wikiffcd2022:start
Differenze
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wikiffcd2022:start [2022/05/30 17:02] – [A Phoney monocoque chassis] ebertocchi | wikiffcd2022:start [2023/01/19 10:16] (versione attuale) – ebertocchi | ||
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==== Frontal crash absorber collapse loadcase (inertia relief) ==== | ==== Frontal crash absorber collapse loadcase (inertia relief) ==== | ||
At the element faces belonging to the '' | At the element faces belonging to the '' | ||
+ | |||
+ | ==== How to set a damped response ==== | ||
+ | |||
+ | <hidden Click here to expand> | ||
+ | |||
+ | In order to include a small degree of structural damping (eg. 1% of the critical value) into a MSC.Marc/ | ||
+ | * enter the menu '' | ||
+ | * preemptively define a modulating table 1/ω | ||
+ | * menu '' | ||
+ | * define '' | ||
+ | * set // | ||
+ | * define //table// through '' | ||
+ | * go back to '' | ||
+ | * select the various model materials, and for each of them enter the submenu '' | ||
+ | * leave alone the '' | ||
+ | * define a '' | ||
+ | * set a frequency modulating function, namely //TABLE//, by hitting the '' | ||
+ | * select the just defined '' | ||
+ | * in this way, I defined damping as a function of the $\alpha$ e $\beta$ coefficients introduced by the Rayleigh proportional damping model, with zero $\alpha$ and hence no contribution of the mass matrix. In particular $\zeta = \frac{1}{2}(\frac{\alpha}{2 \pi f}+2 \pi f \beta)$ with $\alpha=0$ and $\beta= 0.01 \cdot g(f)=\frac{0.01}{\pi f}$, from which $\zeta=0.01$ as desired. | ||
+ | * enter the '' | ||
+ | * enter the job '' | ||
+ | * Enter the '' | ||
+ | * substitute them with the //AVAILABLE ELEMENT SCALARS// | ||
+ | * '' | ||
+ | * '' | ||
+ | * the //REAL HARMONIC// e //IMAG HARMONIC// stress resultant equivalents for the beam elements, '' | ||
+ | * insert from the //AVAILABLE ELEMENT TENSORS// block | ||
+ | * '' | ||
+ | * '' | ||
+ | * run the simulation as usual with '' | ||
+ | * open the post file as usual with '' | ||
+ | * The deformed shape may be visualized //according to a given phase// within the oscillation cycle (see also the '' | ||
+ | * Please note that the real component has a 0° phase ($\cos(\omega t)$ modulation) whereas the imaginary component has a 270° phae ($-\sin(\omega t)$ modulation). | ||
+ | * Please also note that in resonance conditions the **imaginary component** becomes dominant and reaches the peak values, whereas the real component vanishes (resonant response is in fact ~90° out of phase with respect to the real, 0° excitation). | ||
+ | * Lets e.g. collect the displacement in $z$ direction of the node at the center of the excited wheel contact area: | ||
+ | * enter the POSTPROCESSING '' | ||
+ | * define the locations for the response sampling with '' | ||
+ | * define the range of the sub-increments to be collected with '' | ||
+ | * proceed with the definition of collected response diagrams by entering th '' | ||
+ | * By hitting '' | ||
+ | * response peaks are now finite (they were theoretically unbounded in the absence of damping), and peaks disappear in correspondence of natural modes that are weakly coupled with the exciting force. In the absence of damping, bounded response at resonance is obtained for **strictly uncoupled** natural modes only. | ||
+ | |||
+ | </ | ||
+ | |||
+ | ===== Buckling ===== | ||
+ | [[https:// | ||
+ | |||
+ | {{ : | ||
+ | {{ : | ||
+ | {{ : | ||
+ | {{ : | ||
+ | {{ : | ||
+ | {{ : | ||
===== Sparse material ===== | ===== Sparse material ===== | ||
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===== Exercises ===== | ===== Exercises ===== | ||
[[https:// | [[https:// | ||
+ | |||
+ | ===== Exam turns ===== | ||
+ | |||
+ | [[https:// |
wikiffcd2022/start.1653930162.txt.gz · Ultima modifica: 2022/05/30 17:02 da ebertocchi