OPEN-LOOP FOG SIGNAL TESTING AND WAVELET ELIMINATING NOISE

An open-loop fiber optic gyro (FOG) testing system is designed. The noise characteristic of open-loop fiber optic gyro signals is analyzed. The wavelet eliminating noise method is discussed and compared with other methods, such as smoothing and low-pass filter methods. Results indicate that the wavelet eliminating noise method can satisfy the measuring demand of the FOG weak output signal with noise disturbing. The wavelet analysis method can efficiently eliminate the noise and reserve the information of the signal. The eliminating noise effect of using different wavelet base functions is compared. The effectiveness of multiresolution wavelet analyses of eliminating noise is proved by experimental results.     

WIFI AIDED INTEGRITY IMPROVEMENT IN MEMS INS/GNSS INTEGRATION

The reliability of global navigation satellite system （GNSS） positioning degrades when satellite signals are interfered. Such degradation is hard to be deteced by a micro-electro mechanical system （MEMS） based inertial system（INS）/GNSS, integrating navigation system with a conventional Kalman filtering, which results in poten- tial integrity problem of the system. Hence, an algorithm combining wireless fidelity （WiFi） signal with a federa- ted Kalman filter （FKF） is proposed to identify the system integrity in dense urban navigation. The criterion of the system integrity detection is created followed by the derivation of the integrity coefficient. The field test shows that integrity changes can be captured by applying WiFi, and the maximum positioning error is reduced by 67~ without compensation of inertial sensors in integrity deterioration.     

Optimizing Control for Rotor Vibration with Magnetorheological Fluid Damper

The aim of this work is to analyze and design a control system for vibration reduction in a rotor system using a shear mode magnetorheological fluid （MRF） damper. A dynamic model of the MRF damper-rotor system was built and simulated in Matlab/Simulink to analyze the rotor vibration characteristics and the vibration reduction dfeet of the MRF damper. Based on the numerical simulation analysis, an optimizing control strategy using pat- tern search method was proposed and designed. The control system was constructed on a test rotor bench and ex- periment validations on the effectiveness of the proposed control strategy were conducted. Experimental results show that rotor vibration caused by unbalance can be well controlled whether in resonance region （70~） or in non- resonance region （30 ~）. An irregular vibration amplitude jump can be suppressed with the optimization strategy. Furthermore, it is found that the rapidity of transient response and efficiency of optimizing technique depend on the pattern search step. The presented strategies and control system can be extended to multi-span （more than two or three spans） rotor system. It provides a powerful technical support for the extension and application in target and control for shafting vibration.     

Fractional Pfaff-Birkhoff Principle and Birkhoff′s Equations in Terms of Riesz Fractional Derivatives

The dynamical and physical behavior of a complex system can be more accurately described by using the fractional model.With the successful use of fractional calculus in many areas of science and engineering,it is necessary to extend the classical theories and methods of analytical mechanics to the fractional dynamic system.Birkhoffian mechanics is a natural generalization of Hamiltonian mechanics,and its core is the Pfaff-Birkhoff principle and Birkhoff′s equations.The study on the Birkhoffian mechanics is an important developmental direction of modern analytical mechanics.Here,the fractional Pfaff-Birkhoff variational problem is presented and studied.The definitions of fractional derivatives,the formulae for integration by parts and some other preliminaries are firstly given.Secondly,the fractional Pfaff-Birkhoff principle and the fractional Birkhoff′s equations in terms of RieszRiemann-Liouville fractional derivatives and Riesz-Caputo fractional derivatives are presented respectively.Finally,an example is given to illustrate the application of the results.     

Approach to Interference Aircraft Automatic Riveting Process Control of Drilling and Riveting

Interference fit riveting is an effective way to improve the fatigue life of aircraft. The accurate control of riveting interference of aircraft automatic drilling and riveting equipment is achieved by process parameters including upsetting force and upset head height. It is valuable for aircraft manufacturing engineering. An approach to interference riveting process control based on the analysis of interference riveting stress field is proposed. According to assembly structure, the upsetting force is calculated by the material property and interference fit level, and the upset head height is deduced by the upsetting force. The experimental result shows that the interference fit level can be controlled accurately by the upsetting force and upset head height, and then, the quality of aircraft auto- matic riveting can be improved. The proposed approach is verified by the good match between the predicted result and the experimental result.     

