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LMNO Engineering, Research, and Software, Ltd. |

Index to all Newsletters LMNO Engineering home page
email: LMNO@LMNOeng.com |

2005

December 21, 2005. Gradually Varied Flow and Rapidly
Varied Flow

October 27, 2005. Flow Calculations

August 2, 3005. Drainage Basin Peak Discharge

May 2, 2005. Closed Conduit Flow Measurement and
Bernoulli equation

March 17, 2005. Weymouth and Panhandle Equations for
Compressible Gas Flow

January 8, 2005. Open Channel Flow Measurement

LMNO Engineering, Research, and Software, Ltd.

The fluid flow calculations website: http://www.LMNOeng.com

7860 Angel Ridge Rd. Athens, Ohio 45701 USA +1(740) 592-1890

LMNO@LMNOeng.com

Newsletter. December 21, 2005.

Gradually Varied Flow (GVF) and Rapidly Varied Flow (RVF)

GVF and RVF are terms used to classify open channel flows - such as flow in rivers,
canals, and culverts. RVF occurs over short distances such as when water flows over a weir
or dam, drops off the end of a pipe, or encounters an hydraulic jump. GVF occurs over long
distances such as the water approaching a weir, dam, or drop-off; or following a sluice
gate.

In long prismatic (constant cross-section geometry) channels, the water will attempt to
reach the "normal depth". Normal depth is the water depth determined using
Manning's equation (or Chezy's equation). How the water depth changes with distance as it
approaches its normal depth is called a GVF profile. A GVF profile is a computation of
water depth versus distance along the channel length. A GVF computation typically involves
starting at a known depth (e.g. at a dam) and making successive computations upstream
using the continuity equation and energy slope in Manning's equation (rather than using
the channel bottom slope). It is a numerical computation and for best accuracy you want to
use the smallest distance increments possible. If you have had a course in open channel
flow, you might recall the different GVF profile types - such as M1, M2, M3, S1, S2, S3,
etc.

RVF computations require the continuity equation and the energy equation (like Bernoulli
equation but with losses) and/or momentum equation. To analyze an hydraulic jump,
continuity and momentum are required. To analyze flow over a dam/weir, continuity and
energy are used. Often, empirical methods are used to analyze flow over weirs.

You can find equations and calculations for GVF and RVF under the Open Channels/Culverts
heading on our home page http://www.LMNOeng.com .

Thank you for your interest in the LMNO Engineering newsletter,

Ken Edwards, Ph.D., P.E. (Owner/Engineer/Programmer)

LMNO Engineering, Research, and Software, Ltd.

http://www.LMNOeng.com

LMNO Engineering's previous newsletters can be viewed at http://www.LMNOeng.com/Newsletters/newsletter7.htm

You received this free newsletter because you requested it at our website. If you no
longer wish to receive it, send a message stating "Discontinue Newsletter" to LMNO@LMNOeng.com .

(c) 2005 LMNO Engineering, Research, and Software, Ltd.

LMNO Engineering, Research, and Software, Ltd.

The fluid flow calculations website: http://www.LMNOeng.com

7860 Angel Ridge Rd. Athens, Ohio 45701 USA (740) 592-1890

LMNO@LMNOeng.com

Newsletter. October 27, 2005

What calculation should I use?

Need the flowrate through a pinhole in a leaky pipe? Try our Bernoulli calculator: http://www.LMNOeng.com/Flow/bernoulli.htm

Need to know if a pump is required to carry water through your pipe? Try our
Darcy-Weisbach or Hazen-Williams calculations without pump curve. Solve for pump head. If
a pump is required, pump head will be positive. http://www.LMNOeng.com/DarcyWeisbach.htm
or http://www.LMNOeng.com/HazenWilliamsDesign.htm

Need to know if a blower is required to carry air through your pipe? Try our
Darcy-Weisbach calculation without pump curve: http://www.LMNOeng.com/DarcyWeisbach.htm
. Solve for pump head like above. Note that you can't use Hazen-Williams for air since
Hazen-Williams is only valid for water.

