In order to extract structural information from the bridge structural dynamic signal with high noise level, a novel adaptive decomposition and reconstruction method is proposed by combining the ensemble empirical mode decomposition (EEMD) and principal component analysis (PCA) for the specific characteristics of bridge structural dynamic signals. Based on the in-depth analysis of mode mixing in empirical mode decomposition, the uniformity of probability density function for white noise is adopted to improve the pattern one of mode mixing, and the correlation analysis is used to ameliorate the pattern two of mode mixing, then the calculation efficiency and decomposition accuracy are upgraded greatly in the improved EEMD. The multi-scale principal components analysis is implemented on all of the intrinsic mode functions (IMFs) obtained by the improved EEMD for noise reduction and selection of IMFs. Moreover, the dynamic signal is reconstructed. The effectiveness of the proposed method is verified by both of the simulated signal and testing signal from real bridge structure. The verified results showed that the proposed method can decompose adaptively and denoise effectively the bridge dynamic signal with high noise, and can extract accurately the structural information from the testing signal, furthermore it is applicable in the dynamic testing analysis of real bridge structure.

Some impact dynamics topics motivated by the ship-bridge collision process are analyzed in this paper. It is shown that (1) in order to reduce the impact force a flexible (i.e. with low structural dynamic generalized wave impedance) crashworthy device should be applied. (2) The work done by the impact force is transformed via wave propagation into the internal energy (deformation energy) and kinetic energy. The larger the irreversible part of the former is, as well as the greater the overall role played by the crashworthy device is, the better the buffer role played by the crashworthy device will be. Moreover, how to make the ship as soon as possible to end the collision and carry away as much as possible the remaining kinetic energy should be a key point. (3) Viscous dissipation of energy can buffer the collision process, prolong the dissipation duration, and help the crashworthy device to play an overall role, and create the condition for turning ship away to end the collision. Thus the scientific design idea of crashworthy device should be based on (i) impact flexibility in terms of low structural wave impedance, (ii) viscous dissipation in terms of damping collision process, (iii) let the crashworthy device plays an integral role as soon as possible so that the intense impact concentrated force could be changed into a weaker distributed load, and (iv) let ship turns away as soon as possible, and thus takes away the remaining kinetic energy as much as possible. As an engineering application example, such design idea is reflected in the new flexible crashworthy device consisting of hundreds of steel-wire-rope coils. Its validity has been confirmed by the engineering practice and the real ship collision tests.

Along with the increase of scale of hydropower station and single unit capacity, the vibration problems of hydropower houses are becoming acute. It is useful to assess a hydropower station safe, if the structural vibration characteristics of a hydropower house can be known. In this paper, basing on correlation analysis of the prototype observation vibration data of a huge underground power plant, the vibration prediction model of the hydropower house was established using relevance vector machine method (RVM). With the model, the vertical vibration responses of the powerhouse can be predicted by the vibration data of units and pressure pulsation data of the draft tube. The results show that the prediction model has high accuracy.

In order to realize the precise identification of the acoustic vibration test parameters about the supersonic aircraft, a new filtering method combining phase space reconstruction and singular spectrum decomposition is proposed. Firstly, feasibility of this method is demonstrated through numerical simulation. Secondly, in order to separate the signal subspace and the noise subspace, phase space reconstruction of the test parameters is processed, and the attractor track matrix is also decomposed with singular value decomposition (SVD). Finally, aiming at the shortage of the maximum difference spectrum theory, the concept of optimizing difference spectrum theory is given, and reconstruction is proposed on the basis of the peak position of the optimizing difference spectrum. Reconstruction results show that the proposed method is suitable for processing the acoustic vibration test data of the supersonic aircraft, providing a solution for the precise description of the supersonic aircraft flying state.

By using modal filtering method, a modified sensor fault detection approach based on structural dynamic characteristics is presented. An array of accelerometers attached on the surface of the beam are taken as sensors. The differences between the reconstructed signals by modal filtering and the measurement signals are obtained, then the curvature of the errors are taken as sensitive index to detect and identify the simulated fault sensor of sensor array. The numerical simulation and experimental result show that the proposed method can detect the fault sensor efficiently. Furthermore, this method is independent of the location of the excitation and it can be used for real-time monitoring system.

