Mesh Blocks Research Articles

An Approach for Measuring Spatial Accessibility to Services/Facilities by Urban Community Aged Population

Abstract. Population aging is a global trend and a world-wide challenge to many governments. The high-quality life of the elderly cannot be separated from the support of basic services and facilities. Therefore, it is necessary to conduct analysis and research on the accessibility of urban community services and facilities. It is worth noting that the research in this article is based on master thesis (Bai, 2013). Drawing on the data, methods, and conclusions from the master's thesis, in this paper, an approach is designed for measuring spatial accessibility to services/facilities by a spatially dispersed ageing population in urban areas. The local government area (LGA) of Monash in the Melbourne metropolitan area has been selected the case study area. This study combines GIS-based spatial analytical procedures and two-step floating catchment area (2SFCA) method, in conjunction with mesh block level 2011 population data, service/facility data and transportation network data, to measure and map spatial variations in potential accessibility to services and facilities deemed essential to the aged population. Service facilities considered in the study include bus stops, train stations, bank facilities, shopping centres, post offices, churches, parks, public libraries, community centres, pharmacies, GP clinics and hospitals in Monash LGA. The research results can be used to optimize the spatial planning and layout of public facilities for ageing population.

Co-evolution of public transport access and ridership

While transport infrastructure and travel demand are known to be correlated, their causal relationship has not been systematically investigated. Granger causality tests have been conducted in the context of transport infrastructure and economic growth, and land use and transport. This research extends their application to network investments and travel demand by examining the co-evolution of public transport access and ridership in the Greater Sydney region for a period spanning over a century, from 1855 onward. We hypothesise a mutual feedback between public transport ridership and access, and corroborate the hypothesis in all causal models estimated – between aggregate public transport ridership and access, station ridership and access, and mesh block public transport shares and access. The causality was more evident in disaggregate models and was stronger between ridership and access to jobs than with access to population when employment data were available. Ours is the first longitudinal investigation into the causal relationship between public transport access and ridership. The findings strengthen the case for using access as a planning measure and lay the groundwork for evolutionary strategic transport modelling.

Statistical modelling under differential privacy constraints: a case study in fine-scale geographical analysis with Australian Bureau of Statistics TableBuilder data

ABSTRACT Consistent with the principles of differential privacy protection, the Australian Bureau of Statistics artificially perturbs all count data from the Australian Census prior to its release to researchers through the TableBuilder platform. This perturbation involves the addition of random noise to every non-zero cell count followed by the suppression of small values to zero. A consequent problem encountered by researchers working with geographical TableBuilder outputs is that the aggregate sums of cell counts over fine-scale units are often much lower than the direct query totals of their coarser enclosing units. Hierarchical Bayesian modelling is here proposed as a powerful methodology for achieving consistent multi-scale statistical reconstructions suitable for downstream spatial modelling. The utility of this framework is demonstrated for the toy problem of reconstructing Multiple Family Household counts by Mesh Block in the Perth Greater Capital City area.

Arbitrary-Lagrangian-Eulerian finite volume IMEX schemes for the incompressible Navier-Stokes equations on evolving Chimera meshes

In this article we design a finite volume semi-implicit IMEX scheme for the incompressible Navier-Stokes equations on evolving Chimera meshes. We employ a time discretization technique that separates explicit and implicit terms, accommodating the multi-scale nature of the governing equations, which involve both time scales of diffusion and advection operators. The finite volume approach for both explicit and implicit terms allows to encode into the nonlinear flux the velocity of displacement of the Chimera mesh via integration on moving cells. The numerical solution is then projected onto the physically meaningful solution manifold of non-solenoidal fields that stems from the energy equation. To attain second-order time accuracy, we employ semi-implicit IMEX Runge-Kutta schemes. These novel schemes are combined with a fractional-step method, thus the governing equations are eventually solved using a projection method to satisfy the divergence-free constraint of the velocity field. The implicit discretization of the viscous terms allows the CFL-type stability condition for the maximum admissible time step to be only defined by the relative fluid velocity referred to the movement of the frame and not depending on the viscous terms. Communication between different grid blocks is enabled through compact exchange of information from the fringe cells of one mesh block to the field cells of the other block. The continuity of the solution is recovered in one-shot during the solution of the arising algebraic systems by not involving neither direct discretization of the differential operators on fringe cells nor an iterative Schwartz-type method. Free-stream preservation property, i.e. compliance with the Geometric Conservation Law (GCL), is respected at the order of the scheme. The accuracy and capabilities of the new numerical schemes are proved through an extensive range of test cases, demonstrating ability to solve relevant benchmarks in the field of incompressible fluids.

