A high-performance 3 Degree of Freedoms Dynamic Structural Testing System (3DOFs testing system) which is mainly built by MTS servo-hydraulic system was developed in this paper. Its prominent advantages are accurate control and comprehensive function. A two-loop feedback control strategy was indicated and extended to multiple actuators’ coupled control. To demonstrate the performance of the proposed testing system and control strategies, a full-scale steel column is considered. It is concluded that, by using the coupled control strategy, the testing system can perform perfectly in the quasi-static test, the vertical force can be kept constant, and shear-mode loading can be achieved simultaneously. Furthermore, by applying α-OS method in the hybrid test, it is proved that the 3DOFs testing system can accurately simulate the complex boundary conditions of column substructure, harmonious loading of multiple actuators can be successfully implemented. The results may promote other studies on multi-axial testing system.
A bio-jumping mechanism inspired from locust take-off mechanism is designed and fabricated. Firstly, the kinematics and mechanical characteristics of the locusts’ take-off phase were investigated by high-speed camera experimental study. The results show that the locust saltatorial leg has a non-linear force output characteristic in take-off phase, which could effectively avoid the impact of instantaneous force changes. Then, a bio-jumping mechanism inspired from locust take-off mechanism was designed. By adopting a six link mechanism as the saltatorial leg and a linear spring as storage mechanism, the linear force generated by the spring can be converted into nonlinear output force of foot. Finally, a prototype of bio-jumping mechanism was developed and the experiments for the take-off phase were carried out. The experimental results show that the designed bio-jumping mechanism has the similar movement characteristics as that of the locust during take-off phase, and it can realize relative to 129% of its own jumping height. The results provide a new approach for design of the jumping robot.
The governing differential equations for axially moving Timoshenko beam made of functionally graded material are obtained based on the Hamilton principle. A single fourth-order partial differential equation is derived by introducing a new unknown function. For simply supported FGM Timoshenko beam, the characteristic equation is obtained by using WDQ method, and the relation of the first three orders complex frequencies of the beam with axial movement speed are given. The form of instability of the FGM Timoshenko beam in different value of axial movement speed is analyzed in detail, and compared with that of the homogeneous material beam. The effects of length-to-height ratios and gradient index on the stability of the FGM Timoshenko beam are discussed.
The two-dimensional model of sound absorption layer containing period cylindrical holes indicates that: when the plane wave normally incidents, the acoustic performance of sound absorption layer has been controlled by the first axisymmetric wave, under the frequency where the propagating attenuation of the first mode is lower than that of other higher modes. Based on this conclusion, the effective impedance of cylindrical tube, which represents the unit cell of sound absorption layer, has been derived. Besides, together with the transfer matrix method, the simplified model for the acoustic performance prediction of sound absorption has been obtained. Next, the genetic algorithm has been used to simultaneously optimize material properties and structural parameters of sound absorption layer which contains periodical cylindrical-conical holes, and the conclusion indicates that compared to the single optimization of material properties, the simultaneous optimization of material properties and structural parameters may result the higher sound absorption coefficient in a wider frequency range.
In this paper, the rubber bearing/shaft system is simplified into a nonlinear elastic bearing/shaft system. A general bearing/shaft rubbing system with nonlinear elastic support of stator is established and is analyzed by the modern nonlinear dynamics and bifurcation theories. The boundaries for the existence of the no-rub responses are determined analytically, and the synchronous full annular rub solution are derived and the stability is analyzed to determine the region of the synchronous full annular rub response. The results provide an opportunity for a better understanding of the dynamical characteristics, such as the synchronous full annular rub motion, the jump phenomena as well as the transition between the full annular periodic rub motion and the unstable rub motions. A systematic study on the influence of the system parameters such as damping and eccentricity on the dynamics characteristics is carried out. An overall picture of the response characteristics of this model is then obtained by drawing the existence boundaries in the parameter space. The present results provide good understanding on the relationship between the different rubbing responses and the system parameters.
