Lagrangian Modeling Approach Research Articles

Lagrangian Stochastic Modeling of Stratified Atmospheric Boundary Layer

A single-column turbulence model for stratified atmospheric boundary layer (ABL), which solves the transport equations of turbulence probability density function (PDF) using a Lagrangian stochastic modeling (LSM) approach, is proposed in this study. This study adopts previously developed stochastic differential equations (SDEs) for particle velocity and temperature and extends the LSM to simulate inhomogeneous turbulence. The proposed LSM is tested for its ability to fully simulate statistics of inhomogeneous stratified turbulence. In the model, particles evolve by SDEs, and turbulence statistics are calculated by averaging the properties of particles. The model provides a full representation of turbulence PDF and simulates turbulent transport without any modeling assumption. The model performance is evaluated against large-eddy simulation (LES) results in the simulations of convective and stable ABL cases. For the convective ABL, LSM realistically simulates the entrainment process with the temperature and heat flux profiles that closely match with LES. The joint PDF simulated by LSM reproduces a curved and highly skewed shape, and some distinct features, like the asymmetric distribution of vertical velocity and the separation of the PDF in the entrainment zone, are simulated. LSM also reproduces the entrainment enhancement by wind shear in the simulation of sheared convective ABL. The LSM simulation of stable ABL predicts realistic turbulence intensity and mean field profiles, where Gaussian-like PDFs are simulated both in LSM and LES.

Vector-borne disease models with Lagrangian approach.

We develop a multi-group and multi-patch model to study the effects of population dispersal on the spatial spread of vector-borne diseases across a heterogeneous environment. The movement of host and/or vector is described by Lagrangian approach in which the origin or identity of each individual stays unchanged regardless of movement. The basic reproduction number [Formula: see text] of the model is defined and the strong connectivity of the host-vector network is succinctly characterized by the residence times matrices of hosts and vectors. Furthermore, the definition and criterion of the strong connectivity of general infectious disease networks are given and applied to establish the global stability of the disease-free equilibrium. The global dynamics of the model system are shown to be entirely determined by its basic reproduction number. We then obtain several biologically meaningful upper and lower bounds on the basic reproduction number which are independent or dependent of the residence times matrices. In particular, the heterogeneous mixing of hosts and vectors in a homogeneous environment always increases the basic reproduction number. There is a substantial difference on the upper bound of [Formula: see text] between Lagrangian and Eulerian modeling approaches. When only host movement between two patches is concerned, the subdivision of hosts (more host groups) can lead to a larger basic reproduction number. In addition, we numerically investigate the dependence of the basic reproduction number and the total number of infected hosts on the residence times matrix of hosts, and compare the impact of different vector control strategies on disease transmission.

Characterization and mechanism of cutter parameters in tubing milling

Downhole string milling is becoming increasingly difficult due to the increasing complexity of oilfield development technology and material quality advances, especially for downhole tubing milling. In this paper, a Lagrangian modeling approach is used to investigate the mechanism and effects of cutting parameters on tubing milling characteristics. The cemented carbide cutter parameters, including the cutting angle, lateral angle, weight on cutter, and rotating speed, are determined to obtain the maximum cutting rate. A cutting tool is designed, manufactured, and tested. The simulation results are in good agreement with the test results, yielding the maximum equivalent stress generated by the cutter of 1163 MPa, which is much higher compared to the tubing yield strength. The tubing cutting volume and mass increased with the cutting angle, up to 12.5°, while the maximum value obtained using the lateral angle is 5°. With an increase in weight on cutter, the maximum von Mises equivalent stress and equivalent strain generated by the cutter also increased. Furthermore, the cutting volume and mass increase rapidly with the rotational speed at the start, followed by a slow increase when the rotational speed is above 70 rpm. The cutter mainly generated continuous chips. Finally, industrial tests are successfully carried out, confirming the milling efficiency increase of 40.1% compared to the traditional milling methods.