Comparative GIS Analysis of Public Transport Accessibility in Metropolitan Areas

With urban areas facing rapid population growth, public transport plays a key role to provide efficient and economic accessibility to the residents. It reduces the use of personal vehicles leading to reduced traffic congestion on roads and reduced pollution. To assess the performance of these transport systems, prior studies have taken into consideration the blank spot areas, population density, and stop access density; however, very little research has been performed to compare the accessibility between cities using a GIS-based approach. This paper compares the access and performance of public transport across Melbourne and Sydney, two cities with a similar size, population, and economy. The methodology uses spatial PostGIS queries to focus on accessibility-based approach for each residential mesh block and aggregates the blank spots, and the number of services offered by time of day and the frequency of services at the local government area (LGA) level. The results of the study reveal an interesting trend: that with increase in distance of LGA from city centre, the blank spot percentage increases while the frequency of services and stops offering weekend/night services declines. The results conclude that while Sydney exhibits a lower percentage of blank spots and has better coverage, performance in terms of accessibility by service time and frequency is better for Melbourne’s LGAs, even as the distance increases from the city centre.

Multiresolution approximation for shallow water equations using summation-by-parts finite differences

Abstract We present spatial approximation for shallow water equations on a mesh of multiple rectangular blocks with different resolution in Cartesian geometry. The approximation is based on finite-difference operators that fulfill Summation By Parts (SBP) property – a discrete analogue of integration by parts. The solution continuity conditions between mesh blocks are imposed in a weak form using Simultaneous Approximation Terms (SAT) method.We show that the resulting discrete divergence and gradient operators are anti-conjugate. The important consequences are the discrete analogues for mass and energy conservation laws along with the proof of stability for linearized equations. The numerical shallow water equations model based on the presented spatial approximation is tested using problems with meteorological context. Test results prove high-order accuracy of SBP-SAT discretization. The interfaces between mesh blocks of different resolution produce no significant noise. The local mesh refinement is shown to have positive effect on the solution both locally inside the refined region and globally in the dynamically coupled areas.

Integrating a non-gridded space representation into a graph neural networks model for citywide short-term crash risk prediction

Current applications of Graph Neural Networks in citywide short-term crash risk prediction have been limited by a gridded representation of space, which restricts the network’s capability to effectively capture the spatial and temporal dependency of crash occurrences. In addition, a grided representation does not match most geographic units used for administrative purposes, limiting the use of crash risk predictions by practitioners. This paper applies a gated localised diffusion graph neural network (GLDNet) model to compare the use of two alternative geographic units, Mesh Block (MB) and grid, to forecast locations where crashes are likely to occur in a future time window. The GLDNet relies on a graph-based representation of geographic units and a weighted loss function to address the sparsity of crash occurrences. The tests are performed using crash data from the City of Melbourne, Australia, over a period of one year. The predictions are made at six-hour intervals, and the results show that the GLDNet consistently outperforms baseline methods, with differences in prediction accuracy from 10% to 21% in relation to historical average and benchmark deep learning models. In terms of geographic units, the MB-based GLDNet performed better than its grid counterpart, with differences in prediction accuracy of up to 12.3%. The better performance stems from the underlying information attached to the MB units (i.e., land use) and the network properties (i.e., degree of centrality), which enhance the GLDNet capability to identify crash risk in both central and peripherical areas. Regarding its applicability, the MB-based GLDNet directly integrates with other data sources, which provides contextual information about crash hotspots that helps decision-makers develop police patrolling and rescuing strategies.

