The multiple echoes caused by periodic structure of drillstring in acoustic telemetry while drilling tend to result in the serious intersymbol interference and high bit error rate. According to the multipath transmission characteristics of drillstring, based on the analysis of multi-carrier acoustic transmission experiment along a short drill pipe, a finite difference model for a periodic channel composed of multiple drill pipes and tool joints is established. Considering the surface noises and multipath echo interferences in channel, a Least Mean Square adaptive equalization method is introduced. Then the multi-carrier modulation performance is simulated by using a drillstring structure comprising four drill pipes and three tool joints. The simulation results show that the orthogonal frequency division multiplexing (OFDM)-based multi-carrier modulation can obtain the bit error rate (BER) of 50 % less than phase-shift-keying (PSK) modulation. Although it is more sensitive to non-periodic channel structure, the BER is more superior to PSK modulation and can be effectively improved by use of phase sub-carrier phase compensation.

Local mean decomposition（LMD）can decompose complex multi-component signal into a linear combination of a finite set of product functions(PFs), and after obtaining the instantaneous amplitudes and instantaneous frequencies of all PF components the marginal spectrum based on LMD can be calculated. Aiming at the big end-point error problem of the direct instantaneous frequency extraction method, an improved direct method was put forward. The new rolling bearing fault diagnosis method named marginal spectrum based on LMD was proposed, and was applied in actual rolling bearing fault diagnosis. The analysis results show that the fault characteristic frequency can be extracted effectively, and the fault position can be determined.

Since solving the dispersion characteristics of complex waveguide structure it’s difficult, such as rail, this paper takes the method of vibration modal analysis to extract the propagation characteristics of ultrasonic guided wave. Base on the principle that vibration characteristic frequency and wave solutions could transform into each other, the solutions of frequency characteristics obtained from vibration modal analysis convert into wave solutions, and then extract the dispersion characteristics of the rail. Deformation information from vibration analysis of structure, and wave structure of ultrasonic guided could be calculated. Analysis disperse information and wave structure information of low-level model ultrasonic guided wave, select the type of ultrasonic guided model and frequency range, all these will be used as a follow-up study of theoretical support of designing of special ultrasonic guided wave sensor and testing of experimental.

The effects of local openings on wind loads on enclosed large span spatial structures were considered. Wind loads distribution on enclosed three-center cylindrical latticed shell with local openings is studied via rigid model wind pressure test in wind tunnel, Compare with wind force coefficients and wind loads distribution on structures in different local openings cases, the variation of wind loads distribution with local openings is cleared，such as the suction on structure surface was proved to decrease with the openings in strong negative wind pressure region whereas increase with the openings in positive wind pressure region, and provide suggestion for wind-resistant design and wind-resistant measurements development.

The integrated and single teeth meshing stiffness are calculated by tooth contact analysis and load tooth contact analysis under assembly misalignment. A corner meshing impact calculation model is put forward considering contact ratio, and 12-degree of freedom nonlinear double helical gear vibration model is established considering meshing stiffness, corner mesh impact, and backlash. Take the ship transmission system as an example, verified by changing the contact ratio. Teeth contact ratio is changed by adjusting tooth height modification coefficient, the meshing impact model in this paper is proved effective through comparing to calculation results in the literature [8]. The results also show that under the constant load, the system's vibration reduce with the increasing contact ratio; however, when contact ratio exceeds the value 4.07, vibration shows increasing trend.

By means of an explicit nonlinear dynamic finite element computer code LS-DYNA，regarding 75g column and 200g bulk TNT as explosion resource respectively，the nonlinear dynamic response process of the cylindrical shell subjected to explosion laterally were numerically simulated with Euler-Lagrange coupling method，the dynamic responses of setting different ways of explosion source were described. Numerical simulation results show that failure characteristics of shell wall were close connection with charge Q and setting ways of explosion source，setting vertical way of explosion with 75g column TNT source had fierce failure effect and setting parallel way of explosion with central line of 200g bulk TNT long side had the same result. The results provide important reference for the blast-resistant properties analysis and safety assessment of oil-gas pipes safety.

