Surge Conditions Research Articles

Research on Detection Evaluation and Reinforcement Technique of Piled Wharf

Accidents, such as storm surge, typhoon, non-normal impacting and other abnormal operating conditions will all cause damage to the structure of piled wharf. To improve the bearing capacity of structure and extend service life, it is need to detect, evaluate and reinforce the piled wharf. This paper analyzes different reasons and ways of destruction then puts up some detection methods for piled wharf’s different components. The evaluation procedures and steps of piled wharf are also disused and mechanism of various reinforcement methods are researched in the same time. The results of this study can provide reference for the detection, assessment and reinforcement of piled wharf structures.

Critical storm thresholds for significant morphological changes and damage along the Emilia-Romagna coastline, Italy

The definition of storm morphological thresholds along the coast of the Emilia-Romagna Region strictly depends on its configuration and variability. The region is located in northern Italy, facing the Adriatic Sea. The coastline is characterised by very different levels of economic development, ranging from natural zones with dunes to highly developed stretches protected by breakwaters and groynes. The Integrated Coastal Zone Management effort is mainly concentrated on preserving urban areas that generate significant income for the regional economy. Natural areas, while small in comparison to the urbanised zone, are important for environment preservation. Because of such a multiplicity of issues at stake, it was decided to produce two different thresholds: one for the morphological impact on natural sectors and another for inundation and damage to structures along urbanised zones.The “forcing” component of the threshold definition for natural areas was calculated by summing the effects of surge+tide+waves (run-up elevation) to find the Maximum Water Level (MWL) reached by the sea during one, ten and one-hundred year storm return periods. For urbanised zones, historical storm information was collected starting from the 1960s in order to identify the forcing conditions causing real damages. Each storm was classified in terms of wave height, period, direction and surge level. Morphological information were obtained from Lidar flights performed in 2003 and 2004 and from direct surveys undertaken in September 2008 and February 2009 as part of the monitoring programme for the MICORE Project.The computed MWL for each return period was then compared to beach elevations along natural areas in order to calculate the Dune Stability Factor (DSF), an index that accounts for the eroded sediment volume above the MWL during a storm. Based on analysis along 41 profile lines at a 500m spacing, it was found that the 1-in-1year return period wave height+1-in-1year return period surge are able to erode and/or overwash 2/3 of the dunes.The historical storm hydrodynamic information was used to estimate which wave and surge conditions are able to inundate at least 2/3 of the beach profiles. The MWL was again compared to beach elevations, this time along 63 anthropogenic profiles spaced 500m apart (or 1/3 of the urbanised coastline). It was found that a wave heights >=2m and surge+tide levels >=0.7m are able to flood between 18% and 36% of the built-up coast.The defined thresholds are related to the present coastal characteristics and are not “static”, meaning that they are likely to change according to future evolution of the coastline. They are very important because they can be used as thresholds to issue warnings and alert the Civil Protection. Moreover they are the first thresholds defined for the Emilia-Romagna coastline and will be used as starting values to generate “dynamic” thresholds based on numerical model predictions of morphological change for a given wave and surge level.

Behaviour of grounding systems: A quasi-static EMTP model and its validation

The transient behaviour of grounding systems subject to lightning strokes may be studied by means of approaches based to simple and approximated circuit models or to the more rigorous electromagnetic field theory. Both philosophies have pros and cons.In the paper a circuit model, developed by the authors in the past years and implemented with modern simulation software, is presented. The model is suitable to describe with sufficient accuracy the behaviour of complex and realistic grounding systems under surge condition, and, in particular, the peculiarity of this model is the inclusion of current controlled voltage sources into the classical RLC circuit, in order to take into account the resistive coupling among the elementary electrodes of a complex grounding system.In order to validate the model and to identify the frequency range of applicability, simulation results have been compared to ones based on electromagnetic field theory available in literature.

An Enhanced Greitzer Compressor Model Including Pipeline Dynamics and Surge

The modeling of a centrifugal compressor system with exhaust and plenum piping acoustics is presented in this paper. For an experimental centrifugal compressor test rig with modular inlet and exhaust piping, a mathematical model of the system dynamics is derived based on the Greitzer compression system model. In order to include the dynamics of the piping acoustics, a transmission line model is added to the original compressor equations and different compressor-piping configurations were tested. The resulting mathematical representations of the compression system dynamics are compared with the measured response of the experimental setup. Employing active magnetic bearings to perturb the axial impeller tip clearance of the compressor, the compression system is excited over a wide frequency range and the input-output response from the impeller tip clearance to the plenum pressure rise is analyzed. Additionally, the simulated surge oscillations are compared with the measured response in the surge condition. A good agreement is observed between the experimental and theoretical frequency responses of from the tip clearance to the output pressure, both in stable operation and during surge.

