In order to study free vibration characteristics of K6 and K8 aluminum alloy single-layer spherical latticed shells with gusset joints, large amounts of finite element (FE) analyses were performed using the software ANSYS considering effects of rise-span ratio, span, roof load, span-thickness ratio, grid density and constraint conditions, etc.parameters.Based on the FE simulation analysis results, the formula to estimate the fundamental natural frequency of single-layer spherical latticed shells not considering effects of joint stiffness was derived.Then, by introducing the amplification factor for the fundamental natural frequency, the formula to estimate the fundamental natural frequency of aluminum alloy shells considering effects of their gusset joints’ stiffness was proposed.Finally, the calculated value obtained with the proposed formula was compared with the measured fundamental natural frequency of a certain actual shell with gusset joints in tests.It was shown that both of them agree well each other, so the effectiveness of the proposed formula is verified.

 

A mechanical model was built for the double-direction fluid-structure interaction problems of marine propellers by the 3D frequency domain panel method combined with the finite element method.The added mass and damping matrices due to fluid-structure interaction were derived, and effects of propeller’s skew angle and incoming flow velocity on the two matrices were analyzed.The results showed that the incoming flow velocity significantly affects the added damping matrix, but it has little effect on the added mass matrix; when considering the effect of added mass, the larger the skew angle of propeller, the more the first order bending modal frequency of the propeller drops, while the opposite trend is observed for the first order torsional modal frequency of the propeller.The study methods and results provided a theoretical reference for design of low-noise propellers.

 

Deep rock mass is a block-hierarchical structure, it plays an important role in rock nonlinear dynamic behaviors.Here, a test system was developed to investigate dynamic characteristics of deep rock mass.The test system mainly was composed of a loading device and a measurement system.Vibration exciters were taken as dynamic sources in the loading device to apply various forms of load dynamic and static combinations, such as, horizontal static load, horizontal impact and vertical impact to a structural system consisting of rock blocks.The measurement system consisted of acceleration sensor, charge amplifier, laser fiber displacement meter and dynamic signals measurement & analysis system.One-dimensional dynamic impact tests of a granite block model were performed to obtain the frequency spectrum and amplitude characteristics of elastic wave propagation.Test results showed that the test system's design is reasonable, it is easy to operate and has a high measurement accuracy; it can be used to study nonlinear rock mechanical phenomena of block rock mass.

Here, random initial imperfection configuration of an oil storage tank was modeled with a linear combination of its buckling modes, and the imperfection amplitude was assumed to be a normal random distribution with mean of zero.Geometric initial imperfection samples were generated with Latin hypercube sampling method.Then, the incremental dynamic analysis method was employed to obtain the relation between the peak of acceleration and the maximum radial displacement of the tank wall, and according to Budiansky-Roth criterion, the critical buckling stress of the tank wall was determined under the action of earthquake.Furthermore, a user-defined subroutine based on ABAQUS was used to realize seismic response analysis of the imperfect oil storage tank with the added mass method.Finally, the reliabilities of the oil storage tank considering geometric initial imperfections and not considering them under the action of random earthquake were solved.The contrastive analysis showed that with increase in seismic action, the dispersion degree of the maximum compression stress of the tank wall increases; its probability distribution exhibits non-normal characteristics; the random geometric initial imperfections significantly reduce the aseismic reliability of oil storage tanks.

Bridges’ seismic pounding leads to local damage of a structure, and even causes serious disarsters, such as, falling beam and collapsing.The irregularity of curved bridges makes their pounding effects be significantly different from those of straight beam bridges.A multi-scale finite element model of a typical 3-span curved bridge was established and poundings among its upper part’s main beams were simulated using the 3D contact-friction model combined with the explicit dynamic contact algorithm.The influences of pounding effects on the seismic response of the curved bridge under near-fault earthquake were analyzed.Meanwhile, a detailed parametric effect analysis was performed including ground motion parameters, pounding stiffness, expansion joint clearance and curvature radius, etc.parameters.The numerical results indicated that the seismic response of the curved bridge is significantly affected by inhomogeneous poundings and poundings restrict relative displacements of main beams; near-fault impulse earthquakes affects the pounding effect of the curved bridge more significantly than other two types earthquakes do; the maximum pounding force increases with increase in pounding stiffness and curvature radius, and decreases with increase in expansion joint clearance while main beams’ relative displacement response has the opposite changes; falling beam may occur at the curved beam outside due to excessive large outside tangential displacement.

Aiming at problems of rolling bearings’ weak failures being difficult to identify, a rolling bearing weak fault identification method based on fusion of the variational mode decomposition (VMD) and the singular value entropy was proposed.Firstly, VMD was done for vibration signal of a rolling bearing to obtain 4 intrinsic mode functions (IMFs).According to a mean square deviation-Euclidean distance index, IMF components containing rich fault information were chosen to perform signal reconstruction.Then, the singular value decomposition (SVD) was done for the reconstructed signal to obtain the diagonal matrix of singular values, and the diagonal matrix’s singular value entropy was obtained using the information entropy theory.Finally, the singular value entropy was used to distinguish working state and fault type of the bearing.The new method was verified with rolling bearing vibration signals of American West Storage University.The results showed that compared with the traditional EMD singular value entropy fault diagnosis method, this method can more clearly delineate rolling bearing weak fault classes to correctly identify a bearing’s weak fault.This study provided a reliable basis for weak fault diagnosis of rolling bearings.

