Promod vohra thesis

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Promod vohra thesis

To conserve computational resources and obtain results within one to two days for a case, the analysis was done as a single phase flow with the water surface assumed to be flat using a symmetric boundary condition that allows for a slip velocity.

Diagram of flooded deck in flume The scour process that changes the location of the sediment bed through entrainment of stationary particles at the bed interface with the moving stream takes place within the boundary layer at the bed.

Maintaining an accurate position of the bed interface with a well resolved bed contour and high quality computational mesh in the vicinity of the bed is an approach to scour modeling that appears to provide the basis for a robust model.

In this approach, processes that are occurring within the porous media stationary sediment bed would be modeled as a separate subdomain of the problem.

Because the primary goal in the current study was to establish and evaluate procedures for displacing the sediment bed under conditions where erosion will occur, the process is taken to be a series of steps in which the bed is displaced in proportion to the shear stress above the critical shear stress for the onset of particle entrainment from the bed.

The entrainment rate, sediment transport, and settling are not included in this initial modeling effort. The model was kept as simple as possible to concentrate on testing iterative displacement of the bed surface in a threedimensional domain to obtain the asymptotic scour hole contour after a long period of time.

As shown in Figure 3, the process of displacing the bed includes many steps using several commercial and open source software components to maintain a high quality mesh during iterative bed displacement driven by the computed shear stress distribution.

Because the flow time scale is on the order of milliseconds while the erosion time scale is initially on the order of minutes and extends to hours as the asymptotic bed contour is approached, the RANS turbulence model flow computation step can be treated as quasi-steady and computed as a steady state.

The modeling process is an iterative procedure in which 1 the flow field is solved using the current bed contour to obtain the bed shear stress distribution, 2 the bed shear stress distribution is used to displace the bed, 3 the flow domain is remeshed to maintain a high mesh quality as the bed is displaced, and 4 the process is repeated until the bed shear stress is everywhere at or below the critical shear stress within a small tolerance value.

Each solve of the flow field is done as a batch job submitted to a high performance computer cluster. The mesh contains about 1. Starting from flat bed conditions as in the experiments, reaching the final scour hole contour required between and iterations of the procedure depending on the case.

When a human carried out the steps to run the various software needed to complete one iteration, only a few iterations could be completed per day, which would have required at best one to several months to complete a single case analysis.

Therefore the entire process was automated with various programming scripts as shown in Figure 3 to bring the iterative case analysis time down to 1 to 2 days with minimal human intervention. A Bash script acts as the master process to carry out the sequence of steps in each iteration.

Promod vohra thesis

Because Python is proficient in parsing and manipulating text, a Python program was developed to process a file containing the bed shear stress distribution and generate a file of thousands of commands to displace the bed at vertices in a CFD preprocessor software component.

Data was obtained from a series of scour experiments conducted at TFHRC on bridge pressure flow scour under clear water conditions. The experiments were designed to refine a two dimensional analysis procedure, and while there were no piers in the experiments to introduce 3D effects, bed stress near the side walls of the flume is lower than in the center region under the flooded bridge decks and does produce a 3D effect.

Data for extensive 3D bathymetry maps of the scoured test section was collected using a laser distance sensor [9]. This data compares well to the results of analysis with the CFD modeling procedure given the simplicity of the procedure and that it is intended to provide a basis for implementing and testing more extensive erosion physics models.

The flow domain with dimensions is shown in Figure 1. The experiments were designed to come close to the maximum clear water scour under the flooded bridge deck.

For 1 mm sand the mean velocity is 0. For the 2 mm sand cases, the unobstructed channel mean flow velocity was 0. Results for a case with a fully submerged bridge deck 16 cm hb above the initial and upstream bed using 2 mm sand are presented for illustration and discussion.

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The relaxation of accelerated flow under a flooded bridge deck blockage when the scour hole forms as a consequence of the elevated shear stress generated on the bed is shown in Figure 4.

The upper part of the figure shows a high velocity zone in red to orange 0. These higher velocities above the bed yield a shear stress that is more than two times the critical shear stress on the initial flat bed.

The lower plot in the figure shows the equilibrium scour hole profile down the flume centerline with the lower velocity distribution that is a consequence of increased cross section flow area. The shear stress on the bed in the lower figure is at or below critical in the vicinity of the deck.

A comparison of the bathymetry of the scour hole and up and downstream bed is shown in Figure 5. The scoured bed d c 0. The critical shear stress for 2 mm sand is 1.

A correction for sloped beds is often applied based on the bed slope with respect to the flow velocity and gravity vectors.

In the cases included in this study, the slope of the bed in the scour hole that forms under the deck is very small and neglected in this initial work.

Sediment bed displacements are computed from the shear stress distribution using: The max function prevents displacing the bed when the shear stress is less than critical.

After each quasi-steady flow solve step i, the bed contour is updated according to: The bed shear is computed through the use of wall functions, and the computed shear is a function of the effective roughness of the wall. Depending on particle diameter, the values from the different formulae may vary by a factor of more than 2.Illinois Official Reports.

Appellate Court. People ex rel. Rahn v. Vohra, IL App (2d) Appellate Court Caption THE PEOPLE OF THE STATE OF . Clifford Mirman, & Promod Vohra. Energy Conservation Projects to Benefit the Railroad States.

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@article{osti_, title = {Transporation Energy}, author = {Clifford Mirman and Promod Vohra}, abstractNote = {This Transportation Energy Project is comprised of four unique tasks which work within the railroad industry to provide solutions in various areas of energy conservation. These tasks addressed: energy reducing yard related decision issues; alternate fuels; energy education, and energy storage .

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