Time Spatial Domain Research Articles

Dynamic response analysis for bridges subjected to moving vehicle loads by using the analytical dynamic stiffness method

This paper presents a highly efficient and accurate analytical method for the dynamic analysis of subjected to moving loads. Bridges with complex cross section and considering damping are modelled as plate built-up structures by the dynamic stiffness method with few degrees of freedom. Different moving loads with time-varying amplitudes travelling at different speeds can be modelled semi-analytically: The moving vehicle loads with varying amplitude are transformed into the frequency-wavenumber domain by the analytical sine transform combined with the fast Fourier transform; then the time-spatial domain dynamic response of the bridge is computed by the associated inverse transforms from the frequency-wavenumber domain response of the dynamic stiffness model. The most commonly used box girder railway bridge is taken as an example, and the results of both free vibration and dynamic response subject to moving train wheel loads computed by the proposed method are validated well by the finite element software ANSYS. The proposed method uses about 1.2% time of that taken by the ANSYS but achieves a similar level of accuracy. The proposed method can serve as an efficient alternative tool of modal and dynamic response analysis for the design and optimization of a wide range of complex bridges.

Dynamic response of a stratified transversely isotropic half-space with a poroelastic interlayer due to a buried moving source

Response of a ground subjected to dynamic sources is a classical problem in many fields. This paper develops a transversely isotropic (TI) half-space ground model which considers the alternating distribution of different media: a TI elastic surface layer, a TI poroelastic interlayer and a TI elastic half-space from top to bottom. The model can consider soils with different properties and the existence of groundwater. Dynamic responses of the model subjected to a buried moving source are investigated. General solutions to the TI poroelastic interlayer in the wavenumber domain are derived by Fourier transform and a potential function method in a Cartesian coordinate system. The layered system with different media is solved adopting an ‘adapted stiffness matrix method’ for a buried source scenario. Dynamic responses in the time-spatial domain are obtained by inverse fast Fourier transform (iFFT) and numerical integration. The performance of the method in this study is first tested by comparison with existing research, and the influences of the existence of pore water in the interlayer, transverse isotropy, and source features are comprehensively investigated. The effect of pore water is more significant for a TI ground compared with isotropic ground, and the model in this study cannot be simplified by an ‘equivalent’ layered TI elastic model. Peak values of displacement and pore pressure exist with increasing source speed. Source speeds corresponding to them are related to the wave speeds of the medium and affected by transverse isotropy.

Comparative study of effects of group-velocity dispersion on midinfrared quantum-cascade lasers with Fabry–Perot and ring cavities

We focused on the effects of group-velocity dispersion (GVD) on the coherent pulse progression in midinfrared quantum-cascade lasers (QCLs). We carried out the study on Fabry–Perot (FP) cavities. Comparison of GVD effects on the two kinds of typical QCL cavities, i.e., FP and ring cavities, brings insight into the interaction between the GVD and spatial hole burning (SHB) effect, which is only supported by FP cavities but not ring cavities. The theoretical model is built based on the Maxwell–Bloch formulism accounting for two-way propagations of electric field and polarization as well as the couplings among the electric field, polarization, and population inversion. The pulse evolution in time–spatial domains is simulated by the finite-difference method with prior nondimensionalization, which is necessary for a convergent solution. Results predict that the SHB could broaden the QCL gain bandwidth and induce additional side modes closely around the central lasing mode with an intensity more pronounced than that of GVD associated side modes. Moreover, owing to the SHB, the lasing instability caused by GVD is weaker in an FP cavity than a ring cavity.

Is the crack opened or closed in soft-matter pentagonal and decagonal quasicrystal

The hydrodynamic model for possible pentagonal and decagonal soft-matter quasicrystals is investigated, the effect of fluid which describes the difference of fracture theory between traditional structural material and the present novel material is considered. With this model, taking into account of equation of state, a complete hydrodynamics analysis is carried out. In the plane field of the soft-matter quasicrystals, the phonon, phason and fluid fields in time-spatial domain are quantitatively explored. A fluid stress intensity factor is suggested for the first time, whose physical action here leads to the closing of the crack surface, so is different from that of elastic (or phonon) stress intensity factor which leads to opening of the crack surface. The authors consider the cracking process of soft-matter quasicrystals is a process of competition between action of elastic stress and fluid stress to each other. In other words, the situation around the crack tip of the matter in stable or unstable lies in the competition results.

Coherent Pulse Progression of Mid-Infrared Quantum-Cascade Lasers Under Group-Velocity Dispersion and Self-Phase Modulation

The effect of group-velocity dispersion (GVD) and self-phase modulation (SPM) on the coherent pulse progression in mid-infrared quantum-cascade lasers (QCLs) is investigated. The background saturable absorber (SA) effect is included in this paper. In this case, the lasing pulses can be built up from the instable continuous wave operation condition related to both SA effect and GVD under the influence of a small initial disturbance. The theoretical model is built based on the Maxwell–Bloch formulism accounting for the couplings among the electric field, the polarization, and the population inversion. The pulse evolution in time-spatial domains is simulated by the finite difference method with prior nondimensionalization, which is necessary for convergent solution. It is found that the anomalous GVD, which receives less attention in the study of QCL dynamics, can significantly narrow the spectrum splitting between side modes. The SPM can broaden the linewidth of the spectral modes. Their combined effects can lead the possibility of forming solitons.

