Search

Study region: Marikina–Pasig basin, Philippines Study focus: A multiscale rainfall-runoff and inundation model was developed to simulate the severe flooding caused by a high-intensity short-duration storm rainfall event in the urban domain. The model used the 2D shallow-water flow and finite volume schemes with second-order space–time accuracy to automatically incorporate the runoff into the flood inundation. The adaptive mesh refinement scheme—a variable grid-sizing technique—was implemented to dynamically refine the mesh from a watershed-scale to a more precise inundation in a subcatchment floodplain. The digital terrain and surface models were used to represent the variations in flood propagation along buildings and artificial barriers in the urban area. Additionally, the simulated flood depths and extent were validated by comparison with the observed data. New hydrological insight: The severe inundation produced by the extreme rainfall event was perceived to be caused by a combination of fluvial and pluvial flooding; exacerbated by the domain’s flat and low-lying elevation and its geographical features acting as a flood water receiving catchment accrued from the adjacent mountainous regions. The proposed method can be used to identify the flood depth and water accumulation, estimated peak time, potential flash-flood prone areas, and imperceptible flood origins without the need to establish first the water level and stream discharge boundary conditions. The domain-specific flood simulations can be used for early warning and to identify a broader scope of possible evacuation points during storm-based flooding events.

This paper presents numerical analyses of lateral jets in supersonic cross flows on a flat plate and on a generic missile. The freestream Mach number is 4 for the flat plate and 3 for the missile, and the jets are sonic for both cases. The numerical results are validated with wind tunnel data such as Schlieren images and surface pressure distributions. The flow structure due to the jet interaction with the supersonic free-stream is examined in terms of the vortex structure. A 3-dimensional compressible RANS solver is used for the study. To describe the effects of high temperature, a thermally perfect gas is assumed. When high temperature is applied, the shock structure changes, which affects the separation region and recirculation zone. Next, the effects of turbulence models on the jet interaction flow are investigated. The Spalart–Allmaras, Menter's shear-stress transport k–ω, Huang and Coakley's k–e, and Coakley's q–ω models are used to analyze the flows. The differences in pressure distribution among the turbulence models are larger in the case of the flat plate than the missile. In addition, several numerical flux functions are compared to investigate their effects on the jet interaction: the Roe scheme with Sanders's H-correction, RoeM scheme, and the HLLE scheme. Although the HLLE scheme shows a little difference at the indent of the barrel shock, the three numerical flux schemes give similar C P distributions on the wall.

Wing flexibility affects the flight performance of flapping-wing micro air vehicles. In this paper, we present a computational approach for the aeroelastic analysis of realistic insect-like flexible flapping wings with hovering and forward-flight modes. A three-dimensional preconditioned Navier–Stokes solver is used with a deforming mesh technique for the aerodynamic analysis of a flapping wing. For the structural analysis, co-rotational (CR) finite elements and CR shell elements are used. As seen from the numerical analysis, wing flexibility leads to thrust increments with the increasing flapping frequency. The advance ratio, however, is the cause of the thrust decrease for flexible flapping wings with high flapping-frequency motions.

Coupled 1D-2D modelling is a widely used approach to predict water movement in complicated surface and subsurface drainage systems in urban or peri-urban areas. In this study, a hybrid parallel code, H12, is developed for 1D-2D coupled urban flood modelling. Hybrid-1D-2D, or H12, enables street-resolving hyper-resolution simulation over a large area by combining Open Multi-Processing (OpenMP) and Message Passing Interface (MPI) parallelization. Variable grid sizing is adopted for detailed geometric representation of urban surfaces as well as efficient computation. To assess the capability of H12, simulation experiments were carried for the Johnson Creek Catchment (∼40 km2) in Arlington, Texas. The LiDAR-derived digital elevation model (DEM) and detailed land cover map at 1-m resolution are used to represent the terrain and urban features in flood modelling. Hybrid parallelization achieves up to a 79-fold reduction in simulation time compared to the serial run and is more efficient than either OpenMP or MPI alone especially in hyper-resolution simulations.

Shallow water models are used for simulating flood and lake hydrodynamics. However, the computational cost of those models is often high and require high performance computing. We present the SW2D-GPU: a two-dimensional shallow water model accelerated by General Purpose Graphics Processing Unit. The model is implemented in parallel using CUDA C/C++. We exemplify the use of the model with two case studies: (i) Flood simulation in an urban area and (ii) water level simulation in a lake catchment. We have included potential evaporation in the formulation which expands its application to water level simulations in lakes and reservoirs. The SW2D-GPU model is approximately 34 times faster than its equivalent sequential version. The model can be run in any computer equipped with a NVIDIA GPU. Integrated simulations of surface waters in lake watershed and simulations of floods caused by dam break are some of the potential applications.

