scholarly journals Improving a real-time helicopter simulator model with linear input filters

2021 ◽  
Author(s):  
Pavle Šćepanović ◽  
Frederik A. Döring
Keyword(s):  
Feedback Control ◽  
Time Domain ◽  
Flight Test ◽  
Flight Mechanics ◽  
Mean Square ◽  
Qualification Test ◽  
Model Inversion ◽  
Helicopter Flight ◽  
The Time Domain ◽  
Mean Square Errors

AbstractFor a broad range of applications, flight mechanics simulator models have to accurately predict the aircraft dynamics. However, the development and improvement of such models is a difficult and time consuming process. This is especially true for helicopters. In this paper, two rapidly applicable and implementable methods to derive linear input filters that improve the simulator model are presented. The first method is based on model inversion, the second on feedback control. Both methods are evaluated in the time domain, compared to recorded helicopter flight test data, and assessed based on root mean square errors and the Qualification Test Guide bounds. The best results were achieved when using the first method.

3D time-domain airborne electromagnetic inversion based on secondary field finite-volume method

Geophysics ◽  
2018 ◽  
Vol 83 (4) ◽  
pp. E219-E228 ◽  
Author(s):  
Xiuyan Ren ◽  
Changchun Yin ◽  
James Macnae ◽  
Yunhe Liu ◽  
Bo Zhang
Keyword(s):  
Finite Volume ◽  
Time Domain ◽  
High Efficiency ◽  
Background Field ◽  
Field Method ◽  
Secondary Field ◽  
Model Inversion ◽  
Airborne Electromagnetic ◽  
The Time Domain ◽  
Volume Method

We investigate an algorithm for 3D time-domain airborne electromagnetic (AEM) inversion based on the finite-volume (FV) method and direct Gauss-Newton optimization, where we obtain high efficiency by constraining the modeling volume to the AEM volume of influence (VOI) of a 3D source within the earth, rather than using the larger VOI of the AEM system. A half-space or layered earth is used to model the background field in the time domain, taking into account the transmitter waveform through convolution. Assuming that the 3D source of any secondary field detected at a survey point lies within the moving VOI of the airborne system, we conduct time-domain forward modeling and Jacobian calculation using an FV method within the 3D source VOI that requires a small number of cells for discretization. A local mesh and direct solver are shown to further speed up the computation. A synthetic isolated synclinal conductor inversion shows good agreement with the model geometry and provides a good fit to the data contaminated with noise. A synthetic multiple-body model inversion was also quite successful, showing that our algorithm is effective and about four times faster than inversion using the total-field method. Finally, we inverted GEOTEM data over the Lisheen deposit, where our inversion result was consistent with the published geology.

An Optimized Combination of Frequency Domain Adaptive Equalizers

2014 ◽  
Vol 548-549 ◽  
pp. 766-770
Author(s):  
Ke Cheng Leng ◽  
Cheng Bie ◽  
Xi Gong ◽  
Ran Xu ◽  
Ye Cai Guo
Keyword(s):  
Frequency Domain ◽  
Mean Square Error ◽  
Time Domain ◽  
Blind Equalization ◽  
Mean Square ◽  
Constant Modulus ◽  
Equalization Algorithm ◽  
Adaptive Equalizers ◽  
Simulation Results ◽  
The Time Domain

In order to overcome the defects of the high computational loads and selecting the threshold of mean square error (MSE) for time domain decision-directed constant modulus blind equalization algorithm (DD+CMA), a frequency domain parallel decision multi-modulus blind equalization algorithm based on frequency domain MMA(FMMA) and frequency domain LMS (FLMS) algorithm is proposed. The proposed algorithm is composed of the FMMA and FLMS, and the FMMA and FLMS run automatically in soft switching parallel manner. In running process, it is not necessary to selecting the threshold of the MSE. Moreover, the computational loads can be reduced by circular convolution in the frequency domain signals instead of linear one of the time domain signals. Simulation results show that performance of the proposed algorithm outperforms the FLMS and the FMMA algorithm.

Dynamics of Half-Car Models Under Stochastic Road Excitations

2003 ◽  
Author(s):  
Walter V. Wedig
Keyword(s):  
Time Delay ◽  
Time Domain ◽  
Time Delays ◽  
Noise Filtering ◽  
Mean Square ◽  
Symbolic Programming ◽  
Software Packages ◽  
Road Surfaces ◽  
Programming Software ◽  
The Time Domain

The vertical dynamics of half car models riding on irregular road surfaces is characterized by base excitations with time delays determined by the ratio of the car speed and the axle distance between front and rear wheels. Root mean square values of the stationary car vibrations are analytically investigated to derive closed-form results by means of symbolic programming software packages. In particular, the paper discusses modelling aspects when noise filtering and time-delay shifts are interchanged in order to obtain more simple calculations in the frequency domain and in the time domain, as well.

