Gate Grooves Research Articles

A topology-alterative two-phase flow solver and its validation for a dynamic hydraulic discharge process

ABSTRACTIn this paper, a domain-topology-based, two-phase, incompressible flow model is proposed to simulate transient flow variations associated with the gate opening motions of water conservancy projects, such as hydropower stations with plain and radial gates. The research source code is written in the OpenFOAM platform and incorporates the interDyMFoam solver. Two benchmark experiments were performed in the laboratory to validate the numerical results. The water level, pressure, flow pattern and development of vortices were recorded for comparison with numerical solutions. The results show that the relative error associated with the weir flow time was less than 5.00%. Moreover, good agreement was obtained between the time history curves of the free surface elevation and pressure based on numerical and experiment results. The detailed flow pattern reflects the simulation capability of the model, which can be used to numerically investigate the generation mechanisms of vertical vortices around gate grooves. The proposed model can be applied to further investigate flow variations in real hydraulic engineering applications.

A Topology-alterative Algorithm for Transient Dynamic Hydraulic Response Investigation

In this paper, a hexahedra-based topology-alterative algorithm is proposed to simulate dynamic boundary issues of the gate opening motions in water conservancy projects. The algorithm, which cooperates with the two-phase, incompressible solver of OpenFOAM platform, enables researchers to investigate transient hydraulic characteristic variations comprehensively. Two benchmark experiments were performed to validate the numerical results under the working conditions of moving sluice gates and unsteady weir head. The time history response of water level and pressure on specified monitoring points, flow pattern scenario near moving gate, furthermore, the development of antisymmetric-revolving vertical vortices around gate piers were recorded to assess the accuracy of the proposed model. The cross-contrasting results show that the relative error of weir flow time is less than 5.00 %. Moreover, good agreement has been obtained about time history curves of free surface elevation and pressure between numerical and experiment solutions. The vivid flow pattern shows the simulating capability of the current model and indicates an inspiring way to numerically investigate generation mechanism of vertical vortex inside gate grooves. The proposed algorithm is believed to be a useful utility on the further investigation on flow variation in real hydraulic engineering applications, such as improvement of semi-empirical discharge formulas, reduction of cavitation damage, elimination of pipe hammer pressure even spectral analysis of sluice gates with a fluid structure interaction interface.

Research on flow in water intake of a run-of-river hydropower plant

The work shows the importance of flow research in parts of canal systems at hydropower plants. The authors researched a mathematical model of water intake at run-of-river hydropower plant. ANSYS software was used. The 3D model created by the authors described the upper part of the water intake extended to the approach area in front of it. The work was aimed at identifying flow parameters in the flow-narrowing zone of the water intake. The work describes the research method and presents graphical calculation results. Whirling areas were discovered in the upper part of water intake and in gate grooves. It was noted that the flow in gate grooves is spiral-shaped and runs downwards. The work highlights the danger of such flow because it increases the amount of small rubbish gravitating onto the lower part of the groove, which can cause gate hang up (blocking) when it is shut in emergency. The results are of high importance for increasing safety of intakes at run-of-river hydropower plants.

Short gate-length InAlAs/InGaAs MODFETs with asymmetry gate-recess grooves: electrochemical fabrication and performance

We report the realization of asymmetric recess etching in the fabrication of gate grooves for MODFETs based on InAlAs/InGaAs heterojunctions. The novel technology employs asymmetric electrochemical etching when the surface metal of Pt and Ni are deposited on the source and drain pads, respectively. Devices fabricated with this technology, though still immature, show similar DC performance to those fabricated by conventional technology for symmetric devices. Furthermore, due to the formation of a ‘step’ on the InP etch-stopper as a result of the asymmetric etching, the effective gate length of the devices has been made shorter than its nominal value. This, combined with the asymmetric groove profiles, produces higher f T and f max values than the usual symmetric devices.

