The Influence of Non-linear Longitudinal Aerodynamic Characteristics on the Power Spectral Response of Aircraft to Atmospheric Turbulence

1973 ◽  
Vol 24 (4) ◽  
pp. 284-294
Author(s):  
P A T Christopher ◽  
J M H Dunn
Keyword(s):  
Root Mean Square ◽  
Normal Force ◽  
Spectral Response ◽  
Aerodynamic Characteristics ◽  
Pitching Moment ◽  
Mean Square ◽  
Acceleration Response ◽  
Spectral Technique ◽  
Power Spectral ◽  
Normal Acceleration

SummaryThe power spectral technique has been extended to show the effect of aerodynamic non-linearities on the normal acceleration response of a rigid aircraft in the cruise configuration. Non-linearities in the normal force and pitching moment variations with incidence have been considered. The resulting changes from the linear root-mean-square values of normal acceleration were only 3 to 5½% for a root-mean-square vertical gust velocity of 20 m/s.

scholarly journals Validation of ESA Sentinel-2 L2A Aerosol Optical Thickness and Columnar Water Vapour during 2017–2018

2019 ◽  
Vol 11 (14) ◽  
pp. 1649 ◽  
Author(s):  
María Ángeles Obregón ◽  
Gonçalo Rodrigues ◽  
Maria Joao Costa ◽  
Miguel Potes ◽  
Ana Maria Silva
Keyword(s):  
Water Vapour ◽  
Root Mean Square ◽  
Optical Thickness ◽  
Spectral Response ◽  
Aerosol Optical Thickness ◽  
Mean Bias Error ◽  
Mean Square ◽  
Response Functions ◽  
Mean Square Errors ◽  
Sentinel 2

This study presents a validation of aerosol optical thickness (AOT) and integrated water vapour (IWV) products provided by the European Space Agency (ESA) from multi-spectral imager (MSI) measurements on board the Sentinel-2 satellite (ESA-L2A). For that purpose, data from 94 Aerosol Robotic Network (AERONET) stations over Europe and adjacent regions, covering a wide geographical region with a variety of climate and environmental conditions and during the period between March 2017 and December 2018 have been used. The comparison between ESA-L2A and AERONET shows a better agreement for IWV than the AOT, with normalized root mean square errors (NRMSE) of 5.33% and 9.04%, respectively. This conclusion is also reflected in the values of R2, which are 0.99 and 0.65 for IWV and AOT, respectively. The study period was divided into two sub-periods, before and after 15 January 2018, when the Sentinel-2A spectral response functions of bands 1 and 2 (centered at 443 and 492 nm) were updated by ESA, in order to investigate if the lack of agreement in the AOT values was connected to the use of incorrect spectral response functions. The comparison of ESA-L2A AOT with AERONET measurements showed a better agreement for the second sub-period, with root mean square error (RMSE) values of 0.08 in comparison with 0.14 in the first sub-period. This same conclusion was attained considering mean bias error (MBE) values that decreased from 0.09 to 0.01. The ESA-L2A AOT values estimated with the new spectral response functions were closer to the correspondent reference AERONET values than the ones obtained using the previous spectral response functions. IWV was not affected by this change since the retrieval algorithm does not use bands 1 and 2 of Sentinel-2. Additionally, an analysis of potential uncertainty sources to several factors affecting the AOT comparison is presented and recommendations regarding the use of ESA-L2A AOT dataset are given.

scholarly journals A minimal time-scale for the spectral states of GX 339−4

2020 ◽  
Vol 499 (2) ◽  
pp. 2513-2522
Author(s):  
E Sonbas ◽  
K Mohamed ◽  
K S Dhuga ◽  
A Tuncer ◽  
E Göğüş
Keyword(s):  
Black Hole ◽  
Root Mean Square ◽  
Time Scale ◽  
Power Spectra ◽  
Mean Square ◽  
X Ray ◽  
Minimal Time ◽  
Power Spectral ◽  
Power Spectral Densities ◽  
Spectral States

ABSTRACT Black hole transients are known to undergo spectral transitions that form q-shaped tracks on a hardness intensity diagram. In this work, we use the archival Rossi X-ray Timing Explorer data to extract a characteristic minimal time-scale for the spectral states in GX 339−4 for the 2002–2003 and 2010 outbursts. We use the extracted time-scale to construct an intensity variability diagram for each outburst. This new diagram is comparable to the traditional hardness intensity diagram and offers the potential for probing the underlying dynamics associated with the evolution of the relevant emission regions in black hole transients. We confirm this possibility by connecting the minimal time-scale with the inner disc radius, Rin (estimated from spectral fits), and demonstrate a positive correlation between these variables as the system evolves through its spectral transitions. Furthermore, we probe the relation between the minimal time-scale and the break frequencies extracted from the power spectral densities. Lastly, we examine a possible link between the extracted time-scale and a traditional measure of variability, i.e. the root mean square, determined directly from the power spectra.

