Surge Characteristics Research Articles

Decadal changes in surface air temperature variability and cold surge characteristics over northeast Asia and their relation with the Arctic Oscillation for the past three decades (1979–2011)

Decadal changes in surface air temperature (SAT) variability and cold surge characteristics over Northeast Asia during late winter (January–March) are analyzed for the past three decades. Power spectrum analysis of SAT reveals that the low‐frequency variabilities with a period longer than 10 days are significantly enhanced, while the high‐frequency variabilities with a period shorter than 10 days are weakened in the 1980s and 2000s. Moreover, cold surges were stronger and lasted longer during the 1980s and 2000s compared to those that occurred in the 1990s. Here, we propose that large‐scale atmospheric conditions manifested by a different phase of the Arctic Oscillation (AO) provide preconditioning for a cold surge event, which showed a prominent decadal fluctuation. The more (less) frequent strong and long‐lasting cold surge occurrences in the 1980s and 2000s (1990s) are preceded by the more dominant negative (positive) phase of the AO. Lag‐composite analyses for cold surge events categorized by the AO phases indicate that stronger and longer‐lasting cold air advection dominates at the lower‐level, when upper‐level wave train and coastal trough are developed over East Asia under the strong negative AO phase. These results suggest that the decadal changes in SAT variability and cold surge characteristics are strongly associated with the decadal changes in the phase distribution of the AO.

Variations of storm surge caused by shallow water depths and extreme tidal ranges

A few studies have analyzed the characteristics of storm surge because of the difficulties involved in laboratory experiments and field observations, and little is known about the variations of storm surge on different tidal ranges. This study analyzes the influence of water depth and astronomical tide upon storm surge by using storms virtually generated by PBL-ADCIRC, a verified numerical analysis program. To examine the potential errors of the conventional method which estimates the maximum water level by linear superposition of tides and storm surge, we conducted our simulations in the seas around the Korean Peninsula which have quite different water depths and tides. Storm surge was found to be in an inverse proportion to water depth and tide. The simulation results confirmed that the coupling of storm surge and tides is essential in the coast of small water depth and large tides.

Unsteady behavior of surge and rotating stall in an axial flow compressor

Unsteady behaviors as well as unsteady cascade flow fields of a single-stage axial flow compressor were experimentally investigated by detail measurements of unsteady performance characteristics and casing wall pressure and internal flow velocity fluctuations. The main feature of the test compressor is a capacity tank connected directly to the compressor outlet in series through slits and a concentric duplex pipe, and also jet nozzles in order to inject compressed air toward the rotor tip region. Research attention is focused on the post-stall characteristics of surge and rotating stall which occur simultaneously. When the compressor was connected to the capacity tank, surge was generated with rotating stall in accordance with the capacitance increment of whole compressor system. The surge behavior changed irregularly with throttling valve installed behind the compressor, and several types of surge cycles were observed. In addition, the surge cycle changed by jet injection to the rotor tip region. The results suggested that the blockages of the cascade flow which were generated by a stall cell play an important role in deciding the surge behaviors.

Storm surge disaster evaluation model based on an artificial neural network

Back propagation is employed to forecast the current of a storm with various characteristics of storm surge; the technique is thus important in disaster forecasting. One of the most fuzzy types of information in the prediction of geological calamity is handled employing the information diffusion method. First, a single-step prediction model and neural network prediction model are employed to collect influential information used to predict the extreme tide level. Second, information is obtained using the information diffusion method, which improves the precision of risk recognition when there is insufficient information. Experiments demonstrate that the method proposed in this paper is simple and effective and provides better forecast results than other methods. Future work will focus on a more precise forecast model.

Natural Frequency Study of Automotive Engine Valve Spring by Experimental Method

This paper presents a frequency response function method to measure the natural frequency of automotive engine valve springs with respect to different spring height. A new apparatus is developed for changing the spring height within the range of valve lift. The test results indicate that the natural frequency changing highly depends on the different pitch type of the spring. The measured natural frequencies of valve spring can be direct applied to the estimation of valve spring surge characteristics.

