Добірка наукової літератури з теми "Abnormal operation modes"

This paper reports the occurrence of some abnormal operational modes in soft-switching converters. By constructing a Boolean matrix based on the states of the switching components, some unexpected topological states are identified. Consequently, these states excite the abnormal or sneaking operational modes as referred. A three-stage step-up zero- current switching converter is used as an illustrative example and detailed analysis has been carried out. The phenomenon has also been confirmed in experiences, where performance degradation is noticed.

Robot assistants and wearable devices are highly useful; however, these artificial systems are susceptible to hackers. In this article, two sets of experiments were conducted. The first part of this study simulated a malicious attack on a prosthetic arm system to adversely affect the operation of the prosthetic system, while the perception of 10 human subjects was surveyed. These 10 able-bodied subjects controlled the prosthetic arm and hand with electromyogram signals, while an artificial sensation of touch was conveyed to their arms as they operated the system, which enabled them to feel what the prosthetic hand was grasping as they were asked to transport an object from one location to another. This haptic feedback was provided in both the normal and abnormal operational modes but was disabled in the extremely abnormal mode. The electromyogram control signals for the arm were reversed in both the abnormal and extremely abnormal modes. Results from the simulated malicious attack on a prosthetic arm system showed that the subjects found the haptic feedback helpful in both the normal and abnormal modes of operation. Both the abnormal and extremely abnormal modes of operation negatively impacted the self-reported levels of trust, satisfaction, and frustration with the prosthetic system as the subjects grasped and transported an object. While these metrics were negatively impacted by system malfunctions resembling a malicious attack on the control functionality, it was possible to rebuild them to their former higher levels after the functionality of the prosthetic system was restored. A parallel study in this article involved simulating a malicious attack on a robot assistant to unfavorably affect the delivery operation modes, while the perception of 20 human subjects was surveyed. Results showed that the simulated malfunctions unfavorably impacted the perception of trust, satisfaction, and frustration, but it was possible to restore these metrics in two different ways as the device functionality was restored.

The modern technologies and technical means providing energy efficient modes of natural gas pumping through main gas pipelines are considered. According to statistics, the main reasons for the high energy consumption of compressor stations are: deviations of the gas pipeline operating modes from the design, changes in the charac-teristics of technological units, unsatisfactory equipment condition, abnormal load distribution between work-shops and individual electric drives. It is shown that the traditional scheme of operation of unregulated gas com-pressor units leads to an overconsumption of electricity by 8 – 15 % in comparison with the operation in the de-sign mode. It is proposed to use the group connection of frequency-controlled electric-driven gas-pumping units in compressor workshops with high-voltage frequency converters. It is shown that the coordination of the operat-ing modes of all units within the compressor workshops with a decrease in the productivity of the gas pipeline by 5 % of the nominal with the help of frequency regulation allows saving up to 1.05 MW of power consumption, and at 10 % - more than 1.74 MW per year.

In order to improve the effect of refueling training in nuclear power plant, the simulation system of refueling machine was designed and developed, combining the virtual reality technology with a real control console. The 3D virtual refueling environment of nuclear power plant was established by 3D modeling. Signals from touch screen and console are gathered by PLC and transmitted to PC graphics workstation, control the motion of virtual refueling machine, which realize the refueling operation simulation. The operation in failure modes was also realized in the system through the programming of failure database. The results show that the system runs normally and can simulate refueling operation in normal and abnormal modes, the training of refueling personnel is implemented effectively.

<p><span>The design of a supervision system based on the external model by structuring the industrial process according to several modes of operation (degraded and normal). The disadvantage of this model is that it describes the industrial process components as functions regardless of their dynamics without going into detail. Hence the interest of the bond graph model to fill the external model limits. The performance of the proposed supervisory system using both models lies in the detection and location of faults for each mode of operation. The bond graph model enriched by the concept of causality and thanks to these structural properties can clearly display the elements of the physical system taking into account their dynamics in normal and abnormal operation. The results of our research have been applied to central air conditioning system; the development of the proposed project has proceeded from the modeling stage to the reconfiguration stage of the system.</span></p>

The commissures of knee joint develop after operation or knee trauma at the expense of abnormal proliferation of fibrous tissue provoking limitation of amplitude of motion, arthralgia and joint stiffness. So far, pathogenesis of commissure of knee joint remains unclear. however, there is information that after operation increased secretion of fibroblasts accelerates deposit of extracellular matrix as main mechanism of development of commissures. The application of innovative medical technologies to operate knee joint ameliorated outcomes of treatment and quality of life of patients. However, after surgical operations some patients experience painful sensations and limitation of amplitude of motion of knee joint. The study was targeted to ameliorating of prognosis of operative interventions by means of investigation of pathogenesis of commissure process and possible modes of its prevention.

This paper presents the development of a novel nuclear radiation monitoring and detection system. With the lightweight and global positioning features, the implemented wireless nuclear detection node can easily be deployed to discover unusual or abnormal radioactivity and map the events. ZigBee-based multi-hop mesh communication is adopted between nuclear detection nodes. All wireless nuclear detection nodes are designed with two working modes, continuous operation and timing operation. The two modes can be switched at any specified time to save energy consumption. Meanwhile, the features of anti-jamming against 802.11 network of ZigBee technology are tested and evaluated.

The approaches that ensure the trouble-free operation of marine power system in abnormal modes were considered. Such modes are usually associated with the system elements failure during operation. Particular attention was paid to the processes occurring in the circuit during transition of one of the generators to the motoring operation mode. The relevance of the considered marine power system issue was substantiated. According to the research results, using time-delay when generating a signal to disable a failed unit operating with reverse power can contribute to defect development in the primary motor. Moreover, time-delay can also lead to zero voltage in the marine electric power system. This circumstance creates the possibility of an emergency that can potentially lead to a shipping accident with the most serious consequences. The problem of timely shutdown of a faulty electrical machine before its transition to the motoring mode is defined in the research, as well as the overload prevention problem for primary motors remaining in working condition. An original diagnostic indicator was proposed based on study, which allows identifying the inoperative state of generator unit during operation. The new approach was developed, which implements the preventive control method for the marine power system in case of element failure. The forecasting of the system operation modes in case of a generator set failure, and its structural adaptation to the occurred malfunction is carried out. In contrast to the existing methods, the practical implementation of the proposed solution will allow accident-free transition of marine power system to a partially operational state without the emergency. This will have a beneficial effect on the safety of ship as a whole.

