Showing papers in "Transactions of Famena in 2016"

Simulation of a Two-Stroke Slow Speed Diesel Engine Using a Quasi-Dimensional Model

Abstract: The paper describes a diesel engine quasi-dimensional numerical model, implemented in a previously developed 0D model. The presented model uses direct solution to the conservation equations set for cylinder pressure and zone temperatures without numerical iterations which are customary in these models. Numerical model validation was performed on a four-stroke diesel engine at four operating points. After successful validation, modifications were implemented in the numerical model allowing the simulation of a marine two-stroke diesel engine. It is important to emphasize that the simulation model logic remained unchanged. The only significant differences are the changes in the engine working processes and different calculation of the engine operating parameters which are characteristic of two-stroke engines. The results of the diesel engine simulations using the quasidimensional model were compared to the test-bed measurements of the two-stroke engine found in available literature. Good agreement between the measurements and the simulation results for the two-stroke engine has been obtained. The developed quasi-dimensional numerical model can accurately predict operating parameters of the four-stroke and the twostroke diesel engine.

Method of Processing and an Analysis of Meshing and Contact of Circular Arc Tooth Trace Cylindrical Gears

Abstract: This paper presents the investigation into the tooth profile features, meshing characteristics and the principle of forming circular arc tooth race cylindrical gears (CATT gears). Based on the meshing theory of the curvilinear gear, tooth surface equations and meshing line equations of the gears and rack shave been established. The graphical analysis of these equations shows meshing performances. The results reveal that an ideal CATT gear can mesh with each other at a line contact and the rack cutter can machine an ideal CATT gear by translational motion. A planetary gear train is proposed to be used as processing device. The device consists of one or several gear pairs and it can be fixed to multiple tools. The new device can machine ideal tooth profiles and the teeth have the same thickness in the circumferential direction. The processing results show that the device can also adjust the forming radius of the tooth trace without grades and that it performs continuous cutting without introducing imbalance into the mechanism.

Experimental Examination of Effects of Punch Angle and Clearance on Shearing Force and Estimation of Shearing Force Using Fuzzy Logic

Abstract: A significant challenge faced when using blanking/piercing to machine sheet metal is the handling of the shearing force required for high strength and thick stock. Increased shearing forces lead to the requirement of higher performance expected from the pressing machine and result in increased wear on the punch tool and die. Clearance, employed to increase precision and quality in blanking/piercing operations, affects the shearing force as well. One of the techniques used to reduce the force required is the employment of a punch shear angle. In this study, the effects of punch shear angle and clearance on the forces required for blanking/piercing were examined on a grade of steel broadly used in the manufacturing industry, DC01. Experiments were carried out using five different punch shear angles, namely 0°, 2°, 4°, 8°, and 16°. Six matrices with varying clearance rates (0.4%t, 0.5%t, 0.6%t, 0.7%t, 0.8%t, and 0.9%t) were used in this study, and these clearances were altered by modular matrices on the die. This study shows that shearing forces can be reduced by 80 % when 16° punch angle is used. The results of the experiments were transferred to a fuzzy logic model to obtain extrapolated results for intermediate values which had not been obtained from the experiments. The results obtained from the experiments and the output from the fuzzy logic model were compared and found to be highly similar. These results have showed that the model developed using fuzzy logic can be used to determine different shear angles and clearance values.

A Model for Predicting Motor Vehicle Life Cycle Cost and its Verification

Abstract: In the paper there is a draft of a general model to be used for calculating life cycle costs and determining an optimum period of durability of a motor vehicle. This model is created in the MATLAB software environment. The paper contains calculations and input data which are necessary for making a model that would predict motor vehicle life cycle costs and determine the optimum period of durability. The suggested model might be used for working out life cycle costs of a new vehicle type for which the costs have not been determined yet. This model can also be applied when comparing several types of motor land vehicles of the same category during purchase. It is advisable to use the model mainly during tenders, since life cycle costs are one of the major criterion when selecting a supplier. The model enables us to calculate not only life cycle costs, but also vehicle amortization which depends upon mileage and age of a vehicle. All cumulative values might be transformed into unit values related to the mileage.

