scholarly journals Gust Response Analysis for Helicopter Rotors in the Hover and Forward Flights

2017 ◽  
Vol 2017 ◽  
pp. 1-20 ◽  
Author(s):  
Linpeng Wang ◽  
Yuting Dai ◽  
Chao Yang
Keyword(s):  
Shear Force ◽  
Thrust Force ◽  
Vertical Direction ◽  
Beam Theory ◽  
Response Analysis ◽  
Forward Flight ◽  
Helicopter Rotors ◽  
Aerodynamic Model ◽  
Aeroelastic Model ◽  
The Time Domain

Dynamic load due to gust for helicopter rotors directly affects the structural stress and flight performance. In case of gust, it may cause the loss of trust force or the increase of deflection for rotors. In current work, an effective coupled aeroelastic model based on a medium-deflection beam theory and a nonlinear unsteady aerodynamic model in the time domain were constructed. Three types of gust in vertical direction were added in the model. The dynamic response and structural load for helicopter rotors under three types of gust were calculated, respectively. Results indicated that when rotors suffer a gust in hover at downward direction, the thrust force on rotor disk would decrease significantly when the gust amplitude increases, which should be paid attention in the design. Among the three gust types with the same gust strength, the maximum instantaneous shear force due to impulse shape gust is the largest. When the rotors suffer a gust in a forward flight, the shear force at the root of rotors would increase with the gust strength first but then it decreases. More attention should be paid to the decrease of thrust force and the increase of structural load in a forward flight.

scholarly journals Dynamic Gust Load Analysis for Rotors

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Yuting Dai ◽  
Linpeng Wang ◽  
Chao Yang ◽  
Xintan Zhang
Keyword(s):  
Structural Model ◽  
Beam Theory ◽  
Bending Moment ◽  
Iteration Algorithm ◽  
Beam Model ◽  
Euler Beam ◽  
Helicopter Rotors ◽  
Aeroelastic Model ◽  
Flap Deflection ◽  
The Time Domain

Dynamic load of helicopter rotors due to gust directly affects the structural stress and flight performance for helicopters. Based on a large deflection beam theory, an aeroelastic model for isolated helicopter rotors in the time domain is constructed. The dynamic response and structural load for a rotor under the impulse gust and slope-shape gust are calculated, respectively. First, a nonlinear Euler beam model with 36 degrees-of-freedoms per element is applied to depict the structural dynamics for an isolated rotor. The generalized dynamic wake model and Leishman-Beddoes dynamic stall model are applied to calculate the nonlinear unsteady aerodynamic forces on rotors. Then, we transformed the differential aeroelastic governing equation to an algebraic one. Hence, the widely used Newton-Raphson iteration algorithm is employed to simulate the dynamic gust load. An isolated helicopter rotor with four blades is studied to validate the structural model and the aeroelastic model. The modal frequencies based on the Euler beam model agree well with published ones by CAMRAD. The flap deflection due to impulse gust with the speed of 2m/s increases twice to the one without gust. In this numerical example, results indicate that the bending moment at the blade root is alleviated due to elastic effect.

Helicopter Response to Atmospheric Turbulence in Forward Flight

1990 ◽  
Vol 35 (2) ◽  
pp. 51-59
Author(s):  
Andrew S. Elliott ◽  
Inderjit Chopra
Keyword(s):  
Time Integration ◽  
Stochastic Perturbation ◽  
Rotor Blades ◽  
Stream Velocity ◽  
Forward Flight ◽  
Aerodynamic Model ◽  
Power Spectral ◽  
Model Helicopter ◽  
Space Formulation ◽  
The Time Domain

The response of a helicopter rotor‐body system in forward flight to a nonstationary random gust field is examined analytically, using a state space formulation in the time domain. The statistically sufficient characteristics of the nonstationary response, namely the mean vector and covariance matrix, are obtained by direct time integration of the stochastic differential equations. Threshold crossing and peak value statistics are derived far arbitrary threshold levels. The hingeless. rotor blades are modelled structurally as rotating elastic beams, while the hub and fuselage are considered as a single rigid body. The aerodynamic forcing is developed using a two‐dimensional unsteady aerodynamic model with compressibility effects included. The external environment consists of a uniform free‐stream velocity, plus a one‐dimensional, nonstationary, Gaussian stochastic perturbation with known mean and standard deviation and von Karman power spectral density distribution. Results are presented for a model helicopter at various combinations of advance ratio, turbulence intensity, and scale length typical of law altitude and nap‐of‐the‐earth flight environments. Nonstationarity in the gust field is shown to have little effect on the response, while choice of altitude and airspeed may significantly alter the hub and blade motions.

