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11
Analyzing & Optimizing Stiffened Panels / Why use DSP?
« Last post by David Hughes on February 20, 2020, 10:22:25 AM »
Hi,

What are the benefits of sizing with Discretely Stiffened Panels compared to sizing the Stiffeners and Skins separately?

If the FEA and HS geometry match, would it be best to set the backdoor setting "use summed panel loads for object analysis" to "No" to avoid unusual object loads calculated when combining segment load components from the tension/compression loops?

I believe one advantage of DSPs is that more global failure modes can be considered, including flexural-torsional buckling, plastic bending and crippling (inc. effective skin). Is this right? Are there any others that require the summed segment loads?

Kind Regards,
David.
12
Analyzing & Optimizing Stiffened Panels / FEA loads procesing for DSP
« Last post by David Hughes on February 20, 2020, 07:53:31 AM »
Hi,

I am trying to follow how HyperSizer is calculating the Discrete Stiffened Panel loads for technique 2 so as I can understand the limitations. Apologies for the long message, but I have a few questions:

1) When creating the segments there is an option to create a stringer or frame segment. What’s the difference?

2) After upgrading to v8.0.47 I noticed that there is a new DSM backdoor option:
"Modify technique 2 beam fea moments to account for stiffener height"
What does this mean? Is it something related to bar offsets, or is it the moment correction for Cruciform sections, or is it something else?

3) V8 now incorporates the integral cruciform concept into the native environment, however there is no specific documentation. Is it the same as the method/equations used for the Metal Grid Stiffened Plugin?

4) Within the FEA Loads tab why are the tension and compression tables empty?

5) Within the FEA Loads document, section 4 gives the equations for the N-sigma methods. Do similar equations apply for BAR elements using length instead of area? Also, I cannot match the standard deviation values. Is the equation missing an n term (where n=number of elems) or is it something else?
   SD = (Sum((Ni - Navg)^2*Ai)/(((n-1)/n)*Sum(Ai)))^0.5

6) Within the FEA Loads document for Discretely Stiffened Panels I believe the transformation equations are incorrect (eq. 1 to 3):
   Nxy = -Fx*cos(q)*sin(q) + Fy*cos(q)*sin(q) + Fxy(cos^2(q)-sin^2(q))
   Similar for Mxy
   Qxx = +Vx*cos(q)+Vy*sin(q)
   Qyy = -Vx*sin(q)+Vy*cos(q)

7) For the Discretely Stiffened Panel’s transverse shear summation (eq. 41), I’ve found cases when the skin load relieves the total. I haven’t noticed this for Nx,seg and I’m still working on Mx,seg. I believe the full Qx,seq equation is:
   Qx,seg = (V1 + sign(V1)*(Qxx,L*wL/2+Qxx,R*wR/2)))/(1/2*(wL+wR))
   Where:   V1 = if |V1,t|>|V1,c| then V1,t else V1,c
   Similarly for Qxx,L and Qxx,R
Test case;
   wL/2 = 100   wR/2 = 100
   Qxx,t,L = 0.5   Qxx,t,R = 6.0
   Qxx,c,L = -1.0   Qxx,c,R = -3.0
   V1,t = 200   
   V1,c = -500   
      
   V1 = -500
   Qxx,L = -1.0
   Qxx,R = 6.0

   Qx,seg = (-500 - (-1.0*100 + 6.0*100))/200 = (-500+100-600)/200 = -5N/mm
Note that the LH Skin is relieving the load.

Kind Regards,
David
13
Software Installation / Re: Installation of v8.0.47
« Last post by Stephen on January 31, 2020, 08:49:25 AM »
Hi Ruben,

This looks like a licensing issue. I am reaching out via email for more information.

-Stephen
14
Software Installation / Installation of v8.0.47
« Last post by Ruben on January 31, 2020, 08:42:57 AM »
Hi,

I have been using version 7 fine, however after installing v8.0.47 I get the attached screenshot. How do I get past this issue?

