Preliminary instability-analysis of deepwater riser with fairings

Instability of deepwater riser with fairings is investigated in this study. Despite the advantages over other devices for suppressing vortex-induced-vibration (VIV), fairings may be susceptible to flutter type instability. A two-body mathematical model is established for the coupled transverse-torsion motion of a top tensioned riser with fairings. The inner part (riser) can only move transversely while the outer part (fairing) has transverse-torsion motion. The effect of the transverse velocity on the angle of attack is taken into account and damping is considered for both degrees of freedom. An eigenvalue analysis is employed to examine the issue of stability. The emphasis is on identifying the critical current speed for a given riser and fairing configuration. The effects of key parameters are investigated and the results indicate that the section hydrodynamic characteristics of the fairings have a significant impact on the instability

Fast B-spline Curve Fitting by L-BFGS

We propose a novel method for fitting planar B-spline curves to unorganized data points. In traditional methods, optimization of control points and foot points are performed in two very time-consuming steps in each iteration: 1) control points are updated by setting up and solving a linear system of equations; and 2) foot points are computed by projecting each data point onto a B-spline curve. Our method uses the L-BFGS optimization method to optimize control points and foot points simultaneously and therefore it does not need to perform either matrix computation or foot point projection in every iteration. As a result, our method is much faster than existing methods

An interactive boundary-layer approach to multielement airfoils at high lift

A calculation method based on an interactive boundary-layer approach to multielement airfoils is described and is applied to three types of airfoil configurations with and without flap-wells in order to demonstrate the applicability of the method to general high-lift configurations. This method, well tested for single airfoils as a function of shape, angle of attack, and Reynolds number, is here shown to apply equally well to two-element airfoils and their wakes, to a flap-well region, and to a three-element arrangement which includes the effects of co-flowing regions, a flap well, and the wake of the elements. In addition to providing accurate representation of these flows, the method is general so that its extension to three-dimensional arrangements is likely to provide a practical, accurate and efficient tool to assist the design process

Configuration design studies and wind tunnel tests of an energy efficient transport with a high-aspect-ratio supercritical wing

The results of design studies and wind tunnel tests of high aspect ratio supercritical wings suitable for a medium range, narrow body transport aircraft flying near M=0.80 were presented. The basic characteristics of the wing design were derived from system studies of advanced transport aircraft where detailed structural and aerodynamic tradeoffs were used to determine the most optimum design from the standpoint of fuel usage and direct operating cost. These basic characteristics included wing area, aspect ratio, average thickness, and sweep. The detailed wing design was accomplished through application of previous test results and advanced computational transonic flow procedures. In addition to the basic wing/body development, considerable attention was directed to nacelle/plyon location effects, horizontal tail effects, and boundary layer transition effects. Results of these tests showed that the basic cruise performance objectives were met or exceeded

Dictionary Learning-based Inpainting on Triangular Meshes

The problem of inpainting consists of filling missing or damaged regions in images and videos in such a way that the filling pattern does not produce artifacts that deviate from the original data. In addition to restoring the missing data, the inpainting technique can also be used to remove undesired objects. In this work, we address the problem of inpainting on surfaces through a new method based on dictionary learning and sparse coding. Our method learns the dictionary through the subdivision of the mesh into patches and rebuilds the mesh via a method of reconstruction inspired by the Non-local Means method on the computed sparse codes. One of the advantages of our method is that it is capable of filling the missing regions and simultaneously removes noise and enhances important features of the mesh. Moreover, the inpainting result is globally coherent as the representation based on the dictionaries captures all the geometric information in the transformed domain. We present two variations of the method: a direct one, in which the model is reconstructed and restored directly from the representation in the transformed domain and a second one, adaptive, in which the missing regions are recreated iteratively through the successive propagation of the sparse code computed in the hole boundaries, which guides the local reconstructions. The second method produces better results for large regions because the sparse codes of the patches are adapted according to the sparse codes of the boundary patches. Finally, we present and analyze experimental results that demonstrate the performance of our method compared to the literature