Past to future extreme events in Liverpool Bay: model projections from 1960–2100

Knowledge of the likely future wind, wave and surge climate in Liverpool Bay is of importance for coastal flood defence management. We examine a 140-year time series (1960–2100) of wind and wave model projections at the WaveNet buoy location in Liverpool Bay and also of surge model projection at two ports in Liverpool Bay, namely Liverpool and Heysham. To this end we use model projections from the UK Climate Projections 09 (UKCP09) programme. We use a medium emissions scenario ensemble from the HadCM3 climate model sensitivity tests. A continental shelf model (CS3) with ~12 km resolution was used to separately simulate the waves and the surge. The models are forced by hourly wind and pressure data from the Met Office (Hadley Centre) regional climate model (RCM). Swell wave boundary conditions are generated over the full Atlantic using global climate model (GCM) winds. Analysis of significant changes in the statistics over time shows that there is little change in extreme wave and surge conditions in Liverpool Bay. Although there is a slight increase in the severity of the most extreme events, the frequency of extreme wind and wave events is slightly reduced, while the frequency of extreme surge events slightly increases over the 140-year period. From the model projections, we find that the trends in the local wind are directly reflected in the wave field within Liverpool Bay. The trends in the skew surge projections deviate slightly from those in the wind patterns.

Tripping Characteristics of Residual Current Devices Under Nonsinusoidal Currents

This paper presents an experimental investigation into the operating characteristics of residual current devices (RCDs) under an unbalanced current. The unbalanced current included the harmonic current, ground fault current, and surge current. A testing system was first set up in the laboratory, and the minimum values of the current causing RCD samples to trip were recorded. To obtain consistent testing results, RCD samples under test were demagnetized prior to each test. It is found that RCD tripping is primarily determined by the peak value of the unbalanced current. Under a ground fault, RCDs installed in healthy circuits may trip. It would be necessary to limit the maximum leakage current in the circuits to avoid such nuisance tripping. Under surge conditions, RCDs could withstand a large short-duration current. However, a long-duration surge current can easily cause RCDs to trip.

An agent-based model for risk-based flood incident management

Effective flood incident management (FIM) requires successful operation of complex, interacting human and technological systems. A dynamic agent-based model of FIM processes has been developed to provide new insights which can be used for policy analysis and other practical applications. The model integrates remotely sensed information on topography, buildings and road networks with empirical survey data to fit characteristics of specific communities. The multiagent simulation has been coupled with a hydrodynamic model to estimate the vulnerability of individuals to flooding under different storm surge conditions, defence breach scenarios, flood warning times and evacuation strategies. A case study in the coastal town of Towyn in the United Kingdom has demonstrated the capacity of the model to analyse the risks of flooding to people, support flood emergency planning and appraise the benefits of flood incident management measures.

Proving That Bladder Surge Tanks Cured Excessive Surge Conditions in a 30” Force Main

Proving That Bladder Surge Tanks Cured Excessive Surge Conditions in a 30” Force Main

Model Validation for an Active Magnetic Bearing Based Compressor Surge Control Test Rig

In this paper, we present experimental test data for the validation of a recently introduced mathematical model for centrifugal compression systems with variable impeller axial clearances. Employing the active magnetic bearings (AMBs) of a compressor built for the experimental study of surge, the axial clearance between the impeller and the static shroud is servo controlled, and the measured variations in the compressor output flow are compared with the mathematical model. The steady state and the dynamic responses of the compression system induced by varying the impeller tip clearance are measured and compared with the theoretical predictions, and the states of the compression system in surge condition are collected and analyzed. Parameters in the compression system model, such as the Greitzer parameter B and Helmholtz frequency ωH are experimentally identified. Also, the servo dynamics of the magnetic bearing that controls the axial impeller position is determined experimentally. To further validate the mathematical model and the feasibility of using the impeller tip clearance for controlling surge, we present a design example for an active surge controller based on the derived model, and simulate the response of the compression system. This design exercise also helps us understand the possible challenges that one could face in the design and implementation of a successful surge controller.

