Identification of aerodynamic models for maneuvering aircraft

Due to the requirement of increased performance and maneuverability, the flight envelope of a modern fighter is frequently extended to the high angle-of-attack regime. Vehicles maneuvering in this regime are subjected to nonlinear aerodynamic loads. The nonlinearities are due mainly to three-dimensional separated flow and concentrated vortex flow that occur at large angles of attack. Accurate prediction of these nonlinear airloads is of great importance in the analysis of a vehicle's flight motion and in the design of its flight control system. A satisfactory evaluation of the performance envelope of the aircraft may require a large number of coupled computations, one for each change in initial conditions. To avoid the disadvantage of solving the coupled flow-field equations and aircraft's motion equations, an alternate approach is to use a mathematical modeling to describe the steady and unsteady aerodynamics for the aircraft equations of motion. Aerodynamic forces and moments acting on a rapidly maneuvering aircraft are, in general, nonlinear functions of motion variables, their time rate of change, and the history of maneuvering. A numerical method was developed to analyze the nonlinear and time-dependent aerodynamic response to establish the generalized indicial function in terms of motion variables and their time rates of change

Aeroelastic analysis of wings using the Euler equations with a deforming mesh

Modifications to the CFL3D three dimensional unsteady Euler/Navier-Stokes code for the aeroelastic analysis of wings are described. The modifications involve including a deforming mesh capability which can move the mesh to continuously conform to the instantaneous shape of the aeroelastically deforming wing, and including the structural equations of motion for their simultaneous time-integration with the governing flow equations. Calculations were performed using the Euler equations to verify the modifications to the code and as a first step toward aeroelastic analysis using the Navier-Stokes equations. Results are presented for the NACA 0012 airfoil and a 45 deg sweptback wing to demonstrate applications of CFL3D for generalized force computations and aeroelastic analysis. Comparisons are made with published Euler results for the NACA 0012 airfoil and with experimental flutter data for the 45 deg sweptback wing to assess the accuracy of the present capability. These comparisons show good agreement and, thus, the CFL3D code may be used with confidence for aeroelastic analysis of wings

Aeroelastic analysis for propellers - mathematical formulations and program user's manual

Mathematical development is presented for a specialized propeller dedicated version of the G400 rotor aeroelastic analysis. The G400PROP analysis simulates aeroelastic characteristics particular to propellers such as structural sweep, aerodynamic sweep and high subsonic unsteady airloads (both stalled and unstalled). Formulations are presented for these expanded propeller related methodologies. Results of limited application of the analysis to realistic blade configurations and operating conditions which include stable and unstable stall flutter test conditions are given. Sections included for enhanced program user efficiency and expanded utilization include descriptions of: (1) the structuring of the G400PROP FORTRAN coding; (2) the required input data; and (3) the output results. General information to facilitate operation and improve efficiency is also provided

Application of CFD techniques toward the validation of nonlinear aerodynamic models

Applications of Computational fluid dynamics (CFD) methods to determine the regimes of applicability of nonlinear models describing the unsteady aerodynamic responses to aircraft flight motions are described. The potential advantages of computational methods over experimental methods are discussed and the concepts underlying mathematical modeling are reviewed. The economic and conceptual advantages of the modeling procedure over coupled, simultaneous solutions of the gasdynamic equations and the vehicle's kinematic equations of motion are discussed. The modeling approach, when valid, eliminates the need for costly repetitive computation of flow field solutions. For the test cases considered, the aerodynamic modeling approach is shown to be valid

Machining stability and machine tool dynamics

Machining is a common manufacturing process in industry due to its high flexibility and ability to produce parts which excellent quality. The productivity and quality in machining operations can be limited by several process constraints one of which is the self-excited chatter vibrations. Under certain conditions, the process may become unstable yielding oscillations with high amplitudes which result in poor surface finish and damage to the cutting tool, part and the machine tool itself. Stability analysis of the dynamic cutting process can be used to determine chatter-free machining conditions with high material removal rate. Since chatter is a result of the dynamic interactions between the process and the structures both cutting and machine tool dynamics are important elements of the stability analysis. In this paper, methods developed for stability analysis of cutting processes and machine tool dynamics will be presented. Implications of these methods in the selection of process parameters and machine tool design will be also discussed with example applications

