Newsletters
2020 - 2022

LMNO Engineering, Research, and Software, Ltd.

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2020
January 2, 2020. Focus on Hydrology - Impact of Culvert Replacement
January 22, 2020. Open Channel Uniform and Non-Uniform Flow
February 19, 2020. Gas Leak Rate Calculator - New
May 6, 2020. Calculators
August 13, 2020. Gradually Varied Flow

2021
March 11, 2021. Water Hammer
October 18, 2021. Parshall Flume for Stream Flow Measurement

2022
February 8, 2022. Gas Flow Conversions
March 2, 2022. Open Channel Flow Modeling


LMNO Engineering, Research, and Software, Ltd.
The fluid flow calculations website: https://www.LMNOeng.com
7860 Angel Ridge Rd. Athens, Ohio 45701 USA   (740) 707-2614
LMNO@LMNOeng.com

Newsletter. January 2, 2020.

Focus on Hydrology - Impact of Culvert Replacement

We recently completed a culvert design consulting project. Culvert design is a mature field, so it would seem that most of the nuances have been worked out. However, sometimes the impacts of culvert replacement are overlooked. A culvert may be replaced due to its having been partially crushed or having deteriorated so that it no longer properly conveys the intended design flow at the original design upstream head (water depth). It is tempting to simply replace the culvert with the same or larger size. While this is usually the strategy, it can have unintended downstream consequences.

Replacing a culvert with the same or larger diameter, and clearing brush/debris, results in less flow resistance - which is a desirable consequence. However, the failed culvert may have provided stormwater detention upstream of the culvert. Upon replacement, there is less flow resistance resulting in less upstream stormwater detention and an increased risk of downstream flooding.

Please let me know if questions. Thank you for your interest in the LMNO Engineering newsletter,

Ken Edwards, Ph.D., P.E. (Owner/Engineer)
LMNO Engineering, Research, and Software, Ltd.
https://www.LMNOeng.com     LMNO@LMNOeng.com

Culvert design calculator: https://www.LMNOeng.com/Pipes/hds.php


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.

© 2020 LMNO Engineering, Research, and Software, Ltd.


LMNO Engineering, Research, and Software, Ltd.
The fluid flow calculations website: https://www.LMNOeng.com
7860 Angel Ridge Rd. Athens, Ohio 45701 USA   (740) 707-2614
LMNO@LMNOeng.com

Newsletter. January 22, 2020.

Open Channel Uniform and Non-Uniform Flow

The empirical Manning equation is the most commonly used equation for open channel flows. In open channel flow, the water surface is open to the atmosphere. For instance, open channel flow can be in a partially full pipe, in a natural stream or river, or in a manmade channel. The Manning equation is of the form:

Q = A k R2/3 S1/2 / n

where: Q = Flow rate (m3/s or ft3/s). A = Cross-sectional flow area (m2 or ft2). k = Unit conversion factor = 1 for SI units or 1.49 for English units. R = Hydraulic Radius (m or ft) = A/P, where P = Wetted perimeter (m or ft). S = Energy slope = Change in water surface elevation per unit length of channel (m/m or ft/ft). n = Manning roughness factor.

If the channel or pipe that water is flowing through is long with unchanging dimensions (a "prismatic" channel), then the water depth will be nearly constant along the channel's length. This situation is called uniform flow; the water surface is modeled as being parallel to the channel bottom. In this case, the slope of the channel can be used as the energy slope S. However, if the channel is not prismatic or the water depth changes with distance (near a channel drop-off for instance), then the energy slope S is the slope of the water surface, rather than the slope of the channel.

In many instances, we know the flow rate in the channel and need to determine the water depth. In this case, the Manning equation is solved for water depth numerically since S, A, and P (thus R) are functions of the water depth. If flow is uniform, then water depth is constant along the entire channel, so the Manning equation only needs to be solved numerically once for depth. If the water depth varies along the channel length (non-uniform flow), then the Manning equation is solved numerically for water depth, not just once, but over and over at small distance increments successively moving upstream or downstream along the channel.