Extremity analysis of storm surge for fixing safe design water level

Phenomenal storm surge levels associated with cyclones are common in East Coast of India. The coastal regions of Andhra Pradesh are in rapid stride of myriad marine infrastructural developments. The safe elevations of coastal structures need a long-term assessment of storm surge conditions. Hence, past 50 years (1949–1998), tropical cyclones hit the Bay are obtained from Fleet Naval Meteorological & Oceanographic Center, USA, and analyzed to assess the storm surge experienced around Kakinada and along south Andhra Pradesh coast. In this paper, authors implemented Rankin Hydromet Vortex model and Bretschneider’s wind stress formulation to hindcast the surge levels. It is seen from the hindcast data that the November, 1977 cyclone has generated highest surge of the order of 1.98 m. Extreme value analysis is carried out using Weibull distribution for long-term prediction. The results reveal that the surge for 1 in 100-year return period is 2.0 m. Further the highest surge in 50 years generated by the severe cyclone (1977) is numerically simulated using hydrodynamic model of Mike-21. The simulation results show that the Krishnapatnam, Nizampatnam and south of Kakinada have experienced a surge of 1.0, 1.5 and 0.75 m, respectively.

Numerical simulation of a low-lying barrier island's morphological response to Hurricane Katrina

Tropical cyclones that enter or form in the Gulf of Mexico generate storm surge and large waves that impact low-lying coastlines along the Gulf Coast. The Chandeleur Islands, located 161 km east of New Orleans, Louisiana, have endured numerous hurricanes that have passed nearby. Hurricane Katrina (landfall near Waveland MS, 29 Aug 2005) caused dramatic changes to the island elevation and shape. In this paper the predictability of hurricane-induced barrier island erosion and accretion is evaluated using a coupled hydrodynamic and morphodynamic model known as XBeach. Pre- and post-storm island topography was surveyed with an airborne lidar system. Numerical simulations utilized realistic surge and wave conditions determined from larger-scale hydrodynamic models. Simulations included model sensitivity tests with varying grid size and temporal resolutions. Model-predicted bathymetry/topography and post-storm survey data both showed similar patterns of island erosion, such as increased dissection by channels. However, the model under predicted the magnitude of erosion. Potential causes for under prediction include (1) errors in the initial conditions (the initial bathymetry/topography was measured three years prior to Katrina), (2) errors in the forcing conditions (a result of our omission of storms prior to Katrina and/or errors in Katrina storm conditions), and/or (3) physical processes that were omitted from the model (e.g., inclusion of sediment variations and bio-physical processes).

An investigation of recent decadal‐scale storm events in the eastern Irish Sea

The Proudman Oceanographic Laboratory Coastal Modelling System coupled to the WAve Model (POLCOMS‐WAM) modeling system has been used to model combined tides, surges, waves, and wave‐current interaction in the Irish Sea on a 1.85 km grid. A method for data analysis is presented to determine what factors and interactions contribute to extreme conditions in a region of interest. An 11 year hindcast (1996–2006) has been performed to investigate the meteorological conditions that cause extreme surge and/or wave conditions in Liverpool Bay. A one‐way nested model approach was used. For waves, a 1° North Atlantic WAM model forces the boundary of the Irish Sea model, driven by ERA‐40 wind (∼1° resolution every 6 h). To capture the external surge generated outside of the Irish Sea, the (1/9° × 1/6°) Proudman Operational surge model extending to the continental shelf edge was run for tide and surge and was forced by Met Office mesoscale winds (∼12 km resolution every hour). The data implied that the largest surges at Liverpool are generally driven by winds from the south to the west while the largest waves are forced by winds from the west to the northwest. The worst storm conditions in Liverpool Bay result under southwesterly wind conditions that veer to the west. The large tidal range in the region acts to enhance the impact of the surge through tide‐surge interaction. Moreover, the highest water levels in Liverpool Bay are in response to southwesterly winds combined with high‐water spring tide. Even though no significant surge occurs at this time, the flood threat is at its greatest.