Modeling of Surge Characteristics in Turbo Heat Pumps

This paper presents a new analytical model of surge dynamics in turbo heat pumps. Turbo heat pumps use refrigerants as the working fluid and consist of a centrifugal compressor, condenser, expansion valve, and evaporator. Compared with a gas turbine engine, the turbo heat pump system introduces additional complexities. First, the turbo heat pump forms a closed-loop system. Second, the system has two plenums, condenser and evaporator, which are coupled to each other. Third, the heat pump runs on a refrigeration cycle with two phases: vapor and liquid. Fourth, heat transfer effects of evaporation and condensation have to be considered. Fifth, unlike air, a refrigerant has strong real gas effects and thus cannot be modeled as an ideal gas. The new model addresses such additional complexities on the basis of the first principles of conservation of mass, momentum, and energy. When applied to a gas turbine system, the new model’s predictions become identical to those from the Greitzer’s model. Furthermore, comparison with the available experimental data shows that the model can also accurately predict surge behavior in actual turbo heat pumps. Finally, the effects of Greitzer’s B parameter and the ratio of evaporator and condenser volume have been examined. Parameter B influences both surge shape and frequency. Finally, surge frequency is extremely sensitive to the ratio of the two plenum volumes.

EFFECTS OF COASTAL LANDFORM CHANGES ON STORM SURGE ALONG THE HATTERAS ISLAND BREACH AREA

Storm surge is known to be the source of many coastal problems including dune erosion, overwash deposits and inlet breaching. The work discussed in this paper arises out of an effort to develop geospatial tools and workflows that integrate with process based numerical models in order to improve the understanding of the importance of landform and complex landform changes in these processes building on the use of existing models. The effects of landform changes on calculation of storm surge characteristics (elevation and velocity) are investigated for three different cases created using the geospatial workflows coupled with ADCIRC modeling efforts.

Design and Characterization of a Centrifugal Compressor Surge Test Rig

A detailed description of a new centrifugal compressor surge test rig is presented. The objective of the design and development of the rig is to study the surge phenomenon in centrifugal compression systems and to investigate a novel method of surge control by active magnetic bearing servo actuation of the impeller axial tip clearance. In this paper, we focus on the design, initial setup, and testing of the rig. The latter two include the commissioning of the rig and the experimental characterization of the compressor performance. The behavior of the compressor during surge is analyzed by driving the experimental setup into surge. Two fundamental frequencies, 21 Hz and 7 Hz, connected to the surge oscillation in the test rig are identified, and the observed instability is categorized according to the intensity of pressure fluctuations. Based on the test results, the excited pressure waves are clearly the result of surge and not stall. Also, they exhibit the characteristics of mild and classic surge instead of deep surge. Finally, the change in the compressor performance due to variation in the impeller tip clearance is experimentally examined, and the results support the potential of the tip clearance modulation for the control of compressor surge. This is the first such demonstration of the feasibility of surge control of a compressor using active magnetic bearings.

The Cross-Equatorial Northerly Surge over the Maritime Continent and Its Relationship to Precipitation Patterns

This study describes the characteristics of the cross-equatorial northerly surge (CENS), a northerly flow that appears intermittently over the equatorial region between October and April, and its relationship to the precipitation patterns over the Maritime Continent. The CENS in this study was defined as the area-averaged northerly wind exceeding 5 m s-1 over 105°E-115°E, 5°S-EQ based on the QuikSCAT sea surface wind data. During the 10 winters from December 2000 to March 2009, 62 CENS events were extracted and classified into the following patterns: 11 events were associated with cold surges and termed the CS pattern; 20 events were associated with tropical intra-seasonal variations and termed the MJO pattern; 16 events were associated with both cold surges and tropical intra-seasonal variations and termed the CS-MJO pattern; and other 15 events were not associated with these patterns. In the CS pattern, the development and dissipation processes of the cold surge appeared, and the increased precipitation to the north of the island of Java was significant. In the MJO pattern, a wide area of northerly winds in the vicinity of the depression around 10°S continued for a longer period than in the CS pattern, and the increased precipitation west of Sumatra and south of Java was significant. The CS-MJO pattern showed features of the northerly wind fields of both the CS and MJO patterns and was associated with the greatest increase in precipitation of the three patterns in the Maritime Continent, in particular, in northwestern Java and both north and south of Java. The generation of CENS was an important environmental factor for inducing the wide positive precipitation anomaly compared to the climatological mean over the Maritime Continent.

