scholarly journals Single-Doppler Retrieval of the Three-Dimensional Wind in a Deep Convective System Based on an Optimal Moving Frame of Reference

2007 ◽  
Vol 85 (5) ◽  
pp. 559-582 ◽  
Author(s):  
Yu-Chieng LIOU
Keyword(s):  
Three Dimensional ◽  
Frame Of Reference ◽  
Moving Frame ◽  
Convective System

Nonlinear cellular motions in Poiseuille channel flow

1974 ◽  
Vol 64 (2) ◽  
pp. 319-346 ◽  
Author(s):  
J.-P. Zahn ◽  
Juri Toomre ◽  
E. A. Spiegel ◽  
D. O. Gough
Keyword(s):  
Fourier Series ◽  
Steady State ◽  
Infinite System ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Single Mode ◽  
Frame Of Reference ◽  
Moving Frame ◽  
System Of Equations ◽  
Plane Poiseuille Flow

We expand the equations describing plane Poiseuille flow in Fourier series in the co-ordinates in the plane parallel to the bounding walls. There results an infinite system of equations for the amplitudes, which are functions of time and of the cross-stream co-ordinate. This system is drastically truncated and the resulting set of equations is solved accurately by a finite difference method. Three truncations are considered: (I) a single mode with dependence only on the downstream co-ordinate and time, (II) the mode of (I) plus its first harmonic, (III) a single three-dimensional mode. For all three cases, for a variety of initial conditions, the solutions evolve to a steady state as seen in a particular moving frame of reference. No runaways are encountered.

scholarly journals A Moving Frame Trajectory Tracking Method of a Flying-Wing UAV Using the Differential Geometry

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Yi Zhu ◽  
Xin Chen ◽  
Chuntao Li
Keyword(s):  
Flight Control ◽  
Trajectory Tracking ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Elliptic Cylinder ◽  
Dynamic Equations ◽  
Moving Frame ◽  
Moving Frames ◽  
Tracking Method ◽  
Tracking Process

The problem of UAV trajectory tracking is a difficult issue for scholars and engineers, especially when the target curve is a complex curve in the three-dimensional space. In this paper, the coordinate frames during the tracking process are transformed to improve the tracking result. Firstly, the basic concepts of the moving frame are given. Secondly the transfer principles of various moving frames are formulated and the Bishop frame is selected as a final choice for its flexibility. Thirdly, the detailed dynamic equations of the moving frame tracking method are formulated. In simulation, a moving frame of an elliptic cylinder helix is formulated precisely. Then, the devised tracking method on the basis of the dynamic equations is tested in a complete flight control system with 6 DOF nonlinear equations of the UAV. The simulation result shows a satisfactory trajectory tracking performance so that the effectiveness and efficiency of the devised tracking method is proved.

Effect of Ability on Twisting Techniques in Forward Somersaults on the Trampoline

1995 ◽  
Vol 11 (3) ◽  
pp. 267-287 ◽  
Author(s):  
Ross H. Sanders
Keyword(s):  
Dimensional Analysis ◽  
Twist Angle ◽  
Three Dimensional ◽  
Frame Of Reference ◽  
Flexion Angle ◽  
Lateral Flexion ◽  
Analysis Techniques ◽  
Half Twist

This study was designed to investigate the effect of ability on technique in the forward somersault with half twist (Barani) and the forward somersault with one and one half twists (Rudi) on the trampoline. Eleven trampolinists ranging in ability from elite (national representative) to early intermediate (regional representative) were analyzed using three-dimensional analysis techniques. Cumulative twist angle, rate of twist, angle of tilt of the twist axis, chest rotation, hip angle, and hip lateral flexion angle were measured. Characteristics of the arm actions were also assessed using an internal frame of reference. To generate twist in the Baranis, trampolinists tilted the axis between 5° and 14°; the amount of tilt was inversely related to ability (p < .05). In the Rudis, subjects tilted the axis between 15° and 23° using more asymmetrical arm actions and larger and more rapid hip extensions, hip lateral flexions, and chest rotations than in the Baranis. The timing and magnitude of the actions differed among the subjects and were related to ability.

