Letter from D. M. Featherston to Aikins & Judge. 1 May 1900

Letter sent from Holly Springs, Mississippi; regarding Featherston divorce.https://egrove.olemiss.edu/ciwar_corresp/1294/thumbnail.jp

Letter from D. M. Featherston to Mrs. Connell. 19 August 1899

Letter sent from Holly Springs, Mississippi; regarding Featherston divorce.https://egrove.olemiss.edu/ciwar_corresp/1291/thumbnail.jp

Exact strip postbuckling analysis of composite plates under compression and shear

Stiffened wing and fuselage panels often have a postbuckling reserve of strength, enabling them to carry loads far in excess of their critical buckling loads. Therefore allowing for postbuckling in design can reduce their weight, hence reducing fuel consumption and environmental impact. The present paper extends the postbuckling analysis in the exact strip software VICONOPT to more accurately reflect the skewed mode shapes arising from shear load and anisotropy. Such mode shapes are represented by a series of sinusoidal responses with different half-wavelengths which are coupled together using Lagrangian multipliers to enforce the boundary conditions. In postbuckling analysis the in-plane deflections involve responses with additional half-wavelengths which are absent from the out-of-plane deflection series. Numerical results are presented and compared with finite element analysis for validation. The present analysis gives close results compared to the finite element and finite strip methods and saves computational time significantly

Jet fuel property changes and their effect on producibility and cost in the U.S., Canada, and Europe

The effects of changes in properties and blending stocks on the refinery output and cost of jet fuel in the U.S., Canada, and Europe were determined. Computerized refinery models that minimize production costs and incorporated a 1981 cost structure and supply/demand projections to the year 2010 were used. Except in the West U.S., no changes in jet fuel properties were required to meet all projected demands, even allowing for deteriorating crude qualities and changes in competing product demand. In the West U.S., property changes or the use of cracked blendstocks were projected to be required after 1990 to meet expected demand. Generally, relaxation of aromatics and freezing point, or the use of cracked stocks produced similar results, i.e., jet fuel output could be increased by up to a factor of three or its production cost lowered by up to $10/cu m. High quality hydrocracked stocks are now used on a limited basis to produce jet fuel. The conversion of U.S. and NATO military forces from wide-cut to kerosene-based jet fuel is addressed. This conversion resulted in increased costs of several hundred million dollars annually. These costs can be reduced by relaxing kerosene jet fuel properties, using cracked stocks and/or considering the greater volumetric energy content of kerosene jet fuel

A hybrid method for modelling damage in composites and its effect on natural frequency

Delamination is a frequent cause of failure in laminated structures, reducing their overall stiffness and hence their critical buckling loads. Delaminations tend to grow rapidly in postbuckling, causing further reductions in structural strength and leading ultimately to sudden structural failure. Many studies have investigated the effects of delaminations on buckling and vibration of composite structures. Finite element analysis is often used to model complex geometries, loading and boundary conditions, but incurs a high computational cost. The exact strip method provides an efficient alternative approach using an exact dynamic stiffness matrix based on a continuous distribution of stiffness and mass over the structure, so avoiding the implicit discretization to nodal points in finite element analysis. However due to its prismatic requirements, this method can model damaged plates directly only if the damaged region extends along the whole length of the plate. This paper introduces a novel combination of exact strip and finite element analysis to model more complex cases of damaged plates. Comparisons with pure finite element analysis and a previous smearing method demonstrate the capability and efficiency of this hybrid method for a range of isotropic and composite plates. The effect of damage on the lowest natural frequency is studied

Inverse design under uncertainty with surrogate models

In the drive towards net zero the aerospace industry is motivated to develop more efficient aerostructures that can accommodate the next generation of propulsion systems that fall outside of the well understood types that are currently in use. The lack of established standards for such designs means that engineers are faced with an increased level of uncertainty in their design choices before any prototypes are built. Machine learning models are becoming a popular tool for expediting the development of novel designs due to their ability to explore and predict the optimal parameters of large design spaces. It is also possible to quantify and introduce uncertainty into particular models so that practitioners can be made aware of the potential variation in their realised designs. In this paper Gaussian Process surrogate models of the performance metrics of the early-stage design of an aircraft wing are created to optimize a subset of design parameters based on some prescribed limits of the intended real system response. This defines the inverse design problem that is solved using Markov Chain Monte Carlo sampling. The approach taken requires novel formulation of a Bayesian machine learning framework. In particular, the work investigates the formation of likelihood functions that are flexible given inputs of different scales, can perform marginalisation of stochastic parameters, account for uncertainty in the surrogate model, and optimise the parameters given more than one constraint. A case study is presented in this paper that highlights both a successful implementation of the framework along with a limitation. It is found that the optimization is sensitive to changes in the variances of the likelihoods such that it can be used as a weight to direct the optimization towards a quantity of interest, therefore adjustment of this parameter is used to balance the optimization

Mechanical Forces Due to Lightning Strikes to Aircraft A Pseudo-Stereo DIC Technique for Measuring Full-Field Displacement

Abstract. One of the major considerations currently affecting the design of composite aircraft structures is the damage resulting from lightning attachment. Full-field measurements of the displacement of materials under lightning attachment would provide a greater understanding of the forces induced by the high current waveform. Furthermore the understanding of the forces involved would allow for the validation of finite element models to simulate the effects of lightning attachment, therefore aiding in the design of solutions to reduce damage to aircraft structures. The study aimed to develop a pseudo-stereo high speed digital image correlation technique in order to obtain full-field information during lightning attachment based on a 100kA initial strike over a 500μs duration, the most severe waveform experienced. The technique that was developed gave full-field measurements for a 550x550x2mm 6082-T6 aluminium panel under a 100kA lightning attachment. Two correlation measurements were recorded at 3000 and 5000 frames per second. The displacement results are comparative with the theory of a cylindrical pressure expansion arising from the acoustic shockwave on attachment to the material. Further developments to this system could allow for more reliable results and higher frame rates which can be used to develop finite element simulations based on measured physical data

Eliminating End Effects for Theoretical Panel Buckling with FEM

This is a conference paper. It was presented at the 51st AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference [© AIAA]. The definitive published version can be found at: http://www.aiaa.org/content.cfm?pageid=2The theoretical buckling performance of thin walled panels under compression can be predicted using classical plate theory (CPT) and using tools such as the VICONOPT, which uses the finite strip method, and Abaqus, a finite element modelling program (FEM). VICONOPT is much more computationally efficient than FEM, and is able to optimise panel design for buckling and pseudo-postbuckling performance. This work forms part of a larger project to use VICONOPT to optimise panel designs that are allowed to buckle in a stable manner below the maximum allowed loading. Because VICONOPT can only make a first approximation of postbuckling performance, a method is required to validate the optimisation results against a more accurate method

Design and construction of the MicroBooNE detector

This paper describes the design and construction of the MicroBooNE liquid argon time projection chamber and associated systems. MicroBooNE is the first phase of the Short Baseline Neutrino program, located at Fermilab, and will utilize the capabilities of liquid argon detectors to examine a rich assortment of physics topics. In this document details of design specifications, assembly procedures, and acceptance tests are reported