Surge Conditions Research Articles

Conceptual design of sacrificial sub-systems: failure flow decision functions

This paper presents a method to conceptually model sacrificing non-critical sub-systems, or components, in a failure scenario to protect critical system functionality through a functional failure modeling technique. Understanding the potential benefits and drawbacks of choosing how a failure is directed in a system away from critical sub-systems and toward sub-systems that can be sacrificed to maintain core functionality can help system designers to design systems that are more likely to complete primary mission objectives despite failure events. Functional modeling techniques are often used during the early stage of conceptual design for complex systems to provide a better understanding of system architecture. A family of methods exists that focuses on the modeling of failure initiation and propagation within a functional model of a system. Modeling failure flow provides an opportunity to understand system failure propagation and inform system design iteration for improved survivability and robustness. Currently, the ability to model failure flow decision-making is missing from the family of function failure and flow methodologies. The failure flow decision function (FFDF) methodology presented in this paper enables system designers to model failure flow decision-making problems where functions and flows that are critical to system operation are protected through the sacrifice of less critical functions and flow exports. The sacrifice of less critical system functions and flows allows for mission critical functionality to be preserved, leading to a higher rate of mission objective completion. An example of FFDF application in a physical design is a non-critical peripheral piece of electrical hardware being sacrificed during an electrical surge condition to protect critical electronics necessary for the core functionality of the system. In this paper, a case study of the FFDF method is presented based on a Sojourner class Mars Exploration Rover (MER) platform.

Experimental Investigation and Modeling of Surge in a Multistage Compressor

Abstract Surge is recognized as the most significant flow instability of the compressor as it strongly influences the performance causing pulsations of pressure that generate reversal flow. This phenomenon obviously has to be taken into consideration when designing the compression piping system, upstream and downstream of the compressor. Therefore, the prediction of the transient response of the compressor and the occurrence of surge, with its characteristic oscillations, is a crucial aspect which has acquired high consideration in literature. This paper deals with (i) the experimental analysis of the unstable response of a multistage compressor during surge conditions and ii) the development and tuning of a nonlinear model for simulating the dynamic behavior of the compression system. The dynamic model is implemented in Matlab®/Simulink® environment and developed by means of a general bond graph approach which leads to a highly modular lumped parameter structure.

In silico investigation of cornea deformation during irrigation/aspiration in phacoemulsification in cataract surgery

To analyze the stress, strain and displacement of the human cornea under the action of negative intraocular pressure, which occurs during phacoemulsification in cataract surgery, a multidisciplinary approach including biomedical engineering, solid mechanics, numerical analysis, and fluid dynamics was used. Fluid-structure interaction method was implemented using 3-dimensional nonlinear finite element analysis of cornea tissue in conjunction with CFD analysis of anterior chamber fluid flow to study the deformation of the cornea under negative gage pressure during irrigation and aspiration (I/A). The computational model of the eye includes both cornea and sclera. To increase the accuracy of the computational model, both cornea hyperelasticity and thickness variation were included in the analysis. The simulation was performed for both coaxial and bimanual I/A systems with different flow rates. The cornea deformations for various flow rates were evaluated, and the possibility of an unstable anterior chamber was assessed. The results show that the critical pressure in the anterior chamber, which may lead to the surge condition due to buckling of the cornea, is sub-ambient (below zero gauge pressure). Anterior chamber instability occurs at higher volume flow rates for coaxial I/A system compared with that for bimanual system, but the deformation of the cornea is more intense for the bimanual system.

