Transverse Elastic–Friction Vibrations of a Running Aircraft

An analytical model of the plane-parallel running of an aircraft under crosswind load is proposed. The compliance of the internal constraints of the aircraft and the nonlinearity of the side force on the landing gear wheels are taken into account. The model is intended to study the transverse elastic friction vibrations of the aircraft hull and landing gears. The steady motion of the aircraft is considered. The dependence of the lateral friction force on the slip angle is assumed to have the form of a sinusoidal segment. The Routh–Hurwitz instability conditions are derived in an explicit form     

飞机起落架着陆撞击动力分析

根据现有沿－气式缓冲器结构形式,针对模拟起落架着陆撞击过程的落 震试验模型,考虑起落架航向刚度和阻尼的影响,依据撞击过程中各变量间的运动关系,建立了描述着陆过程中的运动微分方程组,并采用龙格库塔法对运动微分方程组进行求解。最后采用该方法对Ｋ８飞机主起落架（单腔）和某机起落架（双腔）落震试验过程进行了模拟,并与试验结果进行了比较,发现计算结果与试验结果吻合较好。     

Numerical continuation analysis of a three-dimensional aircraft main landing gear mechanism

Nonlinear Dynamics - A method of investigating quasi-static landing gear mechanisms is presented and applied to a three-dimensional aircraft main landing gear mechanism model. The model has 19...     

基于落震试验的油—气式起落架气体压缩多变指数变化规律研究

气体压缩多变指数是油气式起落架缓冲性能计算中的重要参数。通过对某型飞机油气式起落架落震试验中气腔压力数据的监测,对不同落震投放高度下气体压缩多变指数进行识别。利用最小二乘法,对多变指数变化曲线进行三次拟合,得出活塞杆压缩过程中气体多变指数的变化规律。本文建立了某型飞机起落架落震试验仿真分析模型,将拟合曲线引入仿真计算模型,对比了定常多变指数计算模型和非定常多变指数计算模型仿真结果。相对于定常多变指数模型,非定常多变指数计算模型仿真结果和试验对比误差小于定常多变指数计算模型,提高了仿真分析精度。     

Multi-parameter bifurcation study of shimmy oscillations in a dual-wheel aircraft nose landing gear

We develop and investigate a mathematical model of an aircraft nose landing gear with a dual-wheel configuration. The main aim here is to study the influence of a dual-wheel configuration on the existence of shimmy oscillations. To this end, we consider a model that describes the torsional and lateral vibrational modes and the non-linear interaction between them via the tyre-ground contact. More specifically, we perform a bifurcation analysis (with the software package auto) of the model in the two-parameter plane of forward velocity of the aircraft and vertical load on the nose landing gear. This two-parameter bifurcation diagram allows one to identify regions of different dynamics, and the question addressed here is how it depends on two key parameters of the dual-wheel configuration. Namely, we consider the influence of, first, the separation distance between the two wheels and, second, of gyroscopic effects arising from the inertia of the wheels. For both cases, we find that with increasing separation distance and wheel inertia, respectively, the lateral mode becomes more stable and the torsional mode becomes less stable. More specifically, we present associated bifurcation scenarios that explain the transitions between qualitatively different two-parameter bifurcation diagrams. Overall, we find that the separation distance and gyroscopic effects due to wheel inertia may have a significant influence on the quantitative and qualitative nature of shimmy oscillations in aircraft nose landing gears. In particular, the torsional and the lateral modes of a dual-wheel nose landing gear may interact in a quite complicated fashion.     

飞机起落架收放疲劳实验系统设计及应用

研制了一套用于飞机起落架收放机构、锁机构疲劳寿命实验和可靠性验证的收放疲劳实验系统。提出和实现了精确模拟气动力的凸轮加载方案,并解决了收起、放下过程不对称加载的技术难题。应用PLC技术实现了实验过程的自动化。实验结果表明,该系统工作稳定可靠,可连续数小时工作,载荷模拟最大误差不大于10%,已成功进行7000多次实验循环。实验系统可用于起落架收放疲劳实验,收放动应力测量和锁机构可靠性考核。     

Adaptive computation of aeroacoustic sources for a rudimentary landing gear

We present our simulation results for the benchmark problem of the flow past a rudimentary landing gear using a General Galerkin FEM, also referred to as adaptive DNS/LES. In General Galerkin, no explicit subgrid model is used; instead, the computational mesh is adaptively refined with respect to an a posteriori error estimate of a quantity of interest in the computation, in this case, the drag force on the rudimentary landing gear. Turbulent boundary layers are modeled using a simple wall‐layer model with the shear stress at walls proportional to the skin friction, which here is assumed to be small and, therefore, can be approximated by zero skin friction. We compare our results with experimental data and other state of the art computations, where we find good agreement in sound pressure levels, surface velocities, and flow separation. We also compare with detailed surface pressure experimental data where we find largely good agreement, apart from some local differences for which we discuss possible explanations. Copyright © 2013 John Wiley & Sons, Ltd.     