Unsteady Friction Modeling Technique for Lagrangian Approaches in Transient Simulations

This study investigates the simulation of celerity attenuation and head damping in transient flows using a Lagrangian approach rather than an Eulerian approach. Typically, the Lagrangian approach requires orders of magnitude fewer calculations, resulting in the rapid solution of very large systems. Additionally, it is based on a simple physical model. As the method is continuous in both time and space, it is less sensitive to the structure of the network and the length of the simulation process. Most recent studies, however, have focused on the development and improvement of computational routines for modeling in an Eulerian environment. This results in the development of adequate models that are suitable for Eulerian models but not applicable in Lagrangian-based models. As a result of this fixation, a bias was created towards using Eulerian approaches in transient simulations. It also diverts resources from further development of Lagrangian models. Consequently, it is necessary to develop a friction model that is more accurate and compatible with Lagrangian methods without compromising their performance. To the authors’ knowledge, such a model is yet to be published in the literature. This study presents a new friction modeling technique that compensates for both the local and convective acceleration terms for the Lagrangian transient modeling approach without compromising the computational time.

Experimentally validated numerical models to assess tsunami hydrodynamic force on an elevated structure

Recently, the North American and Japanese authorities began combining the tsunami forces with other loads in their structural design guidelines. Nonetheless, due to the infrequent nature of tsunamis, the provisions may benefit from complementary insights on the qualitative and quantitative characterization of the extreme phenomena and their interaction with coastal structures. The goal of this paper is to explore reliable and relatively accessible computational techniques to determine pressures and forces due to tsunami-like waves on elevated structures. Hydrodynamic flow quantities are simulated for the tsunami-like waves using an Eulerian scheme (Shallow Water equations solved by the Finite Volume method), a Lagrangian scheme (Navier–Stokes equations solved by the Smoothed Particle Hydrodynamics method), and a coupled Eulerian Lagrangian modeling approach. The numerical solutions are validated against experimental data acquired from an experimental campaign performed at the large wave flume of the Hinsdale Wave Research Laboratory, Oregon State University. The correlations between the experimental data and the numerical solutions highlight the advantages and disadvantages of the simulation techniques used, contributing to increase the confidence levels in their use in determining tsunami forces for use in structural assessments and design.

A Lagrangian study of the contribution of the Canary coastal upwelling to the nitrogen budget of the open North Atlantic

Abstract. The Canary Current System (CanCS) is a major eastern boundary upwelling system (EBUS), known for its high nearshore productivity and for sustaining a large fishery. It is also an important but not well quantified source of nitrogen to the adjacent oligotrophic subtropical gyre of the North Atlantic. Here, we use a Lagrangian modeling approach to quantify this offshore transport and investigate its timescales, reach and contribution to the fueling of productivity in the offshore regions. In our Lagrangian model, we release nearly 10 million particles off the northwestern African coast and then track all those that enter the nearshore region and upwell along the coast between 14 and 35∘ N. We then follow them as they are transported offshore, also tracking the biogeochemical transformations, permitting us to construct biogeochemical budgets along the offshore moving particles. The three-dimensional velocity field as well as the biogeochemical tracers and fluxes are taken from an eddy-resolving configuration of the Regional Ocean Modeling System (ROMS). Our Lagrangian model analysis reveals a very intense offshore transport of nitrogen, with about 20 %–40 % in the form of organic nitrogen. The transport varies greatly along the coast. Even though the central CanCS (21–28∘ N) transports the largest amount of water offshore, its offshore transport of nitrogen is somewhat smaller than that in the southern CanCS (14–21∘ N), primarily because of the higher nitrogen content of the upwelling waters there. Around one-third of the total offshore transport of water occurs around major capes along the CanCS. The persistent filaments associated with these capes are responsible for an up to 4-fold enhancement of the offshore transport of water and nitrogen in the first 400 km. Much of this water and nitrogen stems from upwelling at quite some distance from the capes, confirming the capes' role in collecting water from along the coast. North of Cape Blanc and within the first 500 km from the coast, water recirculation is a dominant feature of offshore transport. This process, likely associated with mesoscale eddies, tends to reduce the efficiency of offshore transport. The Canary upwelling is modeled to supply around 44 and 7 mmol N m−2 yr−1 to the North Atlantic Tropical Gyral (NATR) and the North Atlantic Subtropical Gyral East (NASE) Longhurst provinces, respectively. In the NATR, this represents nearly half (53 ± 26 %) of the estimated total new production, while in the NASE, this fraction is small (4 ± 2 %). Our results highlight the importance of the CanCS upwelling as a key source of nitrogen to the open North Atlantic and stress the need for improving the representation of EBUS in global coarse-resolution models.

