Section Of Conduit Research Articles

Influence of Local Gas Sources with Variable Density and Momentum on the Flow of the Medium in the Conduit

In this article, the analysis of mechanical energy changes in a gas medium flow with stable and variable density was presented. To determine the energy losses, the various sources of momentum and mass were used, which had an influence on air flow through the conduit in the system without heat exchange with the environment. The occurrence of varying density gas flow in the conduit (caused by local inflow of mass and momentum) in inclined pipes generates a natural depression–internal mechanical energy. The local momentum sources can facilitate or hinder the gas flow through the conduit. This phenomenon often appears in the network of underground mine workings and in ventilation and air conditioning installations. The characteristic for gas flow through a pipe or mining excavation is the equivalent aerodynamic resistance, the value of which is influenced by the mass and momentum of local sources. This value determines the facilitation or difficulty in gas transport through a section of conduit in relation to the mass stream of the medium. In this article, the dependency of mass flow and gas momentum with different densities on the value of the gas medium flow resistance in the conduit was analyzed. On the basis of the obtained results, the loss of mechanical energy and energy efficiency of flows were determined. In this work, two cases of fan work in suction and blowing modes were analyzed. For these examples, a gas inflow with three different mass streams, a density higher than the main stream density, and with a zero momentum value for this stream was modeled. Ten cases of mass inflow sources were considered. The results of the gas mass flow calculation through the fan m˙w and gas m˙0 and the coefficient of transport efficiency are graphically presented in the paper.

Multi-parametric characterization of explosive activity at Batu Tara Volcano (Flores Sea, Indonesia)

Batu Tara is an active but poorly studied volcano located in the Lesser Sunda Archipelago (Indonesia). Its last known long-lasting eruptive phase, dating 2006–2015, was characterised by frequent short-lived explosions, similar in style and magnitude to those of the well monitored Stromboli volcano (Italy). On September 2014, we collected high-frequency multi-parametric measurements of the ongoing explosive activity to investigate the dynamics of intermediate-size volcanic explosions. We acquired synchronized acoustic, thermal and visible high-speed imaging data, and parameterized different spatial and temporal properties of each explosive event: i) maximum height and ejection velocity of bombs and plumes, ii) duration, iii) amplitude of acoustic and thermal transients, iv) acoustic and thermal energy, v) spectral features of the acoustic signals. The latter ones justify the assumption of a pipe resonance of the uppermost conduit section, likely in response to the arrival of over-pressurized gas at the free magma surface. The variability of the investigated parameters agrees with previous observations of intermediate-size explosions at other volcanoes, reflecting the complexity of the related source processes.

Step-like rising and falling of a breakthrough curve observed at a karst spring

Spring breakthrough curves induced by conventional advection and dispersion often present a gentle (smooth) change of concentration with time. We investigated an electrical-conductivity breakthrough curve which originated from a chemical release into the aquifer matrix and was measured in June 2007 at Qinglondong Spring, southwest China. The curve presented abrupt rising and falling limbs. Modeling efforts were focused on the migration of the contaminants from the conduit wall to the spring. The conduit production segment was defined to be the conduit section where the chemical plume entered the conduit from aquifer fractures. The first model assumed that the time variance of the plume front reaching the conduit wall was much shorter than transport time over the conduit production segment. The model yielded a decrease of spring discharge which was inconsistent with the observed increase with time. In the second model, the above assumption was relaxed, and wall contaminant flux was inverted as function of downstream distance and time. The observed abrupt rising and falling in the breakthrough curve were interpreted as: (1) Taylor dispersion was too small to identify for a short conduit; (2) seepage from the fractures to the conduit was monodirectional and diluting.

Explicit Solution for Critical Depth in Closed Conduits Flowing Partly Full

Critical depth is an essential parameter for the design, operation, and maintenance of conduits. Circular, arched, and egg-shaped sections are often used in non-pressure conduits in hydraulic engineering, irrigation, and sewerage works. However, equations governing the critical depth in various sections are complicated implicit transcendental equations. The function model is established for the geometric features of multiple sections using the mathematical transform method and while considering non-dimensional parameters. Then, revised PSO algorithms are implemented in MATLAB, and the right solution’s formula for the critical depths in various non-pressure conduit sections is established through optimization. The error analysis results show that the established formula has broad applicability. The maximum relative errors of the formula for critical depths are less than 0.182%, 0.0629%, and 0.170% in circular, arched, and egg-shaped sections, respectively, which are more accurate than those of existing formulas; the form of the formula proposed in this work is also more compact than that of the existing formulas. The results of this research may be useful in design, operation, and maintenance in conduit engineering.