Reliability theory makes it possible to determine the probabilities of destruction, reaching limit states, equipment and pipeline failures (E&P). Normative documents, as a rule, define requirements for integral indicators of reliability or safety of objects, but do not establish requirements for admissible values of probabilities for individual systems and data elements of objects. This article proposes the approach for determining the permissible values of the probabilities of reaching the yield stress or ultimate strength by operating stresses on the basis of design data on loads and data from certificates on the mechanical properties of metal. During operation, the achievement of the working stresses in metal of E&P value of the permissible stress values is a probabilistic event, in this fact, the probabilistic approach has been developed to obtain the safety factor of probability reaching limiting states. The developed approach is based on the methods of strength science, statistical analysis and probability theory. The object of application of the developed approach is thermal mechanical equipment used in different branches of technology. Using the example of the main circulation pipeline of the NPP with WWER-440, the presence of a reserve in the probability of reaching the limit state is shown and a relationship is established between the stress variation coefficient and the calculated probability for normal operation and abnormal operation. This approach determines the reserve for the probability of destruction, which will justify the extension of the resource or optimize the operating parameters of the objects under consideration.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.03 – "Електротехнічні комплекси та системи" – Харківський Національний Університет Міського Господарства імені О. М. Бекетова, Національний технічний університет "Харківський політехнічний інститут" МОН України, Харків, 2020. Дисертація присвячена вирішенню науково-практичної задачі підвищення ефективності тягового асинхронного електропривода (ТАЕП) з автономним джерелом живлення за критерієм максимізації співвідношення момент-струм (МТРА) за рахунок оптимізації системи керування тяговим асинхронним двигуном (ТАД) з урахуванням зміни підведеної потужності. Розглянуто існуючі підходи до оптимізації з та без урахування впливу характеристики намагнічування ТАД. Серед недоліків підходу до оптимізації за критерієм максимізації ККД наведено, що вона потребують значних стендових випробувань тягового електроприводу. Для подальших досліджень був обраний критерій оптимізації MTPA. Встановлено, що існуючі підходи до оптимізації за критерієм МТРА створювались за умови повного використання автономного інвертора за напругою і не враховують режимів роботи в умовах обмеження потужності ТАД. Розглянуто особливості проведення дослідження роботи ТАЕП (на базі моделювання), що дозволило визначити структуру імітаційної моделі та її необхідні складові. Встановлено, що для більш поглибленого аналізу (на базі моделювання) процесів, що відбуваються у ТАЕП, у тому числі і під час нештатних режимів, необхідні: імітаційна модель електричної та керуючої частини ТАЕП; імітаційна модель механічної частини рухомого складу, включаючи контакт "колесо − рейка"; імітаційна модель профілю колії. Для проведення досліджень, в якості базового зразка було обрано рухомий склад з автономним джерелом живлення – дизель-поїзд ДЕЛ-02. Створення імітаційних моделей ТАЕП, узгоджених з результатами випробувань ТАЕП базового зразка дозволили оцінити адекватність результатів дослідження оптимізованого ТАЕП. Послідовність виконання дослідження реалізовано за наступним алгоритмом: для отримання адекватної моделі ТАЕП досліджена система керування ТАЕП базового зразка; після верифікації імітаційної моделі в системі керування здійснена заміна структури та алгоритму керування ТАЕП, а саме заміна скалярної системи керування на векторну систему, що оптимізована за критерієм МТРА; оцінені результати імітаційного моделювання поїзних режимів оптимізованого ТАЕП. Розроблено імітаційні моделі складових та загальну модель ТАЕП, що адаптована для проведення досліджень за обраними задачами. Імітаційну модель джерела живлення подано спрощеною, оскільки перехідні процеси дизель-генераторної установки мають значно більшу інерційність, ніж процеси розвитку аварійних та нештатних режимів у електричній та механічній частинах ТАЕП. При імітаційному моделюванні системи автономний інвертор напруги – тяговий асинхронний двигуи (АІН – ТАД) проведено перевірку реалізації нелінійності магнітного кола імітаційної моделі ТАД шляхом моделювання досліду холостого ходу для восьми значень лінійної напруги ТАД. Для оцінювання, отримана характеристика холостого ходу порівнювалася з результатами стендових випробувань восьми серійних ТАД типу АД906 (виробництва ДП "ЗАВОД "ЕЛЕКТРОВАЖМАШ"), що дало змогу відобразити статистичне відхилення параметрів діючих зразків ТАД від розрахункових, що не перевищують 5 %. Для підтвердження адекватності загальної моделі ТАЕП було проведено порівняльний аналіз результатів імітаційного моделювання та результатів поїзних випробувань базового зразка при русі зі швидкістю 5 км/год та при розгоні до швидкості 50 км/год по рівній ділянці колії. Встановлено, що відхилення результатів імітаційного моделювання від результатів експерименту за F-критерієм Фішера не перевищують 5 %. При вирішенні задачі синтезу системи керування ТАД, оптимізованої за критерієм МТРА, запропоновані аналітичні вирази обчислення кута положення вектора струму ТАД, значення модуля вектора потокозчеплення ротора ТАД, що враховує зміну величини підведеної потужності. Обґрунтовано вибір способу апроксимації характеристики потокозчеплення ротора ТАД у режимі послаблення поля, отриманий у ході проведення дослідження перехідних процесів у системі АІН – ТАД у режимі послаблення поля. Встановлено, що апроксимація характеристики потокозчеплення тягового двигуна типу АД906 за допомогою лінійної функції призводить до значних відхилень величини потужності двигуна, а саме до рівня 82.6 % від номінальної, що в свою чергу призводить до зниження величини електромагнітного моменту на 20%. Встановлено, що при апроксимації характеристики потокозчеплення складеною функцією з двох лінійних дозволяє зменшити такий ефект, проте на ділянці зламу характеристики мають місце збурення величини споживаної потужності та перевантаження асинхронного двигуна за потужністю на 4 %. Апроксимація характеристики намагнічування за допомогою полінома 4-го порядку не мають таких ефектів, чим і обумовлений вибір способу апроксимації. Встановлено, що без вживанні спеціальних заходів щодо виявлення та припинення надлишкового проковзування у контакті колесо – рейка відбувається розвиток фрикційних коливань, що супроводжуються знакозмінними значеннями електромагнітного моменту ТАД, які перевищують допустимі (1.2 – 1.5 рази). Тому, для ТАЕП запропоновано математичний опис блока корекції та розподілу задання струму ТАД залежно від поточних частот обертання роторів ТАД, що дозволило обмежити прискорення частот обертання, для контролю динаміки руху або створення ефективного захисту від надмірного проковзування колісних пар (боксування, юза). Ефективність роботи такої системи була досліджена при імітаціному моделюванні поїзних режимів роботи при русі по ділянці колії з незадовільними умовами зчеплення колеса з рейкою. Встановлено, що застосування блоку корекції та розподілу струму ТАД виключають надмірне проковзування колісних пар при реалізації граничного за умовами зчеплення тягового зусилля. Розроблено імітаційну модель оптимізованого ТАЕП і встановлено, що використання оптимізації за критерієм МТРА з урахуванням величини підведеної до ТАД потужності дає змогу збільшити електромагнітний момент ТАД в залежності від величини обмеження потужності від 2 % до 53 % у режимі пуску, а коефіцієнт потужності на 17.6 %. Таким чином в ході проведеного дослідження показано, що застосування оптимізації за критерієм МТРА з урахуванням величини підведеної до ТАД потужності підвищує ефективність автономного тягового електроприводу.
Thesis for a candidate degree by speciality 05.09.03 – Electrical complexes and systems. – National Technical University "Kharkov Politechnical Institute", Kharkiv, 2020. The dissertation is devoted to solving the scientific and practical problem of increasing the efficiency of traction asynchronous electric drive (TAED) rolling stock with autonomous power supply by the criterion of maximizing the ratio of moment to current (MTPA) by optimizing the control system of asynchronous motor (AM). The existing approaches to optimization with and without taking into account the influence of the magnetization characteristics of AM are considered. Among the disadvantages of the approach to optimization by the criterion of efficiency maximization is that it requires significant bench tests of the traction electric drive. The MTPA optimization criterion was chosen for further research. It is established that the existing approaches to optimization according to the MTPA criterion were created under the condition of full use of the autonomous voltage inverter and do not take into account the operating modes in the conditions of AM power limitation. The peculiarities of the study of TAED (based on modeling) are considered, which allowed to determine the structure of the simulation model and its necessary components. It is established that for a more in-depth analysis (based on modeling) of the processes occurring in TAED, including during non-standard modes, it is necessary: simulation model of the electrical and control part of TAED; simulation model of the mechanical part of the rolling stock, including the contact "wheel – rail"; simulation model of track profile. For research, a rolling stock with an autonomous power supply – a diesel train DEL-02 was chosen as a basic sample. The creation of simulation models of TAED, consistent with the results of TAED tests of the basic sample allowed to assess the adequacy of the results of the study of optimized TAED. The sequence of the study was implemented according to the following algorithm: to obtain an adequate model of TAED, the control system of TAED of the basic sample was investigated; after verification of the simulation model in the control system, the structure and control algorithm of TAED were replaced, namely the replacement of the scalar control system with a vector system optimized by the MTPA criterion; the results of simulation modeling of train modes of optimized TAED are estimated. Simulation models of components and the general model of TAED which is adapted for carrying out researches on the chosen tasks are developed. The simulation model of the power supply is presented in a simplified way, because the transients of the diesel generator set have a much greater inertia than the processes of development of