|Title of Invention||
"AN IMPROVED STILLING- WELL DEVICE USEFUL FOR ENABLING ERROR- FREE SEA LEVEL MEASUREMENTS"
|Abstract||The present invention provides an improved stilling-well device useful for enabling error free sea level measurements , which comprises a stilling-well characterized in that the entire submerged portion of the said stilling well being provided with an array of perforations wherein each of the said perforation having a hollow bush fitted into each perforation with means .|
|Full Text||The present invention relates to an improved stilling-well device useful for enabling error free sea level measurements.
The present invention particularly relates to an improved stilling-well device allowing free exchange with ambient waters resulting in reduced error in sea level measurements.
The device of the present invention is part of a float driven gauge used to measure sea levels in coastal and estuarine environments with improved accuracy so as to enable the extraction of the weak but crucial 'climate signal' from sea level measurements.
Hitherto known stilling-well devices used since 1831 [ H.R. Palmer (1831), in Philosophical Transactions of the Royal Society of London ] in numerous float-driven gauges in several parts of the world, and protective wells as used with modern guided-air-acoustic gauges [ Anon (1991) US Dept. of Commerce, NOAA ] have the objects of :-
• Creating a wave-free water surface within the well.
• Provide adequate protection to the float and its tether for float gauges or the
sounding tube for air-acoustic gauges .
The drawback of hitherto known stilling-well devices is the introduction of an error usually manifested as an over-estimation of sea level measurement as a consequence of trapping of a water body having a different density structure from that outside the well. Previous studies [G.W. Lennon and W. Mitchell (1992) IOC Workshop Report ) indicated water level anomalies as large as 8 cms and an overall bias of more than 2 cms to mean sea level estimates arising from the trapping effect observed in the Mersey Estuary, U.K. Similar water density anomalies have been measured
quantitatively by us over a 2 year period in the Zuari Estuary, Goa, India. These observed errors are of a sufficiently serious nature to merit attention and correction for a realistic estimation of the contributory role of global climate changes on mean sea level variations.
The main object of the present invention is to provide an improved stilling-well device useful for enabling error free sea level measurements specifically avoiding water
trapping effects which are a major drawback in hithero known devices. In the drawings
accompanying this specification :
Fig.1 illustrates a typical shape of a conventional stilling-well. This comprises a
cylindrical well  normally made from mild steel (MS), and having a conical inlet 
with an orifice  at the extreme bottom of the well.
Fig. 2 shows measurements of the densities inside ( solid line ) and outside ( dashed
line ) of B stilling well of the type shown in Fig.1 in the Zuari Estuary, Goa, India.
These measurements span a two year period from June 1995 to October 1997.
Fig. 3 shows an embodiment of the improved stilling well device of the present
invention having an array of circular perforations over its usually submerged portion;
wherein (4) is the stilling well, (5) are the perforations on the well surface, and (6) is a
hollow copper bush inserted in the perforation.
Accordingly the present invention provides an improved stilling-well device
useful for enabling error free sea level measurements, which comprises a stilling-well
 being provided with an array of perforations  on the entire submerged portion of
the said stilling well, each of the said perforations having a hollow bush  fitted into
each perforation with means 
In an embodiment of the present invention the array of perforations may be such as axially symmetric array of circular perforations drilled perpendicularly on the submerged surface of the stilling-well.
In another embodiment of the present invention, the hollow bush may be inserted and fitted into each perforation by mean such as a flexible gasket of electrochemically inert material sandwiched between the bush head and the circumferential face of the perforation.
The schematic diagram of the improved stilling well is depicted in Fig.3(a) & 3(b) of the drawings. This comprises of a cylindrical well [ 4] made usually from mild steel (MS) in float driven gauges, and PVC in the case of guided-air-acoustic gauges. Perforations  are drilled on the wetted surface of the well, and copper bushes are made from cut sections of copper tubings to diametrically match the perforations. Bushes are inserted as shown in Fig.3. The bush length may not necessarily match the wall thickness of the well, but must not protrude appreciably on the outer surface of the well from hydrodynamic considerations.
The perforated wall of the present stilling-well can be considered as a two-dimensional array of orifices. The flow through the perforated wall at 90 degrees incident angle can be considered as effluxes of free jets emanating from these orifices. These jets result in swirl motions at the wall together with attenuated axial and radial velocities towards the longitudinal axis of the well [ H. Schlichting ( 1968) in Boundary Layer Theory , McGraw Hill book Company ( 6th edition) ]. Wave and tidal current-induced water motions in the vicinity of the well provide the necessary jets, and leads to mixing of waters inside the well.
The materials used in stilling wells are prone to biofouling after prolonged exposure in euphotic waters, as is the case in all coastal installation of sea level
gauges. As copper is known to act as a toxic agent that inhibits marine growth [ J.E. Huguenin & F.J. Ansuini (1975), IEEE Oceans 75], copper bushes inserted into all the perforations avoid their closure from marine bio-fouling. Teflon bushes prevent electrochemical reaction between dissimilar metals, in the MS stilling-wells. The main advantage of the present invention is :-
Removes water trapping in wells for sea level gauges by permitting free eychange with ambient waters, thereby removing the error in sea level measurement arising from the water trapping effect.
1. An improved stilling-well device useful for enabling error free sea level measurements, which comprises a stilling-well  being provided with an array of perforations  on the entire submerged portion of the said stilling well, each of the said perforations having a hollow bush  fitted into each perforation with means .
2. An improved stilling well device as claimed in claim 1 wherein the array of
circular perforations is such as axially symmetric array of circular perforations drilled perpendicularly on the submerged surface of the stilling well.
3. An improved stilling well device as claimed in claims 1 & 2 wherein the hollow
bush is inserted and fitted into each perforation by means such as a flexible
gasket, sandwiched between the bush head and circumferential face of the
4. An improved stilling well device useful for enabling error free sea level
measurements substantially as herein described with reference to fig 3(a) &
3(b) of the drawings accompanying this specification.
|Indian Patent Application Number||2378/DEL/1998|
|PG Journal Number||12/2008|
|Date of Filing||13-Aug-1998|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110001, INDIA.|
|PCT International Classification Number||G01C 13/00|
|PCT International Application Number||N/A|
|PCT International Filing date|