Úloha proudění v tepelné analýze motoru

The paper presents the relations used for CFD simulation of the flow around the body. The procedures for creation of practically usable computer model of bigger mechanical parts and application of its boundary conditions are described, obtained results are presented. The aim of the work was the analysis of temperature field and cooling parameters of current motor geometry with expectation of further optimization to achieve better cooling power and to reduce the mass of the motor.Předložený článek prezentuje vztahy uživané při numerické CFD analýze obtekaného tělesa. Jsou popsány postupy pro tvorbu prakticky použitelného počítačového modelu strojního celku větších rozměrů, aplikace okrajových podmínek a jsou prezentovány získané výsledky. Cílem práce byla analýza teplotního pole a parametry chlazení současné geometrie motoru s výhledem na případnou optimalizaci tvaru za účelem lepší chladivosti a snížení hmotnosti motoru

Tangent modulus in numerical integration of constitutive relations and its influence on convergence of N-R method

For the numerical solution of elasto-plastic problems with use of Newton-Raphson method in global equilibrium equation it is necessary to determine the tangent modulus in each integration point. To reach the parabolic convergence of Newton-Raphson method it is convenient to use so called algorithmic tangent modulus which is consistent with used integration scheme. For more simple models for example Chaboche combined hardening model it is possible to determine it in analytical way. In case of more robust macroscopic models it is in many cases necessary to use the approximation approach. This possibility is presented in this contribution for radial return method on Chaboche model. An example solved in software Ansys corresponds to line contact problem with assumption of Coulomb’s friction. The study shows at the end that the number of iteration of N-R method is higher in case of continuum tangent modulus and many times higher with use of modified N-R method, initial stiffness method

Study of optimal cam design of dual-axle spring-loaded camming device

The spring-loaded camming device (SLCD), also known as "friend", is a simple mechanism used to ensure the safety of the climber through fall prevention. SLCD consists of two pairs of opposing cams rotating separately, with one (single-axle SLCD) or two (dual-axle SLCD) pins connecting the opposing cams, a stem, connected to the pins, providing the attachment of the climbing rope, springs, which simultaneously push cams to a fully expanded position, and an operating element controlling the cam position. The expansion of cams is thus adaptable to allow insertion or removal of the device into/from a rock crack. While the pins, stem, operating element, and springs can be considered optimal, the (especially internal) shape of the cam allows space for improvement, especially where the weight is concerned. This paper focuses on optimizing the internal shape of the dual-axle SLCD cam from the perspective of the weight/stiffness trade-off. For this purpose, two computational models are designed and multi-step topology optimization (TOP) are performed. From the computational models' point of view, SLCD is considered symmetric and only one cam is optimized and smoothened using parametric curves. Finally, the load-bearing capacity of the new cam design is analyzed. This work is based on practical industry requirements, and the obtained results will be reflected in a new commercial design of SLCD.Web of Science148art. no. 194

Tvarová optimalizace - vliv užité symetrie výpočtového modelu

The contribution presents the cooling rib optimization on the two numerical models with the aim to show the influence of used model geometry on the optimization problem properties. The parameters of used computational models (the models differ in used symmetry conditions) and the application of boundary conditions are presented. The obtained results show the necessity to take into account the authentic rib space arrangement in model simulations of optimization problem.Článek prezentuje optimalizaci chladicího žebrování na dvou výpočtových modelech, s cílem poukázat na vliv rozdílnosti modelů na vlastnosti optimalizační úlohy. Jsou popsány parametry použitých počítačových modelů (modely se liší v užitých podmínkách symetrie) a aplikace okrajových podmínek. Získané výsledky dokumentují nutnost zohlednění věrného prostorového uspořádání žeber v modelových simulacích úlohy optimalizace

Neproporcionální namáhání materiálu

Import 09/02/2007Prezenční339 - Katedra pružnosti a pevnost

Užití numerických metod při řešení méně častých úloh technické praxe

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Parametric studies of total load-bearing capacity of steel arch supports