Crack Length Quantification Based on Planar Eddy-Current Sensor Array and Two-Dimensional Image

Eddy-current (EC) testing is an effective electromagnetic non-destructive testing (NDT) technique.Planar eddy-current sensor arrays have several advantages such as good coherence,fast response speed,and high sensitivity,which can be used for micro-damage inspection of crucial parts in mechanical equipments and aerospace aviation.The main purpose of this research is to detect the defect in a metallic material surface and identify the length of a crack using planar eddy-current sensor arrays in different directions.The principle and characteristics of planar eddy-current sensor arrays are introduced,and a crack length quantification algorithm in different directions is investigated.A damage quantitative detection system is established based on a field programmable gate array and ARM processor.The system is utilized to inspect the micro defect in a metallic material,which is carved to micro crack with size of 7mm(length)×0.1mm(width)×1mm(depth).The experimental data show that the sensor arrays can be used for the length measurement repeatedly,and that the uncertainty of the length measurement is below ±0.2mm.     

IMPROVED DELAUNAY TRIANGULATION FOR TRIMMED NURBS SURFACE

An improved algorithm of Delaunay triangulation is proposed by expanding the scope from a convex polygon to an arbitrary polygon area in which holes can be contained in the subdivision procedure. The data structure of generated triangles and the exuviationslike method play a key role, and a single connectivity domain (SCD) without holes is constructed as the initial part of the algorithm. Meanwhile, some examples show that the method can be applied to the triangulation of the trimmed NURBS surface. The result of surface tessellation can be used in many applications such as NC machining, finite element analysis, rendering and mechanism interference detection.     

Weak GPS L1 Signal Acquisition Based on BPDC

It is difficult to achieve accurate acquisition of weak global positioning system（GPS） signals with traditional methods. A weak signal acquisition strategy based on block processing and differentially coherent （BPDC） is put forward after analyzing the advantages and disadvantages of coherent and non-coherent integration algorithms. Code phase parallel search of the pre-coherent integration is conducted by using fast Fourier transform（FFT）, and the results are then differential coherent processed and block processed. BPDC method reduces computation cost compared with coherent and non-coherent（CNC） algorithm. The performance of the two algorithms is also compared based on simulated signals. The result shows that the noise suppression effect of BPDC algorithms is superior to that of traditional CNC algorithm, and the superiority of BPDC is more apparent with the reduction of carrier to noise ratio （CNR）. In the case that the pre-coherent integration length is 4 ms and CNR is reduced to 28 dB-Hz, CNC algorithm cannot yet acquire signal correctly while BPDC has well acquisition performance. Therefore, for weak GPS signal acquisition, BPDC algorithm can acquire the signal with lower CNR and has better acquisition property.     

METHOD FOR DETECTING AND REPAIRING CYCLE SLIPS IN GPS NAVIGATION

A new method is proposed for detecting and repairing cycle slips in GPS navigation based on the dual frequency observations. It can be implemented through the following three steps: (1) The integer ambiguities of the current epoch are substituted by that of the previous epoch, so the ambiguity parameters are removed from the observation equations. (2) The abnormal observations are detected using the quasi accurate detection (QUAD) method and the satellite pairs of these abnormal observations are determined. Then the coefficient matrix of these satellite pairs is recovered. (3) The cycle slips of these satellite pairs are calculated using the LAMBDA method and integer ambiguities of the current epoch can be determined by adding the cycle slips into the integer ambiguities of the previous epoch. The key of this method is that the abnormal observations must accurately he detected, i.e. , the satellites having cycle slips must correctly be judged. Finally, compared with other methods the feasibility of the method is verified.     

Effects of Thermo-Mechanical Loads on Aeroelastic Instabilities of Metallic and Composite Panels

Panel flutter phenomena can be strongly affected by thermal loads,and so a refined aeroelastic model is presented.Higher-order shell theories are used as structural models.The aerodynamic forces are described using the Piston theory.The temperature is considered uniform over the thickness of the panel.The aero-thermo-elastic model is derived in the framework of the Carrera unified formulation(CUF),therefore the matrices are expressed in a compact form using the″fundamental nuclei″.Composite and sandwich structures are considered and different boundary conditions are taken into account.The effects of the thermal load on the aeroelastic behavior are investigated.     

