Вимірювальна техніка та метрологія
Permanent URI for this communityhttps://ena.lpnu.ua/handle/ntb/2123
Browse
3 results
Search Results
Item Математичнемоделювання якості підземних трубопроводів в умовах корозійної втоми(Видавництво Львівської політехніки, 2016) Юзевич, Лариса; Національний університет “Львівська політехніка”Розроблено рекомендації щодо оцінювання довговічності та якості підземних металевих трубопроводів в умовах втоми. Встановлено особливості раннього виявлення кризових (передаварійних) ситуацій. Розроблено методику розрахунку ризику в смузі проходження траси трубопроводу з урахуванням його технологічної специфіки і впливу місцевих чинників різної природи на можливість розвитку аварії. Разработаны рекомендации относительно повышения качества математических моделей мониторинга сложных объектов техники с низким уровнем динамики процессов, которые характеризуются особенностями раннего выявления кризисных (предаварийных) ситуаций. The presence of fatigue cracks on the surface of metallic underground pipelines sharpens the problem of calculation values of strength characteristics at the action of corrosive environments, that did not find the complete decision nowadays. In this connection it is needed to correct the row of defects and normative and technical documents related to insufficient actuality of corresponding. In normative documents from exploitation of construction elements on this time the reasonable norms of legitimate values of corrosive damages, reduction of bearing strength of construction elements are absent. It creates complications in the ground of normative terms of exploitation and evaluation of the maximum state of metallic constructions, in planning of charges on exploitation of construction elements and repair and restoration work. An object of researches is underground metallic pipelines that are in the conditions of corrosion-fatigue destruction. The subject of a study is normative document. It is expedient to specify and perfect on the basis of the information got on results monitoring of functioning of underground metallic pipelines. Aim of this article – formulation of criteria and scientifically reasonable recommendations for providing of quality of underground metallic pipelines exploitation in the conditions of fatigue and influence of aggressive environment, and also forming of normative principles in sphere of pipeline transport. Only underground main gas pipelines in the ground electrolyte in the conditions of low cycle fatigue should be considered. For the improvement of normative documents it is expedient to build a complex mathematical model, that will unite the physical and chemical model of corrosion-fatigue processes, model of piling up description of damages in metals and elements theory of risks. For the modeling of speed increasing of fatigue crack on the middle rectilineal area of kinetic curve equation that binds length of fatigue corrosive crack and amount of cycles of loading to the coefficient of intensity of mechanical tensions is used. Corresponding equation is improved for a metal in corrosive environment and the pH-value of environment, and also electrode potential of metal, is here taken into account. For the base model of damage accumulation for metals in the conditions of irregular deformation a model that is based on the curvilinear change of damages, and power going is used near description of process of low cycle fatigue, that is a base on criterion of fatigue strength of V. T. Troschenko. Critical specific work that answers the origin of fatigue crack is included in a criterion. For description of the irregular cyclic loading of metal expression, power descriptions of metal and function of relative value of amplitude intensity of tensions, that characterizes the degree of mechanism influence of fatigue on the fatigue curve is also used. Evolutional equation is written in for the modeling of low cycle fatigue of metals. Lviv Polytechnic National University Institutional Repository http://ena.lp.edu.ua Вимірювальна техніка та метрологія, №77, 2016 р. 137 Correlation for description of low cycle corrosion fatigue of material in metallic underground pipelines is complemented by equations for the evaluation of risks within the limits of investment project that executes corresponding organization (enterprise). For optimization of informative streams of enterprise and improvement of the defence system of metallic underground pipelines from a corrosive fatigue the quality functional is used taking a feed-back in methodology of risk evaluation of investment project into account. The aim of that application is the improvement of the corresponding normative and technical providing. In zones with non-stationary plasticity strain it is expedient to use the criteria of adhesion strength, biocorrosive aggressiveness of soils, mechanical criterion for the coefficient of intensity of tensions (the overstrain of corrosive process takes into account), the criterion of corrosive stability of pitting, criterion correlation for the evaluation of speed of stability corrosion of metal in the defect of isolating coverage together with entered by diagnostic weight of signs and diagnostic value of inspections, that will complement, will specify and will perfect the system of the corrosive monitoring of pipelines and able to be used for control of corrosive process. With their help optimization of terms of construction elements defence of oil and gas industry, that is described and regulated by a state standard, can be conducted. As