Surge Characteristics Research Articles

The comparative role of physical system processes in Hudson Strait ice stream cycling: a comprehensive model-based test of Heinrich event hypotheses

Abstract. Despite their recognized significance on global climate and extensive research efforts, the mechanism(s) driving Heinrich events remain(s) a subject of debate. Here, we use the 3D thermomechanically coupled glacial systems model (GSM) to examine the Hudson Strait ice stream surge cycling and the role of three factors previously hypothesized to play a critical role in Heinrich events: ice shelves, glacial isostatic adjustment, and sub-surface ocean temperature forcings. In contrast to all previous modeling studies examining HEs, the GSM uses a transient last glacial cycle climate forcing, global viscoelastic glacial isostatic adjustment model, and sub-glacial hydrology model. The results presented here are based on a high-variance sub-ensemble retrieved from North American history matching for the last glacial cycle. Over our comparatively wide sampling of the potential parameter space (52 ensemble parameters for climate forcing and process uncertainties), we find two modes of Hudson Strait ice streaming: classic binge–purge versus near-continuous ice streaming with occasional shutdowns and subsequent surge onset overshoot. Our model results indicate that large ice shelves covering the Labrador Sea during the last glacial cycle only occur when extreme calving restrictions are applied. The otherwise minor ice shelves provide insignificant buttressing for the Hudson Strait ice stream. While sub-surface ocean temperature forcing leads to minor differences regarding surge characteristics, glacial isostatic adjustment does have a significant impact. Given input uncertainties, the strongest controls on ice stream surge cycling are the poorly constrained deep geothermal heat flux under Hudson Bay and Hudson Strait and the basal drag law. Decreasing the geothermal heat flux within available constraints and/or using a Coulomb sliding law instead of a Weertman-type power law leads to a shift from the near-continuous streaming mode to the binge–purge mode.

Characteristics of the 15-year surge of Mittie Glacier, SE Ellesmere Island, Canadian Arctic

Characteristics of the 15-year surge of Mittie Glacier, SE Ellesmere Island, Canadian Arctic

Topography and accumulation rate as controls of asynchronous surging behaviour in the eastern and western branches of the Western Kunlun Glacier, Northwestern Tibetan Plateau

ABSTRACT The western Kunlun main peak region is among the areas in High Mountain Asia where surge-type glaciers are highly concentrated. Here, we analyse the surging characteristics of the eastern and western branches of the Western Kunlun Glacier and the factors controlling the asynchronous behaviour of their surges. The eastern branch entered an unstable state in 1999 and remained so until the culmination of its surge in the summer of 2019, spanning 21 years. Conversely, the surge of the western branch commenced in the summer of 2020. The surge duration for this glacier was four years, characterized by a rapid acceleration and deceleration process. Based on the glacier surge characteristics, we posit that western branch of Western Kunlun Glacier was influenced by hydrological mechanisms, while eastern branch was affected by subglacial thermal processes. These process intensifies crevasse formation on the glacial surface, providing conduits for surface meltwater to reach the glacier bed, thus elevating subglacial water pressure. The difference of subglacial hydrology and thermal processes caused by different subglacial topography and mass accumulation rates was the main factor of the asynchronous behaviour of the west and east branches of the West Kunlun glacier.

Trend of landfalling tropical cyclones in the East China Sea and their storm surge response

In recent years, the influence of global tropical cyclones (TCs) has a tendency to expand towards the polar direction, and the proportion of high-intensity TCs has also increased greatly. The Northwest Pacific is a high incidence area of TCs, the northward shift of landfalling TCs in China and the increase of high-intensity TCs will lead to an increased risk of storm surge in the East China Sea (ECS). However, due to the lack of long-term observations in the ECS, previous studies have focused on the analysis of individual TC, and the response mechanism of storm surge to long-term trends of TCs is not clear. Based on the long-term observations of TCs from 1949 to 2022 and the numerical experiments of storm surge, the trend of landfalling TCs in China and the response characteristics of storm surge in the ECS were studied in this paper. The observations showed that the probability of TCs entering ECS became greater in the latter 37 years compared with the former 37 years. The average intensity of landfalling TCs (maximum wind speed) increased by 36% to 30 m/s, and the average speed of landfalling TCs increased by 100% to 8 m/s. The model results showed that the intensity of the storm surge is closely related to the intensity and translation speed of TCs. Under the condition of the same translation speed of TCs, the storm surge enhanced with the intensity of TCs. For the TCs with high intensity (strong typhoon and super typhoon), the intensity of the storm surge continues to increase as the translation speed of the TCs increases. However, for the TCs with low or medium intensity (severe tropical storms and typhoons), the intensity of the storm surge reaches a peak with the increase of the translation speed of TCs. The intensity of the storm surge is determined by both the wind speed and the duration of strong wind. The TCs with faster translation speed can produce a stronger wind field but shorter duration of strong wind. Therefore, the intensity of the storm surge decreases when the translation speed of TCs exceeds the threshold value.