Impact of recess-etching-assisting resist-openings on the shapes of gate grooves for short gate length InAlAs/InGaAs heterojunction FET's

When resist openings are employed to monitor the drain current of InAlAs/InGaAs-heterojunction-based FET's during wet-chemical gate recess, etching rates for InGaAs and InAlAs can be significantly modified by the exposure of the surface metal on the nonalloyed ohmic electrodes to citric-acid-based etchants. Surface metal of Ni enhances the recess etching rate to a degree that is much higher than that in its absence. With nonselective citric acid-based etchant, the presence of Pt surface metal, however, leads to a preferential etching of InGaAs over InAlAs. This behavior of selective etching is attributed to the excess oxidation of InAlAs induced by the high electrode potential of Pt via electrochemical effects. This investigation discloses that the selection of the surface metal that lies beneath the resist openings can be very important if gate recess grooves with desired shapes are to be fabricated.

High-Resolution Scanning Electron Microscopy Observation of Electrochemical Etching in the Formation of Gate Grooves for InP-Based Modulation-Doped Field-Effect Transistors

We show that during the wet-chemical formation of gate grooves for InAlAs/InGaAs-heterojunction-based modulation-doped field-effect transistors, the etching rates of InGaAs and InAlAs can be significantly modified by the exposure of the non-alloyed ohmic electrodes to citric-acid-based etchant. The presence of a Ni surface metal enhances the recess etching rate to a degree that is much higher than that in its absence. The presence of a Pt surface metal, however, causes this originally non-selective etchant to preferentially etch InGaAs over InAlAs. This selective etching behavior is attributed to the excess oxidation of InAlAs induced by the high electrode potential of Pt via an electrochemical effect. This study reveals the important impacts of electrochemical etching on the fabrication of gate recess grooves.

Self-compensation of short-channel effects in sub-0.1-μm InAlAs/InGaAs MODFETs by electrochemical etching

We show that by making full use of the features of electrochemical etching in InAlAs/InGaAs heterostructures, deep gate grooves with small side etching can be fabricated. The most important advantage of this technology is that the vertical etching in the small gate openings will be remarkably enhanced by a self-organized process. Therefore the electrochemical etching provides a what we call self-compensation of the short channel effects. The effectiveness of this technology is evidenced by the excellent performance combined with the alleviation of the threshold-voltage shift and suppression of transconductance degradation in MODFET's with gate lengths below 0.1 /spl mu/m.

Electrochemically induced asymmetrical etching in InAlAs/InGaAs heterostructures for MODFET gate-groove fabrication

We have achieved a self-controlled asymmetrical etching in metalorganic chemical vapor deposition-grown InAlAs/InGaAs heterostructures, which can be suitable for fabricating modulation-doped field-effect transistors (MODFETs) with gate-groove profiles for improved performance. The technology is based on electrochemical etching phenomena, which can be effectively controlled by using different surface metals for ohmic electrodes. When surface metals of Pt and Ni are deposited on the source and the drain, respectively, the higher electrode potential of Pt results in slower etching on the source side than on the drain side. Thus, asymmetry of gate grooves can be formed by wet-chemical etching with citric-acid-based etchant. This represents a new possibility to conduct “recess engineering” for InAlAs/InGaAs MODFETs.

The importance of electrochemistry-related etching in the gate-groove fabrication for InAlAs/InGaAs HFETs

For the first time, the surface metal on nonalloyed ohmic electrodes is found to significantly change the profiles of gate grooves, when resist openings are employed to monitor drain current during wet-chemical gate recess for sub-micron InAlAs/lnGaAs heterojunction field-effect transistors (HFETs). The surface metal of Ni enhances the etching rate in comparison with that in the absence of electrodes by a factor of 4 and 10, laterally and vertically, which is favorable to fabricate deep gate grooves with small side etching. The Pt surface metal, however, leads to preferential etching of InGaAs over InAlAs, which can be useful to realize large side etching. The existence of an electrochemistry-related etching component, which arises when the ohmic electrodes are present during recess etching, is considered to be responsible for these behaviors.

