Gate Failure Research Articles

Sault Ste. Marie Lock reconstruction: hydraulic model studies of the stop log emergency closure and lock filling and emptying systems

In July 1987, a section of the southwest wall of Sault Ste. Marie Lock failed during a locking operation when a portion of limestone facing, 60 m by 8 m, separated from the rubble backing wall. Engineering investigations resulted in the selection of the Recreational Lock Option, involving either downsizing the lock chamber within the existing lock or constructing a new lock as the most viable solutions. A Dry Dock Option, where the lock would be used to store craft during the winter months, was also considered. However, this option was abandoned during the course of testing. The engineering investigations also revealed that the emergency swing dam, constructed upstream of the existing lock to protect the system should the lock gates be damaged or carried away (as happened in 1909), was in poor condition and required rehabilitation in the order of over $0.5 million. A stop log emergency system was proposed as an alternative safety device designed to stop the flow of water through the canal in the event of gate failure. Physical hydraulic model studies were carried out to evaluate the feasibility of using an emergency stop log system. The tests showed that stop logs constructed with solid horizontal web plates top and bottom result in unacceptably high hydraulic downpull forces. Open truss stop logs can be deployed to stop the flow of water through the canal in the event of gate failure. The follower should also be constructed as an open truss such that the areas of steel exposed to the flow at the top and bottom of the follower are minimized. Hydraulic uplift forces that could prevent closure can be reduced by increasing the space between the stop log and the follower. Physical hydraulic model studies of the lock filling-emptying systems are described. The first and preferred option consists of downsizing the existing lock and retaining part of the existing wooden culverts and emptying system, if possible. A new filling port, filling valves, and supply culvert would be constructed upstream. In the event that the existing wooden culverts are found to be unserviceable, a second option was considered. This second option would be to fill in the wooden culverts and then construct a new filling port, filling valves, and supply culvert that would discharge into the lock through the upstream breast wall just above floor level. The existing emptying system would be retained or rebuilt. The third option, if both the filling and discharge culverts have to be condemned, would be to build a new lock. The results of the hydraulic model studies carried out to explore these three options are described.Key words: emergency closure, stop logs, follower, canal, lock, downpull, uplift, crane capacity, filling-emptying system, culverts.

On the Design of Reliable Boolean Circuits That Contain Partially Unreliable Gates

We investigate a model of gate failure for Boolean circuits in which a faulty gate is restricted to output one of its input values. For some types of gates, the model, which we call theshort-circuit model of gate failure, is weaker than the traditionalvon Neumann modelin which faulty gates always output precisely the wrong value. Our model has the advantage that it allows us to design Boolean circuits that can tolerate worst-case faults, as well as circuits that have arbitrarily high success probability in the case of random faults. Moreover, the short-circuit model captures a particular type of fault that commonly appears in practice, and it suggests a simple method for performing posttest alterations to circuits that have more severe types of faults. A variety of bounds on the size of fault-tolerant circuits are proved in the paper. Perhaps, the most important is a proof that anyk-fault-tolerant circuit for any input-sensitive function using any type of gates (even arbitrarily powerful, multiple-input gates) must have size at leastΩ(klogk/loglogk). Obtaining a tight bound on the size of a circuit for computing the AND of two values if up tokof the gates are faulty is one of the central questions left open in the paper.

Impact of oxide thickness on SEGR failure in vertical power MOSFETs; development of a semi-empirical expression

This paper investigates the role that the gate oxide thickness (T/sub ox/) plays on the gate and drain failure threshold voltages required to induce the onset of single-event gate rupture (SEGR). The impact of gate oxide thickness on SEGR is experimentally determined from vertical power metal-oxide semiconductor field-effect transistors (MOSFETs) having identical process and design parameters, except for the gate oxide thickness. Power MOSFETs from five variants were specially fabricated with nominal gate oxide thicknesses of 30, 50, 70, 100, and 150 nm. Devices from each variant were characterized to mono-energetic ion beams of Nickel, Bromine, Iodine, and Gold. Employing different bias conditions, failure thresholds for the onset of SEGR were determined for each oxide thickness. Applying these experimental test results, a previously published empirical expression is extended to include the effects of gate oxide thickness. In addition, observations of ion angle, temperature, cell geometry, channel conductivity, and curvature at high drain voltages are briefly discussed.

Sensorimotor Gating and Schizophrenia

Human and animal model studies of sensorimotor gating allow us to understand the functional significance of attentional abnormalities and monoaminergic alterations in patients with schizophrenic disorders. Clinically, schizophrenic patients report oversensitivity to sensory stimulation that theoretically correlates with stimulus overload and leads to cognitive fragmentation. Paradigms using cortical event-related potentials and the prepulse inhibition of startle responses show that schizophrenic patients also have impaired central nervous system inhibition (sensorimotor gating). Animal model studies demonstrate that increased systemic aminergic activity and increased nucleus accumbens dopamine tone causes sensorimotor gating failure, similar to that seen in schizophrenic patients. The time course of the observed schizophrenic and animal model deficits is compatible with the "temporal map" of monoaminergic neuron functions (le, several hundred milliseconds). Studies of sensorimotor gating allow investigators to comment on the spatial and temporal mapping of neurons, trait and state deficits, and vulnerability factors in the schizophrenic spectrum of disorders. By translating attentional theories into testable hypotheses, the neurobiology of schizophrenic disorders becomes clearer.

