Deep Water Pathways In The North Pacific Ocean Revealed By Lagrangian Particle Tracking

Lagrangian particle tracking experiments are conducted to investigate the pathways of deep water in the North Pacific Ocean. The flow field is taken from a state-of-the-art deep circulation simulation. An unprecedented number of particles are tracked to quantify the volume transport and residence time. Half of the North Pacific deep water returns to the Southern Ocean, and its principal pathway is along the western boundary current in the Southwest Pacific Basin in the deep layer. About 30 % is exported to the Indian Ocean after upwelling to the shallow layer in the western North Pacific Ocean. The rest is transported to the Arctic Ocean through the Bering Strait or evaporates within the Pacific Ocean. Upwelling of deep water is confined in the western North Pacific Ocean owing to the strong vertical mixing. The mean residence time of deep water in the North Pacific Ocean is estimated to be several hundred years, which is considerably shorter than the conventional understandings of the deep Pacific Ocean circulation.

Interface topology and evolution of particle patterns on deformable drops in turbulence

The capture of neutrally buoyant, sub-Kolmogorov particles at the interface of deformable drops in turbulent flow and the subsequent evolution of particle surface distribution are investigated. Direct numerical simulation of turbulence, phase-field modelling of the drop interface dynamics and Lagrangian particle tracking are used. Particle distribution is obtained considering excluded-volume interactions, i.e. by enforcing particle collisions. Particles are initially dispersed in the carrier flow and are driven in time towards the surface of the drops by jet-like turbulent fluid motions. Once captured by the interfacial forces, particles disperse on the surface. Excluded-volume interactions bring particles into long-term trapping regions where the average surface velocity divergence sampled by the particles is zero. These regions correlate well with portions of the interface characterized by higher-than-mean curvature, indicating that modifications of the surface tension induced by the presence of very small particles will be stronger in the highly convex regions of the interface.

On three-dimensional SPH modelling of large-scale landslides

Lagrangian particle-based smoothed particle hydrodynamics (SPH) is increasingly widely used in landslide modelling. This paper investigates four important issues not addressed by previous studies on SPH modelling of large-scale landslides, i.e., convergence property, influence of constitutive parameters, scale effect and friction reduction, and influence of different treatments of the viscous effect. The GPU-acceleration technique is employed to achieve high-resolution three-dimensional (3D) modelling. The Baige landslide is investigated by comparing numerical results with field data, and detailed analyses on the four issues are provided. Suggestions on particle resolution, constitutive parameter, and formulations of viscous discretization are also presented for future SPH modelling of large-scale landslides.

A Numerical Analysis on Coral Larval Networks across Reef Areas on the Northwest Coast of Okinawa Main Island, Japan

Coral bleaching has recently occurred extensively over the world’s oceans, primarily due to high water temperatures. Mesophotic corals that inhabit at depths of approximately 30–150 m are expected to survive during bleaching events and to reseed shallow water corals afterward. In particular, in Okinawa, Japan, mesophotic coral ecosystems (MCEs) have been reported to serve as a refuge to preserve genotypic diversities of bleaching-sensitive corals. Connectivity of larval populations between different habitats is a key element that determines the area to be conserved for desirable coral ecosystems. Coral larvae generally behave passively to the surrounding currents and are transported by the advective and dispersive effects of ambient ocean currents. Thus, numerical ocean circulation models enable us to quantify connectivity with detailed spatiotemporal network structures. Our aim in this study is to quantify the short-distance and vertical connectivity of coral larvae in reef areas on the northwest coast of Okinawa Main Island. For the reason that both short-distance and vertical larval transport are influenced by complex nearshore topography, a very high-resolution 3-D circulation model is required. Therefore, we developed a quadruple nested high-resolution synoptic ocean model at a lateral spatial resolution of 50 m, coupled with an offline 3-D Lagrangian particle-tracking model. After validation of the developed model, short-distance horizontal coral connectivity across reef areas on the northwest coast was successfully evaluated. Furthermore, a series of Lagrangian particle release experiments were conducted to identify the vertical coral migration and 3-D connectivity required for the preservation of MCEs. The model revealed that coral larvae released from the semi-enclosed areas tended to remain near the source area, whereas they were diffused and dispersed gradually with time. The mesophotic corals were dispersed vertically to the deeper zone below the mixed layer, while upward transport occurred to induce the mesophotic corals to emerge near the surface, under the influence of the surface mixed layer. The model results solidly indicated significant connectivity between MCEs and shallow coral ecosystems.

CFD modelling of the condensation, evaporation, coagulation and crystallization processes in the cooling tower emissions

The aim of the paper is to develop the CFD model for the environmental impact assessment of the cooling tower. The methods applied for this problem are the single-phase turbulent multispecies flow modelling with the DPM Lagrangian particle tracking. The simulations have been carried out in the steady state SIMPLE solver using the ANSYS Fluent software. User Defined Functions have been defined to enhance the accuracy and versatility of the modelling approach in terms of turbulence, fog formation, evaporation, coagulation and crystallization modelling. The Chalk Point cooling tower experiment, laboratory tests with freezing droplets and analytical correlations are used to verify the customized parts of the new CFD model. The arbitrary small-town geometry is used to demonstrate the simulation capabilities of the fog and drift deposition as well as the temperature and relative humidity values near ground and buildings. The results indicate that the new CFD model is able to predict the cooling tower plume parameters, icing and salt contamination risks as well as drift deposition.