Improved control strategy for fixed-speed compressors in parallel system

Control systems for parallel compressor trains consist of a discharge pressure, anti-surge and load-sharing regulation. Control of a parallel compressor system has proven to be challenging because the control targets usually exhibit control interactions between the different control loops. To decouple this control interference, Mitsubishi Heavy Industries has developed an advanced feed-forward control structure for parallel fixed-speed compressor systems. However, operation in the presence of an unpredictable disturbance presents a few technical challenges for this structure. Most of these problems result in poor load sharing and then operation in the recycle mode in order to protect the system from surge conditions. Moreover, an anti-surge control delay occurs when operating under a low load. To overcome these problems, an improved control structure that incorporates an additional discharge flow controller signal and a nonlinear signal calculator for anti-surge valve control is proposed. To demonstrate the benefits of the proposed method, the control performance of the conventional control structure is compared to that of the proposed control structure. The target process is a parallel fixed-speed compressor system for a fuel gas supply plant. The improved control structure allows for desired load-sharing control, which is not possible with the conventional control structure. The improved control structure manages to exit the anti-surge control region, whereas the conventional control structure activates the interlock system.

Wave runup on a surging vertical cylinder in regular waves

The wave runup caused by a vertical cylinder surging in regular waves is studied both experimentally and numerically. The so-called DualSPHysics Smoothed Particle Hydrodynamics (SPH) code is used for the 3-D numerical modelling. A wide range of cylinder sizes and wave conditions is investigated with results comparing favourably between the experimental and SPH model under both fixed and forced-surge conditions. The experimental and SPH results are further used to predict the maximum runup amplification, in particular the ratio of the runup caused by the surging cylinder to that of the fixed, over the phase difference between the incident wave and surge motion. This maximum runup ratio has been analysed for its dependence on factors such as wave steepness, wave scattering and surge amplitude. An empirical equation is proposed for predicting the maximum runup ratio from known incident wave and surge conditions. Comparison with results from linear solvers suggests that the linear solvers under-predict the full nonlinear runup by a factor of 1.3–1.5.

Vegetation-wave interactions in salt marshes under storm surge conditions

Vegetation-wave interactions are critical in determining the capacity of coastal salt marshes to reduce wave energy (wave dissipation), enhance sedimentation and protect the shoreline from erosion. While vegetation-induced wave dissipation is increasingly recognized in low wave energy environments, little is known about: (i) the effect of vegetation on wave dissipation during storms when wave heights and water levels are highest; and (ii) the ability of different plant species to dissipate waves and to maintain their integrity under storm surge conditions. Experiments undertaken in one of the world’s largest wave flumes allowed, for the first time, the study of vegetation-wave interactions at near-field scale, under wave heights ranging from 0.1–0.9m (corresponding to orbital velocities of 2–91cms−1) and water depths up to 2m, in canopies of two typical NW European salt marsh grasses: Puccinellia maritima (Puccinellia) and Elymus athericus (Elymus). Results indicate that plant flexibility and height, as well as wave conditions and water depth, play an important role in determining how salt marsh vegetation interacts with waves. Under medium conditions (orbital velocity 42–63cms−1), the effect of Puccinellia and Elymus on wave orbital velocities varied with water depth and wave period. Under high water levels (2m) and long wave periods (4.1s), within the flexible, low-growing Puccinellia canopy orbital velocity was reduced by 35% while in the more rigid, tall Elymus canopy deflection and folding of stems occurred and no significant effect on orbital velocity was found. Under low water levels (1m) and short wave periods (2.9s) by contrast, Elymus reduced near-bed velocity more than Puccinellia. Under high orbital velocities (≥74cms−1), flattening of the canopy and an increase of orbital velocity was observed for both Puccinellia and Elymus. Stem folding and breakage in Elymus at a threshold orbital velocity≥42cms−1 coincided with a levelling-off in the marsh wave dissipation capacity, while Puccinellia survived even extreme wave forces without physical damage. These findings suggest a species-specific control of wave dissipation by salt marshes which can potentially inform predictions of the wave dissipation capacity of marshes and their resilience to storm surge conditions.