a result a new complex mathematical model is offered in relation to upgrading of corrosion protection of metallic underground pipelines from positions of corrosion fatigue, electrochemistry, physics of surface processes, mechanics of destruction and theory of risks. The conducted modeling takes piling up of damages in metals into account and allows to study the mechanisms of distribution of corrosive fatigue cracks in underground metallic pipelines that are in aggressive environments, in particular, in saltwater and ground electrolyte. The results of mathematical modeling are the basis of methodology development and improvement of normative and technical documents for metallic underground pipelines, that are under the action of the regular and irregular cyclic loading in the conditions of low cycle corrosive fatigue. The joint use of corrosive fatigue criteria and corrosive monitoring criteria of pipelines offered in this article will allow in detail enough from positions of corrosive fatigue, electrochemistry, physics of surface processes, mechanics of destruction and theory of risks to study the mechanisms of distribution of corrosive fatigue cracks in underground metallic pipelines that are in aggressive environments.Item Аналіз граничних умов працездатності вимірювальних перетворювачів імітансу на базі операційних підсилювачів(Видавництво Львівської політехніки, 2016) Івах, Роман; Хома, Володимир; Хома, Юрій; Питель, Іван; Національний університет “Львівська політехніка”Показано місце та роль активних вимірювальних перетворювачів імітанс-напруга у структурі частотного аналізатора. Проаналізовано фактори, які обмежують працездатність активних вимірювальних перетворювачів. Наведено формалізовані моделі цих перетворювачів та на їх основі встановлено граничні умови, пов’язані з їх стійкістю. Показано место и роль активных измерительных преобразователей иммитанс-напряжение в структуре частотного анализатора. Проанализированы факторы, которые ограничивают работоспособность активных измерительных преобразователей. Приведены формализованные модели этих преобразователей и на их основе установлены предельные условия, связанные с их устойчивостью. Development of specialized portable measurement tools for impedance spectroscopy is quite challenging and up-to-date technical task. Portable impedance analyzers are required to satisfy certain criteria among which the most important are the following: stability of metrological characteristics of measurement channel over a wide frequency range, high dynamics, fast frequency sweep and the probe signal with appropriate step as well as high resolution of impedance/admittance measurement results. Autobalancing circuits are widely used in impedance analyzers design. However, their applications is followed by some problems related to operation stability caused by global feedback loop. The aim of the paper is to study the stability of the active measurements converter based on autobalancing circuits as well as determining their operation limits. The article shows the place and role of active measuring converters immitance-voltage in the structure of the frequency analyzer. Formal models of active converters were used to analyses operational limits related to system stability. The main results of research can be summarized as following: – To determine operating frequency range of the autobalancing circuit can successfully convert impedance to voltage, following rule have been formulated. The upper limit of the frequency range should be taken at least ten times smaller than operational amplifier bandwidth. The lower limit is formally unlimited. – Circuit operational limits related to system stability depends on relation of operational amplifier bandwidth to closedloop knee frequency as well as relation of closed-loop knee frequency to operational circuit time constant (product of reference resistor to input capacitance). – The system is considered to be operating at normal conditions if relation of operational amplifier output resistance to reference resistance is equal or smaller then one. If the ratio excides this threshold, then measurement circuit will lose amplification properties at high frequency..Item Моделювання та якість моніторингу діагностичних систем(Видавництво Львівської політехніки, 2015) Чабан, Олеся; Юзевич, ЛарисаРозроблено рекомендації щодо поліпшення якості математичних моделей моніторингу складних об’єктів техніки та медицини з низьким рівнем динаміки процесів, що характеризуються особливостями раннього виявлення кризових (передаварійних) ситуацій. Разработаны рекомендации относительно повышения качества математических моделей мониторинга сложных объектов техники и медицины с низким уровнем динамики процессов, которые характеризуются особенностями раннего выявления кризисных (предаварийных) ситуаций. The example of improvement of the mathematical model of monitoring of difficult objects of technique and medicine with the low level of dynamics of processes is examined. The article of researches is normative documents, which should be expediented to specify and perfect on the basis of thein formation, got as a result of analysis of results, mathematical models of monitoring of difficult objects of technique, medicine got with a help with the low level of dynamics of processes. An aim of the put article is an evaluation of quality of theim proved mathematical model of monitoring of difficult objects of technique, medicine with the low level of dynamics of processes. As an example, the diagnostic system of the corrosive