The article presents a study conducted to analyze the vulnerable zones of horizontal axis wind tu... more The article presents a study conducted to analyze the vulnerable zones of horizontal axis wind turbine (HAWT) wings, the nacelle, and the tower during the rotor revolution. The objective of the study is to establish relations between the extreme values of the investigated variables (wind velocity and pressure, von Mises stresses, displacements, etc. vs. angle of rotation or position of the rotor) in order to explore the vulnerable zone. The numerical model, as a computer-aided design (CAD) model geometry of the turbine assembly, was developed using freeform outline of the blade profile according to a previously designed twisted and tapered blade shape and a simplified outline of the nacelle. The tower was assumed to be made of a pipe and unites pipes of increasing diameter; hence its outline is a conic form. All solid bodies, i.e., blades of fiber glass composite and the tower and nacelle of alloy steel, are meshed using parabolic tetrahedral finite elements. The article demonstrates the used simulation technique and the results that are visualized using diverse graphical tools. Though it is hard to precisely point out the location of the vulnerable zone, the results indicate that the highest stresses appear along the trailing edge when the blade is in vertical direction.
In this paper the results of experimental tests aimed to determine the friction coefficient in sh... more In this paper the results of experimental tests aimed to determine the friction coefficient in sheet metal forming operations for various sheet metal materials and at different operative conditions are presented. The research has considered the frictional characterization of three kinds of drawing quality steels that are commonly used in automotive industry. These are a drawing quality steel (DQ), a deep drawing quality steel (DDQ), and extra deep drawing quality steel (EDDQ). For measurement of the sheet surface topography, a 3D stylus instrument Alicona InfiniteFocus was used. To determine the friction coefficient three tribological tests, i.e. a strip drawing test, a draw bead test and a pin-on-disc tribometer, have been conducted. The experimental results have ascertained several relationships showing the effect of sheet metal surface roughness, lubricant conditions and sheet orientation on the value of friction coefficient in sheet metal forming processes. The results further showed that the surface topography and sample orientation in the rolling direction of the sheet are significant factors that influence the friction coefficient. It was found that the tested steel sheets, selected from automotive industry applications, exhibit anisotropic resistance to the friction corresponding to the measured orientation in relation to the rolling direction of the sheet.
This paper presents a method of determining the friction coefficient in metal forming using multi... more This paper presents a method of determining the friction coefficient in metal forming using multilayer artificial neural networks based on experimental data obtained from strip drawing test. The number of input variables of the artificial neural network has been optimized using genetic algorithm. This process is based on surface parameters of the sheet and dies, sheet material parameters and clamping force as input parameters to train the neural network. In addition to demonstrating the fact that regression statistics model using genetic selection and intelligent problem solver are better than models without preprocessing of input data, the sensitivity analysis of the input variables has been conducted. This avoids the time-consuming testing of neurons in finding the best network architecture. The obtained results from this study have also pointed out that genetic algorithm can successfully be applied to optimize the training set and the outputs agree with experimental results. This...
The chapter discusses the numerical investigation of anisotropic properties of sheet metal formin... more The chapter discusses the numerical investigation of anisotropic properties of sheet metal forming using finite element method (FEM) in ABAQUS, a computer-aided engineering tool that deals with the most influent parameters in a forming process such as simulating sheet metal forming. Stamping of rectangular parts was simulated by the static and explicit approach in the presence of contact conditions with friction. The experimental and numerical results of rectangular cup drawing are presented. The aim of experimental study is to analyze the material behavior under deformation and further use the results to verify numerical simulation results taking into consideration friction and material anisotropy. Implicit and explicit nonlinear analyses were carried out using ABAQUS/Standard and ABAQUS/Explicit. Frictional properties of the deep drawing quality steel sheet were determined by using the pinon-disc tribometer. A comparison of quadratic Hill anisotropic yield criterion and von Mises yield criterion with isotropic hardening has been done. It is found that plastic anisotropy in ductile sheet metal has influence on deformation behavior of the material. The study indicates that FEM analysis undoubtedly guarantees the most approximate numerical results to real process when material and friction anisotropy are taken into consideration.
