磁性流体を用いたバックドライブ可能な油圧アクチュエータの開発

早大学位記番号:新7478早稲田大

PERFORMANCE EVALUATION OF A SMALL-SCALE MAGNETORHEOLOGICAL DAMPER FOR CIVIL ENGINEERING APPLICATIONS

Magnetorheological dampers (MRDs) are devices that adjust their damping properties in response to an external magnetic field. Large-scale MRDs have been successfully used as vibration control devices in structures. This study focuses on modelling and optimizing an MRD using COMSOL Multiphysics. Various parameters, such as coil turns and current, are optimized to achieve the maximum flux value in the MRD. The simulation yielded a maximum magnetic flux of 0,44 T with 500 coil turns. Based on the optimized MRD parameters, a numerical equation is then used to calculate the total damping force. The maximum numerical and experimental damping forces corresponding to a 2,0 A current were 989,39 and 1004,63 N, respectively. The numerical damping force is then compared to the experimental results to validate the accuracy of the model. The MRD is integrated into a scaled-down reinforced concrete frame and subjected to a cyclic loading test for performance evaluation. The results show that the MR dampers improve the performance of the frame structure, increasing its load-carrying capacity and energy dissipation by 19,45 % and 20,43 %, respectively. The findings of the study provide valuable insights into the behaviour of MRDs and their optimization using numerical simulations, as well as highlight the importance of experimental validation for accurate prediction of the performance of MRDs in practical civil engineering applications

Emerging Trends in Mechatronics

Mechatronics is a multidisciplinary branch of engineering combining mechanical, electrical and electronics, control and automation, and computer engineering fields. The main research task of mechatronics is design, control, and optimization of advanced devices, products, and hybrid systems utilizing the concepts found in all these fields. The purpose of this special issue is to help better understand how mechatronics will impact on the practice and research of developing advanced techniques to model, control, and optimize complex systems. The special issue presents recent advances in mechatronics and related technologies. The selected topics give an overview of the state of the art and present new research results and prospects for the future development of the interdisciplinary field of mechatronic systems

Semi-Active Magneto-Rheological Damper and Applications in Tension Leg Platform / Semi-Submersible

A reliable and cost-effective way to protect the hydrocarbon production modules in harsher environments has been crucial to the success of offshore oil and gas projects. Nevertheless, the excessive tension variations in the top-tensioned risers (TTRs) can lead to catastrophic structural integrity issues. Magneto-rheological (MR) damper is a controllable device which can reduce the tension variations. However, the integration and behaviors of MR damper are remained as significant challenge for floating platforms. The main purpose of this research is to develop numerical analysis tool to analyze the specific characteristics of MR damper in offshore structural dynamics and interactively changing the structural behaviors correspond to various external loadings. The research methodologies were initiated by modeling the hydro-pneumatic tensioner (HPT) of TTR in component-level, which included hydro-pneumatic components and viscous fluid frictional effect. The HPT model was numerically incorporated with MR damper. This numerical tool combined with CHARM3D, a fully-coupled time-domain dynamic analysis program for floating bodies, mooring lines, and risers. The responses of combined numerical model were simulated by coupling with tension leg platform (TLP) and dry-tree semi-submersibles (DTS), respectively, under 100-year extreme condition and 1000-year survival condition of central Gulf of Mexico (GOM). The MR damper was controlled by using semi-active controllers that were developed in fuzzy-logic and skyhook schemes. Mathieu’s stability analysis was utilized to predict TTR’s parametric stability. The results manifested that total required stroke length in DTS can be reduced by as much as 0.963 meter in the studied case after MR damper was incorporated with semi-active fuzzy logic controller. By providing damped and deformed contact surface, MR damper was able to redistribute the excessive tension in the tensioner cylinders during extreme bottom-out motion. Moreover, the dynamic tension variations of TTR can be suppressed by 94 percent in the case of TLP. In conclusion, these results are beneficial to assure service life span of TTR’s tensioner and moderate the relevant operational expenditure (OPEX). In addition, the reductions of the total required stroke length and tension variations in DTS have enabled the platform designer to be more flexible in the sizing of the DTS and TTR tensioners

THE EFFECTS OF UNMITIGATED IDLE TIME ON THE PERFORMANCE OF MAGNETORHEOLOGICAL DAMPERS AS A STRUCTURAL PROTECTIVE SYSTEM.