Have a rectangular duct instead of a circular pipe? See our newsletter dated Feb. 17,
1999: http://www.LMNOeng.com/Newsletters/newsletters.htm

Need to know the flowrate through a pipe with a pump already installed? Try Darcy-Weisbach
with pump curve (any liquid or gas) or Hazen-Williams with pump curve (water only): http://www.LMNOeng.com/Pipes/DWpump.htm
or http://www.LMNOeng.com/Pipes/HWpump.htm

Need to know pressure change in a pipe due to an expansion or contraction? Try our
Bernoulli calculator: http://www.LMNOeng.com/Flow/bernoulli.htm

Need a Moody friction factor? Try our Moody friction factor calculation: http://www.LMNOeng.com/moody.htm

Need to determine velocity using a pitot tube? Try our Bernoulli calculation: http://www.LMNOeng.com/Flow/bernoulli.htm

Need to determine discharge over a dam but our rectangular weir calculation gives
"parameter out of range" messages? Try our Bernoulli calculation - not as
accurate but no limits on the variables: http://www.LMNOeng.com/Flow/bernoulli.htm

Need the flowrate through an orifice plate, but our orifice calculation gives you a
"parameter out of range" message? Try our Bernoulli calculator - not as accurate
but no limits on the variables: http://www.LMNOeng.com/Flow/bernoulli.htm

Need to know pond storage volume required to attenuate a flood? Try our Detention basin
storage calculation: http://www.LMNOeng.com/Hydrology/storage.htm

Need to analyze a network of pipes? Try http://www.LMNOeng.com/Pipes/PipeNetwork.htm

Need to determine gas viscosity? Try http://www.LMNOeng.com/Flow/GasViscosity.htm

Need to determine the volume of a partially full tank? Try http://www.LMNOeng.com/Volume/CylConeSphere.htm

Need to determine runoff from a watershed? Try http://www.LMNOeng.com/Hydrology/hydrology.htm

Have another question? Send me an e-mail ( LMNO@LMNOeng.com
) or give me a call (USA: 740/592-1890).

Ken Edwards, Ph.D., P.E. (Owner/Engineer/Programmer)

LMNO Engineering, Research, and Software, Ltd.

You received this free newsletter because you requested it at our website. If you no
longer wish to receive it, send a message stating "Discontinue Newsletter" to LMNO@LMNOeng.com .

(c) 2005 LMNO Engineering, Research, and Software, Ltd.

LMNO Engineering, Research, and Software, Ltd.

The fluid flow calculations website: http://www.LMNOeng.com

7860 Angel Ridge Rd. Athens, Ohio 45701 USA (740) 592-1890

LMNO@LMNOeng.com

Newsletter. August 2, 2005

Drainage Basin Peak Discharge

Today's topic is runoff during a storm. In order to size culverts, pipes, and channels to
convey runoff from a watershed, a design discharge (i.e. flowrate; units typically are
gpm, cfs, or cms) must be determined.

Two common methods for determining the peak discharge from a storm are the SCS TR-55 Peak
Discharge Method and the Rational Method. The Rational Method is usually used for sizing
storm sewer inlets and culverts in urban areas, where drainage areas are small and times
of concentration are short. The SCS method is for somewhat larger watersheds with times of
concentration between 6 minutes and 10 hours.

Both methods require knowing the storm intensity (typical units are inch/hour or cm/hour).
The storm intensity is a function of the return period and storm duration. The return
period is usually specified by a local government and depends on the impact of
under-designing conveyances. Return periods may be 10-yr, 25-yr, 50-yr, or even 100-yr.
The larger the return period, the larger the storm and the more conservative the design.

The SCS method uses a 24-hr duration storm. For the Rational Method, the storm duration is
equivalent to the time of concentration. The time of concentration is the time required
for the most distant (time-wise) water particle in the watershed to reach the mouth of the
watershed.

In addition to the storm intensity, the Rational and SCS methods require knowing the
drainage area and runoff coefficient. The SCS method has additional inputs depending on
the degree of detail required.

