Stoppers are often installed with the isolation bearings in bridges to avoid that the upper girder drop from the pier during earthquakes. In this paper a novel energy-dissipation stopper is proposed. The stopper remains elastic and provides reaction force to restrain the displacement of upper girder during small earthquakes. On the other hand when large earthquakes occur it can yield and dissipate energy, and reduce the seismic responses of the bridge. To verify the performance of the stopper, 5 specimens are designed and the experiment study is carried out. The results show that a reasonable designed stopper has reliable strength and can provide adequate energy dissipation capacity.
3D FE model of long air gap and composite laminate was built.Positive streamer growth probability model of along rod-plate gap is a stochastic dischargeone based on the traditional streamer theory. The detailed simulation process includes potential calculation of each grid point in air gap, routes list of all streamer developed around the pole, growth time calculation of route developed for each streamer and route definition with the minimum growth time as the selected priority one. When the streamer reaches composite plate, cross point of the streamer and plate is regarded as the attachment pointof lightning strike. Potential, temperature and heat stress distribution of composite plate can be obtained under high voltage wave of lightningstrike through direct effect analysis. The results show that high potential, temperature and heat stress produced instantaneously by fast streamer mainly spread out symmetrically along direction with the maximum conductivity on top plate. But the study in this paper only provides the preliminary analysis results as a quality description. In order to more accurately simulate the process of composite discharge effect under lightning strike, damage mechanism of ablation and heat mechanics for composite laminate needs to further take into account.
Study on finite element modeling and parameter identification of bolted joints which are widely applied in engineering is conducted in this paper. By adopting the basic theory of the thin-layer element with isotropic constitutive relationship, a method based on parameter identification for recognizing the mechanical characteristics of contact surface in bolted structures is proposed. Finite element modeling for single and multiple bolted structures are investigated respectively, ignoring the hole and the mass of the bolt, and the contact surface is modeled by using of thin-layer element. An optimization problem is formulated using experimental modal data for identifying the constitutive parameters of thin-layer element. When the identify parameters are adopted in the finite element model, the maximum error of the computational modal frequencies compared with the experimental data is reduced reasonably. It is shown that thin layer element with the identified parameters can be used for accurately simulating the normal and tangential stiffness of the contact surface. The proposed approach in this paper is available for precisely simulating the single and multiple bolted structures.
Adaptive delayed inverse model of mechanical system is adopted to determine time histories of multiple input forces aimed at the shortcoming that existing inverse system method relies on the state-space model. Adaptive algorithm is applied to identify delayed inverse model, followed by time domain force estimation using operational response combined with inverse model of mechanical system. Multi-input forces of simply supported beam were reconstructed by dynamic accelerations without and with noise disturbance. Simulation results illustrate that reconstruction accuracy decrease under noise condition but relatively satisfied and the method for multi-input identification is feasible. Furthermore, this method is validated experimentally.
The numerical simulation way studied hypervelocity impact has been discussed. Damage mechanism and the process of the debris cloud forming has been studied with the SPH method of ANSYS/AUTODYN code when spherical projectile hypervelocity impact thin shield. Tungsten alloy and RHA(Rolled Homogeneous Armor) material models and parameters have been given, using the methods, material models and parameters of the numerical simulation results in good agreement with the experimental results. fragmentation-initiation threshold velocity of the projectile, the average fragment size and the distributing of fragment size have been researched including its relation with the impacting velocities when the projectile hypervelocity impact the target.
Because of the existence of velocity pulse, the dynamic response of structure under near-fault and far-field earthquake may be different. Taking the equivalent pier of a typical railway bridge built in deep-water as an example, the vibration characteristic and dynamic response under the two kinds of earthquake were contrasted based on the potential-based fluid method from fluid-structure interaction theory. The research results show that, the vibration characteristic of pier is changed because of the water around it. With the increase of the depth of water, the natural vibration period of pier becomes larger and the first period increases by 10.4% when the water depth is 30m. The distribution of hydrodynamic pressure along the pier is parabolic, which is larger by near-fault earthquake, and the difference becomes more obvious with the addition of water depth. There is also significant difference between the dynamic response under near-fault and far-field earthquake, in addition, the dynamic response under near-fault ground motions is greater than that of far-field earthquake.The diplacement at the top of pier, the moment and shear force at the bottom of pier increase by 34.5%, 37.8% and 51.3% respectively under near-fault earthquake; while these three indicators are 17.0%, 21.8% and 40.0% for far-field earthquake. In summary, the destructive capacity of near-fault ground motions with obvious velocity pulse is far greater than far-field earthquake, so special attention should be paid to those bridges surrounded by deep-water in near-fault zone.
