Pressure sensors for measuring pressure field on the bottom of the planing hull?

[M&M Ovenden]

I think this is more suitable for steady-state tests. I am looking for an accurate way to measure pressures when driving at high speeds into waves etc. I have been looking at a pressure scanner, which is essentially a manifold with sensors from which a network of liquid filled tubes extent out to wherever you want to measure. Talking to the supplier, they admit that the length of the tubes and the liquid inside them will provide some dampening of the pressure, thus making it more suitable for steady-state.

Hi Hildershavn,
The aircraft wing project I spoke about was on a jet fighter for dynamic stall behavior (very fast response time). The transducers were installed in the fairing to avoid any lag due to hose length, and set up as Dcockey mentions. We collected 1200Hz data which provided the detail of what was happening over the leading edge. I'm pretty it's possible what you want to capture, but the engineering effort will be about how invasive it will be to your candidate hull.

Mark

 

[Hildershavn]

as a suggestion, so if I was to put 9 small holes (or more for that sake) to a panel on the hull and have all these holes connected up and share one common pressure sensor, then I should be able to read the "average" pressure from these sensors? The ultimate goal for me is to have a pressure to add to my quasi-static strength analysis, so I am interested in the average for a panel( between ribs and struts). Do you have a recommendation for sensors I could use?

 

[Barry]

http://papersciences.com/Ghadimi-Univ-J-Fluid-Mech-Vol2-2014-4.pdf

A paper on mathematical pressure derivation for planing pressures

 

[DCockey]

as a suggestion, so if I was to put 9 small holes (or more for that sake) to a panel on the hull and have all these holes connected up and share one common pressure sensor, then I should be able to read the "average" pressure from these sensors?

Scanivalve - Intelligent Pressure and Temperature Instrumentation http://scanivalve.com/

 

[gonzo]

Standard practice in wind tunnel and tow tank testing to measure surface pressure is small holes with a sharp edge which is perpendicular to the surface, and the small holes are connected to pressure transducers. The pressure in the hole will be the same as the pressure of the air or water going past the entrance to the hole.


Assumptions are needed about how much the hull deflects at the strain gauge locations in response to assumed pressure fields to deduce surface pressure from strain gauge measurements.

The strain sensors can be calibrated by applying known forces.

 

[M&M Ovenden]

as a suggestion, so if I was to put 9 small holes (or more for that sake) to a panel on the hull and have all these holes connected up and share one common pressure sensor, then I should be able to read the "average" pressure from these sensors? The ultimate goal for me is to have a pressure to add to my quasi-static strength analysis, so I am interested in the average for a panel( between ribs and struts). Do you have a recommendation for sensors I could use?

I thought you needed dynamic data , wanting to avoid the lag in hose lengths. My gut feeling is to avoid hoses as much as possible so you don't end up chasing air bubbles. Just a quick thought without actually knowing what you are after.
Mark

 

[TANSL]

Excuse me if the question is irrelevant, but do you need to measure pressures or impacts?

 

[baeckmo]

In biomechanical testing of reaction forces from animal (specifically dogs) movements, I have come across pressure-sensitive "mats" with multiple sensors. I'll go back and see if I cab find where they were made. Perhaps useful over limited area regions.

 

[Hildershavn]

I thought you needed dynamic data , wanting to avoid the lag in hose lengths. My gut feeling is to avoid hoses as much as possible so you don't end up chasing air bubbles. Just a quick thought without actually knowing what you are after.
Mark

Yes, I do need to measure dynamic pressure, however, I would use the readings from multiple sensors on one panel to average the pressure used in my quasi-static analysis. But you are right to question my intentions here, because I think now that averaging the value from multiple pressure inputs could result in the loss off of information. It would be better to have all sensors work independently and use a filter on the raw data to calculate the average during post-processing instead.

 

[Hildershavn]

Excuse me if the question is irrelevant, but do you need to measure pressures or impacts?

Well, I would use pressure sensors in a combination with strain gages and linear displacement sensors to find out the minimum timeframe relevant to average pressure for use in quasi-static fea simulation of the panel. A peak pressure lasting for a very short time period may not at all have a relevant impact on the hull as I understand it.

 

[gonzo]

Sharp peaks are relevant to structural studies. Think of an extreme, like a bullet-proof vest. It acts like a soft fabric when the velocity is low. When a bullet hits it at high velocity, it acts like a plate. Forces acting at high velocities will create stress risers because of the shear between the area being accelerated and the rest.

 

[jcamilleri]

https://www.researchgate.net/public...l-scale_measurements_and_numerical_simulation

 

[Hildershavn]

Sharp peaks are relevant to structural studies. Think of an extreme, like a bullet-proof vest. It acts like a soft fabric when the velocity is low. When a bullet hits it at high velocity, it acts like a plate. Forces acting at high velocities will create stress risers because of the shear between the area being accelerated and the rest.

True enough for a dynamic analysis. However, short impulse peak pressures will not necessarily transfer much energy to the structure if the structure is flexible enough. In a quasi-static analysis, peak pressures may be omitted. As with a torsion stick, when the torque is high enough the rod flexes, and because of the limited stroke of the air wrench only a little fraction of this torque is actually transferred to the nut/bolt head.

 

[gonzo]

I agree, there is a threshold for short peaks. However, there should also be a minimum threshold for amplitude, not just duration. I suppose it will be dependent on the material properties you are studying.