A recursive coupling-decoupling approach to improve experimental frequency based substructuring results

Substructure decoupling techniques allow identifying the dynamic behavior of a substructure starting from the dynamic behavior or the assembled system and a residual subsystem. Standard approaches rely on the knowledge of all FRFs at the interface DOFs between the two substructures. However, as these typically include also rotational DOFs which are extremely difficult and most of the time impossible to measure, several techniques have been investigated to overcome these limitations. A very attractive solution consists in defining mixed or pseudo interfaces, that allow to substitute unmeasurable coupling DOFs with internal DOFs on the residual substructure. Additionally, smoothing/denoising techniques have been proposed to reduce the detrimental effect of FRF noise and inconsistencies on the decoupling results. Starting from these results, some recent analysis on the possibility of combining coupling and decoupling FBS to validate the results and compensate for inconsistencies will be presented in this paper. The proposed method relies on errors introduced in the substructuring process when assuming that the interface behaves rigidly, while it is generally known that this assumption is seldom verified. Consequently, a recursive coupling-decoupling approach will be used to improve the estimation of the dynamic response of either the residual structure (for decoupling) or the assembly (for coupling). The method, validated on analytical data, will be here analyzed on a numerical example inspired by an experimental campaign used to validate the finite element models and on which standard substructuring techniques showed some limitations. The results discussed in this paper will be then used as guidelines to apply the proposed methodologies on experimental data in the future

Structural validation of a realistic wing structure: the RIBES test article

Several experimental test cases are available in literature to study and validate fluid structure interaction methods. They, however, focus the attention mainly on replicating typical cruising aerodynamic conditions forcing the adoption of fully steel made models able to operate with the high loads generated in high speed facilities. This translates in a complete loss of similitude with typical realistic aeronautical wing structures configurations. To reverse this trend, and to better study the aerolastic mechanism from a structural point of view, an aeroelastic measurement campaign was carried within the EU RIBES project. A half wing model for wind tunnel tests was designed and manufactured replicating a typical metallic wing box structure, producing a database of loads, pressure, stress and deformation measurements. In this paper the design, manufacturing and validation activities performed within the RIBES project are described, with a focus on the structural behavior of the test article. All experimental data and numerical models are made freely available to the scientific community

DATA DRIVEN AND MODEL-BASED VERTICAL SLOSHING REDUCED ORDER MODELS FOR AEROELASTIC ANALYSIS

A thorough understanding of the effects of sloshing on aircraft dynamic loads can be exploited for the future design of aircraft to be able to reduce their structural mass. Indeed, the high vertical accelerations caused by the vibrations of the structure can lead to the fragmentation of the fuel free surface. Fluid impacts on the tank roof are potentially a new source of damping for the structure that have hardly been considered before when computing the dynamic loads of the wings. This work aims at applying recently developed reduced-order models for vertical sloshing to a representative aeroelastic testbed, to investigate their effects on the wing’s response under pre-critical and post-critical conditions. The vertical sloshing dynamics is considered comparing three different reduced order models based, respectively, on neural networks, equivalent mechanical model, and surrogate model then integrated into the aeroelastic syste

Thioredoxin 80-Activated-Monocytes (TAMs) Inhibit the Replication of Intracellular Pathogens

BACKGROUND: Thioredoxin 80 (Trx80) is an 80 amino acid natural cleavage product of Trx, produced primarily by monocytes. Trx80 induces differentiation of human monocytes into a novel cell type, named Trx80-activated-monocytes (TAMs). PRINCIPAL FINDINGS: In this investigation we present evidence for a role of TAMs in the control of intracellular bacterial infections. As model pathogens we have chosen Listeria monocytogenes and Brucella abortus which replicate in the cytosol and the endoplasmic reticulum respectively. Our data indicate that TAMs efficiently inhibit intracellular growth of both L. monocytogenes and B. abortus. Further analysis shows that Trx80 activation prevents the escape of GFP-tagged L. monocytogenes into the cytosol, and induces accumulation of the bacteria within the lysosomes. Inhibition of the lysosomal activity by chloroquine treatment resulted in higher replication of bacteria in TAMs compared to that observed in control cells 24 h post-infection, indicating that TAMs kill bacteria by preventing their escape from the endosomal compartments, which progress into a highly degradative phagolysosome. SIGNIFICANCE: Our results show that Trx80 potentiates the bactericidal activities of professional phagocytes, and contributes to the first line of defense against intracellular bacteria

Associazione Italiana di Aeronautica e Astronautica

L'associazione Italiana di Aeronautica e Astronautica promuove lo studio delle materie di interesse aero-spaziali attraverso l'attribuzione di un premio per la miglior tesi di Laurea