The article presents a study conducted to analyze the vulnerable zones of horizontal axis wind tu... more The article presents a study conducted to analyze the vulnerable zones of horizontal axis wind turbine (HAWT) wings, the nacelle, and the tower during the rotor revolution. The objective of the study is to establish relations between the extreme values of the investigated variables (wind velocity and pressure, von Mises stresses, displacements, etc. vs. angle of rotation or position of the rotor) in order to explore the vulnerable zone. The numerical model, as a computer-aided design (CAD) model geometry of the turbine assembly, was developed using freeform outline of the blade profile according to a previously designed twisted and tapered blade shape and a simplified outline of the nacelle. The tower was assumed to be made of a pipe and unites pipes of increasing diameter; hence its outline is a conic form. All solid bodies, i.e., blades of fiber glass composite and the tower and nacelle of alloy steel, are meshed using parabolic tetrahedral finite elements. The article demonstrate...
This paper presents design study of a wind turbine blade for dynamic periodic-excitation analysis... more This paper presents design study of a wind turbine blade for dynamic periodic-excitation analysis. The 3D CAD model of a blade is developed based on input data of blade profile calculated and coded in MatLab. The spatial finite element model is then established in SW Simulation toolbox that is built in SolidWorks software. The dynamic behavior of the blade for the first five modes of the natural frequency is analyzed and the obtained results are verified through approximated manual calculations. Further, the study of feasible design domain using Campbell diagram shows that resonance is not likely to occur at the selected rotor operating speed if the speed shows slight variations.
Strojniški vestnik – Journal of Mechanical Engineering, 2015
During the forming of draw pieces with complex shapes, such as car bodies, it is necessary to use... more During the forming of draw pieces with complex shapes, such as car bodies, it is necessary to use dies with varying outline curvatures and varying radii of edge fillets. In such conditions, using the cylindrical counter-samples for friction modelling on the die fillet surface does not fully reflect the friction conditions on the edge of the die. In this article, a proposal for an experimental numerical method of friction determination on the rounded profiles of punch edges is presented. The method involves a bending under tension (BUT) test that is devised to simulate the frictional conditions over the punch radii. Numerical simulations of BUT tests were conducted with ABAQUS software. An elastic-plastic approach with anisotropic material formulation and isotropic strain hardening were considered. Results of both experimental and numerical approaches confirmed the usefulness of the proposed method.
The article presents a study conducted to analyze the vulnerable zones of horizontal axis wind tu... more The article presents a study conducted to analyze the vulnerable zones of horizontal axis wind turbine (HAWT) wings, the nacelle, and the tower during the rotor revolution. The objective of the study is to establish relations between the extreme values of the investigated variables (wind velocity and pressure, von Mises stresses, displacements, etc. vs. angle of rotation or position of the rotor) in order to explore the vulnerable zone. The numerical model, as a computer-aided design (CAD) model geometry of the turbine assembly, was developed using freeform outline of the blade profile according to a previously designed twisted and tapered blade shape and a simplified outline of the nacelle. The tower was assumed to be made of a pipe and unites pipes of increasing diameter; hence its outline is a conic form. All solid bodies, i.e., blades of fiber glass composite and the tower and nacelle of alloy steel, are meshed using parabolic tetrahedral finite elements. The article demonstrates the used simulation technique and the results that are visualized using diverse graphical tools. Though it is hard to precisely point out the location of the vulnerable zone, the results indicate that the highest stresses appear along the trailing edge when the blade is in vertical direction.
In this paper the results of experimental tests aimed to determine the friction coefficient in sh... more In this paper the results of experimental tests aimed to determine the friction coefficient in sheet metal forming operations for various sheet metal materials and at different operative conditions are presented. The research has considered the frictional characterization of three kinds of drawing quality steels that are commonly used in automotive industry. These are a drawing quality steel (DQ), a deep drawing quality steel (DDQ), and extra deep drawing quality steel (EDDQ). For measurement of the sheet surface topography, a 3D stylus instrument Alicona InfiniteFocus was used. To determine the friction coefficient three tribological tests, i.e. a strip drawing test, a draw bead test and a pin-on-disc tribometer, have been conducted. The experimental results have ascertained several relationships showing the effect of sheet metal surface roughness, lubricant conditions and sheet orientation on the value of friction coefficient in sheet metal forming processes. The results further showed that the surface topography and sample orientation in the rolling direction of the sheet are significant factors that influence the friction coefficient. It was found that the tested steel sheets, selected from automotive industry applications, exhibit anisotropic resistance to the friction corresponding to the measured orientation in relation to the rolling direction of the sheet.