The shaking table test of a 1/6 scale multi-rib composite wall supported on frame, the test structure has undergone elastic stage, cracking up the whole process of destruction, the dynamic characteristics and the dynamic response of the structure in the various stages, inputting the El Centro wave, Taft wave, artificial seismic wave input, according to the seismic fortification intensity of 7 degree frequent, basic, rare, very rare and 8 degree frequent, basic, rare, very rare earthquake test,to study the model structure in each phase under the action of earthquake acceleration, displacement and strain responses, as well as the structure of the failure mode and failure mechanism. The results showed that: frame supported ribbed composite wall structure of its conversion layer shear failure mode of destruction, plastic deformation is mainly concentrated in the conversion layer; frame supported ribbed composite wall structure layers absolute acceleration response depends primarily on the first two bands formation, formation of a small order, wherein the first phase formation plays a role in absolute control.
In order to further broaden the design thought of vehicle suspension applying inerter, two types of vehicle ISD suspension have been designed based on the two parallel elements‘inerter and spring’ by using the anti-resonance of the inerter-spring-mass structure. Using genetic algorithm to get the optimized structural parameters of suspension, analysis in frequency showed that, compared with the passive suspension, the designed suspension structures can suppress the vibration at the offset frequency of the body resonance. Experiment on the second generation suspension has been carried out, a quarter vehicle suspension test bench including the second suspension structure has been built. In the random road input, the suspension working space square mean root has improved by 16.24%, the dynamic tire load square mean root has improved by 6.75%, and the body acceleration square mean root has also improved. The results show that the designed suspension structure can effectively improve ride performance and control stability.
In order to analyze the dynamic response mode of Kiewitt-6 single-layer reticulated shell with the substructure under impact, the shell with steel pipe column for numerical analysis was established by the ANSYS/ LS-DYNA program. Four dynamic response modes were put forward according the dynamic response. The influences of the impact energy, impact location, the stiffness of ring beams were studied. The impact test on single-layer reticulated shell model with steel pipe column was conducted. The dynamic stress, dynamic displacement and acceleration were measured and analyzed, and the damage patterns of impact columns were studied. The results show that the typical characteristics of response mode are the damage patterns of impact columns(slight damage, local dent, press-bend failure, shear failure).The dynamic response of reticulated shell with impact energy increases in addition to the response mode 4. The most unfavorable impact position is central column. The dynamic response of reticulated shell decreases with the increase of the stiffness of ring beams. And the numerical model is also proved to be reasonable by comparing the theoretical and experimental results.
In order to reducing the vibration of herringbone gear transmission system more effectively, vibration reduction design methodsare put forward respectively from vibration excitation source of herringbone gear transmission system (tooth meshing quality) and vibration transmission path (box structure). Tooth surface three-dimensional modification is choosen to optimizing the vibration between the herringbone gear meshing teeth under multi-loads. Topology optimization is carried out target with static (box deformation) and dynamic (lower natural frequency) in order to improve the gearbox dynamics structure, and the optimization results can indicate which parts of redundant material and which structure needs to be strengthened. Accordingly, gearbox structural size is optimized to obtaining minimum acceleration of gearbox feet. Example calculations and experimental results show that the method of tooth three-dimensional modification reduce vibration of 18.9% by experiment test and 20.5% by theoretical analysis,the method of gearbox structural optimization reduce vibration of 12%. The better effect of 27.3% decline is obtained by combination of two methods.
An external periodic load is considered to act on a fluid-conveying pipe clamped at both ends, and the nonlinear forced vibration for such a system is explored by the multidimensional Lindstedt-Poincaré (MDLP) method. According to the analysis, when the second natural frequency of the system is nearly thrice the first one, and the excitation frequency is near the middle of first two natural frequencies, a combination resonance with internal resonance may occur. The characteristics of this response are discussed, where the motions of first two modes are investigated in detail. The influence of excitation amplitude on the internal resonance is analyzed. Numerical examples reveal rich and complex dynamic behaviors caused by internal resonance and show that the occurrence tendency of internal resonance will die down and the response forms will vary with the excitation amplitude increasing. The convenience and efficiency of the MDLP method in predicting nonlinear dynamics are as well demonstrated by the results of the study.
The solution of scattering of SH-wave was given by the method which to use an circular boundary of large radius to approximate the straight boundary of surface layer. With the theory of Helmholtz, the general solution of the Biot’s wave function was achieved. Utilizing the complex function method and the boundary conditions, we could transform the present problem into the problem in which we needed to solve the infinite linear algebraic equations with unknown coefficients. Numerical results of the ground motion were provided. The effects of incident wave number, incident angle, buried depth, stiffness of inclusion and layer on ground motion were analyzed qualitatively. The results in numerical examples show that greatly impact on ground motion can occur due to strong interaction between the surface layer, circular cavity and inclusion.