Effects of wave-induced forcing on a circulation model of the North Sea

The effect of wind waves on water level and currents during two storms in the North Sea is investigated using a high-resolution Nucleus for European Modelling of the Ocean (NEMO) model forced with fluxes and fields from a high-resolution wave model. The additional terms accounting for wave-current interaction that are considered in this study are the Stokes-Coriolis force, the sea-state-dependent energy and momentum fluxes. The individual and collective role of these processes is quantified and the results are compared with a control run without wave effects as well as against current and water-level measurements from coastal stations. We find a better agreement with observations when the circulation model is forced by sea-state-dependent fluxes, especially in extreme events. The two extreme events, the storm Christian (25–27 October 2013), and about a month later, the storm Xaver (5–7 December 2013), induce different wave and surge conditions over the North Sea. Including the wave effects in the circulation model for the storm Xaver raises the modelled surge by more than 40 cm compared with the control run in the German Bight area. For the storm Christian, a difference of 20–30 cm in the surge level between the wave-forced and the stand-alone ocean model is found over the whole southern part of the North Sea. Moreover, the modelled vertical velocity profile fits the observations very well when the wave forcing is accounted for. The contribution of wave-induced forcing has been quantified indicating that this represents an important mechanism for improving water-level and current predictions.

Global reconstructed daily surge levels from the 20th Century Reanalysis (1871–2010)

Studying the effect of global patterns of wind and pressure gradients on the sea level variation (storm surge) is a key issue in understanding the recent climate change effect on the dynamical state of the ocean.The analysis of the spatial and temporal variability of storm surges from observations is a difficult task to accomplish since observations are not homogeneous in time, scarce in space, and moreover, their temporal coverage is limited. A recent global surge database developed by AVISO (DAC, Dynamic Atmospheric Correction) fulfilled the lack of data in terms of spatial coverage, but not regarding time extent, since it only includes the last two decades (1992–2014).In this work, we use the 20th Century Reanalysis V2 (20CR), which spans the years 1871 to 2010, to statistically reconstruct daily maximum surge levels at a global scale. A multivariate linear regression model is fitted between daily mean ERA-interim sea level pressure fields and daily maximum surge levels from DAC. Following, the statistical model is used to reconstruct daily surges using mean sea level pressure fields from 20CR. The verification of the statistical model shows good agreements between DAC levels and the reconstructed surge levels from the 20CR. The validation of the reconstructed surge with tide gauges, distributed throughout the domain, shows good accuracy both in terms of high correlations and small errors. A time series comparison is also depicted at specific tide gauges for the beginning of the 20th century, showing a high concordance.Therefore, this work provides to the scientific community, a daily database of maximum surge levels; which correspond to an extension of the DAC database, from 1871 to 2010. This database can be used to improve the knowledge on historical storm surge conditions, allowing the study of their temporal and spatial variability.

인버터 서지와 온도 스트레스 하에서 Magnet Wire 절연 수명평가

Coil specimen was prepared by coating a copper wire with two varnish thin layers: the first was polyamideimide (PAI)/nanosilica (5 wt%) varnish and the second was anti-corona PAI/nanosilica (15 wt%) varnish. Insulation breakdown voltage was investigated under inverter surge condition at <TEX>$20^{\circ}C$</TEX>, <TEX>$70^{\circ}C$</TEX>, <TEX>$100^{\circ}C$</TEX>, <TEX>$150^{\circ}C$</TEX>, <TEX>$200^{\circ}C$</TEX>, <TEX>$250^{\circ}C$</TEX>, respectively. The insulation lifetime of the two layered coil was tens of times longer than that of original PAI coil. And the insulation lifetime decreased with increasing ambient temperature because there was weak binding strength between copper and varnish layer.

Characterization of surge superposition following 2-stage load rejection in hydroelectric power plant

When calculating the maximum upsurge in surge tank due to load rejection in a hydroelectric power plant, it has been natural and customary to believe that the maximum surge amplitude occurs in simultaneous load rejection of all units at 100% load. As 2-stage load rejection (2-stage LR), involving a step-wise reduction in load, is not considered since it is assumed to produce less severe surge conditions. This study formulates the surge superposition associated with 2-stage LR and shows, surprisingly but significantly, that such 2-stage LR sometimes produces more severe surge conditions than simultaneous and complete load rejection (SCLR). The results indicate that this unexpected phenomenon is ascribable to the resistant effect of throttled surge tank, whose increase will lead to a greater difference in the maximum upsurges between 2-stage LR and SCLR conditions. Different time intervals during 2-stage LR correspond to different maximum upsurges. The analytical formula predicting the worst interval time is derived exactly and verified with two numerical cases.