The Effect of Mixing Time on the Homogeneity of Multi-Component Granular Systems

Abstract: Mixing of granular materials is unquestionably important. Mixing solids is common in industrial applications and frequently represents a critical stage of the processes. The effect of mixing determines the quality of products. The objective of this study was to determine the effect of mixing time on the quality of multi-component granular mixtures. Experimental studies were conducted at the mixing process line in an industrial feed mill. The applied granular systems are feed mixtures with different weight proportions of individual components, varying in their diameter dimensions and bulk densities. Estimation of the degree of homogeneity was performed based on the scale of the mixture quality proposed by Boss according to the relation suggested by Rose. The mixing degree M as a function of time for granular mixtures was extended by presenting it according to different levels of collecting samples. Studies were performed for four mixtures varying according to their granular mixture formulas for five different mixing times. The quality of granular mixtures consisting of eight components was defined as 'very good' for mixing times of 30, 40, 50, and 60 minutes and as 'good' for the 20-minute mixing time. For the 12-component mixture BF, the quality was considered as 'excellent' for the 40-minute mixing time, and as 'very good' for mixing times of 20, 30, 50, and 60 minutes. For the 12-component mixture WM and the 14component mixture WW, the quality was considered as 'excellent' for all mixing times (M>0.96).

Influence of tip relief profile modification on involute spur gear stress

Abstract: This paper deals with the effects of linear tip profile modification on tooth root and tooth flank stress of involute spur gears. The increase in tooth flank stress due to tip profile modification is potentially hazardous due to increased risk of micro pitting initiation. The amount of required tip relief profile modification depends on the amount of tooth elastic deformation that needs to be compensated. In order to study the effects of linear tip profile modification on gear stress, two matching finite element models of involute spur gear pairs have been created, and tip relief profile modification has been applied to one pair. Tooth root and tooth flank stresses for both gear pairs have been compared in order to establish the effect of tip relief profile modification on gear stress.

An Energy Efficient Turning Process for Hardened Material with Multi-Criteria Optimization

Abstract: This paper presents a systematic procedure for the optimization of machining parameters such as cutting speed, feed rate, nose radius, edge radius, and rake angle to reduce specific material removal energy and improve energy efficiency in the hard turning of AISI 4140 steel. A simulation approach was applied in conjunction with the design of experiment (DOE), mathematical approximation with a meta-model to develop specific energy as well as an energy efficiency model in terms of cutting parameters. A hybrid approach that combines the Multi-Objective Particle Swarm Optimization (MOPSO) and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) using entropy weights was adopted to determine the best solution from the Pareto set. The results showed that energy efficiency could be improved by 11%, whereas specific energy decreased by approximately 15% compared to a non-optimal case. Therefore, this study is expected as a contribution to making the turning process of hardened materials greener and more efficient.

Response Analysis of Buried Pipeline Subjected to Reverse Fault Displacement in Rock Stratum

Abstract: Response analysis of the buried pipeline subjected to reverse fault displacement is very important for design, detection and protection of buried pipelines. This paper looks at the buckling behavior of a buried pipeline subjected to reverse fault displacement in the rock stratum. Effects of internal pressure, wall thickness, fault displacement and burial depth on the buckling mode and the axial strain of the buried pipeline are discussed. The results show that there are two buckling locations on the buried pipeline subjected to reverse fault displacement in the rock stratum and that the buckling modes of the buried pipes with different internal pressures are different. The two buckling locations are not symmetrically distributed along the fault plane. The buckling mode ranges from collapse to wrinkle as the internal pressure increases. The buckling phenomenon becomes more serious as the fault displacement increases, and the shape of the deformation curve changes from the S-shape to the Z-shape. The process of pipeline deformation can be divided into three stages. There is no buckling in the first stage. The second stage is a transition stage, buckling appears on the buried pipeline. Buckling is more serious in the third stage. Fault displacement has a small effect on the maximum strain position of the buried pipeline. The deformation curve of the buried pipeline is smoother as the wall thickness increases. The maximum axial strain of pressure pipes first increases and then decreases as the wall thickness increases.

Modelling of an Artificial Neural Network for Electrical Discharge Machining of Hot Pressed Zirconium Diboride-Silicon Carbide Composites

Abstract: Modelling is carried out to map the relationship between the input process parameters and the output response, considered in the machining process. To represent real-world systems of considerable complexity, an artificial neural network (ANN) model is often utilized to replace the mathematical approximation of the relationship. This paper explains the methodological procedure and the outcome of the ANN modelling process. The percentage of SiC in the workpiece material, the product of thermal conductivity and the melting point of the tool material, the pulse on time, and the pulse off time are considered as input parameters, while the material removal rate (MRR), the tool wear rate (TWR), roughness, roundness, taper angle and overcut are considered as output responses. The network is trained initially with one neuron in the hidden layer, i.e.,-a 4-4-6 topology is considered for training. In the subsequent phases, the number of hidden neurons in the hidden layer is increased gradually and then the network is tested with two hidden layers with the same number of hidden neurons in the second hidden layer. A feed forward back propagation neural network model with one hidden layer having 35 neurons is found to be the optimum network model (4-35-356). The model has the mean correlation coefficient of 0.92408.

