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Reliable operation of the feeding system plays a crucial role in ensuring the safe and efficient production of the working face of backfilling gob-side entry retaining (GER). In the process of vertical feeding of the roadside support body material, the problem of blocking of the feeding shaft has occurred to the test mine, which seriously affects the production safety in mines. In this paper, based on the theoretical analysis, a fluid-solid coupling numerical model was established. The change rules of the speed of sacked gangue, pressure of air below it, and speed vector distribution with different vent diameters were obtained. The blocking mechanism of the feeding system was revealed. The results show that if the exhaust vent of the stock bin was shut, the speed of gangue in the mine increased and then decreased and finally blocked in the feeding shaft. If the exhaust vent of the stock bin was opened for pressure discharge, with the increase of diameter of the exhaust vent, the maximum speed and ending speed of sacked gangue increased, pressure differential reduced, and speed vector was uniformly distributed. The energy criterion of blocking of the feeding shaft was further obtained. Based on the engineering conditions of the test mine, when the feeding shaft is blocked, the critical value of diameter of the exhaust vent is 30 mm. The research results provide basis for the design of key parameters of the vertical feeding system, ensuring the safe and efficient production of gob-backfilled GER working face.

The acoustic response has many important roles in seismic exploration and nondestructive testing. It enables the development of fracture classification and sizing. In this paper, we combined Hudson’s effective medium scheme and finite-difference time-domain modeling method to simulate acoustic wave propagation in fractured media. Fractures are represented by discrete fracture networks, allowing for a state-of-the-art representation of natural fracture networks by a negative Exponential Law length distribution. The propagation of acoustic waves that are emitted by a point source and reflected from a fractured area in a 2D digital rock model are examined numerically with the purpose of developing an acoustic inference of fracture properties. In these fractured models, we vary the number and mean length of fractures to explore the relation between internal structure of rock and acoustic wave field characters. The modeling results indicate that acoustic wave field is more sensitive to the fracture number than to the mean of the fracture length. Moreover, a fracture-dependent attenuation analysis of the reflection records of discrete stochastic fractured models is obtained. The frequency- and time- dependent attenuation profiles feature two parts in frequency, (1) fracture-to-background at lower frequencies and (2) fracture-to-fracture at higher frequencies. Our results indicate that accounting for attenuation effects may not only allow for improving estimation of fracture number, but also provide information about geometrical characteristics of length distribution. Such an approach can be used to estimate nature fracture network properties with given acoustic records.

Energy storage is becoming indispensable for increasing renewable energy integration, and it is critical to the future low-carbon energy supply. Large-capacity, grid scale energy storage can support the integration of solar and wind power and support grid resilience with the diminishing capacity of baseload fossil power plants. With the development of thermal energy storage (TES) for concentrating solar power systems, standalone TES for grid integration becomes attractive due to the declining renewable generation cost and an increasing need for energy storage. The standalone TES system introduced in this paper can play a big role in the carbon-free energy future with capacity larger than batteries and cost likely lower than other energy storage methods such as pumped storage hydropower and compressed air energy storage, both of which also have geological limitations. To this end, we describe a TES system that uses stable, inexpensive solid particles as a TES media to provide scalable, low cost energy storage. The particle-based TES has the ability to drive various thermal power cycles including conventional steam-Rankine, air Brayton turbine with combined-cycle ability, or the emerging supercritical carbon dioxide Brayton power cycle. This work describes the containment design method including a concrete silo and an internal-insulation layer for the particle-TES system. The economic analysis shows significantly low storage cost when the particle-TES is integrated with Brayton combined-cycle power generation. The paper shows the design approach of the particle-TES system and its economic potential for bulk energy storage. The advantage of the particle-TES system as a promising bulk energy storage method is its ability to economically support dispatchable renewable grid penetration for larger capacity and longer discharging hours than current battery storage technologies.

Solid particles can operate at higher temperature than current molten salt or oil, and they can be a heat-transfer and storage medium in a concentrating solar power (CSP) system. By using inexpensive solid particles and containment material for thermal energy storage (TES), the particle-TES cost can be significantly lower than other TES methods such as a nitrate-salt system. The particle-TES system can hold hot particles at more than 800°C with high thermal performance. The high particle temperatures increase the temperature difference between the hot and cold particles, and they improve the TES capacity. The particle-based CSP system is able to support high-efficiency power generation, such as the supercritical carbon-dioxide Brayton power cycle, to achieve >50% thermal-electric conversion efficiency. This paper describes a solid particle-TES system that integrates into a CSP plant. The hot particles discharge to a heat exchanger to drive the power cycle. The returning cold particles circulate through a particle receiver to absorb solar heat and charge the TES. This paper shows the design of a particle-TES system including containment silos, foundation, silo insulation, and particle materials. The analysis provides results for four TES capacities and two silo configurations. The design analysis indicates that the system can achieve high thermal efficiency, storage effectiveness (i.e., percentage usage of the hot particles), and exergetic efficiency. An insulation method for the hot silo was considered. The particle-TES system can achieve high performance and low cost, and it holds potential for next-generation CSP technology.

