The half elliptical hole with an edge crack in a thermopiezoelectric material is studied by using the complex variable method. First, the mapping function which maps the outside of the elliptical hole and the crack in the right half plane into the outside of a circular hole in a full plane is given by the method of conformal mapping. Then, the complex potential functions and the field intensity factors (FIF) are presented according to the boundary conditions, respectively. Some useful results can be found by numerical analysis: 1) The influence of the heat flux on FIF depends on the model of the crack; 2) The shape and the size of the hole possess a significant effect on the field distribution at the crack tip.
In this study, the effects of the bonding joints that are partly embedded in the adherent on the tensile behaviour of reinforcing plate adhesive joint have been investigated by 2D finite element method. In the study, the SBT 9244 material was used as the adhesive, and the adherent was the AA2024-T3 material. Three different models were built for the height of the embedded part in the adherent (a) and five models for the length of the embedded part (b), while three models were built for the total overlap length (c). Results showed that with the increase of the height of the embedded part and total overlap length, the strength of the joint was considerably increased. The increase of the length of the embedded part was initially led to an increase in the strength of the joints but after 0.25 value of the b/c the strength was reduced.
Temperature non-homogeneities in a catalytic reactor with periodic change in the direction of the reaction mixture feed is investigated in the present work. The temperature of the reaction mixture is described using a numerical algorithm for simulation of the work of the catalytic reactor, graphically shown and commented. The influence of the higher catalyst layer porosity in the wall area upon the temperature distribution in the reactor is studied. The existence of two different regimes is shown - a high temperature one in the middle part of the layer and a low temperature one in the high porosity area of the layer in contact with the reactor wall. This leads to not very effective usage of the catalyst in these parts of the catalyst layer in the reactor. This simulation can be used for better understanding and controlling of the examined catalytic process.
A thick hollow cylinder with finite length made of two- dimensional functionally graded material (2D-FGM) is considered and its natural modes are determined, based on great importance of mode shapes information in order to understand vibration behaviour of structures. Three dimensional theory of elasticity implemented for problem formulation, since mode shapes of a thick cylinder are three dimensional even with axisymmetric conditions. The axisymmetric conditions are assumed for the 2D-FGM cylinder. The material properties of the cylinder are varied in the radial and axial directions, with power law functions. Effects of volume fraction distribution on the different types of symmetric mode shapes configuration and vibration behaviour of a simply supported cylinder are analyzed. Three dimensional equations of motion are used and the eigen value problem is developed, based on direct variation method.
I.-K. Fontara, F. Wuttke, S. Parvanova and P. Dineva
The mechanical model and the accompanied computational technique, based on the boundary integral equation method (BIEM) and Green’s function for continuously inhomogeneous half-plane were described in the first part of this work. 2D elastodynamic problem for quadratically inhomogeneous and heterogeneous geological area was defined in the first part of our work. The aim of the current second part is to demon-trate the accuracy and the convergence of the proposed computational tool. Furthermore, subsequent extensive parametric study will illustrate, that the seismic wave field is a complex result of mutual play of different key factors as free-surface relief, wave characteristics, as frequency and wavelength, seismic source properties, type and characteristics of the material gradient, existence of different type of heterogeneities and their interactions.
An analytical solution for a specific case of the forced Duffing oscillator is proposed. The excitation force contains two harmonics with significant difference frequencies. This case corresponds to a presence of a defect in the machinery and is in the art of the machinery vibration diagnostics. The results obtained show an amplitude modulation. Therefore, the presence of an amplitude modulation in the vibration signal may be used as an indicator for a malfunction. Analytical solution derived clarifies how the amplitude modulation occurs. Also, a numerical solution is realized and compared with the analytical one. For this, the Duffing equation is solved numerically and then, the spectrograms of vibrations are obtained through a Discrete-time Fourier Transform.
This paper presents a robotic system designed for holding and placing objects based on their colour and shape. The presented robot is given a complete set of instructions of positions and orientation angles for each manipulation motion. The main feature in this paper is that the developed robot used a combination of vision and motion systems for holding and placing the work-objects, mounted on the flat work-plane, based on their shapes and colors. This combination improves the flexibility of manipulation which may help eliminate the use of some expensive manipulation tasks in a variety of industrial applications. The robotic system presented in this paper is designed as an educational robot that possesses the ability for holding-and-placing operations with limited load. To process the various instructions for holding and placing the work objects, a main control unit - Manipulation Control Unit (MCU) is used as well as a slave unit that performed the actual instructions from the MCU.
The known deterministic relationships to estimate the elastic characteristics of materials are not well accounted for significant variability of these parameters in solids. Therefore, it is given a probabilistic approach to determine the modules of elasticity, adopted to random values, which increases the accuracy of the obtained results. By an ultrasonic testing, a non-destructive evaluation of the investigated steels structure and properties has been made.
The proposed paper considers small urban vehicles with electric hybrid propulsion systems. Energy demands are examined on the basis of European drive cycle (NEUDC) and on an energy recuperation coefficient and are formulated for description of cycle energy transfers. Numerical simulation results show real possibilities for increasing in achievable vehicle mileage at the same energy levels of a main energy source - the electric battery. Kinetic energy storage (KES), as proposed to be used as an energy buffer and different structural schemes of the hybrid propulsion system are commented. Minimum energy levels for primary (the electric battery) and secondary (KES) sources are evaluated. A strategy for reduced power flows control is examined, and its impact on achievable vehicle mileage is investigated. Results show an additional increase in simulated mileage at the same initial energy levels.
The present paper mathematically investigates the effect of temperature dependent viscosity on the onset of instability in thermohaline convection problems of Veronis and Stern type configurations, using linear stability theory. A sufficient condition for the stability of oscillatory modes for thermohaline configuration is derived. When the compliment of this sufficient condition is true, the oscillatory motions of neutral or growing amplitude may exist, and hence the bounds for the complex growth rate of these neutral or unstable modes are derived, when viscosity of the fluid is an arbitrary function of temperature. Some general conclusions for the cases of linear and exponential variations of viscosity are worked out. The present analysis thus shows that the oscillations in thermohaline convection problems can be modulated or arrested by considering the temperature dependent viscosity of the fluid.