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| 2. |
- Lin, Chang, et al.
(författare)
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Visualizing Conduit Flows around Solitary Air Pockets
- 2014
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Ingår i: Journal of engineering mechanics. - : American Society of Civil Engineers (ASCE). - 0733-9399 .- 1943-7889. ; 141:5
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Tidskriftsartikel (refereegranskat)abstract
- Understanding flow characteristics around air pockets is fundamental in the study of air entrainment and transport in pipelines. This study deals with the use of flow visualization technique (FVT) and high-speed particle image velocimetry (HSPIV) in exploration of the characteristics around stationary air pockets in horizontal-pipe flow. The air-pocket volume varies from 0 to 10.0 mL, and the air pocket is injected into a fully developed turbulent flow with Reynolds numbers between 17,000 and 18,400. In the plane of symmetry, the main flow features include (1) a horseshoe vortex upstream, (2) a stagnation point on the frontal interface, (3) a separation point and a separated shear layer beneath, (4) a reattached shear layer downstream of the reattachment point (for air-pocket volumes greater than 2.0 mL), and (5) a reverse-flow region downstream. The deformable air pocket in the turbulent flow causes streamwise random movements of both the stagnation and separation points around their mean positions. The flow pattern is categorized based on the occurrence of either separated flow or flow reattachment. Fully separated flow (Mode I) occurs at air-pocket volumes less than 2.0 mL. Intermittently reattached flow (Mode II) occurs if the volume is within 2.0–5.0 mL. Fully reattached flow (Mode III) is evident at volumes greater than 5.0 mL. Water particles on the air-pocket surface move with the adjacent flow, thus forming a slip boundary. The evolution of mean streamwise velocity beneath the air pocket demonstrates the formation of either a separated or a reattached shear layer. Using nonlinear regression analysis, appropriate characteristic velocity and length scales are determined to obtain similarity profiles in the separated shear layer beneath.
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| 3. |
- Yuan, Z. H., et al.
(författare)
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Closed-Form Analytical Solution for Vibrations from a Tunnel Embedded in a Saturated Poroelastic Half-Space
- 2017
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Ingår i: Journal of Engineering Mechanics - ASCE. - : American Society of Civil Engineers (ASCE). - 1943-7889 .- 0733-9399. ; 143:9, s. 04017079-
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Tidskriftsartikel (refereegranskat)abstract
- A closed-form analytical solution for ground-borne vibrations from a tunnel embedded in a saturated poroelastic half-space is proposed in this paper. The tunnel modeled as an elastic hollow cylinder is surrounded by the water-saturated poroelastic material. The total wave field in the poroelastic half-space with a cylindrical cavity consists of the outgoing cylindrical waves and the down-going plane waves. In addition to the traction-free condition on the ground surface and the continuous conditions of displacement and stress at the tunnel-soil interface, hydraulic boundary conditions on these two scattering surfaces are required to solve this multiple-scattering problem. The transformation properties between the plane and cylindrical wave functions are employed to apply the boundary conditions expressed in both the rectangular and cylindrical coordinate systems. Numerical results for the displacements of the solid on the ground surface and the pore pressure in the saturated soil attributable to a harmonic point load applied at the tunnel invert are presented. The influence of the soil permeability and the hydraulic boundary at the tunnel-soil interface on the free-field responses is investigated. The proposed solution can serve as a benchmark for other computational methods and as an efficient tool for predicting vibrations from a tunnel embedded in a saturated poroelastic half-space.
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| 4. |
- Challamel, Noël, et al.
