# 3.7.14: Result Vectors on Shells

## **Principal Force Directions on Shells**

![Fig. 3.7.14.1: Cantilever analyzed as shell structure: directions of second principal normal forces](https://442610158-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MCkDlhlZpqUmakSqOrp%2Fsync%2F43b154e7d05dbde0a6c2de8b05a8765beb1e3f2e.png?generation=1595316053694859\&alt=media)

The “Principal Force Directions on Shells”-component lets you retrieve principal normal forces and moments at element centers (see fig. 3.7.14.1). All shells of a model get considered by default. Use the input-plug **“ElemIds”** to select a subset. Results refer to the selected load-case at the nearest upstream **“ModelView”**-component.

The order of all result lists corresponds to the order of faces in the mesh used to generate the shell. Output-plug **“P”** lists the coordinates of the element centers where the normal forces and bending moments were calculated. **“N1-Vec”**, **“N2-Vec”**, **“M1-Vec”** and **“M2-Vec”** deliver the first and second principal normal force and moment directions as vectors. Their length corresponds to the absolute value of the corresponding quantity in kilo Newton per meter (for forces) or kilo Newton meter per meter (for moments). The output plugs **“N1-Val”**, **“N2-Val”**, **“M1-Val”** and **“M2-Val”** return the values of the principal normal forces and moments.

## **Principal Stress Directions on Shells**

![Fig. 3.7.14.2: Triangular mesh of shell elements and principal stress directions at their centers](https://442610158-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MCkDlhlZpqUmakSqOrp%2Fsync%2F0b460e257b3c209c9d9e9876b5fe433c076e4b2d.png?generation=1595316053781224\&alt=media)

This components provides the same results as the **“Princ. Stress 1-2”** option of the **“ShellView”**-component (see fig. 3.7.14.2). The output-plug **“P”** renders the positions of the elements centers. **“Sig1-Vec”** and **“Sig2-Vec”** return vectors for the first and second principal stresses there. **“Sig1-Val”** and **“Sig2-Val”** output the values of the first and second principal stresses. Thin out results by setting **“Result Threshold”** of **“ModelView”** (needs to be upstream of the data-flow) to a value of less than 100 %. Like for isoline and force-flow lines a specific load case or superimposition of load cases can be set via **“ModelView”**. By default all load-case results get added up using unit load factors.