Generalized Aerodynamic Modeling of Dynamic Wake Curvature for Open Rotors With Slender Blades

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Ioannis Goulos
Keyword(s):  
Fluid Mechanics ◽  
Vortex Tube ◽  
Flight Test ◽  
Accurate Method ◽  
Flight Mechanics ◽  
Theoretical Development ◽  
Small Scale ◽  
Helicopter Flight ◽  
Transient Control ◽  
Control Response

This paper elaborates on the theoretical development of an analytical approach, capable of modeling the effect of dynamic wake curvature on the aeroelastic response of open rotors with slender blades. The classical solution of incompressible, potential flow derived for a curved vortex tube of uniform vorticity strength is employed. The previously developed curved vortex tube analysis is mathematically generalized to account for arbitrary radial and circumferential variations of circulatory disk loading. An orthogonality analysis is carried out to obtain a finite set of inflow perturbation coefficients that describe the aerodynamic effect of wake curvature in a generalized manner. The end result is a set of integral expressions that provide the interharmonic coupling between the inflow perturbations on the rotor disk due to a curved trailing wake and the corresponding variations of disk loading. The obtained perturbation coefficients are subsequently superimposed upon an existing finite-state induced flow model that assumes a skewed, noncurved cylindrical wake. The developed mathematical approach for fluid mechanics is coupled with an unsteady blade element aerodynamics model, a rotor blade structural mechanics model, and a nonlinear rotor dynamics model. The combined formulation is implemented in an existing helicopter flight mechanics code. The overall method is initially employed to assess the effect of wake curvature on the dynamic response of a small-scale articulated rotor with a flap frequency ratio equal to unity. Subsequently, the integrated model is deployed to investigate the influence of wake curvature and inflow modeling fidelity on the predicted oscillatory blade loads and transient control response of a full-scale helicopter rotor. Comparisons are carried out with flight test measurements as well as with complex free-wake analysis methods. It is shown that including the effect of wake curvature is essential for predicting the transient control response of the investigated rotor. Good agreement is demonstrated between the proposed analytical model and nonlinear predictions carried out by resolving the complex wake geometry. The developed fluid mechanics formulation is a time-accurate method derived from first-principles and is applicable to both axial and nonaxial flow conditions.

scholarly journals Development of a hand-held magnetic resonance sensor for the nondestructive quantification of fat and lean meat of fresh tuna

2020 ◽  
Vol 14 (6) ◽  
pp. 2947-2955
Author(s):  
Yoshito Nakashima
Keyword(s):  
Magnetic Resonance ◽  
Root Mean Square ◽  
Time Domain ◽  
Subcutaneous Fat ◽  
Mean Square ◽  
Fat Quantification ◽  
Lean Meat ◽  
Root Mean Square Residual ◽  
Resonance Sensor ◽  
The Time Domain

Abstract For the in-situ nondestructive fat quantification of fresh tuna meat, an original lightweight (5.7 kg) hand-held sensor that consists of a planar radio-frequency coil and a single-sided magnetic circuit was developed as a subunit of a time-domain proton magnetic resonance (MR) scanner system. The investigation depth of the sensor unit is 12 mm, which is sufficient to probe the meat section beneath thick skin with scales and the underlying subcutaneous fat layer of large fish such as tuna. The scanner was successfully applied in a laboratory to a fillet of a bluefin tuna (Thunnus thynnus) to measure meat sections 12 mm beneath the skin. The required measurement time was 100 s for each section. The results of MR scan at 11 locations on the fillet were compared with those of conventional destructive food analysis. Reasonable agreement with an error (root-mean-square residual) of as small as 1.8 wt% was obtained for fat quantification. The time-domain MR relaxometry for the same tuna fillet also allowed lean meat quantification with a small root-mean-square residual of 6.7 wt%.

Apodisation in the time domain

1992 ◽  
Vol 2 (4) ◽  
pp. 615-620
Author(s):  
G. W. Series
Keyword(s):  
Time Domain ◽  
The Time Domain

JOINT INTERPRETATION OF AIRBORNE ELECTROMAGNETIC DATA IN THE TIME DOMAIN AND FREQUENCY DOMAIN

2018 ◽  
Vol 12 (7-8) ◽  
pp. 76-83
Author(s):  
E. V. KARSHAKOV ◽  
J. MOILANEN
Keyword(s):  
Fourier Transform ◽  
Frequency Domain ◽  
Time Domain ◽  
Frequency Interval ◽  
Single Spectrum ◽  
Simultaneous Inversion ◽  
Homogeneous Half Space ◽  
Time Domain Data ◽  
The Time Domain

Тhe advantage of combine processing of frequency domain and time domain data provided by the EQUATOR system is discussed. The heliborne complex has a towed transmitter, and, raised above it on the same cable a towed receiver. The excitation signal contains both pulsed and harmonic components. In fact, there are two independent transmitters operate in the system: one of them is a normal pulsed domain transmitter, with a half-sinusoidal pulse and a small "cut" on the falling edge, and the other one is a classical frequency domain transmitter at several specially selected frequencies. The received signal is first processed to a direct Fourier transform with high Q-factor detection at all significant frequencies. After that, in the spectral region, operations of converting the spectra of two sounding signals to a single spectrum of an ideal transmitter are performed. Than we do an inverse Fourier transform and return to the time domain. The detection of spectral components is done at a frequency band of several Hz, the receiver has the ability to perfectly suppress all sorts of extra-band noise. The detection bandwidth is several dozen times less the frequency interval between the harmonics, it turns out thatto achieve the same measurement quality of ground response without using out-of-band suppression you need several dozen times higher moment of airborne transmitting system. The data obtained from the model of a homogeneous half-space, a two-layered model, and a model of a horizontally layered medium is considered. A time-domain data makes it easier to detect a conductor in a relative insulator at greater depths. The data in the frequency domain gives more detailed information about subsurface. These conclusions are illustrated by the example of processing the survey data of the Republic of Rwanda in 2017. The simultaneous inversion of data in frequency domain and time domain can significantly improve the quality of interpretation.

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