Use of Suspended Plastic Conduit Arrays during Brown Trout and Rainbow Trout Rearing in Circular Tanks

AbstractEnvironmental enrichment is the modification of otherwise sterile hatchery rearing units to provide structural complexity. We investigated the use of an array of suspended plastic conduit sections as enrichment in large circular tanks during two experiments. Brown Trout Salmo trutta and Rainbow Trout Oncorhynchus mykiss were reared for 126 and 61 d, respectively, in covered, 3.63‐m‐diameter circular tanks that were either void of any structure or enriched with a suspended array of twenty 0.94‐m‐long sections of plastic conduit. Total tank weight gain and feed conversion ratio were significantly improved for both Brown Trout and Rainbow Trout reared with suspended conduit as enrichment compared to unenriched tanks. Enrichment did not significantly affect individual fish length, weight, or condition factor in either experiment, likely because of small sample sizes. The suspended array did not interfere with tank hydraulic self‐cleaning. Based on the results of this study, the use of vertically suspended enrichment structures in circular tanks is recommended to improve trout rearing efficiencies.

Effect of rotational speed on the hydraulic performance for flow conduits of shaft extension tubular pumping system

In order to investigate the effect of rotational speed on hydraulic performance of inlet and outlet conduits for S-shaped shaft extension tubular pumping system, the three dimensional steady turbulent flow in pumping system was simulated using computational fluid dynamics technology. The experiment results are compared with the CFD results. The hydraulic performance parameters of inlet and outlet conduits were analyzed quantitatively considering the hydraulic interaction of conduits and impeller. The change trend of relationship curves between hydraulic loss ratio value and flow rate coefficient is same in different rotational speed. With the increase of flow rate coefficient, the hydraulic loss ratio value increases gradually, the hydraulic efficiency increases firstly then decreases gradually, and the average velocity circulation of outlet section increases firstly then decreases gradually in the same rotational speed. With the increase of rotational speed, the average velocity circulation increases gradually in the same flow rate coefficient. With the increase of flow rate coefficient, the relative swirl angle decreases firstly then increases in different rotational speed. With the increase of rotational speed, the static pressure ratio of outlet conduit increases gradually, and the distribution of drift angle in inlet section of outlet conduit is same. There is no linear functional relationship between the square of hydraulic loss and flow rate for outlet conduit.

The influence of cross-sectional morphology on the compressive resistance of polymeric nerve conduits

Artificial nerve conduits are proposed as an alternative to repair peripheral nerves injuries; while mechanical properties are of great importance for successful clinical application of nerve conduits. In this work, the poly (d,l-lactide-co-glycolide) (PLGA) nerve conduits were fabricated by the dry-jet wet spinning, and the compressive resistance of nerve conduits was systematically measured. It was found that the compressive resistance of nerve conduits significantly increased with the PLGA concentration of dope fluids. A numerical model was developed to simulate the compression tests of nerve conduits; where the hyperelastic–plastic constitutive law and the morphological characters of the cross sections of nerve conduits were implemented. The numerical results indicated the layered morphology of the cross sections of nerve conduits played the most important role in determining the compressive resistance. In addition, the accuracy of the numerical model was well validated by good agreement of experimental and numerical results of nerve conduit compression tests. This study helps understanding how to characterize the compressive resistance of porous polymeric nerve conduits and how the morphology influences the compressive resistance, leading to better design of fabrication setup and material selection for nerve conduits.

Methods for Analysis of Transition Regimes in Water-Carrying Runs at Hydroelectric Power Plants Based on Self-Organizing Mathematical Models

Results are presented for development of self-adapting sets of numerical models permitting analyses of complex pipeline systems with a variable flow regime in individual sections (empty, movement over dry bottom, transition from a gravity-flow regime of water in tunnels to a pressure regime, and conversely, and so forth. This system controls movement of the boundaries of the modeling domain (during filling and emptying of sections of conduits), and selects appropriate boundary conditions for variation in the flow regime on the boundary of the modeling domain of the flow (non-overflow spillway — overflow spillway, etc.).

