Difference between revisions of "Module Sand"

Revision as of 10:56, 8 March 2011

Overview

Module Sand was the result of the accumulated experience gain by Hidromod in the framework of many enginnering projects. Many of the projects were done with a old version programmed in F77. More recently Hidromod develop a new Module using the present MOHID Programming philosophy. The concepts of this module were described an tested in detail by Carmo (2005) see [1].

Algorithm

From a conceptual point of view this module is very simple. The bed load fluxes are compute in Arakawa-C grid [2]. In each centre cell (Z point) is compute the transport flows. The user to compute the transport flows can choose from a set of formulations presented below. In a second step the Zonal (or X) component flows are interpolated to the U points and the meridional (or Y) components are interpolated to the V points. Finally to estimate the evolution of the sand thickness in the centre cell (Z point) a mass balance is done. The availability of sand in a cell is limited by the depth of the bed rock.

Transport formulas implemented

In this section are enumerated the transport formulas implemented in the MOHID system. Based in the formulas characteristics and Hidromod experience the formulas can be devided by area of application:

Rivers

Meyer-Peter, E; Müller, R. (1948)

Estuaries

Ackers and White (1973)

Coastal areas

Bijker-Battachraya (1968) Van Rijn (1984, 1993) Bailard (1981,1984) Dibajnia (1992)

Main options

In this section it is briefly described the options available in Module Sand. The different options provided by the module can be defined through an input data file, similarly to other MOHID modules. The name of the Module Sand for run number x is Sand_x.dat (see Mohid GUI)

Keyword TRANSPORT_METHOD is used to choose from the list presented above the transport formula the user wants to test. The options are: no transport, MeyerPeter, Ackers, VanRijn1, VanRijn2, Bailard, Dibajnia, Bijker. Keyword SAND_DT is the time step used to compute the transport formula by default is equal to the global model time step (see - Choose the model time step). The keyword OLD (0 - OFF; 1 - ON) is ON when the user wants to do a hot start (OFF - cold start).

TRANSPORT_METHOD : MeyerPeter
SAND_DT          : 60.
OLD              : 0

The user can choose if the compute bed loads change or not the bathymetry and consequently the hydrodynamics. If the user wants to take in consideration the effect of bathymetry changes in the other Mohid modules than BATHYM_EVOLUTION : 1. The keyword BATIM_DT is used to define the frequency of actualization of the model bathymetry by default is equal to the global model time step (see - Choose the model time step).

BATHYM_EVOLUTION : 1 
BATIM_DT         : 60.

Keywords to define the boundary condtions. The keyword BOUNDARY is used to define the open boundary condition. The options are 1 (null gradient)and 2 (cyclic boundary - used in academic studies mainly). The keyword DISCHARGES is use to activate a set of sinks or sources of sediments (0 - OFF, 1 - ON). These sikns/sources of sediments are define in the discharge_x.dat input file see Module Discharges. To define a set of sinks/sources of sediments see How to create discharges in MOHID.

BOUNDARY : 1

DISCHARGES : 0

The follow keywords are used to define the sediments diameter. This are one of the main inputs of transport formulas.

<beginD90>
NAME                  : D90
UNITS                 : m            
DESCRIPTION           : Diameter below which 90 percent of the particles are finer
FILE_IN_TIME          : ASCII_FILE            
FILENAME              : D90Field.dat 
<endD90>
<beginD50>
NAME                  : D50
UNITS                 : m            
DESCRIPTION           : Diameter below which 50 percent of the particles are finer
FILE_IN_TIME          : ASCII_FILE            
FILENAME              : D50Field.dat 
<endD50>
<beginD35>
NAME                  : D35
UNITS                 : m            
DESCRIPTION           : Diameter below which 35 percent of the particles are finer
FILE_IN_TIME          : ASCII_FILE            
FILENAME              : D35Field.dat 
<endD35>

The follow keywords are used to define the sediments availability (bed rock concept). The SAND_MIN keyword is to define the limit (in meters) below which the transport stops to avoid sediment negative thicknesses.

<beginrock>
NAME                  : bed rock
UNITS                 : m            
DESCRIPTION           : Depth from sediment surface below which there is no sediment to be transported
FILE_IN_TIME          : ASCII_FILE            
FILENAME              : BedRock.dat
<endrock>
SAND_MIN : 0.01

The field properties D90, D50, D35 and bed rock are defined using the options available in Module Fillmatrix.

Advanced options

The follow keywords are used to convert sediments from mass per sqaure meter in meters (POROSITY - porosity and DENS_SAND - sand density).

POROSITY : 0.1
DENS_SAND : 2650.

The follow keywords are used to smooth the solution. The transport formulas are highly non-linear and tend to generate very noisy solutions. Keyword - FILTER_SCHEME, options: No Filter (filter OFF), Modify Lax (filter ON). This filter distributes 50% of the bathymetry evolution in the adjecent cells. The keyword FILTER_RADIUS is used to define the radius (in number of cells) that is used to define the adjcent areas under the effect of sediment redistribution.

FILTER_SCHEME : No Filter
FILTER_RADIUS : 4

A factor to speed up morphodynamic processes. This factor must be use with caution. This factor multiplies by he transport loads

TRANSPORT_FACTOR : 1.

The maximum limit for the bottom shear stress used in the Meyer Peter formula can be defined with the follow keyword:

TAU_MAX = 10.

The flux perpendicular to the flux is a percentage of the paralel flux

SMOOTH_SLOP : 0
CRITICAL_SLOP : 0.1
FLUX_SLOP : 0.1

Outputs

The user in this module can output: time series of fields (HDF5 files), time series in a point (Time Series ASCII files) and time series of integral results for an area (Boxes ASCII files).

