Time-domain computations for floating bodies

A review of the research carried out at the University of Michigan and elsewhere on the use of time-domain panel methods to compute the hydrodynamic forces acting on floating bodies is presented. Both linear and fully nonlinear computational techniques are presented. The linear problem is solved using a time-domain Green function approach. The fully nonlinear computations are done using an Euler-Lagrange method. At each time step the resulting mixed boundary value problem is solved using a desingularized isolated source. Results are presented for simplified bodies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31913/1/0000866.pd

Uncertainty Estimation Based on Global Sensitivity Analysis for CFD Simulations of Supersonic Flow Over Missile

Though Computational Fluid Dynamics (CFD) approach has proven itself as a cost-e ective in designing of missiles, CFD simulations cannot accurately estimate the experimental data due to such reasons as unphysical sub-models, insufficient resolution, inaccurate boundary conditions, and initial conditions, etc. To account the uncertainty due to such sources, Global Sensitivity Analysis (GSA) approach is proposed in the current work of supersonic ow over cruciform missile of ogive-cylinder fuselage-wings- ns con guration. The output parameters of interest considered are the coefficient of rolling moment, the coefficient of drag, and coefficient of lift. A grid convergence study is done to check grid independence and Grid Convergence Index (GCI) for these global coefficients, and local mach number and stagnation pressure change eld variables are estimated. A nominal case is established. Global Sensitivity Analysis is performed by perturbation of the parameters from their nominal case value after identifying the sources of uncertainty and the input variables with greater in uence on output global parameters are identi ed

Elastic buckling of latticed and thin walled columns. Studies in overall and component stability

Columns in general can be regarded as built up of components. These components may be of different structural form, such as the column legs and the latticing of a Latticed Column, or may be of the same form, such as the flange and web plates of a Thin Walled Column. In any one case failure may occur either by integral column action - "Overall Instability" or by failure of one of the components - "Component Instability". The contents of the thesis are divided into two main parts. Part I presents a review of published Analytical and Experimental Investigations of Latticed Columns, followed by a short critical discussion. This reveals, on the experimental side, the lack of complete column distortion data and on the theoretical side, the absence of stability analysis of the column leg components as distinct from the panel elements. The review is followed by the presentation of the experimental work carried out on a model latticed column, from which the complete distortion of the column legs were obtained by measurement of the lateral deflections at 18 points along their length. Using the experimental work as a guide an analysis is developed, which gives the buckling load of Latticed Columns based on the stability of the column legs. Account is taken of the action of lateral loads' on the column legs, the magnitude of these loads being dependent on the elasticity of the latticing. In its application, the critical stress given by this treatment is taken as the "ideal column" buckling stress of the Perry-Robertson formula, which is then utilised to complete actual failure stresses. Values calculated in this manner are compared with the published experimental results of other Investigators. Part II gives a brief survey of the relevant published theories of flexural and torsional integral column stability, and flexural plate stability under compressive actions. The thesis then presents the experimental work carried out on thin walled columns consisting of some 70 tests to destruction of 3 ft. long channel section specimens. The tests were designed to cover the complete range of integral column and plate component failure. Special study was made of the conditions obtaining under simultaneous overall column and plate component collapse. The characteristics of flange plate failure were further investigated on two 12 ft. long channel section columns tested to destruction. Complete edge deflection data for the flanges together with a stress survey of the flange surface are presented. The experimental buckling stress results of the plate failure range, are analysed on the basis of the classic plate buckling theory, leading to the evaluation of the degree of edge fixity of the flange plates. This is followed by a comparison of the experimental results with calculated distributions given by the Perry-Robertson formula - the plate critical stress being taken as the "ideal column" buckling stress and by the present day stress basis of American design. The findings of the investigations presented in the thesis fall into two categories, namely (i) Specific characteristics - appertaining to details of theoretical and experimental behaviour. These are given in the Summaries at the end of each section. (ii) General features appertaining to a substantiation of the Perry Robertson formula, while developed originally for the "Overall" type of failure it is shown to be applicable to the "Component" failure range also provided the values of the imperfection factor and the "ideal column" buckling stress correspond to the characteristics of the weakest column component

The influence of local buckling on the structural behavior of singly-symmetric cold-formed steel columns

INTRODUCTION Cold-formed steel sections are formed from thin steel sheets, of typical thickness 0.015-0.25 inches, by either production cold roll forming or by specialized press braking. As a result, it is possible to produce economically a variety of cross-sectional shapes, which have high strength-to-weight ratios. Some structural applications include primary and secondary load-carrying framing members, such as columns, purlins and wall studs; and shear diaphragms, such as floor and roof decks and wall panels (Yu [1973]). Their design is governed by the American Iron and Steel Institute (AISI) Specification [1980], which is unique because of its generality, e.g., no specific shape is presumed. The philosophy behind cold-formed steel structural members is illustrated with the following example, adopted from Seaburg [1981]. Suppose it is required to design a 10-foot column, of any shape, to support a given axial load. One solution would be to employ a 3/4-inch square mild steel bar. However, a subsequent analysis of this slender column would show that it would fail, by flexural buckling, at a load of only about 500 pounds. Alternately, this same bar could be rolled into a thin strip about 12 inches wide and, in turn, used as the column. In this case, the strip would buckle essentially under its own weight. On the other hand, if this strip is formed, or bent, into the shape, say, of a lipped channel, its load-carrying capacity would be increased by twenty times that of the original bar. This simple example illustrates. of course, that the structural efficiency of a section is dependent on the manner in which the available material is distributed, which is a basic property utilized in the design of cold-formed steel members. Equally important is that this property leads to the proportioning of very thin structural sections which are prone to local buckling of the individual plate elements, or portions of the section between bends. It is this latter area that the present investigation addresses

