1. Element coordinate system The reference vector may be specifying local element axis, see the option LOCAL ELEMENT AXIS. If the line is a blade in a wind turbine and LOCAL ELEMENT AXIS is not specified, the reference vector will be found as the cross product between the local x-axis of the shaft and the local x-axis of the blade element. If the reference vector is not given by either of these two methods, the default method will be used to determine the local element axis. Default procedure If the element is not vertical, the reference vector is found as the cross product between the global z-axis and the local x-axis. If the element is vertical, the positive or negative global y-axis will be used as the reference vector; positive if completely vertical or tilted in the positive global x-direction and negative otherwise. This will give a horizontal y-axis and, if possible, a local z-axis oriented upwards. Once the reference vector is found by one of these methods, then The local z-axis is found as the cross product between the local x-axis and the reference vector. The local y-axis is found as the cross product between the local z-axis and the local x-axis. For beam elements, the element axes are found at the stress-free configuration and will subsequently follow the element. Examples: If the element is in the global xz-plane and the local x-axis is completely vertical or tilted in the positive global x-direction, the global y-axis will be used as the reference vector. If the local x-axis is tilted in the negative global x-direction, the negative global y-axis will be used as the reference vector. If local x-axis is tilted 45 deg wrt to global z-axis, the reference vector will point in the positive global y-direction. If the local x-axis is along the global x-axis, the reference vector will point in the global y-direction. The initial local element axes will be aligned with the corresponding global axes. If the local x-axis is along the global y-axis, the reference vector will point in the negative x-direction. The local z-axis will point in the positive global z-direction and the local element y-axes in the negative global x-direction. If the local x-axis points in the direction (1,2,3), the reference vector will point in the direction (-2,1,0). The local z-axis will point in the direction (-3,-6,5) and the local y-axis will coincide with the reference vector. If the local x-axis points in the direction (1,2,-3), the reference vector will point in the direction (-2,1,0). The local z-axis will point in the direction (3,6,5) and the local y-axis will coincide with the reference vector. Figure 1. Local axis - example 1 Figure 2. Local axis - example 2 Figure 3. Local axis - example 3 Figure 4. Local axis - example 1 Figure 5. Local axis - example 1 Figure 6. Local axis - example 1 Figure 7. Local axis - example 1 System topology Boundary conditions