Drag coefficient of this contraption?
Drag coefficient of this contraption?
(OP)
Civil engineer needing advice - figured here was a reasonable place to get it.
Consider this product:

It's basically a floating trash scooper you anchor into a stream or river and it collects litter. I can calculate the design flow rates and velocities easily, but I need to know the drag force to tell the structural engineer how to design the anchors.
I can get plans of the product, but there's no budget for testing, so I need to come up with a conservative drag coefficient and calculate the drag force on the contraption. I foresee two possible approaches. 1) I make some assumptions about simple geometry and pull Cds from a table, or 2) I jump down the rabbit hole of computational fluid dynamics and try to model the thing in Solid Works or similar. The latter avenue seems burdensome.
Any advice?
Consider this product:

It's basically a floating trash scooper you anchor into a stream or river and it collects litter. I can calculate the design flow rates and velocities easily, but I need to know the drag force to tell the structural engineer how to design the anchors.
I can get plans of the product, but there's no budget for testing, so I need to come up with a conservative drag coefficient and calculate the drag force on the contraption. I foresee two possible approaches. 1) I make some assumptions about simple geometry and pull Cds from a table, or 2) I jump down the rabbit hole of computational fluid dynamics and try to model the thing in Solid Works or similar. The latter avenue seems burdensome.
Any advice?
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com





RE: Drag coefficient of this contraption?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Drag coefficient of this contraption?
My initial impression is that it will be almost entirely dominated by form drag, and my inclination is to just calculate the area facing the oncoming flow and treat the thing as a vertical plane, with a Cd around 2. Love to hear other opinions though.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Drag coefficient of this contraption?
I'd have thought the mechanical overload drag when it collects a powerboat/tree or whatever would be the limit case.
If you really want to model it then look for a program called Michlet, which calculates the wave froming drag for symmetrical hull shapes.
However, that seems over the top. Cd=2 seems reasonable to me as well.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Drag coefficient of this contraption?
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Drag coefficient of this contraption?
I did have another thought, presumably there are charts for calculating the resistance of rough river beds and the like, which given the amount of junk in that thing might not be a bad approximation.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Drag coefficient of this contraption?
@GregLocock: I'd also think that the overload case would be the limit case. However much force is required to anchor this thing in a current, it's going to be much higher when some large object comes its way.