Experimental and numerical studies of seismic fluid‐structure interaction in a base‐supported cylindrical vessel

AbstractSeismic design and qualification of advanced reactors will rely heavily on the use of verified and validated numerical models capable of capturing the interaction of the vessel, its contained fluid, and the internal equipment: fluid‐structure interaction (FSI) analysis. Analytical solutions can be used for preliminary sizing and design of such vessels but their application is limited to simple geometries and boundary conditions, and small amplitude, translational (and rotational) inputs. To validate numerical models for seismic FSI analysis in finite element codes, a comprehensive set of experiments was performed on a liquid‐filled cylindrical vessel, using a 6 degree‐of‐freedom earthquake simulator. Results in terms of sloshing frequency, damping ratio in sloshing modes, and hydrodynamic responses (wave height, hydrodynamic pressure, base shear, and base moment) for multidirectional earthquake simulator inputs are reported and compared with analytical solutions for liquid‐filled vessels. The impact of seismic (base) isolation on hydrodynamic responses was studied using earthquake simulator inputs generated using a virtual isolation system. Data from the experiments are used to validate a numerical model of the fluid‐filled vessel using the Arbitrary Lagrangian Eulerian (ALE) solver in the commercial finite element program LS‐DYNA. Validation studies are presented for multidirectional seismic inputs, including rocking motions. Lagrangian modeling approaches using an elastic material formulation for the fluid are also investigated and their limitations and possible applications are identified. The results are broadly applicable to the seismic response of base supported, liquid‐filled vessels.

Assessment and Validation of Internal Aerodynamics and Mixture Preparation in Spark-Ignition Engine Using LES Approach

<div class="section abstract"><div class="htmlview paragraph">A workflow for the assessment and validation of internal aerodynamics and mixture preparation in a representative high-tumble optical engine using Large Eddy Simulation with the commercial code CONVERGE<sup>TM</sup> is proposed. First, the prediction of the aerodynamic movement in the engine is compared to Particle Image Velocimetry (PIV) measurements. The global velocity fields and position of the center of the tumble for the average experimental and simulation cycles are compared, showing a very good match of the global behavior. The cycle to cycle aerodynamic variability is investigated thanks to velocity profiles, showing that the simulated cycles feature comparable velocity fluctuations to the experiments. In a second part, to account for Direct Injection (DI), a Lagrangian spray modeling approach is used to take into account the injection process. Experimental spray penetration data are used for the calibration of the spray models, leading to a faithful representation of the spray. Mixture preparation in the engine is then assessed, comparing the fuel air equivalence ratio of the LES in the central plane to LIF diagnostics. This qualitative comparison shows a good prediction of the evolution of the position of the fuel-rich areas and overall mixing during the compression stroke. The cycle to cycle variability of the mixing process is found comparable to the experiments, though underestimated. An evaluation of this methodology is given and the next steps towards combustion computations are discussed.</div></div>

Towards a Better Representation of Fog Microphysics in Large-Eddy Simulations Based on an Embedded Lagrangian Cloud Model