HSCT mission analysis of waverider designs

In the second quarter the development of the two waverider design tools was continued, and the groundwork necessary for the incorporation of waverider technology into the realm of the High Speed Civil Transports (HSCT's) was laid out. Advances in each of these areas is summarized. Work on the WIPAR code included the addition of an upper surface geometry generator and characteristic flow solver and the inclusion of viscous analysis in the performance computations. Details of these changes are given. In the course of the second project quarter, much of the analysis performed during the first quarter was incorporated into a working computer code. To date, utilities were developed for the definition of arbitrary 3-D shock surfaces, the computation of post-shock flow conditions, and the marching of the solution in a roughly cross-stream direction away from the shock surface. These utilities are briefly described. During the second quarter groundwork for the analysis of complete configurations was initiated. This involved the development of computational utilities for the integration of powerplants with the waverider forebodies, and the acquisition of a number of configuration analysis software packages. Work in these areas is discussed

Heat-transfer and pressure measurements on a simulated elevon deflected 30 deg near flight conditions at Mach 7

Heat transfer rates and pressures were obtained on an elevon plate (deflected 30 deg) and a flat plate upstream of the elevon in an 8 foot high-temperature structures tunnel. The flight Reynolds number and flight total enthalpy for altitudes of 26.8 km and 28.7 km at Mach seven were duplicated. The heat transfer and pressure data were used to establish heating and pressure loads. The measured heating was compared with several theoretical predictions, and the closest agreement obtained with a Schultz-Grunow reference enthalpy method of calculation

Some lessons learned with wind tunnels

A review is presented of some of the lessons learned from wind tunnel tests since World War II. Wind tunnels achieved a very high productivity rate during the war due in part to development testing of numerous military aircraft concepts. Following the war, in addition to development testing, a rapid increase in basic research testing occurred in order to explore areas of interest revealed by the conduct of war and to expand on advanced technology that became available from Germany and Italy. The research test areas discussed are those primarily related to the transition from subsonic flight to supersonic flight

Fairing-PIA: Progressive iterative approximation for fairing curve and surface generation

The fairing curves and surfaces are used extensively in geometric design, modeling, and industrial manufacturing. However, the majority of conventional fairing approaches, which lack sufficient parameters to improve fairness, are based on energy minimization problems. In this study, we develop a novel progressive-iterative approximation method for fairing curve and surface generation (fairing-PIA). Fairing-PIA is an iteration method that can generate a series of curves (surfaces) by adjusting the control points of B-spline curves (surfaces). In fairing-PIA, each control point is endowed with an individual weight. Thus, the fairing-PIA has many parameters to optimize the shapes of curves and surfaces. Not only a fairing curve (surface) can be generated globally through fairing-PIA, but also the curve (surface) can be improved locally. Moreover, we prove the convergence of the developed fairing-PIA and show that the conventional energy minimization fairing model is a special case of fairing-PIA. Finally, numerical examples indicate that the proposed method is effective and efficient.Comment: 21 pages, 10 figure

The Theory and Practice of Estimating the Accuracy of Dynamic Flight-Determined Coefficients

Means of assessing the accuracy of maximum likelihood parameter estimates obtained from dynamic flight data are discussed. The most commonly used analytical predictors of accuracy are derived and compared from both statistical and simplified geometrics standpoints. The accuracy predictions are evaluated with real and simulated data, with an emphasis on practical considerations, such as modeling error. Improved computations of the Cramer-Rao bound to correct large discrepancies due to colored noise and modeling error are presented. The corrected Cramer-Rao bound is shown to be the best available analytical predictor of accuracy, and several practical examples of the use of the Cramer-Rao bound are given. Engineering judgement, aided by such analytical tools, is the final arbiter of accuracy estimation