Cold-formed structure connections utilizing gusset plates are usually semi-rigid. This paper investigates the behaviours of rectangular gusset plates in cold-formed connections of elements whose columns and beams are made with lipped back-to-back C-sections. Methods of calculating strength and stiffness are necessary for such semi-rigid joints. The main task of this paper is to determine a method capable of calculating these characteristics. The proposed analytical method could then be easily adapted to the component method that is described in part 1993-1-8 of the Eurocode. This method allows us to calculate both the strength and stiffness of rectangular gusset plates, assuming that the joint deforms only in plane. This method of design moment resistance calculation was presented taking into account that an entire cross-section shall reach its yield stress. A technique of stiffness calculation was presented investigating the sum of deformations acquired at the bending moment and from shear forces which are transmitted from each beam bolt group. Calculation results according to the suggested method show good agreement of laboratory experimental results of specimens with numerical simulations. Two specimens of beam-to-column connections were tested in the laboratory. Lateral supports were used on the specimens to prevent lateral displacements in order to better investigate the behaviour of the rectangular gusset plate in plane. Experiments were simulated by modelling rectangular gusset plates using standard finite element software ANSYS Workbench 14.0. Three-dimensional solid elements were used for modelling and both geometric and material nonlinear analysis was performed.
The paper refers to previous publications of the author, focused on criteria of casting feeding, including the thermal criterion proposed by
Niyama. On the basis of this criterion, present in the post-processing of practically all the simulation codes, danger of casting compactness
(in the sense of soundness) in form of a microporosity, caused by the shrinkage phenomena, is predicted. The vast majority of publications
in this field concerns shrinkage and feeding phenomena in the cast steel castings – these are the alloys, in which parallel expansion
phenomenon does not occur as in the cast irons (graphite crystallization). The paper, basing on the simulation-experimental studies,
presents problems of usability of a classic, definition-based approach to the Niyama criterion for the cast iron castings, especially of
greater massiveness, for prediction of presence of zones of dispersed porosity, with relation to predictions of the shrinkage type defects.
The graphite expansion and its influence on shrinkage compensation during solidification of eutectic is also discussed.
Superalloys show a good combination of mechanical strength and resistance to surface degradation under the influence of chemically
active environments at high temperature. They are characterized by very high heat and creep resistance. Their main application is in gas
turbines, chemical industry, and in all those cases where resistance to creep and the aggressive corrosion environment is required. Modern
jet engines could never come into use if not for progress in the development of superalloys. Superalloys are based on iron, nickel and
cobalt. The most common and the most interesting group includes superalloys based on nickel. They carry loads at temperatures well in
excess of the eighty percent of the melting point. This group includes the H282 alloy, whose nominal chemical composition is as follows
(wt%): Ni - base, Fe - max. 1.5%, Al - 1.5% Ti - 2.1%, C - 0.06% Co - 10% Cr - 20% Mo - 8.5%. This study shows the results of thermal
analysis of the H282 alloy performed on a cast step block with different wall thickness. Using the results of measurements, changes in the
temperature of H282 alloy during its solidification were determined, and the relationship dT / dt = f (t) was derived. The results of the
measurements taken at different points in the cast step block allowed identifying a number of thermal characteristics of the investigated
alloy and linking the size of the dendrites formed in a metal matrix (DAS) with the thermal effect of solidification. It was found that the
time of solidification prolonged from less than ome minute at 10 mm wall thickness to over seven minutes at the wall thickness of 44 mm
doubled the value of DAS.
Nickel alloys belong to the group of most resistant materials when used under the extreme operating conditions, including chemically
aggressive environment, high temperature, and high loads applied over a long period of time. Although in the global technology market
one can find several standard cast nickel alloys, the vast majority of components operating in machines and equipment are made from
alloys processed by the costly metalworking operations. Analysis of the available literature and own studies have shown that the use of
casting technology in the manufacture of components from nickel alloys poses a lot of difficulty. This is due to the adverse technological
properties of these alloys, like poor fluidity, high casting shrinkage, and above all, high reactivity of liquid metal with the atmospheric air
over the bath and with the ceramic material of both the crucible and foundry mold. The scale of these problems increases with the expected
growth of performance properties which these alloys should offer to the user.
