articles by John Williams
Application of the SPH method to solitary wave impact on an offshore platform

Engineering Computations, 2017
Volume mapping of spherical particles to a Cartesian grid with grid elements smaller than the sph... more Volume mapping of spherical particles to a Cartesian grid with grid elements smaller than the sphere radius is typically required in application of simple immersed boundary conditions in coupled engineering simulations. However, there exists no unique analytical solution to computation of the volume of intersection between spheres and cubes. In this work, existing numerical techniques for computing intersection volume are reviewed and compared in terms of accuracy and performance. In addition to this a more efficient linear relationship is proposed and included in this comparison. We find in this work that a simple linear relationship is both acceptably accurate, and more computationally efficient than the contemporary techniques. This simple linear approach may be applied to accurately compute solutions to fluid-particle systems with very large numbers of particles.
Multiphase lattice Boltzmann simulations for porous media applications
Smoothed particle hydrodynamics and its applications for multiphase flow and reactive transport in porous media
Lattice Boltzmann methods for the simulation of heat transfer in particle suspensions
Lattice Boltzmann methods for the simulation of heat transfer in particle suspensions
Papers by John Williams

Physical Review E, 2014
This paper numerically investigates particle saltation in a turbulent channel flow having a rough... more This paper numerically investigates particle saltation in a turbulent channel flow having a rough bed consisting of two to three layers of densely packed spheres. The Shields function is 0.065 which is just above the sediment entrainment threshold to give a bed-load regime. The applied methodology is a combination of three technologies, i.e., the direct numerical simulation of turbulent flow; the combined finite-discrete element modeling of the deformation, movement, and collision of the particles; and the immersed boundary method for the fluid-solid interaction. It is shown that the presence of entrained particles significantly modifies the flow profiles of velocity, turbulent intensities, and shear stresses in the vicinity of a rough bed. The quasi-streamwise-aligned streaky structures are not observed in the near-wall region and the particles scatter on the rough bed owing to their large size. However, in the outer flow region, the turbulent coherent structures recover due to the weakening rough-bed effects and particle interferences. First-and second-order statistical features of particle translational and angular velocities, together with sediment concentration and volumetric flux density profiles, are presented. Several key parameters of the particle saltation trajectory are calculated and agree closely with published experimental data. Time histories of the hydrodynamic forces exerted upon a typical saltating particle, together with those of the particle's coordinates and velocities, are presented. A strong correlation is shown between the abruptly decreasing streamwise velocity and increasing vertical velocity at collision which indicates that the continuous saltation of large-grain-size particles is controlled by collision parameters such as particle incident angle, local bed packing arrangement, and particle density, etc.

Proceedings on the second ACM symposium on Solid modeling and applications - SMA '93, 1993
This paper introduces a novel approach for automatically creating computer models of existing, ph... more This paper introduces a novel approach for automatically creating computer models of existing, physical artifacts. Based on the projected silhouettes of the object, when viewed from different vantage points, our algorithm efficiently combines the digital information into an incrementally refined three-dimensional representation. We have designed the algorithm with two requirements in mind, namely: a) accurtac~, i.e. the resulting computer model should retain the overall properties of the real object and alao preserve fine details; b) progressive refinement, i.e. a relatively coarse model should be rapidly generated and finer detail progressively reconstructed as more images are available. We demonstrate our algorithm by comparing the original artifacts and resulting computer models, Keywords: octree intersection. Quaternion camera model. 3D model synthesis. Incremental reconstruction Permission m copy without fee all or part of this material is granted provided tha(the copies are trot made or distrihu[ed for direc(commercial advantage, !he ACM copyright notme and the title of the publication and its da~e appear, and notice is given Ihat copying is by permmwon of the As~octation for Comput#ng Machinery. To copy otherwise, or to republish, requires a fee and/err specific pmnissimr.

Geophysical Research Letters, 2006
In this paper we quantify the influence of geometry and 9 distribution of surface roughness to th... more In this paper we quantify the influence of geometry and 9 distribution of surface roughness to the directional 10 anisotropy of fluid flow and transport properties of a 11 single fracture. Roughness of fractures appears to have first 12 order control on how they behave mechanically and 13 hydraulically. We directly quantified the surface roughness 14 of a single fracture using high-resolution laser scanning 15 confocal microscopy. This roughness was input into directly 16 coupled numerical models of fluid flow and transport. We 17 simulated the transport of colloids (microspheres) through 18 the fracture. We found tailing in the breakthrough and 19 sensitivity of the breakthrough to flow direction in the 20 fracture. Microspheres were observed to be trapped in 21 low velocity zones on the lee side of fracture walls. This 22 was not observed in smooth or sinusoidal varying fracture 23 wall geometries. These observations have significant 24 implications for quantifying the transport of dissolved and 25 solid phase materials (colloids) through fractured rock.

A direct simulation method for particle‐fluid systems
Engineering Computations, 2004
A coupled numerical method for the direct simulation of particle‐fluid systems is formulated and ... more A coupled numerical method for the direct simulation of particle‐fluid systems is formulated and implemented. The Navier‐Stokes equations governing fluid flow are solved using the lattice Boltzmann method, while the equations of motion governing particles are solved with the discrete element method. Particle‐fluid coupling is realized through an immersed moving boundary condition. Particle forcing mechanisms represented in the model to at least the first‐order include static and dynamic fluid‐induced forces, and intergranular forces including particle collisions, static contacts, and cementation. The coupling scheme is validated through a comparison of simulation results with the analytical solution of cylindrical Couette flow. Simulation results for the fluid‐induced erosive failure of a cemented particulate constriction are presented to demonstrate the capability of the method.
Proceedings of the 16th annual conference …, 1989
Many of the problems of simulating and rendering complex systems of non-rigid objects can be min-... more Many of the problems of simulating and rendering complex systems of non-rigid objects can be min-imized by describing the geometry and dynamics separately, using representations optimized for ei-ther one or the other, and then coupling these rep-resentations together. We ...

Journal of Geophysical …, 2007
A detailed understanding of the coupling between fluid and solid mechanics is important for under... more A detailed understanding of the coupling between fluid and solid mechanics is important for understanding many processes in Earth sciences. Numerical models are a popular means for exploring these processes, but most models do not adequately handle all aspects of this coupling. This paper presents the application of a micromechanically based fluid-solid coupling scheme, lattice-Boltzmann discrete element method (LBDEM), for porous media simulation. The LBDEM approach couples the lattice-Boltzmann method for fluid mechanics and a discrete element method for solid mechanics. At the heart of this coupling is a previously developed boundary condition that has never been applied to coupled fluid-solid mechanics in porous media. Quantitative comparisons of model results to a one-dimensional analytical solution for fluid flow in a slightly deformable medium indicate a good match to the predicted continuum-scale fluid diffusion-like profile. Coupling of the numerical formulation is demonstrated through simulation of porous medium consolidation with the model capturing poroelastic behavior, such as the coupling between applied stress and fluid pressure rise. Finally, the LBDEM model is used to simulate the genesis and propagation of natural hydraulic fractures. The model provides insight into the relationship between fluid flow and propagation of fractures in strongly coupled systems. The LBDEM model captures the dominant dynamics of fluid-solid micromechanics of hydraulic fracturing and classes of problems that involve strongly coupled fluid-solid behavior.
Uploads
articles by John Williams
Papers by John Williams