(författare)
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Lateral-torsional buckling of partially composite horizontally layered or sandwich-type beams under uniform moment
- 2013
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Ingår i: Journal of engineering mechanics. - 0733-9399 .- 1943-7889. ; 139:8, s. 1047-1064
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Tidskriftsartikel (refereegranskat)abstract
- This paper is devoted to the analytical and numerical modeling of the lateral-torsional stability of horizontally layered composite beams. Composite beams are classified as horizontally layered beams with interlayer slip or sandwich beams with a weak shear core. The governing differential equations of the out-of-plane behavior of horizontally layered composite beams are supported by variational arguments. In the theoretical analysis, a distinction is made between the influence of the shear connection at the interface with respect to the in-plane or transversal deformations and to the out-of-plane or lateral deformations, respectively. Some engineering results are presented for a partially composite beam under pure bending moment. In the case of noncomposite in-plane action (orthotropic connection), a simple closed-form solution is derived for the lateral-torsional buckling moment, and it is shown that the exact dimensionless buckling moment depends only on two structural parameters for beams composed of two identical subelements. The results are analogous to those obtained for the in-plane buckling of partially composite or sandwich-type beams, where the buckling moment increases with the stiffness of the shear connection. Prandtl’s valid solution for lateral-torsional buckling of ordinary beams is also found for composite beams in the case of noncomposite action in both the transversal and lateral directions. A generalization of Prandtl’s valid solution for composite beams with partial composite action in the lateral direction and noncomposite action in the transversal direction is derived. It is shown that the lateral-torsional buckling formulas are strongly affected by the kinematics of the connected shear layer. Also, the lateral-torsional buckling of partially composite beams with both in-plane and out-of-plane slip behavior is analyzed using the Rayleigh-Ritz method. This mathematical problem leads to a system of differential equations with nonuniform coefficients. An approximated solution is derived for the isotropic connection with isotropic noncomposite actions, whereas an exact solution is presented for the orthotropic connection with noncomposite in-plane action. Finally, the Rayleigh-Ritz approach is compared with some numerical results associated with the exact resolution of the differential equations with nonuniform coefficients. The Rayleigh-Ritz approach appears to be efficient to capture the main phenomena, including the nonmonotonic dependence of the buckling load to the connection parameter.Read More: http://ascelibrary.org/doi/abs/10.1061/(ASCE)EM.1943-7889.0000489
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| 5. |
- Birmpilis, Georgios, 1988, et al.
(författare)
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Fabric Investigation of Natural Sensitive Clay from 3D Nano- And Microtomography Data
- 2022
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Ingår i: Journal of Engineering Mechanics - ASCE. - 1943-7889 .- 0733-9399. ; 148:2
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Tidskriftsartikel (refereegranskat)abstract
- The three-dimensional (3D) fabric in natural sensitive clay is quantified from a combination of high resolution nano and microtomographies, scanning electron microscopy, and dynamic light scattering. Although the speckle arising from clay particles and the pores they enclose is discerned in the nanotomography data and compare well with scanning electron microscopy (SEM) images on the same clay, the individual platelet-shaped clay particles cannot be segmented for subsequent quantitative analysis. Regardless, a very wide range of particle sizes - 0.1-300 μm - was detected using the current state-of-the-art in imaging and postprocessing. The measured aspect ratios range was 2.5±1; hence, the particles identified were not clay platelets but, rather, mechanically weathered particles embedded in the clay matrix. Furthermore, the smaller particle sizes <80 μm presented a consistent 22-23° deviation in orientation from the horizontal plane, whereas the larger fractions had a horizontal orientation. The latter finding agrees well with prior findings on the inclination of the clay minerals using small angle X-ray scattering. Finally, the measured mean particle size of 450 nm determined from the nano data is corroborated by an independent determination of particle sizes using dynamic light scattering.
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| 6. |
- Nilenius, Filip, 1982, et al.