In order to meet the environment vibration requirements of building which is sensitive to vibration, four different measures of track vibration mitigation are adopted. The difference of various vibration mitigation measures in different frequency domain is known by comparing on-site vibration test results in the time domain and frequency domain, including Ⅲ style rail vibration absorber, flexible short sleeper, ladder sleeper and steel spring floating slab track in underground circular shield tunnel. The results show that: (1) Four measures can respectively reduce degree of Z direction vibration is 4 dB, 7.6 dB,.8 dB, 19.0 dB at tunnel wall. (2) High frequency mitigating vibration effect is higher than low frequency, and the weighted vibration acceleration level is significantly lower than the non-weighted. (3) spring floating slab track have obvious mitigating vibration effect above 12.5 Hz. Flexible short sleeper, ladder sleeper, and rail vibration absorber have obvious mitigating vibration effect above 50 Hz.
The rotor of high-Speed motorized spindles with eccentric mass generates two loads that are unbalanced magnetic pull and centrifugal force. Based on electromagnetic theory, unbalanced magnetic pull model has been developed. And the amplitude and frequency characteristics of the two eccentric loads have been also analyzed theoretically. The rotor finite element model used Timoshenko beam theory is established, which includes bearing stiffness matrix and the two eccentric loads. The natural frequency and vibration mode are calculated from the rotor dynamical equations. The analysis of dynamic behaviors of the rotor affected by eccentric loads shows that the unbalanced magnetic pull and centrifugal force are the main excitation force. Finally, an overall experiment on a motorized spindle is carried out under several operating conditions. The good agreement between the theoretical results and the experimental data indicates that the two eccentric loads seriously influence dynamic characteristics of the rotor.
According to the shortcoming of traditional sandwich beam theory that the sandwich beam is incompressible in the thickness direction, a new sandwich beam theory is proposed by introducing independent variables in terms of the displacements of top face sheet, middle plane of soft core and bottom face sheet. The displacement of soft core is approximated by a second order polynomial in the thickness direction. Using continuity conditions along the face sheet and soft core, transverse displacement of soft core is obtained. Normal strain and shearing strain of soft core in the thickness direction are also obtained. Based on Hamilton principal, the governing equation of the system is established. Galerkin truncation method was used to solve the governing equation. It was found that (1) the first mode of soft sandwich beam displays that the face sheet and soft core move together in transverse direction and there is no relative deformation between face sheet and soft core, in this case it is consistent with the traditional sandwich beam theory; (2) the second mode of soft sandwich beam shows that the face sheet moves in opposite direction and the middle plane of soft core does not move, so the soft core is in the state of tension or in compression; (3) the third mode of soft sandwich beam displays that the face sheet moves in the same direction and the soft core moves in opposite direction, so the upper part and lower part of soft core are in different state (tension or compression). By researching the modal sharps, mode functions, response of free vibration, the effect of axially moving velocity on frequencies and so on, we can obtain that the incompressible model of sandwich beam is the special form of soft sandwich beam we establish in this paper.
Muzzle strong impact is a feasible test method of gun-power-recoil. For the waveform generator design of gun-power-recoil test machine, built finite element model of gun-power-recoil test machine based on ABAQUS. Through rubber tests, selected Arruda-Boyce model as constitution model of waveform generator. With average relative error of recoil dynamic properties between simulation test and live firing as design objective, built initial sample data based on orthogonal design method, and adopted QPSO-LS-SVM algorithm to optimize the waveform generator. This research will provide a theoretical reference for the design of gun-power-recoil test machine.
In order to consider the effects of honeycomb cardboard on the cushion performance of foam packaging system, the paper analyzes the dynamic performance of foam packaging system based on the finite element code Abaqus/Explicit. The simulation results reveal that the foam layer plays the key role in the buffer system under low initial impact kinetic energy, however, when the initial impact kinetic energy reaches a relative large value, the foam layer is insufficient to reduce the impact velocity and the honeycomb cardboard will assume important responsibility in the whole buffer process. The honeycomb cardboard can reduce the peak acceleration of the impact object significantly and thus improve the cushion performance of the whole system. So it is necessary to take the honeycomb cardboard into consideration in the process of designing cushion packaging system to avoid excessive package.