飞机主起落架收放摇臂的动力学分析

本地运七飞机主起薄架系统，在接近收上位置到碰锁的过程建立了简化的流固耦合的有限元总体模型。利用动态增量非线性有限元程序（ＡＤＩＮＡ８４年版），对主起落架系统收上碰锁过程进行了动力学流固耦合的有限元分析，在此基础上对摇臂建立了更为精细的有限元地其进行了静力分析，无论总体模型还是精细模型均能够起初地反映实际情况，且模型中的有关参数的选取也是合理的，计算结果与试验结果也是吻合的，这说明本文关于飞机主起落     

Wheel slip measurement in 2WD tractor

A microcontroller-based slip sensor was developed for a 2WD tractor to indicate slip values during on-farm use. The ‘zero condition’ considered for the development of slip sensor was – tractor supplied with a driving torque to propel any device across a tarmacadam surface while delivering zero net traction (self-propelled condition). This sensor comprised of four components: power supply; sensing of throttle position, gear position, and wheel rpm; processing of collected data; and display unit. Power was taken from the tractor battery. Rotary potentiometer and proximity switches were installed on the tractor to measure throttle position and wheel revolution, respectively. The performance of developed slip sensor was evaluated both on tarmacadam surface as well as in the field. The variations between indicated and actual slip were found to be within 0–5% for both the surfaces, thus indicating the accuracy of slip measurement by the developed slip sensor.     

Interaction of torsion and lateral bending in aircraft nose landing gear shimmy

In this paper we consider the onset of shimmy oscillations of an aircraft nose landing gear. To this end we develop and study a mathematical model with torsional and lateral bending modes that are coupled through a wheel-mounted elastic tyre. The geometric effects of a positive rake angle are fully incorporated into the resulting five-dimensional ordinary differential equation model. A bifurcation analysis in terms of the forward velocity and the vertical force on the gear reveals routes to different types of shimmy oscillations. In particular, we find regions of stable torsional and stable lateral shimmy oscillations, as well as transient quasiperiodic shimmy where both modes are excited.     

Aeroelastic analysis of an idealized landing gear door in subsonic potential flow

Landing gear doors on aircraft have experienced flutter during preliminary flight testing. While designs vary widely, landing gear doors are typically plate-like structures with a relatively rigid actuator attached to their inside surface. To better understand the aeroelasticity of landing gear doors, this study investigates the aeroelastic stability of an idealized model. The model consists of a hinged plate with an interior constraint approximating the actuator attachment. The plate is subject to uniform flow, and an unsteady vortex lattice model is coupled to the structural model to predict critical flow velocities. The location and footprint area of the internal constraint, along with plate aspect and mass ratios, are varied to investigate a large parameter space. Results reveal that the critical flow speed and instability mechanism are sensitive to the postulated actuator placement. In general, flutter is the dominant mode of instability when the actuator is postulated in the leading quarter of the plate. In other postulated locations, divergence dominates. However, the exact shape and location of the boundary between flutter and divergence is configuration dependent and found to be especially sensitive to changes in aspect ratio.     

A novel MAV with treadmill motion of wing

The Magnus effect is well known phenomena for producing high lift values from spinning symmetrical geometries such as cylinders, spheres, or disks. But, the Magnus force may also be produced by treadmill motion of aerodynamic bodies. To accomplish this, the skin of aerodynamic bodies may circulate with a constant circumferential speed. Here, a novel wing with treadmill motion of skin is introduced which may generate lift at zero air speeds. The new wing may lead to micro aerial vehicle configurations for vertical take-off or landing. To prove the concept, the NACA0015 aerofoil section with circulating skin is computationally investigated. Two cases of stationary air and moving air are studied. It is observed that lift can be generated in stationary air although drag force is also high. For moving air, the lift and drag forces may be adopted between the incidence angles 20° to 25° where lift can posses high values and drag can remain moderate.     

Stress-strain state of ice cover during aircraft takeoff and landing

We consider the linear unsteady motion of an IL-76TD aircraft on ice. Water is treated as an ideal incompressible liquid, and the liquid motion is considered potential. Ice cover is modeled by an initially unstressed uniform isotropic elastic plate, and the load exerted by the aircraft on the ice cover with consideration of the wing lift is modeled by regions of distributed pressure of variable intensity, arranged under the aircraft landing gear. The effect of the thickness and elastic modulus of the ice plate, takeoff and landing regimes on stress-strain state of the ice cover used as a runway.     

Leveraging circuit theory and nonlinear dynamics for the efficiency improvement of energy harvesting

Nonlinear Dynamics - The Hopf–Hopf bifurcations of an aircraft nose landing gear model are investigated in this paper based on two pairs of continuation parameters. It is shown that due to...     