This paper presents synthesis of acoustic-emission (AE) wave propagation in multi-layer materials and simulation of AE wave responses at free surface. In particular, the AE source is modelled as an arbitrary-orientation dislocation over an inclined-to-surface fault within one layer or at the layer-to-layer interface, while the materials are assumed as multi-layer media, each of which is homogeneous, isotropic and linearly elastic. With the use of the integral transformation approach, the three-dimensional wave propagation in the materials is solved in transformed or frequency-wavenumber domain. Subsequently, a closed-form solution for wave responses at free surface is found, which can then be converted in time-space domain. Numerical examples are finally provided for illustration.

This study presents fundamental response features of seismic shear motion in multi-story buildings with a continuous–discrete model and its degenerated ones, and shows their applications in inverse parametric identification. In particular, the building is modeled as a series of continuous shear-beams for inter-story columns/walls and discrete lumped-masses for rigid floors. Shear motion response at one location of the building is then obtainable to an impulsive motion at another location in the time and frequency domains, termed here as generalized impulse and frequency response functions (GIRF and GFRF). The GIRF and GFRF are not only fundamental in relating seismic responses at the two locations of a building structure subjected to ground seismic excitation that is not fully known due to the complicated soil–structure interaction. They also play a key role in characterizing structural responses, as well as in identifying dynamic parameters of the building. For illustration, this study examines response features of ten-story building of Millikan Library in Pasadena, California with the Yorba Linda earthquake of September 3, 2002. With the use of the continuous–discrete model as well as its degenerated ones, structural responses are interpreted from the perspective of wave propagation, and more importantly validated with the pertinent recordings and discrete-model-based results. Parametric identification of the building with a pair of seismic recordings is then presented. This study finally comes up a conclusion that the proposed approach with continuous–discrete modeling is efficient and robust in forward predicting analysis and inverse system identification.

The minimum ignition energy of tapioca starch was studied by using 1.2L Hartmann tube, and the three main influencing factors: tapioca starch quality, ignition delay time and dusting pressure were tested. The experimental results show that the effect of dusting pressure on the minimum ignition energy is the most obvious. With the increase of powder pressure, the minimum ignition energy first decreases and then increases, and when the powder pressure is 90Kpa, the minimum ignition energy is the smallest, which is 58mj; ignition delay time is different, the degree of dust dispersion is different, and the optimum ignition delay time is 30ms. The minimum ignition energy decreases first and then increases with the increase of the quality of tapioca starch. When the mass is 0.5 g, the ignition energy is the smallest. It is 60mJ.

This paper presents synthesis of acoustic-emission (AE) wave propagation in multi-layer materials and simulation of AE wave responses at free surface. In particular, the AE source is modelled as an arbitrary-orientation dislocation over an inclined-to-surface fault within one layer or at the layer-to-layer interface, while the materials are assumed as multi-layer media, each of which is homogeneous, isotropic and linearly elastic. With the use of the integral transformation approach, the three-dimensional wave propagation in the materials is solved in transformed or frequency-wavenumber domain. Subsequently, a closed-form solution for wave responses at free surface is found, which can then be converted in time-space domain. Numerical examples are finally provided for illustration.

a b s t r a c t This study examines one-dimensional wave propagation in a multi-story building with seismic excitation. In particular, the building is modeled as a series of shear beams for columns/walls and lumped masses for floors. Wave response at one location of the building is then derived to an impulsive motion such as displacement and acceleration at another location in time and frequency domains, termed here as wave- based or generalized impulse and frequency response function (GIRF and GFRF), which is dependent upon the building characteristics above the impulse location. Not only does this study illustrate features of GIRF and GFRF in terms of building properties, it also shows broad-based applications of the modeling. Two examples are presented with the use of the modeling. One is wave-based characterization of ten-story Millikan Library in Pasadena, California with the recordings of Yorba Linda earthquake of September 3, 2002. The other is analysis for influence of stochastic floor-to-column mass ratio, story-height and seismic input in seismic wave responses.

This study proposes an approach to identify earthquake-induced site liquefaction and/or nonlinearity from Hilbert–Huang–Transformation- or HHT-based data analysis of seismic motion recordings. The proposed approach fully utilizes unique features of the HHT method in characterizing instantaneous frequency and damping as well as temporal-frequency motion from the recordings, so as to single out and quantify liquefaction- and/or nonlinear-soil-related nonlinear phenomena shown in the recordings. With post-earthquake, site investigation as a reference, this study shows that the proposed approach is effective in characterizing site nonlinearity, quantifying nonlinear influences in site amplification, and diagnosing site liquefaction. Major results from this study are listed below.1. Predominant instantaneous frequency of earthquake motion is defined as the frequency with the largest amplitude in Hilbert amplitude spectra of the motion at a time instant, and subsequently used together with other motion features for identifying site liquefaction conditions. Analysis of 29 sets of seismic recordings with different liquefaction conditions shows that the proposed approach is more effective in detecting site liquefaction than other Fourier-based methods.2. HHT-based site amplification is defined as the ratio of marginal Hilbert amplitude spectra, similar to the Fourier-based one that is the ratio of Fourier amplitude spectra. The HHT-based site amplification can be used for effectively quantifying site nonlinearity in terms of frequency downshift in the low-frequency range and amplification-reduction factor in intermediate-frequency range in comparison with the Fourier-based one.3. Instantaneous damping, and Hilbert and marginal Hilbert damping spectra are defined in way similar to instantaneous frequency, and Hilbert and marginal Hilbert amplitude spectra, respectively. Consequently, the HHT-based site damping is found as the difference of marginal Hilbert damping spectra, which can be used as an alternative, complementary index to measure influences of site nonlinearity in seismic ground responses.