An urban flood is an integrated phenomenon that is affected by various uncertainty sources such as input forcing, model parameters, complex geometry, and exchanges of flow among different domains in surfaces and subsurfaces. Despite considerable advances in urban flood modeling techniques, limited knowledge is currently available with regard to the impact of dynamic interaction among different flow domains on urban floods. In this paper, an ensemble method for urban flood modeling is presented to consider the parameter uncertainty of interaction models among a manhole, a sewer pipe, and surface flow. Laboratory-scale experiments on urban flood and inundation are performed under various flow conditions to investigate the parameter uncertainty of interaction models. The results show that ensemble simulation using interaction models based on weir and orifice formulas reproduces experimental data with high accuracy and detects the identifiability of model parameters. Among interaction-related parameters, the parameters of the sewer–manhole interaction show lower uncertainty than those of the sewer–surface interaction. Experimental data obtained under unsteady-state conditions are more informative than those obtained under steady-state conditions to assess the parameter uncertainty of interaction models. Although the optimal parameters vary according to the flow conditions, the difference is marginal. Simulation results also confirm the capability of the interaction models and the potential of the ensemble-based approaches to facilitate urban flood simulation.

An effective time-domain aeroelastic framework for bridge deck flutters is presented based on a modified implicit coupling algorithm with grid deformation techniques. The grid deformation is accomplished by radial basis function interpolation as well as by the rigid movement of the initial grid. In this paper, for computational efficiency, a coupling frequency control technique is adopted for the implicit coupling algorithm. To verify the time-domain aeroelastic framework by using the grid deformation technique, the vortex-induced vibration of the cylinder and H-section bridge deck flutter are computed, and the results are compared with published results. The effect of the coupling frequency with the grid deformation technique is presented for the flutter analysis of the Great Belt East Bridge suspension girder section.

Software-defined networking (SDN) is being strongly considered as the next promising networking platform, and studies regarding SDN have been actively conducted accordingly. However, the security of SDN remains undefined and unknown when considering the enhancement of network security in SDN. In this paper, we verify whether SDN can enhance network security. Specifically, the idea of enabling security functions with diverse SDN features is explored thoroughly. In order to elucidate the feasibility of SDN-based security functions, we implement four types of security functions with SDN in Floodlight applications: (i) in-line mode security functions (e.g. firewalls and IPS), (ii) passive mode security functions (e.g. IDS), (iii) network anomaly detection functions (e.g. scan and DDoS detector), and (iv) advanced security functions (e.g. stateful firewall and reflector networks). Furthermore, we focus on discovering issues that might arise throughout the implementation of SDN-based security applications and discuss how these issues can be addressed. In order to appropriately prove the feasibility of the SDN-based security applications, we evaluate our Floodlight applications in real testbeds that consist of SDN-enabled switches and a number of physical hosts.

The flow characteristics on and around an airfoil at moderate Reynolds number are studied to understand the generation mechanism of tonal noise from a symmetrical airfoil NACA0018 in a uniform flow. The separation and reattachment of the flow on the airfoil surface are evaluated from the liquid-crystal visualization and the velocity field across the boundary layers over the airfoil are measured by particle image velocimetry (PIV). These results indicate that the separation and reattachment points of laminar boundary layers over the airfoil move along the airfoil surface, depending on the angle of attack variations. When the airfoil is inclined at a small attack angle to meet with the condition of tonal noise generation, the boundary layer on the pressure surface experiences the separation along the surface and reattaches near the trailing edge of the airfoil. Then, the periodic vortex structure is generated over the pressure surface near the trailing edge, which is followed by the formation of periodic vortex shedding in the airfoil wake. With further increase in attack angle, the flow over the suction surface separates near the leading edge of the airfoil and the boundary layer on the pressure surface keeps fully attached flows on the airfoil surface, resulting in the disappearance of tonal noise.

When ranking fuzzy values, there is an ambiguity in selecting the most-preferred ranked sequence from a collection of candidate sequences because every sequence has a possibility to which the preference relations in the sequence are correct. In this paper, we propose a method for ranking the sequences of fuzzy values that assigns a preference degree to each ranked sequence. Each preference degree indicates the relative preference of the given sequence over the other sequences. The proposed method gives information regarding which sequence could be classified as the most-preferred sequence and which sequences as alternatives.

A new method for enhancing the convergence rate of iterative schemes for the numerical integration of systems of partial differential equations has been developed. It is termed the Distributed Minimal Residual (DMR) method, and is based on general Krylov subspace methods. The DMR method differs from the Krylov subspace methods by the fact that the iterative acceleration factors are different from equation to equation in the system. At the same time, the DMR method can be viewed as an incomplete Newton iteration method. The DMR method has been applied to Euler equations of gasdynamics and incompressible Navier-Stokes equations. All numerical test cases were obtained using either explicit four stage Runge-Kutta or Euler implicit time integration. The DMR method was found capable of reducing the computation time by 20–80% depending on the test case. When directly compared with an implicit residual smoothing, the DMR method performed consistently better and more reliably. The formulation for the DMR method is general in nature and can be applied to explicit and implicit iterative algorithms for arbitrary systems of partial differential equations.