A Necessity-Based Method for Product Requirement Elicitation and Classification

Abstract: A new necessity-based method for the elicitation and classification of requirements in the early phases of the product design process is presented. The purpose is to guide a design engineer through the process of requirement elicitation so as to compile a more appropriate requirement list and avoid underand over-constraining a product. The new method is based on the extended Form, Fit and Function approach. Its steps are derived from an in-depth analysis of literature sources. The applicability of the method is shown on a case study on residential solar panels. The method is validated by a case study on an air ventilation register box and by expert opinion. The necessity-based method fills the gap in the well-established methods for requirement elicitation and classification. It gives an insight into which requirements are important for certain product. The elicitation part of the new method reminds a design engineer of important case-related requirements. The classification part helps establishing rules on mandatory requirements.

Design, Meshing Characteristics and Stress Analysis of Cylindrical Gears with Curvilinear Tooth Profile

Abstract: Curvilinear tooth gears are commonly produced on a face milling cutter and a hob cutter. However, this paper proposes a kind of curvilinear tooth gear which is processed by a parallel linkage with a single blade cutter. For the purpose of identifying the meshing and contact characteristics of curvilinear tooth gears, the paper covers the following: (i) equations of tooth surfaces are deduced from the meshing theory, and a parameterized geometric model is developed by applying computer graphics; (ii) an investigation into meshing characteristics for an ideal assembly condition is performed, and an instantaneous contact curve is obtained from the developed tooth contact algorithm; (iii) based on the application of the finite element method, the evolution of contact and bending stresses during the cycle of meshing and between different arc radii of the curvilinear tooth is illustrated by numerical examples. The result shows that curvilinear tooth gear drives possess a higher contact ratio, severe contact stresses on the top edge of the tooth, and lower contact and bending stresses between appropriate arc radii, hence they may replace spur gears in the future.

Aerodynamic performance of the underbody and wings of an open-wheel race car

Abstract: Basic aerodynamic characteristics of a generic open-wheel race car equipped with various aerodynamic devices are studied. The focus is on the influence of car underbody design and the front and rear wings on aerodynamic forces experienced by the car. Computational simulations are carried out assuming the steady viscous fluid flow and using the Reynolds-averaged-Navier-Stokes equations and the standard shear stress transport (SST) k-ω turbulence model. The lift force in the configuration with a flat car underbody (without a rear diffuser at the trailing edge of the car underbody) and without the wings is positive (undesirable upforce), while a negative lift force (favourable downforce) is obtained in all configurations with aerodynamic devices (underbody rear diffuser, front wing, rear wing). The aerodynamic devices create an increased, undesirable drag force in comparison with the configuration without the aerodynamic devices. The downforce and the drag force are similar when wings consisting of two and three elements are used. This indicates that, for the same overall chord and wind incidence angle, the number of wing elements is not a very important factor influencing the aerodynamic loads experienced by this type of open-wheel race car with a similar front and rear wing layout. The optimal configurations with respect to the lift-to-drag ratio are those with the rear diffuser and wings in place. In the configuration with threeelement wings, streamlines in the region of the rear wing are analysed both computationally and experimentally using the tuft flow technique. Good agreement between the computational and limited experimental results regarding streamlines is achieved. However, this would need to be further analysed quantitatively in order to fully validate the developed computational model.

The Effect of Winding Angle on Unwinding Yarn

Abstract: In the production of fabric, the unwinding of thread occurs in the warping and weft insertion processes. In order to achieve low and constant tension of thread or yarn it is necessary to optimize the process of unwinding. Computer simulations are now in use for this purpose, so it is important to obtain a mathematical description of yarn motion. This article is devoted to the derivation of boundary conditions that considerably affect the form of the balloon. In this way, a mathematically well defined model of yarn unwinding will be obtained which could be solved by using the tools of numerical mathematics. The unwinding of yarn from an optimally designed package can be simulated and this knowledge can be used to find an optimal design of packages.