Motion analysis of FPSO in multidirectional seas : the West African offshore region

PhD ThesisThe use of experiment remains the most accurate method in the prediction and evaluation of roll damping. Several models ranging from CFD to analytical and empirical techniques and tools have been developed over the years for this purpose. However, the issue of accurately capturing the adherent multilinear behaviour for hulls with sharp edges and bilge keels remains a challenge until date. The elaborate works of Oliveira and Fernandes (Oliveira and Fernandes ,2006,2010,2014) identified and characterized the existence of two regimes using the bilinear model, later modified to the hyperbolic model. Following their work, and identifying this gap, an enhancement in their formation lead to the introduction of a third damping term, which represented the transition between the large angle side and the small angle regions. A modified hyperbolic model has been proposed and tested against existing models with reasonable agreement in terms of regenerating the measured decay. The model’s capture of the transition region was validated using the rigorous procedure of the bilinear methodology. The relative uncertainty associated with the predictive model was evaluated to fall within 3.5% to 5.9% .The decay data were used to modify the regression model of Oliveira and Fernandes and the enhanced model reduced the predictive error in the model parameters from second to first order range. The extracted damping coefficient and model where implemented in a code to study the influence of directionality and spectrum type on the roll motion response of the freefloating unit (typical FPSO) in real sea environment. Interactive contour plot representation was used to capture the sensitivities of spectrum type, directionality and the multidirectional wave streams summation techniques developed prior to roll motion response simulation. A barred region for the number of regular waves to be used was established using the maximum spectra energy density and the estimated significant wave height as the indicators. A 6dof code was developed using simplified methods and techniques. The novel frequency-spectra weighted technique was proposed for the estimation of the excitation force components of the equation of motion in irregular short crested seas from regular wave formulations. The method was validated by running similar scenarios in HydroD and the irregular wave test on scaled model. The roll motion response from the proposed method compared favourably within first order error range against the HydroD simulations and the irregular wave experiment conducted for ii JONSWAP spectrum for the targeted significant wave heights. Similar error margins were also observed for the measured as well as the estimated wave elevations and all other motion modes. The interactive results from the contour plots when translated into roll motion was very evident in the estimated magnitudes in different sea state spectra combinations (type and directions). The use of the suggested spectra form (lognormal or triangular for the swell sea and JONSWAP-Glenn for the wind sea) for the West African region identified variations in the roll response of between 1-23% or more than 5.5o This goes to further show the need to use site or region specific spectrum for the determination of design and operational parameters for offshore structures and associated units and for personnel seakeeping comforts.Niger delta development commission (NDDC) in Nigeri

Investigation of Northrop F-5A wing buffet intensity in transonic flight

A flight test and data processing program utilizing a Northrop F-5A aircraft instrumented to acquire buffet pressures and response data during transonic maneuvers is discussed. The data are presented in real-time format followed by spectral and statistical analyses. Also covered is a comparison of the aircraft response data with computed responses based on the measured buffet pressures

Ionization Electron Signal Processing in Single Phase LArTPCs I. Algorithm Description and Quantitative Evaluation with MicroBooNE Simulation

We describe the concept and procedure of drifted-charge extraction developed in the MicroBooNE experiment, a single-phase liquid argon time projection chamber (LArTPC). This technique converts the raw digitized TPC waveform to the number of ionization electrons passing through a wire plane at a given time. A robust recovery of the number of ionization electrons from both induction and collection anode wire planes will augment the 3D reconstruction, and is particularly important for tomographic reconstruction algorithms. A number of building blocks of the overall procedure are described. The performance of the signal processing is quantitatively evaluated by comparing extracted charge with the true charge through a detailed TPC detector simulation taking into account position-dependent induced current inside a single wire region and across multiple wires. Some areas for further improvement of the performance of the charge extraction procedure are also discussed.Comment: 60 pages, 36 figures. The second part of this work can be found at arXiv:1804.0258