{"id":72017,"date":"2026-02-04T09:13:52","date_gmt":"2026-02-04T14:13:52","guid":{"rendered":"https:\/\/blogs.sw.siemens.com\/simcenter\/?p=72017"},"modified":"2026-03-26T06:53:34","modified_gmt":"2026-03-26T10:53:34","slug":"the-rocket-that-refused-to-behave-the-ultimate-guide-to-spider-element-automation-for-rocket-and-aerospace-structures","status":"publish","type":"post","link":"https:\/\/blogs.sw.siemens.com\/simcenter\/the-rocket-that-refused-to-behave-the-ultimate-guide-to-spider-element-automation-for-rocket-and-aerospace-structures\/","title":{"rendered":"The rocket that refused to behave – The ultimate guide to spider element automation for rocket and aerospace structures"},"content":{"rendered":"\n

How one engineer wrestled misaligned interfaces, unexpected modes, and stubborn joints into submission \u2014 with help from Simcenter 3D<\/em><\/strong><\/h2>\n\n\n\n

The first time the upper stage of the launch vehicle met the vibration table, everyone expected a smooth characterization test. What they got instead was a shriek.<\/p>\n\n\n\n

A sharp resonance spiked far above predictions. Technicians flinched, and the stop button was fully utilized. The room fell silent except for the low hum of cooling fans.<\/p>\n\n\n\n

The rocket was already fighting the team, and David<\/strong>, the structural dynamics engineer on duty, took it personally. He\u2019d seen bad simulation models before, but this rocket was different. It was like it was designed to model something completely different. It insisted it was far stiffer than any physical measurement could justify.<\/p>\n\n\n\n

Joints that live in a different reality<\/strong><\/h2>\n\n\n\n

David dug into the digital model and immediately found the first culprit:
“The interface between two stacked cylindrical rocket sections had been represented as a continuous glue\u2011like surface connection<\/strong>, even though the physical attachment was through a series of discrete circumferential connection points<\/strong>“, David explained to us.<\/em> “The digital model was created so that the structure was a perfectly bonded, perfectly rigid ring. The real hardware was nothing of the sort.<\/em>“<\/p>\n\n\n\n

His problem did not end there; worse, the meshes around the circumference of the two sections didn\u2019t even align. Loads couldn\u2019t be transferred cleanly. The rocket, physically and digitally, was living in two different realities.<\/p>\n\n\n\n

The simulation never stood a chance of representing reality, and he had just completed an expensive test to prove it.<\/p>\n\n\n\n

A problem shared is a problem halved<\/strong><\/h2>\n\n\n\n

Some engineers may have tweaked parameters, adjusted boundary conditions, maybe smoothed over the discrepancy. David did something else:
He went after the real source of the problem, the connection definition itself.<\/strong>

He wrote to Siemens support engineers with a seemingly simple question, but it had some complex implications.<\/p>\n\n\n\n

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“Does your preprocessor support efficient creation of spider elements?”<\/em><\/p>\n\n\n\n

David, Structural Dynamics Engineer <\/p>\n<\/blockquote>\n\n\n\n

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David\u2019s plan was to find nodes in cylindrical space and pair inner\u2011diameter nodes with their matching outer\u2011diameter partners. However, he knew that, given the model’s size, it would take him half a lifetime to manually find and match each node pair.<\/p>\n\n\n\n

Mark\u2019s challenge<\/strong><\/h2>\n\n\n\n

It was Mark, one of Simcenter 3D<\/a> expert users, who got back to him.<\/p>\n\n\n\n

\u201cThis situation was primarily an accurate geometry searching challenge in a cylindrical context. Simcenter 3D has very capable out-of-the-box capabilities, and it could deliver an out-of-the-box solution,\u201d <\/em>Mark told us.
He continued, \u201cThe user\u2019s question asked if there were any \u2018efficient\u2019 methods, and I took this to mean automated tools or methods to deliver a solution. Usually, this is answered by Siemens staff with a simple \u201cYES! It\u2019s possible with NX Open<\/a>\u201d, but I wanted to put that answer to the test. Could I deliver an NX Open application that provides a complete solution for 100% of the use cases? And let\u2019s be clear, Simcenter 3D could handle all the use cases individually, but this question was about efficiency. Could it efficiently <\/strong>create spider elements?\u201d<\/em><\/p>\n\n\n\n

Let\u2019s take a look at the list of challenges Mark faced in answering this question and the answers he came up with.<\/p>\n\n\n\n

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  1. How can you identify a source node connected to N target nodes through geometric search in a cylindrical context?

    Mark\u2019s answer – Bounded volume selection recipes can find objects using cylindrical contexts<\/em><\/li>\n<\/ol>\n\n\n\n
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    1. Can you parameterize geometric searches?

      Mark\u2019s answer – Yes, with bounded volumes as rectangular boxes, cylinders and spheres, dimensions are editable expressions<\/em>.<\/li>\n<\/ol>\n\n\n\n
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      1. Can you create a spider element (1 node to many nodes) as a rigid or constraint element?

        Mark\u2019s answer – The 1D Connection command has done this for maybe 2 decades<\/em><\/li>\n<\/ol>\n\n\n\n
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        1. How do you turn the steps a user makes into reusable code?

          Mark\u2019s answer – Journals can be recorded in NX and Simcenter 3D in multiple languages, including Python, Visual Basic, C++, and more<\/em><\/li>\n<\/ol>\n\n\n\n
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          1. As a very novice software developer (I\u2019m a user after all), can I build a simple script that iterates inside a loop to make the out-of-the-box (OOTB) labor-intensive process free from significant user interaction

            Mark\u2019s Answer – Perhaps it is better if I show you<\/em><\/li>\n<\/ol>\n\n\n\n

            Mark provided us with the same videos that he sent to David, the first of which demonstrated the problem with the out-of-the-box solution. It shows the creation of a series of rigid connections around a cylinder. There are 240 connections in this model, from 240 nodes at an inner-diameter location to 720 nodes at an outer-diameter location. Each individual connection is from a single node to 3 nodes. All connected nodes have one thing in common: they all have the same angular position in space relative to a cylindrical coordinate system.<\/p>\n\n\n\n

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