Axial-Flow Compressor Performance Prediction in Design and Off-Design Conditions through 1-D and 3-D Modeling and Experimental Study

In this study, the main objective is to develop a one dimensional model to predict design and off design performance of an operational axial flow compressor by considering the whole gas turbine assembly. The design and off-design performance of a single stage axial compressor are predicted through 1D and 3D modeling. In one dimensional model the mass, momentum and energy conservation equations and ideal gas equation of state are solved in mean line at three axial stations including rotor inlet, rotor outlet and stator outlet. The total to total efficiency and pressure ratio are forecasted using the compressor geometry, inlet stagnation temperature and stagnation pressure, the mass flow rate and the rotational speed of the rotor, and the available empirical correlation predicting the losses. By changing the mass flow rate while the rotational speed is fixed, characteristic curves of the compressor are obtained. The 3D modeling is accomplished with CFD method to verify one dimensional code at non-running line conditions. By defining the three-dimensional geometry of the compressor and the boundary conditions coinciding with one dimensional model for the numerical solver, axial compressor behavior is predicted for various mass flow rates in different rotational speeds. Experimental data are obtained from tests of the axial compressor of a gas turbine engine in Sharif University gas turbine laboratory and consequently the running line is attained. As a result, the two important extremities of compressor performance including surge and choking conditions are obtained through 1D and 3D modeling. Moreover, by comparing the results of one-dimensional and three-dimensional models with experimental results, good agreement is observed. The maximum differences of pressure ratio and isentropic efficiency of one dimensional modeling with experimental results are 2.1 and 3.4 percent, respectively.

Medical readiness: evaluating the robustness of medical clinic staffing solutions

Medical readiness requires Department of Defense medical clinics to be robust to changes in patient demand. Minor fluctuations in patient demand occur on a regular basis, but major increases can also occur. Major demand increases can result from a number of occurrences, including mass military deployments, medical incidents, outbreaks, and overflow from Veterans’ Affairs clinics. This research evaluates a system of clinics at Wright-Patterson Air Force Base in order to determine its ability to handle a 200% surge in patient demand. In addition, this study evaluates the relative effectiveness of six different staffing mix options to minimize patient wait times, also under the surge demand conditions. This evaluation is conducted using discrete-event simulation to estimate patient wait times and includes a sensitivity analysis of the increased patient demand, as well as a cost–benefit analysis to determine the most cost-effective alternative scenario. The study finds that adjustments to staffing mix enable cost savings while meeting current demands. In addition, the study finds that adjusting the staffing mix will not have a negative impact on patient wait time in the surge conditions, relative to the current staffing mix.

Improving understanding of the spatial dimensions of biophysical change in atoll island countries and implications for island communities: A Marshall Islands’ case study

Using coarse-scale approaches, existing national assessments of vulnerability and adaptation highlight physical land instability as a major threat to atoll island nationhood. However, such evaluations are bereft of detailed, ground-truthed analyses of the physical impacts of climatic change on reef islands, treating islands as homogenous in both biophysical and social characteristics. The distinct geomorphic context of two proximate reef islands (Jeh and Jabat) in the Marshall Islands was examined through conventional land survey techniques. A template documenting the nuances in island topography was used to evaluate simple inundation scenarios, reflecting current and future sea-level changes under storm surge conditions. The variations in local scale community exposure to inundation were discernible. The study highlights the importance of treating coarse-scale assessments with caution and underscores the need for continued commitment to resolving variations in community experiences to environmental change. Notions of risk and exposure are complex and embedded in both the biophysical and social contexts of each island community. Despite a number of targeted urban vulnerability studies in the Pacific there remains a need for efforts to document localised differences in experience to better inform contemporary adaptation efforts.

Artificial sandbanks in the Elbe Estuary mouth: a method for surge mitigation?

