The state and behavior of dynamicaly loaded structures in extreme operating conditions

Osnovna ideja na kojoj se zasnivaju bazni ciljevi disertacije je identifikacija ekstremno teških uslova eksploatacije mašinskih struktura i njihovih opterećenja koji predstavljaju kompleksnu interakciju izuzetno visokih toplotnih i nehomogenih uticaja, intenzivnih uticaja strujanja fluida, uticaja visokih brzina rotacije, sopstvenih i prinudnih vibracija i dr. Ovi su uticaji prisutni kod gasogeneratora turbomlaznih i turbovratilnih motora za koji je bilo potrebno razviti inovativno konstrukcijsko rešenje multifunkcionalne pregrade između rotora kompresora i turbine. Za realizaciju postavljenog cilja razvijena je odgovarajuća metodologija inženjerskog dizajna zasnovana na iterativnom razvoju, ispitivanju i analizi stanja i razaranja delova pregrade, pod nazivom Failure-based Design – FBD. Razvijen je skup od pet konstrukcijskih rešenja ove pregrade. Četvrto rešenje je postalo prihvatljivo za eksploataciju u ovim uslovima, a peto rešenje je ostvarilo sve funkcije i zadovoljilo sve zahteve. Za ovu svrhu sprovedena su mnoga eksperimentalna ispitivanja, brojne numeričke analize strujanja fluida (CFD), analiza toplotnog stanja (raspodele temperature), proračuna napona i deformacija delova pregrade, razvoj konstrukcijskih rešenja i dr. Radi realizacije osnovnog cilja, rad je obuhvatio širok spektar eksperimentalnih sadržaja, značajan broj numeričkih analiza i proračuna, analiza brojnih specifičnih havarijskih oštećenja i predloženih konstrukcijskih rešenja da bi se ova razaranja izbegla.The general idea on which the basic goals of the dissertation are founded on is the identification of extremely hard conditions of mechanical structures and their loads which represent a complex interaction of several influences, i.e. extremely high heat, nonhomogeneous influences, intensive influences of fluid flow, high rotation speeds, its natural and forced vibrations etc. These influences are present at the gas generator of turbojet and turboshaft engines for which there was a need to develop an innovative construction solution for the multifunctional bulkhead between the compressor rotor and the turbine. In order to accomplish the set goal, an appropriate methodology of engineering design was developed which is based on iterative development, testing and analysis of the state and damage of the parts of the bulkhead, which is called Failure-based Design – FBD. A set of five construction solutions for the bulkhead was developed. The fourth solution became acceptable for exploitation in these conditions, while the fifth solution accomplished all functions and met all the requirements. In order to achieve this, numerous experimental testings were performed, along with many numerical analyses of the fluid flow (CFD), heat state (temperature distribution), stress and deformations calculations of the bulkhead parts, the development of construction solutions etc. In order to achieve basic goal, the paper encompassed a wide range of experiments, a significant number of numerical analyses and calculations, analyses of many specific damages and suggested construction solutions so as to avoid these damages

Calculation of the Archard's wear coefficient of the polymer-based composite sliding bearings

Prediction and calculation of wear of the mechanical components in contact is one of the most important tasks in modern engineering. Due to time consumptive experiments and quite expensive test rig, it became even more challenging to evaluate wear by means of the computer simulation instead of the real experiments. With rapid improvement of the computer resources, this task became more realistic, and the results are more concurrent to those obtained by experiments. Since the most of the solvers evaluate wear by means of the Archard's equation, to perform the simulation it is mandatory to determine Archard's coefficient K. This paper provides necessary steps, experimental investigations and measurements in order to calculate Archard's coefficient K, as an input value for the simulation of wear of the polymer-based composite sleeve bearings

Heat transfer and lubrication of turboshaft motor-reducer

Turboshaft engines, as the rule, contains gear transmission unit - reducer and belong to the group of drive systems with the name motor-reducer. These are the compact and autonomous assemblies for various applications. In the case of turboshaft engine in combination with high speed reducer, arise the set of phenomenon which has to be solved. Majority of them are in relation to reducer protection of overheating and of gears and bearings failures. The article contains analysis of heat sources, heat transfer through design structure and heat taking out in order to maintain acceptable temperature level of reducer lubricant. Theoretical discussions are supported with various experimental results and testing procedures, including analytic calculations. The set of design solutions for reducer protection when reducer located in the area of hot gas flow, is the main content. The case study is innovative design of turboshaft motor-reducer with free turbine which provides flexible operation and compact design structure

Wear simulation of the polymer based composite sliding bearings by means of ansys

Polymer based composite sliding bearings are increasingly applied in many industries, due to their economic (usually low cost of production) and technical (good tribological properties) benefits. In order to predict their life cycle, it is necessary to perform numerous experiments and evaluate their wear rate. This is generally quite expensive and time consuming. By applying only one series of the experiments and determining Archard’s wear coefficient, and embedding it into the code of the Ansys software, it is possible to simulate the wear, and thus save the time and the financial resources. This paper explains the procedure of the wear simulation in case of known Archard’s coefficient, for sliding bearings made of PTFE polyamide composite material in contact with shaft of steel. The output of the simulation is the contact pressure in relation of time and the amount of worn volume for 3 revolutions of the shaft

Wear simulation of the polymer based composite sliding bearings by means of ansys