In order to study the dynamic mechanical properties and failure laws of coalmine rock material under passive confining pressure conditions, Ø50 mm variable cross-section split Hopkinson pressure bar (SHPB) apparatus was used to conduct impact compression tests in different loading rates with 45 # steel sleeve providing constraint conditions. Test results show that ductility and damage resistance of rock material increase under passive confining pressure. The failure axial stress of rock specimens under passive confining pressure is about 1.2 times as large as that without passive confining pressure. And its failure strain is also about 1 to 2 times bigger than without passive confining pressure. The radial stress increases with axial stain growing. The failure mode for rock specimens with or without passive confining pressure is different, with passive confining pressure is compression-shear mode.
Applying the semi-numerical approximate analytical algorithm, The property of period-doubling bifurcations in the Duffing oscillator was verified and analyzed. High order with high precision harmonic approximate analytical solution of the Duffing oscillator was obtained by incremental harmonic balance method. This verified and analyzed process have higher precision than experimental methods and do not need to compute the frequency spectrum with high frequency resolution. The results is in agreement with Feigenbaum’s theory. The theory is proved right further.
A new type of mechanical vibration table was put forward. Mathematical equations of the vibration elements curved surface were built up by analyzing the structure and the working principle of the mechanical vibration table. Through establishing dynamics equations of the vibration mechanism, functional relationships between the amount of spring preload and critical frequencies were obtained. A 3D model of the vibration table was created and motion simulation experiments were carried out on this basis. Then, the acceleration waveform distortions were obtained by analyzing the frequency spectrums and power spectrums of the output waveforms. Meanwhile, the relationships between the amount of spring preload and critical frequencies were verified. The test results show that the precision of the vibration table output waveforms and the upper limiting frequencies are higher than traditional mechanical vibration tables. Thus this kind of exciting method is proved to be feasible and effective.
Taking into account the coupling of rotor whirl and drum vibration, the dynamic model of a disk-drum-shaft system is established for the drum-disk type rotors in turbo-machines. Based on this model, effect of the unbalanced rotor whirl on drum vibration is studied in this paper. The results show that the unbalanced rotor whirl is coupled with the drum vibration modes which carry one circumferential wavenumber. If the support stiffness of the shaft is linear, the centroid motion locus of the shaft will be a circle and the steady-state vibration cannot be maintained. However, the centroid motion locus will be complex provided that the support stiffness of the shaft is nonlinear. Under this circumstance, slight and steady-state vibration of drum will be induced by the whirl of the unbalanced rotor.
Experimental and numerical simulation investigations were carried out on the dynamic buckling response of the liquid-filled and hallow thin-wall cylindrical shells subjected to lateral explosion loading. Impact experiments of explosion loading caused by 75g and 200g TNT charge on the steel cylindrical shells were carried out. The deformation modes of cylindrical shells were obtained under different explosion conditions. By means of an finite element computer code LS-DYNA，the nonlinear dynamic response process of the cylindrical shells subjected to explosion loading were numerically simulated with Lagrangian-Eulerian coupling method. The deformation process of the shell-wall，the time history of the velocities of some key nodes on the cylindrical shell and internal pressure of water were described. The numerical simulation results were in good agreement with experimental data. The results show that internal pressure of water will increase when subjecting to impact loading because of the incompressibility and liquid-filled cylindrical shells have better impact resistance than the hallow cylindrical shells.
The mechanical model was established for the series cushioning system made of dirrerent buffer materials on the basis of macroscopic constitutive relationships identified by the experiment data. The virtual mass method was introduced and then the optimization design procedures were presented . Then windows software package was made by using MATLAB/GUI, which can be isolated from main software MATLAB. A series of programmes mentioned in this paper give direct methods to optimized packaging structure design.