Australia’s Black Summer wildfires recovery: A difference-in-differences analysis using nightlights

This study examines how communities of New South Wales (NSW), Australia, recovered from the extreme wildfire event of 2019–2020 (i.e., the Black Summer fires). Using monthly night-time radiance as an indicator of economic activity in a geographic area (i.e., a mesh block) from January 2017 to June 2021, I conducted a spatio-temporal and socio-economic analysis of economic recovery after the 2019–2020 wildfires using the difference-in-differences method. This is the first study to examine the intersectional role of space with time and socio-economic characteristics for extreme wildfire recovery. The findings reveal that wildfire-affected locations had about 0.038σ and 0.026σ lower night-time radiance in major cities and rural hinterlands (i.e., inner regions), respectively, than the unaffected areas. These numbers translate to approximately 30% reduction in economic activities in both areas. The findings remain consistent when using Facebook’s movement range data. The pace of recovery varied spatially across time and socio-economic groups. In rural hinterlands of NSW, wildfire-affected communities, both poor and non-poor, followed a slower recovery trajectory than wildfire-affected city dwellers. In major cities, the economic recovery of poor communities lagged behind non-poor communities. Accounting for such spatial, temporal and socio-economic heterogeneity in the natural hazard recovery process can support the design of equitable wildfire risk reduction and management strategies and programs. If unaddressed, gaps in wildfire recovery can increase location and economic group specific vulnerabilities to future wildfires. Note that nightlights are not a good proxy for economic activity in heavily forested remote and rural areas; thus limiting the application of the use of high frequency satellite data for wildfire recovery analysis only in major cities and rural hinterlands.

Contact Tracing With District-Based Trajectories

Identifying the places an infected person has visited during a virus incubation time in order to conduct contact tracing is currently done using manual interviews since proximity-based contact tracing methods do not store geolocation information due to privacy concerns. During the incubation time, an infected person might visit several locations and either forget where they went or are reluctant to disclose their trip details. To minimize manual location tracing while preserving the user's privacy, the authors propose a mesh block sequence method where the trajectories are transformed into a mesh block sequence before being shared with health authorities. These simulations show that this a useful method by which to protect user privacy by concealing specific details related to a trajectory. While this simulation uses an Australian administrative region structure, this method is applicable in countries which implement similar administrative hierarchical building blocks.

An efficient tree-topological local mesh refinement on Cartesian grids for multiple moving objects in incompressible flow

This paper develops a tree-topological local mesh refinement (TLMR) method on Cartesian grids for the simulation of bio-inspired flow with multiple moving objects. The TLMR nests refinement mesh blocks of structured grids to the target regions and arrange the blocks in a tree topology. The method solves the time-dependent incompressible flow using a fractional-step method and discretizes the Navier-Stokes equation using a finite-difference formulation with an immersed boundary method to resolve the complex boundaries. When iteratively solving the discretized equations across the coarse and fine TLMR blocks, for better accuracy and faster convergence, the momentum equation is solved on all blocks simultaneously, while the Poisson equation is solved recursively from the coarsest block to the finest ones. When the refined blocks of the same block are connected, the parallel Schwarz method is used to iteratively solve both the momentum and Poisson equations. Convergence studies show that the algorithm is second-order accurate in space for both velocity and pressure, and the developed mesh refinement technique is benchmarked and demonstrated by several canonical flow problems. The TLMR enables a fast solution to an incompressible flow problem with complex boundaries or multiple moving objects. Various bio-inspired flows of multiple moving objects show that the solver can save over 80% computational time, proportional to the grid reduction when refinement is applied.

