The Analysis of Dynamic Stresses in Aircraft Structures During Landing as Nonstationary Random Processes

1955 ◽  
Vol 22 (4) ◽  
pp. 449-457
Author(s):  
Y. C. Fung
Keyword(s):  
Maximum Stress ◽  
Impact Load ◽  
Bending Moment ◽  
Random Processes ◽  
Dynamic Loads ◽  
Dynamic Stresses ◽  
Nonstationary Random Process ◽  
Time Histories ◽  
Drop Tests ◽  
The Mean

Abstract The basic fact is recognized that throughout the service life of an airplane there occurs a variety of landing conditions and, consequently, it is subjected to transient dynamic loads of varied time histories. Accordingly, a statistical analysis is proposed. The landing-gear impact load is regarded as a nonstationary random process. In this paper the ensemble means and the correlation functions of landing impacts are defined and their experimental determination from flight or drop tests is illustrated. From these the mean response (displacement, bending moment, shear, or stress), the root mean square deviation from the mean, and higher statistical moments are computed. The results are used to find the most probable maximum stress (at any point in the structure) attained in a given number of landings, or the most probable total number of landings a given aircraft can withstand. A stress envelope can be derived which represents the distribution of the severest stress in the structure for a large number of landings. A design based on such an envelope, statistically, will have a uniform factor of safety over the entire aircraft with respect to landings.

Analysis of the Nonstationary Response of Vehicles With Multiple Wheels

1986 ◽  
Vol 108 (1) ◽  
pp. 69-73 ◽  
Author(s):  
R. F. Harrison ◽  
J. K. Hammond
Keyword(s):  
Random Processes ◽  
Time Variable ◽  
Variable Delay ◽  
Excitation Process ◽  
Nonstationary Random Process ◽  
Nonstationary Response ◽  
The Mean ◽  
Autocovariance Matrix ◽  
Ground Profile ◽  
Mean Vector

Vehicles moving on rough surfaces are subject to inputs which are often conveniently regarded as random processes. In general, the excitation process is “perceived” by the vehicle as a nonstationary random process either due to inhomogeneity in the ground profile or variations in the vehicle’s velocity, or both, Hitherto this second case has not been tractable analytically due to the time variable delay between inputs. In this paper this difficulty is overcome and expressions are derived for the propagation of the mean vector and zero-lag autocovariance matrix. An example of a vehicle modelled by a bicycle configuration is discussed.

Effects of Moving Speeds of Dynamic Loads on the Deflections of Gear Teeth

1981 ◽  
Vol 103 (2) ◽  
pp. 357-363 ◽  
Author(s):  
K. Nagaya ◽  
S. Uematsu
Keyword(s):  
Dynamic Response ◽  
Timoshenko Beam ◽  
Gear Tooth ◽  
Bending Moment ◽  
Dynamic Loads ◽  
Gear Teeth ◽  
Moving Speed

For the dynamic response problems of gear teeth, the dynamic loads which act upon the gear teeth should be considered as a function of both the position and the moving speed. In previous studies, the effects of the moving speed have not been considered. In this paper the effects of the moving speed of dynamic loads on the deflection and the bending moment of the gear tooth are investigated. The results are obtained from the elastodynamic analysis of the tapered Timoshenko beam.

scholarly journals Numerical Simulation of Dynamic Response and Evaluation of Flexural Damage of RC Columns under Horizontal Impact Load

2021 ◽  
Vol 11 (23) ◽  
pp. 11223
Author(s):  
Bin Hu ◽  
Jian Cai ◽  
Jiabin Ye
Keyword(s):  
Static Load ◽  
Impact Load ◽  
Bending Moment ◽  
Internal Force ◽  
Displacement Curve ◽  
Fe Model ◽  
Damage State ◽  
Rc Columns ◽  
Equivalent Static Load ◽  
The Impact

By using the ABAQUS finite element (FE) model, which has been verified by experiments, the deformation and internal force changes of RC columns during the impact process are investigated, and a parametric analysis is conducted under different impact kinetic energies Ek. According to the development path of the bottom bending moment-column top displacement curve under impact, the member is in a slight damage state when the curve rebounds before reaching the peak and in a moderate or severe damage state when the curve exceeds the peak, in which case the specific damage state of the member needs to be determined by examining whether there is a secondary descending stage in the curve. Accordingly, a qualitative method for evaluating the bending failure of RC column members under impact is obtained. In addition, the damage state of RC columns under impact can also be quantitatively evaluated by the ratio of the equivalent static load Feq and the ultimate static load-bearing capacity Fsu.

scholarly journals ‘Hardcastle Hollows’ in loess landforms: Closed depressions in aeolian landscapes – in a geoheritage context