Ignition occurs under friction is one of the important reasons that lead to accidental explosion of pyrotechnic propellant. And the dynamic friction coefficient is a key parameter on determining the energy obtained through friction. A new method for calculating the dynamic friction coefficient is presented. The method combines the physical model of friction sensitivity tester with theoretical modeling and numerical calculations. The dynamic friction coefficient of black powder and expired single-base propellant are measured based on this method and experimental study. Meanwhile the effects of different experiment conditions on dynamic friction coefficient of both the propellants are discussed. The results show that the dynamic friction coefficients of both the propellants are a range value. With the increase of pressure and sliding velocity, the dynamic friction coefficients of both the propellants vary in some degree. Also the dynamic friction coefficient of black powder is greater than expired single-base propellant.
Acoustic Emission(AE) technique is widely used in monitoring material machining process. Scratch is an important removal mechanism during material removal, especially in precision machining. It’s valuable to research AE characteristic of scratch. Copper is semiconductor interconnect material. AE characteristic of scratch on copper surface was researched, and the effect of load and velocity on AE and copper removal mechanism during scratch were analyzed, giving theoretical support for monitoring nano- or micro-removal process on copper surface with AE. The results show: Copper deforms mainly plastically during scratch with a periodic morphology, generating continuous AE signal. Signal power increases as scratch velocity increases, while load has less effect on AE signal. Signal power has an exponential relation with the increase rate of deformed volume. The results show that AE can characterize the scratch process to some extent.
To understand and improve the anti-wave impact performance of coastal breakwater, the dynamic behaviors of the breakwater under wave impact were numerically simulated. The wave movement was modeled by using the multi-material ALE method. The interaction between the breakwater structure and fluid was studied by applying the penalty method. The model and approaches were validated by comparing numerical results with experimental data. Based on the above investigation, numerical simulation was performed to explore the distribution of seawall surface wave pressure and the maximum horizontal thrust. The effect of breakwater structure response to wave pressure was also dealt with in this research. The results show that: the wave pressures were in good agreement with experimental results, the wave impact was enhanced by structural dynamic response, and the rear wall withstands the larger wave horizontal thrust. It can provide references for the anti-wave impact design and overtopping design of the coastal Nuclear Power Plant breakwater.
By researching the bearing behavior of the variable-stiffness rubber bushing, both the finite element numerical analysis and experimental results show that the stiffness curve has obvious nonlinearity. The stiffness value is small and smooth under normal load conditions, while it grows up significantly with obvious inflection point in the stiffness curve under ultimate load. The position of the inflection point in stiffness curve can be directly affected by changing the height dimension of the stop catch in rubber bushing. Hence the stiffness of the rubber bushing can be changed by adjusting height of stop catch according to working conditions. The analysis results of finite element are used to calculate the equivalent stress range of peril point in the rubber bushing under fatigue loading according to hyperelastic characteristics of rubber material, and fatigue life of the rubber bushing is predicted with S-N curve and then is verified by fatigue bench test result. The result indicates that the rubber bushing is not failed after 1.5 million cycles of fatigue test, and the test fatigue life is accordant with the predicted fatigue life.
Acceleration response characteristics of a five-support counter-rotating dual-rotor system are studied. The transient dynamic model of the experimental counter-rotating dual-rotor system is established with finite element analysis software and fixed interface modal synthesis method. The acceleration time-domain characteristics, precession speed variation characteristics and the change laws of centroid of every disk in the rotor system are analyzed in the acceleration process. The study results show that: acceleration response characteristics of various cross-sections have a close relation with critical speeds and mode shapes of the rotor system; complex nonsynchronous precession exists in the acceleration process; centroid shift of inner and outer rotor occurs to their incentive critical speed respectively. Experimental verification was carried out, calculation results are in good agreement with experiment data.