Application of an overset grid method for the performance analysis of flapping airfoils

With the growing importance of renewable energy, the interest in energy-harvesting technologies based on flow-induced vibrations of airfoils has been rekindled in the past few years. Compared to conventional turbines, these devices are centrifugal stress-free and hence they are structurally more robust. They are also environmentally friendly due to the relatively low speeds, thus reducing the impact on flying animals. In order to numerically investigate these types of devices, mesh motion techniques must be used so that the computational grid can adapt to the time-varying shape of the domain and boundaries, thus preserving its robustness and quality. During the last years, many different dynamic mesh approaches have been developed to better predict the behaviour of a flow interacting with solid moving bodies. The aim of the present work is to apply and validate the overset grid method offered by the OpenFOAM software. In this type of mesh, one or more grid blocks are allowed to overlap with other sets of cells to solve the fluid domain with moving bodies, thus showing many potential advantages compared to the other existing dynamic mesh approaches. In the first part of this work, a numerical investigation of the flow over a stationary SD 7003 airfoil at low Reynolds number has been performed using an unsteady RANS approach. The computed results have then been compared to experimental and high-fidelity computational data available from the literature in order to validate the presented model in terms of numerical domain configuration, mesh refinement, and turbulence modelling. Subsequently, unsteady RANS simulations have been performed on the SD 7003 and NACA 0012 airfoils for two different amplitudes of flapping motion, i.e., 30° and 45°. Finally, the results obtained with the OpenFOAM overset grid solver have been compared with the numerical and experimental benchmarks presented by Kurtulus, showing an excellent agreement with both computed and measured data.

Computational analysis of vortex dynamics and aerodynamic performance in flying-snake-like gliding flight with horizontal undulation

This paper numerically studies the flow dynamics of aerial undulation of a snake-like model, which is adapted from the kinematics of the flying snake (Chrysopelea) undergoing a gliding process. The model applies aerial undulation periodically in a horizontal plane where a range of angle of attack (AOA) is assigned to model the real gliding motion. The flow is simulated using an immersed-boundary-method-based incompressible flow solver. Local mesh refinement mesh blocks are implemented to ensure the grid resolutions around the moving body. Results show that the undulating body produces the maximum lift at 45° of AOA. Vortex dynamics analysis has revealed a series of vortex structures including leading-edge vortices (LEV), trailing-edge vortices, and tip vortices around the body. Changes in other key parameters including the undulation frequency and Reynolds number are also found to affect the aerodynamics of the studied snake-like model, where increasing of undulation frequency enhances vortex steadiness and increasing of Reynolds number enhances lift production due to the strengthened LEVs. This study represents the first study of both the aerodynamics of the whole body of the snake as well as its undulatory motion, providing a new basis for investigating the mechanics of elongated flexible flyers.

Study on the static and dynamic performance of active bump-metal mesh foil bearings

The gas foil bearing (GFB) is an important component of high-speed, oil-free micro turbomachinery. However, the instability of GFBs under certain conditions hinders their widespread application. The traditional solution is to decrease the continuity of the gas film and increases the structural damping of GFBs through ‘passive’ structural improvements. Thus, the performances of improved bearings cannot be actively adjusted. This paper proposes an active bump-metal mesh foil bearing (AB-MFB) in which three metal mesh blocks (MMBs) are inserted into the active bump-type foil bearing (ABFB) to control radial preloads through piezoelectric actuators (PZTs) and increase the structural damping. A model coupling of the active-metal mesh substructures, bump foil, and top foil is presented to analyse the mechanical properties of the compliant structure of AB-MFB. Dynamic excitation tests are conducted to validate the model. This study then predicts the static and dynamic performance of the AB-MFB by combining the model and compressible gas Reynolds equation. Finally, the effects of different parameters on the dynamic performance of the AB-MFB are discussed.

