The Design Space of Superalloy-Based Actively Cooled Combustor Walls for H2-Powered Hypersonic Vehicles

The walls of combustion chambers used for air-breathing hypersonic vehicles are subject to substantial thermo-mechanical loads, and require active cooling by the fuel in conjunction with advanced material systems. Solutions based on metallics are preferable to ceramic matrix composites due to their lower cost and greater structural robustness. Previous work suggested that a number of metallic materials (e.g. Nickel, Copper and Niobium alloys) could be used to fabricate actively cooled sandwich structures that withstand the thermo-mechanical loads for a Mach 7, hydrocarbon-powered vehicle (albeit with different weight efficiencies). However, this conclusion changes when the Mach number is increased. This work explores the feasibility of the Nickel superalloy MARM246 for a wide range of Mach numbers (7–12). Since hydrocarbon fuels are limited to Mach 7–8, Hydrogen is used as the coolant of choice. A previously derived analytical model (appropriately modified for gaseous coolant) is used to explore the design space. The relative importance of each design constraint is assessed, resulting in the distillation of essential guidelines for optimal design.

Numerical Study of Time Domain Approach Applied to the Prediction of Noise Radiation From Rotating Blades

Aeroacoustic formulations in time domain are frequently used to model the aerodynamic sound of airfoils, the time data being more accessible. The formulation 1A developed by Farassat, integral solution of the Ffowcs Williams and Hawkings equation, holds great interest because of its adequacy for surfaces in arbitrary motion. The aim of this work is to study the numerical sensitivity of this model to specified parameters and the geometry used in the calculation. The numerical algorithms, spatial and time discretizations, and approximations used for far-field acoustic simulation are presented. A parametrical study of the relevant criteria is carried out based on the Isom’s and Tam’s test cases. A helicopter blade airfoil as defined by Farassat to investigate the Isom’s case is used in this work. According to Isom, the acoustic response of a dipole source with a constant aerodynamic load ρ0c02 is equal to the thickness noise contribution. In practice, this observation is subject to numerical errors that are not systematically well controlled. Variations of these errors depending on the time step, Mach number and the source-observer distance are studied. The analysis is then extended to the Tam’s test case. Tam test case has the advantage of providing an analytical solution for the first harmonic.

Free Bending Vibrations of a Centrally Bonded Symmetric Double Lap Joint (or Symmetric Double Doubler Joint) With a Gap in Mindlin Plates or Panels

In this present study, the “Free Bending Vibrations of a Centrally Bonded Symmetric Double Lap Joint (or Symmetric Double Doubler Joint) with a Gap in Mindlin Plates or Panels” are theoretically analyzed and are numerically solved in some detail. The “plate adherends” and the upper and lower “doubler plates” of the “Bonded Joint” system are considered as dissimilar, orthotropic “Mindlin Plates” joined through the dissimilar upper and lower very thin adhesive layers. There is a symmetrically and centrally located “Gap” between the “plate adherends” of the joint system. In the “adherends” and the “doublers” of the “Bonded Joint” assembly, the transverse shear deformations and the transverse and rotary moments of inertia are included in the analysis. The relatively very thin adhesive layers are assumed to be linearly elastic continua with transverse normal and shear stresses. The “damping effects” in the entire “Bonded Joint” system are neglected. The sets of the dynamic “Mindlin Plate” equations of the “plate adherends”, the “double doubler plates” and the thin adhesive layers are combined together with the orthotropic stress resultant-displacement expressions in a “special form”. This system of equations, after some further manipulations, is eventually reduced to a set of the “Governing System of the First Order Ordinary Differential Equations” in terms of the “state vectors” of the problem. Hence, the final set of the aforementioned “Governing Systems of Equations” together with the “Continuity Conditions” and the “Boundary conditions” facilitate the present solution procedure. This is the “Modified Transfer Matrix Method (MTMM) (with Interpolation Polynomials). The present theoretical formulation and the method of solution are applied to a typical “Bonded Symmetric Double Lap Joint (or Symmetric Double Doubler Joint) with a Gap”. The effects of the relatively stiff (or “hard”) and the relatively flexible (or “soft”) adhesive properties, on the natural frequencies and mode shapes are considered in detail. The very interesting mode shapes with their dimensionless natural frequencies are presented for various sets of boundary conditions. Also, several parametric studies of the dimensionless natural frequencies of the entire system are graphically presented. From the numerical results obtained, some important conclusions are drawn for the “Bonded Joint System” studied here.

Flow/Acoustic Mechanisms in Three-Dimensional Vortices Undergoing Sinusoidal-Wave Instabilities

It has been identified that vorticity in a vortex core directly relates to the frequency of a significant sound peak from an aircraft wake vortex pair where each of the vortices is modeled as an elliptic core Kirchhoff vortex. In three-dimensional vortices, sinusoidal instabilities at various length scales result in significant flow structure changes in these vortices, and thus influence their radiated acoustic signals. In this study, a three-dimensional vortex particle method is used to simulate the incompressible vortical flow. The flow field, in the form of vorticity, is employed as the source in the far-field acoustic calculation using a vortex sound formula that enables computation of acoustic signals radiated from an approximated incompressible flow field. Cases of vortex rings and a pair of counter-rotating vortices are studied when they are undergoing both long- and short-wave instabilities. Both inviscid and viscous interactions are considered and effects of turbulence are simulated using sub-grid-scale models.

