Nelinearna analiza prsta za zaključavanje lakog manipulatora u PWR elektranama

master's thesis

• Title (english): Nonlinear analysis of gripping mechanism on PWR manipulator
• Author: Imra Tadijanović
• Mentor: Igor Karšaj (mentor)
• Mentor: Ante Bakić (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2016-12-09, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering; General Mechanical Engineering (Construction)

Abstract

Nuklearne elektrane PWR (Pressurized Water Reactor ) tipa imaju reaktor s vodom pod tlakom i nalaze se u većini zapadnih zemalja. Redovito podliježu inspekcijama s ciljem provjere njihovog stanja i procjene životnog vijeka. Inspekcija parogeneratora u nuklearnoj elektrani obuhvaća ispitivanje oštećenja na protočnim cijevima pomoću nerazorne Eddy Current metode ispitivanja. Ispitivanje se provodi metodom vrtložnih struja provlačenjem sonde kroz cijelu dužinu protočne cijevi mjereći oštećenja na unutrašnjoj stijenci cijevi. Kvarovi se jako teško uklanjaju, te za posljedicu mogu imati miješanje vode primarnog kruga (voda koja je u direktnom kontaktu s gorivim elementima nuklearnog reaktora) s vodom sekundarnog kruga koja prolazi svim pogonskim točkama elektrane (parna turbina, kondenzator). Posljedice takvog oštećenja su komplicirane te zahtijevaju vrlo visoke investicije i isključivanje elektrane na duže razdoblje. Inspekcije obavljaju robotizirani sustavi umjesto ljudi zbog visoke radijacije.

Tvrtka INETEC je razvila mobilni manipulator Forerunner koji se prvenstveno koristi za ispitivanje oštećenja protočnih cijevi parogeneratora u nuklearnoj elektrani. Forerunner ima sposobnost kretanja poput pauka na vertikalnoj ili horizontalnoj cijevnoj stijeni i jednostavnu prilagodbu na različite konfiguracije i promjere cijevi na parogeneratoru. Sastoji se od dva para gripera koje ga drže i omogućuju gibanje na cijevnoj stijeni. Griper čine prst i pneumatski aktuator. Prst gripera je posebno dizajniran da izdrži sva opterećenja koja se mogu javiti tijekom inspekcije cijevi. Svaki prst ima svoj pneumatski aktuator koji može ostvariti ukupne sile od 500 N do 1800 N. Također ima poseban mehanički sustav zaključavanja koji se koristi kada je prst u cijevi. Mehanički sustav za zaključavanje starog prsta za cijev se sastojao od tri elementa što je povećavalo šansu da neki od elemenata prsta olabavi tijekom inspekcije u cijevi parogeneratora što dovodi u opasnost pada manipulatora s cijevne stijene i oštećenja parogeneratora. Prema preporuci nacionalnih regulatornih tijela potrebno je izmijeniti prst tako da umjesto tri elementa ima samo jedan element. U sklopu ovog rada proveden je kontrolni numerički proračun čvrstoće postojećeg prsta gripera i na osnovu dobivenih rezultata predložen je novi oblik prsta koji se sastoji od jednog komada. Treba paziti da novi prst prilikom zaključavanja za cijev ne ulazi u plastično područje i da su naprezanja znatno manja od granice razvlačenja.

U programskom paketu Abaqus, provedena je numerička analiza pomoću metode konačnih elemenata za razvoj novog prsta manipulatora koja je detaljno opisana kao i modeliranje kontakta u Abaqus-u. Verifikacijom kontakta dva klina prizmatični konačni element drugog reda s reduciranom integracijom odnosno C3D20R se pokazao kao najbolji element za kontaktne probleme.

Prikazana su dva koncepta novog dizajna prsta, ali je samo jedan detaljno konstrukcijski i numerički razrađen. Prilikom razvoja prsta moralo se paziti na ograničenja novog dizajna prsta kao i na njegovu montažu. Na samom kraju provedena je numerička analiza čvrstoće na konačnoj verziji prsta kako se zaključava u cijev parogeneratora, kako bi se ispitala kvaliteta zaključavanja prsta unutar cijevi.

Abstract (english)

Pressurized Water Reactors (PWRs) have submerged reactor and they are in use in most western countries. PWRs are regularly inspected in order to verify their condition and to assess their operation lifetime. Inspection of steam generators in nuclear power plant includes testing of the tube by using non-destructive Eddy Current method. Testing is carried out by running the probe through the entire length of the tubes in order to check for possible cracks or damage on the tube’s inner wall. Damaged or cracked tubes in a steam generator are very difficult to remove and may result in mixing the primary loop water (contaminated by radioactive materials) with the secondary loop water which passes through all other key operating points of a power plant (turbine, condenser). Consequences of such damage are severe, driving the power plant into a long and expensive maintenance shutdown. Due to high levels of radiation, inspections are not carried out by people but by the highly specialised robotic systems.

INETEC has developed a mobile manipulator Forerunner which is primarily used for automated damage inspection of nuclear power plant steam generator tubing. Forerunner has the ability to move like a spider on both vertical and horizontal tubesheet and it can easily adapt to different tube configurations and diameters. It is made of two pairs of grippers which allow it to grip and to move along tubesheet. Each gripper has a finger and an actuator. The finger is designed to withstand all mechanical loads which can occur during the tube inspection. Pneumatic actuator on each finger can produce between 500 to 1800 N of force. It also has a mechanical locking system when the finger is inside the tube. The old mechanical locking system had three components which increased the possibility that something might become loose and cause the manipulator to fall of the tubesheet and damage the steam generator. By the recommendation of national regulatory authorities the finger should be modified to have only one component. In the scope of this thesis, a control numerical strength analysis of the existing version of the gripper finger was carried out and based on those results a new design of the finger with only one component is proposed. New design is evaluated in a locked position in which no plastic deformation is allowed and stresses should be kept well below the yield point.

A numerical finite element analysis is carried out using Abaqus software package in order to develop a new design of the gripper finger. The analysis procedure and contact modelling are described in detail. After the verification of contact model on two wedges, a prismatic finite element C3D20R (Abaqus) proved to be the most suitable for dealing with contact problems.

Two concepts of new gripped finger are developed, but only one is elaborated and fully analysed. During the development process both structural and assembly requirements had to be fulfilled. In the end, numerical strength analysis of the final design of the gripper finger in a locked position inside the tube was carried out to evaluate the quality of the contact between the manipulator and the tubesheet.

• Keywords: metoda konačnih elemenata; Eddy Current; griper; parogenarator; prst; cijevna stijena.
• Keywords (english): finite element method; Eddy Current; gripper; steam generator; finger; tubesheet
• Language: croatian
• URN:NBN: urn:nbn:hr:235:974139
• Study programme: Title: Mechanical Engineering; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka strojarstva (magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2019-05-22 18:04:57