Within the framework of different EU framework research projects (THESEUS and TIDE), investigations of the efficiency of artificial sandbanks in the mouth of the Elbe estuary for the mitigation of tidal energy and a better storm surge protection were carried out. The efficiency of the artificial sandbanks was analysed by means of two- and three-dimensional hydro- and morphodynamic models. The models calculate the water level and current velocities as well as the transport of dissolved constituents under mean and storm surge conditions. To allow the investigation of the effects of the artificial sandbanks on the water level and currents in the inner estuary, a high spatial grid resolution was used. Overall results of the investigations are presented and an outlook on how those measures can contribute to innovative risk mitigation is shown.

P021: Impact of emergency department surge and end of shift on patient workup and treatment prior to referral to internal medicine

Introduction: The goal of this study was to determine if emergency department (ED) surge and end of shift assessment of patients affect the extent of diagnostic tests, therapeutic interventions performed and accuracy of diagnosis prior to referral of patients to Internal Medicine as well as the impact on patient outcomes. Methods: This study was a health records review of consecutive patients referred to the internal medicine service with an ED diagnosis of heart failure, COPD or sepsis, at two tertiary care EDs. We developed a scoring system in consultation with senior emergency and internal medicine physicians to uniformly assess the treatments and investigations performed for patients diagnosed in the ED with heart failure, COPD or sepsis. These scores were then correlated with surge levels and time of day at patient assessment and disposition. Rate of admission and diagnosis disagreements were also assessed. Results: We included 308 patients (101 with heart failure, 101 with COPD, 106 with sepsis). Comparing middle of shift to end of shift, the overall weighted mean scores were 92.2% vs. 91.7% for investigations and 73.5% vs. 70.0% for treatments. Comparing low to high surge times, the overall weighted mean scores were 89.9% vs. 92.6% for investigations and 68.6% vs. 71.7% for treatments. Evaluating each condition separately for investigations and treatments according to time of shift or surge conditions, there were no consistent differences in scores. We found overall high admission rates (93.1 % for heart failure, 91.1% for COPD, 96.2% for sepsis patients), and low rates of diagnosis disagreement (4.0 % heart failure, 10.9% COPD, 8.5% sepsis). Conclusion: We found that surge levels and end of shift did not impact the extent of investigations and treatments provided to patients diagnosed in the emergency department with heart failure, COPD or sepsis and referred to internal medicine. Admission rates for the patients referred were above 90% and there were very few diagnosis disagreements or diversion to alternate service by internal medicine. We believe this supports the emergency physician's ability to adapt to time and surge constraints, particularly in the context of commonly encountered conditions.

Shoreline change rate and erosion risk assessment along the Trou Aux Biches–Mont Choisy beach on the northwest coast of Mauritius using GIS-DSAS technique

The present study investigates the rate of shoreline change and erosion risk along the Trou aux Biches–Mont Choisy beach in the northwest coast of Mauritius using digital shoreline analysis system (DSAS). In this analysis, the long-term shoreline change rate and coastal erosion and accretion pattern are estimated along the coastal stretch using multi-temporal aerial photographs and high resolution satellite images for the past 45 years (1967–2012). The shoreline change rate and erosion/accretion pattern at each transects are estimated by five statistical parameters functionalized in DSAS 4.5 software such as end point rate (EPR), shoreline change envelop (SCE), net shoreline movement (NSM), linear regression rate (LRR), and least median of squares (LMS). The measurement of shoreline change rate and coastal erosion and accretion pattern has been described for three segments namely (1) North–North–West (NNW) to South–South–East (SSE); (2) North–East (NE) to South–West (SW); (3) North–North–East (NNE) to South–South–West (SSW) based on the coastal configuration. The analysis reveals that the severe erosion risk (−1.75 to −0.03 m/year) was noticed between transects 41 and 61 in NE–SW segments and moderate erosion risk (−1.09 to −0.18 m/year) between transects 62 and 95 of the NNE–SSW segments. The NNW–SSE segment shows low erosion risk with an EPR value of −0.55 to −0.05 m/year. The values of shoreline change rate of these transects indicate the occurrence of severe erosion along the coastal area over the periods of 1967–2012. However, the coastal segment in NNW–SSE configuration faces least erosion rate and the protective coral reefs reduce the wave energy action which leads to the formation of sustainable coast in the area. Moreover, poor set back and management activities with reference to high energetic waves, storm surge and cyclonic conditions produce direct impacts on the coastal morphology and degradation of coral reef ecosystem. The shoreline change studies through integrated remote sensing and GIS technology is considered of paramount importance for accurately focusing on planning, management and coastal intervention in long-term purpose.

