Surge Simulation Research Articles

Improvements in wind field hindcast for storm surge predictions in the Bay of Bengal: A case study for the tropical cyclone Varadah

Forecasting the storm surges is crucial to prevent the enormous devastation of coastal ecosystems, habitats, and economic losses. Further, estimating ocean wave parameters in tropical areas is difficult due to the complexity of wind fields associated with tropical cyclones (TCs). Usually, parametric and global model wind fields are the two primary sources to acquire wind and pressure fields to estimate the storm surges. The parametric models usually depict a better wind field near the cyclone center. Unlike the parametric models, the wind fields from global models have better accuracy in the areas far away from the eye of the cyclone. Owing to this inconsistency, a blended wind field approach has been introduced. However, there are no consensus on selecting parametric and background wind models due to the lack of a rigorous assessment of different wind models in the Bay of Bengal (BoB) region. Hence, in this study, five well-known parametric wind models, namely, Jelesnianski (SLOSH), rankine vortex (RV), Willoughby (WL06), Holland (HL80), and generalized asymmetric holland model (GAHM); and, two global wind models, namely, european center for medium-rangeweather forecasts (ECMWF), and weather research forecast (WRF) models were investigated with the available predictions and measurements in BoB. After investigating the best wind model in this region, a detailed analysis was carried out for the TC Varadah in the BoB region. Further, this study provides insight into the deviations in the resulting simulated surge, wave characteristics, and inundation induced by the different atmospheric forcing wind models. The results reveal that a blended wind model based on GAHM and WRF can better simulate the background wind field and the internal structure of the cyclone for the BoB region.

The utilization of physically based models and GIS techniques for comprehensive risk assessment of storm surge: A case study of Huizhou

Quantitative analyses of storm surge risk, which are mostly focused on physical vulnerability, have been widely used to help coastal communities mitigate impacts and damage. Such assessments, however, overlook the social aspect of vulnerability in storm surge risk. By considering both the community’s social vulnerability and buildings’ physical vulnerability, this study proposed a methodology that incorporates social vulnerability into the framework for making quantitative risk assessments of storm surge using a coupled hydrodynamic and wave model, Geographical Information System (GIS) techniques, and the Principal Component Analysis (PCA) method. The coastal area of Huizhou was chosen as the case study due to its high concentration of oil and gas infrastructure in China’s southern Guangdong Province. By combining hazard, exposure, physical vulnerability, and social vulnerability, it was possible to explore the effect of social vulnerability on the physical vulnerability-based risk assessment of storm surge and determine the overall risk level. First, the Gumbel distribution was utilized to establish five representative and plausible hypothetical typhoon events with different return periods (10, 20, 50, 100, and 1000 years) for the study area. Then, using the well-validated fully-coupled model, the Simulating Waves Nearshore (SWAN) model and the ADvanced CIRCulation (ADCIRC) model, storm surge simulations for defined return periods were run, and the geographical distribution of the maximum surge elevations displayed on a GIS platform was used to assess hazard levels. In terms of the physical aspect, the depth-damage functions for buildings were established to estimate direct economic losses and assign risk levels accordingly. For the social vulnerability of a community, a composite score was computed using the PCA method by combining and aggregating indicators representing various characteristics of the social group. The results show that the overall risk level, taking into account both social vulnerability and physical vulnerability, has decreased on average. It suggests that social vulnerability-based risk assessment may account for a significant portion of the overall risk assessment, which is frequently overlooked in traditional storm surge risk assessment. Additionally, the comprehensive and precise risk maps can assist local policymakers in identifying areas at different risk levels and developing evacuation plans, thereby minimizing potential losses, especially in high-risk areas.

