Mechanical and tribological behaviour of PA6 and short aramid fiber composites

This paper presents the results of mechanical and tribological characteristics for two composites: PA6 as matrix and 5% aramid whiskers as additive material and PA6 + 10% aramid whiskers, comparing them to those made of PA6 (polyamide 6). To improve the mechanical and thermal properties of polyamide (PA6), the composites were prepared via the Brabender lab mixer and mould forming under given pressure and temperature conditions. Test specimens made of pure PA6 and PA6 mixed with 5 wt.% and 10 wt.% aramid whiskers were subjected to mechanical tests (three-point bending and impact), thermo–mechanical test (HDT - heat deflection temperature), tribological test (block-on-ring) and analyzed from morpho-structural point of view. Compared to the PA6 samples, the mass concentrations of aramid whiskers improved the HDT deflection temperature values. In the case of samples with 5% aramid whiskers, the absorbed energy increased by 13% and for those with 10% aramid whiskers they increased by 30%. Aramid whiskers-doped materials performed much better on severe tribological testing as compared to PA6 samples. Increasing the deflection temperature, also improved their resistance from a tribological point of view.

Trailing Edge Thickness Effect on Tonal Noise Emission Characteristics from Wind Turbine Blades

Broadband noise generation from wind turbine blades is one of the fundamental aspects of flow-induced noise. Besides the turbulent boundary layer flow over the blades, factors such as the angle of attack, the turbulence intensity, the trailing edge thickness of the blade and their shapes strongly influence the overall sound power levels at high frequencies, i.e. f > 8 kHz. In large operating wind farms, a trade-off between noise generation and power production is considered by power utility firms to maximize the return on investment (ROI) and minimize the fatigue damage on wind turbine components. The present work deals with the analysis of the thickness effect on trailing edge bluntness noise level at hub height average wind speeds of 7 m/s, 10 m/s. A semi-empirical BPM model was used to predict the sound pressure levels from the 37 m blade length of a 2MW wind turbine. The receiver configuration was fixed at a distance of 120 m from the source height of 80 m. The results demonstrated that as the trailing edge height increased from 0.1 % to 0.5 % of the local chord, the sound power level increased by ~ 17 dB for frequencies > 200 Hz, but decreased by 16 dB when the thickness is 0.1 % local chord. The computed results of the sound power level using the BPM model have been validated using experimental data and showed a good agreement for the tonal frequencies, f ~ 10 kHz, where the trailing edge bluntness noise becomes dominant.

Small Satellite Operational Phase Thermal Analysis and Design: A Comparative Study

This paper is about the modeling and design of the passive thermal control system for the European Student Earth Orbiter (ESEO) satellite. A detailed thermal model was created in Thermal Desktop software. The model was running for the operative phase which includes cycles of 28 orbits. During these 28 orbits, there are several modes (10 modes). Each mode has a specific duration, attitude (Sun-nadir), and certain internal heat dissipation. The design of the passive thermal control system was based on controlling the conductive and radiative heat exchange between the internal components and the mounting panels, between panels themselves, and controlling external radiation exchange to achieve the desired components temperature ranges. The temperature results from simulations were presented to show the expected component temperatures and to demonstrate that the passive thermal control system met the requirements of the temperature limits. The final passive thermal control design shows that the satellite components temperatures were always maintained within their required limits during the operational phase

Analysis and characterization of additive manufacturing processes

Recently, additive manufacturing (AM) processes have expanded rapidly in various fields of the industry because they offer design freedom, involve layer-by-layer construction from a computerized 3D model (minimizing material consumption), and allow the manufacture of parts with complex geometry (thus offering the possibility of producing custom parts). Also, they provide the advantage of a short time to make the final parts, do not involve the need for auxiliary resources (cutting tools, lighting fixtures or coolants) and have a low impact on the environment. However, the aspects that make these technologies not yet widely used in industry are poor surface quality of parts, uncertainty about the mechanical properties of products and low productivity. Research on the physical phenomena associated with additive manufacturing processes is necessary for proper control of the phenomena of melting, solidification, vaporization and heat transfer. This paper addresses the relevant additive manufacturing processes and their applications and analyzes the advantages and disadvantages of AM processes compared to conventional production processes. For the aerospace industry, these technologies offer possibilities for manufacturing lighter structures to reduce weight, but improvements in precision must be sought to eliminate the need for finishing processes.

The mathematical description of the bulk fluid flow and that of the content impurity dispersion, obtained by replacing integer order temporal derivatives with general temporal Caputo or general temporal Riemann-Liouville fractional order derivatives, are objective

In the field of fractional calculus applications, there is a tendency to admit that “integer-order derivatives cannot simply be replaced by fractional-order derivatives to develop fractional-order theories”. There are different arguments for that: initialization problem, inconsistency, use of nonsingular or singular kernels, loss of objectivity. In this paper it is shown that the mathematical description of the bulk fluid flow and that of the content impurity spread replacing integer order temporal derivatives with general temporal Caputo or general temporal Riemann-Liouville fractional order derivatives, are objective. More precisely, it is proven that, the mathematical description of the bulk fluid 2D flow and that of the content impurity spread, in a horizontal unconfined aquifer, obtained replacing integer order temporal derivatives with general temporal Caputo or general temporal Riemann-Liouville fractional order derivatives, are objective. It is also proven that, the mathematical description of a Newtonian, incompressible, viscous bulk fluid 3D flow and that of the contained impurity dispersion, obtained replacing integer order temporal derivatives with general temporal Caputo or general temporal Riemann-Liouville fractional order derivatives, are objective. The obtained results show the compatibility of the general temporal Caputo and general temporal Riemann-Liouville fractional order derivatives with the understanding of the “measured time” evolution. In the same time these results reveal that, the objectivity violation, when integer order temporal derivatives are replaced by classic temporal Caputo or classic temporal Riemann-Liouville fractional order derivatives, is originated in the incompatibility of the classic fractional order derivatives, with the understanding of the “measured time” evolution.

