Explicit dynamic formulation to demonstrate compliance against quasi-static aircraft seat certification loads (CS25.561) – Part I: influence of time and mass scaling

Abstract

A finite element model of an aircraft seat subjected to static certification loads (Certification Specifications CS25.561) involves material, geometric and contact non-linearities. Implicit algorithms can model the physics of such problems appropriately but suffer from shortcomings such as significant finite element modelling efforts, high disk space and memory requirements and unconverged solutions. Explicit finite element schemes offer a more robust alternative for convergence for quasi-static loadcases but may come at an even higher computational cost as smaller solution time steps are required, in addition to unwanted inertial effects. A methodology to apply an explicit formulation for simulating static certification loading for an aircraft seat-structure is presented and validated in this article. The first part reviews the design novelties of the triple seat-structure considered, the safety regulations used in aircraft seat certification. The key theoretical aspects of an explicit solver are presented, together with the numerical challenges faced when applied to solving quasi-static problems. Time scaling, mass scaling and damping are common approaches to assist in artificially reducing the computational time but previous articles provide little insight into how to apply these techniques correctly and the level of checking that is required to ensure the quality of the results are unaffected by these modifications. The main focus of this article is to clearly define the procedure to establish appropriate factors for mass scaling, time scaling and damping. Quality checks, such as ratio of kinetic energy to internal energy and their time-histories have been investigated to ensure a quasi-static solution. finite element analysis results are validated against experimental testing for the 8.6 g downward loadcase. Parameters such as kinematic behaviour and deflections at key locations been used for comparison. An acceptable level of correlation between finite element analysis results and physical tests validates the proposed methodology, which will be extended in a future article (Part II) to consider additional contact complexities with the inclusion of body blocks.

Analysis of Crashworthiness of Bishoftu Pickup Vehicle Structure during Side Pole Crash

“…As demonstrated in Figure 18, the energy ratio value ranges between 1 and 0.99975 for the 0.16 s simulation. Since the energy ratio result is within the range of 1.00 ± 0.07 [18], it is acceptable. Te given value is so appropriate.…”

“…Without doing an experimental investigation, the verifcation method has the potential to check whether the results produced from computer simulations are adequate. Verifcation is possible in the case of LS-DYNA simulation [14,18]. Te most typical and sensible approaches are as follows:…”

Analysis of Three-Wheeler Vehicle Structure at the Event of Side Pole Crash

“…With the absence of experimental data, the appropriateness of the values obtained on computer simulations can be cheeked by the verification process. In the case of LS-DYNA simulation, verification can be made [23]. e most common and logical ways are listed as follows: e maximum deformation for the existing model and modified model is equal to 345 mm and 286 mm, respectively.…”

“…As can be seen in Figure 22, for the 0.1 s simulation, the energy ratio value varies between 1.048 and 1.0466. Since the energy ratio value is acceptable if it is in the range of 1.00 ± 0.07 [23], the indicated value is acceptable.…”

“…If the hourglass energy is less than 5% of the total energy, the finite element model is reliable [23]. As we can see from Figure 23, the hourglass curve is much lower than that of total energy, or in other words the ratio is less than 5%.…”