A deep-learning model for semantic segmentation of meshes from UAV oblique images

ABSTRACT Though mesh generated by UAV-based oblique photogrammetry has revolutionized the large urban scene data representation, its semantic segmentation still challenging due to structural irregularities. In this paper, a deep learning model is proposed for the mesh semantic segmentation. To efficiently capture local geometry and neighbourhood context within the mesh, graph concept and transformer blocks are employed for mesh representation and feature learning. Based on these components, a hierarchical network architecture is presented. Experimental results demonstrate that the proposed network performs well on the self-made Wuhan dataset. The ablation study shows the improvement brought by each component in the network. By comparison, both mIoU and mF1 of our network are much higher than the prior work on the public SUM dataset, achieving 83.7% and 73.7%.

Supporting farming smart documentation system by modular blockchain solutions

For more than a decade, various farm-specific models have been developed by collaborating and integrating sensing technologies as a step toward successful data-farm documentation and effective decision-making. However, the stored and gathered data continues to rely on cloud infrastructure or centralized platform control, which is particularly vulnerable to threats such as data tampering, data distortion, confidentiality, and manipulation, which caused the farm product data difficult to trace to its provenance. In this paper, we propose a farm transaction model by demonstrating a flow of farm transaction simulation implicated by MBC sensing instrument with an array of sensors, controllers, networking hardware, computing equipment, and internal memory functions to enhance data integrity and security farm object. Based on the proposed model, a proof-of-concept experimental system called Encapsulating Block Mesh (EBM) integrates blockchain technology with the specific application case of cocoa production has been implemented. Results have shown that farm objects represented by MBC take turn recording information on the process of generating, transacting, and consuming a farm product and encrypting it into a block was validated and linked in the EBM with the hash of transaction data that connected to each cocoa farm object in a simulation environment.

COVID‐19 test sites in Victoria approaching Stage 4 restrictions: evaluating the relationship between remoteness, travel time and population serviced

ObjectiveIn Australia, people residing remotely typically experience increased travel time to health services, and remote health services often have unfavourable population‐to‐provider ratios. The state of Victoria was treated as a case study and a spatial analysis investigated the impact of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) point‐of‐care‐test (POCT) site location (Major City, Inner Regional or Outer Regional) on the mean travel time for closest residents and the number of closest residents. MethodsA network analysis established the travel time from every mesh block in Victoria to the closest POCT site. Inferential analyses investigated the impact of POCT site location on travel time and the number of closest residents. ResultsCompared to urban locations, the mean travel time for closest residents to rural POCT sites was significantly higher, while rural POCT sites had significantly fewer residents to service. ConclusionsFindings confirm Australian health service literature suggesting that rural regions have poorer proximate availability of health services, while also contrasting to literature indicating that Australian rural regions have fewer health services per capita. Implications for public healthLocalities within outer regional Victoria are candidates for a localised response to reduce unnecessary travel. Employing innovative service models may improve health service access and use and reduce population‐to‐provider ratios in rural locations.

Dispersion and Stability Analysis for TLM Unstructured Block Meshing

The insatiable demand to optimize and engineer new functionalities in electromagnetic devices has risen their geometrical complexity to unprecedented levels. This usually results in computationally multiscale problems with some tiny components of great importance to the overall behavior of these devices. Block meshing is a powerful technique for treating such problems. The usage of variable mesh size is adaptable for adequately representing the geometrical details without exhausting the computational resources with a uniform fine grid in the entire computational domain. In addition, block meshing allows the use of cubic cells only for which time step in maximum and velocity error is minimal in each subregion. In this article, we present a mathematical formulation for stability and dispersion analysis when using block meshing in the transmission-line matrix (TLM) method. These relations permit us to compute the maximum mesh size and time step that guarantee a tolerable level of numerical dispersion, hence minimizing the computational expenditures. Moreover, we study the case of adopting the local time step and demonstrate the origins of the instability that may appear in this case. Finally, some numerical experiments are presented to show the advantages of the proposed approach when using TLM block meshing. A similar procedure can be used for FDTD or FIT with block meshing.