emergency and non-standard modes in the electrical and mechanical parts of TAED. In the simulation of the system autonomous voltage inverter – traction asynchronous motor (AIN – AM), the implementation of the nonlinearity of the magnetic circuit of the simulation model AM was checked by simulating the no-load experiment for eight values of the linear voltage AM. For evaluation, the obtained idling characteristic was compared with the results of bench tests of eight serial AM type AD906 (manufactured by SE "ZAVOD" ELEKTROVAZHMASH"), which allowed to display the statistical deviation of the parameters of existing samples of AM from the estimated not exceeding 5%. To confirm the adequacy of the general model of TAED, a comparative analysis of the simulation results and the results of train tests of the base sample when driving at a speed of 5 km / h and when accelerating to a speed of 50 km / h on a flat section of track. It is established that the deviation of the simulation results from the results of the experiment according to Fisher's F-test does not exceed 5%. When solving the problem of synthesis of AM control system optimized by MTPA criterion, analytical expressions for calculating the angle of position of AM current vector, value of modulus of flux coupling vector of AM rotor, taking into account change of supplied power value are offered. The choice of the method of approximation of the flux coupling characteristic of the AM rotor in the field weakening mode, obtained during the study of transients in the AIN – AM system in the field weakening mode, is substantiated. It is established that the approximation of the flux coupling characteristic of the traction motor type AD906 using a linear function leads to significant deviations of the engine power, namely to the level of 82.6% of the nominal, which in turn reduces the electromagnetic torque by 20%. It is established that when approximating the flux coupling characteristics by a composite function of two linear ones allows to reduce this effect, however, at the fracture site the characteristics disturb the power consumption and overload the induction motor by 4%. Approximation of the magnetization characteristic using a 4th order polynomial does not have such effects as the choice of the approximation method. It is established that without taking special measures to detect and stop excessive slippage in the wheel – rail contact, the development of frictional oscillations is accompanied by alternating values of the electromagnetic moment of AM, which exceed the allowable (1.2 – 1.5 times). Therefore, for TAED the mathematical description of the block of correction and distribution of the AM current depending on current rotational speeds of AM rotors is offered that allowed to limit acceleration of rotational frequencies, for control of dynamics of movement or creation of effective protection against excessive slipping of wheel pairs (boxing, yuz). The efficiency of such a system was studied in the simulation of train modes of operation when moving along the track with unsatisfactory conditions of traction of the wheel with the rail. It is established that the use of the correction and current distribution unit AM excludes excessive slippage of the wheelsets in the implementation of the ultimate in terms of traction. A simulated model of optimized TAED was developed and it was found that the use of optimization according to the MTPA criterion taking into account the amount of power supplied to AM allows to increase the electromagnetic torque of AM depending on the power limit from 2% to 53% in start-up mode and power factor by 17.6%. Thus, in the course of the study it was shown that the use of optimization according to the criterion of MTPA taking into account the amount of power supplied to the AM increases the efficiency of the autonomous traction drive.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.03 – "Електротехнічні комплекси та системи" – Національний технічний університет "Харківський політехнічний інститут" МОН України, Харків, 2020. Дисертація присвячена вирішенню науково-практичної задачі по підвищенню ефективності тягового асинхронного електроприводу (ТАЕП) з автономним джерелом живлення за критерієм максимізації співвідношення момент-струм (МТРА) за рахунок оптимізації системи керування тяговим асинхронним двигуном (ТАД) з урахуванням зміни підведеної потужності. Розглянуто існуючі підходи до оптимізації з та без урахування впливу характеристики намагнічування ТАД. Встановлено, що існуючі підходи до оптимізації за критерієм МТРА створювались за умови повного використання автономного інвертора за напругою та не враховують режимів роботи в умовах обмеження потужності ТАД. Розглянуто особливості проведення дослідження роботи ТАЕП (на базі моделювання), що дозволило визначити структуру імітаційної моделі та її необхідні складові. Для проведення досліджень був обраний рухомий склад з автономним джерелом живлення – дизель-поїзд ДЕЛ-02, як базовий зразок. Розроблені імітаційні моделі складових та загальна модель ТАЕП, що адаптована для проведення досліджень за обраними задачами. Імітаційна модель джерела живлення представлена спрощеною, оскільки перехідні процеси дизель-генераторної установки мають значно більшу інерційність, ніж процеси розвитку аварійних та нештатних режимів у електричній та механічній частинах ТАЕП. При імітаційному моделюванні системи автономний інвертор – ТАД проведена перевірка реалізації нелінійності магнітного кола імітаційної моделі ТАД шляхом моделювання досліду холостого ходу для восьми значень лінійної напруги ТАД. В якості оцінки, отримана характеристика холостого ходу порівнювалася з результатами стендових випробувань восьми серійних ТАД типу АД906 (виробництва ДП "ЗАВОД "ЕЛЕКТРОВАЖМАШ"), що дозволило відобразити статистичне відхилення параметрів діючих зразків ТАД від розрахункових, що не перевищують 5%. Для підтвердження адекватності загальної моделі ТАЕП був проведений порівняльний аналіз результатів імітаційного моделювання та результатів поїзних випробувань базового зразка при русі зі швидкістю 5 км/г та при розгоні до швидкості 50 км/г по рівній ділянці шляху. Встановлено, що відхилення результатів імітаційного моделювання від результатів експерименту за F-критерієм Фішера не перевищують 5%. При вирішенні задачі синтезу системи керування ТАД, оптимізованої за критерієм МТРА, запропоновані аналітичні вирази обчислення кута положення вектора струму ТАД, значення модуля вектора потокозчеплення ротора ТАД, що враховує зміну величини підведеної потужності. Обґрунтований вибір способу апроксимації характеристики потокозчеплення ротора ТАД в режимі послаблення поля, отриманий в ході проведення дослідження перехідних процесів у системі автономний інвертор напруги – ТАД в режимі послаблення поля. Для ТАЕП запропонований математичний опис блоку корекції та розподілу завдань струму ТАД в залежності від поточних частот обертання роторів ТАД, що дозволило обмежити прискорення частот обертання, для контролю динаміки руху або створення ефективного захисту від надмірного проковзування колісних пар (боксування, юзу). Розроблено імітаційну модель оптимізованого ТАЕП та встановлено, що використання оптимізації за критерієм МТРА з урахуванням величини підведеної до ТАД потужності дозволяють збільшити електромагнітний момент ТАД на 53% в режимі пуску, а коефіцієнт потужності на 17.6%, що підтверджує ефективність запропонованих рішень.
Thesis for a candidate degree by speciality 05.09.03 – Electrical complexes and systems. - National Technical University "Kharkov Politechnical Institute", Kharkiv, 2020. The dissertation is devoted to solving the scientific and practical problem of increasing the efficiency of traction asynchronous electric drive (TAED) with autonomous power supply by the criterion of maximizing the ratio of moment to current (MTPA) by optimizing the control system of asynchronous motor (AM). Existing approaches to optimization with and without the influence of AM magnetization characteristics are considered. It is established that the existing approaches to optimization by the criterion of MTPA were created under the condition of full use of the standalone inverter by voltage and do not take into account the modes of operation under conditions of power limitation of AM. Component simulation models and a general TAED model have been developed, adapted for conducting research on selected tasks. The simulation model of the power source is simplified, since the transients of the diesel generator set have much greater inertia than the processes of the growth of emergency and abnormal modes in the electrical and mechanical parts of the TAED. In the simulation of the system, the standalone inverter-AM is tested for the implementation of the nonlinearity of the magnetization curve of the AM simulation model by simulating the idling test for eight values of the linear AM voltage. As an estimate, the obtained idling characteristic was compared with the results of bench tests of eight serial AMs of AD906 type (manufactured by SE "ELEKTROVAZhMASH"), which allowed to reflect the statistical deviation of the parameters of the existing AM samples from the calculated, not exceeding 5%. In order to confirm the adequacy of the general model of TAED, a comparative analysis of the simulation results and the results of train tests of the basic sample was carried out when driving at a speed of 5 km / h and at acceleration to a speed of 50 km / h in a flat section of the road. It is established that the deviations of the simulation results from the results of the Fisher F-test do not exceed 5%. In solving the problem of synthesis of the control system AM, optimized by the criterion of MTPA, analytical expressions of calculating the angle of position of the vector of AM current are proposed, the value of the module of the vector of coupling of the rotor AM, taking into account the change of the magnitude of the input power. The rational for choosing of the method for constructing a characteristic flux linkage of the AM rotor in the field attenuation mode, obtained during the study of transients in the system autonomous voltage inverter-AM in the field attenuation mode. For TAED, a mathematical description of the block of correction and distribution of tasks current AM was proposed, depending on the current rotational speed of the AM rotors, which allowed to limit the acceleration of rotation frequencies, to control the dynamics of movement or to create effective protection against excessive slippage of wheel pairs (boxing, yuz). An optimized TAED simulation model was developed and it was found that using the MTPA criterion optimization, taking into account the magnitude of the AM power, allows to increase the AM electromagnetic moment by 53% in the start mode, and the power factor by 17.6%, which confirms the efficiency of the proposed solutions.

