Archive of Mechanical Engineering

The paper presents the core design, model development and results of the neutron transport simulations of the large Pressurized Water Reactor based on the AP1000 design. The SERPENT2.1.29 Monte Carlo reactor physics computer code with ENDF/BVII and JEFF 3.1.1 nuclear data libraries was applied. The full-core 3D models were developed according to the available Design Control Documentation and the literature. Criticality simulations were performed for the core at the Beginning of Life state for Cold Shutdown, Hot Zero Power and Full Power conditions. Selected core parameters were investigated and compared with the design data: effective multiplication factors, boron concentrations, control rod worth, reactivity coefficients and radial power distributions. Acceptable agreement between design data and simulations was obtained, confirming the validity of the model and applied methodology.

In rotating machineries, misalignment is considered as the second most major cause of failure after unbalance. In this article, model-based multiple fault identification technique is presented to estimate speed-dependent coupling misalignment and bearing dynamic parameters in addition with speed independent residual unbalances. For brevity in analysis, a simple coupled rotor bearing system is considered and analytical approach is used to develop the identification algorithm. Equations of motion in generalized co-ordinates are derived with the help of Lagrange's equation and least squares fitting approach is used to estimate the speed-dependent fault parameters. Present identification algorithm requires independent sets of forced response data which are generated with the help of different sets of trial unbalances. To avoid/suppress the ill-conditioning of regression equation, independent sets of forced response data are obtained by rotating the rotor in clock-wise and counter clock-wise directions, alternatively. Robustness of algorithm is checked for different levels of measurement noise.

The small number of available complete modern pump characteristics makes the safety analysis of nuclear and conventional power plants based on the characteristics made over half a century ago of specific speeds n_q=24.6, 147.1 and 261.4. The aim of the paper is to check sensitivity of the power plant system response for different complete pump characteristics - modern and available from older tests for n_q=24.6, 147.1 and 261.4. It has been shown that Suter's characteristics for modern pumps give a different response to the pumping system of a power plant in breakdown than those used so far.

The disposal of ash in a thermal plant through the slurry pipe is subjected to some erosion wear due to the abrasive characteristics of the slurry. A simulation study of particle-liquid erosion of mild steel pipe wall based on CFD-FLUENT that considers the solid-liquid, solid-solid and solid-wall interaction is presented in this work. The multi-phase Euler-Lagrange model with standard k-epsilon turbulence modeling is adopted to predict the particulate erosion wear caused by the flow of bottom ash-water suspension. Erosion rate for different particle size and concentration is evaluated at variable flow rate. It is observed that the pressure drop and erosion rate share direct relationships with flow velocity, particle size and concentration. The flow velocity is found to be the most influencing parameter. A model capable of predicting the erosion wear at variable operating conditions is presented. The simulation findings show good agreement with the published findings.

This paper presents the design methodology of a small guided bomb for Unmanned Aerial Vehicles. This kind of next-generation munition has recently gained a lot of attention in the military market. The bomb is planned to be equipped with inertial measurement unit and infrared seeker. The nose shape and fin optimization procedure was described shortly. Aerodynamic characteristics were calculated by means of theoretical and engineering-level methods. The flight dynamics model of the bomb was obtained and implemented in Simulink software. The numerical simulations of uncontrolled and controlled trajectories were compared. The results indicate that the usage of such a guided small munition, like the designed bomb, might improve significantly the offensive capabilities of Unmanned Aerial Vehicles.

An important phenomenon of delta wing is the mechanism of vortex core, which indicates the increase in lifting force until the occurrence of the vortex breakdown. The computational fluid dynamics (CFD) is very helpful in visualizing and providing analysis of the detailed data. The use of turbulent models will affect the quality of results in obtaining the vortex breakdown phenomenon. This study used several models of turbulence to capture the occurrence of vortex breakdown and compare it with experiments using water tunnel test facility. The results show that all turbulence models give good results at a low angle of attack (AoA), but at a high AoA the DES model gives the results closest to experimental ones with Cl error value of about 1%. Taking into account the time required and the acceptable level of accuracy, the use of SST and k-omega models is an alternative option for use in the detection of vortex breakdown.

In thermosfluid dynamics, free convection flows external to different geometries, such as cylinders, ellipses, spheres, curved walls, wavy plates, cones, etc., play major role in various industrial and process engineering systems. The thermal buoyancy force associated with natural convection flows can play a critical role in determining skin friction and heat transfer rates at the boundary. In thermal engineering, natural convection flows from cylindrical bodies has gained exceptional interest. In this article, we mathematically evaluate an entropy analysis of magnetohydrodynamic third-grade convection flows from permeable cylinder considering velocity and thermal slip effects. The resulting non-linear coupled partial differential conservation equations with associated boundary conditions are solved with an efficient unconditionally stable implicit finite difference Keller-Box technique. The impacts of momentum and heat transport coefficients, entropy generation and Bejan number are computed for several values of non-dimensional parameters arising in the flow equations. Streamlines are plotted to analyze the heat transport process in a two-dimensional domain. Furthermore, the deviations of the flow variables are compared with those computed for a Newtonian fluid and this has important implications in industrial thermal material processing operations, aviation technology, different enterprises, energy systems and thermal enhancement of industrial flow processes.

This paper presents an elasticity solution of adhesive tubular joints in laminated composites, with axial symmetry. In this model, adherends are orthotropic shells and the stacking sequences can be either symmetric or asymmetric. Adhesive layer is homogenous and made of isotropic material. They are modelled as continuously distributed tension/compression and shear springs. Employing constitutive, kinematics and equilibrium equations, sets of differential equations for each inside and outside of overlap zones are obtained. By solving these equations, shear and peel stresses in adhesive layer(s), as well as deflections, stress resultants and moment resultants in the adherends are determined. It is seen that the magnitude of peel stresses due to transverse shear stress resultant is much greater than that obtained from axial stress resultant. The developed results are compared with those obtained by finite element analysis using ANSYS software. The comparisons demonstrate the accuracy and effectiveness of the aforementioned methods.