This study proposes a conceptual framework of in-situ vibration tests and analyses for quality appraisal of non-slender, cast-in-place piles with irregular cross-section configuration. It evaluates a frequency index from vibration recordings to a series of impulse loadings that is related to total soil-resistance forces around a pile, so as to assess if the pile achieves the design requirement in terms of bearing capacity. In particular, in-situ pile-vibration tests in sequential are carried out, in which dropping a weight from different heights generates series impulse loadings with low-to-high amplitudes. The high-amplitude impulse is designed in way that the load will generate equivalent static load that is equal to or larger than the designed bearing capacity of the pile. This study then uses empirical mode decomposition and Hilbert spectral analysis for processing the nonstationary, short-period recordings, so as to single out with accuracy the frequency index. Comparison of the frequency indices identified from the recordings to the series loadings with the design-based one would tell if the total soil resistance force remains linear or nonlinear and subsequently for the quality appraisal of the pile. As an example, this study investigates six data sets collected from the in-situ tests of two piles in Taipu water pump project, Jiangshu Province of China. It concludes that the two piles have the actual axial load capacity higher than the designed bearing capacity. The true bearing capacity of the piles under investigation can be estimated with accuracy if the amplitude of impact loadings is further increased and the analyses are calibrated with the static testing results.

This study proposes a recording-based approach to characterize and quantify earthquake-induced site nonlinearity, exemplified as soil nonlinearity and/or liquefaction. Alternative to Fourier spectral analysis (FSA), the paper introduces time–frequency analysis of earthquake ground motion recordings with the aid of so-called Hilbert-Huang transform (HHT), and offers justification for the HHT in addressing the nonlinear features shown in the recordings. With the use of the 2001 Nisqually earthquake recordings, this study shows that the proposed approach is effective in characterizing site nonlinearity and quantifying the influences in seismic ground responses. Major results from this study are listed below. 1. HHT-based site amplification is defined as the ratio of marginal Hilbert amplitude spectra, similar to the Fourier-based one that is the ratio of Fourier amplitude spectra. The HHT-based site amplification can be used in effectively quantifying site nonlinearity in terms of frequency downshift in the low-frequency range and amplification-reduction factor in intermediate-frequency range in comparison with the Fourier-based one. 2. Instantaneous damping, and Hilbert and marginal Hilbert damping spectra are defined in ways similar to instantaneous frequency, and Hilbert and marginal Hilbert amplitude spectra, respectively. Consequently, the HHT-based site damping is found as the difference of marginal Hilbert damping spectra, which can be used as an alternative, complementary index to measure the influences of site nonlinearity in seismic ground responses.

Reconnaissance reports and pertinent research on seismic hazards show that liquefaction is one of the key sources of damage to geotechnical and structural engineering systems. Therefore, identifying site liquefaction conditions plays an important role in seismic hazard mitigation. One of the widely used approaches for detecting liquefaction is based on the time-frequency analysis of ground motion recordings, in which short-time Fourier transform is typically used. It is known that recordings at a site with liquefaction are the result of nonlinear responses of seismic waves propagating in the liquefied layers underneath the site. Moreover, Fourier transform is not effective in characterizing such dynamic features as time-dependent frequency of the recordings rooted in nonlinear responses. Therefore, the aforementioned approach may not be intrinsically effective in detecting liquefaction. An alternative to the Fourier-based approach is presented in this study, which proposes time-frequency analysis of earthquake ground motion recordings with the aid of the Hilbert-Huang transform (HHT), and offers justification for the HHT in addressing the liquefaction features shown in the recordings. The paper then defines the predominant instantaneous frequency (PIF) and introduces the PIF-related motion features to identify liquefaction conditions at a given site. Analysis of 29 recorded data sets at different site conditions shows that the proposed approach is effective in detecting site liquefaction in comparison with other methods.

This paper presents the implementation of a method for nonlinear, nonstationary data processing, namely the Hilbert–Huang transform (HHT) in traditional vibration-based approaches to characterizing structural damage and shows the frequency signature of local structural damage in nonstationary vibration recordings. In particular, following the review of traditional approaches to characterizing structural damage from nonstationary vibration recordings, this study first offers the justifications of the HHT as an alternative and complementary data process in addressing the nonstationarity of the vibration. With the use of recordings from controlled field vibration tests of substructures in the Trinity River Relief Bridge in Texas in its intact, minor- and severe-damage pile states, this study then shows that the HHT-based approach can single out some natural frequencies of the structure from a mixed frequency content in recordings that also contain the time-dependent excitation and noise frequencies. Subsequently, this study exposes that the frequency downshift for the damaged pile relative to the undamaged one is an indicative index for the damage extent. The above results are also validated by an ANSYS model-based analysis. Finally, a comprehensive HHT-based characterization of structural damage is discussed, and the potential use for cost-effective, efficient structural damage diagnosis procedures and health-monitoring systems is provided.