Analysis of the Effect of Multirow and Multipassage Aerodynamic Interaction on the Forced Response Variation in a Compressor Configuration—Part I: Aerodynamic Excitation

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Harald Schoenenborn
Keyword(s):  
Three Dimensional ◽  
Forced Response ◽  
Frame Of Reference ◽  
Aerodynamic Damping ◽  
Aerodynamic Interaction ◽  
Blade Row ◽  
Random Mistuning ◽  
Compressor Map ◽  
Response Variation ◽  
Turbomachinery Design

The aeroelastic prediction of blade forcing is still a very important topic in turbomachinery design. Usually, the wake from an upstream airfoil and the potential field from a downstream airfoil are considered as the main disturbances. In recent years, it became evident that in addition to those two mechanisms, Tyler–Sofrin modes, also called scattered or spinning modes, may have a significant impact on blade forcing. It was recently shown in literature that in multirow configurations, not only the next but also the next but one blade row is very important as it may create a large circumferential forcing variation, which is fixed in the rotating frame of reference. In the present paper, a study of these effects is performed on the basis of a quasi three-dimensional (3D) multirow and multipassage compressor configuration. For the analysis, a harmonic balancing code, which was developed by DLR Cologne, is used for various setups and the results are compared to full-annulus unsteady calculations. It is shown that the effect of the circumferentially different blade excitation is mainly contributed by the Tyler–Sofrin modes and not to blade-to-blade variation in the steady flow field. The influence of various clocking positions, coupling schemes and number of harmonics onto the forcing is investigated. It is also shown that along a speed-line in the compressor map, the blade-to-blade forcing variation may change significantly. In addition, multirow flutter calculations are performed, showing the influence of the upstream and downstream blade row onto aerodynamic damping. The effect of these forcing variations onto random mistuning effects is investigated in the second part of the paper.

Cognitive Issues in Virtual Reality

1995 ◽  
Author(s):  
Christopher D. Wickens ◽  
Polly Baker
Keyword(s):  
Virtual Reality ◽  
Closed Loop ◽  
Three Dimensional ◽  
Open Loop ◽  
Frame Of Reference ◽  
Realistic View ◽  
Static Images ◽  
Sense Of Reality ◽  
Inside Out

Virtual reality involves the creation of multisensory experience of an environment (its space and events) through artificial, electronic means; but that environment incorporates a sufficient number of features of the non-artificial world that it is experienced as “reality.” The cognitive issues of virtual reality are those that are involved in knowing and understanding about the virtual environment (cognitive: to perceive and to know). The knowledge we are concerned with in this chapter is both short term (Where am I in the environment? What do I see? Where do I go and how do I get there?), and long term (What can and do I learn about the environment as I see and explore it?). Given the recent interest in virtual reality as a concept (Rheingold, 1991; Wexelblat, 1993; Durlach and Mavor, 1994), it is important to consider that virtual reality is not, in fact, a unified thing, but can be broken down into a set of five features, any one of which can be present or absent to create a greater sense of reality. These features consist of the following five points. 1. Three-dimensional (perspective and/or stereoscopic) viewing vs. two-dimensional planar viewing. (Sedgwick, 1986; Wickens et al., 1989). Thus, the geography student who views a 3D representation of the environment has a more realistic view than one who views a 2D contour map. 2. Dynamic vs. static display. A video or movie is more real than a series of static images of the same material. 3. Closed-loop (interactive or learner-centered) vs. open-loop interaction. A more realistic closed-loop mode is one in which the learner has control over what aspect of the learning “world” is viewed or visited. That is, the learner is an active navigator as well as an observer. 4. Inside-out (ego-referenced) vs. outside-in (world-referenced) frame-of-reference. The more realistic inside-out frame-of-reference is one in which the image of the world on the display is viewed from the perspective of the point of ego-reference of the user (that point which is being manipulated by the control). This is often characterized as the property of “immersion.” Thus, the explorer of a virtual undersea environment will view that world from a perspective akin to that of a camera placed on the explorer’s head;

Bow Echo Sensitivity to Ambient Moisture and Cold Pool Strength

2006 ◽  
Vol 134 (3) ◽  
pp. 950-964 ◽  
Author(s):  
Richard P. James ◽  
Paul M. Markowski ◽  
J. Michael Fritsch
Keyword(s):  
Convective Available Potential Energy ◽  
Three Dimensional ◽  
Cold Pool ◽  
Convective System ◽  
Cold Air ◽  
Convective Systems ◽  
Cold Pools ◽  
Bow Echo ◽  
Dry Conditions ◽  
Water Vapor Mixing Ratio

