Center for Light and Environmentally-Friendly Structures ZELUBA®

Research topic

Numerical Simulation

In research and development, numerical simulation is a very popular tool in all situations in which the practical experimental outlay is too high or no analytical solutions are known for the specific problem. Validated simulation models enable a minimization of the practical experimental outlay and can represent difficult or non-measurable phenomena with reasonable outlay. In addition, numerical simulation not only enables parameter studies to be carried out quickly and automatically under varying boundary conditions but also facilitates the application of optimization algorithms.

 

© Fraunhofer WKI | Pablo Guindos

Mechanical testing of the load-bearing behavior of plywood flooring – real test (right) and numerical model (left)

© Fraunhofer WKI | Pablo Guindos

Hygrothermally induced tension in parquet, which cannot be determined metrologically with reasonable outlay. Here: validation by means of the actually occurring effects: deformations and crack formation

© Fraunhofer WKI | Pablo Guindos

Validation of an individual parameter (here: heat release rate) by means of an experiment in the Cone calorimeter

At the Fraunhofer WKI, we use numerical simulations for analyses at the material, component and system level. In addition to mechanical models, the spectrum of our fields of application thereby also includes the calculation of moisture and thermal transport processes as well as fluid-mechanical examinations. A further core competence lies in the coupling of physical problems, which provides us with a holistic view of complex issues. Due to the interdisciplinary fields of application, the ZELUBA® simulation team works closely with the other specialist departments of the Institute.

The demands placed upon the simulation software differ widely depending on the problem and the application purpose. We have access to a variety of programs which we deploy in accordance with the individual case. For the verification of the plausibility of simulations and to compare them with reality, the results are always validated through real experiments. For this, we have access to diverse testing facilities and measuring techniques in the Technology for Wood and Natural Fiber-Based Materials department. These include, amongst other things, optical measuring techniques.
 

Mechanics

We perform mechanical analyses by means of finite element simulations. These include, for example, investigations into strength, serviceability or vibration behavior in the case of an earthquake. For the calculation of hybrid structures, we have a wide diversity of material models - including non-linear and anisotropic material behavior. We can thereby take into account the fiber orientation in wood and fiber-reinforced materials as well as deformations of a non-elastic nature. Crack propagation and the mechanical behavior of glued joints are modeled using the cohesive-zone method, whilst load-dependent and moisture-dependent creep processes are simulated with the aid of viscoelastic and mechanosorptive formulations.
 

Coupled multi-field simulation

The behavior of wood and wood-based materials is largely dependent on climatic conditions. A variable air humidity, for example, can lead to swelling and shrinkage processes within a joint. In turn, the changing joint geometry influences the moisture and temperature distribution. Through the coupling of physical parameters in COMSOL Multiphysics, we are able to depict such interactions with a reasonable outlay. The consideration of fluid-mechanical problems is also possible. Furthermore, we can expand our multi-field models through user-defined formulations on a needs-oriented basis.
 

Heat and moisture transport

With the program WUFI, we simulate heat and moisture transport processes for the moisture-related evaluation of wall systems. For the calculation of thermal bridges in floor plans, we again use the software WinIso 2D. We also apply WUFI in the performance of investigations into indoor climate and the comfort assessments based thereon. Predictions of mold risk are also possible by means of biohygrothermal models. In order to evaluate the influence of climate change on building facades, we utilize data sets from climate research as input parameters.

Result of a simulation: temperature and charred area of a piece of paper

The simulation shows hygrothermally induced tensions in parquet, which cannot be determined metrologically with reasonable outlay. In this example, the validation was performed by means of the actually occurring effects – in this case specifically deformations and crack formation