One of the most basic issues in fluid mechanics is the description of flow in closed flows; more precisely, the calculation of pressure drops and the description of the flow form. Therefore, in this paper, the numerical simulation of the flow through the elbow was presented. This case was used to comprehensively describe the most important phenomena that should be taken into account during closed flows. The elbow was chosen as one of the most frequently used fittings in practice. The simulation was made with ANSYS Fluent, with the use of the turbulent model k-ω, SIMPLE simulation method, and at Reynolds number $Re=500-100,000$. The minor and major pressure loss were presented and discussed in the paper. The minor loss coefficient at the high Reynolds number was equal to around 0.2, which is close to the value of 0.22 used in engineering calculations. The influence of the Reynolds number on the shift of the stream separation point in the elbow was described. The secondary flow in the elbow was observed and the vortex structure was discussed and shown with the use of the Q-criterion (Q iso surface for level 0.005). This analysis allowed us to better visualize and describe the complex flow structure observed in the investigated case.

This study proposes to design a road support structure subjected to high-strain-rate loading occurring during vehicle collisions. The strain-rate affects both the hardening process and the material failure process. For modeling the strain-rate influence on material, various mathematical material models are used including the Johnoson-Cook model. The main goal of the study is to presenta method for determining the parameters for the Johnson-Cook damage model, a hybrid method which requires Charpy impact tests on a standard specimen with an annular notch and a series of calculations using finite element method simulating the test. The advantages of the presented method compared to existing methods are the high availability of the equipment, simple and quick processing of results and significantly lower costs.

The goal of the research program implemented by the authors was to develop methodology to be used for determination of constants for Johnson-Cook material model using Charpy impact test. This model is used in programs for modeling by the FEM method in order to account for the influence of strain rate on the strength properties. The method we propose involves selection of the material constants by comparing behavior of a specimen during Charpy test with results of simulation using the FEM method, in LS-DYNA program. Measurement of strain on the specimen surface involved recording Charpy test by means of a fast video camera and time –lapse measurement of changes in the distance of markers.

The basis for the study was the necessity to design a supporting structure of the road infrastructure subjected to high strain rates occurring during vehicle accidents. Mathematical models of hardening due to the high strain rates are reviewed. Commonly used methods for determining constants for one of the models, i. e., Johnson-Cook model are characterized. The main section of the study presents a proposed method for determining the strain rate sensitivity of the material. It is a hybrid method which requires Charpy tests using unnotched specimens and a series of calculations using the finite element method to simulate the tests. Several variants of strain measurement of specimen subjected to failure in Charpy tests, as required for the proposed method are analyzed. Using the suggested method, a strain rate sensitivity factor was obtained with a value similar to the value obtained using the split Hopkinson pressure bar technique. The advantages of the suggested method compared to the existing me... Kurzfassung Die Basis für die diesem Beitrag zugrunde liegende Studie bestand in der Notwendigkeit, eine Stützstruktur für die Fahrbahninfrastruktur auszulegen, die hohen Dehnraten infolge von Fahrzeugunfällen ausgesetzt ist. Mathematische Modelle der Verfestigung aufgrund der hohen Dehnraten werden überprüft. Die gewöhnlich angewandten Verfahren zur Bestimmung der Konstanten für eines der Modelle, dem Johnson-Cook-Modell, werden charakterisiert. Der Hauptteil der Studie stellt ein propagiertes Verfahren vor, um die Dehnratensensitivität des Werkstoffes zu bestimmen. Hierbei handelt es sich um ein Hybridverfahren, das Charpy-Tests mit einer ungekerbten Probe und eine Reihe von Berechnungen unter Verwendung der Finite Elemente Methode erfordert, um den Versuch zu simulieren. Verschiedene Varianten der Dehnungsmessung der Proben, die einem Versagen im Charpy-Test ausgesetzt waren und die für das propagierte Verfahren erforderlich waren, werden analysiert. Unter Anwendung des vorgeschlagenen Verfahrens wurde...

The paper presents results of the numerical analysis of the fire damper used in ventilation systems under the earthquake loading. The research was conducted in accordance with the recommendations of the Nuclear Safety Standards Commission. The aim of the analysis was to examine the fire damper with respect to its resistance to service loadings, structural integrity, and capability to stay operative after an earthquake. The analysis was carried out using the Finite Element Method in LS-Dyna software. The earthquake loading was modelled as accelerations, measured in three directions during the earthquake. For modelling of the materials behaviour, material models taking into account the influence of strain rate on hardening were used. The analysis consisted of three stages, which were: loading the construction with the earth gravity, earthquake simulation by loading with accelerations in three directions, and, finally, closing the fire damper. The analysis has shown that some of the construction elements undergo plastic deformations. However, the performed simulation of fire damper closing showed that despite these deformations, the device remains capable to keep its functionality and the damper closes hermetically. The results of the analysis were important design indications for the fire damper prototype.

The article presents experimental validation of the numerical model of a testing platform impact on a support structure mast. Numerical analysis of explicit type was performed in LS-Dyna environment. Experimental tests of crash test type were conducted on testing track. Comparison of values of deformations measured at selected mast characteristic points with the values of deformations specified during numerical analyses was performed.