The development of radiation fog is influenced by multiple physical processes such as radiative cooling and heating, turbulent mixing, and microphysics, which interact on different spatial and temporal scales with one another. Once a fog layer has formed, the number of fog droplets and their size distribution have a particularly large impact on the development of the fog layer due to their feedback on gravitational settling and radiative cooling at the fog top, which are key processes for fog. However, most models do not represent microphysical processes explicitly, or parameterize them rather crudely. In this study we simulate a deep radiation fog case with a coupled large-eddy simulation (LES)–Lagrangian cloud model (LCM) approach for the first time. By simulating several hundred million fog droplets as Lagrangian particles explicitly (using the so-called superdroplet approach), we include a size-resolved diffusional growth including Köhler theory and gravitational sedimentation representation. The results are compared against simulations using a state of the art bulk microphysics model (BCM). We simulate two different aerosol backgrounds (pristine and polluted) with each microphysics scheme. The simulations show that both schemes generally capture the key features of the deep fog event, but also that there are significant differences: the drop size distribution produced by the LCM is broader during the formation and dissipation phase than in the BCM. The LCM simulations suggest that its spectral shape, which is fixed in BCMs, exhibits distinct changes during the fog life cycle, which cannot be taken into account in BCMs. The picture of the overall fog droplet number concentration is twofold: For both aerosol environments, the LCM shows lower concentrations of larger fog droplets, while we observe a higher number of small droplets and swollen aerosols reducing the visibility earlier than in the BCM. As a result of the different model formulation we observe higher sedimentation rates and lower liquid water paths for the LCM. The present work demonstrates that it is possible to simulate fog with the computational demanding approach of LCMs to assess the advantages of high-resolution cloud models and further to estimate errors of traditional parameterizations.

Turbulence Adjustment and Scaling in an Offshore Convective Internal Boundary Layer: A CASPER Case Study

AbstractThe characteristics of a convective internal boundary layer (CIBL) documented offshore during the East Coast phase of the Coupled Air–Sea Processes and Electromagnetic Ducting Research (CASPER-EAST) field campaign has been examined using field observations, a coupled mesoscale model (i.e., Navy’s COAMPS) simulation, and a couple of surface-layer-resolving large-eddy simulations (LESs). The Lagrangian modeling approach has been adopted with the LES domain being advected from a cool and rough land surface to a warmer and smoother sea surface by the mean offshore winds in the CIBL. The surface fluxes from the LES control run are in reasonable agreement with field observations, and the general CIBL characteristics are consistent with previous studies. According to the LESs, in the nearshore adjustment zone (i.e., fetch < 8 km), the low-level winds and surface friction velocity increase rapidly, and the mean wind profile and vertical velocity skewness in the surface layer deviate substantially from the Monin–Obukhov similarity theory (MOST) scaling. Farther offshore, the nondimensional vertical wind shear and scalar gradients and higher-order moments are consistent with the MOST scaling. An elevated turbulent layer is present immediately below the CIBL top, associated with the vertical wind shear across the CIBL top inversion. Episodic shear instability events occur with a time scale between 10 and 30 min, leading to the formation of elevated maxima in turbulence kinetic energy and momentum fluxes. During these events, the turbulence kinetic energy production exceeds the dissipation, suggesting that the CIBL remains in nonequilibrium.

Numerical investigation of nanofluid particle migration and convective heat transfer in microchannels using an Eulerian–Lagrangian approach

An Eulerian–Lagrangian modelling approach was employed in order to investigate the flow field, heat transfer and particle distribution in nanofluid flow in a parallel-plate microchannel, with a focus on relatively low Reynolds numbers ($Re\leqslant 100$). Momentum and thermal interactions between fluid and particle phases were accounted for using a transient two-way coupling algorithm implemented within an in-house code that tracked the simultaneous evolution of the carrier and particulate phases while considering timescale differences between the two phases. The inaccuracy of assuming a homogeneous particle distribution in modelling nanofluid flow in microchannels was established. In particular, shear rate and thermophoresis were found to play a key role in the lateral migration of nanoparticles and in the formation of particle depletion and accumulation regions in the vicinity of the channel walls. At low Reynolds numbers, nanoparticle distribution near the walls was observed to gradually flatten in the streamwise direction. On the other hand, for relatively higher Reynolds numbers, higher particle non-uniformities were observed in the vicinity of the channel walls. Furthermore, it was established that convective heat transfer between channel walls and the bulk fluid can either improve or deteriorate with the addition of nanoparticles, depending on whether the flow exceeded a critical Reynolds number of enhancement. It was also established that Brownian motion and thermophoresis had a major role in nanoparticle deposition on the channel walls. In particular, Brownian motion was the main deposition mechanism for nano-sized particles, whereas due to thermophoresis, nanoparticles were repelled away from channel walls. The result of the competition between the two is that deposition gradually increased along the streamwise direction.

