| 1. |
- Yuan, Z. H., et al.
(författare)
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Analytical solution for calculating vibrations from twin circular tunnels
- 2019
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Ingår i: Soil Dynamics and Earthquake Engineering. - : Elsevier BV. - 0267-7261. ; 117, s. 312-327
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Tidskriftsartikel (refereegranskat)abstract
- The calculation of vibrations from a single tunnel embedded in a full- or half-space due to underground moving trains has been well studied in the literature. A common assumption made in the majority of vibration prediction models is to neglect the presence of a neighboring tunnel, however, twin tunnels are a particularly preferred construction for urban underground railways with one as the inbound tunnel and the other as the outbound tunnel. The neglect of the interaction between twin tunnels may lead to inaccuracies of the calculation of vibrations from underground railways. The present paper proposes a novel analytical solution, which takes the multiple scattering effects between the two tunnels into account. The two tunnels are modelled as elastic hollow cylinders and the soil surrounding the tunnels as an elastic, homogeneous full-space containing two cylindrical cavities. The wave field in the full-space with two cavities consists of outgoing waves from each tunnel outside the two scattering surfaces while the wave field in the tunnel wall is a combination of outgoing and regular cylindrical waves. The translation of the outgoing cylindrical wave functions is required to satisfy the boundary conditions at the other tunnel. Numerical results show that there are two critical velocities for a twin tunnel in a full-space system, both of which are around the shear wave velocity of the soil. Through comparison with the single tunnel solution, the addition of a second tunnel at different separation distances and angles has a significant influence on the soil response, especially in the high frequency range, but the response at the tunnel with the source is not much affected.
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| 2. |
- Yuan, Z. H., et al.
(författare)
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Analytical wave function method for modelling a twin tunnel embedded in a saturated poroelastic full-space
- 2019
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Ingår i: Computers and Geotechnics. - : Elsevier BV. - 0266-352X .- 1873-7633. ; 114
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Tidskriftsartikel (refereegranskat)abstract
- An analytical wave function method for the calculation of vibrations from two tunnels embedded in a saturated poroelastic full-space due to a harmonic point load is given, in which the multiple scattering between twin tunnels is considered exactly. The two tunnels made of viscoelastic material are modelled as two hollow cylinders. The soil surrounding two tunnels is water-saturated, and modelled as a two-phase poroelastic material. The wave field in the full-space with two circular cavities is a superposition of outgoing waves outside the two cavity surfaces. As there is water in the soil, the hydraulic boundary at the tunnel-soil interface is necessary when solving this multi-scattering problem. The translation properties of outgoing waves are adopted to apply boundary conditions described in two sets of cylindrical coordinates. The proposed analytical method for modelling twin tunnels provides a new tool to study the interaction between twin tunnels buried in a poroelastic medium. Some typical numerical results are given to illustrate the influence of the soil permeability and the permeability of the tunnel-soil interface on the displacement and pore pressure responses. In addition, the results for a single tunnel are compared to those of a twin tunnel with various separation distances and angles.
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| 3. |
- Yuan, Z. H., et al.
(författare)
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The wave function method for calculation of vibrations from a twin tunnel in a multi-layered half-space
- 2019
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Ingår i: Soil Dynamics and Earthquake Engineering. - : Elsevier BV. - 0267-7261. ; 125
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Tidskriftsartikel (refereegranskat)abstract
- The ground vibrations due to underground moving trains cause disturbances to nearby buildings and their residents, which has been viewed as an important environmental issue. Various numerical or semi-analytical models are used to calculate the vibrations from underground railways, however, most of the prediction models adopt a single tunnel-soil system for modelling vibrations from underground trains and neglect the influence of a neighboring tunnel. In this paper, a semi-analytical wave function method is proposed for modelling vibrations from twin tunnels in a multi-layered viscoelastic and poroelastic half-space. The two tunnels are modelled as two hollow cylinders while the surrounding soil is modelled as a multi-layered half-space containing two circular cavities. The vibrations of the tunnel walls are taken as a superposition of outgoing and regular cylindrical waves. The wave field in the soil layer containing two cavities consists of down-going and up-going plane waves and cylindrical waves propagating outwards from each tunnel. In the wave function method, the transformation and translation of the plane and cylindrical waves make it possible to apply the boundary conditions at the scattering surfaces. Numerical results show that the half-space model predicts higher surface vibrations than a full-space model at equivalent surface locations. When the second tunnel is added near a deeper existing tunnel, a wider range of the free-field response above the two tunnels is significantly changed, however, the response below twin tunnels is less affected. If the separation distance between the two tunnels is smaller than five times the tunnel diameter, a twin tunnel model in a half-space is more suitable for an accurate vibration prediction at the ground surface. The cutoff effect of the rigid base is more visible for shallow bedrock at lower frequencies while the influence of the bedrock is quite limited at higher frequencies.
