A review of wildland fire spread modelling, 1990-present 3: Mathematical analogues and simulation models

In recent years, advances in computational power and spatial data analysis (GIS, remote sensing, etc) have led to an increase in attempts to model the spread and behvaiour of wildland fires across the landscape. This series of review papers endeavours to critically and comprehensively review all types of surface fire spread models developed since 1990. This paper reviews models of a simulation or mathematical analogue nature. Most simulation models are implementations of existing empirical or quasi-empirical models and their primary function is to convert these generally one dimensional models to two dimensions and then propagate a fire perimeter across a modelled landscape. Mathematical analogue models are those that are based on some mathematical conceit (rather than a physical representation of fire spread) that coincidentally simulates the spread of fire. Other papers in the series review models of an physical or quasi-physical nature and empirical or quasi-empirical nature. Many models are extensions or refinements of models developed before 1990. Where this is the case, these models are also discussed but much less comprehensively.Comment: 20 pages + 9 pages references + 1 page figures. Submitted to the International Journal of Wildland Fir

Pedestrian Movement at the Unpaid Concourse Area in KLCC Train Station

This study investigates the pedestrian movement during three different peak hours by considering their walking speed and density at the unpaid concourse at a train station. The data for analyses; pedestrian hourly volume and pedestrian walking speed in this study was extracted from the CCTV video footage at the train station in KLCC. The findings show the walking speed at the study area can be considered as fast with the highest walking speed was 1.68m/s during the afternoon peak hour and the slowest walking speed was 0.98m/s during the morning peak hour. The study area was divided into several segments in order to simulate the pedestrian density by using VISWALK. Pedestrian density was highest during the evening peak hours. The study also found that the pedestrian tended to walk in oblique movement to avoid collision with other pedestrian in the crowd during the peak hours. The findings in this study give some insights for pedestrian crowd management in the train station to increase the pedestrian flow and may useful for emergency evacuation planning

Connected Coordinated Motion Planning with Bounded Stretch

We consider the problem of coordinated motion planning for a swarm of simple, identical robots: From a given start grid configuration of robots, we need to reach a desired target configuration via a sequence of parallel, continuous, collision-free robot motions, such that the set of robots induces a connected grid graph at all integer times. The objective is to minimize the makespan of the motion schedule, i.e., to reach the new configuration in a minimum amount of time. We show that this problem is NP-hard, even for deciding whether a makespan of 2 can be achieved, while it is possible to check in polynomial time whether a makespan of 1 can be achieved. On the algorithmic side, we establish simultaneous constant-factor approximation for two fundamental parameters, by achieving constant stretch for constant scale. Scaled shapes (which arise by increasing all dimensions of a given object by the same multiplicative factor) have been considered in previous seminal work on self-assembly, often with unbounded or logarithmic scale factors; we provide methods for a generalized scale factor, bounded by a constant. Moreover, our algorithm achieves a constant stretch factor: If mapping the start configuration to the target configuration requires a maximum Manhattan distance of d, then the total duration of our overall schedule is ?(d), which is optimal up to constant factors

ADOPTION OF DIGITAL TWIN WITHIN THE DEPARTMENT OF THE NAVY

Digital twins have the potential to support the decision-makers that design, build, operate, and maintain the platforms that the Department of the Navy (DON) relies upon to conduct naval operations. However, the thin body of knowledge on digital twins presents a challenge for the DON as the range of applications and risks associated with onboarding digital twins are still unclear. This thesis conducts a qualitative technology assessment to determine the effects that adopting digital twins has on the DON’s enterprise architecture. Analysis of an enterprise-wide adoption identifies opportunities and risks of digital twins within the context of the DON’s strategy, processes, people, technology, cyber security, and risk management. The business value provided by digital twins is principally dependent upon the aggregate risk value of the physical platform and the fidelity and frequency of the digital twin’s synchronizations.Captain, United States Marine CorpsCaptain, United States Marine CorpsApproved for public release. Distribution is unlimited

The feasibility of using standard Z notation in the design of complex systems

Formal design methods are becoming increasingly recognised as being useful for specifying complex systems. Incorporating formal methods in the early stages of a design process introduces the possibility of using mathematical techniques, hence improving the effectiveness of a design process. The Z notation has been applied mainly to specifying software, although it has also been used for specifying hardware and general systems. The Z notation fulfils two functions in this thesis. The first function is as a notation for representing specifications of complex systems, and the second function is as a notation for representing implementations of the same complex systems. The suitability of the Z notation for these functions is investigated in three studies. Both the specifications and implementations are represented as unified collections of Schemas that describe the behaviour in response to each set of input conditions. In each of the studies, both the specifications and implementations of the complex system take place at an early stage in a design process. Throughout this thesis non rigorous proof sketches prove that the implementations meet the requirements of the specifications