Regards,
Ruben
15
Material Strength Composites: Ply Approach / LaRC03 Fiber Failure Theory
« Last post by Ömer on January 24, 2020, 06:56:22 AM »
First of all, we calculated toughness ratio (g) by using thin ply formulas as mentioned in "Ply Based Composite Strength Document" to obtain fiber failure.

Because of the lack of fracture toughness terms (G1c, G11c), we assume Ytis= Yt and Sis=S. Also, the angle of fracture is taken as 53 degree as shown in "Composite Strength,Ply Based" Document".

For the our case of fiber compression (Sigma11<0), ply stresses are transformed into the new m coordinates and Margin of Safety(MoS) values has been calculated. In our case, Sigma22m is bigger than 0.

The example case is given in Attachments. We calculated MoS as 0.7, but HyperSizer shows 0.134.

We have been seen that the results of HyperSizer and the aforementioned document are very different.

What is the reason of this difference? Which one is more reliable? And, if HyperSizer result is more acceptable, how can we calculate the same value analytically? Could you please check it by using any values that are necessary for LaRC03?

Thank you.
16
Thanks James

Is the segment approach designed around the using the summed object loads?  I asking because I believe the preferred approach to sized a discretely stiffened panel is to use Plate and Bars concepts first, which does not use the summed object loads and then do a final sizing with stringer segments.  As this approach is deemed quicker.

However if the Plate and Bar approach doesn't use the summed object load, and the uses the individual object loading, then stringer segments will want to but more loading within the skin instead of the stiffener.

Is there a preferred process for sizing a discretely stiffened panel?

Gawain
17
It's okay to keep the segment loads flag set = Yes for final MS.

It depends whether you want to use the FEA-computed local object loads, or allow HyperSizer to compute the local object loads from the total segment load. Perhaps on the final pass you may want to use the FEA-computed local object loads because the FEM and the dimensions/materials in HyperSizer are the same. If you're okay with always using the segment loads approach to determine the object loads, then keep it = Yes.

FYI.. there's good documentation on this load summation approach. See: http://hypersizer.com/download.php?type=analysis&file=AID000_Panel_Segment_Loads_HME.pdf

I hope this is helpful.

-James
18
Hi

The Hypersizer help states that this Backdoor data tab should be switched 'ON' for sizing, but yet switched 'OFF' for final margins.  Is there a reason for this, as switching this setting off and on makes a big difference to the final panel sizes.

Gawain
19
Panel Buckling / Re: Orthotropic Flat Plate SSSS Shear Buckling
« Last post by Stephen on January 17, 2020, 10:09:34 AM »
Hi,

It turns out that the HME document you are referring to actually has a couple of typos that are resulting in the difference you are seeing there. The actual reference equations are correctly reproduced in Word stress reports from the software, and attached below for reference. I've noted this so we can address it in a future revision of the HME.

An additional consideration if you are attempting to replicate the HyperSizer result is that we always use compressive stiffnesses when doing buckling calculations, even for shear.

Thanks,
Stephen
20
Panel Buckling / Orthotropic Flat Plate SSSS Shear Buckling
« Last post by Ömer on January 17, 2020, 02:38:46 AM »
We calculated shear buckling critical load, Nxy_cr, both in HyperSizer and according to Method Documentation of HyperSizer (Plate and Shell Equations.HME in Buckling of Failure Analysis). We made this comparison for a few component and we saw that these two result which belong to HyperSizer and Method Document are very different in some cases, although they are similar sometimes.

For the parameters below:

D is the stiffness matrix,
D11: 1050575
D12: 184745
D22: 428207
D33: 211547.5

Buckling Spans,
a: 538.3 mm
b: 1405.5 mm

Shear Load,
Nxy: -40 N/mm

Method Result: 108.76 N/mm
Result is showed by HyperSizer: 158.6 N/mm

What is the reason of this difference? Which one is more reliable? And, if HyperSizer result is more acceptable, how can we calculate the same value analytically?

Thank you
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