As a generalization of the spectral correlation density, modulation intensity distribution (MID) can extract the amplitude modulations of either discrete carrier signals or random ones satisfactorily. However, the computational effort of modulation intensity factor in MID is so heavy that it can not satisfy the real time request of industrial applications. Then, a new method, that is combination slice analysis of MID (C-SMID), is proposed in the paper to detect the characteristic frequency of bearing faults. Firstly, the speed variation range of the rolling bearing is used to decide the possible frequency fluctuation range of the bearing fault signal in the new method. Then, the value range of the selectivity factor △f is set and the character slices of MID is calculated out. Finally, the bearing fault type is judged based on the signal energy comparison between different slices. Comparing with the original MID, the new method has better anti-noise property and less amount of calculation. In order to verify the feasibility and superiority of the new method, several comparative experiments between it with the common envelope demodulation method had been executed based on the simulate signals and the measured ones that acquired from the rolling bearing fault simulation experiment platform of QPZZ-II. The experiment results show that the new method has higher detection precision for such bearing faults as inner race, outer race and rolling parts.

According to the innovative technique features of high-speed bogies for European vehicles, an optimized design methodology for the rubber suspensions of under-floor masses was proposed based on rigid-flex coupling simulation techniques. Lateral vibration coupling mechanism is meant the coupling mechanism of lateral high-frequency vibrations caused by the lateral secondary suspensions in the interface of coach to running gear, and the three important particularities are as follows: anti-hunting high-frequency impedance, higher damping of coach yaw and the aluminum-alloy coach without longerons and skeletons. The modal vibrations of 1st order lateral bending mode in coach bottom will have therefore the very negative impacts on the technical specifications of 30-year life-time coaches. For the rubber suspensions of under-floor masses, the proportional damping is one of active factors in suppressing the lateral vibrations of under-floor masses. But there is optimal value for lateral acceleration of middle floor, i.e. the minimum value of (RMS)3 in full frequency-band can be achieved when the proportional damping is 0.5. Meanwhile the limits of the above damping technique shall be paid much attention, i.e. it is possible that the lateral coupling vibrations of under-floor masses will be produced under the exceptional conditions of running gear.

The effects of seven different roof opening configurations on the net mean wind loads in a closing-ground building were examined using wind tunnel tests. The lift coefficients of roof, shape coefficients of center-line taps on roof and wall, local shape coefficients were specially studied and compared with the values from Code. It is shown that the net mean suctions on the roof are reduced for the configuration of roof center opening, the biggest value of positive shape coefficient on the center-line is +0.32, which should be taken account into the design of structure efficiently. The positive wind pressures in the configuration of roof corner opening are larger than that of roof center opening configuration, which are unfavorable for structure. The Chinese Code was found to significantly underestimate the local wind pressures of corner area Ra for roof center opening configuration, and the local wind pressures for roof corner opening configuration are larger than that of roof center opening configuration, which may be the result of continuing destroyed for the building. The positive wind loads on the windward wall are increased for roof center opening configuration, up to 86%, and the suctions on the backward and leeward wall are reduced largely.

Topology optimization design of steady-state heat conduction structure with interval parameters under dissipation of heat transport potential capacity constraint is discussed. The topology optimization model of heat conduction structure with interval parameter is constructed, which is based on non-probabilistic reliability with dissipation of heat transport potential capacity constraint. The total volume of heat conductive material is to be minimized and the relative thermal conductivity of elements is regarded as the design variables here. The computational expressions of numerical characteristics of dissipation of heat transport potential capacity based on interval factor method are presented. Evolutionary structural optimization method is used in the optimization. A filtering technique is employed to eliminate numerical instabilities in process of topology optimization. The numerical examples are presented to demonstrate the feasibility and effectiveness of the optimal model and solving approach.

In order to reasonably describe the seismic damage forms of corroded steel frame and the effects of different levels of corrosion on the seismic performance of steel frames, on the basis of the seismic damage model of steel structure which is proposed by Ou Jinping, et al, the seismic damage model of corroded steel frame is built. To determine the seismic damage model parameters of corroded steel structure, the calculation methods of the bilinear restoring force model feature points of corroded beams and columns member are given, and other model parameter values are obtained by elastic-plastic time history analysis. Using the weighted partial coefficient method to study the multi-scale effect of migration and transformation from member damage to structure damage, the overall seismic damage model of corroded steel frame is established. Combined with the characteristics of damage model in this paper, the corresponding structural damage index ranges with different damage levels are defined. Finally, elastic-plastic time history analysis has been performed for 5 specimens of flat steel frame structures with different corrosion rates, the results show that the damage model in this paper can reflect the degradation of steel frame structure with the corrosion degree in the certain degree.