Modeling sensitivities of thermally and hydraulically driven ice stream surge cycling

Abstract. Modeling ice sheet instabilities is a numerical challenge of potentially high real-world relevance. Yet, differentiating between the impacts of model physics, numerical implementation choices, and numerical errors is not straightforward. Here, we use an idealized North American geometry and climate representation (similarly to the HEINO (Heinrich Event INtercOmparison) experiments – Calov et al., 2010) to examine the process and numerical sensitivity of ice stream surge cycling in ice flow models. Through sensitivity tests, we identify some numerical requirements for a more robust model configuration for such contexts. To partly address model-specific dependencies, we use both the Glacial Systems Model (GSM) and the Parallel Ice Sheet Model (PISM). We show that modeled surge characteristics are resolution dependent, though they converge (decreased differences between resolutions) at finer horizontal grid resolutions. Discrepancies between fine and coarse horizontal grid resolutions can be reduced by incorporating sliding at sub-freezing temperatures. The inclusion of basal hydrology increases the ice volume lost during surges, whereas the dampening of basal-temperature changes due to a bed thermal model leads to a decrease.

The time-dependent deformation and damage constitutive model of rock based on dynamic disturbance tests

Abstract In the deep rock excavation process, the rock will produce deformation and damage under multiple dynamic disturbances, while there is also unrecoverable time-dependent deformation. In order to research this deformation characteristic, a sine wave disturbance triaxial loading test was carried out on red sandstone to simulate the failure process of deep underground rock mass under dynamic disturbance loads with low confining pressure. Based on the results that the deformation of the rock increases suddenly during dynamic disturbances and varies with the number of disturbances, a novel disturbance damage model relating the number of disturbances to the deformation of the disturbances is created to describe the deformation and damage accumulation of the rock under multiple disturbances and an operator is developed to ensure that the model works. In order to describe the time-dependent deformation of rocks, the elasticity model in the traditional Bingham model was improved to a nonlinear elasticity model that varies with time, and its viscous and plasticity models were retained. The time-dependent deformation and damage constitutive model is obtained by combining the improved Bingham model with the disturbance damage model. The model parameters were identified according to the test data, and the finite-element calculation of the model was realized with the secondary development program. The results show the strain of rock increases suddenly under multiple disturbances, and the main reason for rock damage is the action of dynamic disturbances. The fitted curves and finite-element results are consistent with the experimental results. The time-dependent deformation and damage constitutive model of rock not only reflects the decaying rheological and steady-state rheological properties of rock under static loading but describes the characteristics of strain surge and disturbance damage accumulation caused by dynamic disturbances. This article contributes to the characteristics of the deformation of deep rock mass.

Numerical model of predicting surge boundaries in high-speed centrifugal compressors

A numerical model of the whole compression system is established in this paper. The introduction of the Laval nozzle and opening boundary methods adaptively simulate the physical fluctuating boundary conditions during the surge without any artificial hypothesis. Based on the model, the steady simulation method has the capacity to well predict the low-order systematical oscillations during the surge by monitoring flow parameters on several representative surfaces. The surge boundaries of a high-speed centrifugal compressor, including the mild surge and the deep surge, are predicted based on the current numerical model in different flow regimes. The discrepancies of the mild surge boundary between experimental data and numerical predictions are within 5% in the transonic regime, but within 0.5% in the subsonic and supersonic regimes. The sensitivities of the mild surge to the throttle opening degree differ much in different flow regimes: the highest is in the transonic regime and the lowest is in the supersonic regime. In the supersonic regime, there exist various mild surges in a wide range of throttle opening degrees and an unstable equilibrium point (UEP) which is the most typical characteristic of the two-regime surge. To the best knowledge of the authors, it is the first time that all the oscillation characteristics of various mild surges and the existence of UEP in the supersonic regime are well predicted by one numerical method.