Selection of surface ohmic metal for fabricating 0.1 [micro sign]m InAlAs/InGaAs heterojunction FETs with wet-chemically-recessed gates

The authors show that the profiles of gate grooves can be effectively manoeuvered by the selection of surface metals of ohmic electrodes. The Ni surface metal is advantageous over Pt, since the recess etching is independent of materials and is more spatially homogeneous. These different etching behaviours and resulting gate-groove profiles are attributed to the existence of electrochemical effects during recess etching.

Characteristics of the behavior of the Sayano-Shushenskoe dam during filling of the reservoir to the normal pool level

1. Processes of variation of the “dam-foundation-abutments” system are not fading away, the operating regime of the structure has not stabilized. 2. The unsteady and inelastic work of the bank abutments, evidently, is one of the causes of irreversible radial movements and development of fracturing in the first column of the dam. 3. Cracking on the upstream face and progressive seepage through the concrete of the first column worsen the state of the concrete and the cracks are subject to healing by polymer materials. Polymer injections do not improve the work of the structure, but if the cracks are not healed promptly the volume of necessary repair works will increase with the course of time. 4. To evaluate the stress state of the dam it is necessary to make calculations with consideration of the large stress raisers: water intakes, gate grooves, etc. 5. It is required to evaluate the fact of the excess by a factor of 2–3 of the increments of the maximum arch stress over the design values in various load ranges.

Stripe stabilization in vertical Bloch line memory

Partially grooved, long, rectangular grooves on the garnet surface were used to stabilize minor loop stripes in a vertical Bloch line memory. These stripes reside beneath the stripe confinement groove. The test chip contained 10 or 20 minor loop grooves, 10 read/write (r/w) gate grooves, and a major line groove. The film thickness was 4.76 μm, and the groove was 0.5 μm deep. Each minor loop groove was 500 μm long, four widths were tried: 3.5, 4, 4.5, and 5 μm. Two groove periods were tried: 10 and 20 μm. For stripe initialization, a bubble was nucleated in every minor loop groove by a single current pulse at a 90 Oe bias field. As the bias field was decreased slowly, bubbles began to stripe out at 80 Oe. At 75 Oe, all 10 stripes were stretched to the full groove length. These stripes were stable at bias fields between 70 and 80 Oe. Stripes decreased in length at higher fields, and escaped from the confinement groove at low fields. When stripes escaped from the groove, it always occured from the end not facing a r/w gate groove. These bias field values and the stripe-escape asymmetry are confirmed by computer simulation.

Experience with operation of the 50th anniversary of the great October Bratsk hydroelectric plant over several years

1. In multiple-unit hydroelectric plants, where year-round attendance by the personnel is ensured, it is not necessary to use centralized maintenance methods, with the exception of specialized work such as replacement of transformer and generator windings. Experience with operation of the Bratsk plant has shown that by the economic method it is possible to carry out a large volume of reconstruction work in shorter periods and at a lower cost than by the centralized method; thus, a high work effectiveness of the maintenance personnel is achieved. 2. At large hydroelectric plants it is necessary to have design groups and to engage engineering—technical workers and front-rank production specialists for solving problems relating to increasing the reliability, lengthening the intermaintenance periods, and developing special equipment and instruments. 3. Combining the trades of on-duty machine operator and on-duty electrician, as well as of the shift superintendents of the turbine and electric shops, and concentrating all on-duty personnel in the electric shop, contribute to their better training, improvement of qualifications, and increase in responsibility, reduce the probability of errors, and increase the effectiveness of the work under normal and emergency conditions. 4. It is necessary to devote more attention to the control of unit efficiency. Experience acquired at the Bratsk plant has shown that comparative checking of the efficiencies of all the units should be performed using accessible locations for current meters (e.g., emergency gate grooves). Efficiency measurements should be carried out by the relative method before and after major maintenance operations, and the runner blade geometry should be checked. 5. The manual labor required for maintenance of the plant area and buildings can be reduced by using reliable machines operated by a single person and fitted with suspended equipment for removing snow, sand, and gravel from footpaths and for loading such material into hoppers; reliable machines complete with suspended equipment for mowing and gathering grass, and small lawn-mowers with attachments for raking up the grass; and multipurpose machines for cleaning the machine halls (floors, walls, and window openings).