This paper examines the rationale of a method of nonstationary data processing and analysis, referred to as the Hilbert-Huang transform (HHT), for its application to a recording-based approach in quantifying influences of soil nonlinearity in site response. In particular, this paper first summarizes symptoms of soil nonlinearity shown in earthquake recordings, reviews the Fourier-based approach to characterizing nonlinearity, and offers justifications for the HHT in addressing nonlinearity issues. This study then uses the HHT method to analyze synthetic data and recordings from the 1964 Niigata and 2001 Nisqually earthquakes. In doing so, the HHT-based site response is defined as the ratio of marginal Hilbert amplitude spectra, alternative to the Fourier-based response that is the ratio of Fourier amplitude spectra. With the Fourier-based approach in studies of site response as a reference, this study shows that the alternative HHT-based approach is effective in characterizing soil nonlinearity and nonlinear site response.

This study proposes an approach for estimating the damping factor of non-linear soil and its role in seismic wave responses at soil sites from earthquake recordings. In particular, the paper first reviews the Fourier-based approach to characterizing the dynamic features of soil sites in seismic ground motion and shows the deficiencies for assessing non-linear site amplification and damping. It then offers an alternative approach, i.e., the Hilbert–Huang transform (HHT) for non-linear and non-stationary data process, in addressing the non-linearity issues. This study focuses on discerning the signature of non-linear site damping from the general non-linear features in the motion that are typically shown in the frequency-dependent site amplification. As a result, the study proposes an HHT-based approach to estimate site damping with non-linear soil from earthquake recordings and to measure the influences in the motion at soil sites. With the use of recordings from the mainshock and aftershock of the 2001 Nisqually earthquakes, this study shows that the proposed approach is able to assess appropriately the site damping that can be used to estimate the influences of soil damping in non-linear site responses.

For far-field wave-motion response to a point dynamic dislocation source, the temporal and spatial features of the source mechanism are characterized, respectively, by two factors, i.e., a source time function for dislocation growth and a combination of nine couples of impulse forces that is equivalent to the final dislocation. The mathematical representation for each of the couples, referred to as spatial couples, is a couple of impulses acting in opposing directions with an infinitesimal separation distance or, in the limit, by the derivative of the impulse with respect to the separation-distance parameter. This study proposes a temporal-spatial pulse representation for the nine couples, referred to as temporal-spatial couples, and subsequently for the dislocation source modeling. Each temporal-spatial couple consists of two impulses acting in opposite directions with both an infinitesimal separation distance and an infinitesimal time delay. By examining dynamite source modeling, this study shows that the proposed representation can intrinsically integrate the spatial and temporal features of the dislocation sources from the response point of view. This study also shows an example of a point, shear-slip seismic source modeling using traditional and proposed pulse representations for far-field wave motion. Discussion is finally provided for the implications of the proposed representation in broad applications.

This paper aims to identify the natural frequencies and modal damping ratios of the Tsing Ma suspension bridge during Typhoon Victor using the newly emerged empirical mode decomposition (EMD) method in conjunction with the Hilbert-transform (HT) technique. Stationary tests on the acceleration responses of the bridge recorded at different locations and in different directions during Typhoon Victor are first carried out to classify the recorded response data. Natural frequencies and modal damping ratios identified by the EMD-HT method are then compared with those obtained by the traditional fast Fourier transform (FFT)-based method. The modal parameters identified by the EMD-HT method from the bridge responses recorded at different locations are compared with each other to check their consistency. Furthermore, the variations of natural frequency and total modal damping ratio with vibration amplitude and mean wind speed are examined. The results demonstrated that the EMD-HT method is applicable to modal parameter identification of large civil structures under typhoons. The EMD-HT method and the FFT-based method produced almost the same natural frequencies but the FFT-based method gave higher modal damping ratios than the EMD-HT method in general.

Modal vibration tests combined with the Hilbert-Huang transform (HHT) method were used to analyze previous recordings of controlled field-vibration tests of one concrete pile substructure of the Trinity River Relief Bridge No. 4 in Texas in its intact, minor-, and severe-damage states. Piles were excavated and broken to simulate flood and earthquake damage to a bridge substructure. The HHT algorithm is unique in that it reveals the quantitative difference in the instantaneous frequency of sound and damaged structures, consistent with the damage states and with what a simple structural model predicts. This approach differs from traditional modal vibration analyses in that a short-lived shift downward in resonant frequency can be seen in the HHT from a damaged member, whereas this shift is often lost due to the averaging effect of a modal vibration analysis. Accordingly, an HHT-based structural health monitoring procedure is discussed.

This study examines the rationale of Hilbert-Huang transform (HHT) for analyzing dynamic and earthquake motion recordings in studies of seismology and engineering. In particular, this paper first p...

This paper presents galloping analysis of multiple-degree-of-freedom (MDOF) structural roofs with multiple orientations. Instead of using drag and lift coefficients and/or their combined coefficient in traditional galloping analysis for slender structures, this study uses wind pressure coefficients for wind force representation on each and every different orientation roof, facilitating the galloping analysis of multiple-orientation roof structures. In the study, influences of nonlinear aerodynamic forces are considered. An energy-based equivalent technique, together with the modal analysis, is used to solve the nonlinear MDOF vibration equations. The critical wind speed for galloping of roof structures is derived, which is then applied to galloping analysis of roofs of a stadium and a high-rise building in China. With the aid of various experimental results obtained in pertinent research, this study also shows that consideration of nonlinear aerodynamic forces in galloping analysis generally increases the critical wind speed, thus enhancing aerodynamic stability of structures.