This thesis discusses the long-term performance degradation of seismic protective systems due to age and inactivity (termed “idle time effects”). Over the lifetime of a structures there is the potential for a significant reduction in ability for the structural control systems to mitigate earthquakes. This can affect the resilience of the structure and lead to uncertainty in engineering judgement when designing seismic protective systems. Further research into these idle time effects could help to create solutions to mitigate age-dependent performance loss. This paper will use magneto-rheological (MR) dampers, which serve as a good analog for other semi-active control devices, to study idle time effects on seismic protection. MR dampers provide controllable damping through the magnetization of small MR particles in a carrier fluid. These particles can settle over time, influencing their performance. Using a model MR fluid, accelerated testing was performed to analyze the consequences of idle time

Vibration Isolation for Rotorcraft Using Electrical Actuation

The Active Control of Structural Response (ACSR) vibration suppression system, where hydraulic actuators located between the gearbox and the fuselage are used to cancel vibration in large helicopters, has been used successfully for many years. However the power consumed by the actuators can be high, and using hydraulic actuation for smaller rotorcraft has not been seen as practical. In contrast to active vibration reduction systems, passive vibration isolation systems require no external power. Passive vibration isolation systems however have the disadvantage of being limited to working at one specific frequency which will not be acceptable as slowed rotor flight becomes more common for fuel efficiency and noise legislation reasons. In this thesis two electrically powered actuation concepts, one piezoelectric, and one electromagnetic were initially evaluated. An electrically powered actively augmented passive, or hybrid, vibration reduction system based on an electro hydrostatic actuator (EHA) concept was proposed to be developed further. This hybrid actuator will have a wider range of operating frequencies than a purely passive system, and have lower power consumption than a purely active system. The design is termed a “Resonant EHA”; in that the resonant frequency of the coupled fluid, pump and electric motor rotor inertia matches the fundamental vibration frequency. The hydraulic cylinder, fluid and pump act as a single stage gear ratio, and the. brushless electric motor’s inertia is the main resonating mass as in a Dynamic Antiresonant Vibration Isolator (DAVI) passive vibration reduction system. The electrical power is used to compensate for friction in the actuator and other losses, and if needed can shift the operating point away from the resonant frequency. Simulation results indicated that a hydraulic circuit in which the pump leakage is fed back into the low pressure line would introduce unacceptable disturbances in the flows to and from the cylinder. To eliminate the source of the disturbances, a fully integrated electric motor and pump circuit design was chosen in which the electric motor is immersed in hydraulic fluid. An EHA demonstrator was built sized for a 1.5 tonne rotorcraft. For sizing comparison purposes the frameless brushless D.C motor for each strut of 1.5 tonne rotorcraft has a rotor and stator mass of approximately 1 kg, and can produce a continuous stall torque of 2 Nm. The bidirectional pump has a displacement of 1.5 cm3/rev, the mean system pressure was taken as 90 bar, and the double ended hydraulic cylinder has a 32 mm diameter bore, and 18 mm rod. Initial test results for the proof of concept EHA showed highly significant free play with a reversal of torque direction, resulting in unacceptable loss in transmission stiffness. The free play was traced to the gear pump and a hypothesis for the origin of the free play was put forward. To avoid torque reversals the EHA was further tested with a constant offset torque bias which proved successful in restoring a sufficient stiffness to the transmission. The sizing of the electric motor and power consumed with a non-zero offset torque is greater than a torque reversing motor, which limits the immediate application of the device in the present form. Future research investigating the use of other transmission elements, such as a piston pump, to obtain a more linear stiffness is recommended. As a hybrid vibration isolation system a Root Mean Square (RMS) reduction by a factor of four and near elimination of the fundamental frequency vibrations was achieved for the frequency range of 10 to 20 hertz.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Enhancement of Ride and Directional Performances of Articulated Vehicles via Optimal Frame Steering and Hydro-Pneumatic Suspension