Transport of floating marine litter in the coastal area of the south-eastern Bay of Biscay: A Lagrangian approach using modelling and observations

ABSTRACTMarine litter is identified as the major ocean pollution today, with a significant impact on the environment. The transport of litter by ocean circulation is still poorly understood, and the management of marine litter remains a major challenge for local authorities. This work investigates the transport of floating marine litter (FML) in the coastal area of the south-eastern Bay of Biscay. It provides a first assessment of the use of operational ocean observations and models for the support of FML management in this region. The study is based on a Lagrangian modelling approach, using ocean surface velocity forcing by (i) measurements with High-Frequency Radars and (ii) predictions from the IBI Copernicus model. The IBI model is first assessed in a Lagrangian perspective using different observations of surface ocean currents and transport. Then, analyzing a multiyear hindcast of the Lagrangian model, high retention is shown in the southeast during spring and summer. Northward dispersion is obtained along the French coast during autumn and winter. In winter, large river inflows are not compensated by the inner shelf transport, resulting in the highest material densities along the coast. The results also suggest that the Iberian Poleward Current may act as a cross-shore transport barrier in the area.

Control of a Two-wheeled Machine with Two-directions Handling Mechanism Using PID and PD-FLC Algorithms

This paper presents a novel five degrees of freedom (DOF) two-wheeled robotic machine (TWRM) that delivers solutions for both industrial and service robotic applications by enlarging the vehicle’s workspace and increasing its flexibility. Designing a two-wheeled robot with five degrees of freedom creates a high challenge for the control, therefore the modelling and design of such robot should be precise with a uniform distribution of mass over the robot and the actuators. By employing the Lagrangian modelling approach, the TWRM’s mathematical model is derived and simulated in Matlab/Simulink®. For stabilizing the system’s highly nonlinear model, two control approaches were developed and implemented: proportional-integral-derivative (PID) and fuzzy logic control (FLC) strategies. Considering multiple scenarios with different initial conditions, the proposed control strategies’ performance has been assessed.

Simulation of underwater explosions in close-proximity to a submerged cylinder and a free-surface or rigid boundary

The response of a submerged structure to an underwater explosion (UNDEX) depends on highly nonlinear interactions between the structure, nearby boundaries, the shock wave and the bubble of gaseous explosion products. These complex interactions may significantly influence the loads imparted to a submerged structure by an underwater explosion. This research presents the experimental validation of a coupled Eulerian–Lagrangian numerical modelling approach for simulating the interaction between an underwater explosion, a submerged cylinder, and a free surface or rigid bottom. The three-dimensional simulations in account concurrently for shock wave propagation, cavitation, and gas bubble migration and jetting. The validated simulation methodology is employed to demonstrate how the presence of a submerged cylinder influences bubble migration and its period of oscillation in the vicinity of a boundary.

A Lagrangian approach towards extracting signals of urban CO<sub>2</sub> emissions from satellite observations of atmospheric column CO<sub>2</sub> (XCO<sub>2</sub>): X-Stochastic Time-Inverted Lagrangian Transport model (“X-STILT v1”)