Assessing climate change impacts, sea level rise and storm surge risk in port cities: a case study on Copenhagen

This study illustrates a methodology to assess the economic impacts of climate change at a city scale and benefits of adaptation, taking the case of sea level rise and storm surge risk in the city of Copenhagen, capital of Denmark. The approach is a simplified catastrophe risk assessment, to calculate the direct costs of storm surges under scenarios of sea level rise, coupled to an economic input–output (IO) model. The output is a risk assessment of the direct and indirect economic impacts of storm surge under climate change, including, for example, production and job losses and reconstruction duration, and the benefits of investment in upgraded sea defences. The simplified catastrophe risk assessment entails a statistical analysis of storm surge characteristics, geographical-information analysis of population and asset exposure combined with aggregated vulnerability information. For the city of Copenhagen, it is found that in absence of adaptation, sea level rise would significantly increase flood risks. Results call for the introduction of adaptation in long-term urban planning, as one part of a comprehensive strategy to manage the implications of climate change in the city. Mitigation policies can also aid adaptation by limiting the pace of future sea level rise.

On the Equivalence of a Conducting Plate in a Laboratory Experiment to a Real Earth

This paper investigates the validity and the application limit of experimental results on a scale model above a conducting plate, such as an aluminum (Al) or copper (Cu) plate, representing a real power system, which is too large for experimental measurements. The surge characteristics on a scale model of an overhead conductor above an Al plate are compared with that above a real earth. The experimental results are compared with analytical and numerical simulation results by the electromagnetic transients program and finite-difference time domain method. It is clear that the Al plate can represent the real earth only for an initial part of a surge waveform until reflection comes back from the other end of the conductor. The surge waveform on the Al plate noticeably deviates from that on the real earth as time passes. Correspondingly, the characteristic impedance of the Al plate differs from that on the real earth depending on the conductor height and the separation between the conductors.

Lightning surge characteristics of an actual distribution line and validation of a distribution line model for lightning overvoltage studies

AbstractFor distribution lines in Japan, protection measures against lightning‐induced overvoltages have been taken and can be considered almost complete. The focus of lightning protection measures has moved to overvoltages due to direct lightning strokes. Studies of such overvoltages require simulations using the EMTP (Electro‐Magnetic Transients Program), and components of a distribution line must be modeled appropriately in the EMTP simulation environment. The authors have proposed an EMTP model of a distribution line in a separate paper. This paper consists of two parts. The first part presents surge characteristics of a distribution line obtained by measurement using an actual‐scale test distribution line. In particular, the result reveals noteworthy characteristics of the surge impedance of a reinforced concrete pole and the wavefront‐time dependence of insulator voltages. The second part presents a validation of the distribution line model previously proposed by the authors. The validation shows that the distribution line model accurately reproduces the measured voltage and current waveforms for various wavefront times of the injected currents. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(1): 1–10, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.21002

Is Efate (Vanuatu, SW Pacific) a result of subaerial or submarine eruption? An alternative model for the 1 Ma Efate Pumice Formation

