Hi Mike, Thanks a lot for your answer and explanation, it is very helpful, although I am still a bit puzzled by the difference observed in a simple axial test. All the best, Solenne
Le jeudi 30 juin 2022 à 05:04:07 UTC+2, Mike Taylor a écrit : > Solenne, > > Based on the theory behind the ANCF cable element, it should provide good > results in a pure axial test. See: "Analysis of Thin Beams and Cables > Using the Absolute Nodal Co-ordinate Formulation" by Gerstmayr and Shabana > for the full technical detail on this element (as well as more details on > bending). > > When using ANCF elements, it is important to keep in mind the meaning > behind the nodal coordinates. Taking the ANCF cable element in particular, > the nodal coordinates for each of the two nodes are the position of the > node as well as the position vector gradient along the local element "x" > axis at that node (6 coordinates per node). The position vector gradient > along the local element "x" axis defines the tangent to the beam axis in > global coordinates at that node as well as the stretch along the beam axis > at that node. > > When you fix an ANCF node, you fix all of its coordinates. So for your > axial test, you do not get a constant state of stress in the meshed beam > due to this imposed boundary condition and that is why adding elements will > help you get closer to the analytical solution which assumes that constant > state of stress. > > That being said, I'm not sure if the boundary conditions explain all of > the difference between the static solution and the analytic solution. I > haven't had time to investigate that further, but I wanted to at least pass > on this information. > > Best regards, > > Mike > > On Thursday, June 23, 2022 at 4:05:06 AM UTC-5 SoMdt wrote: > >> Hi all, >> I am simulating a very simple cable element under traction (I also tested >> pure flexion) : one node is fixed, and a force is applied to the end node. >> >> For the code attached, the elongation of the beam is 9.61 mm, while, >> analytically, it should be 12.7 mm. I did the same simulation with >> BeamEuler element, and the result is indeed 12.73 mm. >> With cable ANCF, even with lower force (divided by 10), the error is >> significant (1.11 mm vs 1.27 mm). >> >> The problem is the same in flexion and the error does not seem to be >> linear. >> >> When I increase the number of nodes in the builder, the error decreases >> but it remains significant (10.88 mm vs 12.7 mm with 1000 nodes instead of >> 1). >> >> I am using these elements wrong ? I thought they were suitable for large >> displacement and could replace Beam Euler if no twisting or shear were >> present ? >> >> Thanks a lot for the help, >> Solenne >> > -- You received this message because you are subscribed to the Google Groups "ProjectChrono" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/projectchrono/5837ee0a-306c-42bf-b573-01c7a4f1e0d3n%40googlegroups.com.