This article presents the results of studies of physico-chemical interactions that occur between theH282alloy melt and selected refractory
ceramic materials commonly used in foundry. Own methodology for conducting micro-melts on a laboratory scale was elaborated and
discussed. The results obtained have revealed that the alumina-based ceramics exhibits greater reactivity in contact with the H282 alloy
melt than the materials based on zirconium compounds. In the conducted experiments, the ceramic materials based on zirconium silicate
have proved to be a much better choice than the zirconia-silica mixture. Regardless of the type of the ceramic materials used, the time and
temperature of their contact with the nickel alloy melt should always be limited to an absolutely necessary minimum required by the
technological regime.
Large elongation in one de?nite direction of a crystal of cubic symmetry is considered. The equations of second order elasticity theory are applied. In this approximation three constants of the second order and six constants of the third order characterize the crystal. The stress is a function of the elongation direction. The elongation directions for which the stress reaches an extreme value have been analyzed.
In this paper we propose a sensor-based navigation method for navigation of wheeled mobile robot, based on the Kohonen self-organising map (SOM). We discuss a sensor-based approach to path design and control of wheeled mobile robot in an unknown 2-D environment with static obstacles. A strategy of reactive navigation is developed including two main behaviours: a reaching the middle of a collision-free space behaviour, and a goal-seeking behaviour. Each low-level behaviour has been designed at design stage and then fused to determine a proper actions acting on the environment at running stage. The combiner can fuse low-level behaviours so that the mobile robot can go for the goal position without colliding with obstacles one for the convex obstacles and one for the concave ones. The combiner is a softswitch, based on the idea of artificial potential fields, that chooses more then one action to be active with diRerent degrees at each time step. The output of the navigation level is fed into a neural tracking controller that takes into account the dynamics of the mobile robot. The purpose of the neural controller is to generate the commands for the servo-systems of the robot so it may choose its way to its goal autonomously, while reacting in real-time to unexpected events. Computer simulation has been conducted to illustrate the performance of the proposed solution by a series of experiments on the emulator of wheeled mobile robot Pioneer-2DX.
The standard approach to the wave propagation in an inhomogeneous elastic layer leads to the displacement in a form of a product of a function of space and a harmonic function of time. This product represents the standing, and not the running wave. The part depending on the space variable is governed by the linear ordinary second order differential equation. In order to calculate the propagation speed in the present paper the inhomogeneous material is separated by a plane into two parts. Between the two inhomogeneous parts the virtual homogeneous elastic extra layer is added. The elasticity modulus and the mass density of the extra layer have the same values as the inhomogeneous material on the separation plane. In further calculations the extra layer is assumed to be infinitesimally thin. The virtual layer allows to decompose the motion into two waves: a wave running to the right and a wave running to the left. Energy conservation equation is derived.
The paper presents the theoretical background, computer model, laboratory measurements and SPICE simulation results of a 323 W, 1 MHz Class E inverter operating with an efficiency of 97%. The inverter is built around a CoolMOS transistor from Infineon Technologies. The transistor belongs to a new generation of high quality, optimized for low conduction losses and high speed switching power MOSFET-s. The presented computer model of Class E inverter is based on a state-space description and allows computing the inverter parameters for the optimum operation. Its validity has been confirmed experimentally. The SPICE simulation of the inverter has been also carried out in order to obtain better agreement between measurement and calculation results.
The paper concerns the engineering design of guide vane and runner blades of hydraulic turbines using the inverse problem on the basis of the definition of a velocity hodograph, which is based on Wu’s theory [1, 2]. The design concerns the low-head double-regulated axial Kaplan turbine model characterized by a very high specific speed. The three-dimensional surfaces of turbine blades are based on meridional geometry that is determined in advance and, additionally, the distribution of streamlines must also be defined. The principles of the method applied for the hydraulic turbine and related to its conservation equations are also presented. The conservation equations are written in a curvilinear coordinate system, which adjusts to streamlines by means of the Christoffel symbols. This leads to significant simplification of the computations and generates fast results of three-dimensional blade surfaces. Then, the solution can be found using the method of characteristics. To assess usefulness of the design and robustness of the method, numerical and experimental investigations in a wide range of operations were carried out. Afterwards, the so-called shell characteristics were determined by means of experiments, which allowed to evaluate the method for application to the low-head (1.5 m) Kaplan hydraulic turbine model with the kinematic specific speed (»260). The numerical and experimental results show the successful usage of the method and it can be concluded that it will be useful in designing other types of Kaplan and Francis turbine blades with different specific speeds.
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