An artificial fish swarm algorithm (AFSA) based novel method is proposed for structural model updating and damage detection, which is often converted into a constrained optimization problem in mathematics and is hopefully solved by the AFSA proposed in this paper. The basic principle of AFSA is introduced, some key parameters defined and four fish swarm behaviors simulated simultaneously, including searching, swarm, chasing and random behaviors. An objective function is defined as minimizing the discrepancies between the experimental and analytical modal parameters (namely natural frequencies and mode shapes). One numerical two-story portal frame structure and one laboratory-tested three-story steel frame structure are both adopted to evaluate the efficiency of the proposed method. Some illustrated results show that the proposed AFSA based method can effectively update finite element models, locate damaged elements of structures and identify extents of structural damages under different noise levels and all the damage cases.
In order to extract the vibration feature of remanufactured engine, the vibration signal is decomposed by ensemble empirical mode decomposition(EEMD), and this method is applied to study vibration mode of remanufactured engine. Based on the decomposition of vibration signal, correlation coefficient is introduced to study the correlation between IMF(Intrinsic Mode Function) components and original signal, and sensitive factors of IMF components are calculated using correlation coefficients. Hilbert transform is made with sensitive IMF components. The study results show that vibration feature of remanufactured engine is include in IMF components decomposed by EEMD, the vibration modes of remanufactured engine can be differentiated by Hilbert-Huang spectrum and marginal spectrum based on sensitive IMF components. According to vibration feature, the vibration state of remanufactured engine is divided into cylinder wall, cylinder cover and crankshaft vibration modes, which are important to improve the remanufacture level of engine.
The FEM\BEM acoustic-vibro-coupling method was applied to study the effect of blade outlet angle to centrifugal pump noise caused by the hydrodynamic forces. Firstly, the large eddy simulation method is used to solve the transient flow field of the pump, and the volute surface dipole was obtained. Secondly, the modal of the pump housing structure is analyzed using the finite element method (FEM). Lastly, the acoustic-vibro coupling module of the Virtual Lab software was employed to study the interior sound fields of the pump caused by the unsteady flow. By comparing the computational results with experimental ones, the validation of the LES combined with the FEM\BEM methods for centrifugal pump noise computation was verified. On this basis, the outer sound fields were investigated, and the effect of blade outlet angle to outer sound fields was studied. The results show that the sound power at the BPF becomes large as the blade outlet angle increase; the blade outlet angle should be at suitable range to ensure a lower noise level at low flow rates.
The damage parameters of internal explosion in closed field are analyzed by using the dimension analysis principle, and the scale similarity model for internal explosion in closed field is established based on the similarity theory in this paper. The internal explosion of the original model under incremental charges manner until structural damage and the scale model under critical charge of structure cracks with different scale coefficients values of 0.8, 0.6, 0.4, 0.2 and 0.1 respectively are simulated by LS-DYNA code. The results show that, when the structure size stays constant but the explosive quality is changed, the arrival time of shock wave on the wall obey to similarity law, and the shockwave overpressure obey to similarity law which considered separately and affected by one wall, two walls and three walls respectively, but the impulse is not subject to similarity law due to the influence of structural damage. The shockwave overpressure, scale pulse width and scale impulse on the wall between scale model and original model obey to similarity law when the scale coefficient is no less than 0.1, and the maximum relative error of shockwave overpressure, scale pulse width and scale impulse between scale model and original model are less than 3.3%, 4.96% and 5.1% respectively. As the scale coefficients decrease, the shockwave overpressure, scale pulse width and scale impulse on the wall show a discrete distribution and the similarity degree decreases gradually. So if the scale coefficients are within the scope of this study it is feasible to predict the damage effect of original model under internal explosion using the scale mode experiment.
Research on energy transform rule of armor-piercing on fragment against sandwich plate with fiber reinforced composite cores (is made by superimposing on steel plate、composite material plate and steel plate laminated). The numerical simulation of fragment simulation projectile (FSP) penetrated to different kinds of sandwich plate with high velocity were conducting, the ballistic limits of fragment pierced 16 kinds of sandwich plates were obtained. The credibility of numerical simulation method was verified by comparing with the experimental results. Under fragment critical perforation, the relativity between energy absorption ratio of each part of sandwich plate and structure size was studied by analyzing the numerical simulation results. The research results show that the energy absorption ratio is constant for different thickness cores plate( the aramid fiber cores is 10.41%，the glass fiber cores is 2.68%), the internal energy in core plate is quadratic function increments with the increase of its thickness. Base these, the calculation method of ballistic limit velocity of fragment penetrating sandwich plate with fiber reinforced composite cores was obtained.
