Temperaturne prijelazne pojave u stijenci sfernog spremnika

Uneven and non-stationary temperature field is formed in the reservoir wall while loading pressure reservoir with a liquefied gas in cooling state, at a temperature lower than the saturation temperature at given pressure. Mathematical model of the temperature field is developed by setting and solving differential equation of heat diffusion in the spherical wall in real conditions of the wall getting cold. The model enables computation of the temperature gradient attaining very high values at the liquid level. A simplified procedure for calculating the wall temperature increase in the narrow area above the liquid level was also developed. Understanding of the temperature field in the reservoir wall allows further heat stresses calculation. For this purpose, a temperature discontinuity should be approximated by a continuous function. Approximation was applied by Fourier\u27s orders, and coefficients of an order are determined by the electronic computer program. The model application procedure has been illustrated by the example of spherical pressure reservoir for liquefied carbon dioxide.Tijekom punjenja tlačnog spremnika ukapljenim plinom, pothlađenim ispod temperature zasićenja za zadani tlak, nastaje u stijenci spremnika nejednoliko i nestacionarno temperaturno polje. Matematički model temperaturnog polja razvijen je postavljanjem i rješavanjem diferencijalne jednadžbe provođenja topline u sfernoj stijenci u realnim uvjetima ohlađivanja stijenke. Model omogućava izračunavanje temperaturnog gradijenta koji na visini razine kapljevine poprima vrlo visoke vrijednosti. Razvijen je također i pojednostavljeni postupak za izračunavanje iznosa porasta temperature stijenke u uskom području iznad razine kapljevine. Poznavanje temperaturnog polja u stijenci spremnika omogućava dalje izračunavanje toplinskih naprezanja. U tu svrhu diskontinuitet temperature treba aproksimirati kontinuiranom funkcijom. Primijenjena je aproksimacija pomoću Fourierovih redova, a koeficijenti reda se određuju pomoću programa za elektroničko računalo. Postupak primjene modela ilustriran je na primjeru sfernog tlačnog spremnika za ukapljeni ugljični dioksid

Conceptual Model and Evaluation of Design Characteristics in Product Development

The paper presents an original model of evaluation in the design process, especially developed model transformation features in the conceptual design by an approach for establishing effective mapping and transformation process between product properties and domain requirements from different domains. Model transformation feature in the conceptual process of designing and the valuation model features of products is shown and described mathematically. The proposed meta-level consists of general discrete mathematical models and combinatorial representation. Special mathematical basis for the evaluation of models and combinatorial analysis for each alternative solution is derived from the theory of graphs. All variant solutions must be evaluated according to the range of the set criterions as list of requirements. Using originally developed conceptual model and evaluation model, assumptions were made for the purpose of defining the weight matrix in order to avoid errors in selecting the final solution variants. A short view of the application is given in the example

Analysis of Modification of Spur Gear Profile

The article presents an analysis of the modification of the toothing of spur gears. The aim of the modification of the profile on the tooth tip is to compensate for the tooth deflection under loading and to improve the conditions of gear operation. Cases of longitudinal toothing modification of a convex-convex (Cv-Cv type) tooth are described, where the tooth is biconvex and the gear teeth are convex-concave (Cv-Cc type). The conditions of mating of modified gears have been analyzed. A method of machining gears by the step-by-step method has been proposed, which can be used in unit machining of large-module gears with an arbitrary profile modification system

Design and calculation of planetary transmission with bevel gears

In this paper, the design and calculation of planetary transmission with bevel gears for road vehicles is presented. It must transfer power to the wheels with the possibility that wheels can rotate at different speeds. The basic calculation of transmission is performed for the drive machine, where an internal combustion engine is chosen, and for the driven machine, which is a car, all forces of resistance are calculated so that the transmission needs to be overcome to move the car. Based on the standard ISO 23509:2016 norm, the calculation of geometry is performed for the input gear pair and it is defined as a hypoid gear pair. For the planetary transmission, a calculation of gear module for bevel gears is first performed, and after that, the geometry is calculated. The calculation of the stress for root stress and Hertz contact pressure is performed for all bevel gears in transmission

Biomechanical Analysis of the Gracilis and Superficial Third of the Quadriceps Tendons Concerning MPFL Biomechanics