INVESTIGATION ON SMART SENSORS TO PREDICT FLUTTER AND AEROLASTIC RESPONSE

This research is devoted to the identification of non-linear aeroelastic systems in real time. The proposed studies will be related to develop new sensory techniques to identify aeroelastic modes and unsteady aerodynamics in fixed and rotary wings. These studies are important because the interaction of the vibration natural modes of the aircraft structure with the unsteady aerodynamic loading may become unstable under certain flight conditions, leading to the flutter phenomenon. Moreover, in a less severe scenario, these loads generate high levels of aircraft forced vibration that cause passenger discomfort and lead to structural fatigue and even failure. All these studies, although ultimately directed to helicopter blades, will be initially conducted with fixed-wing configurations, and will include both numerical simulations and experimental work conducted in still air and wind tunnel. From the project originality point-of-view, it is well known that the main line of research on aeroelasticity today is associated with non-linear phenomena. In the low speed range, the non-linearity is often associated with the structure alone (free play of control surfaces in most cases). However, in the high-speed transonic regime, non-linearities are also generated from the aerodynamics unsteadiness, and these are normally associated with localized shocks on supercritical airfoil configurations. There is no efficient method that can be used in the industry today to deal analytically with non-linear phenomena. The development of reliable and computationally efficient analytical methods is of fundamental importance for the industry. However, this development can only be done with the existence of carefully controlled wind tunnel tests to serve as a source of comparison data. As wind tunnel tests are very expensive, reliable experimental data must be acquired in the shortest period of time. The objective of this research is, therefore, to develop new sensory techniques based on smart materials to maximize the efficiency of wind tunnel tests to produce accurate data pertinent to aeroelasticity. In fact, Carleton University is engaged to pursue with several international partners a collaborative project on an experimental investigation to determine the aeroelastic flutter and forced vibration characteristics of a model of a typical commuter aircraft configuration using the National Research Council Canada (NRCC) Institute for Aerospace Research 5-foot square test section of their blow-down wind tunnel facility. The main investigation will be performed in the high-speed transonic regime where non-linear aerodynamic behavior occurs. Notwithstanding the panned NRCC tests, this research will be complemented with low-speed wind tunnel tests on a full-aircraft configuration to be carried out by partners at CTA (Centro Tecnico Aeroespacial) in Brazil to investigate the effect of structural non-linearities on flutter characteristics. This collaborative project is seen of strategic interest in terms of advancing the general knowledge as well as the partners' expertise in a research area that is of great and timely interest for the aerospace industry. It is further proposed that "La Sapienza" becomes a partner in this international research effort. One of the proposed wind tunnel models is a reflection plane wing-body model where a fairing allows a smooth transition between the wing and the fuselage. The model includes a swept-tapered wing, which supports a nacelle and a jet engine modeled as a hollow cylinder. Under terms of this collaboration, the wind tunnel model will be designed and fabricated at Carleton University. The model will be tested for flutter in the NRCC blow-down wind tunnel in the transonic regime for different pitch angles, Reynolds and Mach numbers. A mass damper ("flutter stopper") will be incorporated inside the wing structure to prevent flutter bifurcation and model accidental destruction. This is usually achieved using a mechanical device that is traditionally a small weight that is suddenly moved inside the structure by the release of a spring. The change in the wing mass distribution provided by the device stabilizes the onset of flutter. The wing structure deformation is traditionally measured using two mini-accelerometers mounted near the wing tip in the chord-wise direction. The accelerometers pick up the bending and torsion deformations of the wing, as the sum and difference of the individual signals. However, accelerometers are localized sensors that do not bring enough information to a generalized structural phenomenon such as flutter and aeroelastic response. Hence, piezoelectric fiber (Active Fiber Composite - AFC) sensors will be suitably embedded in the wing to measure its generalized modal deformations as well. This will be one of the main and novel aspects of this research project. These embedded geometric sensors are expected to allow for the first time a better determination of the flutter characteristics, as (distributed) modal sensors can identify the aeroelastic phenomena much more precisely in terms of the "modal participation". This work will be an extension of the studies on AFC-related geometric modal sensors developed in a present collaboration involving EMPA, ETH in Switzerland and Carleton University. It is suggested that Prof. Nitzsche and Prof. Coppotelli will join research efforts during Prof. Nitzsche's proposed tenure at "La Sapienza" to perform feasibility studies aiming to develop advanced smart sensors using AFC-related techniques for aeroelastic modal identification in the transonic regime for immediate application in the programmed wind tunnel tests, including the feasibility of measuring unsteady aerodynamic loads at certain wing cross-sections. In summary, the objective of the planned research is the development of analytical techniques to identify fundamental aspects of aeroelastic phenomena from AFC-generated signals. In this context, advanced studies, performed at "La Sapienza", on the identification of dynamic systems vibrating in the actual operating conditions represent an excellent starting point for the proposed project. This research is seen of great value for the organizations involved, not only for its novelty that will surely allow the publication of a number of joint papers, but also for its special and timely relevance in face of the planned wind tunnel tests, the potential industrial applications, and the basis of a established long-term collaboration