Feature Comparison

Feature Mechanical Offshore Windpower More
Nonlinear structural dynamics
Wind turbine

In multibody applications such as wind turbines, dynamic offshore systems, suspension systems, axle systems, car bodies, satellite appendages, industrial manipulators, medical equipment, high-speed mechatronic systems and so on, some of the mechanism components can be flexible and can experience large elastic deflections and coupling effects. To ensure sufficient accuracy, the simulation solver must account for the mutual dependencies between dynamic properties at the system level and structural flexibility at the component level. These requirements can be efficiently satisfied through a nonlinear structural dynamics approach.

In FEDEM, a nonlinear 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 structural Parts, each represented by a linear elastic finite element (FE) model or a simplified stiffness description, and coupled together with linear or nonlinear joints. After a model reduction of each FE part based on a dynamic superelement formulation, the system equations are assembled and solved with respect to FE degrees of freedom (DOFs), allowing large translations and rotation due to a co-rotated theory.

The FEDEM nonlinear structural dynamics and other features represent a unique and essential software package.

Dynamic solver

The FEDEM Dynamics Solver module performs a nonlinear dynamics simulation. This means a simulation of the motion and deformations of the superelements and the joints, as they respond to load and displacement time histories and Control System output.

In any time step of the simulation the model can be linearized whereby an eigenvalue analysis can be performed.

Part deformations and mode shapes are recovered by the Stress Recovery module and Mode Shape Recovery module.

Mode solver

The Mode Shape Recovery module recovers the mode shapes of each part from the Eigenvalue results of the Dynamic Solver.

Stress recovery solver

The FEDEM Stress Recovery module recovers the internal DOFs from the deformations of the external DOFs simulated by the Dynamics Solver. The element stresses, strains and beam forces are then calculated.

FE-model reducer

The FEDEM Reducer performs a superelement reduction of the FE model representing the mass and stiffness of a part. A superelement reduction reduces the required DOF to a minimum. The retained DOFs, also called external DOFs, are the results of a dynamic superelement reduction technique called Component Mode Synthesis reduction, also known as CMS reduction. More information on this topics can be found in FEM textbooks.

Multi-event analysis
Event list

In many analysis projects using FEDEM, the task is to investigate the response on a given structural model, or a set of almost identical models, for a large set of load cases, or events. To facilitate such projects, FEDEM has introduced the concept of Simulation events.

A simulation event is a small permutation of the structural model, where only a few model parameters, (such as a load amplitude, a spring stiffness, a cross section area, etc.) have different values. Each event is then solved and assigned a separate result database, all within the same model. That way it is efficient to continue working on the model without needing to duplicate the input data more than necessary, when setting up the different load cases. The simuation events can both be run individually, one-by-one, or all together in a large batch execution.

Curve plotter
Curve plotter

FEDEM includes a powerful curve plotter that can be used to plot any of the results data in the detailed results database from object positions to forces and moments. The curve plotter includes important tools, such as curve statistics, fourier analysis and differentiation, rainflow and fatigue, and more.

Nonlinear joints
Mechanism elements

FEDEM has a powerful nonlinear joint modelling capabilities, supporting everything from point-to-point joints (e.g. revolute, ball, rigid and free) to more complex joints like prismatic, cylindric, cam, gear and rack-and-pinion joints. Springs and dampers can be used, force and torque can be applied, sensors can be used to measure, and flexible/rigid surfaces can be used to attach triads to nodes on FE-meshes. You can also define your own functions and plug-ins to extend the capabilities.

Beam cross sections

Beam cross sections are used to describe the cross section properties of a beam element.

Beam cross section
Material properties

Materials are used to describe material properties of beam elements (linear isotropic materials only). They are referred to via the Beam cross section objects (described above).

Control system editor

Real mechanisms are often connected to or acted upon by control elements such as sensors, controllers, and actuators. A control system is therefore necessary to simulate these effects for FEDEM mechanisms. FEDEM’s block-diagram presentation of control systems closely resembles that given in most textbooks about basic control theory. The graphical representation consists of a series of connected control blocks, which you can model to simulate your control requirements.

Control system editor
Generic parts
Generic part

Generic parts are useful for fast modeling of simple structure parts where a full mesh will not be necessary. Generic parts are modelled as a "point cloud" of triads that are rigidly joined together.

Beams, shells and solids import

Detail finite element model possible for all components.

At no cost of calculation speed!

  • Beams
  • Shells
  • Solids
User-defined functions

Functions can be used to control the magnitude of loads, the length of springs, prescribed motion in joints, etc.

The input value can be a system variable measured by a sensor, the output of a control system, the output of a different function, or simply the simulation time. The function shape can be defined in several different ways, and uses a common way of defining function shapes across different objects needing to do so. Road elevations, Control inputs, Control outputs, Spring and Damper characteristics are all examples of objects using a similar way of defining function-like relationships.

Time history input data

A special type of function definitions are the Time history input file object. This object behaves essentially as a function of time, but is optimized to be used for input of time history data from any external files.

Virtual strain gauges

FEDEM provides tools to gauge strain anywhere in the model.