scholarly journals Numerical Calculation of Effect of Elastic Deformation on Aerodynamic Characteristics of a Rocket

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Laith K. Abbas ◽  
Dongyang Chen ◽  
Xiaoting Rui
Keyword(s):  
Lift Force ◽  
Normal Force ◽  
Center Of Pressure ◽  
Aerodynamic Characteristics ◽  
Force Distribution ◽  
Pitching Moment ◽  
Flight Trajectory ◽  
Aerodynamic Coefficients ◽  
Computational Fluid Dynamics Cfd ◽  
Drag And Lift

The application and workflow of Computational Fluid Dynamics (CFD)/Computational Structure Dynamics (CSD) on solving the static aeroelastic problem of a slender rocket are introduced. To predict static aeroelastic behavior accurately, two-way coupling and inertia relief methods are used to calculate the static deformations and aerodynamic characteristics of the deformed rocket. The aerodynamic coefficients of rigid rocket are computed firstly and compared with the experimental data, which verified the accuracy of CFD output. The results of the analysis for elastic rocket in the nonspinning and spinning states are compared with the rigid ones. The results highlight that the rocket deformation aspects are decided by the normal force distribution along the rocket length. Rocket deformation becomes larger with increasing the flight angle of attack. Drag and lift force coefficients decrease and pitching moment coefficients increase due to rocket deformations, center of pressure location forwards, and stability of the rockets decreases. Accordingly, the flight trajectory may be affected by the change of these aerodynamic coefficients and stability.

scholarly journals TESTING, ANALYSIS AND COMPARISON FOR CHARACTERISTICS OF AGRICULTURAL FIELD AND ASPHALT ROAD ROUGHNESS

2020 ◽  
pp. 147-154
Author(s):  
Lijuan Wang ◽  
Jianguo Yan ◽  
Shengshi Xie ◽  
Chunguang Wang
Keyword(s):  
Spectral Density ◽  
Root Mean Square ◽  
Power Spectral Density ◽  
Mean Square ◽  
Agricultural Field ◽  
Power Spectral ◽  
Fitting Method ◽  
Density Fitting ◽  
Asphalt Road ◽  
Surface Profiles

Measuring and analysing the roughness of agricultural field and road have great significance for studying the characteristics of tractor dynamic response. This study was designed to analyse and compare the roughness characteristics of agricultural field and asphalt road profiles. A profiling apparatus was developed to measure field and road surface profiles of parallel tracks. The profile measurements were conducted in a grass field, a corn stubble field, a harvested potato field and on an asphalt road. The root mean square value and two spectrum parameters of surface profiles were calculated and analysed to investigate the roughness characteristics of fields and asphalt road. The results of the study indicate that for the values of the agricultural field and asphalt road surface roughness, waviness and roughness index are both positive associated with the root mean square value. Most of the waviness values of all measured field profiles were less than 2 with the average of 1.8, while the waviness values of all measured asphalt road profiles were greater than 2 with the average of 2.08. The roughness of both field and asphalt road profiles can be distinguished by the power spectral density fitting method. However, it has better performance in characterizing asphalt road profiles than characterizing field profiles with the power spectral density fitting method.

Subsonic Wing-Body Interference for Missile Configurations at Large Angles of Attack

1977 ◽  
Vol 28 (3) ◽  
pp. 163-175 ◽  
Author(s):  
K D Thomson
Keyword(s):  
Normal Force ◽  
Angle Of Attack ◽  
Aerodynamic Characteristics ◽  
The Body ◽  
Supporting Evidence ◽  
Pitching Moment ◽  
Aerodynamic Properties ◽  
Moment Estimates ◽  
Effective Angle ◽  
Series Of Experiments

SummaryAn approximate method is presented for estimating the normal-force and pitching-moment characteristics (including the effects of wing-body interference) of wings mounted on bodies. A pair of wings placed side by side can be specified which, when operating at a certain angle of attack different from the geometrical angle of attack, have the same aerodynamic properties as the wings in the presence of the body. The equivalent wings and effective angle of attack are determined, and these enable the wing-body normal force and pitching moment to be estimated for wing-body combinations at angles of attack up to 90°. Comparisons made with the results of a specially conducted series of experiments on rectangular and delta planform wing-body combinations have provided gratifying supporting evidence for the theory.Estimates are also made of the normal force and pitching moment produced by two cone-cylinder bodies over the angle of attack range 0° to 90°. These estimates, when added to the wing-body normal-force and pitching-moment estimates, have resulted in a set of longitudinal aerodynamic characteristics which are generally close to those found experimentally. The method appears to have application in the preliminary design phase for slewing missiles.

