Radovan Drazumeric

Design of Flexible Propellers with Optimized Load-Distribution Characteristics

The mathematical model and experimental verification of flexible propeller blades are presented in this paper. The propeller aerodynamics model is based on an extended blade-element momentum model, while the Euler–Bernoulli beam theory and Saint–Venant theory of torsion are used to account for bending and torsional deformations of the blades, respectively. The proposed blade-element momentum model extends the standard blade-element momentum theory with the aim of providing a quick and robust model of propeller action capable of treating high-aspect-ratio propeller blades with a blade axis of arbitrary geometry. Based on the proposed mathematical model, a static flexible propeller blade design procedure and its associated analysis algorithm are established. Dynamic aeroelastic phenomena like propeller flutter and divergence are not covered by the presented mathematical model, design, and analysis algorithm. Experimental validation was carried out with an objective of evaluating the performance of the devel...

A novel experimental setup for multiparameter aeroelastic wind tunnel tests

A comprehensive experimental approach to the problem of determining static stability boundary (divergence) or dynamic stability boundary (flutter) of a given multiparameter aeroelastic system in a low speed wind tunnel is presented. The experimental setup with the corresponding measurement algorithm is based on the well-known theoretical model of an elastically supported typical wing section with two degrees of freedom. The design of the experimental system makes it possible to vary structural parameters within the determined parameter space. An automated measurement algorithm for determination of static or dynamic stability boundary by monitoring the aeroelastic system response to an initial impulse in the time domain is developed. The multiparameter experimental results of the case study using a NACA 0012 airfoil are compared to the analytical solutions of the theoretical model. The comparison shows that the experimental setup represents a reliable platform for aeroelastic wind tunnel test purposes. In addition, series of experiments were conducted to investigate the effect of airfoil thickness distribution on dynamic and static stability boundary. The results are compared to those of the NACA 0012 airfoil.

Particularities of Grinding High Speed Steel Punching Tools

A simulation model of a punch grinding process has been used to determine optimal parameters to reduce grinding cycle time and achieve a constant-temperature no-burn situation. Two basic outputs of the simulation model include arc length of contact and specific material removal rate that are both time-variant. A thermal model is included in the simulation to calculate maximum grinding temperature rise. The simulation-based optimization can help to avoid thermal damage, which includes thermal softening, residual tensile stress, and rehardening burn. The grindability of high speed steel (HSS) is presented in terms of specific grinding energy versus undeformed chip thickness and maximum temperature rise versus specific material removal rate. It is shown that for a given specific material removal rate lower temperatures are achieved when grinding fast and shallow. Higher temperatures, characteristic for slow and deep grinding, soften the material leading to a lower specific grinding energy, especially if grinding is timid. Lowest values of specific grinding energy can be achieved in fast and shallow grinding at aggressive grinding conditions.

Thermal Aspects and Grinding Aggressiveness in View of Optimizing High-Performance Grinding Operations in the Automotive Industry

This paper first reviews early contributions to modeling and analysis of thermal aspects in grinding. The role of specific energy in the determination of grinding temperatures is then discussed with respect to both chip thickness and grinding aggressiveness. The underlying modeling of cylindrical grinding is given in general terms, enabling calculation of the instantaneous geometry, kinematics and temperature for any workpiece form. The focus is on the recently developed concept of constant-temperature grinding, which entails choosing process parameters based on a thermal model for achieving a constant temperature and then optimizing the grinding process for either shorter cycle times or higher quality while applying constant temperature. Machine limitations — in terms of maximum speed, acceleration, and jerk in the headstock and wheelhead movement — are considered in the optimization. Case studies and experimental work are presented for high-performance industrial cam-lobe grinding used in the automotive industry.Copyright

Aeroelastic Characteristic of an Airfoil Containing Laminated Composite Plate

The aeroelastic behavior of an elastically supported airfoil is studied in order to investigate possibilities of increasing critical speed by exploiting its chord-wise flexibility. The flexible airfoil concept is implemented using a rigid airfoil-shaped segment, and laminated composite plate conformally attached to its trailing edge. The aeroelastic behavior is studied in terms of the number of laminate plies used in the composite plate for a given aeroelastic system configuration. Such flexible airfoil is characterized by three types of aeroelastic response, the airfoil divergence, the classical airfoil flutter, and the plate flutter. The analysis shows that a significant increase in the critical speed can be achieved in the region where the aeroelastic system exhibits a bimodal behavior, e.g. where two types of the aeroelastic response occur simultaneously. The predicted aeroelastic behavior of a flexible airfoil is experimentally verified by conducting a series of wind tunnel flutter campaigns.

