HyperSizer was selected for use on the NASA Ares HLV project. New capabilities were programmed into HyperSizer specifically in support of the Ares upper stage project.

HyperSizer Orthogrid Test Panel Pretest Predictions

HyperSizer pretest predictions of the MSFC orthogrid 44" square test panel were completed July 2007. The predicted failure load and failure modes are summarized in the table. The failure loads are reported in terms of acreage unit load in (lbs/in). The overall panel failure load was predicted to be 297,000 lbs and included approximate effects of the thickened panel edges.

The unit failure load of the panel was (5300 lb/in), slightly higher than the HyperSizer pre-test prediction of 5035 (lb/in).

Table 2

Local Skin Pocket Buckling Verification to FEA

HyperSizer local buckling analysis of the skin between stiffeners of an orthogrid cylindrical panel is compared to FEA for uniaxial compression loading. The local buckling images and summary table represent a small portion of the MSFC test panel (3 pockets by 3 pockets) and use the same physical dimesnsions (height, spacing, thicknesses). For the test panel, the maximum difference is less than 2% between FEA and HyperSizer skin local pocket buckling.

An extensive verification effort was undertaken for orthogrid and local buckling of skin pockets, including tension field stiffening effects to a variation of tank pressures - as done for the panel buckling shown above.

Cylindrical Panel Buckling Verification to FEA

HyperSizer cylindrical panel buckling analysis was compared to FEA for different internal tank pressures ranging from zero to 50 psi. The average difference between HyperSizer and FEA predictions was 1%. In all cases, the maximum difference was 3%. The cross sectional dimensions from the MSFC test panel (see below) were used as the example orthogrid design. For FEA verification, the cross section was discretely meshed, using HyperFEMgen, with shell elements representing the skin and webs.

The above image is an FEMs generated by HyperFEMgen and analyzed with different loadings to generate the graphs below of axial compressive buckling load versus internal tank pressure.

The left image is the buckling mode shape with zero pressure. The right image is the buckling mode shape with high pressure, displaying the effect caused by tension field hoop stiffening on mode shapes.

The above graph plots failure load prediction as a function of pressure up to 50 psi. Internal pressure causes an increase in axial compressive buckling load due to hoop tension field stiffening. This effect is represented with the set of curves labeled "No axial pressure relief". This hoop tension field stiffening effect is quantified as an intrinsic part of the buckling solution. An additional benefit is the linear superposition of axial tension load (axial pressure relief) which reduces the applied compressive load. The total benefit of pressure stabilazation is plotted with a set of curves labeled "Including axial pressure relief."

The graph below zooms in on the range of zero pressure up to 10 psi. The comparisons of the four analyses are so close, the green HyperSizer line is covered.

There are several observations to make. First is that HyperSizer's buckling method matches FEA solutions for the orthogrid panel, especially at zero or low internal pressures. Second, HyperSizer generated equivalent stiffness terms for 2D planar finite element meshes with NEi are correct based on comparison to the discretely meshed 3D models. Third, that the discretely meshed 3D FEA solutions between Nx and NEi Nastran are the same. Results and explanations are included in the referenced PPT.

Related Resources

Esoteric Capabilities

Below are listed new capabilities programmed into HyperSizer specifically in support of the Ares upper stage project.

Frequently Asked Questions

Below are responses to frequently asked questions from MSFC users.

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Full List of Product Capabilities