Abstract Bow echo development within quasi-linear convective systems is investigated using a storm-scale numerical model. A strong sensitivity to the ambient water vapor mixing ratio is demonstrated. Relatively dry conditions at low and midlevels favor intense cold-air production and strong cold pool development, leading to upshear-tilted, “slab-like” convection for various magnitudes of convective available potential energy (CAPE) and low-level shear. High relative humidity in the environment tends to reduce the rate of production of cold air, leading to weak cold pools and downshear-tilted convective systems, with primarily cell-scale three-dimensionality in the convective region. At intermediate moisture contents, long-lived, coherent bowing segments are generated within the convective line. In general, the scale of the coherent three-dimensional structures increases with increasing cold pool strength. The bowing lines are characterized in their developing and mature stages by segments of the convective line measuring 15–40 km in length over which the cold pool is much stronger than at other locations along the line. The growth of bow echo structures within a linear convective system appears to depend critically on the local strengthening of the cold pool to the extent that the convection becomes locally upshear tilted. A positive feedback process is thereby initiated, allowing the intensification of the bow echo. If the environment favors an excessively strong cold pool, however, the entire line becomes uniformly upshear tilted relatively quickly, and the along-line heterogeneity of the bowing line is lost.

scholarly journals The Impact of Covariance Localization for Radar Data on EnKF Analyses of a Developing MCS: Observing System Simulation Experiments

2013 ◽  
Vol 141 (11) ◽  
pp. 3691-3709 ◽  
Author(s):  
Ryan A. Sobash ◽  
David J. Stensrud
Keyword(s):  
System Simulation ◽  
Three Dimensional ◽  
Radar Data ◽  
Convective System ◽  
State Variables ◽  
Simulation Experiments ◽  
Length Scales ◽  
Convective Scale ◽  
The Impact ◽  
Prior State

Abstract Several observing system simulation experiments (OSSEs) were performed to assess the impact of covariance localization of radar data on ensemble Kalman filter (EnKF) analyses of a developing convective system. Simulated Weather Surveillance Radar-1988 Doppler (WSR-88D) observations were extracted from a truth simulation and assimilated into experiments with localization cutoff choices of 6, 12, and 18 km in the horizontal and 3, 6, and 12 km in the vertical. Overall, increasing the horizontal localization and decreasing the vertical localization produced analyses with the smallest RMSE for most of the state variables. The convective mode of the analyzed system had an impact on the localization results. During cell mergers, larger horizontal localization improved the results. Prior state correlations between the observations and state variables were used to construct reverse cumulative density functions (RCDFs) to identify the correlation length scales for various observation-state pairs. The OSSE with the smallest RMSE employed localization cutoff values that were similar to the horizontal and vertical length scales of the prior state correlations, especially for observation-state correlations above 0.6. Vertical correlations were restricted to state points closer to the observations than in the horizontal, as determined by the RCDFs. Further, the microphysical state variables were correlated with the reflectivity observations on smaller scales than the three-dimensional wind field and radial velocity observations. The ramifications of these findings on localization choices in convective-scale EnKF experiments that assimilate radar data are discussed.

Production and Analytics of a Multi-Linked Robotic System

2019 ◽  
Author(s):  
Thorstein R. Rykkje ◽  
Eystein Gulbrandsen ◽  
Andreas Fosså Hettervik ◽  
Morten Kvalvik ◽  
Daniel Gangstad ◽  
...  
Keyword(s):  
Equations Of Motion ◽  
Three Dimensional ◽  
Robotic System ◽  
Moving Frame ◽  
Moving Frames ◽  
New Approach ◽  
Lie Group Theory ◽  
Senior Design ◽  
Moving Frame Method ◽  
Frame Method

Abstract This paper extends research into flexible robotics through a collaborative, interdisciplinary senior design project. This paper deploys the Moving Frame Method (MFM) to analyze the motion of a relatively high multi-link system, driven by internal servo engines. The MFM describes the dynamics of the system and enables the construction of a general algorithm for the equations of motion. Lie group theory and Cartan’s moving frames are the foundation of this new approach to engineering dynamics. This, together with a restriction on the variation of the angular velocity used in Hamilton’s principle, enables an effective way of extracting the equations of motion. The result is a dynamic 3D analytical model for the motion of a snake-like robotic system, that can take the physical sizes of the system and return the dynamic behavior. Furthermore, this project builds a snake-like robot driven by internal servo engines. The multi-linked robot will have a servo in each joint, enabling a three-dimensional movement. Finally, a test is performed to compare if the theory and the measurable real-time results match.

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