Cubic Meters Per Second = MPH

Good morning, Netmaker.

They don't translate directly because they are two different measures. Cubic meters per time is a measure of flow whereas miles per hour is a measure of speed (scalar) or velocity (vector). Speed and velocity are measured in the same units but there is always a direction associated with velocity.

If you specify what the flow is going through (say a 6" dia pipe?) it can be calculated.

Hi there

The two cannot be linked. Volumetric flow is generally assoiated with a contained flow especially in a pipe where the liquid will be pumped at a certain volumetric flow at pre-determined time to meet the requerements at the set destination. The destination can be a storage tank or a mixing vessel. Liquid pumps are designed with specifiic volumetric flow normally expressed in cubic meters per hour. This is said with a specific pipe diameter and a respective head that a pump must supply the flow to. MPH is assiciated with speed to cover a cetrain distance in a specific time.

"Can someone help me translate the following:"

Can you tell us exactly what you are trying to calculate that includes such incompatible units?

Ok......let me re-phrase this request.

I have a net with the measurements of:

X across the top

y down the sides (2)

Z across the bottom

Q in depth going back and ending in a small PVC tubular chamber.

Basically a pyramid on its side with the base as an open mouth and the pinnacle as the tubular pvc chamber.

If I know the speed of the water going into the mouth of the net (V) and I know the

speed of of the water as it exits the tubular chamber (E)*.......

E* the velocity will be slowed down as the meshes of the netting, 750 microns, will produce drag.

Could there be a formula for figuring how many cubic meters of water have passed through this net in a given period (10 minutes)?

thank You all.

netmaker

If this is a closed container on the sides , it will not give you the measurement that you want. The Volume of water being forced into the pipe will be accelerated by the sides. The speed of the water being forced out the tube is a result of pressure. The drag of the net will not change the pressure.

In the locale of the net, water will accelerate around the line then slow down again to the surrounding speed.

Drag is a simple calculation of force based on area the surface area of the net and the speed in which it is traveling through the medium. See http://en.wikipedia.org/wiki/Drag_(physics)

Since drag changes due to speed. A useful measurement would be to measure the force on the net at the speed it will be used at. The problem is to get an exact speed of water since the currents and eddies will cause different drag in different areas.

The best way to test drag would be to have water in a still tank

Pull 1 square meter of net at a constant (measured) speed through the water

Measure the force with a scale attached between the net and the equipment pulling it. The result would be a force per square meter at a specific speed.

Assuming you know the cubic metres per second to start with, you then need to know the actual cross sectional area at the point you wish to calculate your velocity. See post #7 for the formula.

But since you mention 'drag', you might find it causes a reduction in the velocity - and thus it could affect your original assumption about the volumetric flow - and then you get involved in head pressures etc.

Sorry, can't really help unless the net is almost transparent, in which case Volume is just speed times area. Otherwise, it depends on the grid and gauge of the net, the holes, the hole in the middle, (the calculation is already at top consultancy rates). Then add the amount of fine seaweed the net has already trawled...

Fyz

(Volumetric flow rate)/(cross-sectional area of pipe) = velocity of fluid e.g. (cubic meters per second)/(square meters) = meters per second. (Meters per second X 3600)/(1.6 X 1000) = fluid velocity in miles per hour. That's the only formula you really can use here.

Are you using a hypodermic needle or one meter diameter pipe? Volume transport is dependent on pressure, diameter and time. Your Volume is fixed, time is fixed. you need to change pressure and diameter of pipe and you can calculate the desired speed.

Helping hand

Assume all of the water entering the opening of the net is what is filtered. Some water passes through the net but the contents of matter larger than 750 microns is directed to the catch tube.

First find the area of the opening of the net.

Assume a towing speed of 2 Knots and convert that speed to meters per second.

A Nautical Mile by definition is 1852 meters

For ease of calculation round the towing speed to 1 meter per second.

To find the volume filtered per second multiply the area of the opening of the net times the towing speed in meters per second to obtain the volume per second.

For 1 minute

For 10 minutes

Thank you all.

Although there are some fudge factors involved as how much of a pressure wave is built up inside the netting and the shape of the hole as the net is streched, the formulas provide will give me something to work with.

Thank you all.

netmaker

You can translate from any language to the other. But for you question, no translation, because you can't translate from Flow Rate (volume per time) to Velocity (distance per time).

If you have some details for your problem, I can help you.

Thank you.

If you look up in the thread you will see where I have explained what i am trying to calculate.

thank you.

netmaker

"If you look up in the thread you will see where I have explained what i am trying to calculate."

You will have to try harder to first explain the setup.

All of the water entering the face of the funnel trap passes through the mesh to collect the sample organisms or whatever you are trapping. IF NOT SO PLEASE EXPLAIN.

No water flows out the far end of the small sample tube. Therefore there is no velocity to consider. IF NOT SO PLEASE EXPLAIN.

If there is flow through the sample tube, where does the collected sample go? The Inside Diameter of the sample tube is critical to calculating volume if you know the velocity or speed.

Try this unit converter

http://joshmadison.com/software/convert/

Its for free and works perfect

When downloading my safety programs reported spyware - so be careful when downloading !
regards Uwe

Thank you all for the information.

I did not explain all of this very well but from all of the information, I have been able to make a broad scale calculation on the effects of downsizing the net and meshes.

Just to settle the issue let me explain what happens;

The net is held open by a pair of rectangular trawl doors with a chain bridle and an Angle of Attack of 38 Degrees.

The doors spread the net open about 85% when pulled at a forward speed of 1.5 knots.

Bollard Pull as calculated from a spring type scale ( Cajun Load cell) runs at about 125 kg. with 100 feet of double towline attached to the doors and spliced into swivel (at the Apex).

Water and detritus as well as YOY (young of the year) fishes swim in with the flow.

The water flow does NOT all go through the meshes, there is a current that drafts through the net towards the pvc collection tube 4" wide x 6" with a 750 micron 'bag' attached to the rear of it.

The water begins to build up a head pressure right in front of the pvc bucket...in air plane talk we would say it stalls. In net talk we say Internal Pressure Wave.

The catch which is .5 to .50mm in size, glides into the tube with the current and is deposited in the 750 micron bag at the other end.

This is basically what happens in this trawl net.

The bigger meshes make for more current and more drafting but basically this is what we have learned over 30 years of diving into and through large nets. As you all know, it is difficult to calculate specs when you are downsizing and this is the worst case scenario.

Basically what I did was take the cubic feet of the inside of the proposed new net(using helpful formulas from all of you), calculated how fast the scientists told me the river flow was in knots and then compared this to an existing net with the same design but larger mesh for larger fish.

It is by no means very accurate but it is close enough for me to make a good guess at what the construction will be.

Thank you all once again.

This forum is excellent guys like myself with extremely limited knowledge in the sciences.

Merci Beau Coup

netmaker