The primary goal of this research is the analysis of the biomechanical performances of most common transplants (distal tendon of m.gracilis and upper third of m.quadriceps femoris) used for the reconstruction of the medial patellofemoral ligament (MPFL). The secondary goal is the comparison of the data obtained from the research with the data available in the literature.The research was conducted on 16 samples of the human tendon, of which there are 8 gracilis tendons and 8 quadriceps tendons. Tensile strength is significantly higher in gracilis tendon (26 MPa - 92 MPa) than in quadriceps tendon (30 MPa - 44 MPa). The extensibility is significantly higher in the quadriceps tendon (10% - 15%) than in the gracilis tendon (13% - 17%). Regarding stiffness (N/mm) there are no significant differences between the groups of gracilis and quadriceps tendons. The module of elasticity is significantly higher in gracilis tendon (235 MPa - 855 MPa) in comparison to quadriceps tendon (239 MPa - 361 MPa).The biomechanical characteristics of the distal surface third of the quadriceps tendon are more favourable than the distal tendon of the gracilis which could prove applicable in operative techniques of reconstruction of the medial patellofemoral ligament when choosing a transplant

Solutions to the characteristic equation for industrial robot’s elliptic trajectories

Linearne nezavisne neprojektivne transformacije rabe se za različite vrste aplikacija. Predlaže se direktna analitička metoda za rješenje linearne transformacije karakteristične jednadžbe za industrijskog robota. Teorijska osnova metode proizlazi iz klasičnih rješenja sa simetrijama, ali metoda ne sadržava formule s korijenima. Automorfizmi se dijele na teoriju skupova i opću algebru. To nam omogućuje učinkovitiju primjenu te metode za druge tehničke zadatke.Linear independent non-projective transformations are used for different types of applications. Direct analytical method for solving the linear transformation of the characteristic equation for industrial robot is proposed. The theoretical basis of the method derives from the classical solutions with symmetries, but the method does not contain formulas with radicals. Automorphisms are divided into set theory and universal algebra. This feature allows us to use this method more efficiently for other engineering tasks

Measurement of Fine Grain Copper Surface Texture Created by Abrasive Water Jet Cutting

The paper presents results of experiments performed on copper with commercial purity to determine the influence of material grain size on both mechanical properties and texture of surface machined by abrasive water jet. An Equal Channel Angular Extrusion technology was used for creation of fine-grain copper samples. Hardness and grain size of fine-grain copper were measured, and, subsequently, surface of prepared copper samples was machined by abrasive water jet technology. Surface irregularities produced by the abrasive water jet were evaluated by means of surface profile roughness parameter Ra. It was found that the grain size of the material represents important factor affecting the final shape of surface topography in case of abrasive water jet machining

Experimental research on machine elements of helicoidal shell shape

U radu su predstavljeni modeli za eksperimentalno i numeričko istraživanje zavojne ljuske. Tri oblika su odabrana za eksperiment: model A predstavlja zavojnu ljusku na cilindričnoj ljuski, model B kružnu ljusku na cilindričnoj ljuski, i model C pravokutnu ljusku na cilindričnoj ljusci. Ostvarenje kontinualnog opterećenja po površini ljuske je izvršeno pomoću normalnog tlaka koga osigurava konstrukcija sa dvostrukom zavojnom ljuskom sa posebnim elementima za brtvljenje. Mjerenje naprezanja je izvršeno korištenjem mjernih traka. Usporedni rezultati su dobiveni uporabom softverskog paketa za analizu pomoću metode konačnih elemenata ANSYS Workbench. Eksperimentalna istraživanja su potvrdila da numeričko modeliranje daje mjerodavne rezultate naprezanja, deformacija i ugiba kontinualno opterećene zavojne ljuske.In this paper we present a model for the experimental and numerical study of helical shells. Three different forms were chosen for the experiment: Model A forms a helicoidal shell on a cylindrical shell, Model B is an annular shell on a cylindrical shell and Model C a rectangular plate on a cylindrical shell.. Placing a continuous load on the surface of the shell was achieved by normal pressure, thanks to special sealing elements within the construction of the double helical shell.The strain was measured using strain gauges. Comparable results were obtained using the ANSYS Workbench software package for analysis using the finite element method. The experimental investigation confirmed that the numerical modelling provides relevant results for the stress, deformation and deflections of continuously loaded helical shells

Analiza značajki mehanizama ultra­lake teleskopske dizalice/podesta

Based on the research of mechanical properties of fine-granular high-strength steels and the obtained results, the design of prototype ultra-light telescopic crane was performed. The article presents the analysis results of the crane drive mechanism. The geometric synthesis of shapes and sizes of four joint was performed based on the maximum and minimum slope of each arm and on the minimum weight. Feedback of optimal shape of each mechanism\u27s stick was implemented by the variant solutions evaluation methods. The detailed calculation of stress and strain in each mechanism\u27s stick was performed by finite element method.Temeljem istraživanja mehaničkih svojstava sitnozrnatih visokočvrstih čelika i dobivenih rezultata izvršeno je projektiranje prototipa ultralake teleskopske dizalice. U članku su prikazani rezultati analize pogonskog mehanizma dizalice. Izvršena je geometrijska sinteza oblika i dimenzija četverozgloba na temelju maksimalnog i minimalnog nagiba pojedine ruke i minimuma masa. Ocjena optimalnog oblika pojedinog štapa mehanizma provedena je metodama vrednovanja varijantnih rješenja. Detaljan proračun naprezanja i deformacija u pojedinim štapovima mehanizma izvršen je metodom konačnih elemenata