우수관로 내 토사 퇴적을 고려한 통수능력 분석

우수관로는 설계빈도에 따른 유입량을 원활히 통수시킬 수 있도록 설계된다. 그러나 도심지에서 발생한 침수 사례를 보면 침수피해의 발생 및 피해의 증가 요인으로 관거 내의 토사 퇴적을 원인으로 두는 경우가 종종 있다. 이는 관거의 유지관리상의 문제이기도 하지만 다른 면에서는 관로의 설계 자체에 토사의 퇴적에 따른 영향을 어느 정도 고려해야 한다는 점을 시사하기도 한다. 즉, 관로의 설계 시 관로 내 토사의 퇴적 양상을 고려하여 그에 따른 피해를 줄일 수 있는 방향으로 설계가 이루어져야 할 필요가 있다. 본 연구에서는 실제 도심지 우수관망에서의 관거 내 토사의 퇴적 양상과 이로 인한 침수피해의 발생 영향을 석하기 위하여, 부산시 부전천 유역에 대하여 현재의 우수관로를 대상으로 분석을 실시하였다. 적용 대상 관거는 box형 관거로 관로 내 토사 퇴적을 고려하지 않을 경우 30년, 50년, 80년 및 100년의 설계강우를 지속기간 60분, 120분 180분, 240분에 대하여 충분한 통수능력을 확보할 수 있는 것으로 나타났다. 반면, 관로 내 토사의 퇴적으로 고려할 경우 이상의 모든 설계강우에 대하여 침수가 발생하였다. 또한 현재의 관로에 대하여 임의로 관로 구간 경사를 조정한 결과 관로 내 토사의 퇴적을 감소시킬 수 있으며, 이에 따라 적용된 설계강우들에 대한 월류 발생의 경우 최대 약 65%까지 저감될 수 있음이 분석되었다. 이러한 분석 결과로부터 우수관로의 설계 시 토사의 퇴적 양상에 대한 고려와 이에 따른 통수능력을 최대한 확보할 수 있는 방향으로의 설계가 필요한 것으로 나타났다. The storm sewer is designed to pass the inflow rate depending on the design frequency smoothly. However, taking a look at the example of flooding generated in urban area shows that an increase in the generation and damage of flooding can be often caused by the deposition of sediment in the sewer. This is a problem in the maintenance of sewers, but this implies that the effect of sediment deposition should be considered to some degree for the design of a conduit itself in another aspect. Thus, it is necessary to realize design in a direction to reduce flood damage pursuant to it by considering the deposition aspect of sediment in a conduit when designing a storm sewer. This study conducted an analysis on the current storm sewer for the Bujeon stream basin at Busan in order to analyze the deposition aspect of sediment in a sewer network at an actual urban area and the effect of the generation of flooding damage due to this. The applicable sewer is a box type, which has appeared to be able to discharge capacity enough to discharge a design rainfall over 30, 50, 80 and 100 years for a duration time such as 60, 120, 180 and 240 minutes when not considering the deposition of soil in the sewer network. On the other hand, when considering the deposition of sediment in conduit, flooding took place for all the above design rainfall. In addition, as a result of adjusting the slope of the conduit section arbitrarily for the current conduit, it was analyzed that the deposition of sediment can be reduced and the generation of overflows for the design rainfall applied according to this can be reduced by maximum about 65%. From these analysis results, it appeared as necessary to consider the deposition aspect of sediment when designing a sewer network, and design it in a direction to secure the discharge capacity pursuant to this as much as possible.