In this article we use empirical mode decomposition (EMD) to charac- terize the 1994 Northridge, California, earthquake records and investigate the sig- natures carried over from the source rupture process. Comparison of the current study results with existing source inverse solutions that use traditional data processing suggests that the EMD-based characterization contains information that sheds light on aspects of the earthquake rupture process. We first summarize the fundamentals of the EMD and illustrate its features through the analysis of a hypothetical and a real record. Typically, the Northridge strong-motion records are decomposed into eight or nine intrinsic mode functions (IMF's), each of which emphasizes a different oscillation mode with different amplitude and frequency content. The first IMF has the highest-frequency content; frequency content decreases with an increase in IMF component. With the aid of a finite-fault inversion method, we then examine aspects of the source of the 1994 Northridge earthquake that are reflected in the second to fifth IMF components. This study shows that the second IMF is predominantly wave motion generated near the hypocenter, with high-frequency content that might be related to a large stress drop associated with the initiation of the earthquake. As one progresses from the second to the fifth IMF component, there is a general migration of the source region away from the hypocenter with associated longer-period signals as the rupture propagates. This study suggests that the different IMF components carry information on the earthquake rupture process that is expressed in their different frequency bands.

This study presents vibration analysis of medical devices by a finite element analysis (FEA) model calibrated with test data. The medical device under investigation is the Lifepak500 automated external defibrillator (AED), a product that is frequently exposed to vibration and shock in transportation means such as ambulances and medical-evacuation helicopters. In structure, the AED is a plastic case that contains a printed circuit board (PCB) with various attached electronic components such as capacitors, resistors, inductors, and integrated circuits. In this study, an FEA model of the AED is established with the use of ANSYS based on design specifications and static tests. The model is first calibrated with various static and dynamic tests to verify that the static displacements at selected locations, PCB twist angles, and first three natural frequencies predicted by the FEA model are consistent with those obtained by the tests. The model is then used to examine the dynamic characteristics and vibration transmissibility of the PCB within both rigid and flexible medical device cases. Finally, random vibration analysis of the PCB is presented. This study shows that the predicted frequency data favorably agrees with test data (within 7% error range), while predicted vibration amplitudes are in a reasonable range at major PCB locations when compared with the test data, but do not always agree well at the locations where the PCB has more complicated structural features and boundary conditions. The established FEA model predicts the reliability and functionality of current design of the AED from a vibration viewpoint. It can also help engineers improve the PCB mechanical design and product reliability when used in harsh vibration environments.

This paper introduces a computational model for stochastic wave propagation in long structures of civil and mechanical engineering systems, exemplified as towers and pipelines, and characterized with one-dimensional waveguide materials inter-connected with lumped mass. The model can be used for predictive wave response analysis as well as for system identification and damage diagnosis in structural health monitoring. In this study, wave response at one location of the structure is derived to an impulsive motion at another location in time and frequency domains, termed here as wave-based or generalized impulse and frequency response functions. Not only does this study show vibra- tion features in wave responses with the hybrid model, typically explainable and usable with discrete or multi-degree-of-freedom modeling. The model based responses also capture wave scattering features traditionally comprehensible with continuous modeling. The latter plays a major role in effectively detecting structural damage crack, stiffness degradation, and/or material non-linearity. Two examples are presented with the use of the modeling. One is wave-based charac- terization of ten-story Millikan Library in Pasadena, California with the recordings of Yorba Linda earthquake of September 3, 2002. The other is analysis for influence of stochastic material/geometrical features in wave responses.

This study presents fundamental response features of seismic shear motion in multi-story buildings with a continuous-discrete model and its degenerated ones, and shows their applications in inverse parametric identification. In particular, the building is modeled as a series of continuous shear-beams for inter-story columns/walls and discrete lumped-masses for rigid floors. Shear motion response at one location of the building is then obtainable to an impulsive motion at another location in the time and frequency domains, termed here as generalized impulse and frequency response functions (GIRF and GFRF). The GIRF and GFRF are not only fundamental in relating seismic responses at the two locations of a building structure subjected to ground seismic excitation that is not fully known due to the complicated soil-structure interaction. They also play a key role in characterizing structural responses, as well as in identifying dynamic parameters of the building. For illustration, this study examines response features of ten-story building of Millikan Library in Pasadena, California with the Yorba Linda earthquake of September 3, 2002. With the use of the continuous-discrete model as well as its degenerated ones, structural responses are interpreted from the perspective of wave propagation, and more importantly validated with the pertinent recordings and discrete-model-based results. Parametric identification of the building with a pair of seismic recordings is then presented. This study finally comes up a conclusion that the proposed approach with continuous-discrete modeling is efficient and robust in comparison with the traditional discrete-based ones in forward predicting analysis and inverse system identification.

A generalized earthquake-wave-motion model is established in this study, which considers 3D random heterogeneous media, together with existing models for sources and realistic geological profiles for sedimentary basins and irregular topography. The model can be used not only to examine the influences of random heterogeneous media, but also to explore the multiple interactions of source, site (irregularity and/or heterogeneity), and wave interference on spatial variations of ground motion. Specifically, the earth is modeled as a layered half-space with 3D weak-random heterogeneity media. Seismic waves are generated by a shear-dislocation source buried in one of the layers and then propagated through the modeled earth medium. A first-order perturbation approach together with wave propagation theory is used to solve the problem at hand for wave motion response, which is found as the superposition of the mean and scattered wave responses. The mean wave response is obtained as a wave-motion solution for a layered half-space without heterogeneity subjected to a buried seismic dislocation source. The scattered wave field is obtained as a wave-motion solution for the same layered half-space without heterogeneity subjected to virtual distributed body forces that mathematically replace the heterogeneity. The explicit expressions for the responses in both mean and scattered wave fields are derived in this study. A computational procedure for the wave-motion responses is also presented in detail.