The supports in roadways are dimensioned to the amount of the load applied during the roadway's life. Roadways are exposed to the effect of rock pressure associated with the roadway drivage and with subsequent operations that extract coal, which significantly affect the original stability of rock mass. This induced secondary stress leads to the disturbance of sedimentary rocks, which are mostly of slight and medium strength, and to the significant deformations in roadways. The gate-roads are mainly supported with yielding steel arch support (TH profiles). The load-bearing capacity of the steel arch supports is a key parameter in the design of roadways support. Determination of this parameter can be done using large testing frames in experimental laboratories. Another essentially cheaper way is to create a computer model which exhibits a good correlation with respect to the existing data from equivalent laboratory conditions. In this paper, we present the validated computer model of the steel arch supports through which the influences of important factors, namely different materials, number of the clamps in the yielding friction joints, and different values of tightening torque on the total load-bearing capacity, were determined. This parametrical study was created based on the practical requirements from industry, and the obtained results will be reflected in the design of new types of steel arch supports.Web of Science24322221

Nová aplikace konjugovaného kritéria pevnosti

This article describes experimental results under combined loading of specimens manufactured from construction steel 11523. Specimens were loaded by amplitude of the torque, then by combination of torque and tension prestress. For evaluation of the results the conjugated strength criterion was applied. Further, another approximation based on the same boundary conditions as the described conjugated strength criterion was proposed. The performed experiments and their results embody a good agreement with bellow mentioned conjugated strength criterion. The experiments were performed on modified testing machine.Tento příspěvek popisuje výsledky experimentů při kombinovaném zatěžování zkušebních vzorků vyrobených z konstrukční oceli 11523. Zkušební vzorky byly zatěžovány amplitudou krouticího momentu, dále pak kombinací amplitudy krouticího momentu s tahovým předpětím. Na výsledky experimentů bylo aplikováno konjugované kritérium pevnosti. Dále byla navržena jiná aproximace, která vychází ze stejných okrajových podmínek jako popsané konjugované kritérium pevnosti. Výsledky experimentů vykazují dobrou shodu s použitým kritériem. Zkoušky byly provedeny na upraveném zkušebním zařízení

Algoritmus pro zkoumání rázů v rotorových soustavách uložených v radiálních aktivních magnetických ložiskách

The active magnetic bearings (AMBs) are consist of quite complicated and expensive electromechanical parts and due to this fact they are protected by the auxiliary bearings. If the rotor system design is made so that the clearance between the disc and the stationary part is smaller than between the auxiliary bearing and the shaft journal the contact between those two parts can occur due to the overloading of the rotor system. The influence of radial AMBs and of the impacts in rotor system is usually investigated separately. Eventually, the shaft is modelled as rigid or elastic but massless body. Due to this it is necessary to develop a procedure which makes possible to analyze their mutual behaviour on the rotor system discretized by the finite element method. The proposed procedure is verified on the test rotor system and the influence of Rayleigh coefficient of external damping and of vibration character during the impacts occurring between the disc and the stationary part is investigated by means of numerical simulations.Radiální aktivní magnetická ložiska se skládají ze složitých a drahých elektromechanických částí a proto jsou chráněna pomocnými ložisky před mechanickým poškozením. Jestliže je konstrukční návrh rotorové soustavy proveden tak, že mezera mezi diskem a stacionární části je menší než mezi pomocným ložiskem a stacionární části, může během přetížení rotorové soustavy dojít ke kontaktu mezi těmito částmi. Obvykle je vliv radiálních aktivních magnetických ložisek a rázů v rotorových soustavách zkoumán odděleně. Případně je hřídel modelován jako tuhé nebo pružné, ale nehmotné těleso. Proto je důležité vyvinout proceduru, která umožňuje analyzovat jejich vzájemné působení na rotor diskretizovaný metodou konečných prvků. Navrhnutá procedura je ověřena na testovací rotorové soustavě a numerickými simulacemi je zkoumán vliv Rayleigho koeficientu vnějšího tlumení na charakter kmitání během rázů nastávající mezi diskem a stacionární části

The Stirling engine mechanism optimization

A special type of the gas engine with external combustion is called Stirling engine. The mechanism has two pistons with two volumes inside. The pistons are connected together through cooler, regenerator and warmer. The engine effectivity depends on the piston movement behaviour. The usual sinusoidal time curve leads to low effectiveness. The quick movement from lower to upper position with a certain delay in both top and bottom dead centres is more effective. The paper deals with three types of mechanisms, analyzing the piston movement, and their behavior. Special emphasize is taken to the piston movement regime