monitoring of pipelines (SCMP) is examined, the methodologies described and regulated by a state standard are fixed in basis of functioning of that. Facilities of SCMP are diagnose the stress corrosive spalling of pipelines, that is initiated and develops as defects on the external surface of pipe at using of isolating coverage and cathode defence for simultaneous influence of the mechanical loading and corrosive-active environment. A corrosive environment is designed by an aquasystem with the different value of pH-value. The criterion of damage of sheeting the methods of measuring of protective and polarization potentials is a jection of electric potential, that is compared to the value, set corresponding normative document. It is suggested to use methodology of control of constituents for slushing coverage on the stage of making of steel pipes with coverage on the size of regional corner of moistening. Coverages can be metallic, dielectric. In particular, the three-stratified polyethylene coverage is used in the last time. On the size of regional corner of moistening it is possible to estimate adhesion of coverage, in particular, work of adhesion and energy of adhesive bonds. The criterion of adhesion strength for coverage (metallic or dielectric), that is expressed through the critical values of power descriptions of interface layer on the border of metal of pipe with coverage is introduced. The methods of scientific researches are constantly developed and improved. Therefore in course of time standards need additions, id est bringing of new more actual information. Touches such type of addition integral criterion of evaluation of biocorrosive aggressiveness of soils, that takes into account exceptelectro-resistance also a quantity most corrosive dangerous groups of microorganisms and elements of chemical composition of soils. Possible penetration of oxygen, water and other substances is through sheeting. As a result there is a hasp of passive tape with formation of local cells of corrosion – pitting. Pitting of transformed in microcrack, and on the finishing stage one of microcracks initiates distribution of main crack. Procedure of calculation of durability and longevity of pipeline is offered at presence of defects as a cavity there is pitting in the top of that. Methodologies of calculation of durability of steel pipes at presence of defects are complemented by the criteria of durability, that in the models of SCMP was not examined before. The first criteria represents connection of threshold value of coefficient of intensity of tensions of К1SCC with work off lowage in a calculation on unit of the accrued surface at distribution of crack of PPL and overstrain of anodic reaction z of corrosive dissolution. The parameter of PPL is included in the known formula (criterion of durability) of Griffits-Orovan, that it is also suggested to be used. The criterion of Griffits-Orovan binds the limit of fluidity (to durability) of metal to length of crack, by the Young’s module and by the Poisson’s ratio of material. The system of mathematical correlations of SCMP is suggested to complement correlation for the closeness of current of ia in the top of pitting, that is expressed through a corner in the top of pitting, conductivity of electrolyte, dependency upon resistance change of potential between anodic and cathode parts. This correlation is set forth as a criterion of corrosive firmness of pitting. The model of SCMP is complemented by criterion correlation for determination of speed of remaining corrosion of metal (id est closeness of Ik of corrosive current) in the defect of isolating coverage, polarization potential and potential of corrosion of metal of pipeline are included in that. The new entered criteria of durability and corrosive firmness complement, specify and perfect SCMP and can be used for control of corrosive process and development of recommendations of slushing defence. With their help optimization of terms of defence of elements of constructions of metallic underground pipelines can be conducted. The compatible use of the new entered criteria allows in detailen ough from positions of electrochemistry, physics of superficial processes and mechanics of destruction to study the mechanisms of distribution of corrosive cracks in main pipelines that are in aggressive environments. Monitoring quality is characterized by quality of measuring and recreation of information, in particular: by exactness, comparativeness, authenticity, operationability, stability of estimations of parameters, that is included in the new entered criteria. Recommendations in relation to upgrading of mathematical models of monitoring of difficult objects of technique and medicine with the low level of dynamics of processes touch protective potentials, them uncertainty and gradients. An algorithm that is base on the use of the new entered criterion correlations and allows to optimize oscillation of protective and polarization potentials in time is offered in the system of the corrosive monitoring of underground pipelines, that it is necessary for the correct evaluation of corrosive activity of soil and speed of remaining corrosion of metal of pipeline. Corresponding results give an opportunity to forecast the change of the corrosive state of metal of pipeline in course of time and to expect the resource of capacity of local area and all pipeline on the whole. The indicated innovations will help to perfect normative documents, in particular, standards that touch anticorrosion defence.