Effects of surge and roll motion on a floating tidal turbine using the actuator-line method

This paper employs a dynamic and sliding mesh in the simulation of both uncoupled and coupled surge and roll motions of a tidal stream turbine, utilizing a modified actuator-line method. The modification involves the relocation of blade elements in relation to the grid. Detailed analyses are conducted on the Cp and Cz variations in surge, roll, and coupled motions at various frequencies and amplitudes. It is observed that changing the amplitude and frequency of surge and roll motions both impacts the amplitude of Cp and Cz. Interestingly, the Cp and Cz variations in surge motion are inversely proportional to velocity variations, while they are directly proportional in roll motion. The influence of the surge motion on Cp Cz plays a major role, while the addition of the roll motion increases the mean values of Cp and Cz. Due to the combination of the wake characteristics of both surge and roll, the coupled motion wake exhibits a contraction–expansion oscillation pattern. In a coupled motion with equal periods, the ring and strip tail vortex characteristics of both motions are apparent. A surge period increment diminishes the surge's tail vortex characteristic, whereas an increase in the roll period gradually erodes the roll's tail vortex characteristic. The coefficient variation of the tangential and normal forces (cn, ct) in combined motion mirror that of surge motion, presenting a convex table per surge cycle with depressions at the 1/2T and 1T points. The peak of cn and ct in surge motion are approximately 0.28 and 0.03, respectively, while in roll motion, they are around 0.261 and 0.025. The exploration of cyclic stress impacts on the turbine, and the potential instability on the platform could be valuable directions for future research.

Investigating potential drivers of increased central-line–associated bloodstream infections during the SARS-CoV-2 omicron-variant surge

Background: Central-line–associated bloodstream infection (CLABSI) rates increased nationally during COVID-19, the drivers of which are still being characterized in the literature. CLABSI rates doubled during the SARS-CoV-2 omicron-variant surge at our rural academic medical center. We sought to identify potential drivers of CLABSIs by comparing period- and patient-specific characteristics of this COVID-19 surge to a historical control period. Methods: We defined the study period as the time of highest COVID-19 burden at our hospital (July 2021–June 2022) and the control period as the previous 2 years (July 2019–June 2021). We compared NHSN CLABSI standardized infection ratios (SIRs), central-line standardized utilization ratios (SURs), completion of practice evaluation tools (PETs) for monitoring of central-line bundle compliance, and proportions of traveling nurses. We performed chart reviews to determine patient-specific characteristics of NHSN CLABSIs during these periods, including demographics, comorbidities, central-line characteristics and care, and microbiology. Results: The CLABSI SIR was significantly higher during the study period than the control period (0.89 vs 0.52; P = .03); the SUR was significantly higher during the study period (1.08 vs 1.02; P < .01); the PET completion per 100 central-line days was significantly lower during the study period (23.0 vs 31.5; P < .01); and the proportion of traveling nurses was significantly higher during the study period (0.20 vs 0.08; P < .01) (Fig. 1). Patients with NHSN CLABSIs during the study period were more likely to have a history of COVID-19 (27% vs 3%; P = .01) and were more likely to receive a higher level of care (60% vs 27%; P = .02). During the study period, more patients had multilumen catheters (87% vs 61%; P = .04). The type of catheter, catheter care (ie, dressing changes and chlorhexidine bathing), catheter duration before CLABSI, and associated microbiology were similar between the study and control periods (Table 1). Conclusions: During the SARS-CoV-2 omicron-variant surge, the increase in CLABSIs at our hospital was significantly associated with increased central-line utilization, decreased PET completion, and increased proportion of traveling nurses. Critical illness and multilumen catheters were significant patient-specific factors that differed between CLABSIs from the study and control periods. We did not observe differences in catheter type, duration, or catheter care. Our study highlights key modifiable risk factors for CLABSI reduction. These findings may be surrogates for other difficult-to-measure challenges related to the culture of safety during a global pandemic, such as staff education related to infection prevention and daily review of central-line necessity.Disclosures: None