Minimum Thrust of a Morphing Unmanned Submersible Aerial Vehicle in the Water-to-Air Motion

Abstract: This study proposes a new water-to-air motion pattern that combines morphing with power switch. Under the conditions of this pattern, the vehicle needs a certain thrust to avoid falling back after jumping out of the water. The minimum thrust is among the most important design parameters of a vehicle. The water-exit and take-off dynamic models of the vehicle are constructed through the force and motion analysis before and after morphing. The control model of the vehicle is created by analysing the control problem in the take-off motion. The minimum thrust at different initial water-exit angles is computed using the optimum searching algorithm. The following law is then established: the greater the initial water-exit angle, the smaller the minimum thrust required in the air. Such a relationship becomes insignificant when the initial water-exit angle exceeds 40°.

Application of Alternative Technologies in Combination with Nuclear Energy

Abstract: Studies show that the developed world will need even more energy in the future. At the same time, the reserves of fossil fuels are rapidly running out. Due to ecological and demographic impacts, there is a high probability of a series of changes occurring on our planet over the next fifty to seventy years. One of the best ways how to avoid global warming effect is the use of hydrogen technologies. Hydrogen is used widely by petrochemical, agricultural, manufacturing, food processing, electronics, plastics, metallurgical, aerospace and other industries. The consumption of hydrogen is possibly in many ways but most perspective is the use of fuel cells. One of the biggest problems in hydrogen technology is to produce enough hydrogen for use in all technical applications. One of the most optimistic procedures is hybrid thermochemical decomposition of water and solar photochemical production of hydrogen. In the presented article, we have tried to develop energy analysis which model shows the best results regarding Slovenia region.

Ergonomics and usability in the development of a portable virtual gaming device applied in physiotherapy

Abstract: The field of Physical Medicine and Motor Rehabilitation (PMMR) is a medical specialty that deals with the diagnosis and treatment of different pathologies that affect the human body mobility. This process is characterized by the repetition of movements becoming dull and off-putting for patients under treatment. Over the past few years, new strategies have been introduced, including virtual games, aiming at making this process more fun and motivating. This paper presents the development of a mobile device for using virtual games that support the PMMR professional. It will be used both in the clinical setting as well as at home taking ergonomic and usability issues into account. We intend to offer professionals and their patients a chance to take advantage of the motivational potential of virtual interactive gaming enabling patients to undertake physiotherapy sessions in a more simple and convenient way.

An analytical solution to free rectangular plate natural vibrations by beam modes – ordinary and missing plate modes

Abstract: Relatively simple analytical procedures for the estimation of natural frequencies of free thin rectangular plates, based on the Rayleigh quotient and the Rayleigh-Ritz method, are presented. First, natural modes are assumed in the usual form as products of beam natural modes in the longitudinal and transverse directions, satisfying the grillage boundary conditions. Based on a detailed FEM analysis, the missing of some natural modes, defined as a sum and a difference of the cross products of beam modes, is noted. The frequencies of these modes are very similar and identical in some special cases, manifesting in such a way a double frequency phenomenon. These families of natural mode shapes form a complete natural frequency spectrum of a free rectangular plate as a novelty. The reliable approximation of natural modes enables the application of the Rayleigh quotient for the estimation of higher natural frequencies. The application of the developed procedure is illustrated by the case of a free thin square plate. The obtained results are compared with those determined by FEM and also with rigorous ones from the relevant literature based on the Rayleigh-Ritz method. The achieved accuracy is acceptable from the engineering point of view. Furthermore, the same problem is solved by the Rayleigh-Ritz method using approximate natural modes as mathematical ones. Direct and iterative procedures are presented. A small number of mathematical modes and iteration steps are sufficient to achieve reliable results.

Application of the modified weakly compressible sph method to the 3d turbulent wave breaking impact

Abstract: Summary In this paper, the mesh-less weakly compressible Smoothed Particle Hydrodynamics (SPH) method was used to solve the continuity and momentum equations with laminar viscosity and the sub-particle scale (SPS) turbulence model. To correct the pressure field and improve the accuracy of free surface, modification of the kernel and its gradient is applied to weakly compressible SPH. The modified method, namely the mSPH-T-K, was also equipped with periodic smoothing of the density using the modified kernel. To validate the modified model, the pressure field and the wave front position of the 2D dam break flow were compared with those of experimental data, the standard SPH method and the mSPH-T method, which is the turbulence SPH method without modification of the kernel and its gradients. Finally, a 3D wave impact was simulated using the mSPH-T-K method. A comparison of results with experimental data showed that this model is a powerful tool for the simulation of complicated free surface flows with large deformations and impact.