An Analysis of Track Effects on Storm Surge Simulation

This study investigates the effects of cyclone tracks on water levels during storm surges along the coast of Bangladesh. A numerical hydrodynamical model in Cartesian coordinates has been developed, where the developed equations are solved by a semi-implicit finite difference method. The boundary fitted grid technique is employed to rectangularized the physical domain. Along the north-east corner of the model, the Meghna River fresh water discharge is taken into account. A stable tidal regime over the region of interest is generated with the help of four major tidal constituents, namely M_2 (principal lunar semi diurnal), S_2 (principal solar semi diurnal), O_1 (principal lunar diurnal) and K_1 (principal lunar diurnal) along the southern open boundary of the outermost model. This previously generated tidal regime is used as the initial state of sea in order to obtain water levels due to the nonlinear interaction of tide and surge. Numerical experiments are made with the severe storm April 1991 and some hypothetical storm tracks. The simulated results with the real track are found to be in a good agreement with some observed and some reported data. The water levels are found to be greatly influenced by the hypothetical cyclone tracks.

PyVF: A python program for extracting vertical features from LiDAR-DEMs

Coastal and riverine flooding is one of the most common environmental hazards that affect billions of people worldwide. A coupled hydrologic and coastal storm surge simulation is required to develop an improved understanding of the individual and collective mechanisms that can cause flooding within watersheds. These simulations are dependent on an accurate digital elevation model (DEM); however, it is a challenge to include numerical model resolution as fine as contemporary DEMs due to the enormous computational cost. Therefore, significant vertical features (VFs) such as roadbeds, levees, railroads, and natural ridges must be identified and considered in developing the model representation of the DEM since the VFs can affect flow propagation. PyVF is an open-source program to extract significant VFs from a high-resolution, bare-earth, LiDAR-derived DEM automatically. This paper introduces the methods and shows the automated extraction of VFs for a coastal, urban, mountain and beach area.

Future Thermodynamic Impacts of Global Warming on Landfalling Typhoons and Their Induced Storm Surges to the Pearl River Delta Region as Inferred from High-Resolution Regional Models

Abstract Possible thermodynamic effects of global warming on the landfalling typhoons that affect South China and their associated storm surges over Pearl River Delta region are investigated, using the Weather Research and Forecasting (WRF) Model and the Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model based on the pseudo–global warming (PGW) technique. Twenty intense historical TCs that brought extreme storm surges to Hong Kong since the 1960s are selected and replicated by the 3-km WRF Model, with the outputs to drive the SLOSH model in storm surge simulation. The tracks, intensities, storm structure, and induced storm surges are well simulated. The PGW technique is then used to build a warmer background climate for the 20 selected TCs in the period of 2075–99 under the RCP8.5 scenario. To obtain a better adjusted warming environment, a pre-PGW adjustment method is developed. Comparing the same TCs in PGW experiments and historical runs, the TC lifetime peak (landfall) intensity can be intensified by about 9% ± 8% (12% ± 13%), with a ∼3% increase of TC peak intensity per degree of SST warming being inferred. The TCs are projected to be more compact, with the radius of maximum wind (RMW) reduced by ∼7% ± 10%. TC precipitation is also expected to increase, with the extreme precipitation within the eyewall strengthened by 22% ± 12%. All the above characters have passed the Student’s t test at 0.05 significance level. Finally, the projected induced storm surges near the Hong Kong waters are not significantly tested, although a weak storm surge height increase tendency is revealed.

Simulation of the Boreal Winter East Asian Cold Surge by IAP AGCM4.1

In this study, we evaluate the performances of the Institute of Atmospheric Physics atmospheric general circulation model (IAP AGCM version4.1) and atmospheric component of Chinese Academy of Science Earth System Model, version 1 (CAS-ESM1) in the simulation of the cold surge (CS) events in East Asia. In general, the model can capture the main features of anomalous precipitation and circulation associated with the cold surge days. Compared with climatological means of boreal winter, on CS days, the precipitation increases in the southern part of the South China Sea (SCS), while decreases in the subtropical regions near the southern China. In addition, the climatological northeasterly wind over the SCS region strengthens on CS days. In the first day composites of CS events, it shows a dipole pattern in middle latitude over East Asia, with a positive (negative) sea level pressure (SLP) anomaly in the west (east). Based on the anomalous SLP signs in the two centers of the dipole pattern, the CS days can be further classified into two types: positive-west–negative-east-type and positive-west–positive-east-type. All these features can be reasonably reproduced by IAP AGCM4.1. Although in most CS days there is positive SLP anomaly in the East China, some negative events were investigated in this study. In these negative events the northerly anomaly in SCS is associated with an anticyclonic circulation anomaly around the eastern part of the Tibetan Plateau, rather than descending from the mid-to-high latitude cold air outbreaks. The feature can also be captured by the model.