AbstractThe Efate Pumice Formation (EPF) is a trachydacitic volcaniclastic succession widespread in the central part of Efate Island and also present on Hat and Lelepa islands to the north. The volcanic succession has been inferred to result from a major, entirely subaqueous explosive event north of Efate Island. The accumulated pumice-rich units were previously interpreted to be subaqueous pyroclastic density current deposits on the basis of their bedding, componentry and stratigraphic characteristics. Here we suggest an alternative eruptive scenario for this widespread succession. The major part of the EPF is distributed in central Efate, where pumiceous pyroclastic rock units several hundred meters thick are found within fault scarp cliffs elevated about 800 m above sea level. The basal 200 m of the pumiceous succession is composed of massive to weakly bedded pumiceous lapilli units, each 2-3 m thick. This succession is interbedded with wavy, undulatory and dune bedded pumiceous ash and fine lapilli units with characteristics of co-ignimbrite surges and ground surges. The presence of the surge beds implies that the intervening units comprise a subaerial ignimbrite-dominated succession. There are no sedimentary indicators in the basal units examined that are consistent with water-supported transportation and/or deposition. The subaerial ignimbrite sequence of the EPF is overlain by a shallow marine volcaniclastic Rentanbau Tuffs. The EPF is topped by reef limestone, which presumably preserved the underlying EPF from erosion. We here propose that the EPF was formed by a combination of initial subaerial ignimbrite-forming eruptions, followed by caldera subsidence. The upper volcaniclastic successions in our model represent intra-caldera pumiceous volcaniclastic deposits accumulated in a shallow marine environment in the resultant caldera. The present day elevated position of the succession is a result of a combination of possible caldera resurgence and ongoing arc-related uplift in the region.

Storm Surge in Mikawa Bay Caused by Typhoon No. 0918

An extraordinary high tide was induced by the storm surge in Mikawa Bay, caused by Typhoon 0918 in October, 2009. One of the unique and important characteristics of the storm surge is a sudden sea level rise of 2m in one hour, which occurred after the Typhoon passed by. In this paper, generation mechanism of such a sea level rise and dynamics of the surge is discussed using the ADCP current data obtained during the storm as well as the tide and wind records at the observation stations around the bay. The wave-like behavior of the surge indicates that the main cause of the sudden sea level rise may be attributed to the propagation of water mass form Ise Bay triggered by the sudden change in wind direction. Furthermore, tide records in Mikawa Port for 30 years were analyzed and the risk of the disaster by the storm surge was discussed.

Physical properties and processes in the Bristol Channel and Severn Estuary

This article firstly describes the physical properties of the Bristol Channel and Severn Estuary in the context of its adjacent seas. These properties include tidal ranges and tidal phases at mean spring tides, storm surge characteristics, wind-driven currents and water levels, and frontal evolution. Simulated data on peak current speeds within the Channel at mean spring and mean neap tides are then presented, together with simulated data on annual mean wind speeds and wave heights. Analyses of observed data are described in the second part of the article. The analyses cover elements of three topics: the influences of tides, topography, runoff, salinity, wind and atmospheric pressure on residual currents and mean water levels; the identification of mechanisms involved in residual water, salt and suspended particulate matter (SPM) transport; and the identification of an exceptionally strong estuarine turbidity maximum (ETM) in the upper reaches of the Severn. Gravitational circulation was evident and strong spring-neap variations in near-bed, mid-depth and upper water column residual currents were identified that demonstrated the importance of non-linear tidal generation due to advection of momentum. Near-bed and mid-depth wind-driven residuals generally were oppositely directed to the wind in the central and inner Channel. A combination of data analyses, analytical modelling of vertical current structure and depth-averaged hydrodynamic modelling was used to interpret features of the data. Analyses of the mechanisms driving residual water, salt and SPM transport at a station in the lower Severn during neap tides showed that vertical shear mechanisms were relatively unimportant to salt and SPM transport. The residual advection and tidal pumping transport mechanisms were quantified.

Analysis on the Surge Characteristics of the Solenoid Valve for Anti-Lock Brake System

It is necessary to carry out quantitative analysis for the ABS hydraulic modulator to upgrade the system performances. Mathematical modeling method for the ABS hydraulic modulator, is suggested in the view of electromagnetism and fluid mechanics. Also, an analytic method is proposed for the resultant forces of electromagnetism and hydraulic pressure generated in the real vehicle ABS. The relationships between the design factor of Inlet & outlet solenoid valve and the system performance of ABS, are investigated through the analytical precess.