This paper presents a method of determining the friction coefficient in metal forming using multi... more This paper presents a method of determining the friction coefficient in metal forming using multilayer artificial neural networks based on experimental data obtained from strip drawing test. The number of input variables of the artificial neural network has been optimized using genetic algorithm. This process is based on surface parameters of the sheet and dies, sheet material parameters and clamping force as input parameters to train the neural network. In addition to demonstrating the fact that regression statistics model using genetic selection and intelligent problem solver are better than models without preprocessing of input data, the sensitivity analysis of the input variables has been conducted. This avoids the time-consuming testing of neurons in finding the best network architecture. The obtained results from this study have also pointed out that genetic algorithm can successfully be applied to optimize the training set and the outputs agree with experimental results. This...
The chapter discusses the numerical investigation of anisotropic properties of sheet metal formin... more The chapter discusses the numerical investigation of anisotropic properties of sheet metal forming using finite element method (FEM) in ABAQUS, a computer-aided engineering tool that deals with the most influent parameters in a forming process such as simulating sheet metal forming. Stamping of rectangular parts was simulated by the static and explicit approach in the presence of contact conditions with friction. The experimental and numerical results of rectangular cup drawing are presented. The aim of experimental study is to analyze the material behavior under deformation and further use the results to verify numerical simulation results taking into consideration friction and material anisotropy. Implicit and explicit nonlinear analyses were carried out using ABAQUS/Standard and ABAQUS/Explicit. Frictional properties of the deep drawing quality steel sheet were determined by using the pinon-disc tribometer. A comparison of quadratic Hill anisotropic yield criterion and von Mises yield criterion with isotropic hardening has been done. It is found that plastic anisotropy in ductile sheet metal has influence on deformation behavior of the material. The study indicates that FEM analysis undoubtedly guarantees the most approximate numerical results to real process when material and friction anisotropy are taken into consideration.
The article presents a study conducted to analyze the vulnerable zones of horizontal axis wind tu... more The article presents a study conducted to analyze the vulnerable zones of horizontal axis wind turbine (HAWT) wings, the nacelle, and the tower during the rotor revolution. The objective of the study is to establish relations between the extreme values of the investigated variables (wind velocity and pressure, von Mises stresses, displacements, etc. vs. angle of rotation or position of the rotor) in order to explore the vulnerable zone. The numerical model, as a computer-aided design (CAD) model geometry of the turbine assembly, was developed using freeform outline of the blade profile according to a previously designed twisted and tapered blade shape and a simplified outline of the nacelle. The tower was assumed to be made of a pipe and unites pipes of increasing diameter; hence its outline is a conic form. All solid bodies, i.e., blades of fiber glass composite and the tower and nacelle of alloy steel, are meshed using parabolic tetrahedral finite elements. The article demonstrate...
This paper presents design study of a wind turbine blade for dynamic periodic-excitation analysis... more This paper presents design study of a wind turbine blade for dynamic periodic-excitation analysis. The 3D CAD model of a blade is developed based on input data of blade profile calculated and coded in MatLab. The spatial finite element model is then established in SW Simulation toolbox that is built in SolidWorks software. The dynamic behavior of the blade for the first five modes of the natural frequency is analyzed and the obtained results are verified through approximated manual calculations. Further, the study of feasible design domain using Campbell diagram shows that resonance is not likely to occur at the selected rotor operating speed if the speed shows slight variations.
Strojniški vestnik – Journal of Mechanical Engineering, 2015
During the forming of draw pieces with complex shapes, such as car bodies, it is necessary to use... more During the forming of draw pieces with complex shapes, such as car bodies, it is necessary to use dies with varying outline curvatures and varying radii of edge fillets. In such conditions, using the cylindrical counter-samples for friction modelling on the die fillet surface does not fully reflect the friction conditions on the edge of the die. In this article, a proposal for an experimental numerical method of friction determination on the rounded profiles of punch edges is presented. The method involves a bending under tension (BUT) test that is devised to simulate the frictional conditions over the punch radii. Numerical simulations of BUT tests were conducted with ABAQUS software. An elastic-plastic approach with anisotropic material formulation and isotropic strain hardening were considered. Results of both experimental and numerical approaches confirmed the usefulness of the proposed method.
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