scholarly journals Dynamic Response Analysis of Cable of Submerged Floating Tunnel under Hydrodynamic Force and Earthquake

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Zhiwen Wu ◽  
Guoxiong Mei
Keyword(s):  
Dynamic Response ◽  
Hydrodynamic Force ◽  
Structural Parameters ◽  
Beam Theory ◽  
Response Analysis ◽  
Analysis Model ◽  
Euler Beam ◽  
Earthquake Excitation ◽  
Submerged Floating Tunnel ◽  
The Time Domain

A simplified analysis model of cable for submerged floating tunnel subjected to parametrically excited vibrations in the ocean environment is proposed in this investigation. The equation of motion of the cable is obtained by a mathematical method utilizing the Euler beam theory and the Galerkin method. The hydrodynamic force induced by earthquake excitations is formulated to simulate real seaquake conditions. The random earthquake excitation in the time domain is formulated by the stochastic phase spectrum method. An analytical model for analyzing the cable for submerged floating tunnel subjected to combined hydrodynamic forces and earthquake excitations is then developed. The sensitivity of key parameters including the hydrodynamic, earthquake, and structural parameters on the dynamic response of the cable is investigated and discussed. The present model enables a preliminary examination of the hydrodynamic and seismic behavior of cable for submerged floating tunnel and can provide valuable recommendations for use in design and operation of anchor systems for submerged floating tunnel.

Time Domain Simulations on a Single Point Moored Submerged Sphere of Variable Radius

2005 ◽  
Author(s):  
Joa˜o M. B. P. Cruz ◽  
Anto´nio J. N. A. Sarmento
Keyword(s):  
Wave Propagation ◽  
Time Domain ◽  
Physical Phenomenon ◽  
Single Point ◽  
Vertical Direction ◽  
Equation Of Motion ◽  
Hydrodynamic Coefficients ◽  
Energy Converter ◽  
Submerged Sphere ◽  
The Time Domain

This paper presents a different approach to the work developed by Cruz and Sarmento (2005), where the same problem was studied in the frequency domain. It concerns the same sphere, connected to the seabed by a tension line (single point moored), that oscillates with respect to the vertical direction in the plane of wave propagation. The pulsating nature of the sphere is the basic physical phenomenon that allows the use of this model as a simulation of a floating wave energy converter. The hydrodynamic coefficients and diffraction forces presented in Linton (1991) and Lopes and Sarmento (2002) for a submerged sphere are used. The equation of motion in the angular direction is solved in the time domain without any assumption about its output, allowing comparisons with the previously obtained results.

Nonlinear Dynamics of Orthogonal Metal Cutting: Experimental Studies

1999 ◽  
Author(s):  
Chee-Hoe Foong ◽  
Marian Wiercigroch ◽  
William F. Deans
Keyword(s):  
Nonlinear Dynamics ◽  
Cast Iron ◽  
Metal Cutting ◽  
Thrust Force ◽  
Experimental Studies ◽  
Vertical Direction ◽  
Systematic Analysis ◽  
Orthogonal Metal Cutting ◽  
Time Histories ◽  
Force Components

Abstract The elimination of chatter is one of the major aims in machining to improve geometrical accuracy and surface finish. In this study, occurrence of chatter was investigated experimentally using a specially designed rig by examining time histories of the cutting and thrust force components. A broad experimental study was conducted using brass, cast iron and aluminium samples. It was found that by changing the horizontal stiffness of the rig, the thrust force variations (in the vertical direction) were completely eliminated for the cast iron samples. A systematic analysis of the chip formation for the aluminium alloy is presented.