2018 ◽  
Vol 10 (1) ◽  
pp. 58-63
Author(s):  
Roger Fagg ◽  
Ian Smalley
Keyword(s):  
Monte Carlo ◽  
Random Processes ◽  
Ground Subsidence ◽  
Shape Classification ◽  
Random Shape ◽  
Side Ratio ◽  
Landscape Processes ◽  
Stage Process ◽  
The Mean ◽  
Loess Deposits

Abstract Loess landscapes sometimes contain isolated depressed areas, which often appear as lakes. The outline shape (and distribution) of these depressions could be controlled by random processes, particularly if the depressions are caused by loess hydroconsolidation and ground subsidence. By applying the Zingg system of shape classification it is possible to propose a mean random shape for the closed depressions. A Zingg rectangle with a side ratio of about 2:1 is produced by a very simple Monte Carlo method, which had been used previously to calculate the mean random shape of a loess particle. The Zingg rectangle indicates the basic shape of the mean closed depression. A simple four stage process for the formation of the depressions is proposed. They might be called ‘Hardcastle Hollows’ in honour of John Hardcastle who first reported them, in New Zealand. Studies on Ukrainian deposits suggest that there might be some stratigraphic value in the observation of closed depressions; they are often not superimposed in successive depositions of loess. Hydroconsolidation is important in landscape processes. The hollows provide interesting habitats and enlarge the ecological interest of loess deposits; the geoheritage scene is enhanced.

On Dynamic Fracture of Rock Under Bit Impact Loads

1982 ◽  
Vol 104 (2) ◽  
pp. 105-107 ◽  
Author(s):  
I. E. Eronini
Keyword(s):  
Rock Fracture ◽  
Laboratory Data ◽  
Essential Elements ◽  
Dynamic Force ◽  
Rock Face ◽  
Time Histories ◽  
Drop Tests ◽  
Force Time ◽  
Indiana Limestone

A characterization of the dynamic interaction between an impacting tool and rock is presented. The analysis is based on the concept of rock fracture energy and on simple representations of the amount of fracturing and energy storage in the rock during fracture propagation. The governing equations are not complicated. They contain a small number of parameters and impose minimum restrictions on the form or sophistication of the model of the impacting tool. Simulation results are shown for bit-tooth drop tests on Indiana limestone under different values of the differential pressure across the rock face and for various heights of drop. The predicted dynamic force-penetration curves, force-time, displacement-time and velocity-time histories agree well with reported Laboratory data and demonstrate that the essential elements of tooth drop loading are adequately represented by the model.

Aerodynamic Forces on Multiple Unit Trains in Cross Winds

2009 ◽  
Vol 131 (10) ◽  
Author(s):  
Christopher J. Baker ◽  
Mark Sterling
Keyword(s):  
Pressure Fluctuations ◽  
Decomposition Analysis ◽  
Aerodynamic Characteristics ◽  
Scale Model ◽  
Fluctuating Pressure ◽  
Time Histories ◽  
Multiple Unit ◽  
The Mean ◽  
Proper Orthogonal ◽  
Natural Wind

This paper describes the results of wind tunnel tests that were carried out to measure the aerodynamic characteristics of an electrical multiple unit (EMU) vehicle in a cross wind. The measurements were made on a 1/30 scale model of the Class 365 EMU in a simulation of the natural wind. The time histories of surface pressures were measured at a large number of points over the vehicle from which the aerodynamic characteristics and force coefficients were determined. This paper describes the complex fluctuating pressure field over the vehicle, through a consideration of the mean and fluctuating pressure coefficients and their spectra, and through a proper orthogonal decomposition analysis, which identifies the major modes of this distribution. The mean, fluctuating, and extreme aerodynamic side and lift forces are also discussed. It is shown that the flow pattern around the vehicle is dominated by large windward roof corner pressure fluctuations.

Study on Dynamic Response of Hollow Pile Using the Method of Composite Stiffness Principle and Biparameter

2011 ◽  
Vol 243-249 ◽  
pp. 2679-2683
Author(s):  
Yong Mou Zhang ◽  
Min Yang ◽  
Qiang Gang Yan
Keyword(s):  
Dynamic Load ◽  
Bending Moment ◽  
Dynamic Loads ◽  
Concrete Pile ◽  
Side Resistance ◽  
Geological Conditions ◽  
Internal Forces ◽  
The Finite Difference Method ◽  
Composite Stiffness ◽  
Laterally Loaded

The method of composite stiffness principle and biparameter for laterally loaded pile was used in this paper to calculate the amplitude of deflection and rotation of pile on the ground when the vibration frequency of dynamic load is equal to or close to the natural frequency of pile, i.e. when the pile is in the state of resonance. And the amplitude of the maximum bending moment and its location was also calculated. Then the finite difference method which is simple in principle and easy to program was used to calculate the displacement, soil side resistance and internal forces of pile under horizontal dynamic load. By choosing reasonable parameters, rotation, displacement, and the maximum bending moment of hollow concrete pile and solid pile under the same dynamic loads at pile top in the same geological conditions were calculated respectively. On this basis, the performance differences between hollow pile and solid pile were analyzed. Some advantages of hollow pile were obtained. This research provides a theoretical guidance for the using of hollow pile in engineering.

