×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Calculating Pressure of Moving Water on Foundation

Calculating Pressure of Moving Water on Foundation

Calculating Pressure of Moving Water on Foundation

(OP)
Does anyone have a tip on how to calculate the force exerted on a stationary object by a moving mass of water (e.g. pylon foundation in a river)?

Thank you.

RE: Calculating Pressure of Moving Water on Foundation

Not professing to know much about that specific field, but I believe you are perhaps talking about calculations in the field of fluid dynamics for a sort of "drag" force on the object you are talking about [from the flow(ing fluid)].  I believe plots of "drag coefficients" are available for various shapes and Reynold's numbers e.g. an "infinitely long cylinder" if applicable, to assist in determining the forces.  Some keywords like this may allow you to find much information regarding your specific cases in e.g. fluid dynamics references or the web.  While certainly not insignificant, I suspect these forces might be sometimes quite small compared to getting hit by a big ship, barge, or even floating tree trunk log etc.!!   

RE: Calculating Pressure of Moving Water on Foundation

You need to get the AASHTO Standard Specification for Highway Bridges and refer to Section 3.18 for a complete approach to this issue.

RE: Calculating Pressure of Moving Water on Foundation

Figure V^2/2/g if you like to err on the conservative side for water hitting dead on and stagnating.  If its flow past a shape, you'll have to get the drag factor for the particular shape and angle of attack.

   Going the Big Inch! worm
http://virtualpipeline.spaces.msn.com

RE: Calculating Pressure of Moving Water on Foundation

i don't know that field either but wouldnt it be Force=mass of water * acceleration of the water

RE: Calculating Pressure of Moving Water on Foundation

Does this help?  

Stagnation pressure = (Depth + (water_velocity ^ 2 / (2 * g)) * 62.4 lbs/ft3

   Going the Big Inch! worm
http://virtualpipeline.spaces.msn.com

RE: Calculating Pressure of Moving Water on Foundation

sjhgeotech,


F = (rho)*(A)*(Cd)*(V^2/2g)

where
rho = water density
A = projected area of the obstruction normal to the current
Cd = Coefficent of drag (=2 for sheet pile cofferdams)
V = velocity of the current
g = acceleration due to gravity

in english units rho =~ 2g and using Cd = 2

F = 2AV^2

Good luck!

RE: Calculating Pressure of Moving Water on Foundation

(OP)
Ingy,

Section 13.18.1.1 of the AASHTO gives equation (3-4) as Pavg = K*(Vavg^2), where the Pavg equals pressure in pounds per square foot.

Where did you get your equation F = (rho)*(A)*(Cd)*(V^2/2g)
Also, I have round concrete piers.  What friction factor Cd do you recommend and is there a reference for them?


Thanks.

RE: Calculating Pressure of Moving Water on Foundation

Drag factor for round shapes is 0.8 x width.  Just about any fluids text will show Cd = 0.8 for round shapes as well as the formulas we all gave you for calculating either the pressure or force.  All the formulas yield the same answer in one unit or another.

   Going the Big Inch! worm
http://virtualpipeline.spaces.msn.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources