In order to calculate and analyze the local and global impact factors (IMs) of a simply supported box girder bridge with corrugated steel webs (CSWs) accurately,the motion equations of the bridge and vehicle were established.The two system equations were coupled through the contact condition.Three dimensional vehicle models were established by using the MATLAB software and the finite element model of the PC box girder bridge with CSWs was established by using the ANSYS software,respectively.Considering the random excitation effects of the road roughness,the vibration responses of the bridge nodes could be obtained by using the MATLAB program to solve the dynamic equations of the vehicle-bridge system.According to the relationship between the dynamic and the static deflection,the local and global IMs of the PC box girder bridge with CSWs could be calculated.The obtained local and global IMs were compared and the relationship between the obtained IM and four important parameters,including the type of vehicle,the number of the loaded lanes,vehicle speed,and the road surface condition,was studied.The obtained local and global IMs were also compared with the China code JTG D60—2015 and the AASHTO standard specification.Finally,the reasonable determination method to calculate the local and global dynamic IMs of a simple supported PC box girder bridge with CSWs was presented.The conclusions can provide a reference for determining IMs of this type of bridges.

In order to improve the firing accuracy of a 12.7 mm heavy machine gun system,the effects of the muzzle mass on the muzzle dynamic responses and firing accuracy were studied with rigid-flexible coupling dynamics,exterior ballistic theory,and corresponding experimental test data.Studies show that: as the muzzle mass increase,the shot dispersion parameters R50,R70 will increase first and then decrease.Since excessive muzzle mass will make it not easy to achieve lightweight design of a machine gun system,it is advisable to reduce the mass nearby muzzle.When reduce the muzzle mass to zero,shot dispersion parameters R50,R7 in the initial design will be significantly reduced from 7.7 cm,11.6 cm to 2.7 cm,5.0 cm,and can be increased by 0.65 and 0.57 times,respectively. 

The fluctuation degree of the loaded transmission error curve can reflect the dynamic performance of a gear pair.The greater the fluctuation amplitude,the bigger the noise; the smaller the fluctuation amplitude,the smaller the noise and the transmission is more stable.Firstly,based on the local synthesis method (Synthesis Local),and according to the processing principle of the Gleason hypoid gear,the processing parameters of the HGT hypoid gear were designed.On this basis,the first order derivative of transmission ratio function   and the angle between the contact trace and the root cone   were treated the optimization variables,and the amplitude of the loaded transmission was treated as the objective function,then the optimization design for the processing parameters was done through the genetic algorithm,for improving the dynamic characteristics of the gear pair.It is found that: ① when the gear load torque is 800 N•m and 1 500 N•m, the amplitude of the loaded transmission error is reduced by 37.92% and 16.57% respectively; ② in order to keep the desirable vibration characteristics of gear pair,it should be to work near the load of local minimum amplitude; and with the increase of,the local minimum amplitude is moved to the direction of large load; it illustrates that,in order to make the gear pair with a smaller load bearing capacity,the amplitude of the loaded transmission error is larger.

A steel-concrete composite edge girder is widely used in a long-span cable-stayed bridge,but it frequently leads to remarkable vortex-induced vibration and low flutter critical wind speed.Therefore,aerodynamic measures are always needed to improve the aerodynamic performance when this type of bridge is built in coastal region.Based on two cable-stayed bridges with steel-concrete composite edge girder,the controlling effect of stabilizer on the steel-concrete composite girder was investigated with a series of sectional model wind tunnel tests.The results indicate that the stabilizer can effectively eliminate vortex-induced vibration and increase the flutter critical wind speed of the edge girder section.

The concrete specimen under freeze-thaw environment was experimentally studied through uniaxial compression test with different loading rates.The mass loss of specimen was measured after different freeze-thaw cycles.The complete stress-strain curve of specimen was analyzed.And the variation characteristic of uniaxial compressive strength,peak strain varying with loading rate was given.A preliminary study on the meso-structure of specimen with different loading rates was analyzed by the application of CT technology.The results indicate that the dynamic ultimate compressive strength decreases with the increasing of freeze-thaw cycles under the same loading rates,and that the dynamic ultimate compressive strength raises with the increasing of loading rates under the same freeze-thaw cycles.Cracks appearing in these specimens under low loading rates are less and propagate mainly along the weak interface,which present centralized formation.On the contrary,cracks gradually become scattered at high loading rates,which become reticular formation as well.The cracks penetrate the aggregates evidentially increase with loading rates and the number of aggregating fracture increase at exponential speed.Based on the above data,the dynamic damage mechanism of concrete was systematic studied under freeze-thaw cycles.