A time-frequently approach based on Hilbert vibration decomposition method is introduced in order to extract fault features of multi-component mechanical fault vibration signals accurately. Firstly, the analysis signal of original vibration signal was obtained through Hilbert transform. Secondly, the non-stationary frequency of the largest component was achieved as a low-pass filter of the instantaneous frequency, the corresponding envelope and initial phase was also estimated according to the synchronous demodulation, then the time-frequency information of each component of the initial signal would be detected by each iteration step. Aiming at overcoming the end effects of HVD, a wave characteristics matching extending method based on correlation coefficient criteria is proposed to improve HVD. The analysis of two simulated signals showed a good capacity of HVD in decomposing the non-stationary multi-component signals, and the results inflected that the improved HVD inhibited the end effects. Finally, an oil whirl of rotor system fault diagnosis instance is given to validate the feasibility of this method.

The health of bearing has a tremendous influence on rotating machinery. A failing bearing not only could jeopardize the safety of flight but also induce collateral damages. It is necessary to monitor and judge the tiny earlier fault in an effective way. Compared with the conventional vibration detection approach, acoustic emission (AE) can detect the earlier state of the fault, as well as can diagnose the fault type and damage grade. The principle of rolling bearing fault by AE detection and the novel AE detection technique using fiber Bragg grating (FBG) are introduced. A comparative experimental study on the use of FBG sensor and the commercial PZT based transducers AE analysis for defect identification of the seeded defect on the outer race of the test rolling bearing was carried out. The experimental and analyzed results show that the signal of the FBG has better spectra than the PZT with clearer lines and lower noise basis. The fault frequency and damage degree can then be more easily identified. Finally, the applications of this technique in helicopter maintenance are introduced.

Oil whirl of steam turbine is a self-excited vibration, which results from instability of sliding bearing. The vibration frequency of oil whirl is denoted by half of the rotational frequency of rotor shaft or less. Once the frequency of oil whirl is equal to the first critical rotational frequency of rotor shaft, the vibration of steam turbine is intensified and the stability of steam turbine can be destroyed. Gabor transform is a reversible joint time-frequency distribution method, inverse transform of which has the ability of time reconstruction. In this paper, the vibration signals of 850 MW steam turbine are analyzed based on Gabor transform, and the semi-speed oil whirl component representing instability is detected, then the semi-speed component is separated using band-pass filter in time-frequency domain and reconstructed using inverse Gabor transform, at last a peak-to-peak quantization index is calculated to judge the level of oil whirl. The presented method can provide evidence for oil whirl fault diagnosis of steam turbine.

The analytical solution of moving Griffith crack model with a constant speed is well known as the Yoffe solution. For a static crack, the strip yielding model is well known as the Dugdale model. It is found that when the Dugdale model is generalized to the moving crack case, the crack opening displacement (COD) is discontinuous with the positive and negative infinite at the Rayleigh wave speed. A restraining stress zone is attached to the crack tip while two speed effect functions are introduced. Assume that there is a linear distribution in the restraining stress zone. The complex function approach is employed to solve the problem. Analytical solutions of dynamic stress intensity factor (SIF) and crack opening displacement (COD) are then obtained. The new COD result is continuous and is a finite value at the Rayleigh wave speed. Some numerical results of COD are given. Some valuable conclusions are obtained.

Buffeting forces of structures such as transmission tower usually have highly nonlinear relation to incoming wind fluctuations. Based on wind forces and simultaneous fluctuating wind speed measured from wind tunnel test on a model of 1000kV suspension transmission tower, aerodynamic coefficients and aerodynamic admittance functions are studied. Unsteady aerodynamic coefficients obtained in the test are compared with those estimated starting from linear and Gaussian assumptions. The concept of total aerodynamic admittance including structural aerodynamic damping effect is suggested, which is identified by ratio of power spectral density of wind force to that of fluctuating wind speed. The linear admittances, which represent correlated parts of the wind speeds and wind forces, are also calculated by employing frequency-domain coherence functions. Results show that linear assumption of relationship between time-dependent wind angle of attack and associated aerodynamic coefficient lends more accuracy than Gaussian assumption. Because of the unsteady nature of wind-speed-to-wind-force relation, neglect of aerodynamic admittances will lead to conservative estimation of buffeting responses of the structure. Moreover, effects of wind fluctuations will be underrated if linear admittances are adopted in spite of the prominent nonlinearity between wind speed and wind force.

