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Index to all Newsletters LMNO Engineering home page
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2004

October 27, 2004. Pressured Non-Circular
Ducts/Conduits

September 15, 2004. Gradually Varied Flow

July 14, 2004. End Depth Method for Flow Measurement in
Open Channels

May 18, 2004. Detention Storage to Attenuate Storm
Discharge

April 1, 2004. Force due to Pipe Bend - new calculation

March 3, 2004. Hydraulic Jump

January 21, 2004. Open Channel Flow Measurement

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. October 27, 2004.

Pressurized Non-Circular Ducts/Conduits

Our "Non-Circular to Circular Pipe Conversions" at http://www.LMNOeng.com/PipeDuct.htm allows
one to use the circular pipe design calculations ("Design of Circular Water
Pipes" and "Design of Circular Liquid and Gas Pipes") for non-circular
cross-sections. If you have a rectangular or annular cross-section, the non-circular to
circular calculation will convert your geometry to an equivalent diameter (called
hydraulic diameter) which can then be used in the circular design calculations to predict
velocity.

However, to calculate the flowrate, take the velocity from the circular design calculation
page and copy it to the non-circular to circular calculation page so that the velocity is
multiplied by the actual duct area. This will give the correct flowrate. The flowrate
output in the circular pipe design calculation is computed as VA where A=(pi/4)D^{2},
which is incorrect for a non-circular cross-section. Even though the D is the hydraulic
diameter, (pi/4)D^{2} is not equal to the area computed from the actual duct
geometry.

Conversely, if you use "Design of Circular Water Pipes" to determine a pipe
diameter based on a required velocity, the non-circular to circular calculation can be
used to convert the diameter to a height and width of a rectangular duct or an inner and
outer diameter for an annular cross-section. For the same reasons as in the previous
paragraph, the circular pipe design calculations cannot be used to compute hydraulic
diameter based on flowrate, since A=(pi/4)D^{2} is used.

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/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) 2004 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. September 15, 2004.

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. I'll leave discussion of these to another newsletter!

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.

Additional discussion can be found at http://www.LMNOeng.com/Channels/gvf.htm.

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/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) 2004 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. July 14, 2004

End Depth Method for Flow Measurement in Open Channels

Ever wish you could determine the discharge (Q) of water out of a culvert? Maybe you
thought about using Manning's equation - but you needed to measure the slope and estimate
the Manning coefficient (n). And you realized that a small error in estimating n can give
a large error in Q. Maybe you found Q by measuring the time to fill a 20 liter bucket. For
high flows, the time is too short to measure accurately; and larger buckets get too heavy.

The end depth method doesn't require a slope measurement or an estimation of n. It is
based solely on the water depth (h) and diameter (D) of the culvert. It requires that the
culvert be essentially horizontal and that the water drops off a height greater than h.

We have end depth calculations for circular culverts, rectangular channels, and triangular
channels that have sudden drop-offs (like a waterfall). The rectangular and triangular
channel calculations are fully functional without paying our registration fee. You can see
the rectangular channel calculation at http://www.LMNOeng.com/Waterfall/waterfall.htm.

Thank you for your interest in the LMNO Engineering newsletter,

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

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) 2004 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. May 18, 2004

Detention Storage to Attenuate Storm Discharge

http://www.LMNOeng.com/Hydrology/storage.htm

Communities usually have guidelines stating that peak discharge at some location following
development cannot exceed the peak discharge prior to development. The
"location" is usually somewhere in the watershed where flooding would be
detrimental. Development usually involves clearing trees and brush, paving surfaces, and
constructing buildings. These activities tend to increase runoff volume and peak discharge
from the watershed.

Detention storage can be incorporated into developments to attenuate (reduce) the peak
discharge. For example, say a city requires the 25-yr, 24-hr storm to be the basis for
design. Prior to development, the peak discharge from this storm is, say, 150 cfs (ft3/s)
at a specified location, and the peak discharge due to development is predicted to be,
say, 300 cfs at the same location. The city won't approve the project unless the developer
incorporates enough detention storage to reduce the predicted peak discharge to the
pre-development value of 150 cfs at the specified location.

The engineer can use our calculation to determine the detention storage volume required to
attenuate the peak discharge from 300 to 150 cfs. The storage volume can then be
implemented as a single pond with that volume or several ponds, basins, or depressions
that add up to the required volume. The ponds/basins/depressions must go dry between storm
events and should be located just upstream of the specified location.

Our calculation is based on methodology presented in Technical Release 55, Chapter 6 (SCS,
1986), of the USA Soil Conservation Service (now called the Natural Resources Conservation
Service, NRCS), division of the USDA (USA Department of Agriculture). The NRCS has worked
for decades developing equations and conducting experiments to determine reliable models
for predicting storage volume for detention basins to reduce peak discharge from storm
events. We have made the calculation useful for the international community by allowing a
variety of units.