Wall Model Large Eddy Simulation of a Diffusing Serpentine Inlet Duct

The modeling focus on serpentine inlet ducts (S-duct), as with any inlet, is to quantify the total pressure recovery and ow distortion after the inlet, which directly impacts the performance of a turbine engine fed by the inlet. Accurate prediction of S-duct ow has yet to be achieved amongst the computational fluid dynamics (CFD) community to improve the reliance on modeling reducing costly testing. While direct numerical simulation of the turbulent ow in an S-duct is too cost prohibitive due to grid scaling with Reynolds number, wall-modeled large eddy simulation (WM-LES) serves as a tractable alternative. US3D, a hypersonic research CFD code developed by University of Minnesota was used with inviscid fluxes calculated using 4th order kinetic-energy consistent schemes by Subbareddy and Candler with a flux limiter by Ducro. The WM-LES model by Komives was applied with a constant Vreman sub grid scale model. The use of higher order numerical models on a fully structured grid were assessed with delayed detached eddy simulation (DDES) and WM-LES turbulence models to obtain increased prediction accuracy of the S-duct ow when compared to previous studies and test data. Further, a first of its kind dynamic Vreman model was derived, implemented, and validated in US3D using a flat plate model

Disturbance rejection for U.A.S. aircraft using bio-inspired strain sensing

A bio inspired gust rejection mechanism based on structural inputs is proposed. Insect wings possess a wealth of sensor systems which typically consist of fast reflexive neuronal paths. Stretch and strain sensors on insect wings are used for flight control and can be found across many species. These are used for monitoring of bending and torsion during flight. The fast reflexive and proprioceptive mechanisms based on strain sensing found in nature are the inspiration for this work. A strain feedback controller allows for anticipation of the onset of rigid body dynamics due to gust perturbations. This anticipation stems from sensing of higher order states and the possibility of reacting before lower order states are reached. High bandwidth inner loop compensation is therefore enabled. Forces and moments are proportional to wing strain patterns and can be used in fast reaction inner loops. Strain sensors are used for providing an indirect estimation of the differential forces applied to the aircraft wing and therefore to the aircraft rigid body. These sensors can be distributed over the surface of the aircraft wing to encode multiple degree of freedom disturbances. Sensor locations for disturbance rejection are determined based on metrics associated to the observability Grammian. The locations are preselected based on modal energy analyses and are chosen according to wide field integration patterns. A model for wide field integrated strain based on mass participation factors is proposed as well as one which is based on the physics of the forces and moments acting on the wing producing strain patterns which can be used for disturbance rejection. Models of the differential forces via strains on the wings are proposed. Strain feedback was implemented in four platforms under different types of disturbances. The platforms consisted of a glider, a quadrotor, a wing section for wind tunnel testing and an RC airplane with a full span wing. The disturbances included discrete gusts as well as turbulence. The results of using strain feedback showed not only to be faster than IMU estimations but also to be better when compared to a classical attitude controller implementation

Aeronautical engineering: A special bibliography with indexes, supplement 82, April 1977

This bibliography lists 311 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1977

Modelling trailing vortices from a slender ship hull for manoeuvring calculations

PhD ThesisA particular problem that has been encountered in modelling the forces and moment acting on a manoeuvring ship, has been the correct estimation of the distribution of side force along its length. If traditional slender body theory is used, reasonable agreement can be obtained between theoretical and experimental result over the forebody of the ship. However, moving aft, the two increasingly diverge until there are significant differences at the stem. For this reason manoeuvring coefficients cannot be accurately predicted by this approach. In a number of studies, the reason for the discrepanciesh as been attributed to the influence of trailing vortices that develop along the hull. The conclusion is consistent with sensitivity analyses carried out with augmented slender body theory incorporating vortices of specified location and strength along the ship. The present thesis is concerned with modelling trailing vortices along a ship in drift motion so that they can be used in the calculation of the associated distribution of forces and manoeuvring coefficients. A numerical model based on the Discrete Vortex Method has been developed for the analysis of vortex flow around the ship which is representedb y slender body approximation. The trailing vortices are modelled by a series of transverse two-dimensional multi-vortex solutions marching longitudinally down the hull. Results are presented for six different hull types; a flat plate, the Wigley hull, a block hull, a Series 60 hull, the British Bombardier and the British Bombardier with a pram stem. The effects of varying drift angles are also investigated for each hull types. Good qualitative agreement is shown between the predicted velocity and vorticity fields and results from experimental studies. The distribution of side forces and yaw moments along the hull is also well predicted. The results explain manoeuvring phenomena occurring for the hull forms considered that have been observed experimentally and at full scale.Inha University Samsung Heavy Industr

Low transport stages by water streams of fine, cohesionless, granular and flakey sediments

Imperial Users onl

Waves and turbulence on wavy coastal seabeds inducing vertical scalar transport

The project ”Waves and turbulence on wavy coastal seabeds inducing vertical scalar transport” is part of the graduate school Baltic Transcoast. This graduate school aimed to investigate the interaction between a coastal fen and the Baltic sea. In this work, the mixing and transport of the submarine groundwater discharge (SGD) was investigated in a defined laboratory experiment. For this, a new wave channel ground model was constructed and produced to facilitate the variation of different parameters for the investigations