Title from PDF of title page (University of Missouri--Columbia, viewed on March 10, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Robert M O'Connell. Includes bibliographical references.

Radiation considerations are an integral part of the practice of nuclear cardiac imaging. Concern regarding radiation has increased in recent years, reflected in statements by many professional societies, and likely attributable both to rapid growth in use of nuclear cardiology as well as high doses received by some nuclear cardiology patients. The fundamental principles of medical radiological protection are justification (ensuring that the right test is performed for the right patient at the right time), optimization (ensuring that the test is performed in the right manner), and dose limitation, which while applicable to healthcare workers is not operative regarding patients. Three "As" facilitate and serve as an organizing principle for justification: awareness, appropriateness, and audit. Awareness incorporates knowledge of the benefits and risks of testing involving radiation and effective communication of these to the patient. Appropriateness in nuclear cardiology can be assessed using the American College of Cardiology's appropriateness criteria. Methods that have been demonstrated to improve appropriateness include using a collaborative learning model, a point-of-order decision support tool, and a multifaceted intervention including threatened loss of insurance coverage. A variety of strategies should be considered for optimization to ensure patient-centered imaging. These including strategic selection of both the protocol, e.g. selecting a stress-first protocol and performing stress-only imaging in patients without a high pre-test probability of abnormal findings on stress imaging, or using PET, and also the administered activity, e.g. by using weight-based dosing and/or software- or hardware-based advances in camera technology. Special considerations are required for pregnant, nursing, and pediatric patients.