Aiming at finite element model updating for a long-span concrete cable-stayed bridge, a model updating method was proposed based on the multi-objective optimization to fully use the structure’s static and dynamic test data.The updating objective function was constructed using the structure’s static displacements and dynamic modal frequencies, etc.actual measured data, parameters to be updated were chosen based on the sensitivity analysis.The finite element model of a certain concrete cable-stayed bridge in China was updated with multi-objective optimization using the non-dominated sorting genetic algorithm-II (NSGA-II) to obtain Pareto optimal solution set to the problem of finite element model updating with multi objective optimization.The modified finite element model was verified with the measured static and dynamic data.The results showed that not only the updated model’s static displacements and dynamic calculation results involved in the optimization agree well with the measured values, but also the updated model’s static and dynamic calculation results not involved in the optimization are closer to the measured values; this static and dynamic finite element model updating method for the concrete cable-stayed bridge based on multi-objective optimization has a satisfactory effect, and the updated finite element model can accurately and fully simulate the actual structure.

Based on the combination of the finite element method and the power injection method considering thermal effect, a simply-supported L-shaped folded plate was taken as a study object to investigate effects of nonuniform thermal load on statistical energy analysis’s parameters.Firstly, numerical analysis under the excitation of rain on a roof was conducted to verify the correctness of the acquisition method of statistical energy analysis’s parameters.Then the effects of temperature gradient and average temperature of nonuniform thermal load on structure’s modal density, internal loss factor and coupling loss factor were studied.The results showed that under the action of thermal load with different temperature gradients and the same average temperature, the L-shaped folded plate’s modal density drops and its internal loss factor and coupling loss factor simultaneously decrease with increase in temperature gradient; the effects of nonuniform distribution of thermal load on statistical energy analysis’s parameters of the L-shaped folded plate gradually increase with increase in the average temperature of thermal load.

A great number of long-span truss bridges are built in mountainous areas nowadays.Their flutter performance is usually determined through their elastic sectional model wind tunnel tests.In tests, their main girder torsional centers are set at centroids of the models in general.However, influenced by several factors, the main girder torsional center of long-span cable bridges may offset from its centroids to result in the deviation between the wind tunnel test results and the actual situation.Here, the vertical offset of the torsional center of a truss bridge was simulated through its sectional model wind tunnel tests.Flutter critical wind velocities of a long-span cable-stayed bridge and a long-span suspension one with different torsional center offsets were measured.The effects of elastic rotating center formed due to torsional center offset, moment of inertia, and torsional frequency on these bridges’ flutter critical wind velocities were contrastively studied.The results showed that as a whole, the torsional center offset from centroid causes increase in a truss bridge’s flutter critical wind velocity.

The finite element model modification method based on time domain response sensitivity analysis is widely used in local damage and crack parametric recognitions of linear structural systems.Here, this method was extended in parametric recognition of a nonlinear system.Starting from the motion equation of this nonlinear system, its forced vibration response was obtained with the numerical integration method, and then the time domain response sensitivity with respect to each parameter was derived through differentiating the response with respect to each physical parameter to construct the corresponding response sensitivity matrix for parametric identification inverse problem.Parametric identifications for Holmes-Duffing nonlinear system and the dual-sine Gordon system widely used in physical engineering were taken as examples to illustrate the application process of the proposed method.The results showed that the response sensitivity analysis method can be used to accurately and quickly identify parameters of nonlinear systems, and it has the advantage of being insensitive to measurement noise.

For the state equation   used for nonlinear dynamics system, the generalized precise time step integration method for nonlinear dynamics system is proposed with the combination of the generalized precise time step integration method and predict-correct method. Firstly, in any time-subdomain, the vk is used to estimate the unknown vk+j/m(j=1,2,…m) in the process of computation. And then the discrete nonlinear terms are expanded by using Lagrange interpolation polynomial and treated as load. As a result ,the generalized precise time step integration method can be used to calculate dynamic response, which is an unified  computational and easy programming method. Compared with the four single-step methods, one predict-correct method or the predictor-corrector symplectic time-subdomain algorithm, the numerical results show that the proposed method is more highly accurate and stable, capable of keeping appropriate efficiency. The algorithm can be used to calculate the nonlinear dynamic responses of structural systems with multi-degrees of freedom.

A bridge is a structural system consisting of various interrelated and interacting components, and any component’s damage under earthquake affects the bridge’s functional integrity.Adopting a single component fragility to express the bridge’s system fragility may over-estimate the bridge’s aseismic capacity.A multi-span RC continuous girder bridge was taken as an example, and its finite element model was constructed with the software OpenSEES to conduct a great number of nonlinear time-history analyses.Simultaneously considering seismic damages of bridge pier, lead core rubber bearing, plate-type rubber bearing and bridge abutment, the bound estimation method, Monte-Carlo simulation one and the product of conditional marginal (PCM) one were applied to establish the bridge’s system seismic fragility curves.These fragility curves were contrastively analyzed to judge the applicability and reasonability of the three methods.The results showed that the traditional bound estimation method and the PCM one depend on component fragility analysis results, while Monte-Carlo simulation method is able to directly construct the bridge’s system fragility curve and to independently consider effects of various uncertainties; the PCM method can be used to quickly construct the bridge’s accurate system fragility curve, and it is more applicable for the bridge system fragility analysis considering multiple failure modes.