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| 4. |
- Yuan, Z. H., et al.
(författare)
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Benchmark solution for vibrations from a moving point source in a tunnel embedded in a half-space
- 2017
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 387, s. 177-193
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Tidskriftsartikel (refereegranskat)abstract
- A closed-form semi-analytical solution for the vibrations due to a moving point load in a tunnel embedded in a half-space is given in this paper. The tunnel is modelled as an elastic hollow cylinder and the ground surrounding the tunnel as a linear viscoelastic material. The total wave field in the half-space with a cylindrical hole is represented by outgoing cylindrical waves and down-going plane waves. To apply the boundary conditions on the ground surface and at the tunnel-soil interface, the transformation properties between the plane and cylindrical wave functions are employed. The proposed solution can predict the ground vibration from an underground railway tunnel of circular cross-section with a reasonable computational effort and can serve as a benchmark solution for other computational methods. Numerical results for the ground vibrations on the free surface due to a moving constant load and a moving harmonic load applied at the tunnel invert are presented for different load velocities and excitation frequencies. It is found that Rayleigh waves play an important role in the ground vibrations from a shallow tunnel. (C) 2016 Elsevier Ltd. All rights reserved.
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| 5. |
- Cai, D. Q., et al.
(författare)
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A study of control chart for adjusted processes
- 1999
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Ingår i: The 26th International Conference on Computers & Industrial Engineering (the 26th C & IE) : December 15-17, 1999, Melbourne, Australia. ; , s. 443-447, s. 443-447
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Konferensbidrag (refereegranskat)
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| 6. |
- Yuan, Z. H., et al.
(författare)
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The influence of pore-fluid in the soil on ground vibrations from a tunnel embedded in a layered half-space
- 2018
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 419, s. 227-248
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Tidskriftsartikel (refereegranskat)abstract
- A computationally efficient semi-analytical solution for ground-borne vibrations from underground railways is proposed and used to investigate the influence of hydraulic boundary conditions at the scattering surfaces and the moving ground water table on ground vibrations. The arrangement of a dry soil layer with varying thickness resting on a saturated poroelastic half-space, which includes a circular tunnel subject to a harmonic load at the tunnel invert, creates the scenario of a moving water table for research purposes in this paper. The tunnel is modelled as a hollow cylinder, which is made of viscoelastic material and buried in the half-space below the ground water table. The wave field in the dry soil layer consists of up-going and down-going waves while the wave field in the tunnel wall consists of outgoing and regular cylindrical waves. The complete solution for the saturated half-space with a cylindrical hole is composed of down-going plane waves and outgoing cylindrical waves. By adopting traction-free boundary conditions on the ground surface and continuity conditions at the interfaces of the two soil layers and of the tunnel and the surrounding soil, a set of algebraic equations can be obtained and solved in the transformed domain. Numerical results show that the moving ground water table can cause an uncertainty of up to 20 dB for surface vibrations.
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| 7. |
- Cai, G. Q., et al.
(författare)
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Effects of habitat complexity on stochastic nonlinear ecosystems
- 2016
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Ingår i: International Journal of Dynamics and Control. - : Springer. - 2195-268X .- 2195-2698. ; 4:3, s. 275-283
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Tidskriftsartikel (refereegranskat)abstract
- The term “Habitat Complexity” is used to measure the coupling level between different species in an ecosystem. It plays an important role to an ecosystem in which two or more species are interacting with each other. In the present paper, effects of the habitat complexity on predator–prey ecosystems with or without noise disturbances are investigated. Stochastic analysis methods of the Ito differential equations, the stochastic averaging method, and the Monte Carlo simulation are applied to obtain the stationary probability densities of the predator and prey population densities. It is found that the effects of the habitat complexity on the system dynamical behaviors are quite different for the deterministic case and the stochastic case. In absence of the noises, there are two bifurcation points dividing the level of habitat complexity into three regions: weak, moderate and strong. In the three regions, limit cycles, co-existing equilibrium states, and predator-extinct equilibrium states are present, respectively. In the stochastic case, the stable invariant measures in terms of probability distributions replace both the limit cycles and coexisting equilibriums in the regions of weak and moderate habitat complexity. For the case of strong habitat complexity, although the predator remains extinct, the prey is not in an equilibrium state, but possesses a probability distribution.
