
	The Dynamics module is an add- on for PLAXIS 2D V9 Soil and structures are often subjected not only to static loads due to constructions in and on the ground surface but also to dynamic loads. If the loads are powerful, as in earthqueakes, they may cause severe damages. Dynamics analyses module you can analyse the effects of vibrations in the soil. Even though vibrations often have 3D-characteristics, in PLAXIS 2D V9, the dynamic model is limited to plain strain and axisymmetric conditions. Dynamics is equipped with features to deal with aspects of dynamics loads.

VDO
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Input features

Absorbant boundaries
To prevent the reflection of propagating waves back inside the model the boundary of the geometry can be modeled as absorbent.

Standard earthquake boundaries
Plaxis has a convenient default setting to generate standard boundary conditions for earthquake loading. Standard earthquake boundaries consist of a combination of absorbent boundaries and prescribed displacements, velocities or accelerations.

Prescribed velocities and accelerations
The boundary condition for prescribed displacements in static calculations has been extended such that it can be used for prescribed velocities and prescribed accelerations in case it concerns dynamic loading.

Soil behaviour

Rayleigh damping
Material damping in a soil is generally caused by its viscous properties, friction and the development of plasticity. However, in Plaxis the soil models do not include viscosity as such. Instead a Rayleigh damping term is assumed that is proportional to the mass and stiffness of the soil material. Separate damping coefficients can be assigned to different material sets for both soil and structural elements

Wave velocities
For Mohr-Coulomb and linear elastic models the wave velocities Vp and Vs can be entered as alternatives for the stiffness parameters.

Calculation features

Dynamic time
The duration of most geotechnical processes like excavations or consolidation are measured in terms of days. Dynamic processes however are usually measured in terms of seconds. Therefore dynamic calculations are always performed in seconds and its output as a function of time can be viewed in what is referred to as “dynamic time”, that is the total time of all dynamic processes in seconds while long term process are discarded from the output plots. The dynamic time is, however, part of the total calculation time.

Dynamic loads
Input data for dynamic loads can be read from a user-defined ASCII file. For earthquake data it is possible to read data records from a SMC-file (Strong motion CD file). A third option is the direct input of harmonic loads.

Output features

Time domain vs frequency domain
In the Curves program the results from a dynamic calculation can be shown in the time domain. With a push on a button it is also possible to represent the same data in the frequency domain, that is as a spectrum with either frequency or wave period on the x-axis.

Animations
In the Output program there is an option to generate a AVI movie of most output options. With this option one can visualise for instance the development of stresses in time or the propagation of waves in the soil body. The AVI movie consists of frames created from all available output steps.

Velocities and accelerations
Additional to the output from a static calculation the velocities and accelerations can be shown. Just like any other output it is possible to view velocities and accelerations for the whole geometry at a fixed time in the Plaxis Output program or view the velocities and accelerations in time for a fixed point with the Plaxis Curves program.

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