Numerical and Experimental Analysis of a Frictionless Receding Contact between Cylindrical Indenter, Layer and Substrate

Abstract: This paper investigates the behaviour of a receding contact when a cylindrical indenter presses an unbonded layer resting on a substrate. The problem is analysed by using FEM within the scope of the linear theory of elasticity and under the assumption of plane strain. This paper presents new and original results in the analysis of influence of load intensity and indenter geometry on the contact parameters. In addition, in the investigation into material properties a reference analysis was carried out for the case of material similarity between all three bodies, and material properties were subsequently varied for each body. This class of problems shows nonlinear behaviour, with both contact pressure distributions and contact half-widths found to depend nonlinearly on the applied load. The experimental analysis was carried out by employing the digital image correlation method and the ARAMIS 4M system was used. The obtained measurement results show good agreement with the numerical results.

Measurements of Air Concentration and Velocities in a Free Falling Water Jet

Abstract: The prediction of air entrainment in a free falling water jet (two-phase flow) is affected by large uncertainties. A current research project at the Vienna University of Technology is dealing with this phenomenon by means of experimental tests and CFD-calculations. The experimental investigation was conducted in order to measure the air concentration in such a free falling jet using a fibre-optic probe. The velocity was measured with a high speed camera. The tests were performed on a jet which exits a circular pipe with a diameter of 40 mm. The air concentration was measured transversally at several distances away from the nozzle exit. The test results should provide a data basis for CFD-calculations of the air entrainment in a further research step.

Numerical Predictions of the Mechanical Properties of A356-SiC Composites Fabricated by Powder Metallurgy

Abstract: Pure aluminum nanocomposite reinforced with silicon carbide was produced by powder metallurgy process. The mechanical behavior of this composite was modelled and experimentally investigated. Measurements of density, tensile properties, and hardness showed that the tensile strength and the porosity of composites increased with an increase in the amount of nanoparticles; however, aluminum ductility decreased. On the other hand, the elongation percentage remains constant with an increase in the percentage of nanoparticles. Wear resistance of composite samples was higher than that of aluminium alloy. In the current research, a technique based on Artificial Neural Network (ANN) and Finite Element Method (FEM) was applied for the prediction of mechanical properties. It was observed that prediction results obtained in this study are consistent with the real measurements performed on composites.

Determination of Differential Equations of Motion and Parameters of an Elastic Internal Combustion Engine Crankshaft

Abstract: The goal of this paper is to develop mathematically less complex differential equations of motion of an elastic crankshaft and their solutions with acceptable accuracy in relation to the actual system. The instantaneous angular speed of the free end of the crankshaft consists of the nonuniform rigid body motion mode and elastic deformation mode. In general, the crankshaft, as well as other parts of the engine, could be considered as a structural component with distributed mass and elasticity. This will lead to a system with an infinite number of degrees of freedom, and require solving partial differential equations. Another approach is to discretize the continuous system into a finite set of rigid bodies interconnected with springs and dampers, which is the method chosen here. The lumped mass model of the crankshaft and the corresponding differential equations of motion for each mass simulate the actual dynamics of the crankshaft fairly accurately.

Finite Element Analysis of Heating-Cooling Systems Used for Laminating Tools

Abstract: The paper presents the selection process of an optimal heating-cooling system for laminating tools used in the production of automobile parts covered with leather. Four different configurations of heating-cooling systems are considered. In this research, the following activities are done: design of heating-cooling systems, studying of these designs using the method of finite element analysis from a thermal perspective to obtain the differences between them, estimation of the efficiency of the systems by computing results of thermal loading, and analysis of the results in terms of deformations and tensions. After the selection of the optimal heating-cooling system, deformations and tensions are determined for different values of temperatures using the finite element analysis and are modelled to obtain mathematical relations.

Dynamic Method for Calculating Energy Need in HVAC Systems

Abstract: In this paper the new dynamic method for calculation of energy for heating, cooling and mechanical ventilation is presented. The method is based on a combination of the simple hourly method, from EN ISO 13790, and a modification of the existing calculation procedure for determination of the energy need for mechanical ventilation, described in Algorithm for calculation of the energy need for HVAC systems. Developed method, incorporated in Croatian national Algorithms used for energy certification of buildings, enables the determination of the hourly energy need for heating and cooling which includes all energy flows that occur during the air conditioning process (moistening, dehumidifying, etc.). Simulations are performed for a Croatian reference dwelling, equipped with two different HVAC systems. The results are compared against those obtained from the quasi-steady state monthly method, also described in Algorithms. The comparison proved that the application of the quasi-steady state method would preclude the correct calculations in buildings with air conditioning.