Olivier Dorival

A substructured version of the variational theory of complex rays dedicated to the calculation of assemblies with dissipative joints in the medium-frequency range

Purpose – This paper deals with numerical techniques dedicated to the predictive calculation of complex structures undergoing medium‐frequency vibrations. This field presents challenging difficulties. The first difficulty is the development of an efficient computational method because with the traditional finite element method (FEM), as the frequency increases, it becomes more expensive to control the pollution error. The second difficulty is the availability of sufficiently realistic joint models to take into account damping phenomena because in vibration problems dissipation controls the magnitude of the response directly.Design/methodology/approach – We use the Variational Theory of Complex Rays (VTCR), an approach which effectively avoids the difficulties encountered with traditional FE techniques. Using two‐scale shape functions which verify the dynamic equation and the constitutive relation within each substructure, the VTCR can be viewed as a means of expressing the power balance at the different i...

Influence of the aircraft crash induced local nonlinearities on the overall dynamic response of a RC structure through a parametric study

In the process of nuclear power plant design, the safety of structures is an important aspect. Civil engineering structures have to resist the accelerations induced by, for example, seismic loads or shaking loads resulting from the aircraft impact. This is even more important for the in-structures equipments that have also to be qualified against the vibrations generated by this kind of hazards. In the case of aircraft crash, as a large variety of scenarios has to be envisaged, it is necessary to use methods that are less CPU-time consuming and that consider appropriately the nonlinearities. The analysis presented in this paper deals with the problem of the characterization of nonlinearities (damaged area, transmitted force) in the response of a structure subjected to an aircraft impact. The purpose of our study is part of the development of a new decoupled nonlinear and elastic way for calculating the shaking of structures following an aircraft impact which could be very numerically costly if studied with classical finite element methods. The aim is to identify which parameters control the dimensions of the nonlinear zone and so will have a direct impact on the induced vibrations. In a design context, several load cases (and simulations) are analyzed in order to consider a wide range of impact (different loading surfaces, momentum) and data sets of the target (thickness, reinforcements). In this work, the nonlinear area generated by the impact is localized and studied through a para-metric analysis associated with an sensitivity analysis to identify the boundaries between the elastic domain and this nonlinear area.

A new methodology for assessing the global dynamic response of large shell structures under impact loading

Purpose – The determination of the vibration induced by an aircraft impact on an industrial structure requires dynamic studies. The determination of the response by using classical finite element method associated with explicit numerical schemes requires significant calculation time, especially during the transient stage. This kind of calculation requires several load cases to be analyzed in order to consider a wide range of scenarios. Moreover, a large frequency range has to be appropriately considered and therefore the mesh has to be very fine, resulting in a refined time discretization. The purpose of this paper is to develop new ways for calculating the shaking of reinforced concrete structures following a commercial aircraft impact (see Figure 1). The cutoff frequency for this type of loading is typically within the 50-100 Hz range, which would be referred to as the medium-frequency range. Design/methodology/approach – Taking into account this type of problem and assuming that the structure is approp...

A method for updating joint parameters in medium-frequency vibrations

Joints between substructures play a significant role in the vibrational behavior of complex structures because they govern energy flow and most of the dissipative phenomena. In order to identify joint models, this paper proposes a robust updating method which was initially based on studies of the error in constitutive relation in relation to finite element model updating. Here, it is redesigned in order to focus on joint models in medium-frequency problems. In order to do that, we use an alternative numerical approach called the Variational Theory of Complex Rays (VTCR). After introducing the new formulation, the paper analyzes the effectiveness of the approach in identifying a joint’s stiffness and damping.

Experimental results of medium velocity impact tests for reinforced foam core braided composite structures

Absorbing impact energy at subsystem level is an attractive idea that is emphasized by new composite reinforcement techniques such as stitching or pinning. This paper reports experimental results of medium velocity impact tests carried out on several arrangements of reinforced foam/braided composite structures. The tests consisted of a steel ball shot at a velocity of 110 m/s from a gas gun impacting the structures on their leading edge. Post-mortem tomography analysis delivered very rich information which shed light on the damage mechanisms that the composite structures underwent. In addition, two fast-speed cameras were used to derive the energy absorption during the impact. Absorption capabilities were also compared with those of dynamic crushing tests (reported in a companion paper) and some designs clearly exhibited promising behavior as shock absorbers.

Application Of The Variational Theory Of Complex Rays To The Determination Of Shock Induced Vibration Of A Rc Structure

Security and safety are crucial aspects in the design of nuclear engineering structures. Civil engineering design and the qualification of materials to dynamic loads must consider the accelerations which they undergo. These accelerations could integrate not only seismic activity but also shaking movements consecutive to aircraft impacts with higher cutoff frequency. Current methodologies for handling such a shock in the calculation stage are based on transient analyzes using classical finite element methods associated with explicit numerical schemes or projection on modal basis. In both cases, to represent in a meaningful way a medium frequency content, a fine mesh is required, which is hardly compatible with the size of models of the civil engineering structures. In order to extend the current industrial methodologies and to allow a better representation of the behavior of the structure in the medium frequency range, an approach coupling a temporal and non-linear analysis of the impact area with a frequency approach for the treatment of the resulting shaking with the Variational Theory of Complex Rays (VTCR) has been developed [1]. The aim is to use the computational efficiency of the implemented strategy and to include the medium frequency range to calculate the nuclear structures response to an aircraft impact. 1 INTRODUCTION For nearly three years in the framework of pre-normative research in nuclear construction (RENON), the constructability research institute (IRC) focused some of its efforts on improving the characterization of floor response spectra in the case of aircraft impacts. The study of airplane crash in the design and verification of nuclear engineering structures has two important and distinct aspects: (i) the resistance of the structure subjected to an impact, loading, and (ii) the qualification of inner equipments to the vibrations induced. The calculation of the resistance of the structure and its design do not generally raise problem with current methods, however, the calculation of induced vibrations, although few harmful to inner equipments, requires special attention, especially with the lack of efficiency of current approaches. Indeed the calculation of floor response spectra (FRS) in this case generally exhibits a set of high magnitude accelerations within a frequency range that is generally much higher than the one observed when calculating the FRS due to an earthquake. The

Variability of a Bolted Assembly Through an Experimental Modal Analysis

Industrial structures are mainly assemblies with complex geometries and non-linear characteristics. Friction and joint preload added to fabrication imperfections lead to a substantial gap between numerical models and real structures. In order to develop accurate generic models, it is then necessary to quantify the behavior variability, especially the one related to the joint conditions. The first part of this paper describes the iterative sizing procedure of an academic assembly which characteristics may vary depending on several input variables (e.g. value of the bolt torque, number and position of preloaded bolts, etc.). The properties of the bolted joint were optimized in order to satisfy a set of conditions in terms of tangential slipping, normal displacement and maximum stress level. The second part concerns the experimental modal analysis of the assembly. The main purpose is to characterize the relationship that exists between the input variables and the measured eigenfrequencies and modal damping of the assembly.