Wind exposure categories are currently used to account for the influences of different ground roughness in wind profile that is fundamentally important to wind-resistant structural analysis and design. Since each classified exposure covers a relatively large spectrum of ground roughness with constant indices such as exponent α , this results in uncertain wind-resistant structural analysis and design for structures in each and every categorized exposure. More importantly, such an uncertainty is not only quantitative but also qualitative in terms of aerodynamic instability assessment and economic loss estimation. This study proposes a method to determine the actual wind exposure and estimates its influences in wind-resistant structural analysis and design. In particular, this paper first provides a review of wind exposure categories and illustrates the shortcomings of its use in structural analysis and design. It then introduces a method to determine the actual ground exposure. The method generates formulae for the actual ground roughness exponent on the basis of measured data from both wind-tunnel and full-scale experiments, of ground roughness-induced wind energy dissipation analysis, as well as of current Chinese and other countries’ loading codes. Through examples of hypothetical and practical engineering projects, this study finally investigates the influences of the actual ground roughness exponent on wind-induced structural responses and economic loss estimation, as well as on wind-resistant structural design.

This paper aims to provide some observations on the merits and disadvantages of Cartesian and cylindrical co-ordinate representations (CaCR and CyCR) in modelling of wave propagation in layer-based elastic media and its engineering applications. The observations focus on (1) difference and consistency in solution procedure for wave motion in layer-based elastic media, (2) identification of its fundamental properties, (3) computational efficiency in relation to wave motion synthetics/simulation, and (4) basis for the applications to stochastic wave motion modelling associated with uncertainty in complex medium structure as well as source mechanism. Specifically, modelling of earthquake wave motion in a layer-based elastic half-space is used for illustration. As a foundation for the investigation, CaCR and CyCR for three-dimensional (3-D) wave motion are first constructed in a concise and consistent form. Consequently, some basic characteristics of 3-D wave motion in layered media (e.g., various surface waves) can then be identified in a unified form for the aforementioned different co-ordinate representations. More importantly, the succinct representations for 3-D wave motion provide a stepping stone for further study on wave motion modelling with uncertainty in the Earth medium and source mechanism. These and the other pertinent issues will be investigated in this study from the viewpoint of systematic computer code development and computational efficiency, which is substantial to practical engineering applications.

State of the art in modeling, synthetics, statistical estimation, and engineering applications of strong ground motion is reported in this paper. In particular, models for earthquake wave motion are presented, in which uncertainties both in the earth medium and the seismic source are taken into consideration. These models can be used to synthesize realistic strong earthquake ground motion, specifically near-field ground motion which is quite often not well recorded in real earthquakes. Statistical estimation techniques are also presented so that the characteristics of spatially-correlated earthquake motion can be captured and consequently used in investigating the seismic response of such large scale structures as pipelines and long-span bridges. Finally, applications of synthesized strong ground motion in a variety of engineering fields are provided. Numerical examples are shown for illustration.

The stochastic dynamic response of the 310 m tall Nanjing TV tower in Nanjing, China under turbulent wind is analysed. The turbulent wind speed consists of mean and fluctuating components. The spatial variation of the mean wind speed follows a power law. The fluctuating component is idealized as a stochastic process which is non-white in time and space. Hence, the spatial variation of the fluctuating component along the height of the tower is taken into consideration. The interaction between wind and structure is also accounted for in the analysis. Assuming that the wind direction is slightly off the direction normal to one side of the TV tower (the x-direction), the vibration in the x-direction is induced primarily by the drag force due to the x-component turbulent wind speed, while the y-direction vibration perpendicular to the x-direction is generated primarily by the lift force exerted by vortex shedding resulting from the turbulent wind as well as by the drag force due to the y-component of turbulent wind speed. With the aid of the spectral representation method for numerical simulation of the fluctuating component of wind speed, the static and random vibration response of the TV tower is found for each simulated turbulent wind input. The response trajectories of the TV tower at specific heights are also derived. These results provide fundamentally important input information for the vibration control analysis of the TV tower with passive and/or active mass dampers.

Seismic waves in a layered half-space with lateral inhomogeneities, generated by a buried seismic dislocation source, are investigated in these two consecutive papers. In the first paper, the problem is formulated and a corresponding approach to solve the problem is provided. Specifically, the elastic parameters in the laterally inhomogeneous layer, such as P and S wave speeds and density, are separated by the mean and the deviation parts. The mean part is constant while the deviation part, which is much smaller compared to the mean part, is a function of lateral coordinates. Using the first-order perturbation approach, it is shown that the total wave field may be obtained as a superposition of the mean wave field and the scattered wave field. The mean wave field is obtainable as a response solution for a perfectly layered half-space (without lateral inhomogeneities) subjected to a buried seismic dislocation source. The scattered wave field is obtained as a response solution for the same layered half-space as used in the mean wave field, but is subjected to the equivalent fictitious distributed body forces that mathematically replace the lateral inhomogeneities. These fictitious body forces have the same effects as the existence of lateral inhomogeneities and can be evaluated as a function of the inhomogeneity parameters and the mean wave fleld. The explicit expressions for the responses in both the mean and the scattered wave fields are derived with the aid of the integral transform approach and wave propagation analysis.