Structural Design and Control of a Morphing Winglet to optimize the Aerodynamic Performance of the CRJ-700 Aircraft. Part 2 – Control

In this study, the morphing technology was applied on winglets for the CRJ-700 transport regional aircraft with the aim to improve its aerodynamic performance. The LARCASE Virtual Research Simulator VRESIM is equipped with highest Level D certified flight data for the CRJ-700. The flight and geometrical data of the CRJ-700 were used to quantify the aerodynamic benefits of the CRJ-700 equipped with a morphing winglet versus its reference winglet. The structural design and the mechanism allowing its rotation were used to allow the orientation of the winglet with angles between 90° and -90°. The control of the orientation of the morphing winglet with its mechanism was finally carried out using the Matlab/ Simulink interface. Therefore, a new concept of morphing winglet was obtained in this research.

Hydrostatic pressure loads for a tank using “CID Distributed Loads” fields in a PATRAN FEM model

The purpose of this paper is to present a practical way to introduce distributed loads on the walls of a tank in order to perform a FEM analysis using PATRAN/NASTRAN programs. The problem is generated mainly by the fact that there are gravitational accelerations in the three directions of the moving airplane that produce a great number of combinations of inertial loads and consequently a great number of critical load cases. We compared the performed stress analysis with the loads obtained with this method in different cases for 𝑛𝑛=1. (Different forms of the fuel tanks and different placements of the tank inside the aircraft). The form and the density of the grid do not significantly affect the precision of the real inertia loads. Using the presented method one can reduce the volume of FEM files used in the analysis and can quite accurately reproduce the pressure loads on the fuel of a moving aircraft.

Virtual Reality Safety Limitations

Virtual reality is currently a phenomenon that is transmitted from the scientific field to real life more and more, and its application can be observed in several sectors. This technology provides a whole new perspective on various areas that we, as ordinary mortals, would find very difficult to reach. It allows us to see and even feel things, that are often very difficult to reach in real life. Starting with various simulations of dangerous work activities and ending with complicated scientific experiments, virtual reality provides a wide utilization, that pushes the boundaries of research and human capabilities further again. But is VR suitable for anyone, is it safe enough? Does VR have any limitations that make it impossible for it to be fully exploited and put into practice?

An investigation on dry sliding wear behavior of Al6061/ Titanium carbide/ Basalt hybrid metal matrix composites

Dry sliding wear plays an important role in selecting material for automotive and aerospace applications. Researchers have been exploring novel aluminum matrix composites (AMC), which offer minimum wear rate for various tribological applications. The present work involves multi-objective optimization for dry sliding wear behavior of Al6061 reinforced with 6 % of Titanium carbide and 4% of basalt hybrid metal matrix composites using principal component analysis (PCA)-based grey relational analysis (GRA). In this article, the effects of input variables of wear parameters such as applied load, sliding speed and sliding distance were investigated on different output responses, namely the wear rate, friction force and specific wear rate. Taguchi’s L9 orthogonal array with three-level settings was chosen for conducting experiments. Three output responses in each experiment were normalized into a weighted grey relational grade using grey relational analysis coupled with the principal component analysis. The analysis of variance indicated that sliding distance is the most influential parameter followed by load and sliding velocity that contributes to the quality characteristics. Optimal results have been verified through additional experiments.

Some aspects in Kelvin-Helmholtz instability with and without Boussinesq approximation

The topic of this paper is the Kelvin-Helmholtz instability, a phenomenon which occurs on the interface of a stratified fluid, in the presence of a parallel shear flow, when there is a velocity and density difference across the interface of two adjacent layers. This paper focuses on a numerical simulation modelled by the Taylor-Goldstein equation, which represents a more realistic case compared to the basic Kelvin-Helmholtz shear flow. The Euler system is solved with new modelled smooth velocity and density profiles at the interface. The flux at cell boundaries is reconstructed by implementing a third order WENO (Weighted Essentially Non-Oscillatory) method. Next, a Riemann solver builds the fluxes at cell interfaces. The use of both Rusanov and HLLC solvers is investigated. Temporal discretization is done by applying the second order TVD (total variation diminishing) Runge-Kutta method on a uniform grid. Numerical simulations are performed comparatively for both Kelvin-Helmholtz and Taylor-Goldstein instabilities, on the same simulation domains. We find that increasing the number of grid points leads to a better accuracy in shear layer vortices visualization. Thus, we can conclude that applying the Taylor-Goldstein equation improves the realism in the general fluid instability modelling.