AbstractBatch or semi-batch processes have been utilized to produce high-value-added products in the biological, food, semi-conductor industries. Batch process, such as fermentation, polymerization, and pharmacy, is highly sensitive to the abnormal changes in operating condition. Monitoring of such processes is extremely important in order to get higher productivity. However, it is more difficult to develop an exact monitoring model of batch processes than that of continuous processes, due to the common natures of batch process: non-steady, time-varying, finite duration, and nonlinear behaviors. The lack of exact monitoring model in most batch processes leads that an operator cannot identify the faults when they occurred. Therefore, effective techniques for monitoring batch process exactly are necessary in order to remind the operator to take some corrective actions before the situation becomes more dangerous.

AbstractIn order to ensure the normal operation of the traffic under the bridge, reasonable calculation methods and construction techniques should be adopted for the construction of the newly added railway station. This paper establishes a structural calculation finite element model to calculate and analyze the various construction stages of the steel beam incremental launching construction of the newly-added Gaoping station on the Yichuang-Wanzhou Railway, and systematically study the mechanical properties of the steel beam in the process. The results show that: (1) The deflection of each rod can meet the requirements of the railway bridge steel structure construction specification. However, when the length of the front cantilever of the steel beam reaches 11.4 m, the maximum deflection of the upper and lower chord bars is close to the limit. (2) The load-bearing capacity of each member of the steel beam meets the requirements, which indicates that the structural design of the steel beam and the incremental launching construction plan are reasonable. (3) In view of the complexity and uncertainty of the incremental launching construction process, real-time monitoring of the construction process is required, and the beam should be dropped in time when abnormal conditions occur to ensure the safe operation of the existing line.

Aimed at the detection difficulty of local abnormal signals during pipeline operation, this paper takes the local abnormal signals as the detected targets, and proposes a new method based on target detection to extract abnormal signals with different amplitude and shape; and for the case where there are few actual leak samples, combined with the characteristics that the training samples of each module of the model itself are derivative samples of the original sample, so as to realize the small sample training of the model. Finally, a new pipeline leak detection and location method is proposed by combining the 1D-faster R-CNN with the cross-correlation location method based on signal matching. The experimental results show that the proposed method effectively extracts local abnormal signals, accurately alarms leak signals, and eliminates the false alarms caused by the recognition errors of normal signals.

While many data mining models concentrate on automation and efficiency, interactive data mining models focus on adaptive and effective communications between human users and computer systems. User requirements and preferences play the most important roles in human-machine interactions, and guide the selection of target knowledge representations, operations, and measurements. Practically, user requirements and preferences also decide strategies of abnormal situation handling, and explanations of mined patterns. In this article, we discuss these fundamental issues based on a user-centered three-layer framework of interactive data mining.

This chapter deals with the diagnosis of induction motors (IM) with the so-called motor current signature analysis (MCSA). The MCSA is one of the most efficient techniques for the detection and the localization of electrical and mechanical failures, in which faults become apparent by harmonic components around the supply frequency. This chapter presents a summary of the most frequent faults and its consequences on the stator current spectrum of an IM. A three-phase IM model was used for simulation taking into account in one hand the normal healthy operation and in the other hand the broken rotor bars, the shorted turns in the stator windings, the voltage unbalance between phases of supply, and the abnormal behavior of load. The MCSA is used by many authors in literature for faults detection of IM. The major contribution of this work is to prove the efficiency of this diagnosis methodology to detect different faults simultaneously, in normal and abnormal functional conditions. The results illustrate good agreement between both simulated and experimental results.