Post-Buckling of Functionally Graded Cylindrical Shells

In this study, the post-buckling analysis of functionally graded cylindrical shells was carried out using the non-linear finite element method. The longitudinal shell edges were hinged under a central transverse concentrated load. The shells were composed of ceramic (Al2O3) and metal (Ni) phases and the mechanical properties at the region between the metal and ceramic layers vary continuously through the shell thickness according to a power-law distribution of the volume fractions of the constituents. The arc-length method was implemented. The effects of material composition and layer number as well as various shell thicknesses on the post-buckling response of the functionally graded cylindrical shells were investigated. The functionally graded shells exhibit both snap-through and snap-back post buckling behaviours. The layer number through the shell thickness has a minor effect on the post-buckling behaviour whereas the compositional gradient exponent varies from 0.1 to 10.0 the snap-through behaviour becomes more obvious whilst both the snap-through and snap-back behaviours appear for a thinner shell.

Thermal Measurement of Harsh Environments Using Indirect Acoustic Pyrometry

The inversion of a composite governing equation for the estimation of a boundary heat flux from ultrasonic pulse data is presented. The time of flight of the ultrasonic pulse is temperature dependent and can be used to predict the boundary heat flux. Sensitivities of the approach are examined, results from fabricated data are presented, and example solutions are provided with actual ultrasonic temperature measurement data. The results indicate that compared to the canonical inverse heat conduction problem, the additional step of resolving the time-of-flight data to temperature degrades the sensitivities. Nevertheless, sampling the entire temperature distribution and enhances the results. This method of using ultrasonic pulses to remotely determine heat fluxes is comparable in terms of accuracy to more common heat flux estimation methods.

Nonlinear Response of a Sandwich Plate Subjected to Blast Load

Present work includes in-plane stiffness and inertia effects on the motion of a sandwich plate under blast load. The geometric nonlinearity effects are taken into account with the von Ka´rma´n large deflection theory of thin plates. All edges clamped boundary conditions are considered in the analyses. The equations of motion for the plate are derived by the use of the virtual work principle. Approximate solutions are assumed for the space domain and substituted into the equations of motion. Then the Galerkin Method is used to obtain the nonlinear differential equations in the time domain. The finite difference method is applied to solve the system of coupled nonlinear equations. The results of theoretical analyses are obtained.

Free Vibration Analysis and Design of an Adhesively Bonded Composite Single Lap Joint

In this study the three dimensional vibration analysis of an adhesively bonded cantilevered composite single lap joint was carried out. The first four bending natural frequencies and mode shapes were considered. The back-propagation Artificial Neural Network (ANN) method was used to determine the effects of the fiber angle, fiber volume fraction, overlap length and plate thickness on the bending natural frequencies and the mode shapes of the adhesive joint. The bending natural frequencies and modal strain energies of the composite adhesive lap joint were calculated using the finite element method for random values of the fiber angle, the fiber volume fraction, the overlap length and the plate thickness. Later, the proposed neural network models were trained and tested with the training and testing data. The fiber angle was more dominant parameter than the fiber volume fraction on the natural bending frequencies and corresponding bending mode shapes, and the plate thickness and the overlap length were also important geometrical design parameters whereas the adhesive thickness had a minor effect. In addition, the present ANN models were combined with Genetic Algorithm to search a joint design satisfying maximum natural frequency and minimum modal strain energy conditions for each natural bending frequency and mode shape.

Dynamic and Vibration Analysis of a SAR Membrane Antenna

Synthetic Aperture Radar (SAR) membrane antennas have attracted much attention for their low mass, small stowed volume, large gain and high resolution. To deploy a membrane antenna requires a deployable support structure providing deployment and rigid support after it is fully deployed. A membrane antenna’s vibration may be caused by the disturbance of the satellite attitude-control torque in spacecraft, and it is determined by the mechanical properties of the membrane and its in-plane tension loads. In this paper, the dynamic properties of the deployable structure are studied with ADAMS when the flexibility of the frames is considered. The mode shapes and the natural frequencies of the membrane are analyzed with ABAQUS when the pre-tension loads provided by the tension cable are changed. The random response of the membrane subjected to the base excitation is studied for different tension forces and damping ratios. This work provides a guideline for the vibration control of the membrane by controlling its tension force or damping ratio.

Dynamic Behavior of a Plate Under Air Blast Load Using Differential Quadrature Method

The effect of blast load on the plate and shell structures has an important role on design decision. Blast load experiments are usually difficult and expensive. Therefore, numerical studies have been done on the response of blast loaded structures. However, because of time dependency of the nature of the problem, numerical solutions take long time and need heavy computational effort. The differential quadrature method (DQM) is a numerical solution technique for the rapid solution of linear and non-linear partial differential equations. It has been successfully applied to many engineering problems. The method has especially found application widely in structural analysis such as static and free vibration analysis of beams and plates. The capability of the method to produce highly accurate solutions with minimal computational efforts makes it of current interest. In this paper, the dynamic behavior of isotropic and laminated composite plates under air blast load has been investigated using the differential quadrature method. The results are compared to the numerical and experimental results found in the literature.