Establishment of Prediction Model for Cavitation Surge Frequency and Onset in an Inducer Considering Dynamic Characteristics of Cavitation Compliance and Mass Flow Gain Factor

Abstract An accurate prediction method of cavitation surge is desired to design a reliable turbopump for rocket engines that allow complex operational sequences such as controlled reentry and landing. Therefore, the paper aims to develop a novel model that enables accurate predictions of both frequency and onset of cavitation surge by considering dynamic characteristics of cavitation compliance K and mass flow gain factor M. The paper conducts both experimental and numerical studies in an inducer known to cause cavitation surge. First, characteristics of cavitation surge including frequency and occurrence conditions are experimentally surveyed. Secondary, K and M for the studied inducer are numerically obtained by steady RANS simulations. Then, the one-dimensional model is initially established based on the premises acquired by performed experiments and applied to cavitation surge predictions using quasi-statically evaluated K and M. As a result of comparisons with experiments, the cavitation surge frequency is adequately evaluated by the established model, whereas the cavitation surge onset fails to be estimated only using quasi-static parameters. The new model is thus proposed by including dynamic characteristics of K and M, and it is mathematically clarified that phase properties of K and M may play a key role to trigger cavitation surge. By presuming adequate values of dynamic characteristics based on past literatures, consequently, the developed model succeeds in accurate predictions of the cavitation surge onset in the experiment. This evidences that dynamic characteristics of K and M are essential to predict cavitation surge quantitatively.

Surge margin monitoring of one turboshaft engine with inlet distortion

In order to explore the engine surge when inlet distortion index and engine surge margin, the relationship between the parameter characteristics of research engine surge, strengthen safety monitoring assessment engine, this paper designed a kind of a certain type of engine bench test surge monitoring system, and unstable flow field of a certain type of vortex axis engine working parameters for monitoring and analysis. In this paper, a plug-plate distortion generator is used to induce a surge engine, and the circumferential static pressure changes of the inlet and outlet of the engine, the axial compressor and the centrifugal compressor under different working conditions are obtained. The changes of circumferential unevenness and mean turbulence, the pressure ratio at working point and the converted air flow rate at working point are analyzed with the increase of the height of the plug-plate under different working conditions. The results show that the distortion index of the working point increases and the surge margin decreases with the increase of the height of the plug-plate at the same rotating speed. When the height of the plug-plate is similar, the higher the speed is, the greater the distortion index of the working point is, and the smaller the surge margin is.

Future projections of storm surges and associated coastal inundation along the east coast of India

Abstract This study aims to analyze several aspects of storm surges and associated coastal inundation along the east coast of India. The current study utilizes historical cyclone tracks over the past five decades and, synthetic tracks are projected for the next 100 years to develop a comprehensive analysis of the storm surges in India. The impact of climate change on cyclone path and intensity is also considered. The ADCIRC model is used to compute storm surge heights and associated coastal inundation for historical and future cyclone tracks. An in-depth analysis is carried out using composite maps explaining the storm surge characteristics at various coastal locations. The novelty of this study lies in the comprehensive analysis of potential storm surges and associated coastal flooding related to exaggerated cyclones that are expected in a changing climate scenario. The outcome of the study is beneficial to storm surge operational centers and disaster management applications.

An Experimental Study on Novel Gas Discharge Tubes With Graphene as Electron Emission Material

Electrical equipment is subjected to gas discharge tube (GDT) direct current (dc) breakdown voltage dispersion and breakdown voltage drop after a surge. It is noteworthy that GDT damage may even cause the failure of electrical equipment. Accordingly, the chemical vapor deposition (CVD) of graphene was proposed in this study as an electron emission material of the GDT based on the existing electron powder GDT. The GDT exhibiting a voltage class of 470 V was prepared, and its structure and surge characteristics were analyzed. The effects of gas pressure, aging time, and ambient temperature on the breakdown voltage of the graphene GDT were studied. The surge process of the graphene GDT was simulated using the 8/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu \text{s}$ </tex-math></inline-formula> impulse current generator, and the resistance ability of the graphene GDT against the surge was examined. Moreover, it was compared with the same type of commercial electron powder GDT. As indicated by the experimental results, a positive correlation was identified between the gas pressure and the dc breakdown voltage of the graphene GDT under a certain pressure. The effect of aging time and ambient temperature on dc breakdown voltage was limited. The breakdown voltage of the graphene GDT was first increased and then decreased with the increase in the number of surges. After 100 surges, the breakdown voltage of the graphene GDT stabilized at 350 V, whose stability was better than that of the electron powder GDT. The above-described analysis confirmed that graphene GDT exhibits better surge resistance ability.