Experimental validation of a three-dimensional through-flow model for high-speed compressor surge

This paper describes the validation of surge simulations produced using the low-order code ACRoSS with experimental data from a 4. 5-stage high-speed rig, representative of the front stages of a modern high-pressure compressor (HPC). ACRoSS is an unsteady, 3D through-flow code developed at Cranfield University to predict compressor performance during stall events. The experimental data was derived during the Rig250 build 6B test campaign, carried out in 2016 by the DLR Institute of Propulsion Technology. To correctly represent the surge events, the ducting of the testbed upstream and downstream of the compressor is included in the simulation.The results from the low-order model are compared with measurements from unsteady probes for two surge events at design speed with different downstream plenum sizes. The surge frequency and pressure profiles in time are closely reproduced by the low-order model. Analysis of the unsteady pressure measurement and the acoustic waves modelled by ACRoSS indicates that the surge period is likely to be influenced by the reflection of the initial surge wave in the inlet duct.Using the ACRoSS model, surge can be accurately reproduced both in 3D and 2D. Two-dimensional, axisymmetric simulations are shown to be sufficient for the cases investigated, and surge can be simulated with a computational cost of less than one hour per event using just 40 CPUs. This represents over an order of magnitude improvement in computational power and time required to simulate surge, compared to traditional URANS 3D CFD.

Simulated flood forces on a building due to the storm surge by Typhoon Haiyan

ABSTRACT Haiyan in 2013 was one of the most powerful typhoons to have affected the Philippines, devastating in its path a wide portion of Leyte, and causing extensive damage to structures in Tacloban City. To understand the likely impacts that would be exerted by a storm surge on a structure deemed important, the authors used a coupled model that hindcasted the flooding that took place during Haiyan. This coupled model included the use of the Weather Research and Forecasting (WRF) Model (with Bogussing scheme) to simulate the atmospheric conditions during the passage of Haiyan, the Finite Volume Coastal Ocean Model (FVCOM) to simulate the storm surge and obtain the boundary conditions for the wind and flood (hydrostatic, hydrodynamic, and breaking wave), and the Structural Analysis and Designing Program (STAAD.Pro) to calculate the corresponding axial, shear, and bending moment envelopes based on the storm surge simulation. A 4-floor public school building in Tacloban was modeled and the effects that the storm surge would have on a corner column were analyzed. Based on the results, the axial, shear, and moment at the corner column significantly increased when considering flood loads, indicating the importance of including such loads in the design of essential structures.

Compressor Surges of Near-resonant Type and Convective Type; the Boundaries and the Differences in the Behaviors

Compressor deep surges are observed to be of either near-resonant type or convective type. The differences of the behaviors and the boundaries between both types were tried to make clear in the situations of a single-stage axial compressor on the basis of numerical-experimental results by use of a surge simulation code. In the near-resonant surges, the surge frequencies relative to the resonance frequency range roughly from 0.9 to 1.1, close to the resonance condition. The surges tend to degenerate just above or in the resonance range. The convective type is said to perform actions of emptying and filling the flow in the delivery plenum, showing lower relative surge frequencies less than 0.9. The study for the criteria governing the boundary between both surge types has suggested an axial motion parameter as the candidate. The convective surges are observed to occur above the boundary value of the axial motion parameter. In the environment, the fluctuation amplitudes tend to be larger than those in the near-resonant surges. The situations force the compressor to work over a wider range from the turbine-action zone to the deeply-reverse flow zone along the stage characteristic. The flow reversals thus reinforced will enhance the so-called emptying and filling actions in the convective surges.

The Modified Method of Reanalysis Wind Data in Estuarine Areas

High-quality wind field data are key to improving the accuracy of storm surge simulations in coastal and estuarine water. These data are also of great significance in studying the dynamic processes in coastal areas and safeguarding human engineering structures. A directional correction method for ECMWF reanalysis wind data was proposed in this paper based on the correlation with the measured wind speed and direction. The results show that the accuracies of wind speed and direction were improved after being modified by the correction method proposed in this paper. The modified wind data were applied to drive the storm surge model of the Yangtze Estuary for typhoon events, which resulted in a significant improvement to the accuracy of hindcasted water levels. The error of the hindcasted highest water levels was reduced by 16–19 cm.