ARMA model is employed to simulate fluctuating wind speed time-history series of large-span structures, which has time and space correlativity. And the Whittle iteration method is improved to derive the matrixes of auto-regressive and moving-regressive coefficients. The corresponding computational program is developed by MATLAB software. Numerical examples indicate that this method is efficient and speedy. In addition, Spatial-temporal Kriging interpolation is also proposed to simulate the fluctuating wind speed time-history series of unknown pointes near the simulated points based on ARMA model. Results from the simulations show the approach , swift and accurate , is available to simulate the fluctuating speed time-history series of complex long-span space structures and high-rise buildings containing plenty of joints.

In order to investigate the forming mechanism of local amplification in rail traffic induced ground vibration attenuation, the ground was simplified to be a single soil layer overlaid on an elastic half-space. Dynamic Green's function of vertical ground displacement of the three-dimensional layered site model was derived in frequency domain. The results show that local amplification is controlled by an important buried velocity interface, the location and intensity of the amplification depends on the ratio of elastic modulus of the media in the both sides of the interface (i. e. impedance ratio), the thickness of the overburden layer, exciting frequency and damping ratio of the overburden layer, from analysis of influence on the amplification of factors as modulus ratio of half space to overburden layer media with seven values, overburden layer thickness with four values, exciting frequency with seven values, overburden layer damping ratio with three values. In general, the larger impedance at the interface, the more obvious amplifying; keeping the other conditions the same, the closer of directly arriving time of surface wave to the arriving time of refraction wave from the interface governed by the overburden layer thickness, the more obvious amplifying; the closer of the peaks of the waves governed also by the exciting frequency, the more obvious amplifying; the smaller damping ratio of the overburden layer, the more obvious amplifying.

With the exploration of oil and gas keeping into deep sea, Steel Catenary Risers (SCRs) became the preferred riser systems for the resource import and export, and vortex induced vibration (VIV) is the core problem in the design of SCRs. SCRs are modeled by small extensible slender rods with bending stiffness in the paper, and the two-way VIV model with fluid-structure interaction is proposed, the VIV of SCRs especially in the touch down point (TDP) is then studied based on the improved model. The cases studies show that the model can simulate the VIV of SCRs pretty well and can be used in the deepwater risers VIV analysis in uniform flow field; The VIV response of TDP is fairly large and complex, TDP should be taking as a key point in the VIV study of SCRs.

The vector sensor is composed of omni directional sound pressure sensors and dipole directional particle velocity sensor, and widely used in underwater acoustic fields; but in actual applications, the vector sensor is usually fixed at an installation platform, whose scattering field will inevitably distort the vector sensor’s receiving field, thus affecting its measuring results. Taking the practical application as the background, a sound scattering module of the influence on the vector sensor’s direction measuring under the condition of elastic spherical shell is theoretically built in the essay, and the influences on the accuracy of direction measuring with different incident frequencies, different observing locations, different thickness and radius of the shell are analyzed by simulation. The results provide the theoretical support for the application of vector sensor in underwater acoustic measuring.

Aiming at the problem of extracting fault characteristic from gearbox with compound faults under the condition of changing rotating speed, a compound fault diagnosis method for gearbox based on chirplet path pursuit and ensemble empirical mode decomposition (EEMD) is proposed. In the proposed method, the rotating speed is estimated from original vibration signal by chirplet path pursuit algorithm. In order to transform the time domain signal to the angular domain signal, the even angle resampling is carried out to the original signal according to the obtained rotating speed. The angular domain resampling signal is decomposed by EEMD, and the suitable intrinsic mode function (IMF) is selected according to the correlation coefficient. The selected IMF is analyzed by the Hilbert envelope spectrum and the compound fault diagnosis of gearbox is executed according to the envelope spectrum. The results, obtained by the analysis of algorithm simulation and application examples to the gearbox with compound faults consisted of gear local fault and bearing local fault under the condition of changing rotating speed, show that the proposed method can effectively extract fault characteristic from gearbox with compound faults.

To address the requirement that the sample commands of all the nodes should be triggered synchronously and the synchronization error be less than one sampling period in the course of mechanical vibration synchronous acquisition using Wireless Sensor Net, a WSN Synchronization Trigger protocol based on Beacon Timing Compensation (STBTC_P) is designed. The protocol is developed based on IEEE 802.15.4 Standard, it transmissions acquisition commands with beacon. STBTC_P establishes a good foundation for synchronization acquisition by effectively avoiding the beacon conflict using the centralized associated beacons allocation method first and then achieving trigger synchronous using the beacon timing compensation method for a multi-hop network. Finally, STBTC_P is run on the self-designed acquisition node WSN-G2 and verified its effectiveness.

