Turbogenerator coil retaining rings are shrunk-fitted onto the rotor over the coils, in order to restrain them against the centrifugal force. They are typically subjected to low cycle fatigue, with a cycle being completed at every machine switch-on and switch-off. The subject of this paper consists in the determination of the failure probability of a coil retaining ring. The failure mode of the ring cracking, when it swells in tension, due to the centrifugal force is here considered. The reliability assessment is preceded by the study of the input variables affecting the low-cycle fatigue load and of their stochastic distributions. This question is tackled by the experimental determination of the static, cyclic and fatigue curves of the involved material and by the application of a statistical model to compute related parameters and their standard deviations. Upon the determination of variable distributions, the probability of failure is estimated in the form of a cumulative distribution function by a computationally efficient methodology, based on the Advanced Mean Value approach. The obtained results account for the material response and the local stressstrain states at the most loaded coil retaining ring region. The determined probability at the end of the machine life, in the order of 10-12, is compatible with reference values for structures under fatigue in the mechanical and aeronautical fields.
A method of planning collision-free trajectory for a mobile manipulator tracking a line section path is presented. The reference trajectory of a mobile platform is not needed, mechanical and control constraints are taken into account. The method is based on a penalty function approach and a redundancy resolution at the acceleration level. Nonholonomic constraints in a Pfaffian form are explicitly incorporated to the control algorithm. The problem is shown to be equivalent to some point-to-point control problem whose solution may be easier determined. The motion of the mobile manipulator is planned in order to maximise the manipulability measure, thus to avoid manipulator singularities. A computer example involving a mobile manipulator consisting of a nonholonomic platform (2,0) class and a 3 DOF RPR type holonomic manipulator operating in a three-dimensional task space is also presented.
In the paper, the authors present construction stages of simulation models worked out using SolidWorks and Matlab/Simulink environments. As examples of simulation models, a laboratory truck crane and a forest crane have been shown. These models allow for visualization of movements, tracking of the trajectory, velocity and acceleration of any point of the system.
A design of the centrifugal recirculation blower as well as results of its experimental and numerical investigations are presented in this paper. The blower was designed to work in the unique test stand which is used for long-term tests of turbine flowmeters. A 1D method was used to design this blower, then experimental and numerical studies were conducted in order to verify the 1D method. A comparison of the blower pressure increase obtained from the experiment and the computations is presented. Velocity and pressure distributions from the numerical simulations in selected sections are also shown and discussed. Additional numerical studies of a shrouded rotor and a rotor with a lower tip clearance were conducted and are presented in the paper as well.
The main purpose of this study is to analyze the thermomechanical behavior of the dry contact between the brake disc and pads during the braking phase. The simulation strategy is based on softawe ANSYS11. The modeling of transient temperature in the disc brake is actually used to identify the factor of geometric design of the disc to install the ventilation system in vehicles. The thermal-structural analysis is then used with coupling to determine the deformation established and the Von Mises stress in the disc, the contact pressure distribution in pads. The results are satisfactory compared to those of the specialized literature.
A thermoacoustic heat engine (TAHE) converts heat into acoustic power with no moving parts. It exhibits several advantages over traditional engines, such as simple design, stable functionality, and environment-friendly working gas. In order to further improve the performance of TAHE, stack parameters need to be optimized. Stack’s position, length and plate spacing are the three main parameters that have been investigated in this study. Stack’s position dictates both the efficiency and the maximum produced acoustic power of the heat engine. Positioning the stack closer to the pressure anti-node might ensure high efficiency on the expense of the maximum produced acoustic power. It is noticed that the TAHE efficiency can further be improved by spacing the plates of the stack at a value of 2.4 of the thermal penetration depth, δk. Changes in the stack length will not affect the efficiency much as long as the temperature gradient across the stack, as a ratio of the critical temperature gradient Γ; is more than 1. Upon interpreting the effect of these variations, attempts are made towards reaching the engine’s most powerful operating point.
The effect of hydrogen on short-term strength, low-cycle durability and planestress fracture toughness of 10Cr15Ni27 steel, 04Cr16Ni56 and 05Cr19Ni55 alloys at pressure up to 35 MPa and temperature 293. . . 773 K was investigated. The modes of hydrogen action for which the elongation δ, reduction of area ψ, low-cycle durability N and crack resistance parameters Kc of alloys are minimal were established: hydrogen pressure above 10 MPa (non-hydrogenated specimens of 04Cr16Ni56 alloy) and above 15 MPa (hydrogenated specimens of 10Cr15Ni27 steel and 05Cr19Ni55 alloy, hydrogen concentration 15 and 19 wppm, respectively).
This paper investigates the influence of surface effects on free transverse vibration of piezoelectric nanowires (NWs). The dynamic model of the NW is tackled using nonlocal Timoshenko beam theory. By implementing this theory with consideration of both non-local effect and surface effect under simply support boundary condition, the natural frequencies of the NW are calculated. Also, a closed form solution is obtained in order to calculate fundamental buckling voltage. Finally, the effect of small scale effect on residual surface tension and critical electric potential is explored. The results can help to design piezo-NW based instruments.
Casing treatment in the form of circumferential grooves over a rotor blade tips is used for improvement of an axial compressor performance. Usually, these grooves extend compressor’s stall range (stable operational range) but decrease its efficiency. In the paper, there are presented main results of investigations on grooves that influence positively efficiency of compressor. There were investigated traditional (typical) and newly developed groove configurations. Certain grooves combine increase in efficiency with extension in stall range.
The last decades, when robots have appeared in the operating room, showed the possibility of surgery enhancement by improving precision, repeatability, stability and dexterity. However, taking into consideration still existing limitations of robotics in surgery, and treating the robots as medical devices with the highest degree of safety level requirements, one must take a number of complex actions when preparing the experimental clinical application of a new modern robot Robin Heart. Presented paper describes the current state of procedures carried out in the Robin Heart project of surgery robots prepared for clinical application. Based on experiences with the devices existing on the market and, first of all, thanks to knowledge and expertise gained by our team during last 12 years, intensive work are currently done in order to introduce both mechanical and electronic modifications as well as to improve the safety system. As far as human resources are concerned, a professional team able to carry out the robot-supported surgery is prepared based on the created system of technical and functional trainings on simulation stands, which also includes the developed operation planning procedures. The first telemanipulator designed for clinical practice is the Robin Heart Vision – endoscopic system manipulator.
The paper presents the results of research on the plastic zones formation in thin (3.51 [mm]) shields made of steel C45 with holes of 4, 10 and 20 diameters. The authorship method of identifying plastic macro-strains utilizing optical interference phenomenon was used in the experiments. The basic idea of the method is summarized below as being: “The occurrence of plastic deformations in the active process of loading is testified by a loss of the interference fringes that were previously present or by a clear and rapid change in their character”. In the experiments, the values of the stress initiating the first plastic deformation were determined. In order to explain the processes of plastic deformation appearance a detailed stress state analysis in the holes surrounding area was realized with the use of Finite Element Method. Comparison of experimental results with the results of FEM calculations indicates that there are significant quantitative as well as qualitative differences. Namely stresses initiating plastic deformations clearly exceed the value of ReH, and plastic deformation are of local plastic slides character. Similar results were previously obtained in studies on the shields made of steel 15CrMo with holes.
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