雷サージ解析のための引込線および屋内配線のモデリング

As the information society progresses, a variety of electronic appliances have come into wide use in common houses. If a lightning stroke causes faults or incorrect operations of these electronic appliances, a social economic loss is considered to be large. For this reason, the focus of lightning protection measures for distribution lines in Japan has expanded to include the low-voltage side of the distribution line in addition to the high-voltage side. In order to calculate lightning overvoltages at the low-voltage side, the surge characteristics of service-drop wires and interior-wiring cables have to be modeled accurately.First, this paper describes test results of the surge characteristics of service-drop wires and interior-wiring cables. The modal surge impedances and the propagation velocities of various service-drop wires and interior-wiring cables are obtained by the test. Based on the test results obtained, this paper proposes a modeling methodology of these wires and cables for accurate EMTP (Electro-Magnetic Transients Program) lightning overvoltage simulations. The proposed model is validated by comparing EMTP simulation results with field test results.

Analytical Study on Lightning Surge Characteristics of a Rail Track

AbstractThe development of the effective and economical protection measures is vital for the railway signaling systems because the lightning damages cause the disruption of the railway transportation systems. In general, the railway signaling systems are set up at a wayside and directly connected to the rails through cables. The lightning surges can invade the railway signaling systems via the cables and cause damages to the systems. Accordingly, clarifying the propagation characteristics of lightning surges along the rails is essential to develop the lightning protection measures in the railway signaling systems. We have carried out the field tests to examine both surge impedance and surge propagation velocity of the rails. This paper proposes a calculation model of the surge propagation characteristics along the rails. We measured the frequency‐dependent four‐terminal parameters of the rails to estimate the distributed parameter adopted in the calculation model. The results of surge impedance and surge propagation velocity calculated by the proposed model almost agree with the experimental results. Moreover, the proposed model can calculate the surge attenuation along the rails. This model is applicable to the development of lightning protection measures for the railway signaling systems. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Time- and Frequency-Dependent Lightning Surge Characteristics of Grounding Electrodes

Two phenomena dominantly influence the dynamic performance of grounding electrodes during lightning discharge: 1) the time-dependent nonlinear behavior related to soil ionization during high-current pulses and 2) the frequency-dependent electromagnetic (EM) effects related to fast rise-time current pulses. The first phenomenon improves the grounding performance, while the second might have the opposite effect of impairing the grounding characteristics. It is important to simultaneously analyze these opposing effects; however, modern approaches that take into account both phenomena are mostly based on circuit theory, which does not allow for accurate analysis of fast rise-time pulses. This paper proposes a procedure that combines a rigorous EM approach based on the method of moments with an approximation method for assessing soil ionization effects as recently recommended by the CIGRE and IEEE Working Groups. Based on this procedure, we derive a simple new formula for approximating the surge characteristics that include time-dependent ionization and frequency-dependent inductive effects. We verify the model and formula by comparing our data with published experimental results. We also describe a parametric analysis of the opposing ionization and inductive effects.

Modeling of Grounding Electrodes Under Lightning Currents

More precise modeling of the dynamic performance of grounding electrodes under lightning currents must include both the time-dependent nonlinear soil ionization and the frequency-dependent phenomena. These phenomena might have mutually opposing effects since the soil ionization effectively improves, while frequency-dependent inductive behavior impairs, the grounding performance. Modern approaches that take into account both phenomena are based on circuit theory that does not allow for accurate analysis of high-frequency behavior. This paper aims to further improve the understanding of the dynamic behavior of grounding electrodes under lightning currents by focusing on the following aspects: analyzing the validity domains of popular modeling approaches, based on circuit, transmission line, and electromagnetic theory; providing parametric analysis that takes into account both the propagation and soil ionization effects; analyzing simple formulas for surge characteristics; and comparing the modeling with experimental data. A model and a simple formula that combine the electromagnetic approach, suitable for high-frequency analysis, with the method that accounts for the soil ionization effects, recommended by the International Council on Large Electric Systems (CIGRE) and the IEEE Working Groups, are used for the parametric analysis. Both the model and the simple formula are verified by comparison with experimental results available in the literature.