(författare)
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FE2 Method for Coupled Transient Diffusion Phenomena in Concrete
- 2015
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Ingår i: Journal of Engineering Mechanics - ASCE. - 1943-7889 .- 0733-9399. ; 141:2, s. Art. no. 04014110-
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Tidskriftsartikel (refereegranskat)abstract
- Acoupled finite-element squared (FE2)-framework is formulated and employed for simulation of a transient and coupled moisturechlorideion diffusion problem in concrete. Simulations are carried out on the macroscale, where the material response is obtained concurrentlyin the computations by introducing a representative volume element (RVE) in the macroscale quadrature points. The RVE, in turn, contains themesoscale heterogeneities of concrete in terms of cement paste, aggregates, and interfacial transition zone (ITZ). In this fashion, the RVE comesto serve as a constitutive model for the macroscale.Anumerical example is given to show how the transient macroscale diffusion is influenced bythe composition of the mesoscale constituents. Parametric studies were carried out with respect to the aggregate content within the RVE, bothincluding and excluding the ITZ, and the coupling parameters of moisture and chloride ions.
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| 7. |
- Aidanpää, Jan-Olov, et al.
(författare)
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Experimental and numerical studies of shear layers in granular shear cell
- 1996
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Ingår i: Journal of engineering mechanics. - 0733-9399 .- 1943-7889. ; 122:3, s. 187-196
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Tidskriftsartikel (refereegranskat)abstract
- The stability of a shear layer inside a granular material in a gravity field is studied experimentally and numerically. A shear cell is built of transparent acrylic to visualize the motion of the granular material. This shear cell consists of two concentric cylinders containing layers of uniform spheres in the annular space between the cylinders. The shearing motion of the spheres is produced by rotating the bottom boundary of the cell. Friction of the cylinder walls resists the shear motion, thus creating a single shear layer adjacent to the bottom boundary, while the rest of the layers above move with constant speed as a solid body. As the rotation speed of the bottom boundary increases, two layers adjacent to the bottom boundary begin to shear. This shearing zone quickly thickens and dilates as the rotational speed increases. The transition of this shear motion from a single layer to many layers of shearing is studied by video recording. The initiation of this transition is observed to depend on the material properties and the number of layers overlaying the shear layer. A one-dimensional numerical model is constructed to bring insight into this transitional phenomenon.
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| 8. |
- Dahlblom, Ola, et al.
(författare)
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Smeared Crack analysis Using a Generalized Fictitious Crack model
- 1990
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Ingår i: Journal of Engineering Mechanics - ASCE. - 1943-7889. ; 116:1, s. 55-76
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Tidskriftsartikel (refereegranskat)abstract
- he fictitious crack model is extended so that it includes the effect of crack shearing. By the introduction of the so-called equivalent length, it is possible to establish a smeared version of the fictitious crack model. The equivalent length is a purely geometrical quantity that depends entirely on the size and form of the element and on the crack direction. A realistic modeling of crack shearing is obtained, and the smeared constitutive relations are objective with respect to both loading normal to the crack plane and loading tangential to the crack plane. The existence of multiple cracks is considered, and a consistent theory for unloading and possible closure of the cracks is presented. FE calculations of a concrete specimen using four different element types demonstrate the objectivity of the theory even when distorted meshes are used.
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| 9. |
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| 10. |
- Gustafsson, Lennart, et al.
(författare)
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Studying disk movements by novel image-analysis method
- 1995
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Ingår i: Journal of engineering mechanics. - 0733-9399 .- 1943-7889. ; 121:8, s. 931-934
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Tidskriftsartikel (refereegranskat)abstract
- An image-analysis method developed to study granular flow, the accumulating particle trajectories (APT) method, is shown to be a versatile tool to study the movements of disks. The moving disks, which are provided with suitable dot patterns, are video-recorded and the recorded sequences are analyzed to provide trajectories of the disks and the dots, thus making it possible to study both translational and rotational movements. It is also possible to introduce time markers in the trajectories. Up to eight images per second can be analyzed. The filtering necessary to attenuate electronic noise in the video equipment is performed as time filtering between consecutive images and is very efficient. The method's demands for processing power are very moderate and, therefore, particle movements during time spans corresponding with thousands of video frames can be easily presented as analysis results. The method can be implemented at relatively low cost.
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