Owing to the measured modal data is far less than the under identified parameters and the damage identification equation always have large errors, it leads to the application in complex structure is always limited in the traditional damage detection based on model updating. In this paper, the drawback is solved by dividing structural degrees of freedom into measured and unmeasured parts. Meanwhile, the unmeasured parts of the mode shapes of the damaged structure are characterized as a function of the structural parameter and measured parts of the mode shape. Considering damage as a reduction in element stiffness, then using the calculated modal data of an intact structure and the measured modal data of a damaged structure to establish the damage detect equation. The dual constrained objective function succeeds to recognize the changes in structural parameters, utilizing the trust region optimization method. The proposed method are verified by two numerical simulation cases and a damage detection experiment, the results show that it has a good ability to detect any damage of structures using incomplete measured modal data, and the algorithm also has good robustness.

In order to monitor and maintain turbine gearbox in time, This article presented a diagnosing method to turbine gearbox crack based on wavelet packet and cepstrum analysis. According to the characteristics that gear crack vibration signals being speed-frequency modulating meshing frequency and its octave, the meshing frequency range of the fault parts can be concluded through wavelet packet band energy monitoring, during which the wavelet packet decomposition was put forward to identify the fault features of the vibration signals. Considering that the cepstrum can separate and extract the period component of the dense modulating signals which were difficult to identify, and that it also can recognize the speed-frequency of the fault parts, we diagnosed the type and location of the fault parts through meshing and speeding frequency concluded from the utilization of these two kinds of spectrum analysis method. Experimental research has proved that the proposed method can diagnose the gear crack fault accurately, and moreover, this method can be applied to monitor the degraded condition in complex environment of wind turbine gear and thus preventing major faults from occurring such as broken teeth.

Based on finite element method and control volume method, a finite element model of equipment and its airbag cushion system were established and verified experimentally. The simulation of an impact of a few tenths of a second duration typically required tens of hours of CPU time. As a result, the optimization of the design based on a nonlinear model was very difficult by traditional iterative approach method. In order to overcome this problem with the design optimization of airbag cushion system for airdropping equipment, surrogate models were employed instead of the complex finite element model based on Extended Latin Hypercube method and Radial Basis Function. The height of airbag, the width of airbag and the area of vent hole were chosen as design variables. Then Pareto optimal solution sets based on response surfaces were obtained by multi-objective Genetic Algorithm. After optimization, the maximum acceleration reduces 19%, while the maximum attitude angle reduces 1%.The results show that the cushion performance and stability of airbags cushion system are obviously improved through optimization.

In respect of processing issue of drag reduction structure on oil and gas pipeline inner coating, a method of processing the drag reduction structure of bionic non-smooth surface on the coating surface of inner sides of pipeline was proposed. A structure model of inner sides of pipeline roll processing robot was established, and the movements of double cam component were proceed dynamics analysis. Combined with flow characteristics of the material, the flow characteristics of polymer coating material nearby the glassy state transformation temperature were analyzed. A mathematical model of the viscoelasticity of polymer was presented to describe the rheological behavior of polymer coating. Also, a method of numerical simulation was used to investigate the influence of controlling parameter on the hot rolled surface quality in the hot rolling process, and rolling experiment at the rolling speed of 0.5, 1.0, 1.5 rad/s was finished. The results showed that at constant temperature, the flow deformation of the polymer material was increasing with increasing time, and the stress relaxation phenomenon of Coating pit morphology suspended as the temperature decreased at the end of time. With the constant rolling speed, replication ratio of polymer coated pits increased with the rise of temperature. Also, the creep deformation speed rises when the temperature is high. Specially, when the rolling temperature is maintained in 2/3T of 150 ℃, the effect of morphology of Polymer coated pit obtains the best, and prolonging the dwell time can achieve the same filling effect at low rolling temperature. The pit morphology after rolling is closest to the ideal one at the rolling speed of 0.5 rad/s, which shows well the time dependence of polymer.