scholarly journals Transmission of lateral vibrations to children during car traveling and possibilities for their reduction

2019 ◽  
Vol 287 ◽  
pp. 03007
Author(s):  
Nikolay Pavlov ◽  
Evgeni Sokolov ◽  
Emil Iontchev ◽  
Rossen Miletiev ◽  
Mihail Peychev
Keyword(s):  
Root Mean Square ◽  
Tilt Angle ◽  
Lateral Acceleration ◽  
Mean Square ◽  
Special Design ◽  
Lateral Vibrations ◽  
Road Section ◽  
Power Spectral ◽  
Power Spectral Densities ◽  
Technical Solutions

The publication addresses the need for technical solutions to reduce the transmission of lateral vibrations to passengers, especially children traveling by car in a child seat. A special design of a pendulum type tilting child seat has been proposed. Results of road trial conducted on a specific mountain road section are shown. The differences in the values of lateral accelerations acting on a child traveling in a conventional and in a tilting seat are given. The power spectral densities of lateral accelerations for both types of child seats are presented and compared. The root mean square values of lateral acceleration are given. Results for the values of the seat tilt angle are presented.

scholarly journals The Silencing of U.S. Campuses Following the COVID-19 Response: Evaluating Root Mean Square Seismic Amplitudes Using Power Spectral Density Data

2021 ◽  
Author(s):  
David L. Guenaga ◽  
Omar E. Marcillo ◽  
Aaron A. Velasco ◽  
Chengping Chai ◽  
Monica Maceira
Keyword(s):  
Spectral Density ◽  
Root Mean Square ◽  
Power Spectral Density ◽  
Active Regions ◽  
The United States ◽  
School Closure ◽  
Mean Square ◽  
School Closures ◽  
Power Spectral ◽  
Seismic Amplitudes

Abstract In response to the COVID-19 global pandemic, many populated and active regions have become deserted and show significant reductions in their background seismicity, especially campuses across the United States (U.S.). Seismic sensors located in the vicinity of or within U.S. campuses show that anthropogenic seismic noise remains elevated during the ordinary, nonpandemic, academic year, only subduing during periods of recess (e.g., winter break). Here, we use power spectral density (PSD) data computed by the Incorporated Research Institutions for Seismology Data Management Center for quality assessment to calculate root mean square (rms) amplitude and analyze the effects of the COVID-19 school closures. We processed and analyzed PSD data for 46 seismic stations located within 50 m of a U.S. university or college. Results show that 42 campus stations show an overall rms drop following a statewide school closure.

scholarly journals Unsteady Aerodynamic Characteristics of Antenna Rotating in Different Elevation Angles

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Yanqi Zhang ◽  
Zhaoming Zhang
Keyword(s):  
Root Mean Square ◽  
Elevation Angle ◽  
Aerodynamic Characteristics ◽  
Experimental Results ◽  
Mean Square ◽  
Aerodynamic Coefficients ◽  
Servo Systems ◽  
Reduced Frequency ◽  
The Mean ◽  
Plate Antenna

The aerodynamic characteristics of radar antennas should be considered in computing their wind resistance and designing pedestal servo systems. In this paper, the aerodynamic characteristics of a flat plate antenna with azimuthal rotation are explored using a wind tunnel, and the effects of the antenna elevation angle and reduced frequency on the aerodynamic coefficients are analyzed. The corresponding results of numerical simulation are given to compare with the experimental results. The variation of aerodynamic coefficients with respect to the azimuth angle is found to depend on the reduced frequency and the antenna elevation angle. When the increase in antenna elevation angle is slight, the mean and root mean square values of the aerodynamic coefficients are not monotonic with respect to increases in elevation angle and may increase at individual elevation angles. When the elevation angle increases significantly, the mean, maximum, and root mean square values of the aerodynamic coefficients all significantly decrease. The simulation results are in good agreement with the experimental results, which verify the feasibility of using unsteady numerical simulations to obtain the flow field structure when the antenna is rotating. This approach allows the influence mechanism of the elevation angle change on the aerodynamic characteristics of the rotating antenna to be identified.

Sign in / Sign up

Export Citation Format

Share Document