The sensitivity analysis and design of flexible suspension parameters of hanging devices were proposed to improve the first order vertical bending frequency of the fully equipped car bodies.The vertical bending frequency was optimally designed with the thickness of body frame as design variables based on the modal sensitivity analysis theory.The influence of suspended forms and rigidity of rubber on the first vertical bending frequency was analyzed.The results show that the first vertical bending frequency of the car body can be changed from 9.70 Hz to 10.60 Hz while the mass of car body was increased by 0.93 t.The first vertical bending frequency of FE models of fully equipped car bodies was enhanced to 10.51 Hz by adopting the method of flexible suspension while the mass of the car body was constant.In contrast with the sensitivity analysis,the design of flexible suspension parameters of hanging devices is easier for engineering application and the mass of car body is constant.

A high power wind turbine gearbox is one of the key parts in wind turbine.The stability performance of the wind turbine is influenced by the characteristics of the wind turbine gearbox.According to the parameters and conditions of a typical wind turbine gearbox,the sub-structure model of the wind turbine gearbox transmission system was built considering the time-varying mesh stiffness and transmission errors.Base on the theory of uniform bend Timoshenko bean and cantilever beam,the sub-structure model of the housing structure system was established.On the strength of the deformation compatible conditions for the models of the transmission and box sub-structure,a coupled dynamic model of high power wind turbine gearbox was built and the vibration responses of the coupled system was calculated.The results show that the structure frequencies of the system were excited by the gear meshing of the different stages in the coupled system.The resonance does not occur between the structure response and gear mesh frequencies.The vibration acceleration frequency of the system composed of the frequency modulations except for the gear mesh frequencies of the system.Finally,the analysis results were compared with the results from the rig test.

New concepts including variation probability,variation speed,and variation acceleration,were proposed and a reliability prediction model was established to predict the variation process of reliability of rolling bearing vibration performance based on the maximum entropy principle and Poisson process.The maximum entropy principle was applied to calculate the probability density function of sample data of the intrinsic sequence.According to Poisson process,variation number and variation frequency of performance data outside the confidence interval of intrinsic sequence were achieved for time series subdivided.Variation speed and variation acceleration of rolling bearing vibration performance were calculated by discrimination processing for time.The rolling bearing (type SKF6205) was used as an example to illustrate the applications of maximum entropy principle and Poisson process in analyzing variation process.Experimental investigation shows that the variation probability of reliability presents a nonlinear increase trend with the increase of wear diameter,which can be divided into initial running stage,normal performance degradation stage,and performance deterioration stage.Moreover,the reliability prediction model can be used to analyze variation process of reliability under the condition of poor information,which is proven to be a useful supplement to available reliability methods.

 

Floating wind turbine blade pitch fault followed by emergency shutdown may cause large loads fluctuation in wind turbine drivetrain,nacelle,tower,and support structures.Coupled non-linear aero-hydro-servo-elastic simulations of a submersible platform supported floating wind turbine were carried out for blade pitch fault cases over a range of environmental conditions.The loads and moments in low-speed shaft,nacelle,tow-top,tow-base and the motions of floating platform were investigated.The results show that loads and moments in the wind turbine system increase significantly in blade pitch fault followed by emergency shutdown condition comparing to the normal operation phase.However,the increases of the loads and moments are effectively remitted using the optimized control methods of blade pitch fault followed by high-speed shaft brake and low-speed feathering. 

Based on the torsion spring model and the modified Paris formula,an analytical method was proposed to predict the fatigue life of a cantilever beam with an initial crack under different external temperatures.In the modal analysis process,the temperature module was introduced through the elastic modulus,and the cracked cantilever beam was transformed to two intact elastic beams by using a torsion spring to replace the crack segment; An inherent vibration characteristic equation of the cracked beam would be deduced under different temperatures,and effects of temperatures and crack geometric parameters on the frequency of the cracked beam would be analyzed.In the fatigue life analysis process,the damping loss factor was introduced through the complex elastic modulus.Considering the interaction of the cracked beam vibration and the fatigue crack growth,effects of temperatures,dampings and crack geometric parameters on the fatigue life of the cracked beam would be analyzed based on the modified Paris formula and the timing analysis method.Results indicate: the natural frequency and fatigue life of the cracked cantilever beam gradually decrease with the decreased relative position and the increased relative depth of the crack.And the increase of external temperature leads to the decrease of the natural frequency and fatigue life of the cracked cantilever beam.The fatigue life of the cracked beam gradually increases with the increased damping loss factor. 

