|Title of Invention||
"METHOD OF VISUALIZATION OF SCOUR MECHANISM BY MUD FLOW"
|Abstract||The phenomenon of pier induced scouring in alluvial rivers commences with the formation of a vortex, which wraps around the pier in the shape of a horseshoe vortex when viewed in plan. Viewing of the vortex had always been difficult due to its constricted location and turbulence associated with the phenomenon. Visualization of flow helps in understanding the associated phenomenon. Certain dyes used for the purpose have not been successful in the visualization of phenomenon under study. Mud flow visualization technique helps in viewing the phenomenon of scouring at the sediment-water-pier interaction junction. The technique is very effective in visualizing the phenomenon and thereafter in measuring the size of the vortex which may be used for predicting the scour depth.|
|Full Text||Title of invention:
APPARATUS AND METHOD OF VISUALIZATION OF SCOUR MECHANISM BY MUD FLOW
Field of Invention:
This invention relates to the novel method of visualization of scour, scour mechanism and the scouring horseshoe vortex prior to commencement of scouring of mobile bed and during scouring when the scouring has developed.
Background of invention:
Rivers are natural flowing systems, which cannot be controlled by manmade structures. Construction of a bridge pier across a river obstructs the flow. The flowing water in the river scours the sediment around the bridge piers. Thus, all bridges and structures associated with waterways are potentially at risk of failure due to hydraulic scour.
It has been estimated that 60% of all river bridge failures is attributable to undermining of pier foundations following scouring or erosion of the channel bed. During 1961 to 1976, out of 86 major bridge failures, 46 failed as a result of excessive scour near piers (Murillo 1987). Breusers et al. (1977) present a state of the art report on the mechanism and prediction of scour depth around a bridge pier. The bridge failures of Ganga Pul at Makamah (River Ganga) and on river Tapi are examples of major bridge failures due to scour in India. Reports of Ministry of Railways, India (1967, 1968, and 1972) describe the history of work carried out in India in the direction of bridge pier scour.
The major cause of scouring leading to exposing of the pier is a system of vortices. It commences with the formation of adverse pressure gradient at the upstream front of pier, which results in the formation of this vortex. This vortex wraps around the pier in the form of a horseshoe and dislodges sediment from the bed and releases it downstream.
Many an engineering problem associated with fluid flow need an understanding of the interaction of the flow with the solid boundary. Visualization of the flow-sediment interaction is the first step towards understanding of the phenomenon.
Techniques available to visualize the flow on the bed instantaneously include hydrogen bubble technique and injection of a color dye like potassium permanganate solution etc.
Many projects, especially the larger and more complex ones, require model studies. Techniques available at present involve numerical and physical models. The former will have limited predictive potential although their utility will increase with the formulation of adequate theoretical structures to support them. The latter, the small scale physical model, is at present a much more powerful tool. Visualization of flow helps in understanding the associated phenomenon. Certain dyes used for the purpose have not been successful in the visualization of phenomenon under study. The present technique is very effective in visualizing the phenomenon and therefore in measuring the size of the vortex.
Object of invention:
To provide a method for studying the formation of vortex, which wraps around the pier in the shape of a horseshoe when viewed in plan. Viewing this vortex had always been difficult due to the constricted location and turbulence associated with the phenomenon. Hence object of the invention is to provide a method for viewing and photographing of this complex phenomenon.
Statement of invention:
The invention lies in the method to study the phenomenon of scouring at the sediment-water- pier interaction junction. A summary of invention:
The phenomenon of pier induced scouring in alluvial rivers commences with the formation of a vortex, which wraps around the pier in the shape of a horseshoe vortex when viewed in plan. Viewing of the vortex had always been difficult due to its constricted location and turbulence associated with the phenomenon. The mud flow visualization technique helps in viewing the phenomenon of scouring at the sediment-water-pier interaction junction.
A brief description of the accompanying drawing:
FIGURE 1: Lighting arrangement and mud flow injection
FIGURE 2: Photographic views of horse-shoe vortex before scouring with vortex shining in the presence of mud particles
FIGURE 3: Photographic views of horse-shoe vortex during scouring with vortex shining in the presence of mud particles
Detailed description of the invention with reference to drawing /examples:
The method essentially makes use of a transparent glass pier. But for a small (approximately 2mm) longitudinal slit running through the length of the pier, the rest of the pier was painted black. A bulb as a source of light was lowered into the cylindrical pier when in position. The light from this bulb passed through the thin slit and shone in a vertical plane. A turbid suspension of clay in water was used as visualization media. Clay suspension in water had an advantage over other media like color dyes, etc., as it did not diffuse rapidly in highly turbulent flow field and hence the vortex was clearly visible under proper lighting arrangement. The clay suspension from a small reservoir (wash bottle) was injected in place through a nozzle. A metallic tube 3 mm diameter having a nozzle at its end was bent in a semi-circular shape to embrace the cylindrical pier. The nozzle tube being kept flush with the bed caused minimum interference to the vortex under consideration (Figure 1).
The clay mixed with the turbulent flow and its particles took the shape of the scouring vortex. This region, fully illuminated by the light from within the cylinder, offered a complete picture of the vortex. By this method of flow visualization, it was possible to observe and measure the horseshoe vortex characteristics under different flow conditions. Figures 2 and 3 present photographic views of horse-shoe vortex before and during scouring with vortex shining in the presence of mud particles.
1. The apparatus for visualization of scour and scour mechanism is made up of a
blackened glass cylinder with a small transparent longitudinal slit running throughout
its length, a source of light like a bulb or any other source placed in the cylinder at a
specific height and a 3 mm diameter metallic tube having a nozzle at its end and bent
in the form of a semi circular shape to embrace the circular pier.
2. The apparatus as claimed in Claim 1 wherein a slit of 2 mm is provided running
through the length of the cylinder and the rest of the portion to be painted black (or
wrapped from inside with a thick black paper).
3. The apparatus as claimed in Claim 1 wherein the metallic tube serves as a carrier of
the clay water suspension to the bed-water-pier junction.
4. A method of visualization of scour and scour mechanism by mud flow technique
comprising the steps of:
a. Placing the apparatus, (i.e., a blackened glass cylinder with a small transparent
longitudinal slit running throughout its length, to serve as a model of bridge pier),
b. Transmitting a vertical sheet of light through a slit provided in the apparatus for
generating the plane of study in flowing water.
c. Formation of turbid suspension of clay in water to be used as visualization media
to obtain a complete picture of vortex (as clay mixed with the turbulent flow takes
the shape of the scouring vortex) on the sheet of light and the said suspension of
clay is injected with the aid of a metallic tube 3 mm diameter, with nozzle at its
end and bent in a semi circular shape to embrace the circular pier.
5. The method as claimed in Claim 4 wherein minimum interference to the vortex is
caused by the nozzle tube which is kept flush with the periphery of the pier at the
sand bed level.
6. The apparatus for visualization of scour and scour mechanism by mud flow technique
as described in the specifications and illustrated in the drawings.
7. The method of visualization of scour and scour mechanism by mud flow technique as
described and illustrated in the specifications.
|Indian Patent Application Number||1376/DEL/2005|
|PG Journal Number||40/2007|
|Date of Filing||30-May-2005|
|Name of Patentee||Baldev Setia|
|Applicant Address||Asst. Professor In Civil Engineering, National Institute of Technology Kurushetra (HARYANA) 136119, INDIA.|
|PCT International Classification Number||N/A|
|PCT International Application Number||N/A|
|PCT International Filing date|