Multiple Surges Research Articles

Numerical modelling of debris surges based on shallow-water and homogeneous material approximations

The objective of this contribution is to analyse the formation of debris waves in natural channels. Numerical simulations are carried out with a ID code based on shallow-water equations and on the weighted averaged flux method. The numerical code represents the incised channel geometry with a power-law relation between local width and flow depth and accounts for all source terms in the momentum equation. The debris mixture is treated as a homogeneous fluid over a fixed bottom, whose rheological behaviour alternatively follows Herschel-BulkJey, Bingham or generalised visco-plastic models. The code is applied to real debris flow events that consisted of a single wave and multiple surges, in particular in the Illgraben catchment (Switzerland) and in the Cortina d’Ampezzo area (Dolomites). Numerical results are presented and compared with available flow depth registrations. A statistical analysis of debris waves shows that a good representation of wave statistics can be obtained with a proper calibration of rheological parameters. Wave propagation in time along the channel is investigated to verify if overtaking phenomena like in water roll waves do develop. Finally, an original interpretation for the formation of finite amplitude waves in a transient unstable flow is provided, based both on field data and numerical simulations.

Numerical modelling of debris surges based on shallow-water and homogeneous material approximations

The objective of this contribution is to analyse the formation of debris waves in natural channels. Numerical simulations are carried out with a 1D code based on shallow-water equations and on the weighted averaged flux method. The numerical code represents the incised channel geometry with a power-law relation between local width and flow depth and accounts for all source terms in the momentum equation. The debris mixture is treated as a homogeneous fluid over a fixed bottom, whose rheological behaviour alternatively follows Herschel-Bulkley, Bingham or generalised visco-plastic models. The code is applied to real debris flow events that consisted of a single wave and multiple surges, in particular in the Illgraben catchment (Switzerland) and in the Cortina d'Ampezzo area (Dolomites). Numerical results are presented and compared with available flow depth registrations. A statistical analysis of debris waves shows that a good representation of wave statistics can be obtained with a proper calibration of r...

A complex Quaternary ignimbrite-forming phonolitic eruption: the Poris Member of the Diego Hernández Formation (Tenerife, Canary Islands)

The Poris Member (0.28 Ma) of the Diego Hernández Formation (Tenerife, Canary Islands) is a widespread succession of plinian fall, surge and non-welded ignimbrite deposits. It was erupted from the northeastern sector of the multicyclic Las Cañadas Caldera, the summit caldera complex of the Las Cañadas Edifice. We present new stratigraphic data which allow the evolution of the eruption to be divided into six main stages: (1) an initial surge-producing phreatomagmatic phase. (2) Generation of a buoyant plinian column culminating in vent-wall collapse and temporary vent blockage. (3) A resumption of phreatomagmatic activity, producing accretionary lapilli-bearing ash surges and a phreatomagmatic ignimbrite. (4) Sustained column collapse, resulting in the progressive aggradation of a complex, compositionally layered ignimbrite sequence. (5) A late plinian phase marked by sharp chemical zonation. (6) Final vent destruction and the generation of multiple surges and pyroclastic flows. Volume calculations indicate a total erupted volume in the order of 13–14 km 3 (3–4 km 3 dense rock equivalent), which together with facies and lithic analysis implies that a small-scale caldera collapse occurred, contributing to the incremental enlargement of the Las Cañadas Caldera. The geochemistry and mingling inter-relationships of four magmatic endmembers, ranging from alkaline mafic to evolved phonolitic liquids, indicate that two magma chambers fed stages 4 and 5 of the eruption sequence. The eruption was triggered when mafic magma intruded the two-chamber system.

Study of Surges in a Large-diameter Subteranean Diversion Channel with Multiple Surge Tanks

Study of Surges in a Large-diameter Subteranean Diversion Channel with Multiple Surge Tanks

Stall Inception and Development in an Axial Flow Aeroengine

This paper describes the phenomenon of stall and surge in an axial flow aeroengine using fast response static pressure measurements from the compressor of a Rolls-Royce VIPER engine. It details the growth of flow instability at various speeds, from a small zone of stalled fluid involving only a few blades into the violent surge motion of the entire machine. Various observations from earlier theoretical and compressor rig results are confirmed by these new engine measurements. The main findings are as follows: (1) The point of stall inception moves rearward as engine speed increases, and is shown to be simply related to the axial matching of the compressor. (2) The final unstable operation of the machine can be divided into rotating stall at low speed and surge or multiple surge at high speed. (3) The inception process is independent of whether the final unstable operation is rotating stall or multiple surge. (4) Stall/surge always starts as a circumferentially small flow disturbance, rotating around the annulus at some fraction of rotor speed.

Gut hormones and 'minimal enteral feeding'.