A new Cayley-Hamilton transfer matrix method was proposed by integrating the Cayley-Hamilton theorem and the transfer matrix method.It was based on the theory of differential equations and matrix analysis.Adopting this method,the space vibration transfer matrix of the discrete curved box girder bridge model was derived taking into account the spatial bending,shear,torsion,tension,compression,warping and their coupling effects.With a simply supported single span curved bridge as an example,a calculation programming was conducted to obtain the vibration frequency and vibration mode of the bridge by using the derived matrix.And compared with the results of the finite element method,the results agree well with each other.It demonstrates that this method is effective.

Steel tubes process excellent performance of energy absorption.Sandwich panels have advantages in strength and rigidity.The tube-core sandwich panels used for blast resistant were studied in this paper.Contact blast experiments with 1 kg TNT were carried out to test the five-tube-core sandwich panel,the four-tube-core sandwich panel,and the three-tube-core sandwich panel.For each panel,the deformation and failure subjected to contact blast loading were investigated.The process of deformation and failure were researched by theoretical analysis and numerical simulation.Researches show that the tube-core sandwich panels consume energy mainly by local compression deformation.To reduce the deformation and improve the contact blast resistance of the sandwich panels,it is effective to increase the number of tubes or enlarge the thickness of face sheets and tube walls.

 

Fiber Bragg grating (FBG) sensors have great application prospects in identifying impact location on aircraft,especially for real-time monitoring.Here,a method to identify impact location was designed based on wavelet packet energy eigenvector and the similarity measurement algorithm,according to the relationships between amplitude-frequency characteristics induced by different impact locations,the closer two impact locations,the similar these two amplitude-frequency characteristics.Then,a monitor system was constructed of fiber-reinforced composite laminates and FBG sensors to verify the effectiveness of the proposed method.Initially,an energy eigenvector database was established by impacting all selected points on the laminates.Then,energy eigenvector was recorded by impacting an arbitrary position.By computing the similarity between the energy eigenvector recorded and all energy eigenvectors in database,the impact location could be determined with a tolerable error.Within 16 experiments on a 480 mm×480 mm fiber-reinforced composite laminates,the maximum error was 40mm.

The accuracy of five kinds of formulations were assessed by comparing exact and approximate response spectra for three different damping levels,namely 10%,20% and 30%,respectively.The comparison was referred to 120 ground motion records matched with Class II site condition.The most simple and straightforward solution to get the displacement spectra was to convert the acceleration spectra from seismic design codes using pseudo-spectral relationship,which was correct only for systems without damping,as well as sine and cosine relationship could be neglected.Consequently,it was necessary to evaluate separately for high-damping acceleration response spectra and high-damping displacement response spectra.The results show that the damping modification factors proposed by Lin & Chang is suitable for developing high-damping displacement response spectra,and the damping modification factors proposed by China code for seismic design of buildings is suitable for developing high-damping acceleration response spectra.

In order to study the effect of different positions of branch pipes on gasoline-air mixture explosion,an experiment system of gasoline-air mixture explosion was set up.Gasoline-air mixture explosion experiments with 1.75% oil gas concentration were conducted in a straight pipe and with different positions of branch.The changes of overpressure,rate of pressure rise,flame propagation velocity and flame intensity were analyzed.Experiment results indicate that overpressure,rate of pressure rise,flame propagation velocity,flame intensity,and flame duration are strengthened with the existence of the branch pipe,and when the branch pipe is farther from the ignition point,the effect is greater; the effect of flame propagation velocity on flame duration is also big; the changing curve of overpressure before the branch pipe can be divided into 4 phases: accelerated increasing,inflation pressure relief,oscillation strengthened,and dying out of oscillation; the changing curve of overpressure after branch pipe can be divided into 3 phases: accelerated increasing,oscillation strengthened and dying out of oscillation.