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| 8. |
- Cai, Yangjian, et al.
(författare)
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Coincidence subwavelength fractional Fourier transform
- 2006
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Ingår i: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 23:4, s. 835-841
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Tidskriftsartikel (refereegranskat)abstract
- The coincidence subwavelength fractional Fourier transforms (FRTs) with entangled photon pairs and incoherent light radiation are introduced as an extension of the recently introduced coincidence FRT. Optical systems for implementing the coincidence subwavelength FRTs are designed. The width of the coincidence subwavelength FRT pattern is two times narrower than the width of the coincidence FRT. The coincidence subwavelength FRT with partially coherent light radiation is also studied numerically. Differences between the coincidence subwavelength FRT with entangled photon pairs and that with incoherent light radiation are discussed.
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| 9. |
- Cao, Zhigang, 1983, et al.
(författare)
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Semi-analytical analysis of the isolation to moving-load induced ground vibrations by trenches on a poroelastic half-space
- 2012
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 331:4, s. 947-961
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Tidskriftsartikel (refereegranskat)abstract
- A semi-analytical model is proposed to investigate the screening efficiency of trenches to moving-load induced ground vibrations. The ground is modeled as a fully saturated poroelastic half-space governed by Biot's dynamic poroelastic theory. The trenches are obtained by placing three rectangular elastic layers with appropriate width upon the poroelastic half-space. By Helmholtz decomposition, the displacement fields of the elastic layers are decomposed into three scalar potentials. Analytical solutions are obtained based on Fourier transform and Fourier series in the transformed domain. The time-domain results are obtained by the fast Fourier transform (FFT). The different performances of trenches on a saturated poroelastic half-space and a single-phase elastic half-space to the moving load-induced ground vibration are identified. It is found that the discrepancy of the screening efficiencies between the two models becomes significant when the load speed approaches the Rayleigh wave speed of the ground surface. Also, some parametric studies for the screening efficiency of the trench on the poroelastic half-space are presented.
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| 10. |
- Brandt, Adam R., et al.
(författare)
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Energy Intensity and Greenhouse Gas Emissions from Tight Oil Production in the Bakken Formation
- 2016
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:11, s. 9613-9621
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Tidskriftsartikel (refereegranskat)abstract
- The Bakken formation has contributed to the recent rapid increase in U.S. oil production, reaching a peak production of >1.2 × 106 barrels per day in early 2015. In this study, we estimate the energy intensity and greenhouse gas (GHG) emissions from 7271 Bakken wells drilled from 2006 to 2013. We model energy use and emissions using the Oil Production Greenhouse Gas Emissions Estimator (OPGEE) model, supplemented with an open-source drilling and fracturing model, GHGfrack. Overall well-to-refinery-gate (WTR) consumption of natural gas, diesel, and electricity represent 1.3%, 0.2%, and 0.005% of produced crude energy content, respectively. Fugitive emissions are modeled for a “typical” Bakken well using previously published results of atmospheric measurements. Flaring is a key driver of emissions: wells that flared in 2013 had a mean flaring rate that was ≈500 standard cubic feet per barrel or ≈14% of the energy content of the produced crude oil. Resulting production-weighted mean GHG emissions in 2013 were 10.2 g of CO2 equivalent GHGs per megajoule (henceforth, gCO2eq/MJ) of crude. Between-well variability gives a 5–95% range of 2–28 gCO2eq/MJ. If flaring is completely controlled, Bakken crude compares favorably to conventional U.S. crude oil, with 2013 emissions of 3.5 gCO2eq/MJ for nonflaring wells, compared to the U.S. mean of ≈8 gCO2eq/MJ.
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