More information can be found on our web pages: Uniform flow in pipe: https://www.LMNOeng.com/CircularCulvert.php
Uniform flow in trapezoidal channel: https://www.LMNOeng.com/Channels/trapezoid.php
Non-uniform flow in trapezoidal channel: https://www.LMNOeng.com/Channels/gvf.php (has demo mode and graph; note that non-uniform flow is also called gradually varied flow)

Please let me know if questions. Thank you for your interest in the LMNO Engineering newsletter,

Ken Edwards, Ph.D., P.E. (Owner/Engineer)
LMNO Engineering, Research, and Software, Ltd.
https://www.LMNOeng.com     LMNO@LMNOeng.com


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.

© 2020 LMNO Engineering, Research, and Software, Ltd.


LMNO Engineering, Research, and Software, Ltd.
The fluid flow calculations website: https://www.LMNOeng.com
7860 Angel Ridge Rd. Athens, Ohio 45701 USA   (740) 707-2614
LMNO@LMNOeng.com

Newsletter. February 19, 2020.

New calculator - Gas Leak Rate
https://www.LMNOeng.com/Gas/GasLeakRate.php

Gas can intentionally or unintentionally be vented from a tank or pipe to the surrounding air. The gas venting may occur through an orifice, crack, or other opening. Depending on the type of gas, temperature, and pressures, the gas flow may either be choked or subsonic as it exits through the hole. If flow is choked, the gas exits the tank at sonic velocity (Mach number of 1). If flow is subsonic, then the discharge Mach number is less than 1. As gas leaks through the crack, temperature drops. If the gas contains water vapor, then there is a possibility of freezing of entrained liquid.

In the calculator, you can select the type of gas or enter the specific gravity (or molecular weight) and specific heat ratio. Other inputs include tank pressure, tank temperature, ambient pressure, and hole size. The calculation is for steady state conditions. The computed values include mass flow rate, velocity through the hole, Mach number, and temperature.

Please let me know if questions. Thank you for your interest in the LMNO Engineering newsletter,

Ken Edwards, Ph.D., P.E. (Owner/Engineer)
LMNO Engineering, Research, and Software, Ltd.
https://www.LMNOeng.com     LMNO@LMNOeng.com


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.

© 2020 LMNO Engineering, Research, and Software, Ltd.


LMNO Engineering, Research, and Software, Ltd.
The fluid flow calculations website: https://www.LMNOeng.com
7860 Angel Ridge Rd. Athens, Ohio 45701 USA   (740) 707-2614
LMNO@LMNOeng.com

Newsletter. May 6, 2020.

Calculators

As you know, we offer calculators for pressurized pipe flow, open channel flow, hydrology, and groundwater. Our list of calculators can be found at https://www.LMNOeng.com

Our pressurized pipe flow calculations are for liquid or gas flow. For compressible gases, we solve the Weymouth equation for pipelines and also compute leak rates and consider choked flow. We also offer a pipe network calculation for liquids, water hammer calculations, and pressure relief valve sizing. In addition, we have design calculators for orifice, nozzle, and venturi flow meters. We also have a fire hydrant residual pressure calculation, time to empty a liquid tank, and a general Bernoulli equation calculator.

For open channel flow, we have calculators for circular culverts and trapezoidal channel analysis. In addition, we offer a calculator for inlet and outlet control for culvert sizing. A gradually varied flow calculator computes water depth in a trapezoidal channel for subcritical and supercritical flows. Our inverted siphon calculator sizes pipes for going under rivers, highways, or other obstacles. We also have flow measurement calculators for flumes and weirs.

Regarding hydrology, we have calculators for rainfall-runoff, time of concentration, and storage basin sizing.

Our groundwater calculators compute flow through a permeameter, groundwater flow direction based on well head readings, and solve contaminant transport equations.

We also have calculators to determine the volume of a partially full inclined cylinder, riprap sizing, drag force, gas flow conversions between standard and actual, ideal gas, and gas viscosity as a function of temperature.

We also offer consulting services. If you have any questions, please let me know. Thank you for your interest in the LMNO Engineering newsletter,

Ken Edwards, Ph.D., P.E. (Owner/Engineer)
LMNO Engineering, Research, and Software, Ltd.
https://www.LMNOeng.com     LMNO@LMNOeng.com


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.

© 2020 LMNO Engineering, Research, and Software, Ltd.