Multiharmonic Forced Response Analysis of a Turbine Blading Coupled by Nonlinear Contact Forces

2010 ◽  
Vol 132 (8) ◽  
Author(s):  
Christian Siewert ◽  
Lars Panning ◽  
Jörg Wallaschek ◽  
Christoph Richter
Keyword(s):  
Frequency Domain ◽  
Nonlinear Equations ◽  
Forced Response ◽  
Vibration Response ◽  
Contact Forces ◽  
Dynamic Loads ◽  
Response Analysis ◽  
Dynamic Stresses ◽  
Nonlinear Contact ◽  
Turbine Blading

In turbomachinery applications, the rotating turbine blades are subjected to high static and dynamic loads. The static loads are due to centrifugal stresses and thermal strains whereas the dynamic loads are caused by the fluctuating gas forces resulting in high vibration amplitudes, which can lead to high cycle fatigue failures. Hence, one of the main tasks in the design of turbomachinery blading is the reduction in the blade vibration amplitudes to avoid high dynamic stresses. Thus, coupling devices like underplatform dampers and tip shrouds are applied to the blading to reduce the vibration amplitudes and, therefore, the dynamic stresses by introducing nonlinear contact forces to the system. In order to predict the resulting vibration amplitudes, a reduced order model of a shrouded turbine blading is presented including a contact model to determine the nonlinear contact forces. To compute the forced response, the resulting nonlinear equations of motion are solved in the frequency domain using the multiharmonic balance method because of the high computational efficiency of this approach. The transformation from the time domain into the frequency domain is done by applying Galerkin’s method in combination with a multiharmonic approximation function for the unknown vibration response. This results in an algebraic system of nonlinear equations in the frequency domain, which has to be solved iteratively in order to compute the vibration response. The presented methodology is applied to the calculation of the forced response of a nonlinear coupled turbine blading in the frequency domain.

Rollover Analysis of Heavy Vehicle Bus

2014 ◽  
Vol 660 ◽  
pp. 633-636 ◽  
Author(s):  
Mohd Khir Mohd Nor ◽  
Muhammad Zulhusmi Dol Baharin
Keyword(s):  
Maximum Stress ◽  
Motor Vehicle ◽  
Motor Vehicle Accident ◽  
Impact Load ◽  
Heavy Vehicle ◽  
Loading Test ◽  
Stress Point ◽  
Impact Side ◽  
The Impact ◽  
Static Simulation

Rollover is motor vehicle accident that occurs when vehicle is tipping over onto its side or roof. Due to its fatality rate, the Malaysian government reinforced an Economic Commission for Europe of the United Nations (UN/ECE) Regulation no. 66 (R66) upon bus construction. This is to prevent the catastrophic consequences of rollover accidents. The R66 regulation provides an option of certification based on full-scale vehicle testing that maitaning the survival space. Therefore research that contribute to the development of safe transportation vehicle under rollover is really important. The physical prototype of rollover test can be simplified using simulation model. Using this motivation, the characteristic of heavy vehicle rolleover is investigated in this paper. The simulation was performed using ANSYS simulation tool and simplified by locating the position of the bus in unstable equilibriumm, just before it hit the ground. Another method is to perform a quasi-static loading test. The quasi-static simulation test was performed using impact load that directed towards the side of beam around the centre of frame body. The dynamic response due to rollover impact was determined using an Explicit Dynamic Analysis in ANSYS. The stress maximum stress first developed around the impact area before lag the stress stream to the opposite side. It can be observed that the maximum stress point is located at the middle structure of impact side. After few times of impact, the maximum stress starts to changes to the opposite side. Quasi-static simulation result in higher total deformation on impact side area. It also indicates high maximum stress point around the middle structure.

scholarly journals Characterization and Simulation of Transient Vibrations Using Band Limited Temporal Moments

1994 ◽  
Vol 1 (6) ◽  
pp. 507-527 ◽  
Author(s):  
David O. Smallwood
Keyword(s):  
Energy Spectrum ◽  
Product Model ◽  
Transient Time ◽  
Transient Event ◽  
Time Histories ◽  
Band Pass ◽  
The Mean ◽  
Temporal Moments ◽  
Band Limited

A method is described to characterize shocks (transient time histories) in terms of the Fourier energy spectrum and the temporal moments of the shock passed through a contiguous set of band pass filters. The product model is then used to generate of a random process as simulations that in the mean will have the same energy and moments as the characterization of the transient event.

Sign in / Sign up

Export Citation Format

Share Document