Localized defects in rolling bearings tend to arouse several modes impulse responses in the vibration signals, which affect Laplace wavelet correlation filtering, a novel methodology based on EEMD and Laplace wavelet was proposed to extract the single mode impulse response mode parameters. Fistly, several modes impulse responses in the vibration signals were decomposed into several single mode impulse responses by EEMD. Secondly, the needed single mode impulse response was chosen from decomposed mode impulse responses. Thirdly, the chosen single mode impulse response was analyzed by Laplace wavelet correlation filtering, and then the fault can be diagnosed. The effectiveness of the proposed methodology is demonstrated with the simulation signal and signals of rolling bearing inner ring，outer ring and rolling element.

Fault diagnosis method based on feature selection (FS) and linear local tangent space alignment (LLTSA) is proposed, aiming to solve the problem of non-sensitive features and the high dimension of the feature set. An improved kernel distance measurement feature selection method (IKMD-FS) is proposed, which considers both the distance between classes and the dispersion within class, and the selected sensitive features are weighted by their sensitive-values. The weighted sensitive feature subset is compressed through LLTSA to reduce dimension and get the compressed more sensitive feature subset. Then, the feature subset is fed into weighted k nearest neighbor classifier (WKNNC), whose recognition accuracy is more stable compared with k nearest neighbor classification (KNNC), to recognize the fault type. At last, the validity of the proposed method is verified by the instance of the fault diagnosis of a rolling bearing.

The random vibration of coupled vehicle-bridge system under moving vehicular loads is studied. The bridge and vehicle are modeled as a continuous beam with elastic bearing and a two-DOF system with linear suspensions and tire flexibility respectively. The power spectral density of bridges surface irregularity is taken as input. Modes of continuous beams are obtained by transfer matrix method. According to state space theory and general evolutionary random processes, the method of analyzing random response of coupled system is derived. The effects of types of mid-support, bending stiffness, location of elastic bearing, vehicle velocity，and bridge surface roughness on the random response of coupled vehicle-bridge system are discussed.

To increase the synthesized accuracy of the multi-beam sounding system not only requires to increase the far-field accuracy, but also not to neglect the near-field accuracy. In view of the adoption of the far-field approximation model in the multi-beam sounding system, it made the near-field accuracy sharply insufficient and multi-beam real time kinematic focused beam-forming method on the basis of FPGA was introduced. The method imported the phase shifting focused beam-forming, and proved its feasibility to solve the near-field problem in the multi-beam sounding system, meanwhile, profoundly analyzed the real time processing of each influential factor, and proposed a real time processing structure on the basis of FPGA, in which the structure completed RT-DFBF on the condition of 80 input passages, sampling rate of 28kHz and 128 beams. The pool experiment result testifies the effectiveness and feasibility of the method, and possesses some engineering value.

Wavelet packet decomposition (WPD) can effectively reflect the potential signal characteristics by decomposing the non-stationary signal into the low and high frequencies. Locality preserving projection (LPP) can retain the local features of the analyzed signal in dimensionality reduction. Combining these two benefits, this paper selects the spectral energy of all nodes with WPD as a characterization of the analyzed signal and uses LPP feature extraction to reduce dimensions for pattern recognition of machine faults. Experimental results show the effectiveness of the proposed method by using multiple multi-class dataset of bearing faults with different fault types and defect severities.

The mechanical property of MLCP(short for multilayer corrugated paperboard) with different flutes which exhibit the typical corrugated sandwich structure under various strain rates is investigated in this paper. Comparing with the static flatwise compression, the dynamic plateau stress of MLCP increases apparently due to the different mechanism of deformation during the impact process. The method of Cowper-Symonds under intermediate strain rate is utilized to construct a model in which the flute configuration and strain rate are concerned with the corporation of theory and experimental data. As a result, the plateau stress of MLCP will be on a rise with the increasing of strain rate. The prediction of the dynamic plateau stress of MLCP from the model proposed after being normalized by the elastic modulus of the corrugated medium shows certain accuracy. Meanwhile, the normalized model is valuable to the investigation of mechanical properties of other materials of corrugated sandwich structure.