ROBUST REPETITIVE CONTROL FOR IMPROVING RATE SMOOTHNESS OF TEST TURNTABLE

A robust repetitive control scheme is used to improve the rate smoothness of a brushless DC motor (BLDCM) driven test turntable. The method synthesizes variable structure control (VSC) laws and repetitive control (RC) laws in a complementary manner. The VSC strategy can stabilize the system and suppress uncertainties, such as the aperiodic disturbance and noises, while RC strategy can eliminate the periodic rate fluctuation in a steady state. The convergence of the repetitive learning process is also guaranteed by VSC. A general nonlinear system model is discussed. The model can be considered as an extension of BLDCMs. The stability and asymptotic position tracking performance are validated by using Lyapunov functions. Simulation results show the effectiveness of the proposed approach for improving the rate smoothness.     

Panoramic Imaging System Inspired by Insect Compound Eyes

Inspired by the unique structure of insect compound eyes, a multi-channel image acquisition system is designed to photograph a cylindrical panorama of its surroundings with one shot. The hardware structure consists of an embedded ARM system and one array of 16 micro-image sensors. The system achieves the synchronization of captured photos in 10 ms, as well as 10 f/s video capture. The software architecture includes the TCP/IP proto- col, video capture procedures in ＂Poll/Read＂ or ＂video streaming＂ modes, thread pool monitoring in multi-threa- ding mutex, synchronization control with the ＂event＂ ＂mutex signal＂ and ＂critical region＂ functions, and a syn- thetic image algorithm characterized by its portability, modularity, and remote transmission. The panoramic imaging system is expected to be a vision sensor for mobile robotics.     

BUCKLING OF SPATIAL CURVED RODS WITH CIRCULAR CROSS-SECTIONS

Formulae for determining Green strain of an initially curved and twisted rod with circular cross-sections are derived by using the natural (curvilinear) coordinate system. Finite element analyses are performed for the flexural buckling of initially curved and twisted thin rods under simultaneous action of axial force and torque. Numerical examples demonstrate that the given formulae are correcte. Some numerical results are compared with existing analytical solutions and data obtained by commercial FE software. The convergence of the proposed curved element is better than that of elements in the commercial FE software. It is shown that good accuracy and convergency are achieved by solving three-dimensional problems.     

APPLICATION OF HYBRID GENETIC ALGORITHM IN AEROELASTIC MULTIDISCIPLINARY DESIGN OPTIMIZATION OF LARGE AIRCRAFT

The genetic/gradient-based hybrid algorithm is introduced and used in the design studies of aeroelastic optimization of large aircraft wings to attain skin distribution,stiffness distribution and design sensitivity.The program of genetic algorithm is developed by the authors while the gradient-based algorithm borrows from the modified method for feasible direction in MSC/NASTRAN software.In the hybrid algorithm,the genetic algorithm is used to perform global search to avoid to fall into local optima,and then the excellent individuals of every generation optimized by the genetic algorithm are further fine-tuned by the modified method for feasible direction to attain the local optima and hence to get global optima.Moreover,the application effects of hybrid genetic algorithm in aeroelastic multidisciplinary design optimization of large aircraft wing are discussed,which satisfy multiple constraints of strength,displacement,aileron efficiency,and flutter speed.The application results show that the genetic/gradient-based hybrid algorithm is available for aeroelastic optimization of large aircraft wings in initial design phase as well as detailed design phase,and the optimization results are very consistent.Therefore,the design modifications can be decreased using the genetic/gradient-based hybrid algorithm.     

Numerical Analysis of Dry Friction-Induced Vibration of Moving Slider-Elastic Annular Beam System

A disc-pad friction system is modelled as that two moving pads act symmetrically on an annular beam with flexible boundary condition.Simulation procedure is proposed to deal with the moving interactions and calculation is carried out by using the finite difference method,which shows that only the first-order mode vibration of the beam can be induced.Then the partial differential equation of motion of the disk is reduced to a first-order mode vibration system with time-varying stiffness.As the disk speed is decreased below the critical speeds,the relative equilibrium of the pad on the disk loses its stability and stick-slip type limit cycle vibrations are resulted in all directions′movements.Acceleration of the disk motion on the frictional instability is also investigated.The period of stick-slip vibration with large amplitude will be shortened with higher moving deceleration.     