Removal of electrocardiogram distortion in portable high-power medical device

In this study, we propose a method to remove bio-signal distortions generated when the power is at transient condition in a high-powered portable medical device. To verify the method, three units were designed that consists of a main control unit, bio-signal measurement unit, and power unit. Also, each units were separated with galvanic isolation. For stable operation at the surge condition, the power unit was composed using push-pull converter topology. The design has been examined in both transient and steady state of the operating conditions. The experiment result shows that galvanic isolation between each units was efficient in high-powered potable medical device.

Dynamic Time to Surge Computation for Electric Driven Gas Compressors during Voltage Dips

This paper investigates the influence of voltage dips on large electric driven gas compressors (EDC) considering a typical application in the oil and gas industry. Voltage or power dips are electric disturbances encountered in EDC which are mainly caused by faults in the electrical grid and might last for durations up to 150 ms. For gas compression applications, the loss of driver torque often puts the gas compression process at risk of surge conditions, which is a safety critical constraint. The critical nature of the present problem and the fast dynamics involved, pose challenging requirements for the control and safety systems of the gas compressor and the variable-speed drive system. The main focus of the present paper is the dynamic computation of the time to surge using online information of the estimated motor torque and a process model to predict the future behavior of the compression system. The time to surge can then be used for ride-through or shut-down decisions of the complete system, as well as for manipulating safety valves, e.g. the anti-surge valve. The fulfillment of strict real-time requirements and their direct implications on the complexity of the chosen prediction model and the implementation of the algorithm on an embedded system are also addressed in this article. As an industrial case study, the algorithm is applied to a voltage dip situation using high fidelity simulation data of a compression station.

Empirical wave run-up formula for wave, storm surge and berm width

An empirical model to predict wave run-up on beaches considering storm wave and surge conditions and berm widths (dry beach) has been derived through a synthetic data set generated from a one-dimensional Boussinesq wave model. The new run-up equation is expressed as a function of a new Iribarren number composed of three regions: the foreshore, the berm or dry beach width, and the dune. The dissipative effect of the berm is included as a reduction factor expressed as a function of the berm width normalized by the offshore wavelength. The equation is relatively simple but is shown to be applicable for a fairly wide variety of berm widths and storm wave conditions associated with extreme events such as hurricanes, and it is shown to be an improvement over existing empirical run-up models that do not consider the berm width explicitly. In addition, the new parameterization of the Iribarren number considering the three regions and the berm width reduction factor are shown to improve other empirical models.

Salt marsh surface survives true‐to‐scale simulated storm surges

AbstractA full‐scale controlled experiment was conducted on an excavated and re‐assembled coastal wetland surface, typical of floristically diverse northwest European saltmarsh. The experiment was undertaken with true‐to‐scale water depths and waves in a large wave flume, in order to assess the impact of storm surge conditions on marsh surface soils, initially with three different plant species and then when this marsh canopy had been mowed. The data presented suggests a high bio‐geomorphological resilience of salt marshes to vertical sediment removal, with less than 0.6 cm average vertical lowering in response to a sequence of simulated storm surge conditions. Both organic matter content and plant species exerted an important influence on both the variability and degree of soil surface stability, with surfaces covered by a flattened canopy of the salt marsh grass Puccinellia experiencing a lower and less variable elevation loss than those characterized by Elymus or Atriplex that exhibited considerable physical damage through stem folding and breakage. Copyright © 2015 John Wiley &amp; Sons, Ltd.