Vibration Characteristics of Unsaturated Runways Under Moving Aircraft Loads

2021 ◽  
pp. 2150065
Author(s):  
Chuxuan Tang ◽  
Zheng Lu ◽  
Hailin Yao ◽  
Shuan Guo ◽  
Yukun Han
Keyword(s):  
Fourier Transform ◽  
Critical Speed ◽  
Vertical Displacement ◽  
Elastic Base ◽  
Governing Equations ◽  
Soil Saturation ◽  
Double Fourier Transform ◽  
Base Course ◽  
Airport Runway ◽  
Aircraft Loads

The dynamic vibrations of airport runways induced by moving aircraft loads are semi-analytically studied in this paper. The airport runway consists of an infinite Kirchhoff plate, an elastic base course, and an unsaturated poroelastic half-space. The aircraft loads are modeled according to the mechanical properties of the main landing gear of the A380 civil airliner. The governing equations of the whole system are solved in the wavenumber domain using the double Fourier transform. Then the results in the spatial domain are obtained by applying the inverse double Fourier transform. Various parameters including the observation location, soil saturation, load speed, load frequency, and pavement rigidity on the vibration characters of the whole system are investigated. It is found that all these effects are crucial, and the increase of soil saturation leads to a larger maximum vertical displacement and lower critical speed.

scholarly journals Mechanical Property Analysis of Circular Polymer Membrane under Uniform Pressure

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Sang Jianbing ◽  
Li Xiang ◽  
Xing Sufang ◽  
Wang Wenjia
Keyword(s):  
Mechanical Property ◽  
Polymer Material ◽  
Vertical Displacement ◽  
Polymer Membrane ◽  
Constitutive Parameter ◽  
Deformation Analysis ◽  
Strengthening Effect ◽  
Uniform Pressure ◽  
Governing Equations ◽  
Property Analysis

Mechanical property analysis of circular hyperelastic polymer membrane under uniform pressure has been researched in this work. The polymer membrane material is assumed to be homogeneous and isotropic and incompressibility of materials has been considered. Based on the modified stain energy function from Gao and nonmomental theory of axial symmetry thin shell, finite deformation analysis of polymer membrane under uniform pressure has been proposed in current configuration and governing equations of polymer membrane have been achieved. By utilizing the boundary condition, theoretical results of governing equations have been obtained and vertical displacement distribution and stress distribution have been achieved. The results show that the constitutive parameternhas a strengthening effect on the polymer material and the constitutive parameterαplays a controlling role for the second strain invariantI2, which also has a strengthening effect on the polymer material. This research has revealed the deformational mechanism of polymer membrane and provided reference for the design of polymer membrane.

An automatic means to discriminate between earthquakes and quarry blasts

1990 ◽  
Vol 80 (6B) ◽  
pp. 2143-2160
Author(s):  
Michael A. H. Hedlin ◽  
J. Bernard Minster ◽  
John A. Orcutt
Keyword(s):  
Fourier Transform ◽  
Spectral Features ◽  
Single Event ◽  
Vertical Array ◽  
Signal To Noise ◽  
Spectral Character ◽  
Frequency Pattern ◽  
Time Frequency ◽  
Cepstral Analysis ◽  
Double Fourier Transform

Abstract In this article we discuss our efforts to use the NORESS array to discriminate between regional earthquakes and ripple-fired quarry blasts (events that involve a number of subexplosions closely grouped in space and time). The method we describe is an extension of the time versus frequency “pattern-based” discriminant proposed by Hedlin et al. (1989b). At the heart of the discriminant is the observation that ripple-fired events tend to give rise to coda dominated by prominent spectral features that are independent of time and periodic in frequency. This spectral character is generally absent from the coda produced by earthquakes and “single-event” explosions. The discriminant originally proposed by Hedlin et al. (1989b) used data collected at 250 sec−1 by single sensors in the 1987 NRDC network in Kazakhstan, U.S.S.R. We have found that despite the relatively low digitization rate provide by the NORESS array (40 sec−1) we have had good success in our efforts to discriminate between earthquakes and quarry blasts by stacking all vertical array channels to improve signal-to-noise ratios. We describe our efforts to automate the method, so that visual pattern recognition is not required, and to make it less susceptible to spurious time-independent spectral features not originating at the source. In essence, we compute a Fourier transform of the time-frequency matrix and examine the power levels representing energy that is periodic in frequency and independent of time. Since a double Fourier transform is involved, our method can be considered as an extension of “cepstral” analysis (Tribolet, 1979). We have found, however, that our approach is superior since it is cognizant of the time independence of the spectral features of interest. We use earthquakes to define what cepstral power is to be expected in the absence of ripple firing and search for events that violate this limit. The assessment of the likelihood that ripple firing occurred at the source is made automatically by the computer and is based on the extent to which the limit is violated.