Improved accuracy of storm surge simulations by incorporating changing along‐track parameters

AbstractThe estimation of maximum storm surges along a coast is indispensable for emergency action planning, design, and adaptation of coastal infrastructure. The existing studies on the Bay of Bengal coast have used synthetic tracks with constant track parameters such as the maximum wind speed, radius of maximum wind, and central pressure to estimate the probable maximum storm surges. However, the analysis of the best tracks from the Joint Typhoon Warning Center during 1978–2019 shows that the track parameters vary from origin to landfall locations. The reported studies along the Bay of Bengal have failed to capture such variations and overestimated probable maximum storm surges due to constant track parameters. Therefore, this study proposes a methodology for estimating wind speed of various return periods and associated track parameters that vary along a synthetic track. The wind speed of different return periods is computed at each eye location using the probabilistic approach. Thus, the calculated wind speeds vary from origin to landfall locations, and such a pattern of wind speed variation is observed to be similar to the historical cyclones. The radius of maximum wind and central pressure is calculated using the regression equations derived from historical tracks. The accuracy of the proposed methodology is investigated by simulating the cyclones Thane and Vardah that occurred along the Tamil Nadu coast. The results suggest that the varying track parameters using the proposed methodology produce realistic surge values similar to parameters from best track data, and it overcomes the overestimation of surge heights. The proposed methodology is further utilized to analyse the maximum surge scenarios along the Tamil Nadu coast resulting from various track shifts and angles of attack. The proposed methodology is expected to improve the estimation of storm surges in other basins.

Applicability Study of a Global Numerical Weather Prediction Model MPAS to Storm Surges and Waves in the South Coast of Korea

The south coast of Korea is vulnerable to coastal disasters, such as storm surges, high waves, wave overtopping, and coastal flooding caused by typhoons. It is imperative to predict such disastrous events accurately in advance, which requires accurate meteorological forcing for coastal ocean modeling. In this study, to acquire accurate meteorological data as important forcing variables for the prediction of storm surges and waves, we examined the forecast performance and applicability of a next-generation global weather/climate prediction model, the Model for Prediction Across Scales (MPAS). We compared the modeled surface pressure and wind with observations on the south coast of Korea for three typhoons that damaged Korea in 2020—Bavi, Maysak, and Haishen—and investigated the accuracy of these observations with the MPAS prediction. Those meteorological forcing variables were then used in the tightly coupled tide-surge-wave model, Advanced CIRCulation (ADCIRC) and the Simulating Waves Nearshore (SWAN) for the simulation of a typhoon-induced storm surge and wave. We also performed the hindcast of the wave and storm surges using a parametric tropical cyclone model, the best-track-based Generalized Asymmetric Holland Model (GAHM) embedded in ADCIRC+SWAN, to better understand the forecast performance and applicability of MPAS. We compared the forecast results of the typhoon-induced wave and storm surges with their hindcast in terms of the time-series and statistical indices for both significant wave height and storm surge height and found that wave and storm surge prediction forced by MPAS forecast provides a comparable accuracy with the hindcast. Comparable results of MPAS forcing with that of hindcast using best track information are encouraging because ADCIRC+SWAN forced by MPAS forecast with an at most four-day lead time still provides a reasonable prediction of wave and storm surges.

Mesoscale simulation of typhoon-generated storm surge: methodology and Shanghai case study

Abstract. The increasing vulnerability of coastal megacities to storm surge inundation means both infrastructure and populations are subject to significant threat. Planning for further urban development should include consideration of the changing circumstances in coastal cities to ensure a sustainable future. A sustainable urban plan relies on sound preparedness and prediction of future climate change and multiple natural hazards. In light of these needs for urban planning, this paper develops a general method to simulate typhoon-generated storm surge at the mesoscale (1–100 km in length). Mesoscale simulation provides a general approach with reasonable accuracy that could be implemented for planning purposes while having a relatively low computation resource requirement. The case study of Shanghai was chosen to implement this method. The mesoscale simulations of two historical typhoons not only provides realistic typhoon storm surge inundation results at the city level but is also suitable for implementing a large amount of simulations for future scenario studies. The method will be generally applicable to all coastal cities around the world to examine the effect of future climate change on typhoon-generated storm surge even when historical observation data are inadequate or not available.

