sonar Insight

Over the last thirty years many scientific reports, assessments and comparisons have been published on the different simulation methods of rigid body systems. Also on the advantages and disadvantages of the individual methods with regard to certain phenomena such as contact detection, contact control, friction, damping, multiple contacts, number of objects, object geometry, computational performance, computational accuracy, time step, etc. were held in-depth discussions. The approach used in the sonar Software is uncompromising, comprehensive, and handles all aspects of object-to-object contact in great detail and in a realistic manner. At the center of sonar are the following features:

With the given approach, sonar is currently one of the most advanced simulation programs in the world.  And it goes on …

• Sonar is mathematically a purely explicit code.

• Sonar is ultimately a combination of a multi-body dynamics simulation program with a finite element program.

• Sonar is an approach with rigid bodies that interact elastically with each other and can be elastically connected.

• All contacts in a system of objects are resolved bilaterally and independently during an ongoing simulation. This approach allows for parallel processing of contact calculations within the same computing cycle and high computational power on multicore computers. sonar supports the so-called OpenMP standard.

• Each object can have any number of contacts with one or several other objects at the same time.

• Each contact between two objects is solved with a local and temporary multi-dimensional spring damping system. The time step of the entire calculation system is automatically chosen so small at any time that all currently occurring collision contacts are resolved in at least 100 computing cycles within the contact time frame and thus all contact operations are virtually continuous.

• So sonar’s calculation system mimics real collision contact between two objects. In the case of real objects, the surface of the objects in the contact area is elastically deformed (pressed flat) during a collision process. This is accompanied by an increasing reaction force between the two objects until the impact has reached its maximum penetration depth. Subsequently, the two objects separate again until the force reaches zero and the objects move again without contact. Sonar works the same way, except that the actual deformation of the surface in the contact region is replaced by a mathematical impact model.

• Static contacts work with this model as well.

• When calculating the current time step for a given cycle, the system considers not only the outer dimensions, masses and relative velocities of the objects, but also the surface hardness of the individual objects, which the user specifies in a material-dialog. During the entire interaction time between two objects, energy absorption, damping and friction are considered effects of the vertical and tangential impact vector and relative velocity components. These values and the contact points are continuously calculated and taken into account.

• The elastic connections between the objects are bound to material models that control the elastic-plastic behavior and the fracture behavior.

• All forces and moment of forces on an object are integrated in each calculation cycle with the elementary Newton equations of motion to translatory- or angle-accelerations and velocity- and position-changes. Sonar is based on a force-acceleration model (action = reaction) and works on the most elementary level of cause and effect.

• Sonar theoretically simulates an infinite number of arbitrarily shaped three-dimensional convex and concave objects. The limits of complexity are limited practically only by the current performance of the computers used. As a representative example, reference is made to the simulation “Rockfall Barrier” on http://www.sonarsimulation.com, which comprises about 60,000 objects and was calculated on a normal workstation.

• In sonar the user builds graphically interactively or with the help of dialogues and functions complex objects by addition of primitive bodies which are connected to each other elastically. The construction of complex bodies from primitive bodies works quite similar to the so-called CSG (Constructive Solid Geometry) method in the CAD world.

• In the same way complex structures and primitive bodies can be broken down into a large number of ‘inner’ primitive bodies by introducing inner grid structures, which ultimately simulate the elastic-plastic behavior of the original object.

• The term ‘primitive body’ is a bit broader in sonar than is understood in a CAD system. In sonar exist (as of 2018) 18 primitive bodies. In this sense, sonar also includes, among others, any extruded bodies, bodies of revolution of any cross-sectional shape and free-form surfaces.

• At the heart of the sonar system is a calculation kernel that calculates all possible collision pairings between primitive bodies. With the current number of 18 primitive bodies this results in a total of 171 possible pairings. The calculation kernel continuously calculates the corresponding spatial impact vectors and the exact characteristics of each impact for every pairing and every possible spatial position and type of encounter, object size, etc.

• In sonar, any number of submodels can be combined into more complex models. Frequently used assemblies can thus be managed in a parts library.

• Sonar has its own simulation language (sonar script). Sonar script is used in the sonar environment as a macro and control system language. With the macro language, complete and sophisticated models, e.g. the above-mentioned model “Rockfall Barrier” are stored in pure text form and created at the touch of a button. The macro definition includes the geometry, the physical properties and all boundary conditions. In general macro generated models are ready for simulation.

• Models defined in the macro language can often be changed faster and more conveniently and adapted to new conditions than is possible with manual changes on the screen.

• If the language ‘sonar script’ is used as a control system language, then sonar can be used to simulate virtual machines with associated virtual controls. In such a control, each state variable (geometry, physics) of each object can be queried and set continuously.

• The simulation language ‘sonar script’ opens the doors to the topic ‘autonomous optimization of mechanisms’. In future, the user sets certain goals and subsequently the sonar system is able to perform iterative simulation series by incrementally modifying the underlying model with ‘sonar script’ and performing certain optimizations on the mechanism by comparing specific result values.