Comparison among Several Numerical Integration Methods for Kramers-Kronig Transformation

1988 ◽  
Vol 42 (6) ◽  
pp. 952-957 ◽  
Author(s):  
Koji Ohta ◽  
Hatsuo Ishida
Keyword(s):  
Fourier Transform ◽  
Numerical Integration ◽  
Spectral Data ◽  
Analytical Formula ◽  
Computation Time ◽  
The Other ◽  
Integration Methods ◽  
Fourier Transform Methods ◽  
Double Fourier Transform ◽  
Numerical Integration Methods

Several numerical integration methods are compared in order to search out the most effective method for the Kramers-Kronig transformation, using the analytical formula of the Kramers-Kronig transformation of a Lorentzian function as a reference. The methods to be compared involve the use of (1) Maclaurin's formula, (2) trapezium formula, (3) Simpson's formula, and (4) successive double Fourier transform methods. It is found that Maclaurin's formula, in which no special approximation is necessary for the pole part of the integration, gives the most accurate results, and also that its computation time is short. Successive Fourier transform is less accurate than the other methods, but it takes the least time when used without zero-filling. These results have important relevance for programs used to obtain optical constant spectra and to analyze spectral data.

scholarly journals Analytical Solutions for Steady-State Multiwell Aquifer Tests in Rectangular Aquifers by Using Double Fourier Transform: A Case Study in the Ordos Plateau, China

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Jun-Zhi Wang ◽  
Xu-Sheng Wang ◽  
Qing-Bo Li ◽  
Wei-Feng Wan
Keyword(s):  
Fourier Transform ◽  
Steady State ◽  
Analytical Solutions ◽  
Estimation Method ◽  
Least Square ◽  
Ordos Plateau ◽  
Aquifer Systems ◽  
Aquifer Test ◽  
Double Fourier Transform

Straightforward solutions have long been expected for the analysis of multiwell aquifer tests. In this paper, we derive series analytical solutions of steady-state groundwater flow in a rectangular-shaped aquifer with pumping/injection wells for both confined and unconfined conditions. Double Fourier Transform (DFT) technique is applied to deal with different combinations of impermeable and specified head boundaries on sides. The obtained solutions are compact and concise in mathematics and flexible in terms of well number, well locations, and pumping/injection rates. Hatoucaidang, a groundwater resource field in the Ordos Plateau, Northwestern China, is introduced as a field case study, where a multiwell aquifer test was conducted. One of the analytical solutions derived herein is used to estimate hydraulic conductivities by applying a direct calculation method and a least square estimation method regarding observed versus calculated drawdowns. By comparing with nearby single-well pumping tests, the reliability of the derived analytical solutions is proven. This study facilitates utilizing the multiwell aquifer test to analyze the general behavior of groundwater movement in aquifer systems.

Implementing Fuzzy Logic in the Control of a Biologically Inspired Robotic Cat Leg

2008 ◽  
Author(s):  
Anthony L. Crawford ◽  
Dean B. Edwards
Keyword(s):  
Fuzzy Logic ◽  
Fuzzy Logic Control ◽  
Pid Controller ◽  
Vertical Displacement ◽  
Skeletal Structure ◽  
Governing Equations ◽  
Biologically Inspired ◽  
Logic Control ◽  
Forcing Function ◽  
Force Range

This research discusses the implementation of a fuzzy logic control system to drive the movement of a simplified cat leg model. The system’s movement in this paper addresses a planar motion where the model experiences a fixed horizontal velocity and a harmonic vertical displacement. The fuzzy logic (FL) controller applies membership functions to fuzzify the position and velocity errors and applies height defuzzification to generate the time dependant forcing function for the system’s horizontal and vertical governing equations. A PID controller is also applied as a benchmark for this research. Both controllers are optimized using the simplex method for which the FL controller performed just as well as the PID controller with more promise of accounting for the nonlinear influences that were neglected in this simplified cat leg model and requiring actuators with a lower required force range. This research provides the skeletal structure for which an effective total controller can be built on.

Steady-State Dynamic Response of a Bernoulli–Euler Beam on a Viscoelastic Foundation Subject to a Platoon of Moving Dynamic Loads

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Lu Sun ◽  
Feiquan Luo
Keyword(s):  
Dynamic Response ◽  
Critical Speed ◽  
Complex Function ◽  
Vertical Displacement ◽  
Dynamic Loads ◽  
Dimensionless Frequency ◽  
Vertical Acceleration ◽  
Viscoelastic Foundation ◽  
Efficient Computation ◽  
Euler Beam

A Bernoulli–Euler beam resting on a viscoelastic foundation subject to a platoon of moving dynamic loads can be used as a physical model to describe railways and highways under traffic loading. Vertical displacement, vertical velocity, and vertical acceleration responses of the beam are initially obtained in the frequency domain and then represented as integrations of complex function in the space-time domain. A bifurcation is found in critical speed against resonance frequency. When the dimensionless frequency is high, there is a single critical speed that increases as the dimensionless frequency increases. When the dimensionless frequency is low, there are two critical speeds. One speed increases as the dimensionless frequency increases, while the other speed decreases as the dimensionless frequency decreases. Based on the fast Fourier transform, numerical methods are developed for efficient computation of dynamic response of the beam.

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