More information about peak discharge determination can be found at:

http://www.LMNOeng.com/Hydrology/rational.htm
(Rational Method)

http://www.LMNOeng.com/Hydrology/hydrology.htm
(SCS Method)

Thank you for your interest in the LMNO Engineering newsletter,

Ken Edwards, Ph.D., P.E. (Owner/Engineer/Programmer)

LMNO Engineering, Research, and Software, Ltd.

http://www.LMNOeng.com LMNO@LMNOeng.com

LMNO Engineering's previous newsletters can be viewed at http://www.LMNOeng.com/Newsletters/newsletter7.htm

You received this free newsletter because you requested it at our website. If you no
longer wish to receive it, send a message stating "Discontinue Newsletter" to LMNO@LMNOeng.com.

(c) 2005 LMNO Engineering, Research, and Software, Ltd.

LMNO Engineering, Research, and Software, Ltd.

The fluid flow calculations website: http://www.LMNOeng.com

7860 Angel Ridge Rd. Athens, Ohio 45701 USA (740) 592-1890

LMNO@LMNOeng.com

Newsletter. May 2, 2005

Closed Conduit Flow Measurement and Bernoulli equation

This newsletter will discuss pressure variation with distance through a differential
pressure flow meter, such as an orifice, nozzle, or venturi, carrying an incompressible
fluid (a liquid). The distinction between differential pressure and pressure loss will be
examined.

Differential pressure is the basis for determining the flowrate through one of these
devices. Differential pressure is equal to the pressure upstream of the device minus the
pressure at the throat of the device; these two locations are indicated on the diagrams on
our web pages. The overall pressure loss due to a nozzle or orifice is usually taken as
the pressure at one diameter upstream of the throat minus the pressure at a distance 6
diameters downstream of the throat (ISO, 1991); the pressure loss measurement locations
are intended to be beyond the range of influence of the device.

Differential pressure will be greater than pressure loss because the pressure at the
throat is much smaller than the pressure at 6D downstream. The throat pressure is low
because the throat has a reduced diameter resulting in high velocity. As velocity
increases, pressure decreases. This is in accordance with the Bernoulli equation for a
horizontal flowmeter: P + (d V^{2} ) / 2 = constant, where P is pressure, d is
liquid density, and V is velocity. As V goes up, P goes down.

Thank you for your interest in the LMNO Engineering website,

Ken Edwards, Ph.D., P.E. (Owner/Engineer/Programmer)

http://www.LMNOeng.com LMNO@LMNOeng.com

Reference:

ISO (1991). International Organization of Standards. ISO 5167-1:1991(E). Measurement of
fluid flow by means of pressure differential devices - Part 1: Orifice plates, nozzles,
and Venturi tubes inserted in circular cross-section conduits running full. 1991.

You received this free newsletter because you requested it at our website. If you no
longer wish to receive it, send a message stating "Discontinue Newsletter" to LMNO@LMNOeng.com.

(c) 2005 LMNO Engineering, Research, and Software, Ltd.

LMNO Engineering, Research, and Software, Ltd.

The fluid flow calculations website: http://www.LMNOeng.com

7860 Angel Ridge Rd. Athens, OH 45701 USA (740) 592-1890

LMNO@LMNOeng.com

Newsletter. March 17, 2005

Weymouth and Panhandle Equations for Compressible Gas Flow

http://www.LMNOeng.com/Flow/weymouth.htm

Three equations are often used for modeling the flow of natural gas. They are the
Weymouth, Panhandle A, and Panhandle B equations. These three equations are not just for
natural gas, however. They are valid for most other compressible gases as well. Our
calculation page includes a drop-down menu for you to choose which of the three equations
to use and the gas (air, natural gas, nitrogen, oxygen, butane, carbon dioxide, propane).
You may select the last option in the gas drop-down menu, which allows you to enter the
specific gravity for an unlisted gas. The drop-down menu also allows you to select which
variable to compute (flowrate, pipe diameter, length, or pressure) as well as a variety of
units. Actual and standard volumetric flowrates are shown.

