Received: from hpmsd3.sj.hp.com by opus.hpl.hp.com with SMTP (1.37.109.18/15.5+ECS 3.3+HPL1.1) id AA096918032; Mon, 21 Jul 1997 08:13:52 -0700 Return-Path: <kirk@hpmsd3.sj.hp.com-DeleteThis> Received: from hpoclrf.sj.hp.com by hpmsd3.sj.hp.com with SMTP (1.38.193.4/15.5+IOS 3.22) id AA25745; Mon, 21 Jul 1997 08:13:52 -0700 Sender: kirk@hpmsd3.sj.hp.com-DeleteThis Message-Id: <33D37CB0.2F69@hpmsd3.sj.hp.com-DeleteThis> Date: Mon, 21 Jul 1997 08:13:52 -0700 From: Kirk Lindstrom <kirk@hpmsd3.sj.hp.com-DeleteThis> Organization: Sending from inside Hewlett Packard X-Mailer: Mozilla 3.0 (X11; I; HP-UX A.09.07 9000/735) To: wind_talk@opus.hpl.hp.com-DeleteThis Subject: Visualization for current laging tide height. References: <199707202030.NAA05720@paris.engr.sgi.com-DeleteThis> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit
I believe I have the proper visualization for explaining current lagging
tide height.
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Pardon ASCII graphics....but I have drawn a bucket inside a basin. The
walls of the bucket are higher than the basin and the bucket has a hole
in it. Consider the hole as the Golden Gate. The bucket is the tide
height of the ocean outside the Gate. The basin is the SF Bay. Now
start pouring water into the bucket faster than the hole allows water to
flow into the basin.
Observe that the water will flow FROM the bucket any time the water
level in the bucket is higher than the hole AND higher than the water
level in the basin. This is a flood tide.
Lets say High Tide is when the water level reaches the top of the
bucket. We can stick a siphon tube into the bucket and remove water so
water is now flowing out the siphon tube AND flowing out the hole into
the basin.
Note that the water will CONTINUE to flow (Flood) frow from the bucket
into the basin until either
1) the water level in the bucket drops below the hole or
2) The water level in the bucket equals the water level of the basin.
IF #2 occurs first, then we get an ebb tide until the water level in the
basin falls below the level of the hole in the bucket or until the
siphon tube is removed and we start filling the bucket until the water
level is once again higher than the hole and the water level in the
basin. This is the tide ebbing even after the low tide.
Soooo...it seems to be a function of the size of the hole, the size of
the bucket, the size of the basin, PLUS the rates of water running into
and out of the bucket. Change ANY variable and the relationship will
change.
To make it REALLY interesting, you can put the basin inside a larger
basin, drill a hole in it and model currents at Sherman Isl or in Palo
Alto.
I hope this is better than the old "engineering" way of explaining it
with capacitors and inductors or springs and weights! 8-)
Kirk out
Alain Dumesny wrote:
>
> I've been using the site at http://www.rahul.net/cgi-bin/stain/tide-charts.cgi
> to check the tide height and current at 3rd and always wonder why the current
> and height of tide are not exactly in sync. Seem to be off by about 1 hour.
>
> Seems to me that the lowest height should be right when the current is done
> leaving (ebb) and vice versa for high/flood. Why 1 hour lag ? (is there
> surface and under water currents in opposite directions ?)
>
--"There is more to life than increasing its speed." - Gandhi +----------------------------------------------------------------------+ | Kirk Lindstrom - CSSD Product R&D | Hewlett-Packard Co. M/S: 90UA | | Engineer/Scientist, Hardware | Communication Semiconductor | |------------------------------------| Solutions Division | | kirk_lindstrom@sj.hp.com-DeleteThis | | | Kirk Lindstrom / HP0100/UX | 370 W. Trimble Rd. | | ph 408 435 6404 | fax 408 435 6286 | San Jose, CA 95131-1096 | +----------------------------------------------------------------------+
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