This paper details the architecture and describes the preliminary experimentation with the proposed framework for anomaly detection in medical wireless body area networks for ubiquitous patient and healthcare monitoring. The architecture integrates novel data mining and machine learning algorithms with modern sensor fusion techniques. Knowing wireless sensor networks are prone to failures resulting from their limitations (i.e. limited energy resources and computational power), using this framework, the authors can distinguish between irregular variations in the physiological parameters of the monitored patient and faulty sensor data, to ensure reliable operations and real time global monitoring from smart devices. Sensor nodes are used to measure characteristics of the patient and the sensed data is stored on the local processing unit. Authorized users may access this patient data remotely as long as they maintain connectivity with their application enabled smart device. Anomalous or faulty measurement data resulting from damaged sensor nodes or caused by malicious external parties may lead to misdiagnosis or even death for patients. The authors' application uses a Support Vector Machine to classify abnormal instances in the incoming sensor data. If found, the authors apply a periodically rebuilt, regressive prediction model to the abnormal instance and determine if the patient is entering a critical state or if a sensor is reporting faulty readings. Using real patient data in our experiments, the results validate the robustness of our proposed framework. The authors further discuss the experimental analysis with the proposed approach which shows that it is quickly able to identify sensor anomalies and compared with several other algorithms, it maintains a higher true positive and lower false negative rate.

For EAST operation schedule, auxiliary subsystems like the cryogenic system have to cope with different heat loads which depend on the different EAST operating states. The cryogenic system consists of a cryoplant and a cryodistribution system. All of these cryogenic subsystems have to operate in parallel to remove the heat loads from the magnet, 80K shields, built-in cryopumps and other small users. After a brief recall of the main particularities of a cryogenic system operating in a Tokamak environment, the first part of this study is dedicated to the assessment of the main EAST operation states. A new design of refrigeration loop for the HTS current leads, the updated layout of the cryodistribution system and revised strategy for operations of the built-in cryopumps have been taken into consideration. The relevant normal operating scenarios of the cryoplant are checked for the typical EAST operating states like plasma operation state, short term stand by, short term maintenance, or test and conditioning state. The second part of the paper is dedicated to the abnormal operating modes coming from the magnets and from those generated by the cryoplant itself. Thanks to this analysis, the optimization of the present operational modes is proposed to make match the technical specifications of the cryogenic system with the EAST operation requirements.

The production of LDPE may require huge power, heavy-duty reciprocating compressors, provided with opposite cylinders and special frames to withstand the loads, deriving from the operating pressures. In many new projects larger capacities and higher performance requirements, renew the challenge of engineers to handle the mechanical, thermodynamic, chemical-physical, process and operational aspects. Safety, performance, operation and reliability are usual expectations needing a thorough evaluation of the service and the machine selection is based on positive results in similar applications. Valve, packing and cylinder performance is noticeably influenced by the design, operation and maintenance activities. The cylinders are compound pressure vessels, excluded by design codes, but their design and construction have to consider the extreme internal pressures and the nature of the process gas. The ability to withstand the high fatigue stresses and the need to avoid any leakage of gas around the compressor area implies solutions to minimize such occurrences including abnormal operations and emergencies. The design must foresee all possible failure modes of each component, to have safe and smooth operation. Innovative methods of simulation and modeling, like FEA, CFD, and others, are very important tools for the design of cylinder components. Valves are simulated by mathematical models optimizing performance and ensuring reliable operation, to reach a correct mechanical behavior with minimum energy consumption. The available technological improvements are taken as a base, resulting from the R&D of manufacturers and long experience of End Users. Also the pulsation and related vibration of the piping have to be investigated to keep the plant in operation without hazard. The operation is the stage where all the parameters have to be kept under control and incipient problems have to be identified to minimize shut down and arrange various maintenance works. Automation systems, together with new monitoring and diagnostic systems, allow very high safety levels, availability and optimized maintenance interventions.

Abstract Risk management (RM) is an effective means of safety assessment and reliability management of nuclear power plant (NPP). During the operation of NPP, the main contents of RM work are as follows: 1. Real-time reliability assessment of NPP system, and evaluate NPP risk, so as to ensure that the NPP system can complete the specified functions to deal with the consequences of system failure. 2. Complete the diagnosis and mitigation of abnormal faults, so as to ensure that the NPP system can return to a safe state as soon as possible in the case of abnormal operation of NPP. With the continuous improvement of the requirements of online RM, LPSA (Living PSA) technology, as an effective tool of RM, has been developed and provides more powerful support for the safe operation of NPP. In order to evaluate the reliability of NPP system in real time, LPSA model needs to be updated to match the state of the system. Most of the existing LPSA model updating techniques are based on the premise that the system information is completely knowable and the information is accurate. However, in the process of NPP operation, the accessibility of system information and the accuracy of information are difficult to meet the requirements of updating the existing LPSA model. How to update the LPSA model in the case of incomplete and inaccurate information is one of the difficulties in the application of online LPSA technology. Especially when the NPP is in abnormal conditions, it is more urgent for operators to obtain correct system information in real time to recognize the available state of the plant system. In fact, the required system information needs to be obtained by the operator through his or her cognitive behavior process, such as the fault diagnosis process. At the same time, this information can be used to help operators complete the diagnosis of system status and the evaluation of system reliability. In this study, an information reasoning method is proposed to evaluate the probability of various failure modes under the information known to the operator through the modeling and analysis of the cognitive behavior process of the operator. The method can assist the operator to make the correct fault judgment to complete the fault diagnosis and fault mitigation. In addition, the information obtained by the operator in the process of cognitive behavior, and the results of information reasoning can be used to update the LPSA model in real time, so as to obtain the real-time reliability evaluation results of the NPP system.