Abstract. Urban regions are responsible for emitting significant amounts of fossil fuel carbon dioxide (FFCO2), and emissions at the finer, city scales are more uncertain than those aggregated at the global scale. Carbon-observing satellites may provide independent top-down emission evaluations and compensate for the sparseness of surface CO2 observing networks in urban areas. Although some previous studies have attempted to derive urban CO2 signals from satellite column-averaged CO2 data (XCO2) using simple statistical measures, less work has been carried out to link upwind emission sources to downwind atmospheric columns using atmospheric models. In addition to Eulerian atmospheric models that have been customized for emission estimates over specific cities, the Lagrangian modeling approach – in particular, the Lagrangian particle dispersion model (LPDM) approach – has the potential to efficiently determine the sensitivity of downwind concentration changes to upwind sources. However, when applying LPDMs to interpret satellite XCO2, several issues have yet to be addressed, including quantifying uncertainties in urban XCO2 signals due to receptor configurations and errors in atmospheric transport and background XCO2. In this study, we present a modified version of the Stochastic Time-Inverted Lagrangian Transport (STILT) model, “X-STILT”, for extracting urban XCO2 signals from NASA's Orbiting Carbon Observatory 2 (OCO-2) XCO2 data. X-STILT incorporates satellite profiles and provides comprehensive uncertainty estimates of urban XCO2 enhancements on a per sounding basis. Several methods to initialize receptor/particle setups and determine background XCO2 are presented and discussed via sensitivity analyses and comparisons. To illustrate X-STILT's utilities and applications, we examined five OCO-2 overpasses over Riyadh, Saudi Arabia, during a 2-year time period and performed a simple scaling factor-based inverse analysis. As a result, the model is able to reproduce most observed XCO2 enhancements. Error estimates show that the 68 % confidence limit of XCO2 uncertainties due to transport (horizontal wind plus vertical mixing) and emission uncertainties contribute to ∼33 % and ∼20 % of the mean latitudinally integrated urban signals, respectively, over the five overpasses, using meteorological fields from the Global Data Assimilation System (GDAS). In addition, a sizeable mean difference of −0.55 ppm in background derived from a previous study employing simple statistics (regional daily median) leads to a ∼39 % higher mean observed urban signal and a larger posterior scaling factor. Based on our signal estimates and associated error impacts, we foresee X-STILT serving as a tool for interpreting column measurements, estimating urban enhancement signals, and carrying out inverse modeling to improve quantification of urban emissions.

Understanding the Impact of Environmental Variability on Anchovy Overwintering Migration in the Black Sea and its Implications for the Fishing Industry

Black Sea anchovy (Engraulis encrasicolus) undertake extensive overwintering migrations every fall from nursery grounds to warmer overwintering areas located on the south-eastern coast of the Black Sea. During migration and particularly upon arrival at the Anatolian coast, they support an important fishery and valuable source of income for regional communities. Black Sea anchovy have undergone significant stock fluctuations partly related to climatic conditions; for example, migrating anchovy schools arrived late or failed to arrive at the Anatolian coast when fall temperatures increased. This study invokes a Lagrangian modeling approach applied to satellite derived circulation and temperature data as a first attempt to model anchovy migration dynamics in the Black Sea. This modeling approach takes the influence of the physical environment into account, while the quality of overwintering grounds, schooling and homing behavior is neglected. The model is used to investigate the possible influence of interannual and seasonal variability of temperature and surface currents, as well as the influence of migration behavior on the success of anchovy overwintering migration for both the Black Sea and Azov Sea anchovy. The results of the present work show the possibility that overwintering anchovy fished along the southeastern Anatolian coast may not exclusively originate from the northwestern shelf, but mainly from the eastern Black Sea basin. Migration pathways are identified for both Black Sea and Azov Sea anchovy, which are of importance for the national fisheries efforts of riparian countries. Modeling results are in agreement with general patterns of anchovy migration given in the literature indicating that the physical environment may be a major factor in shaping general migration patterns. Simulation results are used to hypothesize about alternatives to previously determined migration routes and provide potential reasons that explain the inability of the Bulgarian anchovy fishery to recover. Results show that the intensity and timing of autumnal cooling, coupled with current strength, can be of significant importance in determining annual and seasonal variability of migration success. Considering the need for fisheries management to account for the variability in fishable overwintering anchovy stocks a modeling approach as developed in the current study may provide such tool.