In this paper, a novel decentralized feedforward control strategy of plate vibrations without secondary path mod¬eling is proposed. This control method needs no structure information of the plate and is able to control the harmonic disturbances at off-resonance frequency. A theoretical model and an experimental system of active control of plate vibrations using piezoelectric patch actuator and accelerometer are implemented. The stability of the control me-thod is analyzed theoretically and experimentally. Besides, a kind of internal modal filter (IMF) is proposed, through which the acceleration signal can be transformed into velocity signal. This IMF can guarantee the collocated properties of the transducer pairs. Both simulation and experiment results show that the decentralized feedforward control strategy is a kind of effective control method.

Carbon deposition of organic heat transfer heater is a key factor for the fire risk assessment. In this paper, ultrasonic guided wave was used for the carbon layer detection of organic heat transfer heater. Also, the detection principle and its test system were described. However, due to multi-mode and dispersive nature of ultrasonic guided waves in pipes, time-frequency analysis was used for the identification of ultrasonic guided wave modes for carbon layer inspection. Time-frequency representation of received signal is closed to theoretical dispersion curve of L(0,2) mode. Furthermore, the relative error of experimental group velocity of received signals and theoretical group velocity is only 1.88%~3.48% by time difference method. Therefore, received signals mainly consist of L(0,2) mode. The research results provide a significant theoretical foundation for the carbon layer detection technology of the organic heat transfer heater.（蓝色部分为修改意见1的修改，英文摘要已经重写，实验部分为过去式，实验结果为一般现在时，做到简短、明了和达意）

In actual production and service condition of heavy freight car, the wheel/rail interaction is influenced not only by incentive effect from all kinds of track irregularity, but also by incentive effect from changes of wheel state. From the perspective of wheel running state, change and trend of wheel/rail interaction is studied , which is based on parameters of wheel status with wheel tread shape, wheel polygonization, wheel eccentric mass and wheelset structural deformation. The result indicates that wheel tread shape changes area of contact spot and distribution of contact stress; in different speed, depth, phase and order of wheel polygonization have different influence on wheel/rail vertical force; Wheel eccentric mass produces periodic vertical impact between wheel and rail, but the amplitude of vibration is not large; the change of wheel/rail dynamic contact load with the deflection change of wheelset is remarkable, especially structural bending vibration of wheelset intensifies the wheel/rail vertical action force.

In order to reduce diesel engine vibration, low vibration optimization design was proposed based on empirical mode decomposition and time-frequency analysis. Firstly, Multibody Dynamics and finite element method was used to simulate the engine block vibration and the simulation results were verified by the test results very well.Then the empirical mode decomposition was used to decompose the vibration velocity signal of crankcase skirt. And the component of the decomposition results ,which has the largest vibration energy, was time-frequency changed by wavelet analysis. The time-frequency analysis results provided the main basis for structure optimization. At last, the vibration responses of the original block and the optimized structure were validated qualitatively by the wavelet analysis result and quantitatively by the Hilbert transform result.Results show that the vibrating intensity of the optimized block is reduced by 26.81% and the engine vibration is dramaticlly reduced. Therefore, it vertifies the effectiveness of the method.

The isolation efficiency of multiple friction pendulum bearings (MFPB) is checked by shaking table test. The results show that changes of load on the isolation layer make no difference in the isolation effect of MFPB and the cooperation of MFPB with viscous dampers can control the displacement of the isolated structure. The test also verify that the vertical seismic input has no significant impact on the isolation effect of MFPB and it is feasible to simulate MFPB by using friction-connection element in SAP2000, with precision which can meet the requirement for application in engineering.

The frequency response transfer function of different pipe lengths is determined with the pressure measurement system. Furthermore, effects of the pipe length on wind pressure coefficients and wind-induced response on a flat roof are investigated without the pressure correction. The results show that a short pipe usually amplifies the fluctuating wind pressure, and a long pipe reduces the pressure. Fluctuating wind pressure diminishes significantly with a very long pipe, especially at the high frequency; the effect of the pipe length on wind-induced response is less than that on wind pressure coefficients on the roof; the relationship between the pipe length and the calculation errors of wind pressure coefficients and wind-induced response is nonlinear and oscillating, and the calculation error is relatively smaller for the pipe length around 100cm; the wind pressure correction is necessary for most pipe lengths.