Planar vibrations of rigid structure on kinematic supports after A.M. Kurzanov

2020 ◽  
pp. 27-38
Author(s):  
Alexander G. Tyapin
Keyword(s):  
Vertical Direction ◽  
Experimental Program ◽  
Response Analysis ◽  
Considerable Decrease ◽  
Rigid Structure ◽  
Initial Excitation ◽  
Parametric Studies ◽  
The Impact ◽  
Planar Vibrations ◽  
Gap Closing

The author carries out parametric studies for the equation of planar vibrations of rigid structure resting on kinematical rolling supports with planar bottom (after A.M. Kurzanov). Both support and the surface below are assumed rigid; no sliding assumed. Varied parameter is the width of the bottom. Horizontal structural acceleration is studied. Three variants of the possible behavior are shown: (i) minor rocking with little decrease in response accelerations as compared to the initial excitation; considerable rocking with considerable decrease in the response accelerations; intensive rocking leading to the overturn of the supports. In vertical direction there appear shocks (infinite accelerations) during gap closings of the supports. The importance of the problem for the seismic response analysis of the unanchored items is noted. The author gives recommendations for the experimental program, aimed to obtain data about damping both for rotation and for the gap closing, and also about the impact of the flexibility of the supports and underlying surface.

Dynamic analysis of a shape memory alloy beam with pseudoelastic behavior

2018 ◽  
Vol 29 (9) ◽  
pp. 1835-1849 ◽  
Author(s):  
Reza Razavilar ◽  
Alireza Fathi ◽  
Morteza Dardel ◽  
Jamal Arghavani Hadi
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Frequency Response ◽  
Kinetic Equations ◽  
Elastic Beam ◽  
Beam Theory ◽  
Response Analysis ◽  
Interesting Phenomenon ◽  
Time Saving ◽  
Solution Approach

This article aims at developing a semi-analytic approach for studying the free and forced vibrations of a pseudoelastically behaving shape memory alloy beam. Based on the Euler–Bernoulli beam theory, equations of motion were derived through Hamilton principle, and the obtained partial differential equations were decomposed by applying the Galerkin approach and were solved using Newmark integration method. A three-dimensional phenomenological model of shape memory alloy, which is capable of identifying the main properties of the shape memory alloy, was employed to model the behavior of the shape memory alloy beam. A closed-form numerical algorithm was introduced to simulate the governing kinetic equations of the shape memory alloy beam coupled with transformation strain. The presented novel solution approach is simple, flexible, and time-saving. Stability analysis was performed using phase state trajectories to show dynamic characteristics of the shape memory alloy beam. Due to hysteric behavior of the shape memory alloy, energy dissipation was clearly observed in early stages of the free vibration and within the transient regions of the forced vibration. The numerical results showed that, due to the hysteric induced damping effect, the vibration amplitude is smaller in comparison to an equivalent elastic beam, and consequently, the shape memory alloy beam exhibits more stable behavior at the resonant frequencies. This property can potentially find applications in energy damping applications and vibration control. Moreover, an interesting phenomenon called jumping was observed in the results of frequency response analysis. At jumping frequency, the amplitude of the frequency response has two distinct levels. This jumping frequency is as a result of the hysteresis behavior of the shape memory alloy, and it is a function of the exciting amplitude.

Continuum Aeroelastic Model and Flutter Analysis for a Variable-Span Morphing Wing

2013 ◽  
Vol 300-301 ◽  
pp. 1136-1143 ◽  
Author(s):  
Ren Huang ◽  
Zhi Ping Qiu ◽  
Xiao Jun Wang
Keyword(s):  
Reduced Order ◽  
Spatial Span ◽  
Aeroelastic Model ◽  
Flutter Analysis ◽  
Basic Parameters ◽  
Variable Span ◽  
The Time Domain ◽  
The Galerkin Method ◽  
The Impact ◽  
Euler Bernoulli Beam

A linear aeroelastic continuum model for a variable-span wing is developed. Considering the fixed inboard part and the movable outboard part of the wing, a stepped Euler-Bernoulli beam with three jumped discontinuities in its spatial span is used for structural modeling. The dynamic analysis of stepped beam is introduced by a dimensionless form. The time-domain aerodynamic forces are calculated by a reduced-order unsteady vortex lattice model. Then the first-order state-space aeroelastic formulations are built by using the Galerkin method. The impact of the different wing configurations is of particular interest for understanding the fundamental aeroelastic behavior of variable-span wing. To clarify the implementation of the proposed method, a simple variable-span wing with the basic parameters of the Goland wing is studied, and numerical simulations are provided to demonstrate the flutter speeds and frequencies for different wing configurations.

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