Seismic wave scattering representation for the layered half-space with lateral inhomogeneities subjected to a seismic dislocation source has been formulated in the companion paper with the use of first-order perturbation (Born-type approximation) technique. The total wave field is obtained as a superposition of the mean and the scattered wave fields, which are generated, respectively, by a series of double couples of body forces equivalent to the seismic dislocation source and by fictitious body forces equivalent to the existence of the lateral inhomogeneities in the layered half-space. The responses in both the mean and the scattered wave fields are found with the aid of an integral transform technique and wave propagation analysis. The characteristics of the scattered waves and their effects on the mean waves or corresponding induced ground and/or underground mean responses are investigated in this paper. In particular, coupling phenomena between P-SV and SH waves and wave number shifting effects between the mean and the scattered wave responses are presented in detail. With the lateral inhomogeneities being assumed as a homogeneous random field, a qualitative analysis is provided for estimating the effects of the lateral inhomogeneities on the ground motion, which is related to a fundamental issue: whether a real earth medium can or cannot be approximately considered as a laterally homogeneous layer. The effects of the lateral inhomogeneities on the ground motion time history are also presented as a quantitative analysis. Finally, a numerical example is carried out for illustration purposes.

An impedance matrix is derived for the relationship between displacements and external excitations of a rigid or flexible foundation embedded in a layered soil medium. The unknown contact distributed force between the foundation and soil is expanded in the frequency domain as a twofold series of azimuthal and radial components; each term represents a basic or fundamental distribution. As a result, the total response of the soil, either of displacements or stresses, has the same type of series expression except for the fundamental distributions replaced by influence functions. The coefficients of the series expansion, appearing in both equilibrium conditions of the foundation and compatibility conditions on the contact surface, relate the foundation displacements and excitations, and, therefore, result in the impedance matrix. Avoidance of integral equations in the soil-structure interaction analysis is the merit of the present approach.

The objective of the present approach is to determine the structural response to external force excitations and earthquake excitations with consideration of soil-structure interaction. The physical model concerned is a flexible structure resting on a rigid or flexible foundation embedded in a layered soil medium. The vibration of the structure is first analyzed using the wave propagation approach without reference to the interaction. The interaction effect is recovered by the impedance relationship developed in the companion paper. In an attempt to use the free field ground motion as the input to the system, the Maxwell's reciprocal theorem is applied to remedy the difference between the free field and real ground motion in the presence of the structure. As a result, the structural response at any location is written as a linear function of external excitations and the seismic source. Such a solution form is convenient for statistical analysis.

This study presents system identification of ten-story Millikan Library in Pasadena, California with a pair of the Yorba Linda earthquake of September 3, 2002. The fundamental of the proposed approach is based on wave features of generalized impulse and frequency response function (GIRF or GFRF), i.e., wave response at one structural response location to an impulsive motion at another reference location in time and frequency domains respectively. With a pair of seismic recordings at the two locations, GIRF/GFRF is obtainable. With a continuous-discrete model for the structure, a closed-form solution of GFRF, and subsequent GIRF with Fourier transformation of GFRF, can also be found in terms of structural physical properties above the impulse location. Matching the two sets of GIRF/GFRF from recordings and the model helps identify system parameters such as wave velocity or shear modulus.

Currently, the kriging and conditional probability density function (CPDF) methods are widely used in solving the conditional simulation problems involving stochastic processes and fields. For the fundamental understanding of these two methods, this paper considers their applications to the conditional simulation of a one-dimensional, univariate and stationary stochastic process or field. The major findings of this study are as follows. First, the two methods are completely equivalent if the stochastic process is Gaussian with a zero mean. Specifically, the best linear unbiased estimate (BLUE) and the kriging variance are identical to the corresponding conditional mean and variance, respectively. Second, when the kriging method is used, the conditional simulation of a nonzero mean stochastic process (with a known value of the mean) is not equivalent to the (nonzero) mean plus the conditional simulation of the zero mean stochastic process obtained by subtracting the nonzero mean from the original process. Third, it can be shown that the second moment of the process conditionally simulated with the help of the kriging method are not identical to the target second moment (a priori known statistics). Finally, the kriging method is not suitable for the conditional simulation of non-Gaussian stochastic processes if no other assumptions or conditions are made for the reasons indicated in the paper, although the estimation (BLUE) may still be performed, as claimed by its proponents.

A discrete wave number approach in conjunction with a propagator-based formalism is used to synthesize the Loma Prieta earthquake ground motion at both the near and the far field, taking into account all kinds of seismic waves (body and surface). A bilaterally propagating shear slip over a rectangular fault is used to describe the seismic source mechanism, while the earth model is based on geological profiles of the Santa Cruz mountain area and consists of three layers overlaying a half-space. The synthesized ground motion is first compared with actual records from the Loma Prieta earthquake and the agreement between the two is found to be satisfactory, as far as magnitude, duration and essential wave form characteristics are concerned. Then, ground motions are synthesized and plotted at a dense grid of observer locations over a large area around the epicenter, at different time instants. Using such plots, it is possible to study the generation ana propagation of different kinds of seismic waves, the spatial variability of ground motion, as well as the development of the permanent gound deformation.