In order to simplify balancer’s self-locking structure, the magnetic balancer obtaining self-locking state by design of magnetic circuit is proposed. When coil is not energized, there is a minimum magnetic resistance between the adjacent two permanent magnets and magnetic toothed discs, so the stable balanced position can be held. When coil is energized, the balancer starts and then moves to the next stable position under the interaction of electromagnetic fields and permanent magnets. The structural parameters of balancer affecting its self-locking torque and starting torque are discussed, and these parameter’s ranges are roughly designed. By finite element electromagnetic analysis, the quantitative relationships between these parameters and self-locking torque and starting torque are obtained. Based on the above results, the design and development of magnetic balancer prototype are completed. Its self-locking reliability calculation and test, starting capability and stability test are accomplished. Compared with the results of calculation and test, the structural design and parameter selection of the developed balancer are correct. This work provides an important reference for the future engineering applications of the proposed balancer.

In order to determine the duration of shock pulse used as an excitation in the absolute calibration of high-g accelerometer, a calibration principle was put forward based on mathematical model of accelerometer. For the accelerometers with different natural frequency, the principle presented the relationship of the first order natural frequency and damp of accelerometer, calibration error and the least excitation pulse duration. With a Hopkinson calibration system, the correctness of the principle was validated by calibration experiments for a high-g accelerometer 988 and SIMIT-AYZ-3. This principle has provided the theoretical basis for the determination of the shock pulse duration in the absolute calibration.

The precision of vibration frequency estimation by adaptive notch filter (ANF) is not satisfactory all the time. The analysis pointed out that the fundamental reason is the ANF error converges to a local optimum value. A feedback corrected ANF is proposed referring to the idea of feedback control. According to the correlation between the input signal and the output signal, a factor evaluating the frequency tracking accuracy is designed to monitor the ANF work status. If the factor is less than a given threshold value, it’s considered the ANF lost vibration frequency. Then, it is demanded to enlarge the bandwidth of the ANF, so that the frequency can be re-tracked accurately. To insure the re-converging speed, a strategy of feedback adjusting the ANF parameters appropriately rather than re-initialization is applied. The ANF based on Steiglitz-McBride method(SMM-ANF) is tacked as an example to illustrate the feedback correction strategy. The signal processing flow and particular algorithm are also exhibited. The performance of Lattice ANF, SMM-ANF and the feedback corrected SMM-ANF are compared by simulations. An application instance of the proposed method in coriolis mass flow meter is given out briefly. Results show that the convergence rate of the feedback corrected SMM-ANF is little lower than original SMM-ANF, higher than the lattice ANF. The continual frequency tracking performance of the feedback corrected SMM-ANF is obviously better than the others.

The vortex shedding response of a box bridge girder deck with and without railings had been investigated by wind tunnel experiments with the objective of identifying the mode of vortex excitation and effects of railings on vortex-induced vibration of bridge deck. Tests on 2 spring suspended models (deck with railings and bare deck) reveals this situation. Measurement of the fluctuating pressure around the deck surface indicates that vortices shed from the downstream section with railings have greatly contributed to the vertical vortex-induced vibration, while the bare section pressure fluctuations over the entire upper and lower surface have little contribution to the vortex response. The presence of railings does not change the mean pressure distribution of soffit plate, but significantly change the pressure distribution on the upper surface. When introducing the railings it is noted that the fluctuating pressures on the entire lower surface and the downstream of upper surface are markedly increased.

An investigation on nonlinear dynamics of panel with boundary condition relaxation is carried out in this paper. The flutter differential equations of a three-dimension panel are set up by using separation of variables and Galerkin method. The first piston theory is employed to calculate the aerodynamic load on the panel. At first, the flutter boundary and stability for the flat pane are analyzed. Then Using the temperature, dynamic pressure and in-plane load as bifurcation parameters, their bifurcations and chaos behaviors were studied. The results demonstrate the rich dynamic behaviors of the panel with boundary condition relaxation and complex dynamic characteristic with variation of bifurcation parameters. Both the buckled region and chaotic region increase as the relaxation of boundary conditions and the stability of system decreases.