Boxes

The user can compute the sediment fluxes between boxes (or areas).

BOXFLUXES : 1

If the user wants to compute fluxes between areas needs to define a network of boxes following the ASCII MOHID format Boxes.

BOX_FILENAME : Boxes.dat 

Time series

The user can also do output of the most signifcant properties in a point related with bed load following the standard methodology used in the other MOHID modules (see Module TimeSerie).

For example, if a user wants to activate the output time series option needs to add to the input file (Sand_x.dat) the follow keyword:

 TIME_SERIES : 1

Maps (HDF5 format)

The user can also do output of the most signifcant properties fields related with bed load following the standard methodology used in the other MOHID modules (see OUTPUT TIME).

For example, if a user wants field results every hour starting from the beginning of the run it needs to define the follow (time is seconds).

 OUTPUT_TIME : 0. 3600.

References

AHMED, S. M., SATO, S. (2003); A sheetflow transport model for asymmetric oscillatory flows. Part I: Uniform grain size sediments; Coastal Engineering Journal 45, 321-337.

ACKERS, P.; WHITE, W.R. (1973); "Sediment Transport: New Approach and Analysis". Journal of the Hydraulics Division (ASCE) 99 (11): 2041–2060.

AL SALEM, A. (1993); Sediment transport in oscilatory boundary layers under sheet flow conditions; PhD thesis, Delft Hydraulics, The Netherlands.

BAGNOLD, R. (1966); An approach of sediment transport model from general physics; US Geol. Survey Prof. Paper 422-I.

BAILARD, J. A. (1984); A simplified model for longshore sediment transport. Proceedings of the 19th Coastal Engineering Conference, pp. 1454– 1470.

BAILARD, J. A., INMAN, D. L. (1981); An energetics bedload model for plane sloping beach: local transport. Journal of Geophysical Research 86 (C3), 2035– 2043.

BAYRAM, A., LARSON, M., MILLER, H., KRAUS, N. (2001); Cross-shore distribution of longshore sediment transport: comparison between predictive formulas and field measurements; Coastal Engineering Journal 44, 79– 99.

BIJKER, E. (1968); Littoral drift as function of waves and current; 11th Coastal Eng. Conf. Proc. ASCE; London, UK; pp. 415–435.

CAMENEN, B., LARROUDÉ, P. (2003); Comparison of sediment transport formulae for the coastal environment; Coastal Engineering 48, 111– 132.

DIBAJNIA, M., WATANABE, A. (1992); Sheet flow under nonlinear waves and currents. Coastal Engineering Journal, 2015– 2029.

DU BOYS, P. (1879); Le rhône et les rivières à lit affouillable; Ann; Ponts Chaussées 18 (5), 171– 195.

FERNANDES, L. (2001); Transporte de Poluentes em Estuários; Trabalho Final de Curso da Licenciatura em Engenharia do Ambiente; Instituto Superior Técnico, Universidade Técnica de Lisboa.

FRIJLINK, H. (1952); Discussion des formules de débit solide de Kalinske, Einstein et Meyer-Peter and Muller compte tenue des mesures récentes de transport dans les rivières néerlandaises; 2nd Journal Hydraulique; Société Hydraulique de France, pp. 98– 103.

KOMAR, P. D. (1998); Beach processes and sedimentation; 2nd Ed.; Pearson Education, New Jersey.

LEITÃO, P.C. (2002); Integração de Escalas e de Processos na Modelação do Ambiente Marinho; Dissertação para a obtenção do grau de Doutor em Engenharia do Ambiente; Instituto Superior Técnico, Universidade Técnica de Lisboa.

LIU, Z. (2001); Sediment Transport; Instituttet for Vand, Jord og Miljøteknik; Aalborg Universitet.

MEYER-PETER, E; MULLER, R. (1948); Formulas for bed-load transport. Proceedings of the 2nd Meeting of the International Association for Hydraulic Structures Research. pp. 39–64.

SANCHO, F. (2002); Apontamentos da disciplina de Processos Fluviais e Costeiros, Mestrado em Hidráulica, Recursos Hídricos e Ambiente; Faculdade de Ciências e Tecnologia da Universidade de Coimbra.

SILVA*, A., NEVES**, R., LEITÃO, J.C. (1997); Modelação de Processos de Transporte por Acção Combinada de Ondas e Correntes; *HIDROMOD - Modelação em Engª, Ldª; **Instituto Superior Técnico; Lisboa.

SMITH, J., SHERLOCK, A., RESIO, D. (2001); STWAVE: Steady-State Spectral Wave Model. User’s Manual for STWAVE, Version 3.0; ERDC/CHL, US Army Corps of Engineers; Washington, DC.

TRANCOSO, A. R. (2002); Modelling Macroalgae in Estuaries; Trabalho Final de Curso da Licenciatura em Engenharia do Ambiente; Instituto Superior Técnico, Universidade Técnica de Lisboa.

VAN RIJN, L.C. (1984); Sediment transport: Part I: Bed load transport; Part II: Suspended load transport; Part III: Bed forms and alluvial roughness. Journal of Hydraulic Division 110 (10), 1431– 1456; 110 (11) 1613– 1641; 110 (12) 1733-1754.

VAN RIJN, L.C. (1993); Principles of sediment transport in rivers, estuaries and coastal seas. Aqua Publication, The Netherlands, Amsterdam.

WANG, P., EBERSOLE B., SMITH E. (2002); Longshore Sand Transport – Initial Results from Large-Scale Sediment Transport Facility; ERDC/CHL, US Army Corps of Engineers, Washington, DC.

WINTER, C. (2004); Perfomance of sediment transport models in tidal environments, Workshop HWK, Delmenhorst.