Vrednovanje kinematičkih struktura robota za zavarivanje na temelju koncepcijskih modela primjenom metode potencijala

The article presents a new systematic approach to evaluate kinematic structures of the robot for welding in the application of certain conceptual solutions in different welded forms of product design. Generated conceptual solutions of the welded structure are independent of the eight kinematic structure models of the robots. Conceptual solutions of welded structures are defined according to the possibility of their practical performance as shown in models of product design in welded form. Five groups of welded structures have been analysed with three characteristic examples in each group of products designed at the conceptual level (such an approach makes 15 varieties of solutions) in the form of welded structures. In the paper we shall described a new model of evaluation by the application of the Potential method (one of the decision making tools) as appropriate choice for the concept of kinematic structures of robots for welding in welding technology of steel structures. Selection is carried out based on the list of requirements with twelve independent parameters. These parameters must define the welding robot in fifteen models of welded structures. List of requirements is determined by types of design products (fifteen variant solutions) in welded form. The originality of the proposed evaluation procedure lies mainly in special application of the potential method for evaluating weight factors of kinematic structures of welding robots based on conceptual welded forms of product design. A model for linking a criteria and alternatives of kinematic structures for robot welding is also shown and described. Introduced is the model to determine the criteria to evaluate kinematic structures according to the criteria for welding the fifteen models of welded structures. These two sets of parameters (parameters of the set of kinematic structures and the set of welded forms of product design) make possible the estimation acceptability for application. In the article is calculated the weighted value of solutions of kinematic structures of welding robot that fully satisfies the theoretical settings and/or practical variants solution of a robot with the highest technical performance. Moreover, in order to implement a thorough evaluation process such as decision making based on defined list of requirements in examples in this paper, we suggest and show the procedure that can serve as a procedure for evaluation of other systems for the same purpose using the Potential method.Članak predstavlja novi sustavni pristup ocjenjivanju kinematičkih struktura robota za zavarivanje u primjeni određenih koncepcijskih rješenja različitih oblika zavarene konstrukcije proizvoda. Generirana koncepcijska rješenja zavarene konstrukcije ne ovise o osam modela kinematičkih struktura robota. Koncepcijska rješenja zavarene konstrukcije definirana su prema mogućnosti njihove praktične izvedbe kao što je prikazano u modelima proizvoda u zavarenom obliku. Analizirano je pet skupina zavarenih konstrukcija s tri karakteristična primjera u svakoj grupi oblikovanog proizvoda na razini koncepcije (takav pristup daje 15 varijanti rješenja) u obliku zavarenih konstrukcija. U radu je opisan novi model vrednovanja primjenom metode potencijala (jedan od alata za donošenja odluka), prikladan za izbor koncepcije kinematičke strukture robota za zavarivanje u tehnologiji zavarivanja čeličnih konstrukcija. Izbor se provodi na temelju liste zahtjeva s dvanaest neovisnih parametara. Ovi parametri moraju definirati robot za zavarivanje za petnaest modela zavarene konstrukcije. Originalnost predloženog postupka ocjenjivanja nalazi se uglavnom u posebnoj aplikaciji metode potencijala za procjenu težinskih faktora kinematičkih struktura robota za zavarivanje na temelju koncepcije zavarenih oblika proizvoda. Također, prikazan je i opisan model povezivanja kriterija i alternativa kinematičkih struktura robota za zavarivanje. Predstavljen je model za utvrđivanje kriterija za ocjenu kinematičkih struktura prema kriterijima za zavarivanje petnaest modela zavarenih konstrukcija. Ta dva seta parametara (parametri skupa kinematičkih struktura i skup zavarenih oblika proizvoda) čine mogućnost čvrste ocjene prihvatljivosti za primjenu. U članku je određena ponderirana vrijednost rješenja kinematičkih struktura robota za zavarivanje koji u potpunosti zadovoljava teorijske postavke i/ili inačice praktičnog rješenja robota s najvišom tehničkom dobrotom. Štoviše, kako bi se obavila temeljita provedba procesa kakvo je odlučivanje na temelju definirane liste zahtjeva u primjerima ovog rada, predlaže se i pokazuje postupak koji može poslužiti kao postupak za ocjenu drugih sustava za istu svrhu, korištenjem metode potencijala