Effect of three decellularisation protocols on the mechanical behaviour and structural properties of sheep aortic valve conduits

PurposeTo determine the best method for decellularisation of aortic valve conduits (AVCs) that efficiently removes the cells while preserving the extracellular matrix (ECM) by examining the valvular and conduit sections separately. Material/methodsSheep AVCs were decellularised by using three different protocols: detergent-based (1% SDS+1% SDC), detergent and enzyme-based (Triton+EDTA+RNase and DNase), and enzyme-based (Trypsin+RNase and DNase) methods. The efficacy of the decellularisation methods to completely remove the cells while preserving the ECM was evaluated by histological evaluation, scanning electron microscopy (SEM), hydroxyproline analysis, tensile test, and DAPI staining. ResultsThe detergent-based method completely removed the cells and left the ECM and collagen content in the valve and conduit sections relatively well preserved. The detergent and enzyme-based protocol did not completely remove the cells, but left the collagen content in both sections well preserved. ECM deterioration was observed in the aortic valves (AVs), but the ultrastructure of the conduits was well preserved, with no media distortion. The enzyme-based protocol removed the cells relatively well; however, mild structural distortion and poor collagen content was observed in the AVs. Incomplete cell removal (better than that observed with the detergent and enzyme-based protocol), poor collagen preservation, and mild structural distortion were observed in conduits treated with the enzyme-based method. ConclusionsThe results suggested that the detergent-based methods are the most effective protocols for cell removal and ECM preservation of AVCs. The AVCs treated with this detergent-based method may be excellent scaffolds for recellularisation.

Stress-Strain State and Reinforcement of Compensating Sections of Steel/Reinforced-Concrete Pressure Conduits

Results of investigations of the stress-train state and strength of compensating sections (built with use of a low-modulus spacer) of steel/reinforced-concrete pressure conduits based on finite-element models are presented. Tensile hoop stresses requiring design (and not structural) reinforcement develop in the reinforced-concrete section of the conduits, which is separated from the inner steel lining by a low-modulus spacer. A procedure is proposed for calculation of the reinforcement, and diagrams are developed for reinforcement of the compensating sections of pressure conduits.

In vivo morphological evaluation of the efficacy of an hydrogel conduit as scaffold for peripheral nerve regeneration

Autologous nerve grafting is considered the gold standard for bridging nerve lesion, although in several cases the use of artificial tubular guides is needed. Nowadays, the research is addressed to identify the ideal treatment able to support complete nerve regeneration and functional recovery. Therefore, the use of artificial synthetic or natural guides is required but, despite numerous studies on several kinds of conduits, the clinicians are still waiting for an alternative scaffolds giving the best regenerative properties. In this light, we evaluated in vivo the efficacy of a polyamidoamine-based hydrogel, shaped as small tubing for nerve regeneration. Studies were done on 3 experimental groups consisting of injured guide-implanted, sham operated and autograft rats (in which sciatic nerve was excised, inverted and re-implanted). In the implanted rats the sciatic nerve was transected and 5 mm gap between proximal and distal stumps was left in the middle of the conduit. Animals were then analyzed at 1, 3, 6, months post-surgery. The gait analysis and the thermal sensitivity analysis demonstrated movement improvement and sensitive recovery. The repaired, control and autograft nerves from all groups analyzed (implanted, sham and autograft) were processed for light microscopy and morphometric analysis. The axon size, myelin thickness and fiber density showed a complete nerve regeneration covering the gap in the central part of the conduit. In particular, the medial segment of the nerve tended to turn similar to sham operated (control) animals, while the autograft rats showed a less extensive regenerative process. Moreover, immunofluorescence analysis of longitudinal sections of the conduits were performed by labeling the axonal neurofilaments. The immunopositivity observed further confirmed that the regenerative process was complete, being the fibres present through the entire conduit between the proximal and the distal stumps. Overall, our data demonstrate that polyamidoamine-based hydrogel conduits are an implantable material providing a good support for the peripheral nerve regeneration. These conduits are biocompatible and biodegradable over the time to non toxic product metabolites. Finally our findings are promising for the achievement of implantable poliamidoamine- based hydrogel conduits functionalized for drug delivery with growth factors. This work has been supported by Fondazione CARIPLO under the Project “Functional Polymeric Hydrogels for Tissue Regeneration” (no. 2010-0501), call for the Scientific Research on Advanced Materials, 2010.

