There is no specific methodology for determining the test point locations on a structure. Modes and deflection shapes will exhibit themselves to varying degrees at each test point location. Therefore, the more test point locations you have, the better visual representation you can create. However, in most cases, you can get a great representation of the mode or operating shape of a structure with just a handful of measurements.
There are a couple of ways you can get full 3-dimensional results from a single axis accelerometer. As you mentioned, you can orient the accelerometer along each of the 3 axis prior to each impact and impact the structure at the same point of impact. Using this method, the impact point is your reference, and you rove the accelerometer. You can also leave the accelerometer at a fixed point, and then rove your hammer to impact the structure at each test point at all 3 axis per point. In this second case, your fixed accelerometer is your reference and you rove your impact hammer. Obviously, using a tri-axial accelerometer is a much more efficient way to test a structure in this method, but it can certainly still be accomplished using a single axis accel.
It will depend upon the stiffness of the foam used. You really just want something stiff enough to support your test article so it is not resting on the table and flexible enough to allow the test article to move while vibrating. You can also use things like the air bags used for shipping packages or suspend the test article using fishing line or shock cord.
do we need to impact a structural in 3-D to get 3-D modal shapes? In my experiment, I used a roving impact test with a triaxial sensor, but impact forces were all in one direction(z). Can I get modal shapes in x-y directions?
Your mode shapes will come from the roving DOFs. If you rove your hammer, your mode shapes will be the points and directions where you impact with the hammer. If you rove your triaxial accelerometer, your mode shapes will be 3D motion at all of the points where you mounted your accelerometer. In your experiment that you described, you will only get response in the (z) direction.
That is not correct. If a triax is used, accelerations are measured in all directions regardless of which direction(s) the input(s) are applied. If the responses along the various axes are highly coupled, as with many structures, the animations can actually be quite good for the "off axis" (i.e. not in the same direction as the impact) responses.
Hi, which DAQ did you use? is there any limitation for hardware such as impact hammer, accelerometer, and DAQ? where can I find these data for this software?
Hi Ashkan, A National Instruments NI-9234 was used for the DAQ. For more info on what DAQ's can be controlled directly by the ME'scopeVES software package as well as more info on the software and its capabilities, visit www.vibetech.com or contact us at sales@vibetech.com. Thanks!
Thanks, I already contacted them to buy the license. I am having two different DAQs: NI 9215, and NI 9239. My accelerometer is PCB 356A25, and my Impact Hammer is PCB 086C03. I used to work with this software for a simple Beam Project. So my question is that with this equipment that I already have, can I run the software for a curvlinear surface?
Yes, curvilinear surfaces are no problem. Any type of 3-dimensional surface or structure can be modeled in ME'scopeVES either by utilizing the software's drawing tools, or by importing one of the many types of 3D model file types imported by ME'scopeVES. Also, all measurement points are adjustable, so normalizing your measurement locations to the surface of the structure to match the alignment of the accelerometer(s) is very easy to do.
We unfortunately do not have an ACQ Window/DAQ Controller for either the NI 9215 or the NI 9239 at this time. However, if you are using Lab View, you can easily export your data blocks in a UFF File Format for import directly into ME'scopeVES and modal analysis using VT-550 Visual Modal Pro. If you have additional technical questions, please direct them to either sales@vibetech.com or support@vibetech.com and we will get you taken care of ASAP. Thank you!
This video would be a lot better without the very distracting music.
I got a doubt, when you show us the different types of vibration of the beam, those are armonics?
Hi, will in any way the force exerted by the hammer affect the natural frequency and modeshape results obtained?
Good Video! How do you determine the test point locations? Thanks.
Thanks very good video..
There is no specific methodology for determining the test point locations on a structure. Modes and deflection shapes will exhibit themselves to varying degrees at each test point location. Therefore, the more test point locations you have, the better visual representation you can create. However, in most cases, you can get a great representation of the mode or operating shape of a structure with just a handful of measurements.
In case of single axis accelerometer do we need to attach 3 different accelerometers for each axis. Or just one is sufficient ?
There are a couple of ways you can get full 3-dimensional results from a single axis accelerometer. As you mentioned, you can orient the accelerometer along each of the 3 axis prior to each impact and impact the structure at the same point of impact. Using this method, the impact point is your reference, and you rove the accelerometer. You can also leave the accelerometer at a fixed point, and then rove your hammer to impact the structure at each test point at all 3 axis per point. In this second case, your fixed accelerometer is your reference and you rove your impact hammer.
Obviously, using a tri-axial accelerometer is a much more efficient way to test a structure in this method, but it can certainly still be accomplished using a single axis accel.
Do you think using foam for a free-free boundary condition would work for plastic beams as well or are they not stiff enough?
It will depend upon the stiffness of the foam used. You really just want something stiff enough to support your test article so it is not resting on the table and flexible enough to allow the test article to move while vibrating. You can also use things like the air bags used for shipping packages or suspend the test article using fishing line or shock cord.
do we need to impact a structural in 3-D to get 3-D modal shapes? In my experiment, I used a roving impact test with a triaxial sensor, but impact forces were all in one direction(z). Can I get modal shapes in x-y directions?
Your mode shapes will come from the roving DOFs. If you rove your hammer, your mode shapes will be the points and directions where you impact with the hammer. If you rove your triaxial accelerometer, your mode shapes will be 3D motion at all of the points where you mounted your accelerometer. In your experiment that you described, you will only get response in the (z) direction.
That is not correct. If a triax is used, accelerations are measured in all directions regardless of which direction(s) the input(s) are applied. If the responses along the various axes are highly coupled, as with many structures, the animations can actually be quite good for the "off axis" (i.e. not in the same direction as the impact) responses.
do we need triaxial accelerometer?
I guess to capture and understand all the mode-shapes i.e. suspension/rigid body vibration and body deformation modes.
Hi, which DAQ did you use? is there any limitation for hardware such as impact hammer, accelerometer, and DAQ? where can I find these data for this software?
Hi Ashkan,
A National Instruments NI-9234 was used for the DAQ. For more info on what DAQ's can be controlled directly by the ME'scopeVES software package as well as more info on the software and its capabilities, visit www.vibetech.com or contact us at sales@vibetech.com. Thanks!
Thanks, I already contacted them to buy the license. I am having two different DAQs: NI 9215, and NI 9239. My accelerometer is PCB 356A25, and my Impact Hammer is PCB 086C03.
I used to work with this software for a simple Beam Project. So my question is that with this equipment that I already have, can I run the software for a curvlinear surface?
Yes, curvilinear surfaces are no problem. Any type of 3-dimensional surface or structure can be modeled in ME'scopeVES either by utilizing the software's drawing tools, or by importing one of the many types of 3D model file types imported by ME'scopeVES. Also, all measurement points are adjustable, so normalizing your measurement locations to the surface of the structure to match the alignment of the accelerometer(s) is very easy to do.
Thank you very much. So can I connect my DAQs (NI 9215, and NI 9239) to the MEscope VES VT-550 Visual Modal Pro?
We unfortunately do not have an ACQ Window/DAQ Controller for either the NI 9215 or the NI 9239 at this time. However, if you are using Lab View, you can easily export your data blocks in a UFF File Format for import directly into ME'scopeVES and modal analysis using VT-550 Visual Modal Pro.
If you have additional technical questions, please direct them to either sales@vibetech.com or support@vibetech.com and we will get you taken care of ASAP.
Thank you!
Please remove the obnoxious music from the video.