Probabilistic characteristics of a sliding structure is investigated by using new versions of stochastic linearization technique. The structure is composed of base part and upper part, which are connected to each other in a spring-damping system. Coulomb friction between the base structure and earth ground is considered. Two alternative versions of stochastic linearization approach, suggested by X. Zhang and I. Elishakoff, respectively, are applied to such a sliding structure to evaluate its statistical properties. Compared with the results of Monte Carlo simulation, the two new approaches are performing much better than the conventional one in their applications to the sliding structure. Moreover, numerical results indicate that the criterion proposed by Elishakoff turns out to be superior to all other versions in the problem under study. Numerical results also suggest that the entire structure may be replaced by the rigid body in the sliding problem as long as the difference of velocity responses are considered less important than those of displacement responses.

An analysis is given of the statistical and probabilistic properties of the random time at which a piece of essential equipment, such as a computer, may topple under base excitations. The equipment is modeled as a rigid block, and the base accelerations are modeled as white noises in horizontal and vertical directions. The cases of a free-standing block and an anchored block are both considered. The white-noise idealization resembles the most intense portion of ground acceleration in a seismic event, which is an acceptable simplification provided that the correlation times of actual base excitations are short compared with the dominant quasi-periods of the induced rocking motion. It is shown that the presence of vertical excitation about one-half the level of horizontal excitation may increase the probability of toppling by 30–40%, and that larger blocks are more stable than the smaller ones of the same geometrical proportion. The analysis is applicable to such objects as monuments, storage tanks, and certain types of tall buildings.

A model for earthquake ground motion is developed using principles of geophysics and stochastics in a sequence of two papers. In the first paper, the earth is idealized as being composed of horizontally stratified layers, with uniform physical properties for each layer. The seismic source is modeled as a concentrated seismic moment located within one of the layers. The partial differential equations for the seismic motion in each layer are solved using a Fourier finite-Hankel transformation approach, and solutions in terms of state vectors of displacements and forces are converted to wave vectors composed of up-going and down-going waves. Transmission and reflection matrices are obtained for each layer, for each layer-to-layer interface, and for the free ground-surface boundary to characterize their roles in transmitting and reflecting a wave motion. The use of these matrices allows the numerical calculation to be channeled in the directions of wave propagation, resulting in better numerical accuracy. An example is included for illustration.

The pulse shape function obtained in a companion paper is incorporated in the development of a stochastic earthquake model. It is assumed that seismic ground motion is caused by shear dislocation that propagates along a line. This line source is further discretized into point sources at equal intervals. The times at which seismic signals are activated are assumed to be Poisson events with a time‐varying average occurrence rate λ(t) per unit time. This is equivalent to assuming an average speed λ(t) for the propagation of shear dislocation. The strengths of seismic signals emitted from discretized point sources are assumed to be independent and identically distributed random variables. A generalized version of the random‐pulse‐train theory is used to compute the mean and auto‐correlation functions of the ground motion at one site, and the cross‐correlation function at two sites. The auto‐correlation and cross‐correlation functions can then be converted to the evolutionary spectral density and evolutionary ...

This paper develops a theory to compute the statistical properties for the response of a surface-mounted pipeline to seismic excitations. Making the assumptions that the pipeline behaves like an infinitely long Euler-Bernoulli beam on evenly spaced supports, that the seismic motion is statistically stationary in time but nonhomogeneous in space, and that the seismic inputs are fed into the pipeline system through the supports, solutions are obtained for the spectral densities of the structural response. The theory developed is aplicable to any spectral distributions.

This paper proposes field-testing-based power spectra of vibration in such environments as helicopters and ground vehicles. The spectra could then be used as important input data to guide accelerated testing, quality analysis and design for medical devices (or products) used in the aforementioned transportation means. Specifically, a broad spectrum of environmental vibration is first measured in a series of field vibration tests at various locations inside the transportation means and at different operational conditions (e.g., take-off, cruise, and landing conditions if medical devices are used in helicopters). Consequently, comprehensive field-testing-based power spectra are constructed, in an attempt to catch the inherent nature of random vibration environment in each and every type of the transportation means, which is not adequately specified in standard codes. As one of the applications of the proposed spectra, accelerated random vibration testing for medical devices used in either helicopters or ground vehicles is proposed, which could be used not only for product field life prediction but also for its consequent reliability analysis and design.

Stochastic dynamic responses of high-rise structures under turbulent wind is analyzed at two directions in this study. In particular, two types of structural configurations, namely, a mega-sub building and a TV tower, are considered. The wind speed consists of mean and turbulent parts. The turbulent part is idealized as a non-white stochastic process with spatial variation along the height of the structures. When the interaction between wind and structure is taken into consideration, the drag force represents the additive and parametric excitation with nonlinear colored noise, while the lift force the parametric excitation with nonlinear colored noise (updated Scanlan-Simiu model). Assuming that the wind direction is slightly off the direction normal to one side of the structures (the x-direction), it is shown that the x-direction vibration is generated primarily by the drag force due to the x-direction wind speed, while the y-direction vibration is generated primarily by the lift force exerted by vortex shedding resulting from the x-direction wind speed, and by the drag force due to the y-direction wind speed. With the aids of spectral representation method and numerical technique, the static and random vibration responses of the structures are then found for each simulated turbulent wind input. The response trajectories of the structures at specific heights are also derived. These results provide fundamentally important information for the vibration control analysis of the high-rise structures with passive and/or active mass dampers.