Experimental and numerical investigation on the dynamic response of sandwich composite panels under hydrodynamic slamming loads

Sandwich structures have been widely used in marine applications due to their properties such as high weight/strength ratio. In contrast, the failure mechanism of these structures has a significant effect on the local and global dynamic responses. In the present study, sandwich panels with polymeric skins and PVC foam cores subjected to slamming impact are investigated experimentally and numerically. A high speed shock machine is used to keep approximately a constant velocity during the impact event. The dynamic resistance was analysed in terms of hydrodynamic loads, dynamic deformation and failure mechanisms for different impact velocities. On the other hand, the slamming model was implemented in Abaqus/Explicit software based on Coupled Eulerian Lagrangian model approach. In addition, different damage modes are incorporated in the numerical model, including the intralaminar, debonding in skin/core interface, and core shear to cover all possible damage modes throughout structures. Two failure criteria (Hashin criteria for the laminate composite and Christensen criteria for the core in sandwich structure) are defined and integrated into VUMAT sub-routine. In addition, the cohesive zone model is used to predict the debonding skin/core. A good agreement in both hydrodynamic loads and damage prediction were found between numerical and experimental results.

A Quantitative Management Tool Reflecting Impact of Nutrient Enrichment from Mariculture in the Levantine Basin

Mariculture production increased significantly in recent years due to global rise in human population. However, in addition to providing food, fish farms are also a source of nutrients and antibiotics to the water column. Here, we research the nutrient pollution originating from fish cages in the Eastern Mediterranean by utilizing a Lagrangian modeling approach that followed trajectories of the water parcels. The effects of farm size and the farm’s distance from the shoreline were included in the model, and biological uptake and sinking of nutrients were incorporated into the analysis. By using computations of back-trajectories examining the water origin of strategically important shoreline areas, such as desalination plants, we were able to identify which of the proposed farm locations were potentially harmful. The results suggest that remotely-located, smaller and spatially distant farms are more preferable to limit the nutrient and antibiotic effluent resulting from mariculture activity.

Manipulating colloidal residue deposit from drying droplets: Air/liquid interface capture competes with coffee-ring effect

Significant efforts have been undertaken in recent years to understand, and ultimately control, the drying patterns of colloidal particle filled droplets on solid substrates. The ubiquitous coffee-ring effect has long been attributed to the drag of radial liquid flow towards the droplet edge, driven by diffusive evaporation. Here we report new results showing that there is a temporal competition between migrating colloidal particles, dispersed randomly inside a droplet, and the air/liquid interface in reaching the solid surface. Using the Lagrangian modelling approach to track the motion of colloidal particles within the evaporating droplets, we reveal a boundary line that separates colloidal particles into two groups: above it colloids are captured by the air/liquid interface prior to reaching the solid surface and vice versa. This critical line allows us to quantify the effectiveness of the two emerging routes for manipulating the coffee-ring effect, which work by controlling the interaction between colloids and either the substrate or the air-liquid interface. Our modelling results affirm recent experimental evidence that the air-liquid interface of sessile droplets plays a vital role in the formation of residual deposits. This improved fundamental understanding provides versatile strategies to control droplet deposition morphology, especially the most desired uniform deposit as well as an unusual “overhang” shape of the cross section of the ring-like deposits.

Bacterial foraging-optimized PID control of a two-wheeled machine with a two-directional handling mechanism

This paper presents the performance of utilizing a bacterial foraging optimization algorithm on a PID control scheme for controlling a five DOF two-wheeled robotic machine with two-directional handling mechanism. The system under investigation provides solutions for industrial robotic applications that require a limited-space working environment. The system nonlinear mathematical model, derived using Lagrangian modeling approach, is simulated in MATLAB/Simulink® environment. Bacterial foraging-optimized PID control with decoupled nature is designed and implemented. Various working scenarios with multiple initial conditions are used to test the robustness and the system performance. Simulation results revealed the effectiveness of the bacterial foraging-optimized PID control method in improving the system performance compared to the PID control scheme.