Polymer based composite sliding bearings are increasingly applied in many industries, due to their economic (usually low cost of production) and technical (good tribological properties) benefits. In order to predict their life cycle, it is necessary to perform numerous experiments and evaluate their wear rate. This is generally quite expensive and time consuming. By applying only one series of the experiments and determining Archard’s wear coefficient, and embedding it into the code of the Ansys software, it is possible to simulate the wear, and thus save the time and the financial resources. This paper explains the procedure of the wear simulation in case of known Archard’s coefficient, for sliding bearings made of PTFE polyamide composite material in contact with shaft of steel. The output of the simulation is the contact pressure in relation of time and the amount of worn volume for 3 revolutions of the shaft

Heat transfer and lubrication of turboshaft motor-reducer

Turboshaft engines, as the rule, contains gear transmission unit - reducer and belong to the group of drive systems with the name motor-reducer. These are the compact and autonomous assemblies for various applications. In the case of turboshaft engine in combination with high speed reducer, arise the set of phenomenon which has to be solved. Majority of them are in relation to reducer protection of overheating and of gears and bearings failures. The article contains analysis of heat sources, heat transfer through design structure and heat taking out in order to maintain acceptable temperature level of reducer lubricant. Theoretical discussions are supported with various experimental results and testing procedures, including analytic calculations. The set of design solutions for reducer protection when reducer located in the area of hot gas flow, is the main content. The case study is innovative design of turboshaft motor-reducer with free turbine which provides flexible operation and compact design structure

Research of expendable turbojet tubular combustion chamber

This paper presents research related to the tubular combustion chamber of an expendable turbojet. Although annular combustors are dominant at present, tubular combustors are still attractive because they are simpler to produce and require lower amounts of air flow for testing. The objective of this research was to assess the combustor's primary zone configuration, and four configurations were tested to obtain experimental answers for use in future work. The configuration of the combustion chamber is a simple and classic design in line with its expendable purpose. The test methodology was to perform initial testing of the primary and secondary zones under atmospheric conditions using the four configurations, and then to subsequently complete the combustor using the best configuration. The complete combustor was then tested under both atmospheric conditions and working conditions. The results showed that the stability margin was wide enough to cover the combustor's entire working area. The measured efficiency and pressure drop were in very good agreement with the corresponding designed values. The design and testing methodology proposed here could be used for similar scientific and engineering research applications

Analysis and design of the gas generator multifunctional bulkhead considering the thermal and structural loads

The operation of gas generators brings relatively high thermo-mechanical loads on the gas generator structure. The objective of this article is to determine the operating conditions, in terms of mechanical loads at extremely high temperatures in very limited and narrow space, of a multifunctional bulkhead for application on specific kinds of gas generators with back-to-back rotor concept. The paper contains numerical analysis and experimental investigation for determining the loads and behavior of the structure. Numerical analysis indicates that there is significant influence of the Tesla turbine effect on flow parameters. Also, uneven pressure distribution and significant thermal loads are identified. With experimental investigation and subsequent exploitation tests, it was concluded that the presented methodology identifies the operating conditions, truthfully simulates the bulkhead stress state and deformations and that the presented design solution satisfied all demands. Regarding results obtained by these numerical simulations, the innovative design solution for the multifunctional bulkhead was proposed

Motivacioni modeli serijskih seksualno motivisanih ubistava

There are various motives of committing a criminal act. When we talk about homicide, we need to say that it can be the result of huge number of motives, first of all, revenge, blood feud, material gain, jealousy, political motives, sexual motives, etc. The authors present motivational model of multiple-serial killers, and pay attention on factors which contribute that a person becomes a serial killer. First of all, they focus on influence of inadequate social environment, events during childhood, model of responsibility and operations directed to others and us.Polazeći od velikog broja determinanti koje mogu uticati na neko lice da izvrši seriju seksualno motivisanih ubistava, autori u radu vrše analizu motivacionih modela, kojima se nastoji dati odgovor na pitanje zašto jedno lice postane učinilac serije takvih krivičnih dela. Pri tome, posebnu pažnju su usmerili na motivacioni model koji su Berdžes i njegovi saradnici koristili u objašnjenju seksualno motivisanih ubistava i model kontrole traume koji je definisao Hiki (Hickey). Na kraju, s ciljem objektivnijeg sagledavanja ubistava, date su kratke informacije o motivacionom spektru koji su Revič i Šlezindžer koristili za klasifikaciju serijskih ubistava

Motivacioni modeli serijskih seksualno motivisanih ubistava

There are various motives of committing a criminal act. When we talk about homicide, we need to say that it can be the result of huge number of motives, first of all, revenge, blood feud, material gain, jealousy, political motives, sexual motives, etc. The authors present motivational model of multiple-serial killers, and pay attention on factors which contribute that a person becomes a serial killer. First of all, they focus on influence of inadequate social environment, events during childhood, model of responsibility and operations directed to others and us.Polazeći od velikog broja determinanti koje mogu uticati na neko lice da izvrši seriju seksualno motivisanih ubistava, autori u radu vrše analizu motivacionih modela, kojima se nastoji dati odgovor na pitanje zašto jedno lice postane učinilac serije takvih krivičnih dela. Pri tome, posebnu pažnju su usmerili na motivacioni model koji su Berdžes i njegovi saradnici koristili u objašnjenju seksualno motivisanih ubistava i model kontrole traume koji je definisao Hiki (Hickey). Na kraju, s ciljem objektivnijeg sagledavanja ubistava, date su kratke informacije o motivacionom spektru koji su Revič i Šlezindžer koristili za klasifikaciju serijskih ubistava