Recent content by Rhei

Hello, after reading this thread Link I have a question about the use of residual vectors in superelements generation. Can the use of residual vectors replace the need of including too many high frequency modes during the condensation run? What I mean is: let's assume I have a structure which...

To make plots with Femap you have to use the charting option. When you click on it, a window will open, then select the symbol xy to open antoher window where you can choose what to plot

Well, the modal analysis compute the natural frequencies and the mode shapes of the structure. The natural frequencies are the frequencies at which the structure naturally tends to vibrate if subjected to a disturbance with that frequency content. The mode shape is the deformed shape at a...

What do you mean when you say " the frequencies are continuously increasing with the number of modes requested" ? Can you post an example?

Hi, I would like to solve an ODE rapresenting a SDOF spring-mass-damper system with Coulomb friction. The system is subjected to base acceleration ÿ, therefore the equation of motion is the following mü + cú + ku = -mÿ - µdN sign(ú) where µd is the dynamic friction coefficient, N the normal...

This equation num_cycles=(zero_crossings/2)-1 is what I was missing. Since I generated the sweep using Matlab, I could just make it count the number of zero-crossing points and use it in the previous equation. Until now I was trying to follow the procedure explained in the book written by...

Hi, I am running a transient simulation in Nastran. The structure undergoes a sine-sweep base acceleration and I need to compute the number of cycles the structure will se during the whole simulation. How do I do that knowing the sweep rate (R [oct/min]), the total duraton (T [s]) and the...

Hi, your beam translates in the y direction because it is not constrained, thus it has a rigid body mode. To constraint the y direction you need to add number 2 in your constrained dofs (which will be 123456). To simulate the base motion you must not use an input defined as a FORCE. Have a look...

Hi, is it possible to retrieve a relationship between friction and damping? I run a non-linear transient solution (Nastran SOL 129) of a model in which I modelled the friction effect using CGAP elements. What I see is that, because of the dissipation, the response at resonance has a lower...

Hi, the normal modes analysis available in Nastran does not take into account the damping, in fact the equation of motion is [M]{a} + [K]{u} = 0 which is the equation of motion for undamped free vibration (where: [M] is the mass matrix, [K] the stiffness matrix, {a} the acceleration and {u}...

The only method I know is the use of the statement "/ENTRY1". To use it you need first to run an analysis using ECHO = SORTED in the CASE. In this way, in your .f06 file you will have all your elements listed. What you need is the ENTRY COUNT, which identifies each element. One you know the...

Hi, if I understood you well you are looking for an alternative to the statement "/ENTRY1" right?

Hi, I am running a non-linear transient analysis using SOL 129 and I was wondering, how can I be reasonably sure I have chosen the right DT value in the TSPENL card? My excitation is a sine-sweep in the range 5-40 Hz and I am now using a DT = 5.E-4. I would say this is enough since it means I...

Hi, what do you mean when you say: " I manage to define them between 2 nodes but for some reason NASTRAN will not solve" ? Do you get a FATAL error? Also, have a look here...

First of all, if you have to work with modal damping you need SOL112, not the 109, because the 109 is a direct solution, which means it does not compute the normal modes and also you cannot define modal damping. Then, there is something that is not clear in your setup: your beam is clamped...