> For the complete documentation index, see [llms.txt](https://docs.enercalc.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.enercalc.com/e3d-training-manual/building-the-model/general-modeling-theory/understanding-model-geometry/shells/shell-quality.md). # Shell Quality Geometric guidelines for quad shells, including planarity, angles, aspect ratio, and size, to ensure quality finite element results. When performing a finite element analysis with quad shells, there are some geometric guidelines to keep in mind for the individual shells in order to ensure quality results. **Order of Node Selection:** We have already seen that it is important to define shells in either a clockwise or counter-clockwise order to avoid warped plates which will produce invalid results. ![](https://3750289988-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FlRZtG5Ynp58kYzLHYbR7%2Fuploads%2Fgit-blob-f1b6049efd17a378c331efa74000f03366d0b284%2FWarped%20shell.jpg?alt=media) NOT GOOD! **Planar Geometry:** Along similar lines, it is important to ensure that all four nodes of a quad shell lie in one plane. ![](https://3750289988-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FlRZtG5Ynp58kYzLHYbR7%2Fuploads%2Fgit-blob-905da49b489c313e8254a31b90c37c8bee49aca0%2FNon-planar%20shell.jpg?alt=media) NOT GOOD! **Shape:** The ideal shape for a quad shell is a square. The more a quad shell deviates from a square, the greater the chances of introducing some error into the results. But in practical situations, it is not always possible to keep shells square, so here are some additional considerations to keep in mind with regard to shell quality: **Angles:** Shells have some ability to tolerate angles other than 90 degrees, but try to avoid extreme skews. Interior angles should range between 60 and 120 degrees. Never create a shell that has an included angle that exceeds 180 degrees. ![](https://3750289988-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FlRZtG5Ynp58kYzLHYbR7%2Fuploads%2Fgit-blob-a0f5f1b88ded14bb2d36f3d31346c49ece830058%2FStar%20Trek%20shell.jpg?alt=media) NOT GOOD! **Aspect Ratio:** Shells have some ability to become rectangular, but try to avoid extreme aspect ratios. It is good to try to keep aspect ratios less than 2:1. Never create a quad shell with an aspect ratio that exceeds 4:1. ![](https://3750289988-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FlRZtG5Ynp58kYzLHYbR7%2Fuploads%2Fgit-blob-c3bc47e78676fd259aab97e50ff9da1e22deea13%2FBad%20aspect%20ratio%20shell.jpg?alt=media) NOT GOOD! Note that when it comes to improving shell quality, the solution is often to just break a poorly shaped shell into more shells that all have better quality. ![](https://3750289988-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FlRZtG5Ynp58kYzLHYbR7%2Fuploads%2Fgit-blob-06038399d2285f304adb17d4fd53d84562127656%2FFix%20to%20shell%20with%20bad%20aspect%20ratio.jpg?alt=media) MUCH BETTER! This is a good segue into the next topic, which is mesh density. **Size Variation:** We will cover the topic of mesh density in great detail in the section titled Mesh Density. But for the purposes of the discussion on shell quality, let it suffice to say that it is good practice to try to make the elements of a given mesh generally about the same size. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.enercalc.com/e3d-training-manual/building-the-model/general-modeling-theory/understanding-model-geometry/shells/shell-quality.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.