Simulation directe du bruit propre de profil à haut nombre de Reynolds

Ce travail propose une étude numérique utilisant la simulation numérique directe (SND) afin d'avoir une meilleure compréhension du mécanisme de génération du bruit au bord de fuite (BF), ou bruit propre de profil. 2 SND compressibles de haute résolution de l'écoulement autour d'un profil NACA6512-63 et du profil CD, ont été effectuées, à un nombre de Reynolds Rec = 150, 000 basé sur la corde et à un nombre de Mach amont Ma = 0.25, en prenant en compte les effets d'installation de la soufflerie. Pour le profil NACA6512-63, même si ce cas est difficile à simuler à cause de l'écoulement étroit du jet de la soufflerie, grâce à des conditions limites bien choisies, les effets d'installation sont généralement bien reproduits en comparant avec les résultats d'essais. A l'intrados, la transition se produit au bord d'attaque (BA) et une couche limite totalement turbulente existe jusqu'au BF. A l'extrados, une couche limite instable et décollée au BF donne une source de bruit supplémentaire par rapport au cas trippé simulé auparavant dans lequel une couche limite turbulente attachée était présente. Il est démontré de plusieurs manières que la couche limite oscillante au BF à l'extrados du cas non-trippé change la topologie de l'écoulement à l'intrados. Des plus grosses structures sont formées au BF à l'intrados en raison de la couche limite instationnaire et la position de la transition a changé au BA. Les analogies acoustiques utilisées donnent une bonne prédiction globale pour les cas trippé et non-trippé. Pour le profil CD, les résultats de cette étude prouve que cette SND peut être considérée comme une base de données de haute fidélité. A l'intrados, l'écoulement reste laminaire jusqu'au BF où un échappement tourbillonaire se produit. A l'extrados, l'écoulement transitionne après une fine bulle de recirculation au BA et puis reste turbulent et attaché jusqu'au BF avec successivement un gradient de pression favorable (GPF), un gradient de pression nul (GPN) et finalement un gradient de pression adverse (GPA) dans la région au BF. L'effet de gradient de pression moyen sur l'écoulement à l'extrados est discuté en utilisant une analyse QR. L'évolution moyenne de la dynamique de l'invariant du tenseur de gradient de vitesse varie fortement avec les gradients de pression moyens différents (GPF, GPN et GPA). Cette évolution change aussi beaucoup en fonction de la distance à la paroi. Le couplage du Hessien de pression et le gradient de vitesse est l'élément majeur qui provoque tous les changements de la dynamique de l'invariant dans cet écoulement. Le gradient de pression donne un effet important au moins dans la zone externe et dans la zone logarithmique de cet écoulement. Le GPA favorise plus d'enroulements des trajectoires moyennes à ces deux zones et empêche l'étirement tourbillonaire. La paroi empêche aussi principalement ce régime. Du point de vue acoustique, on observe la source liée à la transition de l'écoulement dans la bulle de recirculation comme identifié précédemment à bas nombre de Reynolds, celle liée à l'interaction de la couche turbulente avec le BF, et une source supplémentaire dans le proche sillage. C'est la première fois que ce phénomène est observé pour cet écoulement. Après plusieurs vérifications numériques, y compris une nouvelle SGE (Simulation des Grandes Echelles) compressible de haute résolution, cette source de bruit supplémentaire dans cette SND apparaît bien physique.Abstract: This work proposes a numerical study using direct numerical simulation (DNS) to gain a better understanding of the generation mechanisms of the trailing-edge (TE) noise, or airfoil self-noise. 2 high resolution compressible DNS, respectively of the flow over NACA6512-63 airfoil and the CD airfoil, at an airfoil chord based Reynolds number of Rec = 150, 000 and at a freestream Mach number of Ma = 0.25, are conducted taking the mean wind-tunnel installation effects into account. For NACA6512-63 airfoil, although it is a difficult case to simulate because of the narrow stream from the wind-tunnel jet, due to the proper sets of boundary conditions, the mean installation effect is generally well captured when compared with experiments. On the pressure side transition occurs at the leading-edge (LE) and a fully turbulent boundary layer exists close to the trailing edge. On the suction side, a flapping and separated boundary layer at the TE leads to an extra noise source compared with a tripped case previously simulated where an attached turbulent boundary layer is present. It is demonstrated from multiple aspects in this study that the flapping shear layer at the TE on the suction side of the untripped airfoil has changed the flow topology on the pressure side. Larger structures at the TE on the pressure side are formed due to the flapping shear layer and such an influence has even modified the transition location at LE. Acoustic analogies are used and give a good overall prediction for both the untripped and tripped cases. For the CD airfoil, the results from present study prove that this DNS can be considered as a high-fidelity database. On the pressure side, the flow stays laminar until at the TE where minor vortex shedding appears. On the suction side, the flow transitions after a short separation bubble at LE then stays turbulent and attached till the TE experiencing a mean favorable pressure gradient (FPG), zero pressure gradient (ZPG) and finally an adverse pressure gradient (APG) in the TE region. The mean pressure gradient effects on the flow on the suction side are discussed in detail through a QR analysis. The mean evolution of the velocity gradient tensor invariant dynamics is found to vary strongly for regions undergoing FPG, ZPG and APG. This evolution changes also greatly with the distance to the wall. The coupling of the pressure Hessian with the velocity gradient is the major factor that drives all the changes of the invariant dynamics in this flow. The pressure gradients have a significant impact at least in the outer-layer and log-layer of the flow. The adverse pressure gradient leads to more rolling features to the mean trajectories in these two layers and suppresses the vortical stretching regime. The wall is observed to mainly suppress the vortical stretching features of the flow. On the acoustic side, besides the previously observed noise source from the leading-edge transition bubble and the trailing-edge noise from the interaction between the convecting turbulent boundary layer and the trailing-edge, an extra noise source exists in the near wake. Such a phenomenon is found for the first time for such a flow case from a compressible DNS approach. Through multiple measures including a newly produced high resolution compressible LES (Large Eddy Simulation), the extra noise source in the DNS is proved to be actually physical