LMNO Engineering, Research, and Software, Ltd.
The fluid flow calculations website: https://www.LMNOeng.com
7860 Angel Ridge Rd. Athens, Ohio 45701 USA   (740) 707-2614
LMNO@LMNOeng.com

Newsletter. August 13, 2020.

Gradually Varied Flow Calculator: https://www.LMNOeng.com/Channels/gvf.php

My newsletter on May 6, 2020, described many of our flow calculators. Today's newsletter will focus on our gradually varied flow (gvf) calculator.

Unlike uniform flow in an open channel, gradually varied flow equations predict water depth as a function of longitudinal distance upstream or downstream from a location with a known depth. The computation of the water depth allows one to determine if channel over-topping will occur. Further, since water velocity varies with depth, an estimation of scouring can be determined by using the gvf computation of velocity along the channel.

Our calculator has a nice graphical feature where one can view plots of water depth, water surface elevation, velocity, top width, and Froude number with distance along the channel.

The calculator has a demonstration mode which allows one to see the functionality and graphing capabilities.

If you have any questions, please let me know. Thank you for your interest in the LMNO Engineering newsletter,

Ken Edwards, Ph.D., P.E. (Owner/Engineer)
LMNO Engineering, Research, and Software, Ltd.
https://www.LMNOeng.com     LMNO@LMNOeng.com


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.

© 2020 LMNO Engineering, Research, and Software, Ltd.


LMNO Engineering, Research, and Software, Ltd.
The fluid flow calculations website: https://www.LMNOeng.com
7860 Angel Ridge Rd. Athens, Ohio 45701 USA   (740) 707-2614
LMNO@LMNOeng.com

Newsletter. March 11, 2021.

Instantaneous Valve Closure - Water Hammer
https://www.LMNOeng.com/WaterHammer/impulse.php

Let's look at an example:
Water flows steadily out of a reservoir through an 8-inch Schedule 40 horizontal steel pipe (inside diameter 7.981 inch, wall thickness 0.322 inch) at 4 ft/s. The pipe is 100 ft long and has a valve at the end. The valve suddenly closes. How much will the pipeline pressure increase due to the valve closure?

Answer: The rise in pressure is predicted to be 233 psi due to the instantaneous valve closure.

Note: 7.981 inch= 20.27 cm, 0.322 inch= 0.818 cm, 4 ft/s= 1.22 m/s, 233 psi= 16.1 bar

How fast is an instantaneous valve closure? To be considered an instantaneous closure, the valve would need to close faster than the time required for a pressure wave to travel two pipeline lengths. When a valve closes at the downstream end of a pipeline, a pressure wave propagates upstream, bounces off the upstream reservoir/pipe connection, and propagates back down to the valve. Thus, the pressure wave travels two pipeline lengths to get back down to the closed valve. The valve must close quicker than this time period to be considered instantly closed.

In our example, the wave speed (celerity) is 4332 ft/s. Thus:

Instant valve closure if closure time < 2L/c with L=pipe length, c=celerity
Therefore: 2L/c=2(100 ft)/(4332 ft/s)=0.046 seconds

In this example, a closure time less than 0.046 seconds is considered instantaneous. If the valve takes longer than 0.046 seconds to close, the pressure rise would be less than 233 psi.

The type of liquid, velocity, pipe material, pipe diameter, and pipe wall thickness affect the magnitude of the pressure surge. Additionally, the pipe length affects the definition of instantaneous valve closure time.

We also offer a more complex water hammer calculation where you can enter the valve closure or opening time at https://www.LMNOeng.com/WaterHammer/WaterHammer

Thank you for your interest in the LMNO Engineering newsletter,

Ken Edwards, Ph.D., P.E. (Owner/Engineer)
LMNO Engineering, Research, and Software, Ltd.
https://www.LMNOeng.com     LMNO@LMNOeng.com


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.

© 2021 LMNO Engineering, Research, and Software, Ltd.


LMNO Engineering, Research, and Software, Ltd.
The fluid flow calculations website: https://www.LMNOeng.com
7860 Angel Ridge Rd. Athens, Ohio 45701 USA   (740) 707-2614
LMNO@LMNOeng.com

Newsletter. October 18, 2021.

