wikifemfuchde2020:phoneyfsaechassis
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Entrambe le parti precedenti la revisioneRevisione precedenteProssima revisione | Revisione precedente | ||
wikifemfuchde2020:phoneyfsaechassis [2020/05/28 13:13] – ebertocchi | wikifemfuchde2020:phoneyfsaechassis [2020/05/28 16:40] (versione attuale) – ebertocchi | ||
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+ | Initial model | ||
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+ | Step by step evolution: | ||
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+ | Inertia relief model, without added masses | ||
+ | {{ : | ||
+ | and with the added masses {{ : | ||
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+ | Front impact, with or without ground support | ||
+ | {{ : | ||
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+ | Dynamic modal loadcase | ||
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+ | ==== Properties ==== | ||
+ | **Suspension link trusses** | ||
+ | |||
+ | Solid circular beam sections, ø12mm, aluminum. | ||
+ | Essentially rigid with respect to other chassis structures. | ||
+ | |||
+ | **Rear framework** | ||
+ | |||
+ | Hollow circular section beam, aluminum. | ||
+ | |||
+ | Main structure: outer diameter ø40mm, wall thickness 1.8mm. | ||
+ | |||
+ | Stiffeners: outer diameter ø30mm, wall thickness 1.2mm. | ||
+ | |||
+ | **Composite monocoque** | ||
+ | |||
+ | Thicker backbone: 1.8mm aluminum sheet, 25.4mm aluminum honeycomb 3003, density 5.2 lb/ft^3 ({{ : | ||
+ | |||
+ | |||
+ | Thinner panels: 1.8mm aluminum sheet, 6.75mm same aluminum honeycomb, 1.8mm aluminum sheet. | ||
+ | |||
+ | Frontal shock absorber support plate: provisionally as thinner panels, to be defined based on shock. | ||
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+ | |||
+ | **Sway (anti-roll) bar** | ||
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+ | outer diameter ø25mm, wall thickness 2mm, extremely stiff ([[https:// | ||
+ | |||
+ | Such a " | ||
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+ | **Inertial elements** | ||
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+ | {{ : | ||
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+ | ** Notes: ** | ||
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+ | < | ||
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+ | In particular, torsional stiffness should be evaluated in both the limiting cases of | ||
+ | * rigid springs, disconnected sway bars; | ||
+ | * disconnected springs, rigid sway bar. | ||
+ | |||
+ | This second loadcase, which is usually neglected, is however relevant for sizing the sway bar support areas on the chassis structure. | ||
+ | |||
+ | **On the relevance of constraining in dynamic analyses**. | ||
+ | [[https:// | ||
+ | Design is reliable in actual operational conditions ([[https:// | ||
+ | Added constraints stiffen up the structure, thus increasing natural frequencies. | ||
+ | However, a 0 Hz rigid body mode natural frequency may rise to a finite value due to added positioning constraints; | ||
+ | |||
+ | **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. | ||
+ | |||
+ | </ | ||
+ | |||
+ | hellow | ||
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+ | **Poor man dynamic response animated view** | ||
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+ | {{ : | ||
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+ | {{ : | ||
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+ | **Structural damping references** | ||
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+ | ==== Loadcases ==== | ||
+ | |||
+ | * Static test: torsional stiffness; | ||
+ | * preliminary suspension stroke motion test ({{: | ||
+ | * rigid spring or rigid anti-roll bar? | ||
+ | * Front, right wheel bump loadcase (inertia relief); | ||
+ | * Frontal crash absorber collapse loadcase (inertia relief); at the element faces belonging to the '' | ||
+ | * Dynamic modal response; | ||
+ | * Dynamic | ||
+ | |||
+ | ==== Connectors ==== | ||
+ | {{: | ||
+ | {{ : | ||
+ | {{ : |
wikifemfuchde2020/phoneyfsaechassis.txt · Ultima modifica: 2020/05/28 16:40 da ebertocchi