Previously we have identified multiple surges in plasma concentrations of gut hormones postnatally in enterally fed term and preterm infants. In this study on 104 preterm infants we have shown that such surges are induced after ingestion of very small quantities of human milk. Whereas 6-day-old exclusively parenterally fed infants showed no postnatal elevation in enteroglucagon, gastrin, GIP, motilin and neurotensin, infants recovering from hyaline membrane disease who had received restricted enteral nutrition had similar hormone surges to those seen in well infants on full enteral feeds. Significant elevations in enteroglucagon, gastrin and GIP occurred after a cumulative mean enteral feed volume since birth of only 24 ml (12 ml/kg body weight) had been consumed and after a mean total intake of 96 ml (50 ml/kg) the response was maximal. Greater feed volumes were required to produce a neurotensin or motilin surge, but even these volumes were substantially lower than those required for full enteral feeding. In view of the proposed roles of gut hormones in the adaptation to extrauterine nutrition these data have implications for mammalian biology and raise the possibility that 'minimal enteral feeding' might have a clinical therapeutic role in infants undergoing prolonged parenteral nutrition.

Longitudinal study of the surge of gonadotropins induced by exogenous hormones in prepuberal gilts.

The transition at puberty to adult hormonal patterns has been hypothesized to involve a shift in the sensitivity of the hypothalamic-hypophysial axis to hormonal stimulation. Prepuberal gilts were treated with GnRH or estradiol-benzoate (EB) to compare responsiveness of the pituitary at 40, 80, 120, and 160 days of age. Mean BW at each was 15.6, 36.3, 56.4, and 70.7 kg, respectively. Gilts were injected with GnRH (625 ng/kg; iv) or EB (600 micrograms/kg; im) or with vehicles. Blood samples were collected at 10-min intervals for 3 h after injection of GnRH or vehicle or 4-h intervals for 96 h after injection with EB or vehicle. Plasma concentrations of LH and FSH were measured by RIA, and data were analyzed by a general linear model for split plot design. Pretreatment basal concentrations of LH and FSH decreased between 40 and 160 days of age from 1.7 to less than 0.7 ng/ml and from 29.9-4.1 ng/ml, respectively. GnRH-induced surges of LH became more synchronous relative to time of injection and decreased in maximum concentration with age. In the youngest gilts, multiple surges of LH were released after a single injection of GnRH. The magnitude of the initial release of LH decreased with age from 5.6-2.7 ng/ml. Gilts treated with EB had two or more surges of LH at all ages. However, the concentration of the surge was greatest and occurred synchronously 12 h earlier in the 160-day-old gilts than at other ages. Therefore, sensitivity to EB was enhanced both in response time and amount of LH released. Concentrations of FSH were highly variable among gilts, and treatment with GnRH or EB induced an adult-like release of gonadotropins only at 160 days of age. Maturation of the surge mechanism involved at least two distinct alterations for LH. First there was a reduction in the amount of LH released in response to GnRH after day 40. Second an increase in the precision (timing) and magnitude of the surge of LH in response to EB was seen as gilts approached puberty.

Experiments on multiple surges pressure transients

A simple experimental apparatus has been constructed to study the multiple surges pressure transients from the pressurizer of nuclear reactors. Good agreement has been obtained between the semi-empirical model and the experimental results.

A New Electrical Research Laboratory

The outstanding features of this laboratory are the power and surge testing facilities. Power laboratory energy for testing is supplied at 138 kv from a high-capacity utility system. A main transformer designed for short-circuit testing duty provides test voltages ranging from 1.5 kv for 18 kv and currents up to 25,000 amperes rms. Use of additional transformers widens this range. Test initiation can be timed accurately for any desired point on the 60-cycle voltage wave. The power test bus is so arranged that connections can be extended to energize and test full-scale line construction on the unimproved acreage of the laboratory site. The surge laboratory is equipped with five surge generators capable of producing high-voltage surges up to 3,000,000 volts and high-current surges of over 100,000 amperes. The surge generators can be used individually or together for multiple surge phenomena. For combined power and surge testing of lightning protective equipment, surges of predetermined characteristics are applied to equipment energized from the power laboratory test bus. The mechanical laboratory includes universal testing machines equipped with load-deflection graphic recorders, and facilities for full-scale testing of line hardware and structures. Created for the development of electrical and mechanical products for both electric power utility and wire communication systems, the laboratory is an integrated operation, with research, development, building of prototypes, and testing, all at one location.

The recovery-voltage analyzer for determination of circuit recovery characteristics

Widespread interest in transient recovery voltage phenomena has led to the development of a device for determining the recovery characteristics of circuits and apparatus. The problem was solved by making use of the multiple surge testing technique which, in turn, involves the use of a low voltage repeating type surge generator. This paper describes the method and necessary equipment and indicates the range of conditions to which they may be applied. Demonstration tests on miniature and full scale circuits are also shown.