development, testing and application of the multi-block ltfate hydrodynamic and sediment transport...

Development, Testing and Application of the Multi-Block LTFATE Hydrodynamic and Sediment Transport Model

Earl J. HayterEnvironmental Lab

October 25, 2012

Innovative solutions for a safer, better worldBUILDING STRONG®

LTFATE Multi-Block Hydrodynamic, Water Quality and Sediment Transport Modeling System

LTFATE- HYDRO

CH3D

LTFATE-SED SEDZLJ STWAVE

MET

ADCIRCCE-QUAL-ICM


LTFATE Multi-Block (MB) Concept

A conventional hydrodynamic single-block application approach typically requires long simulation time as well as large CPU memory requirements.

Solution: Grid Decomposition and Message Passing Interface (MPI) code.

Grid decomposition splits a single large grid into multiple smaller grids, MB, where each grid runs on it’s own CPU.

Message Passing Interface code allows communication amongst MB grids as the simulation proceeds.

Result: Significant decreases in simulation time and CPU memory.

To date, SEDZLJ applied in a 3D single block (SB) as a nested grid and 2D fully multi-block (MB) system

3


Nested Grid SEDZLJ SB Application

The Mobile District is performing a feasibility study for channel widening of the Pascagoula Lower Sound (PLS)

and Bayou Casotte (BC) navigation channels within the Mississippi Sound (MS). To support the District, ERDC modeled wave- and current-induced sediment transport in a portion of the MS centered about these channels.

Utilize fully 3D hydrodynamic and sediment transport modeling to evaluate the impact of the proposed widening alternatives sedimentation and infilling rates.

Objective of Modeling Study


Physical Setting

Mobile Bay

MS Sound

Bayou Casotte

Pascagoula River

Chandeleur Islands


Physical Setting

Petit Bois Island

Bayou Casotte

Pascagoula River

Horn Island

Round Island


Methodology

• ADCIRC and STWAVE used to generate the tidal boundary and local wave forcing for the Multi-Block (MB) LTFATE model.

• Performed circulation modeling of MS using MB LTFATE to generate hydrodynamic and salinity boundary conditions for the nested single block

(SB) LTFATE model of the Pascagoula Lower Sound (PLS) and Bayou Casotte (BC) navigation channels within the Mississippi Sound (MS).

• Setup the sediment transport model using results from Sedflume and PICS analyzes and existing sediment data.


Methodology (continued)

• Calibrate the sediment transport model by comparing model simulations with measured suspended sediment

concentration (SSC) profiles.

• Validate the sediment transport model by comparing measured and simulated sedimentation volumes in the

Lower Sound and Bayou Casotte reaches of the Pascagoula Harbor Channel.

• Simulate three channel widening scenarios to determine impact of the channel widening on the sedimentation volumes.


MB LTFATE-Hydro is a 3D, non-orthogonal boundary-fitted hydrodynamic model that includes temperature and salinity transport.

MB boundary conditions are river inflow data and tidal forcing from ADCIRC circulation model simulations and time varying wave forcing from STWAVE.

MB LTFATE system provides time varying water surface elevation, flow, and salinity forcing for the SB open-water boundaries.

SEDZLJ is the sediment transport model that is dynamically integrated into the LTFATE hydrodynamic module.

MB-SB LTFATE


Multi-Block (5) LTFATE Grid


Nested SB LTFATE Bathymetry

PLS Channel

BC Channel


Nested SB LTFATE GRID


Sediment Transport ProcessesSimulated in LTFATE

• Erosion of mixed cohesive and non-cohesive sediment beds• Advective and dispersive transport of suspended sediment• Bedload transport of non-cohesive sediment• Settling of flocculated cohesive sediment, and settling of

individual non-cohesive sediment particles.• Effect of bed slope on bedload transport and erosion rate is

represented.• Changes in bottom elevations due to erosion and deposition

are accounted for in calculating the flow field during the next model timestep.

• Current- and wave-induced bed shear stresses are calculated and used in determining erosion rate.


Sediment Transport Model Simulations

LTFATE was run for the same two month time period for the three widened channel configurations. The ratio of sedimentation volumes of the widened channels to those of the existing channel are given below.

Expansion Width Bayou CasotteChannel

Pascagoula LowerSound Channel

75’ East & 75’ West 1.3 1.3

100’ West 1.15 1.25

150’ West 1.2 1.4


SB Summary

3D sediment transport modeling was performed in the MS Sound using a combination of MB and SB LTFATE, which is a state-of-the-art hydrodynamic, salinity, temperature and sediment transport modeling system.

LTFATE can represent the following forcings: time varying water surface elevation due to tides, riverine flows, wind, and spatially and temporally varying wave properties. The latter are used to calculate radiation stresses that are included in the momentum equations solved in LTFATE.

The effect of bed slope on bedload transport and erosion rates is accounted for in LTFATE. Representing the impact of bed slope becomes critical at navigation channels due to relatively rapid changes in bathymetry.


MB SEDZLJ Development

ERDC has further developed the MB LTFATE to dynamically link SEDZLJ within the MB system by developing MPI routines to allow SEDZLJ to be run in every block.


Questions?

development, testing and application of the multi-block ltfate hydrodynamic and sediment transport...

Documents

multiblock mb ltfate

hydrodynamic model

sediment transport modelearl

salinity transport

mb grids

mb boundary conditions

grid decomposition

single large grid