Awareness of Special and General Relativity and Local and General Physical Reality

The paper is based on the awareness of the conformity of Special Relativity Theory with the nature of our local physical reality, and on the awareness of the conformity of General Relativity Theory with the nature of the global physical reality. It includes two discussions – about Special Relativity and about General Relativity. The root cause analysis of the results of Special and General Relativity shows the real physical nature of the Universe what is a base of new ideas for advance in the physics. As a summary about the real physical nature of the Universe – it is the perception of a local certainty in any time-spatial domain (the domain of existence) and the real uncertainty in both micro-world (quantum level) and macro-world (Universe level). This is actually a new model of uncertainty of the Universe, that gives explanations of a lot of problems (such as: “the accelerated expansion of the Universe”; “the dark matter and the dark energy in the Universe”; the answer of the question about “the origin of the energy”, etc.), which have been under research for a long time.

The Speed of Light and Uncertainty Principle of the Macro-world

The facts are:- The speed of light is different in different directions in the reference system connected with the Earth’s surface, moving with 0.46 km/s at the equator. It has been demonstrated in various experiments for almost a hundred years.- There is no experiment carried out in the area near the Earth's surface (our local reality), that proves ether-drift result on the speed of light, due to the Earth’s motion on its trajectory around the Sun, which is approximately 30km/s.- Undeniable fact is that the speed of light in a reference system, connected with the space itself, is constant in a homogeneous gravitational field, or in local time-spatial domain with the same gravitational potential.- The speed of the light in a reference system, connected with the space itself, changes with the change of the intensity of the gravitational field. The Shapiro-time-delay effect and the anomaly in acceleration of the spaceships “Pioneer-10/11”, “Galileo”, and “Ulysses” at the border of the Solar system – are actually proving experiments of this reality.In this paper is shown why in a local time-spatial domain, where the units of the time and space are defined, it is impossible to register the change of the speed of light in a reference system connected with the space itself. It is because of the way of definition of the units of time and length and because of the synchronous change of all local units, all local physical constants – of the entire physical reality. As a conclusion - “uncertainty principle of the macro-world” is proposed.

Geotechnical Engineering Intelligent Monitoring and Controlling System and its Application in Pit Engineering

The shortages and drawbacks of traditional geotechnical engineering monitoring and controlling system(GEMCS) is reviewed and the necessity and inevitability to establish a modern GEMCS are argued and discussed sufficiently. Modern GEMCS are fundamentally divided into two subsystems, remote management subsystem and site management subsystem respectively. Each of the subsystems is introduced and described subsequently by their components, main functions and capability in solving issues. Then, the predominant characteristics and advantages of the modern GEMCS are specified with two facets: components features and unlimited time-spatial domain monitoring. Applications in deep pit constructions are illustrated to visualize the functions of the modern GEMCS, followed by three research strategies of scholars from home and abroad are analyzed and summed up. Last, based on two levels, which are completions and evolutions of monitoring and controlling system itself as well as its generalizations in applications and promotions in geomechanics, developments supposed to achieve in modern intelligent GEMCS in 21st century are prospected and forecasted.

Parallel Factor Analysis of Driver's EEG in Lane Change Maneuver for Cooperative Driver Assistance Systems

Vehicle technology of the better interaction between human and machine has been called human-electronics in Japan. It is necessary to obtain better relationship between human and vehicle. A driver's information, which can be obtained from steering operation, pedal operation, camera images and physiological information, particularly is important to find a method to determine a driver's operational intention. In terms of using this physiological information, an area of focus is using brain activity. Recently, some former researches haves been reported about the investigation of the brain activity of the driver. The traditional decomposition of the electroencephalograph (EEG) has been based on the two-dimension components. In the multiple electrode analysis of EEG, the frequency-spatial domain and the time-spatial domain have been used. However, these conventional methods can only use two-dimensional data. As a multi-channel EEG analysis using multi dimensional data, parallel factor analysis (PARAFAC) method is based on the report. In this paper, we described that the driver's EEG during lane change was decomposed by PARAFAC and we investigated the factor of recognize and judgment from that decomposition result. Consequently, Common to the all subjects has 2 factors which were in the 5-8 Hz and 8-13 Hz. Those factors considered that they were changed by the driver's mental state, during recognition for alpha wave and during judgment for theta wave.

Tyre/road interaction noise—A 3D viscoelastic multilayer model of a tyre belt

Vehicle noise is an increasing local environmental problem. For cars, above a steady speed of 40km/h the noise produced by the interaction of the tyres with the road surface is the dominant noise source.In order to be able to predict this noise, the vibration characteristics of a stationary tyre must be determined. A multilayer viscoelastic cylindrical representation of the tyre belt, located between the sidewalls of the tyre and excluding the tread, is provided which yields the displacement and velocity response of the tyre belt when excited in the radial or tangential directions for a wide range of excitation frequencies, using only data from the design process.This model includes a representation of an air cavity and sidewalls and the response of the tyre belt is determined in both the frequency–wavenumber and time–spatial domains. The model can then be used to determine the noise of a tyre rolling on a rough road.