In order to reduce the interference of noise on aeroengine mechanical fault diagnosis result and improve the classification performance of fault feature set, an integrated fault feature set extraction method based on stochastic resonance(SR) was proposed. First, the stochastic resonance was applied to pretreat the vibration signal, thus improving the Signal to Noise Ratio(SNR) and enhancing the frequency characteristics of the output. Then, the fault feature set was extracted from the output signals of SR system. The fault feature sets based on time domain analysis, frequency domain analysis and time-frequency domain analysis was proposed respectively to test the treatment effect of SR method. And the rotor test data was used to test the extracted feature sets. The results indicate that the fault feature set extracted from the output signals of SR system showed the better classification performance and the diagnosis result had the higher stability than the feature set extracted from the original signals.
Based on the horizontal excitation character of the intelligent vibratory roller and the soil parameters, three compaction conditions such as pure rolling, slip-roll and pure slip were classified during the compaction process. According to the working condition in stages the interacted dynamic process between the drum and soil was analyzed. Taking the XG6133D intelligent roller as an example, the response characteristics were investigated by means of numerical simulation. During the compaction process, the motion of vibratory drum occurred from single periodic motion to periodic doubling motion, the peaks and valleys of its time response were induced to be distorted, and spectrums present in addition to the fundamental wave only rich odd harmonics. In theory the conclusion of the article is valuable to forecast the compaction status and improve the compaction quality.
In order to distinguish leakage noise and valve noise, provide a theoretical basis and the database for leak detection and location based on acoustic method and provide methods to control valves noise, the paper makes a study on aero-acoustics induced by gas flowing through valves in gas pipelines in view of sound generation mechanism and builds a aero-acoustics mode from which the aero-acoustics noise generation, transmission and attenuation disciplines can be concluded. First the transient flow field such as fluctuating pressure and fluctuating velocity is obtained with large eddy simulation model by computational fluid dynamics software when gas flows through valves in gas-pipelines. Then the data is imported into acoustic BEM software SYSNOISE to carry through numerical analysis and transformed into dipole source and quadrupole source. And the aero-acoustics model is built to solve the aero-acoustics problems. Finally the aero-acoustics noise generation, transmission and attenuation disciplines are concluded.
This paper studies the longitudinal vibration of cone-shaped nanotubes/nanorods. The governing equation involved in the problem is a partial differential equation with variable coefficients. A widely applicable, simple and accurate integral equation method is presented to solve the above-mentioned problem. Based on the classical and nonlocal theories of elastic rods, the natural frequencies are determined for various boundary conditions. In particular, a simple approximate expression for the resonant fundamental frequency of clamped-free carbon nanotubes as longitudinal vibration mass sensor carrying a concentrated mass at the free end is derived. A comparison of our results with the previous ones using different approaches indicates that the proposed method is easy-to-implement and effective.
The explicit dynamic algorithm is adopted to perform detailed modeling and refined simulation for dynamic anti-shock problem of diesel engine. Individual and synthesized analyses are conducted as to mechanical motion and dynamic shock simulation with different working conditions. High-performance computing(HPC) resources are utilized to meet the challenge of large scale computing requirement due to debugging and load cases. Through multi-core parallel computing and performance data comparison on different platforms, each parallel speedup phenomenon is analyzed to explore reasonable parallel acceleration strategy. The results shows that such dynamic simulation method makes for integrated kinetic and dynamic characteristics research of diesel engine, and HPC resource provides imperative guarantee for solving and deeper investigation.