Estimating the Influence of Sea Level Rise and Climate Change on Coastal Defences in Western Taiwan

Situated in the Western Pacific Ocean, Taiwan is frequently affected by powerful typhoons. The present research evaluates the storm surges that could take place along the western coastline of Taiwan, and the design water level that will likely be required by coastal structures in the course of the 21st century to protect coastal settlements. To do so, the intensity of a given case study typhoon (Soudelor, which caused great damage to Taiwan in 2015) that could affect the target case study area (Yunlin county) was modified by taking into account climate change and sea level rise (SLR), by changing the sea surface temperature (SST), atmospheric air temperature (AAT), and relative humidity (RH) in an ensemble of 14 GCMs in CMIP5 according to RCP4.5 and RCP8.5, targeting the year 2041~2060 and 2081~2100 time horizons. The Advanced Research Weather Research and Forecasting Model (WRF-ARW) and the Unstructured Finite Volume Community Ocean Model (FVCOM) were utilized to simulate the typhoons and storm surges. The hindcasting of the historical typhoon showed good agreement with the observed data provided by the Central Weather Bureau (CWB) in Taiwan, and the simulations under future climate change scenarios forecasted an increase in typhoon intensity, especially the maximum wind speed. However, the storm surge simulations indicated a limited increase in storm surge height, and even a decrease when considering also SLR. Nevertheless, the estimated maximum water level, including both effect of SLR and future storm surge height, can increase up to 3.53 m and 3.84 m relative to mean sea level at the tidal stations in Yunlin and Chiayi County, respectively. The results showed that storm surges in the study area, characterized by a shallow bathymetry with many sandbars and land reclamation projects, are highly influenced by the change in water depth due to SLR and tidal changes, and the existence of the Central Mountain Range, which can greatly affect the accuracy of the simulated typhoon wind fields.

Compressor-Surge Behaviors Distinguished Between Near-resonant Type and Convective Type

In deep surges in compressors, the behaviors tend to show either a near-resonant one or a convective one, the latter performing emptying and filling actions. However, detailed information on the differences between them have not been obtained so far. In order to understand the situations, surge simulations by a one-dimensional simulation code were conducted with respect to a single-stage centrifugal compressor, paying attention to the effects of changes in the compressor tip speed and in the geometry of the flowpaths. As the results, it has been found that near-resonant surges appear at very low tip speeds and for relatively narrow sectional areas of the delivery flowpath, and they transform to convective surges of emptying and filling actions toward higher speeds and wider sectional areas. The features of the behaviors are generalized in terms of several non-dimensional surge frequency parameters. The results are visualized by several global framework maps showing the relations among the parameters. The obtained results will give deeper understandings on the surge phenomena.

Evaluation and improvement of the ERA5 wind field in typhoon storm surge simulations

Based on ERA5 reanalysis data and an established global storm surge model, storm surge numerical simulations and wind speed analyses of eight historical typhoon events were carried out. The storm surge forcing from the ERA5 wind field was found to be systematically smaller than observed, and an analysis showed that large ERA5 wind speeds are significantly smaller than the observations, with the deviation rising with increasing wind speed. To solve this problem, we improved ERA5 by superimposing the Holland typhoon model wind field onto ERA5 to create a hybrid wind field, and two numerical simulation experiments of storm surges were carried out. The simulation results show that the average relative error of the maximum surge height decreased from 33.4% to 7.9% and from 25.0% to 10.0%. This method can significantly improve the wind speed and storm surge simulation accuracy in the ERA5 wind field near the typhoon center.