Parshall Flume for Stream Flow Measurement
https://www.LMNOeng.com/Flumes/parshall.php

There are many methods for measuring flow rate in streams, generally called open channel flow measurement. One method for flow measurement is the use of flumes. Flumes are built to standardized dimensions. One particular type of flume is the Parshall flume.

LMNO Engineering has a calculation for computing 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 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 (https://www.LMNOeng.com/Flumes/flumes.php) analyzes free flowing trapezoidal, rectangular, U-shape, and Parshall flumes. Both parshall.php and flumes.php 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)
LMNO Engineering, Research, and Software, Ltd.
https://www.LMNOeng.com     LMNO@LMNOeng.com


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.

© 2021 LMNO Engineering, Research, and Software, Ltd.


LMNO Engineering, Research, and Software, Ltd.
The fluid flow calculations website: https://www.LMNOeng.com
7860 Angel Ridge Rd. Athens, Ohio 45701 USA   (740) 707-2614
LMNO@LMNOeng.com

Newsletter. Februrary 8, 2022.

Gas flow conversions
https://www.LMNOeng.com/Flow/GasFlow.php

There is often confusion about how gas flowrates are stated. We have a calculator to aid in unit conversions for gas flow. Some gas flows are expressed in mass units, like kg/s or lb/day. Sometimes, flow units are acfm, scfm, or Nm3/s, to name a few.

Mass flowrate is straightforward. It is the amount of mass flowing per unit time. Volumetric flowrates, however, are either expressed as flow at "actual conditions" or flow at "standard (or normal) conditions". Units for flow at actual flowing conditions often have the letter "a" in front of the unit.

In contrast to flow at actual conditions, flows can be expressed at standard (or normal) conditions. English units usually are prefaced with the word "standard" or letter "s" while metric units are usually prefaced with the word "normal" indicated by the letter "N" (don't confuse with the Newton unit).

Standard (or normal) flows are the volume equivalent to actual flow if the actual flow were at standard temperature and pressure. For the same mass and temperature of gas, one cubic meter of a gas at 10 atmospheres of pressure occupies much more volume when its pressure is reduced to 1 atmosphere. Think of gas in a cylinder acted on by a piston.

Please see our web page https://www.LMNOeng.com/Flow/GasFlow.php for equations and further discussion of gas conversions.

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.

© 2022 LMNO Engineering, Research, and Software, Ltd.


LMNO Engineering, Research, and Software, Ltd.
The fluid flow calculations website: https://www.LMNOeng.com
7860 Angel Ridge Rd. Athens, Ohio 45701 USA   (740) 707-2614
LMNO@LMNOeng.com

Newsletter. March 2, 2022.

Open Channel Flow Modeling

Open channel flow modeling, also called river routing or river modeling, is usually used to determine water surface elevations along a river. The results help communities determine the potential for flooding.

In the U.S., the most common computer model for river routing is HEC-RAS. This stands for Hydrologic Engineering Center - River Analysis System. The model was developed by the U.S. Army Corps of Engineers. The model was originally called HEC-2. HEC-1 was the hydrologic model, now called HEC-HMS (Hydrologic Modeling System).

HEC-2, now HEC-RAS, progressed from one-dimensional steady state modeling to unsteady modeling to multiple dimensional modeling with GIS (Geographic Information System) capabilities.

The core of HEC-RAS has always been, and continues to be, conservation of mass, momentum, and energy. As from its original implementation, the Manning equation is at the heart of the model.

HEC-RAS modeling runs from the basic to the complex. For simpler modeling, LMNO Engineering offers calculations that use the Manning equation for uniform flow steady state design and analysis. We also offer a gradually varied flow calculator that allows the user to enter the upstream or downstream water depth. The program computes the water surface elevation along the channel.

HEC-RAS free download: https://www.hec.usace.army.mil/software/hec-ras/

Design of trapezoidal open channels: https://www.LMNOeng.com/Channels/trapezoid.php

Gradually varied flow (with graphing): https://www.LMNOeng.com/Channels/gvf.php

LMNO Engineering also offers consulting services in open channel flow modeling. 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.

© 2022 LMNO Engineering, Research, and Software, Ltd.


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LMNO Engineering, Research, and Software, Ltd.
7860 Angel Ridge Rd.   Athens, Ohio  USA   (740) 707-2614
LMNO@LMNOeng.com    https://www.LMNOeng.com