Effects of submersion depth on wave uplift force acting on Biloxi Bay Bridge decks during Hurricane Katrina

A large portion of the Biloxi Bay Bridge was submerged and destroyed by surface waves and storm surge associated with Hurricane Katrina in 2005. In this paper, the time history of wave forces exerted on the Biloxi Bay Bridge during Hurricane Katrina was investigated by a wave-loading model. The Volume of Fluid (VOF) method was adopted in the model to track the variations of water surface levels. In order to obtain wave parameters and storm-surge elevation at the bridge site during Hurricane Katrina, a storm surge model and a wave propagation model were coupled to hindcast the hydrodynamic conditions. Outputs of the coupled wave–surge models were imported to the wave-loading model to simulate the dynamic wave forces acting on the bridge deck. In order to evaluate the maximum uplift wave force, five different bridge deck elevations submerged at different water depths were investigated. The processes of wave–bridge interaction were simulated by the wave-loading model. The wave profiles, velocity field in the vicinity of the bridge, and dynamic wave forces on the decks were analyzed. Results indicate that the uplift force on the submerged bridge deck span exceeded its own weight under the extreme wave and storm surge conditions during Hurricane Katrina. Moreover, the numerical simulations suggest that the maximum uplift wave force occurred when the storm surge water level reached the top of the bridge deck.

Experimental Evaluation of the Transient Behavior of a Compressor Station During Emergency Shutdowns

The transient behavior of compressor stations, particularly under rapidly changing conditions, is of vital interest to operators. Predicting transient behavior is an important factor in avoiding damage during events such as emergency shutdowns. A limited number of “accidental” data sets from compressor manufacturers and users are available in the public literature domain. A variety of simulations and modeling approaches have been presented over the last few years at industry conferences. The available experimental data is not of sufficient quality and resolution to properly compare predictions with analytical results or simulations available in current software packages. Necessary information about the compressor, driver, valves, and geometry of the system is often missing. Currently utilized software has not been adequately validated with full-scale realistic benchmark data, as this data is not available in the public domain. Modeling procedures and results of surge control system simulations seldom contain validation data achieved through actual testing. This type of transient test data for a dynamic surge condition is often difficult to obtain. The primary objective of this work is to develop experimental transient compressor surge data on a full-scale test facility, which would facilitate the verification and comparison of existing and future transient surge models. Results of the testing and model comparisons will be documented. Relevant, dimensionless parameters will be presented and validated utilizing the test data. Conclusions from the testing and recommendations for the transient analysis software will be provided.

Predictability of extreme meteo‐oceanographic events in the Adriatic Sea

AbstractThe performance of state‐of‐the‐art meteorological and oceanographic numerical systems in predicting the sea state in the Adriatic Sea during intense storms is assessed. Two major storms that affected Venice are discussed. The first storm occurred on 4 November 1966, when Venice suffered its most dramatic flood event. The damage and loss of life caused by the storm and the associated flood were extremely high also because the event was poorly forecast. The 1966 event is reanalysed using state‐of‐the‐art meteorological and oceanographic numerical systems to investigate whether the poor forecast quality was due to a lack of data or of suitable numerical modelling. The second severe storm took place on 22 December 1979, when Venice experienced the second‐worst ‘acqua‐alta’ conditions in recorded history. Results show that with the present numerical systems both storms and associated wave and surge conditions could have been forecast several days in advance. Potential implications for the prediction of more frequent less intense storms are discussed, and a suitably enhanced system based on a global meteorological model and a limited area one is outlined. Copyright © 2010 Royal Meteorological Society

A case study of combined wave and water levels under storm conditions using WAM and SWAN in a shallow water application

Extreme storm events in Liverpool Bay, UK, are under investigation. A recent storm, 18th January 2007, has been used to investigate different modelling approaches to accurately simulate wave–surge conditions in shallow water. In Liverpool Bay wave and surge influence and their interaction are often considered in many studies. The tide–surge–wave interaction has been modelled in the Irish Sea using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) coupled to the state-of-the-art 3rd generation spectral WAve Model (WAM). Waves are locally generated in Liverpool Bay, while the surge is locally and externally generated. To include the external surge the 1.8 km Irish Sea model has been nested, using a 1-way approach, into the 1/9° by 1/6° operational Continental Shelf surge model. To investigate the performance of POLCOMS–WAM in shallow water a 180 m Liverpool Bay model has been nested within the Irish Sea model. For this high resolution model the state-of-the-art 3rd generation Simulating WAves Nearshore (SWAN) spectral model is used to further develop WAM, modified for shallow water. A POLCOMS–WAM and POLCOMS–SWAN (1-way) coupled model has been implemented to assess the effects of tide–surge–wave interaction at the coast. Investigation of the significant wave height and surge elevation reveals that when modified for shallow water WAM performs as well as SWAN. Two-way coupling between POLCOMS–WAM allows wave-setup to be included in the surge prediction greatly improving the hydrodynamic result. A drawback to using WAM is the computational expense, making SWAN more suitable for simulations exceeding a few days in duration.

