Fedem - Multi Body Dynamics Simulation with Flexible Bodies
Fedem Simulation software is a multibody dynamics package based on the Finite Element Method. It uses FE-models as flexible parts natively and because of an excellent reduction technique, the dynamics solution is approximately as fast as a rigid body solution. Fedem can thus handle simulations of long time series of large FE-assemblies at the speed of normal multibody systems. This, together with our virtual strain gauges, makes Fedem ideal for Fatigue assessments. Fedem can also be used as a conventional MBS package without utilizing the FE capabilities. In that mode Fedem also introduces flexibility for each part that can be tuned and used for studying the effect of flexibility in a particular assembly. Embedded is a Control Systems editor and solver which makes it easy to create complex events and model other subsystems, such as hydraulics and actuators.
Non Linear Structural Dynamics
In Fedem, a non-linear structural dynamics approach is utilized in order to simultaneously solve structural deformations and 3D motion dynamics in the time domain. The mechanical assembly to be simulated is comprised of parts, each represented by a linear elastic finite element model and coupled together with linear or non-linear joints. After a DOF reduction of each part based on a dynamic superelement formulation, the system equations are assembled and solved with respect to finite element degrees of freedom. Fedem utilizes its own element formulations and its proprietary solver to perform the model solution.
This approach provides several advantages over conventional methods:
- Mutual dependencies between structural and dynamic properties are always automatically accounted for.
- The time domain solver is highly numerically stable since strain energy is implicitly represented in the equation system.
- A single stage integrated process replaces a conventional two stage process.
The Fedem approach is practical for the engineer - its logic emulates real life..
Integrated and efficient workflow
The process of modeling and evaluating dynamic and structural properties of a mechanical assembly is highly integrated. When a proposed design is to be verified and a finite element model of each individual part in the assembly has been produced, the engineer has to follow these logical steps:
- Create the model. Build the mechanical assembly by importing each finite element model, positioning the parts relative to each other, adding joints, springs, dampers, forces, control systems, etc. and specifying mechanism drive functions.
- Dynamic Simulation. Define and run the dynamic time domain simulation. Fedem automatically reduces each finite element model to a superelement prior to running the time domain solver. Reduced models can be re-used both for other dynamic events and Fedem models.
- Visualize Results. Post-process and assess results. Dynamic results are readily available from the time domain solver. Structural results are obtained by an integrated superelement recovery process.
Efficient user interface
Structural results are obtained subsequent to the time domain simulation through an integrated superelement recovery process. A complete set of strain and stress components can be recovered for all elements and time increments. However, recovery can also be performed individually on parts or even on pre-defined element groups for selected time increments. Time history summaries, such as max/min stress, are also provided.
Complete library of mechanism entities
A comprehensive set of mechanism entities ensures physically realistic modeling. Entities include a complete joint library - optionally with non-linear spring, damper and friction characteristics, discrete springs and dampers, functions - optionally with references to external data files, forces and control systems, etc. All entities have a 3D graphical representation and all properties are accessible through user interface components.
Embedded Control Systems
To ensure accurate simulation of the interaction between structural dynamics and control systems, a co-simulation technique is applied. The internal control system contains a library of compensators and elementary control blocks. This enables basic modeling of supplementary mechanism units such as hydraulic cylinders, actuators and electrical drives, and control loops.
