Evaluation of Torsion Axis Positon on Turbine Blade Flutter by Direct Measurement Experiment: Rig Design and Numerical Simulation

Flutter has been a very important and severe problem for gas turbines, and its importance is increasing since a modern jet engine has very thin blades to reduce weight. There have been a lot of researches on its mechanism and evaluation technique[1][2][3], however, almost all of these researches are done by CFD, forced excitation and post evaluation of engine test. Among these activities, it became clear that torsion axis plays an important role to suppress flutter onset, however, there are few data on direct measurement during flutter on an influence of torsion axis. In the present study, two blade cascades which has different torsion axis were prepared and evaluate flutter can truly suppressed or not. Test rig was designed not to disturb circumferential disturbance which is generated by flutter at the test cascade, and pressure fluctuation transduces are introduced to measure pressure field during flutter vibration. The first test campaign will be held February 2016, and the experimental data will be compared with design and CFD results. The data will help clarifying the present design criteria can be truly applied to actual flutter onset and suppression. The present paper reports rig and blade design, and these evaluations by CFD simulations.

Research on the Dynamics of the Double Helical Gear Transmission

Against the transmission characteristics of the double helical gear pair, considering the time-varying mesh stiffness, the bearing radial and axial stiffness, the tensile and compressive stiffness of the transmission shaft, the bending stiffness of that, error excitations, and corresponding dampings, a double helical gear pair bending-torsion-axis coupling dynamic model was established by using the lumped parameter method based on the gear meshing theory and Lagrange equations. Based on the model, the dynamic response of double helical gear pair was solved, and taking the right side of helical gear as an example, the frequency spectrum characteristics of dynamic meshing force of the right side of helical gear were mainly analyzed. This research establishes the foundation for dynamic performance optimizations and reliability designs of the double helical gear pair transmission system in the future.

Average Torsion Axis Location of Athletic Movements: Subject Specific or Movement Specific?

Foot torsion angles have previously been studied for different athletic movements. Sport shoes often contain a torsion element even though the location of the rotation axis of the foot is unknown. Therefore, the purpose of this study was to quantify the torsion axis location and determine if the location is influenced by the movement or the subject. The torsion axis location was calculated using a modified finite helical axis approach, which allowed the calculation of the rotation axis between the forefoot and the rearfoot without the influence of forefoot flexion. The torsion axis location during the lateral jab was 9.72 mm below and 26.96 mm lateral to a marker located at the posterior, central heel, whereas the shuffle cut resulted in an axis location of 9.59 mm below and 26.19 mm lateral to the reference marker. There was no significant difference for the average axis location between movements. There was, however, a significant difference for the location between subjects, indicating a subject specificity of the torsion axis. The results of the current study are the first to quantify the torsion axis location of the human foot during athletic movements.

Effect of Relative Marker Movement on the Calculation of the Foot Torsion Axis Using a Combined Cardan Angle and Helical Axis Approach

The two main movements occurring between the forefoot and rearfoot segment of a human foot are flexion at the metatarsophalangeal joints and torsion in the midfoot. The location of the torsion axis within the foot is currently unknown. The purpose of this study was to develop a method based on Cardan angles and the finite helical axis approach to calculate the torsion axis without the effect of flexion. As the finite helical axis method is susceptible to error due to noise with small helical rotations, a minimal amount of rotation was defined in order to accurately determine the torsion axis location. Using simulation, the location of the axis based on data containing noise was compared to the axis location of data without noise with a one-samplet-test and Fisher's combined probability score. When using only data with helical rotation of seven degrees or more, the location of the torsion axis based on the data with noise was within 0.2 mm of the reference location. Therefore, the proposed method allowed an accurate calculation of the foot torsion axis location.

Deformation Characteristics in AlphaType Brass Worked by Torsion

In present work, bar samples of pure copper and Cu-Zn alpha single phase alloys setting 20mm in diameter and 150mm in length processed by torsion in the rotation speed to 1rpm every 60° twist angles. Then, deformed samples were researched microstructure and their characteristics. Microstructures of non-deformation samples were isometric, however, deformed samples streaky. Elements of bar drawn 10×10mm mesh were developed parallelogram. It was trend angle of between stretchable direction in microstructures and torsion axis increased more torsion angles. It was coincident with between the angle and deformed direction of microstructures. Shear strain was calculated by twist angle by theoretical formula. Their value corresponded rough with measurement from mesh variation. Pure copper and Cu-Zn alpha phase alloys were similar deformation microstructure, but fracture twist angle in copper was more than Cu-Zn alloys, and it was trend fracture angle had decreased as concentration of Zn increased. This trend was difference of fracture elongation obtained in tensile test.