emission, for example via shock breakout, gravitational waves or runaway nuclear fusion in deeply plunging TDEs.


2021 ◽  
pp. 108325
Author(s):  
Darpan Das ◽  
Emma Moynihan ◽  
Mark Nicas ◽  
Eric D. McCollum ◽  
Salahuddin Ahmed ◽  
...  

1996 ◽  
Vol 465 ◽  
Author(s):  
B. Gylling ◽  
L. Romero ◽  
L. Moreno ◽  
I. Neretnieks

ABSTRACTA coupled model concept which may be used for performance assessment of a nuclear repository is presented. The tool is developed by integration of two models, one near field and one far field model. A compartment model, NUCTRAN, is used to calculate the near field release from a damaged canister. The far field transport through fractured rock is simulated by using CHAN3D, based on a three-dimensional stochastic channel network concept. The near field release depends on the local hydraulic properties of the far field. The transport in the far field in turn depends on where the damaged canister(s) is located. The very large heterogeneities in the rock mass makes it necessary to study both the near field release properties and the location of release at the same time. In order to demonstrate the capabilities of the coupled model concept it is applied on a hypothetical repository located at the Hard Rock Laboratory in Äspö, Sweden. Two main items were studied; the location of a damaged canister in relation to fracture zones and the barrier function of the host rock. In the study of the near field rock as a transport barrier the effect of different tunnel excavation methods which may influence the damage level of the rock around the tunnel was addressed.


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