Electromagneto-mechanical model of high temperature superconductor insert magnets in ultra high magnetic fields

Second-Generation High Temperature Superconducting (2G HTS) tapes are considered to be the main candidates for the development of future ultra high DC magnetic field magnets. In such application, the usability of the HTS magnets can be strongly impaired by large screening currents developed in the flat strip of the tapes. These currents lead to the generation of a Screening Current Induced Field (SCIF) that can deteriorate the performance by affecting the stability and the homogeneity of the magnetic field. Besides the SCIF, there is also the likely mechanical degradation of the tapes under the action of large Lorentz forces. The mechanical degradation and the presence of large screening currents intertwine to affect the reliable operation of 2G HTS magnets. To study those combined issues, an electromagneto-mechanical model based on tensile mechanical characterization of short samples was built to simulate the coupled electromagnetic and mechanical behaviour of insert magnets made of 2G HTS tapes under very high magnetic field. The coupling is carried out by considering the dependence of the n index and the critical current density Jc on the local relative deformation in addition to the magnetic flux density. The case study is the Little Big Coil (LBC, version 3) which broke the world record of the strongest continuous magnetic field achieved to this date. An analysis of the electromagneto-mechanical behavior of the LBC is conducted on the basis of information extracted from literature to show that the proposed model can assess the current magnitude at which the insert magnet quenched. Additionally, it is shown that the model can also provide some insights on the impact of the mechanical degradation of the tape on the SCIF hysteresis loop. The studies are conducted on the original LBC and on versions that include additional modifications such as harnessing and co- winding with rigid metallic tapes. These modifications are employed to limit the mechanical degradation of the HTS insert magnet under ultra high magnetic field. They are expected to deliver extra safety margin to 2G HTS insert magnets.

Exercise and the brain: a mechanical model for pulsation on flow of cerebrospinal fluid

Exchange of molecules between cerebrospinal fluid (CSF) and brain cells contributes to brain function and protection from dementia, but the route by which CSF is brought close enough to the neural tissue to be exchanged by extracellular diffusion is not clear. Exogenous molecules injected into CSF are carried along channels outside arteries and reach the basement lamina that surrounds the dense capillary network. Transport of solutes by diffusion along the basement lamina, a gel of macromolcules about 100 nm thick, would be too slow; bulk flow in a static geometry would require unphysiologically high pressures. However, it is known that the pulsation of blood aids transport of CSF, and we hypothesized that this is because the pulsation intermittently squeezes the pericapillary lamina. In a primitive mimicry, we have tested whether intermittent squeezing increases flow through an agar gel. In all but one of 216 tests, pulsation caused a reversible increase, sometimes by a factor of 100 or more. The enhancement was greatest for frequencies 5-11 Hz and, over the tested range of pressure heads (20 - 50 cmH2O), was greatest for the lowest pressure. The results suggest one reason why exercise slows the aging of the brain.

Stress analysis of double-walled pipes undergone mechanical drawing process

Double-walled metal pipes are important components for heat exchange and liquid transportation. They can be manufactured by mechanical drawing of two concentric pipes. In this work, a mechanical model is developed to analyze the stress state evolution during the manufacturing process, and the criterion for forming the double-walled pipe was given under the ideal elastoplastic and thick-walled assumptions. The model also encompasses the results deduced under the thin-walled assumption. Numerical simulations confirmed that the accuracy of the analytical model was within 5%. The application on actual steel materials with various parameters varied, including the wall thickness and initial gap, was analyzed. This work can provide theoretical support to industrial manufacturing procedures and help to reduce costs by eliminating required test procedures.

Modeling and Experimental Research of One Kind of New Planar Vortex Actuator Based on Shape Memory Alloy

In order to alleviate the problems of complex structure and low reliability of traditional Shape Memory Alloy (SMA) rotary actuator, a planar vortex actuator (PVA) based on SMA material was proposed to directly output torque and angular displacement. Based on the calculation method of PVA and the constitutive model of the phase transition equation of SMA, the mechanical model is established, and the pre-tightening torque, temperature, output torque, and rotation angle are obtained. The relationship expression between the tests has verified the mechanical model. The results show that the relationship between the excitation temperature and the output torque, the coefficient of determination between the calculated value and the tested value, is 0.938, the minimum error is 0.46%, and the maximum error is 49.8%. In the relationship between angular displacement and torque, the coefficient of determination between the calculated value and the test value is 0.939, the maximum error is 58.5%, and the minimum error is 28.0%. The test results show that the calculated values of mechanical model and experimental data have similar representation form.

Shear Characteristic Changes in Blended Rubber of Elastomeric Bearings due to Aging

Rubber bearings are widely used for seismic retrofit of bridges because they reduce the seismic force by making the vibration period of the bridge longer and distributing the seismic force to all the piers. However, they have the disadvantage of being easily aged compared to steel bearings as well as having variations in the shear stiffness. The shear characteristic changes in the blended rubber for the rubber bearings were analyzed, specifically, the aging accelerated by heat. The higher the aging temperature and longer the exposure time, the greater is the maximum stress and strain at that time, and the greater is the shear stiffness. This implies that the seismic performance gradually deteriorates due to aging as the service period becomes longer. This can provide the basis for the mechanical model of the aging bearing.

Research on dynamic load spectrum of electric vehicle transmission system based on underdamping characteristic

Overall, the electric vehicle transmission system shows an underdamped characteristic. Under changeable road conditions and high-frequency response for the motor, the resulting dynamic load environment may cause multiple failure modes, such as contact fatigue failure and bending fatigue fracture, for the transmission component, which limits the electric vehicle transmission component lifespan and system reliability. To reflect the dynamic load characteristics of the electric vehicle transmission system using a permanent magnet synchronous motor as a power source and accurately calculate the dynamic load of the transmission system, a high-speed helical gear-rotor-bearing coupling mechanical model for the electric vehicle transmission system was built based on simulating actual operation working conditions of the electric vehicle and considering the external load excitation caused by the Electromagnetic torque of the permanent magnet synchronous motor and vehicle driving resistant change as well as internal excitation caused by gear time-varying meshing rigidness and meshing error. Through simulation calculation of the mechanical model, the dynamic meshing force of the gear pair and dynamic contact force of the support bearing was obtained. Based on the Hertz contact theory, the stress-time history was obtained for the key parts, the rain flow counting method was adopted for the statistics collection and analysis of the stress-time history, and the fatigue load spectrum for various key parts of the transmission system was obtained. The result lays a foundation for the fatigue life prediction and reliability analysis for the pure electric vehicle transmission system.