Characteristics of negative and undular surges in an impounded channel

ABSTRACT Physical experiments were conducted in an impounded channel to study the propagation of negative surges advancing in still water and evolution of undular surges against an instantaneously varied flow. The results demonstrated that the initial wave height of a negative surge could be accurately predicted using the simple wave solution of the Saint–Venant equations. Moreover, the wave height evolution during surge propagation could be satisfactorily described using the solution by Ippen and Kulin. The main characteristics of an undular surge were strongly correlated to the surge Froude number and turbulent boundary layer development at the toe of the surge. However, the occurrence of wave breaking at the first wave crest was independent of the inflow conditions and was close to the breaking criterion for solitary waves. Furthermore, the present results indicated the largest turbulent Reynolds stress components beneath the wave crests of an undular surge.

Study of Parallel Compressor System and Real-Time Simulation Based on Modular Dynamic System Greitzer Modeling

The compressor system is widely used in aerospace, chemical industry, and other industrial fields. Modeling a compressor system is of great significance to the study of hydrodynamics and surge characteristics. Modular Dynamic System Greitzer (MDSG) modeling is a real-time model to simulate the dynamic response of complex compressor systems. An industrial air suction parallel compressor system with three compressors is modeled and simulated by the MDSG model, and the results are compared with the experimental results; the average error is less than 3%, which demonstrates that the MDSG model for the parallel compressor systems is reliable and accurate. Finally, a compression system with one valve and two valves is developed by the MDSG model, and the typical surge phenomena of two compression systems are dynamically simulated and discussed. The dynamic performance of the single compressor and parallel compressor systems can be described by the MDSG model.

Sensitivity of Heinrich-type ice-sheet surge characteristics to boundary forcing perturbations

Abstract. Heinrich-type ice-sheet surges are one of the prominent signals of glacial climate variability. They are characterised as abrupt, quasi-periodic episodes of ice-sheet instabilities during which large numbers of icebergs are released from the Laurentide ice sheet. The mechanisms controlling the timing and occurrence of Heinrich-type ice-sheet surges remain poorly constrained to this day. Here, we use a coupled ice sheet–solid Earth model to identify and quantify the importance of boundary forcing for the surge cycle length of Heinrich-type ice-sheet surges for two prominent ice streams of the Laurentide ice sheet – the land-terminating Mackenzie ice stream and the marine-terminating Hudson ice stream. Both ice streams show responses of similar magnitude to surface mass balance and geothermal heat flux perturbations, but Mackenzie ice stream is more sensitive to ice surface temperature perturbations, a fact likely caused by the warmer climate in this region. Ocean and sea-level forcing as well as different frequencies of the same forcing have a negligible effect on the surge cycle length. The simulations also highlight the fact that only a certain parameter space exists under which ice-sheet oscillations can be maintained. Transitioning from an oscillatory state to a persistent ice streaming state can result in an ice volume loss of up to 30 % for the respective ice stream drainage basin under otherwise constant climate conditions. We show that Mackenzie ice stream is susceptible to undergoing such a transition in response to all tested positive climate perturbations. This underlines the potential of the Mackenzie region to have contributed to prominent abrupt climate change events of the last deglaciation.