Describing and mapping diversity and accessibility of the urban food environment with open data and tools

The food environment is a target for policy interventions aimed at improving diet, but there is a lack of consistent evidence to guide such policy interventions, partially attributed to spatial measures of the food environment that are too narrow in scope. This study developed a workflow in the R programming language for characterising food access using multivariate methods adapted from community ecology, not previously applied in food environment research. The workflow was tested in the city of Perth, Western Australia and applied to both standard business directory data and open, crowdsourced data. The workflow was run on all Census Mesh Blocks (MB) in the Perth urban area, using the following steps: 1) collect and process food outlet and MB data, calculating a 15-min walking network isochrone around each MB centroid; 2) cluster the MB based on food outlet availability and verify identified clusters using multivariate methods; and 3) profile clusters using measures of diversity and accessibility. The results show three zones of food access in Perth, differentiated by the type and abundance of food outlets available, with better accessibility and diversity in established suburbs. The workflow is a flexible and quick tool that can help professionals and practitioners to calculate a comprehensive set of indicators of food access in any location where food outlet data is available. The combination of open and standard business directory data provides a more complete picture of the food environment than one dataset alone.

Flow Field Study of Bio-Inspired Corrugated Airfoils at Low Reynolds Number with Different Peak Shapes

This study is intended to understand the fluid flow behaviour of a bio inspired corrugated wing obtained from the mid span of the dragonfly wing with different peak shapes of the corrugations. The aerodynamic effect due to variation of the shape of the first peak is studied with triangular and a curved peak shapes. The coordinates of the corrugated wing of the dragonfly were obtained from the existing literature and scaled up 1:50 to do the computational work on it. The corrugated wing was modeled by using a modeling software, the meshing was done by using ICEMCFD with a rectangular block meshing and simulated in Ansys Fluent software at 35000 Reynolds number and angles of attack ranging from 4° to 12°. The k-ε turbulence modeling was deployed to capture turbulence in the tested domain. The boundary conditions and size of the domain were selected as per available experimental wind tunnel setup. The flow characteristics like pressure and velocity of the triangular and curved peaks were obtained computationally and compared with each other having same geometrical parameters. The simulated results showed that the curved peak performed aerodynamically better than the triangular peak. The leading edge vortices were observed in both models trapped in the trough of the first valley with some different intensity. The validation of the computational flow results was done by existing experimental flow visualization in a wind tunnel and both results agree with each other.

Investigation on the rotordynamic performance of hybrid bump-metal mesh foil bearings rotor system

The rotordynamic performance of a new designed gas foil bearing, hybrid bump-metal mesh foil bearing (HB-MFB), was investigated in this study. The elastic substructure of the HB-MFB was comprised by the foil strips and metal mesh blocks, which is different from the traditional bump-type gas foil bearing. The metal mesh material was introduced to improve the damping of the bearing, thus improving the stability of the rotor system. The new designed HB-MFB was manufactured and tested on a rotordynamic test rig in this study. The rotor responses were measured and analyzed under different operating conditions and bearing parameters. A theoretical model of the HB-MFB rotor system was built and demonstrated by the experiment results. The performance of HB-MFB was compared with traditional bump-type gas foil bearings. The effect of bearing parameters and operating conditions, like imbalance, mesh density, bearing load, and bearing clearance, on the rotordynamic performance of HB-MFB rotor system was studied experimentally and analyzed theoretically. The experiment results demonstrated that introducing metal mesh can suppress the subsynchronous vibration significantly, which means the stability can be improved. The critical speed changes slightly, while the synchronous amplitude increases as the imbalance increases in the whole operating speed range. The rotor responses under different static loads showed the stability was improved as the static load increases because of the improvement of the natural frequency and the threshold speed of instability. The rotordynamic performance of HB-MFB rotor system is sensitive with some of the bearing parameters, like mesh density and bearing clearance.