Development of storm surge which led to flooding in St. Bernard Polder during Hurricane Katrina

Hurricane Katrina caused devastating flooding in St. Bernard Parish, Louisiana. Storm surge surrounded the polder that comprises heavily populated sections of the Parish in addition to the Lower 9th Ward section of Orleans Parish. Surge propagated along several pathways to reach levees and walls around the polder's periphery. Extreme water levels led to breaches in the levee/wall system which, along with wave overtopping and steady overflow, led to considerable flood water entering the polder. Generation and evolution of the storm surge as it propagated into the region is examined using results from the SL15 regional application of the ADCIRC storm surge model. Fluxes of water into the region through navigation channels are compared to fluxes which entered through Lake Borgne and over inundated wetlands surrounding the lake. Fluxes through Lake Borgne and adjacent wetlands were found to be the predominant source of water reaching the region. Various sources of flood water along the polder periphery are examined. Flood water primarily entered through the east and west sides of the polder. Different peak surges and hydrograph shapes were experienced along the polder boundaries, and reasons for the spatial variability in surge conditions are discussed.

Influence of landscape restoration and degradation on storm surge and waves in southern Louisiana

The purpose of this investigation was to examine storm surge and wave reduction benefits of different environmental restoration features (marsh restoration and barrier island changes), as well as the impact of future wetland degradation on local surge and wave conditions. Storm surge simulations of two representative hurricanes were performed using the ADCIRC storm surge model with the inclusion of radiation stress gradients from the STWAVE nearshore wave model. Coupled model simulations were made for a number of landscape configurations that involved both restored and degraded wetland features. The impact of barrier island condition on hurricane surge and waves was also evaluated. Effects of landscape features were represented by changes in elevation and frictional resistance. Restoration and degradation of marsh resulted in decreases (for restoration cases) and increases (for degradation cases) in both surge and waves. The magnitude of change was correlated with the magnitude of the horizontal extent and elevation changes in the marsh. In general, the wave change patterns are consistent with the water level changes. Deflation of the Chandeleur Islands (barrier island chain) resulted in slightly increased surge. Results suggest that coastal marsh does have surge and wave reduction potential. Results also indicate that the impact of the landscape features is amplified in areas where there are levee “pockets.” Barrier islands and coastal ridges reduce wave heights, even if in a degraded condition and thus can reduce wave energy in wetland areas, protecting them from erosion.

Water Resources Policy and Practice Issues Exposed by Katrina

Water Resources Policy and Practice Issues Exposed by Katrina

Hydrodynamic Investigation of Coastal Bridge Collapse during Hurricane Katrina

A number of U.S. coastal bridges have been destroyed by hurricanes, including three highway bridges in Mississippi and Louisiana during Hurricane Katrina (2005). This paper addresses three fundamental questions on the coastal bridge failures: (1) what were the hydrodynamic conditions near the failed bridge during the hurricane; (2) what was the cause of the bridge collapse; and (3) what was the magnitude of the hydrodynamic loading on the bridge under the extreme hurricane conditions. Guided by field observations of winds, waves, and water levels, two numerical models for storm surges and water waves are coupled to hindcast the hydrodynamic conditions. Fairly good agreement between the modeled and measured high watermarks and offshore wave heights is found, allowing an estimate of the surge and wave conditions near the bridges in nested domains with higher resolutions. The output of the coupled wave-surge models is utilized to determine the static buoyant force and wave forces on the bridge superstructure based on empirical equations derived from small-scale hydraulic tests for elevated decks used in the coastal and offshore industry. It is inferred that the bridge failure was caused by the wind waves accompanied by the storm surge, which raised the water level to an elevation where surface waves generated by strong winds over a relatively short fetch were able to strike the bridge superstructure. The storm waves produced both an uplift force and a horizontal force on the bridge decks. The magnitude of wave uplift force from individual waves exceeded the weight of the simple span bridge decks and the horizontal force overcame the resistance provided by the connections of the bridge decks to the pilings. The methodology for determining the hydrodynamic forcing on bridge decks can be used to produce a preliminary assessment of the vulnerability of existing coastal bridges in hurricane-prone areas.