Fault tree truncation error bounds

The solution of large fault trees can only performed if cut sets of a high order or low probability are neglected. This procedure is non-pessimistic since possible contributions to the top gate failure probability are ignored. Since the number of cut sets neglected is generally large, it is possible that their total contribution is significant compared to the total probability of those cut sets included in the evaluation of the top gate failure probability. In this paper a practical method for the estimation of upper bounds on the total failure probability of cuts sets of a given order is presented. This allows bounds on the contribution of all the cut sets neglected through cut-off procedures in fault tree solutions to be calculated, and so validate the top event failure probability. The method given here is much superior to that suggested by Modarres and Dezfuli in that it produces much lower and hence more useful bounds. The method of Modarres and Dezfuli can be refined, but for realistic fault tree examples the method given here always gives the least pessimistic and most practical bounds.

Forces on Lifting Beams Used with Three‐Leaf Intake Gates

At many hydroelectric plants, crane‐lowered, leaf‐type intake gate systems are relied upon to stop turbine flow after failure of the wicket gates. Unfortunately, intake gate systems of that type have a history of operating problems, such as failure of gate leaves to descend, crane overloading, and failure of the lifting beam to release. A review of that history prompted TVA to investigate the efficacy of its intake gate systems. As a starting point, new model tests of the intake gate system at Melton Hill Dam were performed in 1983, 20 years after completion of the dam. The Melton Hill system used three stacked rectangular leaves in each of three bays for closure of a unit. Each of the nine leaves was lowered into position by the same crane and lifting beam. The original design of the system had been based on model tests, which had not included behavior of the lifting beam. In field tests performed shortly after construction of the dam, the gate leaves seated properly in flowing water but the lifting beam...

Some trends in the development of gate construction abroad

1. Even greater attention is being devoted abroad to an increase of reliability of outlet works and gates as one of the virtually important elements of every dam. For this purpose, types of gates, grooves, and mechanisms already checked in practice are, as a rule, used on newly constructed dams [1, 11, 14], and the main efforts of designers are aimed at improving their designs and layouts on structures [1, 2, 5]; the power supply of the mechanical equipment of important outlets, as a rule, comes from two “alternative” sources, e.g., from the central power supply network plus a standby supply from a local diesel electric plant [6]; redundancy of the most important gate components and mechanisms (electric motors, pumps of the oil-pressure system, balance carriages, etc.) is provided for everywhere [3]; technical innovations find use only after comprehensive model and prototype investigations (see, e.g., the proceedings of the 11th and 13th Congresses on large dams). 2. As a consequence of Sec. 1, a trend toward a substantial reduction of the number of types of gates being used is observed everywhere [2, 4]. Serious attention is being devoted to methods of preventing cavitation and vibration [13–18]. 3. An individual (for each gate) drive (as a rule, electrohydraulic), having a number of operational advantages compared with cranes (high efficiency of gate operation, possibility of automatic or remote control of the gates, etc.), is gaining greater popularity. 4. Reliability factors are taken into account also in the operating instructions [6, 7], which, e.g., stipulate the need for periodic testing of the mechanical equipment (especially before passage of a flood), etc. 5. One of the current trends is the fact that many specialists [1, 11, 14, 15] are presently taking a more cautious approach to the use of gates with high design parameters (area of the outlet being closed and head), considering that failure of a large gate (especially during passage of a flood) substantially reduces the discharge capacity (and, consequently, the reliability) of the dam.

Early gate failures in biased GaAs field effect transistors from electromigration-induced damage superimposed on kirkendall voids

Electrical gate failures in GaAs field effect transistors (FETs) were analysed. In the analysis, the TiPt phase growth during high temperature storage was estimated using growth rates which were calculated at 100, 325 and 400°C from a (time) 1 2 dependence. The calculations reveal volume changes by -6.36% and -6.325% as a result of the formation of the TiPt and Ti 3Pt phases respectively. The volume changes and lattice mismatch give rise to mechanical strains causing metallurgical failure of the Ti/Pt layers and consequently the formation of AuAl intermetallics. Compressional stresses in the films relax through the formation of hillocks. In biased FETs a new failure mechanism, electromigration-induced damage superimposed on Kirkendall voids as a result of current crowding, occurs when the current density is as low as 1 × 10 4 A cm −2 and gives rise to early gate failures.

Noise Analysis of Soft Errors in Combinational Digital Circuits Via Walsh Transforms

The noise produced at the output of combinational logic circuits by individual gate failures is analyzed through the use of Walsh functions. Soft errors are modeled by allowing the output of each gate in a particular realization to fail temporarily, possibly introducing an error in the single binary output. The input variables also are allowed to be stochastically driven. The output probability of error contains the Walsh transform of an extended logic function and the Walsh characteristic functions of the input variables as well as the individual gate failure variables. These results are specialized to the case where the inputs are statistically independent of the soft errors. A discussion of the transform of the extended logic function is included.

A Combinatorial Solution to the Reliability of Interwoven Redundant Logic Networks

A combinatorial procedure is given to calculate the reliability of an interwoven redundant logic network to any desired degree of accuracy. The procedure consists of enumerating combinations of gate failure which are tolerated by the redundant network, and is explained with reference to a quadded logic network. Since the exact reliability calculation might be too time consuming for large networks, a formula is given for a lower bound which can be used in conjunction with the exact method to give a very accurate reliability figure with a comparatively small computation time.