Off-road vehicles employed in agriculture, construction, forestry and mining sectors are known to exhibit comprehensive levels of terrain-induced ride vibration and relatively lower directional stability limits, especially for the articulated frame-steered vehicles (AFSV). The transmitted whole-body vibration (WBV) exposure levels to the human operators generally exceed the safety limits defined in ISO-2631-1 and the European Community guidelines. Moreover, the directional stability limits are generally assessed neglecting the contributions due to terrain roughness and kineto-dynamics of the articulated frame steering (AFS) system. Increasing demand for high load capacity and high-speed off-road vehicles raises greater concerns for both the directional stability limits and WBV exposure. The criterion for acceptable handling and stability limits of such vehicles do not yet exist and need to be established. Furthermore, both directional stability performance and ride vibration characteristics are coupled and pose conflicting vehicle suspension design requirements. This dissertation research focuses on enhancement of ride, and roll- and yaw-plane stability performance measures of frame-steered vehicle via analysis of kineto-dynamics of the AFS system and hydro-pneumatic suspensions. A roll stability performance measure is initially proposed for off-road vehicles considering magnitude and spectral contents of the terrain elevations. The roll dynamics of an off-road vehicle operating on random rough terrains were investigated, where the two terrain-track profiles were synthesized considering coherency between them. It is shown that a measure based on steady-turning root-mean-square lateral acceleration corresponding to the sustained period of unity lateral-load-transfer-ratio prior to the absolute-rollover, could serve as a reliable measure of roll stability of vehicles operating on random rough terrains. The simulation results revealed adverse effects of terrain elevation magnitude on the roll stability, while a relatively higher coherency resulted in lower terrain roll-excitation and thereby higher roll stability. The yaw-plane stability limits of an AFSV are investigated in terms of free yaw-oscillations as well as transient steering characteristics through field measurements and simulations of kineto-dynamics of the AFS system. It was shown that employing hydraulic fluid with higher bulk modulus and increasing the steering arm lengths would yield higher yaw stiffness of the AFS system and thereby higher frequency of yaw-oscillations. Greater leakage flows and viscous seal friction within the AFS system struts caused higher yaw damping coefficient but worsened the steering gain and articulation rate. A design guidance of the AFS system is subsequently proposed. The essential objective measures are further identified considering the AFSV’s yaw oscillation/stability and steering performances, so as to seek an optimal design of the AFS system. For enhancing the ride performance of AFSV, a simple and low cost design of a hydro-pneumatic suspension (HPS) is proposed. The nonlinear stiffness and damping properties of the HPS strut that permits entrapment of gas into the hydraulic oil were characterized experimentally and analytically. The formation of the gas-oil emulsion was studied in the laboratory, and variations in the bulk modulus and mass density of the emulsion were formulated as a function of the gas volume fraction. The model results obtained under different excitations in the 0.1 to 8 Hz frequency range showed reasonably good agreements with the measured stiffness and damping properties of the HPS strut. The results showed that increasing the fluid compressibility causes increase in effective stiffness but considerable reduction in the damping in a highly nonlinear manner. Increasing the gas volume fraction resulted in substantial hysteresis in the force-deflection and force-velocity characteristics of the strut. A three-dimensional AFSV model is subsequently formulated integrating the hydro-mechanical AFS system and a hydro-pneumatic suspension. The HPS is implemented only at the front axle, which supports the driver cabin in order to preserve the roll stability of the vehicle. The validity of the model is illustrated through field measurements on a prototype vehicle. The suspension parameters are selected through design sensitivity analyses and optimization, considering integrated ride vibration, and roll- and yaw-plane stability performance measures. The results suggested that implementation of HPS to the front unit alone could help preserve the directional stability limits compared to the unsuspended prototype vehicle and reduce the ride vibration exposure by nearly 30%. The results of sensitivity analyses revealed that the directional stability performance limits are only slightly affected by the HPS parameters. Further reduction in the ride vibration exposure was attained with the optimal design, irrespective of the payload variations