Snakes With an Ellipse-Reproducing Property

We present a new class of continuously defined parametric snakes using a special kind of exponential splines as basis functions. We have enforced our bases to have the shortest possible support subject to some design constraints to maximize efficiency. While the resulting snakes are versatile enough to provide a good approximation of any closed curve in the plane, their most important feature is the fact that they admit ellipses within their span. Thus, they can perfectly generate circular and elliptical shapes. These features are appropriate to delineate cross sections of cylindrical-like conduits and to outline bloblike objects. We address the implementation details and illustrate the capabilities of our snake with synthetic and real data.

Normal and critical depth computations for egg-shaped conduit sections

This technical note presents regression analysis based models to compute the normal and critical depths for an egg-shaped conduit section recommended by Indian Standard Code of Practice IS–4880 (1976) [13]. The consistency of the models is checked through certain application examples. It is found that the estimated normal and critical depths agree well with the actual values computed from the fundamental equations.

Two Enthusiasts

Beginning in San Francisco in 1873, cable railways spread to nearly every large American city and several overseas. Los Angeles had three systems, the most successful of which began operation on Temple Street in 1886. Frederick Wood and John Fowler, who managed the Temple Street Cable Railway, were responsible for several mechanical innovations that they hoped would be adopted by other lines. To demonstrate these, they kept a section of cable track and conduit above ground, and in the summer of 1892 they posed alongside this section. Unfortunately—but probably not yet obvious to them—by 1892 cable railways were on the verge of being rendered obsolete by Frank Sprague's system of electric traction and thus the demand for mechanical novelty had vanished. Total cable railway mileage nationwide peaked the next year at 305; by the time the Temple Street line was converted to electricity in 1902 the total was down to 100, and ten years after that it was down to 20, nearly all of it on the steep hills of San Francisco. For cable-car enthusiasts like Wood and Fowler, Sprague had spoiled the fun.

Development of large current superconductors using high performance Nb3Sn strand for ITER

In the ITER model coil tests, degradations of the critical current were observed in Nb3Sn cable-in-conduit conductors when a large transverse electromagnetic force was applied to them. Both mass production technique of strand having high critical current enough to recover the degradation and also trial fabrication of the ITER-TF cable and conduit section were successfully performed. These results demonstrate feasibility of fabrication of the TF conductor using the high performance Nb3Sn strands. In addition, critical current degradation by spatially periodic transverse load was both experimentally and numerically studied. The simulation results show that the transverse resistance among the filaments is significantly small compared to that calculated from bronze resistivity. It is explained by the effect of superconducting current across the filament cross-section. This current however disappears when a large bending strain is applied to the strand, resulting in deterioration of the transverse resistance. It suggests that small degradation of the TF model coil (TFMC) conductor is not attributed to sufficiently low resistance among filaments as is expected in the optimized design of the ITER conductor but high resistance of the TFMC strand critical current against the transverse load. On the other hand, the developed strand has almost the same resistance against the transverse load as the TFMC strand. Therefore, the small degradation of the TF conductor, i.e., stable operation of the TF conductor is preliminarily anticipated.

Temperature and dynamics of degassing at Stromboli

Between 1999 and 2004 we deployed a series of thermal infrared experiments at Stromboli volcano (Italy) to thermally define the dynamics of gas puffing. These experiments involved targeting degassing vents with thermal infrared thermometers and thermal imagers from a distance of ∼300 m. The data showed that puffs involved a short‐lived gas thrust phase (velocities up to ∼20 m/s) followed by a dominant phase of buoyant rise with constant ascent velocities (∼7 m/s), until cooling caused the puff to stall and disperse. The puff could best be described as a starting plume that rapidly developed into a thermal. Ascent velocities, puff volumes and frequencies were extremely stable over the 6‐year‐long study period, typically being 10 ± 5 m/s, 50–190 m3 per burst and 0.5–1 Hz, respectively. These volumes convert to puff masses of 10–40 kg and give a total gas flux of 7–26 kg/s. Although stable at the system as a whole, at a single vent, gas puffing showed short‐term variation and instability. Gas puffing would wax and wane at individual vents, shifting to other linked vents so that for the system has a whole, puffing activity was maintained. Variations in vent temperature can thus be tied to variations in gas flux, where termination of gas puff activity (a reduction in the flux) at a particular vent results in decreased vent temperature. We suggest that gas puffing is related to a rapid and repeated release (bursting) of gas slugs at the head of the magma column, at a rate of one every 1–2 s. Released gas packets then ascend the empty conduit section to be emitted as the puffing plume. This style of degassing activity persists between Strombolian explosions and operates alongside passive degassing; but has a very different source mechanism. It appears to represent a highly stable and repetitive, but extremely mild, stream of explosive bursts. This style of nonpassive degassing may account for up to 45% of Stromboli's total gas flux.