Field Survey of 2021 Typhoon Rai –Odette- in the Philippines

Typhoon Rai struck the Philippines on the 16th December 2021, damaging and inundating many coastal areas along the Visayas region of the country due to the high winds, storm surges and wind driven waves it generated. In order to understand the various damage mechanisms, the authors conducted a field survey to measure the storm surge heights at several locations in the provinces of Cebu and Bohol. As part of the survey, local residents were interviewed to understand the phenomena and survey the height reached by the storm surge. The maximum storm surge level measured were 2.54 m, 4.24 m and 4.06 m along the provinces of Cebu and Bohol. Finally, some interesting characteristics of the storm surge are summarised, and the lessons learnt in terms of disaster risk management are discussed

Monitoring debris flows in the Gadria catchment (eastern Italian Alps): Data and insights acquired from 2018 to 2020

This work analyses seven debris flows recorded between 2018 and 2020 in the Gadria instrumented catchment (South Tirol). We focus on three aspects not previously explored in this catchment: (i) the debris-flow transfer times between the headwaters and the outlet; (ii) the longitudinal variability of debris-flow velocity between the three downstream monitored cross-sections, and (iii) the characteristics of the secondary surges observed in three debris flows. In most cases, the mean velocity of the debris flow estimated from the upper to the lower channel reaches (for travel distance of 2155 m) is rather low, ranging between 1.9 and 3.9 m/s. This result could indicate a progressive slowing down, and possibly even temporary stops of debris flows along the path. Some variability in flow velocity was observed between two channel reaches in the lower part of the catchment (0.7 – 2.3 m/s in the upstream reach, and 1.4 – 4.7 in the downstream one). Regarding the secondary surges, these have been noted to occur superimposed on slow-moving slurry-type phases. The mean velocity of the secondary surges varied between 3.5 and 8.9 m/s, with an average value close to 6 m/s for all three events. Their regular shape, duration, and depth suggest that such surges were generated by flow instabilities, with no external forcing.

Study on the pressure fluctuation characteristics of the high-pressure common rail system with a distributor

In allusion to the problem of common rail pressure fluctuation when the high-pressure common rail system (CRS) using double rails, a numerical simulation model of a V-type 8-cylinder engine CRS was established by using AMESim software, and the suppression of pressure fluctuation with and without distributor was studied. The optimum structure dimension of the distributor with length of 100 mm and inner diameter of 9 mm was obtained by uniform design method. Then the pressure surge characteristics of CRS was researched. The research results showed that the installation of the distributor cut down the amplitude of the pressure oscillation of the common rail by more than 62.28%. Therefore, the designed distributor can effectively suppress the rail pressure fluctuation and improve CRS stability.

RCP8.5-projected changes in German Bight storm surge characteristics from regionalized ensemble simulations for the end of the twenty-first century

This study investigates climate-induced changes in height, frequency and duration of storm surges in the German Bight. The regionally coupled climate model system MPIOM-REMO with a focus on the North Sea has been utilized to dynamically downscale 30 members of the global climate model system MPI-ESM1.1-LR for the historical period 1950–2005 and a continuation until 2099 with the RCP8.5 scenario. Results of all members have been collected into the historical (1970–1999) and the rcp85 (2070–2099) data pools amounting to 900 years of the corresponding climate state. The global mean sea level rise was not considered. Nevertheless, the mean ensemble German Bight SSH trend amounts to about 13 ± 1 cm/century (PI control: 3 cm/century) due to adaptation of the ocean circulation to the changing climatic conditions. Storm surges were defined as SSH above mean high tidal water plus 1.5, 2.5, 3.5 m for “regular”, heavy, extreme storm surges, and then clustered to events. Our simulated storm surge events show a clear location-dependent increase in frequency (6–11%), median duration (4–24%), and average duration (9–20%) in the German Bight. Only along the central German Bight coast (Cuxhaven), longer lasting events gain more relevance. Heavy storm surge events show also a strong increase in frequency (7–34%) and average duration (10–22%). Maximum sea levels during storm events increase strongest and most significant along the northern German Bight and Danish coasts with more than 30 cm/century for the 60-year return period at Hörnum and 10–15 cm/century for shorter return periods. Levels of return periods shorter than a few years significantly increase everywhere along the southern German Bight coasts (around 5 cm/century for the 2-year return period). Highest SSH maxima do not change, and consequently, extreme storm surge events show hardly any response to climate change. Furthermore, our results indicate a shift of seasonality from the last to the first quarter of a year. As the main driver for the encountered alteration of German Bight storm surge characteristics, we identified a change in wind conditions with a pronounced increase of frequency of strong westerly winds.