Plastic theory and numerical simulations are used to discuss the deformation patterns and the collapse mechanism of longitudinal web girder attached stiffeners in a shoal grounding scenario of a double bottom tanker. In the study, numerical simulation code LS_DYNA is used to calculate the deformation patterns and energy dissipation, and a mathematical model of the progressively deformed stiffener is built. With the application of plastic mechanism theory and numerical simulation method, the distortion energy and mean grounding resistances are obtained, and the results were verified. The analytical expressions obtained can be used to calculate and assess the crashworthiness of a ship during its design phase.

For the end effect of empirical mode decomposition (EMD) in pace with the increase of the filtering level, a new improved method using a combination of extension with variable cosine window is proposed. Firstly, the signal is extended with a certain length of data. Then the extended signal is processed at both ends with variable cosine window before extracting the every Intrinsic Model Function（IMF）, which makes the end effect of each IMF minimized and ensures the correct decomposition and the improvement of the EMD algorithm. Simulation analysis and crack fault diagnosis example show that the improved method can inhibit end effect effectively.

Due to the limitation of linear analysis of suspended pendulum control system with small swing angle, this paper proposed the method of analyzing the structural dynamic response considering the nonlinear property of pendulum, in which the linear stiffness of pendulum is revised to be nonlinear. Taking a 500 KV transmission tower as a numerical example and comparing the results at linear and nonlinear conditions, it can be found that the swing angle of pendulum may exceed the limitation of linear assumption and the nonlinear analysis can simulate the structural dynamic system with large swing angles of pendulum perfectly. The parameters of control system including excitation periods, pendulum length and mass ratio were studied on the influence of the seismic reduction ratio of transmission tower. Three seismic records were used to calculate the response of transmission tower with suspended pendulum. The results showed that the mitigation effect of suspended pendulum on structural response is very obvious under different seismic excitations.

During electromagnetic(EM) rail launch armature, the moving loads due to armature sliding can cause rail dynamic response. In this paper, based on the basic theory of elastic beam, a model is developed to investigate the dynamic response. According to armature velocity and sliding distance which determined by current dates obtaining from launch test, rail deflection under moving loads is approached. The deformations of rail along with rail position and launch time are obtained, and also, deformation under rail repulsion and armature contact force are contrasted. These results can provide references for further design of supporting structure and further analysis of EM railgun life length.

according to the structure of the tracked systems in tracked vehicles，the forces acted on the components of the tracked system were analyzed and a kinetic models for the components were established. The formulation of the track tension and the normal forces between wheels and ground were derived from the kinetic models, and the formulation were verified right by comparing the calculated results on the formulation to the simulation results on Recurdyn. The formulation provided a theoretical reference for the establishment of the tension control system.

To achieve a high performance, the design optimization of lumped parameter for Magneto-Rheological (MR) engine mount is essential. Mathematical model of single degree vibration isolation system was established and multiple interval sensitivity method is proposed to overcome drawbacks of conventional optimization design such as single objective optimization, improper optimization objective, unfeasible machining and so on. Optimization variables in MR engine mount are selected by lumped parameter multiple interval sensitivity analysis. The integral of force transmissibility through normal frequency range of engine is assigned as objective functions, non-dominated sorting genetic algorithm (NSGA-II) is improved and used to optimize design variables. The synthesized distance between Pareto lumped parameters and discontinuous lumped parameters that match along with the physical discretization dimension were calculated to select the most appropriate solution from Pareto lumped parameters.

The rolling bearing vibration signal can be decomposed into a number of intrinsic mode functions (IMF) adaptively according to its own scale by the empirical mode decomposition (EMD) method. The rolling bearing failure will vary the distribution of IMF energy, and the bearing fault diagnosis can be realized by establishing the relationship between the IMF energy distributions and bearing conditions based on the gray relational grade theory. In order to make up for the defects of the traditional gray analysis in pattern recognition, a gray similar relational grade model which can reflect the curve’s shape feature was proposed based on the similarity of the slope. Then combined with the traditional approaching relativity model, the gray comprehensive relativity diagnosis model which can reflect both the curve’s position and shape features was constructed. The simulation results show that the new model can recognize rolling bearing faults more effectively and accurately．