Attenuation in gas-charged magma

Low frequency seismic events observed on volcanoes, such as Soufriere Hills Volcano, Montserrat, are thought to be caused by a resonating system. The modelling of seismic waves in gas-charged magma is critical for the understanding of seismic resonance effects in conduits, dykes and cracks. Seismic attenuation, which depends mainly on magma viscosity, gas and crystal content, is an essential factor in such modelling attempts. So far only two-phase gas–melt systems with the assumption of no diffusion and transport of volatiles between the melt and the gas bubbles have been considered. In this study, we develop a method of quantifying attenuation within gas-charged magma, including the effects of diffusion and exsolution of gas into the bubbles. The results show that by including such bubble growth processes attenuation levels are increased within magma. The resulting complex behaviour of attenuation with pressure and frequency indicates that two factors are controlling attenuation, the first due to viscous hindrance or the melt, and the second due diffusion processes. The level of attenuation within a gas-charged magma conduit suggests an upper limit on the length of a resonating conduit section of just a few hundred meters.

Stability of horizontal gas–liquid sprays in open-air and in a gas–solid fluidized bed

A technique for characterizing the stability of two-phase sprays is reported in this work. The method has been validated by high-speed visualization, and tested for a variety of feed nozzles and test fluids in both open-air and in a gas–solid fluidized bed. The results indicate that the two-phase flow pattern in the conduit leading up to the nozzle strongly influences the spray stability. In this regard, the predictions from the Taitel and Dukler [16] [Y. Taitel, A.E. Dukler, A model for predicting flow regime transitions in horizontal and near horizontal gas-liquid flow, AIChE J. 22 (1976) 47–55.] flow map are in good agreement with the present characterization. Locating a liquid-line restriction, ahead of the two-phase mixing region in the conduit, appears to create an induced bubbly flow, which significantly improved the spray stability by delaying the onset of slugging. It is also believed that the above effect was a consequence of having a shorter conduit section, where fully developed flow did not exist. An important finding from this study suggests that the spray stability is unaffected for injections in both open-air and in a gas–solid fluidized bed. Moreover, strong correlation between the upstream (in the conduit) and downstream (in the spray region) fluctuations was observed by the stability detection probes. The present technique can be easily accommodated for on-line monitoring of nozzles in applications like fluid coking, where the nozzle performance strongly affects the process efficiency.

Physical and chemical characterization of a spring flood event, Bench Glacier, Alaska, U.S.A.: evidence for water storage

AbstractPrevious studies of alpine glaciers have demonstrated that as water discharge increases through the summer, the predominant mode of subglacial drainage shifts from a distributed system to a more efficient conduit drainage system. We observed an early-melt-season speed-up and flood event lasting roughly 2 days in a small, uncomplicated Alaskan glacier that appears to have resulted from a sudden shift of the subglacial system in response to a significant accumulation of meltwater within the glacier. Calculated melt-water inputs exceeded discharge before the event; the implied change in storage over this 10 day period was equivalent to roughly 0.13 m averaged over the entire glacier bed. The pattern of discharge and suspended-sediment variations and the appearance of large ice chunks in the stream suggest that the speed-up occurred during a period of establishment of new subglacial conduits. A culminating flood and associated suspended-sediment pulse appear to have marked the final establishment of the new section of subglacial conduit. The flood ended the episode of high sliding velocity, but released water with high solute concentrations that reflect relatively long contact time with sediments. Discharge of stored water, inferred from high solute concentrations and lack of diurnal variation in discharge, continued for at least 3 days. While events such as this must recur through the melt season as the conduit system extends up-glacier and the locus of meltwater inputs shifts, their manifestations in the outlet stream will likely be more subdued later in the season.