Refined Theories for the Dynamic Analysis of Sandwich Structures

The objective of this study is to give an overview of existing theories for analyzing the behavior of sandwich beams and plates and to develop an approach for evaluating their behavior under dynamic loading. The dispersion relations for harmonic wave propagation through sandwich structures are shown to be a sound basis for evaluating whether the individual layers are modeled properly. The results provide a guide in the selection of existing models or the development of new models.

A Component-Wise Approach for the Failure of Complex Aeronautical Structures

Using advanced beam models based on the Carrera Unified Formulation, this paper presents an analysis of a damaged tapered aircraft structure. Results obtained from static and free vibration analyses are presented to evaluate the evolution of the stress and the modal behaviour in a multi-component damaged structure. This 1-D model is able to modify the material proprieties, then the stiffness, at the local level. In this way, many types of local and global damage can be introduced into the structure. The results show the capability of the present model to obtain with a low computational cost, displacements, stresses and vibration characteristics of damaged structures making him a good candidate for design and maintenance tools.

Rarefied Gas Flow Analysis of a Suborbital Shuttle With the Academic CFD Code Galatea

During the past decade considerable efforts have been exerted for the simulation of rarefied gas flows in a wide range of applications, like the flow over suborbital vehicles, in microelectromechanical systems, etc. Such flows appear to be significantly different from those at the continuum regime, making the Navier-Stokes equations to fail without further amendment. In this study an in-house academic CFD solver, named Galatea, is modified appropriately to account for rarefied gases. The no-slip condition on solid walls is no longer valid, hence, velocity slip and temperature jump boundary conditions are applied instead. Additionally, a second-order accurate slip model has been incorporated, namely, this of Beskok and Karniadakis, increasing the accuracy in the same area but avoiding simultaneously the numerical difficulties, entailed by the computation of the second derivative of slip velocity when complex geometries and unstructured grids are coupled. The proposed solver is validated against rarefied laminar flow over a suborbital shuttle, designed by the Azim’UTBM team. The obtained results are compared with those extracted with the parallel open-source kernel SPARTA, which is based on the DSMC method. A satisfactory agreement is reported between the two methodologies, demonstrating the potential of the modified solver to simulate effectively such flows.

High Fidelity Model of a Ball Screw Drive for a Flight Control Servoactuator

Over the past years, a trend toward “more electric” equipment has arisen including flight control systems, leading to a tendency to replace the electro-hydraulic actuators (EHSAs) with electro-mechanical actuators (EMAs), which have however a too high jamming probability for a primary flight control system. An innovative jam tolerant approach is to make the EMA “jam-predictive” by monitoring its health state using effective prognostic algorithms. The need for a high-fidelity model is then paramount. In this study, basing on a typical architecture of an EMA, a detailed analysis of the developed dynamic non-linear ball screw model is presented. The backlash, friction parameters, a model of the rolling/sliding behaviour of a ball with rolling friction are taken into account, contact stiffness and preload are introduced. A discussion is presented on the results of a sensitivity analysis on the efficiency of the mechanism with respect to the above mentioned characteristic parameters under different operating conditions. The model and the results of the sensitivity analysis can be used to better understand the physics within the actuator and the ensuing fault-to-failure mechanisms which are needed for developing more efficient prognostic algorithms.

Hexafly-INT Experimental Flight Test Vehicle (EFTV) Aero-Thermal Design

Over the last years, innovative concepts of civil high-speed transportation vehicles were proposed. In this framework, the Hexafly-INT project intends to test in free-flight conditions an innovative gliding vehicle with several breakthrough technologies on-board. This approach will help to gradually increase the readiness level of a consistent number of technologies suitable for hypervelocity flying systems. The vehicle design, manufacturing, assembly and verification is the main driver and challenge in this project. The prime objectives of this free-flying high-speed cruise vehicle shall aim at a conceptual design demonstrating a high aerodynamic efficiency in combination with high internal volume; controlled level flight at a cruise Mach number of 7 to 8;an optimal use of advanced high-temperature materials and structures. Present research describes the aero-thermal design process of the Experimental Flight Test Vehicle, namely EFTV. The glider aeroshape design makes maximum use of databases, expertise, technologies and materials elaborated in previously European community co-funded projects LAPCAT I & II [1][2], ATLLAS I & II [3][4] and HEXAFLY [5]. The paper presents results for both CFD and Finite Element aero-thermal analysis, performed in the most critical phase of the experimental flight leading to the selection of materials for the different components and to a suitable Thermal Protection System.