Aeroelastic Design of Propellers with Optimized Load-Distribution Characteristics

The mathematical model and experimental verification of deformable propeller blades are presented in this paper. The propeller aerodynamics model is based on an extended bladeelement momentum model while the Euler-Bernoulli beam theory and Saint-Venant theory of torsion are used to account for bending and torsional deformations of the blades, respectively. The proposed blade-element momentum model extends the standard bladeelement momentum theory with the aim of providing a quick and robust model of propeller action capable of treating high aspect-ratio propeller blades with a blade axis of arbitrary geometry. Based on the proposed mathematical model a propeller blade aeroelastic design procedure and its associated analysis algorithm are established. Experimental validation was carried out with an objective of evaluating the performance of the developed mathematical model and the design strategy. Both theoretical and experimental results are presented along with pertinent concluding remarks.

Simulation of Workpiece Kinematics in Centreless Throughfeed Grinding

This paper deals with the simulation of the workpiece kinematics in centreless throughfeed grinding. The objective of this research was to develop a simulation tool that can be used to create an interactive virtual environment, to place the grinding gap elements in the defined set-up and to visualise process kinematics. The simulation is founded on an analytical 3D model, which includes a parametrical description of all grinding gap elements and their kinematics. The simulation software was programmed in C#. Its platform consists of Windows OS, .NET framework and OpenGL graphics library.

Wheel lift-off in creep-feed grinding: thermal damage, power surge, chip thickness and optimisation

An investigation is made into the phenomenon of early lift-off in creep-feed grinding, where the wheel lifts away from the workpiece before reaching the end of cut. In single-pass operations, early lift-off can result in thermal damage. In multi-pass operations, there is a surge in material-removal rate just before lift-off, which can result in thermal damage and excess wheel wear. This study examines the current inadequate methods of dealing with lift-off. It then develops a geometric and kinematic model for analysing the lift-off phenomenon. It finally proposes a thermal-model-based optimisation method for achieving a constant maximum surface temperature, resulting in shorter cycle times and less risk of thermal damage. The power-surge model is validated experimentally in diamond grinding of tungsten-carbide rotary tools.

Grinding of cermets with cup-wheels

Cup-wheels are frequently used to grind cermets, a difficult-to-grind material. An investigation was made into the transient geometry of the cup-wheel rim, grit dulling, wheel loading, and wheel self-sharpening with chip thickness. Tests were performed on a saw-tip grinding machine and specific energies, G-ratios and rim geometries were measured. Results showed that, like grinding of tungsten-carbide, loading is prevalent. However, unlike grinding of tungsten-carbide, grit dulling is also prevalent and wheel conditioning is of limited use. Much better results, particularly with respect to surface finish, can be obtained if the wheel is trued to a predetermined geometry. In addition, grinding parameters must be chosen to induce wheel self-sharpening. Practical recommendations are given.

Power monitoring, Fourier transforms of power, and electron microscopy in evaluating the performance of abrasives in grinding

The use of electron microscopy and power-monitoring during grinding was investigated in terms of evaluating the fracture and wear characteristics and chip-formation mechanisms of abrasive grains and bond formulations. Diamond abrasives and fused, sintered and sintered triangular-shaped aluminium-oxide abrasives were evaluated. Power was shown to be a useful tool in determining the chip-formation mechanisms and the extent of grit fracture, particularly in triangular-shaped abrasive. Conclusions were supported by electron-microscope analysis. Power was also used to evaluate low-cost diamond vs. premium diamond abrasives. Practical recommendations are given for evaluating grit, wheel and bond performance both in the laboratory and in production.