To extract the sensitive damage features directly from the structural vibration responses, the singular value decomposition and the proper orthogonal decomposition are applied to decompose the structural vibration response matrix into a set of proper orthogonal mode, which can represent the structure natural properties. The singular value decomposition is firstly applied to the structural vibration power spectral matrix to figure out the modal frequencies, then the correlation matrix can be calculated at each modal frequency. The proper orthogonal decomposition method is applied on the correlation matrix, so that the proper orthogonal mode can be got, and the proper orthogonal mode converges to the normal structural mode, so the proper orthogonal modes can be used to construct a damage locating vector, and the damage can be located through the different stress distribution of each elements. The experimental results show that the proposed method can detect and locate the damage effectively.
In order to resist the impact of aircraft crash, Reinforced concrete (RC) or Steel plate concrete (SC) structures are usually used in the design of external walls in nuclear island buildings. For comparing the im-pact resistance performance of the above two types of structures, comparative simulation analyses of a group of 1/7.5 scale aircraft model impact tests are carried out by applying nonlinear finite element code AN-SYS/LS-DYNA based on force time-history analysis method in this paper. The damage modes of the walls and the residual velocity of the scattered debris and the deformation of rear-face steel plate calculated by this paper are compared to the impact test results and the results based on the missile-target interaction analysis method of RC and SC walls, respectively. Of course, it is important that the simulation results with the same thickness walls of different types (RC/HSC/FSC) are compared either. The results indicate that the FEM si-mulation results based on the force time-history analysis method are in good agreement with the test results and the impact resistance performance of SC walls is better than RC walls, especially the rear face steel plate is very effective in preventing the perforation and scabbing of concrete. Therefore, the thickness of SC structures can be reduced in important structures like nuclear power plants against impact of aircraft com-pared to RC structures.
The dynamic response of underground structure impacted by explosion is of great importance in the designing and evaluating of the protective engineering. The computational method for the dynamic response of straight-wall-round-arch structure to explosion seismic wave was investigated on the foundation of common deformation theory and matrix force method, and a rapid computation method is established. By the preseted method, the dynamic response of a typical straight-wall-round-arch structure was studied under different surrounding rock, subcrust and impact loading conditions. Results show that the rock grade, the thickness of subcrust and the loading mode all have notable influence on the structure’s dynamic response. The better the rock is, the lower the displacement and the internal force will be. And as the thickness of the subcrust increases, the peak value of the dynamic response decreases and delays.
Considering the nonlinear and non-stationary features of cutting chatter signals, this paper proposed a chatter recognition method based on Hilbert-Huang transform. By this method, firstly, a chatter signal is decomposed into a series of intrinsic mode functions (IMFs) by empirical mode decomposition (EMD), and then the IMF with rich chatter information is selected and filtered by a band-pass filter, and then the Hilbert spectrum of the filtered IMF is obtained by Hilbert transform, lastly, cutting chatter is quantitatively recognized by the standard deviation of amplitude of Hilbert spectrum. The effectiveness of the proposed method was validated by simulated and actual vibration signals. For comparison, the method by wavelet packet decomposition and wavelet spectrum analysis was also provided.
Based on the principles of cylindrical helical spring compressive deformation, dynamic equations of metal rubber vibration isolation system were derived. The metal rubber dynamic stiffness, frequency response and vibration characteristic were analyzed under the condition of a simple harmonic excitation. According to the method of harmonic balance, the influence of excitation frequency on metal rubber displacement amplitude, and the influences of metal rubber displacement amplitude and excitation frequency on metal rubber dynamic stiffness were analyzed. On the basis of the analysis of metal rubber vibration isolation system, the influences of metal rubber height, working face cross-sectional area and displacement compression on shock isolation coefficient were studied. Shock isolation coefficient could provide a reference on the design of metal rubber and its applications in engineering.
Aiming at analyzing the self-loosening mechanism of bolted joints under vibration, a three dimensional FEA model of bolted joints , which had taken thread into consideration, was built with the application of APDL, and the preload was applied on the bolted joints by dropping temperature, then FEA transient analysis of the bolted joints under transverse cyclic excitation was conducted. Effect of transverse cyclic excitation’s amplitude, initial preload, thread and bearing friction coefficients, the joints’ surface friction coefficient on self-loosening was investigated. The results show that the complete thread slip occurs prior to the complete bearing surface slip under transverse vibration; the smaller amplitude is, and the greater initial preload, thread and bearing friction coefficients are, the more difficult self-loosening is to happen; the joints’ surface friction coefficient has little relationship with self-loosening, however, the larger joints’ surface friction coefficient makes the needed shearing force, which induces the transversal vibration, larger. These are of great significance for understanding of fasteners’ self-loosening and designing of bolted joints’ anti-loosening.