In order to analyze the influence of the forced vibration to the dynamic responses of the multi-body system with a floating base, the system is simplified to two rigid-bodies model connected by a smooth joint. The dynamic responses of the system are solved by the program according to the transfer matrix theory of multi-body dynamics. The time histories of the motion of the system are obtained under the condition of the floating base acted by forced period rolling motion or waves. The results of numerical simulation show that the swing of the weight severe with the increase of the amplitude and the frequency of the forced vibration, but not be influenced by the length variation of the rope. The oscillation amplitudes of the floating base and the weight under the action of the transverse regular wave increase with the length of the rope and the elevation of the arm.
The Wave Based Method (WBM) is a new deterministic method for the vibration problem. It’s based on the indirect Trefftz method, and the vibration are approximate in terms of globe wave functions, which are exact solutions of the vibration control equation. Due to its enhanced computational efficiency as compared to the Finite Element Method (FEM), the WBM can settle the mid-frequency problem. This paper analyses the plate power flow by WBM and compares it with the FEM. The outcome turns out the validity and advantage of the WBM.
Bolt stiffness and pre-tightening force have great impact on structural modal and transfer function, which are often ignored in the actual assembling because of the difficult processing. By comparing the finite element calculation data and test data of three kinds of bolts with different stiffness under different pre-tightening force, changes of structure modal and transfer function are analyzed. First simulation analysis and calculation are made by ANSYS software pre-stressed modal and harmonic response. Then the tests of three kinds of bolts with different stiffness bolts are done under the same pre-tightening force, and the steel bolt is tested under six groups of pre-tightening force. Finally, the differences between calculation data and test data are studied. The study results show that the calculation value differs about 15% from test data because the contact damping is ignored. Under the same pre-tightening force, the natural frequency is increasing with the increasing of the bolt stiffness, but the maximum distortion also increases. The structure transfer function will be easier to find as the pre-tightening force increasing.
A new nesting complex structure was designed to fabricate the one-dimensional phononic crystal. The transmissivity spectrograms of the longitudinal and transverse waves through the phononic crystal have been numerical calculated by using the transfer matrix method. The results show that the band gaps of the new phononic crystal are several times larger than that of the traditional one dimensional phononic crystal, and the local modes are present in the band gaps. We find the most effective factors to produce the huge band gaps and to influence the local modes. The features of the local modes depend strongly on the thickness and location of the impurity, which can extend the filter range of the phononic crystal to a lower frequency area. The mechanisms such as quasi-defects coupling and defects resonance are presented to explicate the results.
This article concentrate on a fast algorithm for precise integration with dimension expanding method with high accuracy for large scale dynamic structures. In order to improve the accuracy of precise integration with dimension expanding method for large scale dynamic system, the non–homogeneous items are approximated by high order polynomial. To reduce the calculation time, and improve the computational efficiency, a fast algorithm is derived. Numerical example shows that by increasing the approximate order of the non-homogeneous items the significantly improvement of accuracy is obtained, and the fast algorithm can improve the computational efficiency significantly, and the algorithm suit to the long time computation for the large scale dynamic systems.
Because of the coupling of environment corrosion and wind-induced vibration, the fatigue properties of angles have degenerated during the service period. However, the fatigue testing data is scarcity owing to time-consuming and costly. In this work, based on the thinking of saving cost and improving precision, an improved regression method for estimating S-N curves of corrosion fatigue was proposed combining with the single-point likelihood method (SPLM) and optimization method of correlation coefficient. And the implementation algorithm for the improved SPLM was also proposed. According to this improved method, a t-P-S-N surface expression of corrosion fatigue was presented. Meanwhile, three types of 18 Q345 equal angles in different corrosion time were studied by the corrosion fatigue test. Through the comparison of results, corrosion fatigue failure modes of specimens were observed and the variation law of P-S-N curves within different corrosion time was obtained. Combining this improved SPLM, the t-P-S-N surface model of Q345 equal angles was proposed. At last, the variation law of Q345 equal angles’ fatigue life was studied by the proposed t-P-S-N surface model. It can be found that: 1）The fatigue life was decreasing sharply with increasing corrosion time under the same load. 2）The effect of corrosion on the fatigue life was becoming more and more serious with decreasing load in the same corrosion time.
