Vibroacoustic Tailoring of a Rod-Stiffened Composite Fuselage Panel with Multidisciplinary Considerations

An efficient multi-objective design tailoring procedure seeking to improve the vibroacoustic performance of a fuselage panel while maintaining or reducing weight is presented. The structure considered is the pultruded rod stitched efficient unitized structure, a highly integrated composite structure concept designed for a noncylindrical, next-generation flight vehicle fuselage. Modifications to a baseline design are evaluated within a six-parameter design space including spacing, flange width, and web height for both frame and stringer substructure components. The change in sound power radiation attributed to a design change is predicted using finite-element models sized and meshed for analyses in the 500 Hz, 1 kHz, and 2 kHz octave bands. Three design studies are carried out in parallel while considering a diffuse acoustic field excitation and two types of turbulent boundary-layer excitation. Kriging surrogate models are used to reduce the computational costs of resolving the vibroacoustic and weight objective Pareto fronts. The resulting Pareto optimal designs are then evaluated under a static pressurization ultimate load to assess structural strength and stability. Results suggest that choosing alternative configurations within the considered design space can reduce weight and improve vibroacoustic performance without compromising strength and stability of the structure under the static load condition considered, but the tradeoffs are significantly influenced by the spatial characteristics of the assumed excitation field

Design of Buckling-Critical Large-Scale Sandwich Composite Cylinder Test Articles

It is well known that the buckling response of thin shell structures can be very sensitive to the presence of small geometric imperfections in the shell. The Shell Buckling Knockdown Factor Project (SBKF) was established by the NASA Engineering and Safety Center to develop new analysis-based shell buckling design recommendations for stiffened-metallic and composite launch-vehicle shell structures. Large-scale buckling tests are used to validate the modeling and analysis methods applied in developing these analysis-based recommendations. Herein, the test-article design methodology for honeycomb-core sandwich composite cylinder validation tests is discussed and 8-ft-diameter cylinder designs are presented. First, the sandwich-composite design space was defined using several nondimensional parameters, and the desired test-article design space was determined by examining the designs of launch-vehicle cylinder structures. Essentially, all test-article designs within certain design parameters were generated and then down-selected based on simple closed-form failure calculations and the nondimensional design-space parameters. Four of these designs span a significant portion of the design space of interest and were predicted to have global buckling as the failure mode. They were selected for higher-fidelity finite-element analysis. It was found that the predicted closed-form buckling loads matched the finite-element analysis well, but that the predicted strains at buckling differed significantly. This difference led to slight redesigns of two of the four test articles. The four selected designs are presented with buckling-response predictions from the closed-form analyses, and from linear and geometrically nonlinear finite-element analyses with perfect geometry and with geometric imperfections

Estimation of Filtration Efficiency – from Simple Correlations to Digital Fluid Dynamics

Aerosol filtration in fibrous filters is one of the principal methods of accurate removal of particulate matter from a stream of gas. The classical theory of depth filtration of aerosol particles in fibrous structures is based on the assumption of existing single fibre efficiency, which may be used to recalculate the overall efficiency of entire filter. Using “classical theory” of filtration one may introduce some errors, leading finally to a discrepancy between theory and experiment. There are several reasons for inappropriate estimation of the single fibre efficiency: i) neglecting of shortrange interactions, ii) separation of inertial and Brownian effects, ii) perfect adhesion of particles to the fibre, iv) assumption of perfect mixing of aerosol particles in the gas stream, v) assumption of negligible effect of the presence of neighbouring fibres and vi) assumption of perpendicular orientation of homogenous fibres in the filtration structure. Generally speaking, “classical theory” of filtration was used for characterization of the steady - state filtration process (filtration in a clean filter, at the beginning of the process) without deeper investigation of the influence of the nternal structure of the filter on its performance. The aim of this review is to outline and discuss the progress of deep-bed filtration modelling from the use of simple empirical correlations to advanced techniques of Computational Fluid Dynamics and Digital Fluid Dynamics

Synthesis of CrOx\text{}_{x}/Al2\text{}_{2}O3\text{}_{3}catalyst in sol-gel conditions

A series of CrO$\text{}_{x}$/Al$\text{}_{2}$O$\text{}_{3}$ samples with various Cr/Al molar ratios (0.1-1.0) have been synthesized by the sol-gel technique from Al(C$\text{}_{3}$H$\text{}_{7}$O)$\text{}_{3}$ (aluminium isopropoxide) and chromic acid precursors. The synthesis applied allowed obtaining the final product in monolithic (nonfractured upon drying) form with no use of drying control chemical additives. All samples are characterized by thermal analysis, XRD, and TEM. The low temperature nitrogen adsorption measurements indicate the presence of mesopores. The use of the sol-gel technique permitted a high degree of homogeneity of binary systems up to the Cr/Al molar ratio of 0.5

Brownian dynamics for calculation of the single fiber deposition efficiency of submicron particles

The motion of submicron particles involves the deterministic terms resulting from the aerodynamic convection and/or electrostatic attraction, and the stochastic term from the thermal displacement of particles. The Langevin equation describes such behavior. The Brownian dynamics algorithm was used for integration of the Langevin equation for the calculation of the single fiber deposition efficiency. Additionally the deterministic and stochastic of the particle motion were derived, using the Lagrangian and Eulerian approaches of particle movement and balance, for the calculation of the single fiber deposition efficiency due to both mechanisms separately. Combination of the obtained results allows us for calculation of the coupling effect of inertia and interception with the Brownian diffusion in a form of correlation. The results of calculation show that the omitting of the coupling effect of particular mechanism and using the simple additive rule for determination of the single fiber deposition efficiency introduces significant error, especially for particles with diameter below 300 nm

Modelling of erythrocyte behaviour in blood capillaries by structural model combined with Lattice-Boltzmann approach

A microstructural model of Red Blood Cell (RBC) behaviour was proposed. The erythrocyte is treated as a viscoelastic object, which is denoted by a network of virtual particles connected by elastic springs and dampers (Kelvin-Voigt model). The RBC is submerged in plasma modelled by lattice Boltzmann fluid. Fluid – structure interactions are taken into account. The simulations of RBC behaviour during flow in a microchannel and wall impact were performed. The results of RBC deformation during the flow are in good agreement with experimental data. The calculations of erythrocyte disaggregation from the capillary surface show the impact of RBC structure stiffness on the process