Thank you for your interest in the LMNO Engineering website,

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

LMNO Engineering, Research, and Software, Ltd.

http://www.LMNOeng.com

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

Reference:

U.S. Soil Conservation Service. Technical Release 55: Urban Hydrology for Small
Watersheds. USDA (U.S. Department of Agriculture). June 1986. Available from NTIS
(National Technical Information Service), NTIS # PB87101580.

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) 2004 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. April 1, 2004

Force due to Pipe Bend - new calculation

http://www.LMNOeng.com/Force/ForceBend.htm

We added a new calculation to our website on March 12. It computes the reaction force
required to hold a pipe bend in place as a fluid flows around a horizontal bend in a pipe.
In order to properly size thrust blocks, hangars, or other devices to hold a pipe in
place, the momentum equation is used to compute the necessary resistive force to hold the
pipe stationary.

Forces in a pipe bend in the horizontal plane are caused by the fluid's momentum and
pressure. If the pipe undergoes a bend in the vertical plane, where the entrance to the
bend is above the exit (or vice-versa), then the weight of the liquid and pipe material
within the bend will contribute to the force. Since computing the volume of fluid and pipe
material within a bend requires considerably more input, we kept our calculation
relatively simple by keeping it in the horizontal plane.

The calculation displays the reaction force in two ways:

1. The x and y components of the reaction force are shown, and

2. The resultant force and its direction are shown.

Equations and flow diagrams can be seen on the web page. The calculation has a
demonstration mode so that you can enter different variables and see the results.

Thank you for your interest in the LMNO Engineering website,

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

LMNO Engineering, Research, and Software, Ltd.

http://www.LMNOeng.com

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) 2004 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. March 3, 2004

Hydraulic Jump - new calculation

http://www.LMNOeng.com/Channels/HydraulicJump.htm

We wrote a new calculation for our website. It is a hydraulic jump calculator for open
channel flow in a rectangular channel. The user enters the channel width, discharge, and
upstream depth. The calculator computes downstream depth, jump length, head loss over the
jump, Froude numbers, and flow velocities.

A hydraulic jump can only occur when the upstream flow is supercritical (F>1). In
addition, to have a jump there must be a flow impediment downstream. The downstream
impediment could be a weir, a bridge abutment, a dam, or simply channel friction. Water
depth increases over a hydraulic jump and energy is dissipated as turbulence.

Often, engineers will purposely install impediments in channels in order to force jumps to
occur. Mixing of coagulant chemicals in water treatment plants is often aided by hydraulic
jumps. Concrete blocks may be installed in a channel downstream of a spillway in order to
force a jump to occur thereby reducing the velocity and energy of the water. Flow will go
from supercritical (F>1) to subcritical (F<1) over a jump.

Please enter the free PIN: jump

into our home page http://www.LMNOeng.com in order to
use the calculations on our site for free through Friday March 5.

Thank you for your interest in the LMNO Engineering website,

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

LMNO Engineering, Research, and Software, Ltd.

http://www.LMNOeng.com

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) 2004 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 21, 2004

Open channel flow measurement

We offer calculations for three commonly used methods for open channel flow measurement -
weirs, flumes, and end depth. The end depth method is the simplest because a structure
does not need to be built - water drops freely from the downstream end of a culvert or
channel. All that is needed are the dimensions of the culvert or channel and the water
depth. Freely discharging culverts are widely used as discharge structures, and a picture
of one is shown at http://www.LMNOeng.com/Waterfall/CulvertDischarge.htm.

Weirs are used for flow measurement when large head losses are acceptable and free
discharge can be accommodated. Weirs are relatively inexpensive to construct, install, and
operate. However, weirs will back up the flow since they are obstructions across the
channel width and cause low velocities upstream of the weir. Sediment will build up behind
the weir. A simple triangular (or V-notch) weir is shown at http://www.LMNOeng.com/Weirs/vweir.htm.

Flumes are more expensive than weirs but have the advantage of much less head loss. They
are flow-through devices that do not cause the water to back up like weirs do. There are
various types of flumes which are designed to allow varying ranges of discharge through
them while minimizing sediment build-up and head loss. A flume photograph can be found at http://www.LMNOeng.com/Flumes/flumes.htm.

Thank you for your interest in the LMNO Engineering website,

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

LMNO Engineering, Research, and Software, Ltd.

http://www.LMNOeng.com

Past newsletters can be viewed at http://www.LMNOeng.com/Newsletters/newsletter5.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) 2004 LMNO Engineering, Research, and Software, Ltd.

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Rights Reserved)**

LMNO Engineering, Research, and Software, Ltd.

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

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