It is important to design products that are strong yet light in weight while resisting damage against impact or unanticipated shocks and vibration. The static analysis assumes that loads are constant or applied very slowly, ignoring the effects of inertial and damping forces. For many practical cases, loads are not applied slowly. In fact, they change with time or frequency. To simulate such conditions, a dynamic analysis is required.
Linear and Nonlinear Analysis
SOLIDWORKS Simulation Premium offers linear dynamics and nonlinear dynamics capabilities. These types of analyses can help you design structural or mechanical systems to perform without failure in dynamic environments. Linear dynamics studies can be used to analyze stress on moving components, earthquake simulations, time-varying loads such as the high-speed impact on landing gear and more.
Linear dynamics studies are based on frequency analysis. The software calculates the response of the model by accumulating the contribution of each frequency mode to the loading environment. The contribution of a mode depends on the load’s frequency content, magnitude, direction, duration and location.
There are four linear dynamics study types available in SOLIDWORKS Simulation Premium.
Modal Time History Analysis
Modal time history analysis is used when the variation of each load with time is known explicitly and you need to find out the response as a function of time.
Typical loads include shock (or pulse) loads, time-varying loads (periodic or non-periodic), and uniform base motion. You have the option to define support motions (displacement, velocity or acceleration applied to selected supports uniformly or non-uniformly). Initial conditions, such as a finite displacement, velocity or acceleration can be applied to a part or the whole model at time t =0. Modal, Rayleigh, composite modal and concentrated dampers are available for modal time history analysis.
After running the study, you can view displacements, velocities, acceleration or stress, strain, reaction forces, etc. at different time steps. Using the response plot, you can also graph results at specified locations versus time. The image below shows the acceleration response of certain components housed inside an electronics enclosure and subjected to shock test in accordance with the MIL-STD-810G, Method 516.5 criteria.
Response Spectrum Analysis
Response spectrum analysis can be used instead of a time history analysis to estimate the response of structures to random or time-dependent loading environments such as earthquakes, wind loads, ocean wave loads, jet engine thrust or rocket motor vibrations. This can be used if you need only the peak response of the structure and not the entire time history solution. Using response spectrum analysis can significantly reduce the solution time compared to a full modal time history type of analysis.
Input to a response spectrum analysis is the response spectrum, which is defined as the peak response of a single degree of freedom oscillator plotted versus its natural frequency. The results of the modal analysis are used in terms of a known spectrum to calculate displacements and stresses in the model. For each mode, a response is read from a design spectrum based on the modal frequency and a given damping ratio. All modal responses are then combined to provide an estimate of the total response of the structure.
A harmonic analysis can be used to calculate the peak steady state response due to harmonic loads or base excitation. Applications include determining stresses or displacement of components such as rotating machinery, subjected to oscillatory loading. Although you can create a modal time history study and define loads as functions of time, you may not be interested in the transient variation of the response with time. In such cases, you save time and resources by solving for the steady state peak response at the desired operational frequency range using harmonic analysis.
After running the study, you can view peak amplitudes of response parameters (stresses, displacements, accelerations and velocities), as well as response graphs of phase angles of response parameters over the range of operating frequencies.
Random Vibration Analysis
The random vibration analysis is used to calculate responses due to nondeterministic loads such as the loads generated on the suspension system of an automobile while moving on a rough road, base accelerations generated by earthquakes or pressure generated on an aircraft by air turbulence, etc.
This study requires the input loads to be described statistically by power spectral density (PSD) functions. For example, units of a PSD curve for acceleration input is g²/Hz. The solution of random vibration problems is formulated in the frequency domain.
After running the study, you can plot root-mean-square (RMS) values, or PSD results of stresses, displacements, velocities, etc. at a specific frequency or graph results at specific locations versus frequency values. This allows you to get a better insight about the frequency content of the output.The drop test in SOLIDWORKS Simulation Professional can be used to find out the stresses generated on a body dropped from a certain height or moving at a certain speed. However, if you need to evaluate the damage on an object impacted by another moving object, such as a projectile hitting a protective barrier, a nonlinear dynamics study is the way to go.
Nonlinear dynamics studies can handle large displacement with various advanced material models including hyper-elasticity, von Mises plasticity, etc. This type of analysis will require substantial computational resources. You can define initial conditions for velocity, displacement, acceleration or uniform base excitation or pressure loads.
With the analysis capabilities described here, you are no longer are limited to test designs against static load conditions. SOLIDWORKS Simulation Premium’s linear dynamics and nonlinear dynamics analysis capabilities will help you test your product’s resilience against shock and vibration.
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