For the initiation of emergency operating procedures and severe accident management of most commercial nuclear reactors worldwide, monitoring of the core temperature is required. Currently, it is not practicable to directly measure the temperature of fuel cladding surface temperature due to some technical limitations. Thus, measurement of the coolant temperature by using thermocouples at the core exit locations is widely used. However, the core exit temperature (CET) may not represent the core temperature properly because the measurement locations are somewhat distant from the heat generating part of fuel rod assembly. In this regard, it is important to assess the difference between the fuel cladding temperature and the CET. The objective of this study is to get the general insight and understanding of the boiling-induced multiphase flow inside fuel rod bundle during an abnormal operation mode following a loss-of coolant accident by comparing the calculation results of the CET deviation from the fuel cladding (or in-core) temperature for the two different cases of the present analysis model subjected to a coolant flowrate of either 100% or 50% of the nominal value. To do this, three-dimensional multi-phase computational fluid dynamics (CFD) calculations of a simplified pressurizer water reactor (PWR) core model were performed for both reactor operating modes. As a result, it was found that the calculated CETs are much lower than the maximum fuel rod cladding temperatures during both operating modes. Consequently, it is considered that the temperature deviation should be taken into account carefully to use the measured CETs for the initiation of emergency operating procedures and severe accident management of commercial nuclear reactors.

Fatigue spall initiation is one of the major modes of premature bearing failure. The spall initiation is often exacerbated by the presence of impurities in the near-surface region (∼400 μm) of the bearing raceways. Once a spall initiates, it can propagate rapidly, leading to abnormal bearing operation and possible catastrophic failure if not detected early. Testing performed at the University of Texas-Pan American (UTPA) has focused on ultrasonically scanned tapered roller bearings found to have inclusion content within 400 μm of the surface of the raceways. These bearings undergo accelerated service life tests in which spall initiation is detected and tracked over time while documenting spall growth. The work presented here provides several study cases that document the spall initiation and propagation on ultrasonically scanned tapered roller bearing components. Results show that spalls generally initiate on locations corresponding to sites of subsurface inclusions, and they grow many times their original size within relatively short operating periods. The study also shows that spalls tend to initiate and propagate at a faster rate on bearing cups (outer rings) than on cones (inner rings).

Abstract With increasing regulation and the push for clean energy, the operation of power plants is becoming increasingly complex. This complexity combined with the need to optimize performance at base load and off-design condition means that predicting power plant performance with computational modeling is more important than ever. However, traditional modeling approaches such as physics-based models do not capture the true performance of power plant critical components. The complexity of factors such as coupling, noise, and off-design operating conditions makes the performance prediction of critical components such as turbomachinery difficult to model. In a complex system, such as a gas turbine power plant, this creates significant disparities between models and actual system performance that limits the detection of abnormal operations. This study compares machine learning tools to predict gas turbine performance over traditional physics-based models. A long short-term memory (LSTM) model, a form of a recurrent neural network, was trained using operational datasets from a 100 kW recuperated gas turbine power system designed for hybrid configuration. The LSTM turbine model was trained to predict shaft speed, outlet pressure, and outlet temperature. The performance of both the machine learning model and a physics-based model were compared against experimental data of the gas turbine system. Results show that the machine learning model has significant advantages in prediction accuracy and precision compared to a traditional physics-based model when fed facility data as an input. This advantage of predicting performance by machine learning models can be used to detect abnormal operations.

It is not uncommon to expect that feedwater heaters will require replacement over their Unit’s service life. In some cases, Unit upgrades, changes in the full range of operation, and the absence of root cause failure analysis can lead to unsuitable replacements. Neglecting these considerations can result in the continuance of similar failures as heaters are either replaced in-kind or not to the extent necessary as dictated by the changes in load and/or how they are operated. The heater technical specification must not only address the obvious issues related to changes in tube material, quality control, and references to the current state-of-the-art heater standards, but also the full range of current and projected modes of operation. An important factor in obtaining a heater that will last reliably for many years is to specify one that will be versatile enough to handle not only the normal base load operation, but will also safely withstand higher loads, higher heat inputs, and other modes of operation reasonably expected. The replacement heater specification must define the full range of projected load impositions to allow the Vendor to consider and adapt his internal layouts and physical geometries to accommodate them safely and conservatively. This paper shall illustrate how performance modeling and predictive rating calculations can be valuable tools in helping to identify the full range of conditions to be considered by the Vendor so as to optimize the specification of the new heater. A variety of hypothetical cases can be examined in order to help determine the optimal design and its effects on the entire heater system as well as projected resultant differences in Unit load and heat rate or efficiency. Constructing a performance mode model, such as the PEPSE example utilized herein, for single heater analysis is quick and relatively easy. The feedwater and drain inlet conditions (temperature, pressure and flow), the heater shell pressure, and the required Terminal Temperature Difference (TTD) and Drains Cooler Approach (DCA) are inputs to the model which then calculates the required steam flow demand and the heater outlet conditions. Using this tool, the initial design, current minimum and full load (from plant historical data or PI data), future full load, abnormal/overload conditions and any other pertinent analysis may be accomplished. The key output data delivered by the model is the required steam and drain flows obtained by the energy balance. This information is then specified to the heater Vendors as it applies to the rating and physical sizing of the replacement. This information can be crucial to ensure that the replacement heater(s) will be capable of providing long, reliable life for even the worst load potentials.

It is well known that hydraulic noise can change as a system warms up. That change can be a factor for misperception of mechanical failure, because noise can play an important role as a signal that indicates abnormal operation. It is therefore important to understand the behavior of hydraulic pressure ripples that are a source of hydraulic noise in operating conditions, and how they change in relation to the temperature of the hydraulic oil. This study has investigated the ripple behavior that results from temperature change in simple hydraulic systems, using mathematical models that took thermal properties into account. Physical properties of the oil and the speed of sound in the oil have been defined as temperature-related variables in the mathematical models. The physical properties that should be used in the mathematical models have been obtained directly from the oil manufacturer. In contrast, the speed of sound in the oil has to be obtained from the isentropic tangent bulk modulus of the oil in an actual operating condition. That has been determined from the specific volume ratio of entrained air to the oil and the isentropic tangent bulk modulus of the only oil. The thermal properties of the speed of sound in the oil have been determined from the thermal characteristics of these variables, and it has been found that the speed of sound in the oil decreases with a rise in the oil temperature. The mathematical models of pressure ripples have shown that there were three distinct phenomena resulting from the temperature change of the oil. The first is the change of wavelength. The second is the spatial dependence of the thermal characteristics of the pressure ripples. The third is the difference of the thermal characteristics of the pressure amplitude at the peak in spatial modes. These changes that result from the temperature variation tend to be large at higher frequency.