二阶滑移边界对微型气浮轴承稳态性能的影响

考虑微型气浮轴承的尺寸特征,内部气流不再满足连续流的假设,根据Knudsen数可确定内 部气流为滑移流. 分别利用一阶速度滑移模型和二阶速度滑移模型对连续流的状态方程进行 修改,得到一阶滑移流和二阶滑移流机制下修正的雷诺方程. 利用有限差分法对连续流、一 阶滑移流和二阶滑移流的雷诺方程分别求解,得出相应的承载力和偏位角. 经过对比分析, 发现采用滑移流模型得到的轴承的稳态力学性能与连续流机制的结果存在较大差异,一阶滑 移流与二阶滑移流间的差异随偏心率增加而增加. 说明在MEMS环境下必须考虑滑移流效应 对微型气浮轴承稳态力学性能的影响. 在大偏心率工作状态下,二阶滑移流模型能够得到最 好的结果.     

Relaxation effects of slip in shear flow of linear molten polymers

The transient shear response of a linear molten polymer (linear low-density polyethylene) in the nonlinear domain was studied using a true shear (sliding plate) rheometer with different gap spacings to detect slip effects. It was found that nonlinear viscoelasticity is further complicated by wall slip phenomena. Experimental evidence suggested that static slip models coupled with Wagner’s constitutive equation cannot adequately describe the experimental data at large and fast shear deformations. A new dynamic slip model involving multiple slip relaxation times is proposed in this paper, together with a method to assess the model parameters. Significant improvement in predicting the stress response is demonstrated by several examples of start-up of steady shear and large-amplitude oscillatory tests of a linear low-density polyethylene.     

Critical shimmy speed of nonswiveling landing-gear wheels subject to lateral loading

The paper presents a nonlinear model describing vibration of the landing gear relative to the fuselage. The model is intended to analyze the dynamic stability of nonswiveling main-gear wheels. The model is used to show that the lateral component of the fuselage speed has a significant effect on the critical shimmy speed __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 9, pp. 134–142, September 2006.     

Direct simulation of multiphase flows with modeling of dynamic interface contact angle

We describe a modeling technique for dynamic contact angle between a phase interface and a solid wall using a generalized Navier boundary condition in the context of a front-tracking-based multiphase method. The contact line motion is determined by the generalized Navier slip boundary condition in order to eliminate the infinite shear stress at the contact line. Applying this slip boundary condition only to the interface movement with various slip ratios shows good agreement with experimental results compared to allowing full fluid slip along the solid surface. The interface slip model performs well on grid convergence tests using both the slip ratio and slip length models. A detailed energy analysis was performed to identify changes in kinetic, surface, and potential energies as well as viscous and contact line dissipation with time. A friction coefficient for contact line dissipation was obtained based on the other computed energy terms. Each energy term and the friction coefficient were compared for different grid resolutions. The effect of varying the slip ratio as well as the contact angle distribution versus contact line speed was analyzed. The behavior of drop impact on a solid wall with different advancing and receding angles was investigated. Finally, the proposed dynamic contact model was extended to three dimensions for large-scale parallel calculations. The impact of a droplet on a solid cylinder was simulated to demonstrate the capabilities of the proposing formulation on general solid structures. Widely different contact angles were tested and showed distinctive characteristic behavior clearly.     

舰载飞机起落架突伸时外筒应力陡增分析

分析了某舰载飞机斜板滑跃起飞试飞时,前起落架在机轮出斜板而卸载后,缓冲器外筒轴向应力未减小反而陡增的现象。在介绍缓冲器结构、工作原理和受力数学模型的基础上,建立了缓冲器外筒轴向应力的计算模型;结合对实测数据的分析,揭示了缓冲器外筒应力陡增的原因。结果表明:外筒轴向应力与缓冲器的行程和活塞运动速度相关,起落架出斜板后外筒应力陡增的主要原因是起落架突伸时,活塞杆高速伸出引起油液阻尼力大幅增加及高速伸出的起落架的下部质量在反阻活门关闭瞬间对外筒底面的撞击。     

Nonlinear vibration and dynamics of ceramic on ceramic artificial hip joints: a spatial multibody modelling

The present study investigates nonlinear vibration and dynamic behaviour of a ceramic-on-ceramic hip implant. The aim of this research is to firstly gain a better understanding of hip squeaking and vibration and secondly to investigate the effect of friction on contact point path during normal gait. For this purpose, a spatial multibody dynamic hip model was developed, using a friction-velocity constitutive law combined with a Hertzian contact model. Furthermore, the physiological three-dimensional rotation angles and forces are taken into account to calculate tangential and normal contact forces, respectively. Comparing the outcomes with that available in the literature allowed for the validation of our approach. It was shown that the cause of hip squeaking is friction-induced vibration owing to different phenomena such as stick–slip friction, negative-sloping friction and contact force changes. Moreover, friction-induced vibration does significantly change contact point path during the gait when compared to non-friction analysis.