Critical Length of Double-Walled Carbon Nanotubes Based Oscillators

The critical lengths of an oscillator based on double-walled carbon nanotubes （DWCNTs） are studied by energy minimization and molecular dynamics simulation. Van der Waals （vdW） potential energy in DWCNTs is shown to be changed periodically with the lattice matching of the inner and outer tubes by using atomistic models with energy minimization method. If the coincidence length between the inner and outer tubes is long enough, the restoring force cannot drive the DWCNT to slide over the vdW potential barrier to assure the DWCNT acts as an oscillator. The critical coincidence lengths of the oscillators are predicted by a very simple equation and then con- firmed with energy minimization method for both the zigzag/zigzag system and the armchair/armchair system. The critical length of the armchair/armchair system is much larger than that of the zigzag/zigzag system. The vdW po- tential energy fluctuation of the armchair/armchair system is weaker than that of the zigzag/zigzag system. So it is easier to slide over the barrier for the armchair/armchair system. The critical lengths of zigzag/zigzag DWCNT- based oscillator are found increasing along with temperature, by molecular dynamics simulations.     

SIMULATION OF BLEED AIR BEHAVIOR DURING AIRCRAFT IN FLIGHT BASED ON FLOWMASTER

Bleed air system is one of the most important components of air management system(AMS).It acts as transfer pipes responsible for air supply at high temperature and pressure.The thermal and flow performance of the bleed air system is a key issue for the design of AMS since the characteristics of air source have a great influence on the anti-ice system,the environmental control system and other downstream system in need of high temperature pressurized air.Based on the one-dimensional lumped parameter technology,a computer analysis model of bleed air system is developed in order to analyze the thermal and flow behaviors of the nodal points in the pipeline network.The simulation are performed with a given flight assignment using the analysis model,and the results verify that the system meets the design requirements.     

Dynamics of Rotor Drop on New Type Catcher Bearing

In an active magnetic bearing(AMB)system,the catcher bearings(CBs)are indispensable to protect the rotor and stator in case the magnetic bearings fail or overload.A new CB structure composed of two ball bearings is introduced.Detailed simulation models containing contact model between rotor and inner race,double-decker catcher bearing(DDCB)model as well as single-decker catcher bearing(SDCB)model are established using multibody dynamics simulation software MSC.ADAMS.Then,using those established models,the rotor orbits and the contact forces between rotor and inner race are simulated respectively after rotor drop on DDCBs and SDCBs.The simulation result shows that the rotor vibration range using DDCBs is significantly smaller than that using SDCBs;the maximum contact forces drop about 15%—27% compared with the contact forces using SDCBs.Finally,the test bench for the rotor drop experiments is built and the rotor drop experiments for different types of CBs are carried out.Labview data acquisition system is utilized to collect the displacement of rotor and the rotating frequencies of both inner race and intermediate races after rotor drop.The experimental results are comparatively analyzed,and the conclusion that DDCB can help to reduce vibration amplitude and collision force is obtained.The studies can provide certain theoretical and experimental references for the application of DDCBs in AMB system.     

OUTPUT MAXIMIZATION CONTROL FOR VSCF WIND ENERGY CONVERSION SYSTEM USING EXTREMUM CONTROL STRATEGY

The energy conversion optimization control strategy is presented for a family of horizontal-axis variablespeed fixed-pitch wind energy conversion systems,working in the partial load region.The system uses a variablespeed wind turbine(VSWT)driving a squirrel-cage induction generator(SCIG)connected to a grid.A new maximum power point tracking(MPPT)approach is proposed based on the extremum seeking control principles under the assumption that the wind turbine model and its parameters are poorly known.The aim is to drive the average position of the operation point close to optimality.Here the wind turbulence is used as search disturbance instead of inducing new sinusoidal search signals.The discrete Fourier transform(DFT)process of some available measures estimates the distance of operation point to optimality.The effectiveness of the proposed MPPT approach is validated under different operation conditions by numerical simulations in MATLAB/SIMULINK.The simulation results prove that the new approach can effectively suppress the vibration of system and enhance the dynamic performance of system.     

SAR IMAGE ENHANCEMENT BASED ON BEAM SHARPENING TECHNIQUE

A major problem encountered in enhancing SAR image is the total loss of phase information and the unknown parameters of imaging system. The beam sharpening technique, combined with synthetic aperture radiation pattern estimation provides an approach to process this kind of data to achieve higher apparent resolution. Based on the criterion of minimizing the expected quadratic estimation error, an optimum FIR filter with a symmetrical structure is designed whose coefficients depend on the azimuth response of local isolated prominent points because this response can be approximately regarded as the synthetic aperture radiation pattern of the imaging system. The point target simulation shows that the angular resolution is improved by a ratio of almost two to one. The processing results of a live SAR image demonstrate the validity of the method.