Recently, the problem of abnormal vibration of the EMU carbody has occurred from time to time. When the carbody is abnormally vibrated, the Sperling index and ride comfort of the vehicle can be greatly reduced, which is unfavorable for its operation. The paper established and a vehicle-shake simulation model which was verified based on the measured wheel-rail profile and vibration data. Additionally, the causes and solutions of abnormal vehicle body vibration were studied. The research results illustrate that the EMU has a relatively high level of wheel-rail equivalent conicity in the shaking section, causing the secondary hunting instability. The main frequency of the instability is 9-10 Hz, which is close to the first-order diamond mode frequency of the carbody. Therefore, the elastic resonance of the carbody occurs, resulting in the shake phenomenon. Through simulation analysis, it is found that wheelset reprofiling and rail polishing can improve the operation stability of EMUs and effectively solve the shaking motion; Furthermore, increasing the first-order diamond mode frequency of the carbody and controlling the hunting phase of the front and rear bogies can also avoid the shaking motion. At the same time, the equivalent conicity management through the detection of the wheel profile can efficiently prevent the hunting instability and carbody shaking, providing a reference for wheel reprofiling and rail polishing.

With its annual Payment Systems Report, Banco de la República offers a complete overview of the infrastructure of Colombia’s financial market. Each edition of the report has four objectives: 1) to publicize a consolidated account of how the figures for payment infrastructures have evolved with respect to both financial assets and goods and services; 2) to summarize the issues that are being debated internationally and are of interest to the industry that provides payment clearing and settlement services; 3) to offer the public an explanation of the ideas and concepts behind retail-value payment processes and the trends in retail payments within the circuit of individuals and companies; and 4) to familiarize the public, the industry, and all other financial authorities with the methodological progress that has been achieved through applied research to analyze the stability of payment systems. This edition introduces changes that have been made in the structure of the report, which are intended to make it easier and more enjoyable to read. The initial sections in this edition, which is the eleventh, contain an analysis of the statistics on the evolution and performance of financial market infrastructures. These are understood as multilateral systems wherein the participating entities clear, settle and register payments, securities, derivatives and other financial assets. The large-value payment system (CUD) saw less momentum in 2019 than it did the year before, mainly because of a decline in the amount of secondary market operations for government bonds, both in cash and sell/buy-backs, which was offset by an increase in operations with collective investment funds (CIFs) and Banco de la República’s operations to increase the money supply (repos). Consequently, the Central Securities Depository (DCV) registered less activity, due to fewer negotiations on the secondary market for public debt. This trend was also observed in the private debt market, as evidenced by the decline in the average amounts cleared and settled through the Central Securities Depository of Colombia (Deceval) and in the value of operations with financial derivatives cleared and settled through the Central Counterparty of Colombia (CRCC). Section three offers a comprehensive look at the market for retail-value payments; that is, transactions made by individuals and companies. During 2019, electronic transfers increased, and payments made with debit and credit cards continued to trend upward. In contrast, payments by check continued to decline, although the average daily value was almost four times the value of debit and credit card purchases. The same section contains the results of the fourth survey on how the use of retail-value payment instruments (for usual payments) is perceived. Conducted at the end of 2019, the main purpose of the survey was to identify the availability of these payment instruments, the public’s preferences for them, and their acceptance by merchants. It is worth noting that cash continues to be the instrument most used by the population for usual monthly payments (88.1% with respect to the number of payments and 87.4% in value). However, its use in terms of value has declined, having registered 89.6% in the 2017 survey. In turn, the level of acceptance by merchants of payment instruments other than cash is 14.1% for debit cards, 13.4% for credit cards, 8.2% for electronic transfers of funds and 1.8% for checks. The main reason for the use of cash is the absence of point-of-sale terminals at commercial establishments. Considering that the retail-payment market worldwide is influenced by constant innovation in payment services, by the modernization of clearing and settlement systems, and by the efforts of regulators to redefine the payment industry for the future, these trends are addressed in the fourth section of the report. There is an account of how innovations in technology-based financial payment services have developed, and it shows that while this topic is not new, it has evolved, particularly in terms of origin and vocation. One of the boxes that accompanies the fourth section deals with certain payment aspects of open banking and international experience in that regard, which has given the customers of a financial entity sovereignty over their data, allowing them, under transparent and secure conditions, to authorize a third party, other than their financial entity, to request information on their accounts with financial entities, thus enabling the third party to offer various financial services or initiate payments. Innovation also has sparked interest among international organizations, central banks, and research groups concerning the creation of digital currencies. Accordingly, the last box deals with the recent international debate on issuance of central bank digital currencies. In terms of the methodological progress that has been made, it is important to underscore the work that has been done on the role of central counterparties (CCPs) in mitigating liquidity and counterparty risk. The fifth section of the report offers an explanation of a document in which the work of CCPs in financial markets is analyzed and corroborated through an exercise that was built around the Central Counterparty of Colombia (CRCC) in the Colombian market for non-delivery peso-dollar forward exchange transactions, using the methodology of network topology. The results provide empirical support for the different theoretical models developed to study the effect of CCPs on financial markets. Finally, the results of research using artificial intelligence with information from the large-value payment system are presented. Based on the payments made among financial institutions in the large-value payment system, a methodology is used to compare different payment networks, as well as to determine which ones can be considered abnormal. The methodology shows signs that indicate when a network moves away from its historical trend, so it can be studied and monitored. A methodology similar to the one applied to classify images is used to make this comparison, the idea being to extract the main characteristics of the networks and use them as a parameter for comparison. Juan José Echavarría Governor