For aircraft system certification a massive amount of testing is required to guarantee safe, robust, and error-free behavior under all operating and environmental conditions.
Typically these tests on a system level are performed on physical test benches where all the relevant components including actuators, sensors, and control computer are integrated.
Due to the conflicting trends of increasing complexity of systems and drastically reduced development times, virtual testing has become one of the solutions to overcome this challenge.
For the high-lift system, multibody simulation is the preferred approach for virtual testing. Since 2002, the high-lift test department at Airbus has developed experience on this topic within R&D projects in collaboration with the Hamburg University of Technology and with partners within the EU project VIVACE Consortium.
Virtual testing activities have been expanded and become more and more established in the meantime, e.g., by using it for risk mitigation purposes or in contributing to system certification.
The approach is based on the strong coupling of physical and virtual test to obtain the highest possible confidence in the simulation results. Starting with a model variant that represents the physical test bench in all relevant details (e.g., external load application), the model will be validated using results from the test bench and then finally extended to a very aircraft-like variant.
Main differences between test bench-like models and aircraft-like models are the application of airloads (discrete load cylinders vs. distributed pressure loads), the interface conditions (attaching the high-lift system to a rigid test bench vs. a flexible wing) and the consideration of load-dependent wing deformation (test bench without deformation vs. application of wing bending and twist according to load case under consideration).
Significant benefit can be achieved using this integrated approach in terms of time and cost reduction together with increasing quality of results.
Modeling is performed according to a detailed modeling process, starting with creation of a block-wise conceptual model. It is used to identify the system’s bodies and its interfaces, i.e., the types of connecting joints. A decision is made on which bodies can be modeled as rigid and which have to be modeled as flexible bodies.
After validation of the conceptual model, a computerized model is set up within MSC Software’s SimXpert and Adams.
Therefore, information from different domains and departments has to be merged.
For performance and archiving reasons, simulations are conducted by using ADAMS Solver in interactive mode; therefore, the model to be simulated and the applied loads and motions are translated to a solver input deck (.adm file) and then executed by a corresponding .acf file.
In general, model validation is performed by comparing time series data or scalar values of computer simulations to corresponding reference data coming from physical test results, respectively other (already validated) simulations, e.g., CAD results (kinematics), FEM calculations (statics), and measurement data (statics and dynamics). Based on the reference data and admissible deviations, a tolerance band for acceptable simulation results is generated. Measurement uncertainties are taken into account (if applicable) by reducing the tolerance band to a guaranteed validation band.
Test accuracy also increases the band for a possible validation; therefore, simulation results leaving the guaranteed validation band don’t automatically lead to a rejected validation but to further investigations.
The use of simulation for aircraft system certification is not just related to build simulation models with sufficient accuracy and quality. Furthermore, regulations from airworthiness authorities also request a well-defined and robust process for the complete data chain involved in the certification.
Currently used requirements-based engineering is the formal way of developing new aircraft and their systems. Within test departments this has led to a requirements-based testing process.
All required functions and properties of the system in terms of performance, safety, etc. are specified verbally within single requirements managed by a database system based on IBM Rational Doors.
Using a Test Management System (TMS) the formal verification of each of the requirements is assigned to one or more of the existing test tools. Each test tool has a local process and data management environment. After test execution, the TMS collects all the test results from the local platforms and generates automatically the required test analysis reports and finally the certification documentation (coverage report).
For successful implementation of virtual testing in the existing test process, a solution was developed based on MSC SimManager.
One of the most important and critical aspects was the correct capturing of the virtual test process itself and its interface with the TMS.
A detailed specification capturing all objects, process steps, and related attributes was established and refined during setup of the portal.
Besides the virtual test process, the modeling process is also driven by the virtual test portal. The process is captured and implemented by execution of scripts (e.g., SimXpert templates) or interactive pre-processor sessions triggered by the portal. Besides configuration control in the sense of answering the question which model was used to generate a certain simulation result, this enables the ability to capture which input data and processes were used to generate the used model.
To increase simulation performance, i.e., to enable sensitivity analysis, variations of tests or design of experiment studies, simulation multi-runs, and corresponding script based post processing launched by the portal are possible.
This article is based on SAE International tech paper 2011-01-2754 by Tobias Ulmer of Airbus, published at the SAE 2011 AeroTech Congress & Exhibition.