Stress contours

FEDEM provides complete and animated visualization of stress contours.

Fatigue contours

FEDEM provides complete and animated visualization of fatigue contours.

Curve fatigue

FEDEM provides tools to easily calculate fatigue on any result curve.

Curve fatigue
Time history export

FEDEM provides support for detailed export of time histories.

Fatigue summary interface

Fatigue summary is another useful tool. You can do a fatigue summary analysis on any graph or set of curves in FEDEM. Just select a graph or set of curves, right click them, and choose "Fatigue Summary..". If you have multiple events in your model, then fatigue summary will be calucated for each event. You can adjust the probability values ("Prob").

Fatigue summary
Beam results diagram

FEDEM provides easy generation of force and moment diagrams along the beam.

Wave-structure interaction

FEDEM provides advanced support for wave-structure interaction.

Wave-structure interaction
Irregular sea states

FEDEM provides support for simulating irregular sea states, such as e.g. JONSWAP, and also supports user-defined wave spectrums.

Current profile

FEDEM provides support for a large range of current functions.

Response amplitude operators

The goal of a vessel Response Amplitude Operator (RAO) is to express the motion of a point on a rigid vessel floating in the sea as a function of the wave height at the same reference point. The concept of a RAOs is associated with the stationary sinusoidal response (or motion) of a linear system due to a stationary sinusoidal load (wave).

Internal fluid in beam elements

FEDEM supports internal fluid calculations on all beam elements.

Marine growth definition

Fixed marine structures in shallow waters are often burdened by extra weight due to marine growth over the years of operation. This added mass contribution may have a significant impact of the dynamic behavior of the structure, when subjected to loads due to wave and/or current.

Soil piles and p-y curves (SSI)
Soil pile

FEDEM provides advanced support for soil-structure interaction.
FEDEM supports finite element models for suction bucket and soil.

Spaceframe import

A spaceframe in FEDEM is an assembly of several Beams which are connected to each other in Triads. An arbitrary number of beams may be connected at each Triad. Thus, it becomes a full FE representation of the structure on the system level. A spaceframe is represented by a Sub-assembly element of the sub-class Jacket in the FEDEM model. A Jacket is a model of a bottom-fixed off-shore structure, which are typically used as foundation for wind turbines and oil exploration platforms. The beam members of a Jacket structure may therefore be assigned properties for hydrodynamic load calculation (added mass and drag coefficients).

Beamstring pair definition

The Beamstring Pair Definition tool is used to generate Free Joints between the triads of a beamstring pair. The primary purpose of this approach is to simulate that the inner pipe hits the outer pipe, and then the inner pipe will bounce back. The Contact stiffness function provides the magnitude of the contact spring that is applied on all joints. The Use radial springs check box indicates whether radial springs are to be used.

Beamstring pair definition
Turbine definition

The Turbine definition dialog box is used to enable easy configuration and creation of wind turbine models. All the fields have predefined default values, so the only thing you need to do in order to generate a valid wind turbine model is to click the "Generate turbine" button.

Turbine definition

FEDEM Windpower uses the AeroDyn software module of the National Renewable Energy Laboratory (NREL) in the USA (http://wind.nrel.gov), for all calculations related to the aerodynamic loads on the wind turbine blades. These loads are then applied onto the structural model of the wind turbine in the FEDEM solvers, to provide response data that can be further analysed.

Blade definition

FEDEM Windpower includes some sample blade designs (e.g., the file "Sample-5MW") within the installation. You can just specify one of these sample blades in the Turbine definition dialog box, if the blades of the turbine are not the main focus area for your simulation. However, most projects will require that the blades are defined in detail for that project. This is performed in the Blade Definition dialog box, shown below.

Blade definition
Airfoil definition

The purpose of the Airfoil Definitions dialog box is to facilitate the creation of a set of airfoils to use in the turbine blade definition. An airfoil is basically a cross section of the blade where different aerodynamic properties (drag and lift coefficients, etc.) are specified around the blade.

FEDEM Windpower uses the AeroDyn airfoil file format of NREL. The Airfoil Dialog box is simply an editor for such files. For information on the airfoil file format, see http://wind.nrel.gov/designcodes/simulators/aerodyn.

The airfoil files are referred to when designing the blades, in the Blade definition dialog box, and when the completed turbine model is being solved, the airfoil files will be read by AeroDyn (via the dynamics solver) to calculate the wind loads.

The Airfoil Definition dialog box is show below:

Airfoil definition
3D turbulent wind

The FEDEM TurbWind tool is used to generate turbulent wind files for the Air environment dialog box in FEDEM Windpower.

FEDEM TurbWind is basically a dialog box front-end for the TurbSim tool by NREL (http://wind.nrel.gov). FEDEM Windpower sends the parameters of the wind turbine to FEDEM TurbWind, such as for example hub height, grid height, time step, duration, output folder, ref. height, etc. You should adjust these fields to match your wind turbine and conditions.

The figure below illustrates FEDEM 3D Turbulent Wind tool:

3D turbulent wind
SESAM integration

FEDEM provides integration features for DNV SESAM.

For a more detailed study of the FEDEM features and capabilities, please have a look at the application examples.