The Adaptive Damping Technique: Improving the Simulation Accuracy of Hydraulic Transients

Hydraulic surges are transient events frequently observed in various industrial and laboratory flow situations. Understanding surge physics and its accurate numerical prediction is crucial to the safety of flow systems. The maximum accuracy achievable for transient surge simulations is limited by the inefficiencies in the mathematical models used. In this work, we propose a mathematical model that incorporates an adaptive damping technique for the accurate prediction of hydraulic surges. This model also takes the compressibility effects in the liquid during the surge process into account. The novel approach of using the local pressure fluctuation data from the flow to adjust the unsteady friction for controlling the dissipation is introduced in this paper. The adaptive-dissipation is actualized through a unique 'variable pressure wave damping coefficient' function definition. Numerical simulation of three different valve-induced surge experiments demonstrates the reliability and robustness of the mathematical model. Numerical results from the proposed model show an excellent match with the experimental data by closely reproducing both the frequency and the amplitude of transient pressure oscillations. A comparative study explains the improvement in the simulation accuracy achieved by replacing the constant damping coefficient with the proposed variable coefficient. The superiority of the new model with the adaptive damping capability over the similar models in literature and those used in commercial software packages is also well established through this study.

ENHANCING COASTAL RESILIENCY OF HYPOTHETICAL LAND RECLAMATION SCENARIOS WITH MANGROVE FOREST AND OYSTER REEF ASSESSED BY ADCIRC AND SWAN STORM SURGE MODEL

Abstract. This study aims to assess the effectiveness of mangrove forests and oyster reefs on reducing the damages from typhoons in hypothetical land reclamation scenarios in Atimonan, Philippines. Storm surge simulations were ran using ADCIRC and SWAN coupled model on the local government unit’s (LGU) land reclamation plan and the proposed crenulate bay reclamation plan, both with concrete seawall, mangrove forests and oyster reefs. Inputs to the model include modified topography and bathymetry, coastline, land cover, typhoon Durian data and tidal potential constituents. Simulations show that the crenulate bay reclamation plan is better by 39.15% than the LGU’s land reclamation plan on reducing typhoon winds and storm surge inundation extent induced by Typhoon Durian. However, this advantage comes with an additional implementation cost of 11.02%. This study is envisioned to help the land reclamation project of Atimonan LGU to be resilient against typhoon winds and coastal inundation.

An efficient covariant frame for the spherical shallow water equations: Well balanced DG approximation and application to tsunami and storm surge

In this work we consider an efficient discretization of the Shallow Water Equations in spherical geometry for oceanographic applications. Instead of the classical 2d-covariant or 3d-Cartesian approaches, we focus on the mixed 3d/2d form of Bernard et al. (2009) which evolves the 2d momentum tangential to the sphere by projecting the 3d-Cartesian right-hand side on the sphere surface. Differently from the last reference we consider the exact representation of the sphere instead of the finite element one, mixed with a covariant basis projection of the momentum. This leads to several simplifications of the Discontinuous Galerkin scheme: the local mass matrix goes back to the standard block-diagonal form; the Riemann Problem does not require any tensor or vector rotations to align the bases on the two sides of an edge. Second we consider well balancing corrections related to relevant equilibrium states for tsunami and storm surge simulations. These corrections allow to compensate for the inherent non-exactness of the quadrature induced by the non-polynomial nature of both the geometrical mapping and of the covariant basis. In other words, these corrections are the order of the cubature error. We show that their addition makes the scheme exactly well balanced, and is equivalent to recasting the integral of the hydrostatic pressure term in strong form. The proposed method is validated on academic benchmarks involving both smooth and discontinuous solutions, and applied to realistic tsunami and a historical storm surge simulation.

Research on 3D Simulation Method of Nearshore Storm Surge Based on FLIP

This paper proposes a FLIP-based three-dimensional storm surge simulation method. Based on the Fluid Implicit Particle (FLIP) method, the flow field is calculated by FLIP fluid, and finally through the standard coloring based on PBR in the Unity engine. The device renders the fluid state model generated at each moment. The experimental results show that the method in this paper not only meets the realistic requirements of nearshore storm surge simulation, but also effectively improves the efficiency of scene rendering. The result can be used not only in game production and movie special effects, but also in engineering simulations such as ocean engineering and environmental engineering, and has a wide range of application prospects and application values.