Background

The Weymouth, Panhandle A, and Panhandle B equations were developed to simulate
compressible gas flow in long pipelines. The Weymouth is the oldest and most common of the
three. It was developed in 1912. The Panhandle A was developed in the 1940s and Panhandle
B in 1956 (GPSA, 1998). The equations were developed from the fundamental energy equation
for compressible flow, but each has a special representation of the friction factor to
allow the equations to be solved analytically.

The Weymouth equation is the most common of the three - probably because it has been
around the longest. The equations were developed for turbulent flow in long pipelines. For
low flows, low pressures, or short pipes, they may not be applicable. If the pressure drop
in a pipeline is less than 40% of upstream gage pressure, then our Darcy-Weisbach
incompressible flow calculation ( http://www.LMNOeng.com/DarcyWeisbach.htm ) may be more
accurate than the Weymouth or Panhandles for a short pipe or low flow. The Darcy-Weisbach
incompressible method is valid for any flowrate, diameter, and pipe length, but does not
account for gas compressibility.

Thank you for your interest in the LMNO Engineering newsletter,

Ken Edwards, Ph.D., P.E. (Owner/Engineer/Programmer)

LMNO Engineering, Research, and Software, Ltd.

http://www.LMNOeng.com LMNO@LMNOeng.com

Reference:

GPSA (Gas Processors Suppliers Association). Engineering Data Book. 11ed. 1998.

LMNO Engineering's previous newsletters can be viewed at http://www.LMNOeng.com/Newsletters/newsletter7.htm

You received this free newsletter because you requested it at our website. If you no
longer wish to receive it, send a message stating "Discontinue Newsletter" to LMNO@LMNOeng.com.

(c) 2005 LMNO Engineering, Research, and Software, Ltd.

LMNO Engineering, Research, and Software, Ltd.

The fluid flow calculations website: http://www.LMNOeng.com

7860 Angel Ridge Rd. Athens, Ohio 45701 USA (740) 592-1890

LMNO@LMNOeng.com

Newsletter. January 8, 2005

Parshall Flume - Submerged and Free Flow

http://www.LMNOeng.com/Flumes/parshall.htm

LMNO Engineering's Parshall flume calculation computes discharge and rating curves for
free flowing or submerged Parshall flumes. A free flowing flume can be identified by the
drop in water depth at the flume throat. In submerged flow, the downstream water backs up
into the throat swallowing the drop - making the drop difficult or impossible to identify.
Analysis of submerged flow requires two head measurements - one in the approach channel
and one in the throat; whereas, free flow requires only the upstream head measurement. Our
Parshall flume calculation is based on the ISO 9826 (1992) standard.

Graphs of discharge versus head and discharge versus submergence ratio can be prepared on
the web page. You can see that increasing the submergence ratio causes the discharge to
decrease for a constant approach head. (Submergence ratio is defined as throat head
divided by approach head.) The Parshall flume equations and methodology are described on
the web page.

Our other flume calculation ( http://www.LMNOeng.com/Flumes/flumes.htm
) analyzes free flowing trapezoidal, rectangular, U-shape, and Parshall flumes. Both
parshall.htm and flumes.htm use identical equations for free flowing Parshall flumes.

Thank you for your interest in the LMNO Engineering newsletter,

Ken Edwards, Ph.D., P.E. (Owner/Engineer/Programmer)

LMNO Engineering, Research, and Software, Ltd.

http://www.LMNOeng.com

Reference:

International Organization of Standards (ISO 9826). 1992. Measurement of liquid flow in
open channels - Parshall and SANIIRI flumes. Reference number: ISO 9826:1992(E).

Past newsletters can be viewed at http://www.LMNOeng.com/Newsletters/newsletter6.htm

You received this free newsletter because you requested it at our website. If you no
longer wish to receive it, send a message stating "Discontinue Newsletter" to LMNO@LMNOeng.com .

(c) 2005 LMNO Engineering, Research, and Software, Ltd.

**© 2005-2016 LMNO Engineering, Research, and Software, Ltd. (All
Rights Reserved)**

LMNO Engineering, Research, and Software, Ltd.

7860 Angel Ridge Rd. Athens, Ohio USA +1(740) 592-1890

LMNO@LMNOeng.com http://www.LMNOeng.com