A Comparative Study: Aerodynamics of Morphed Airfoils Using CFD Techniques and Analytical Tools

This paper presents an aerodynamics study of wing morphing by creating a Computational Fluid Dynamics (CFD) model using ANSYS FLUENT. First, known National Advisory Committee for Aeronautics (NACA) 2410 and 8410 profiles of airfoils are modeled. Models are run using prescribed initial and boundary conditions to simulate the morphed wing and flow around it. The Shear Stress Transport (SST) k–ω turbulence model is used to obtain an accurate comparison with the analytical results. Once satisfied with validation, variable cambers between NACA 2410 and 8410 are used in two ends of a wing to mimic a morphed wing situation. Drag and lift coefficients are analyzed for this configuration to understand effects of the airfoil shape on aerodynamic performance. A refined mesh is created near the airfoil wall to capture the flow details. This study is a step forward towards understanding how to accurately model the dynamic morphing of an airplane wing.

Thermal Analysis of Electron Beam Additive Manufacturing Using Ti-6Al-4V Powder-Bed

Electron Beam Additive Manufacturing (EBAM) is one of the emerging additive manufacturing (AM) technologies that is uniquely capable of making full density metallic components using layer-by-layer fabrication method. To build each layer, the process includes powder spreading, pre-heating, melting, and solidification. The thermal and material properties involved in the EBAM process play a vital role to determine the part quality, reliability, and energy efficiency. Therefore, characterizing the properties and understanding the correlations among the process parameters are incumbent to evaluate the performance of the EBAM process. In this study, a three dimensional computational fluid dynamics (CFD) model with Ti-6Al-4V powder has been developed incorporating the temperature-dependent thermal properties and a moving conical volumetric heat source with Gaussian distribution to conduct the simulations of the EBAM process. The melt-pool dynamics and its thermal behavior have been investigated numerically using a CFD solver and results for temperature profile, cooling rate, variation in density, thermal conductivity, specific heat capacity, and enthalpy have been obtained for a particular set of electron beam specifications.

Adjoint-Based Design Optimization of S-Shaped Intake Geometry

The S-shaped air intakes are very common shapes due to their ease in the engine-body integration or Radar Cross Section, RCS, specifications especially for fighter aircrafts. The numerical shape optimization of an S-shaped air intake using adjoint method is conducted. The flow of a specified air intake that uses S-duct M2129 is simulated using three dimensional (3D) numerical solution of Reynolds-Averaged Navier-Stokes equation along with k-ω SST turbulence model. The main purpose of this optimization scheme is to maximize the total pressure recovery (TPR). Further, the scheme is developed in such a way that would be applicable in industry thru satisfying specified constraint requirements. The cross sectional areas of the geometry of duct inlet and outlet (known as engine face) remain unchanged. In addition, small shape modification in each optimization step is considered. Finally after nine optimization cycles new S-shaped air intake geometry with higher TPR and lower distortion (DC) is generated, that would achieve higher performance during its operation.

Numerical Simulation of Mixed Compression Intake Buzz

Numerical analysis has been conducted to simulate and capture Buzz phenomenon in a supersonic mixed compression air intake. Buzz is an unsteady self-sustained phenomenon occurred in supersonic intakes, especially when operating its subcritical condition, during which the system of compression and shock waves oscillate and move upstream and downstream along the intake. An axisymmetric and unsteady numerical simulation was used to solve Navier-Stokes equations in combination with URANS SST k-ω turbulence model The simulations were performed at M = 2.0 and at a specific subcritical point of the intake operation where buzz was detected experimentally. Results are compared with experimental pressure data. Buzz is captured numerically, and the results show that the buzz oscillation in this intake is periodic, during which the intake duct is loaded and unloaded. The results show that the large separation region on the compression ramp blocks the duct entry and causes the conical and lambda shocks located on the compression ramp to move upstream cause the self-sustained oscillation. The calculated buzz frequency is in agreement with the experimental one, and the difference is less than 0.2%. Further, the peak and trough of both total and static pressure fluctuations, and as a result, the amplitude of buzz are all accurately predicted.

Study of Damping Properties of Polymer Matrix Composites Through Wave Propagation

We conduct a stochastic analysis to investigate the damping properties of polymer composites with viscoelastic matrix and elastic spherical inclusions. Since damping capability of polymer composites is directly related to the ratio of loss to storage modulus known as tan δ, we use computational homogenization techniques to investigate the effect of vibrational frequency, size and volume fraction of inclusions on tan δ. Our results show that tan δ is highly dependent on the frequency of vibrations as well as the volume fraction of inclusions. Our numerical analyses also show that tan δ is not sensitive to the size of inclusions as long as inclusions volume fraction remains the same.