This paper presents a study on the dynamic model and robust controller design for enhancing ride comfort in railway vehicles. An analytical model is introduced, encompassing the lateral, roll, and ...yaw motions of wheelsets, bogies, and the car body, while incorporating an efficient method for computing wheel-rail interactions. Rail irregularities and their impact on vibration excitation are also examined. A robust controller design methodology is proposed to address uncertainty and ride comfort quality, considering the significant variations in mass and moment of inertia experienced by railway vehicles. Through simulations, the designed controller consistently demonstrates an approximate 2 dB improvement in ride comfort across different levels of uncertainty. Future research directions include developing controller designs considering actuator response characteristics and identifying additional conditions for practical implementation. This study contributes to understanding railway vehicle dynamics and lays the foundation for effective control strategies to enhance ride comfort while accommodating uncertain operating conditions.
In-pipe robots have become popular, allowing for non-destructive testing, visual inspection, and cleaning. In-pipe inspection is crucial for maintaining pipeline integrity, but it is difficult for ...humans to access pipelines and perform checks. This article focuses on an in-pipe robot navigating various pipeline structures and diameters. It consists of a center module, a tracking module, and an active pantograph mechanism. The hardware components, such as the motorized gear train, screw, pantograph mechanism, springs, track module, and angular sensors, are discussed. Additionally, the control methods employed by the robot, including normal force control and posture control, are explained. Finally, the tracking algorithms used to estimate the robot’s position and direction within the pipeline are presented.
The effect of design variables on the performance measures in the entire design space can be evaluated by global sensitivity analysis (GSA). Therefore, a high-dimensional engineering problem can be ...transformed to a reduced-dimensional problem by ascertaining important design variables according to GSA. Subsequently, the reduction of design variables helps save computational cost and the duration of design optimization. In this study, GSA was applied to determine the most influential design variable in the design of two reaction hydro turbine components - stay vane and casing. The global sensitivity index technique is selected among GSA methods because it can evaluate both the individual and interaction effects of design variables. Genetic aggregation surrogate models are used to reduce the number of computational fluid dynamics (CFD) analyses for GSA and design optimization. The responses from surrogate models are evaluated to obtain global sensitivity indices for performance measures. The important design variables are selected according to the indices. Using a multiobjective genetic algorithm (MOGA), design optimizations with the selected design variables are performed and the results are compared to the optimum designs with all design variables. The optimum designs using the selected design variables show comparable performances to those of the full-dimensional optimum designs.
To move freely, in-pipe robots must be able to adapt to the various geometric changes of pipes. Previously, we described an in-pipe robot that can adapt to changes in diameter and curvature of center ...curves. This robot is able to estimate the forces exerted on the inner surface of the pipes and balance its posture inside the pipe using angular sensors attached to its rotational joints. In this paper, a method is proposed to estimate the relative attitude between the robot's main body and the pipe using the angular sensors attached to a pantograph mechanism. The use of angular sensors makes the structure of the robot simpler and more effective than the use of force or vision sensors because the normal forces and attitude can be estimated from measured angle information. This geometric estimation of attitude relative to the pipes enables the robot to recognize the inclination of the pipes. The PAROYS-II robot can control its normal force according to the variation in pipe inclination. Thus, the proposed method could reduce power consumption and stress on the robot's parts. The algorithm has been validated by multiple experiments.
S-shaped characteristics in turbine mode are prone to instabilities in associated transient processes. A single value of the speed factor corresponds to multiple values of the discharge factor, ...having the possibility of changing the operating point among the turbine, turbine brake, and reverse pump modes. Because of this characteristic, the S-shaped curves induce instability in transient processes. Understanding the hydraulic behavior of a turbine on the four-quadrant characteristic is important since it provides detailed performance information through the whole discharge range of the turbine. This study was numerically and experimentally investigated the scale effect on the S-shaped characteristics in the turbine transition region. The four-quadrant characteristic curves (full- and laboratory-scale) in the turbine mode were predicted by numerical simulations. To verify the predicted results, a laboratory-scale experiment was performed in the turbine, turbine brake, and reverse pump modes. Although the full-scale experiment was performed in the normal operating head range, the scale effect can be validated by comparing steady operating points between the two models. Based on the verified results, the internal flow and pressure pulsation characteristics were determined at the operating point in a specific transition region.
The pump–turbine unit used in pumped-storage power generation plays a role in backing up and adjusting the power system in a flexible power generation facility, providing stability in response to ...renewable energy power grids with intermittent power generation. Owing to changes in the operating conditions of flexible power generation facilities, pump–turbine units have been operated continuously in off-design conditions. At the high flow rates in off-design conditions, undesirable flow with vortex rope is caused in the draft tube, which leads to operating system instability. Meanwhile, when operating at high flow rates in the turbine mode of the pump–turbine unit, the Thoma number must be considered for relatively stable operations due to cavitation phenomena. Thus, to expand stable operating ranges through the understanding of high flow rates, unsteady internal flow and pressure phenomena were investigated depending on the Thoma number in the turbine mode of the pump–turbine model through analyses with laboratory-scale pump–turbine model experiments and unsteady-state numerical analyses via systematic quantitative and qualitative comparisons. There was no difference in flow characteristics at the runner and draft tube areas based on the Thoma number at the best efficiency point. Nevertheless, torch-shaped visible vortex ropes developed and differences in flow characteristics at the draft tube appeared based on Thoma number under high flow rates.
Magnetic levitation (maglev) trains are environmentally-friendly, require little maintenance, and allow for mass transportation. For these reasons, the demand for ultra-high-speed maglev trains has ...been increasing. Maglev trains can be classified with two suspension types, electro dynamic suspension (EDS) and electromagnetic suspension (EMS). EDS-type trains are suitable for ultra-high-speed because levitation suspension gap is over 100 mm compared with levitation suspension gap of 10 mm for EMS. When speed goes faster, it is hard to control the small suspension gap rapidly in EMS type. To analyze the EDS-type maglev train, electromagnetic forces were calculated with the superconducting coils and magnets using 2D analytical model. Based on the calculated forces, the lookup tables for the levitation and guidance force were employed in the total couple-fielded analysis. Ultra-high-speed maglev train was simulated by using the ADAMS multi-body dynamic program. The simulation was carried out with two car body models, rigid and flexible car body. In order to construct flexible car bodies with the modal information, the finite element method was used and they were constructed with the equivalent elements using ANSYS™. The final framework was constructed in MATLAB Simulink, and we co-simulated the dynamics and the electromagnetics with the constructed simulation frame work. To consider disturbances caused by irregularities, random and power spectral density (PSD) were used to analyze the vibrational interaction. As results, the ride comforts for PSD were a little bit worse than the results for random irregularity because the characteristics of PSD irregularity have more low excitation frequencies. The use of PSD inputs and flexible car body models need to be considered to improve the simulation accuracy.
The tip leakage cavitation phenomenon observed in axial-flow type turbines is one of the major causes of blade tip erosion. This study is focused on the Kaplan turbine cavitation occurring at the tip ...clearance gap between the blade tip and the stationary shroud casing. An unsteady multi-phase cavitation numerical model is studied on a three-dimensional real scale turbine model for five on-cam conditions. The tip leakage cavitation appeared for the optimum cam condition and at high flow rates. The installation of an Anti-Cavity Fin (ACF) on the suction side along the runner blade tip is investigated for its cavitation mitigation functionality. The hydraulic performance, blade loading distribution, vapor volume fraction and tip leakage flow are compared between the blades with and without an ACF. Detailed flow physics on the formation of Tip Leakage Vortex (TLV) and cavitation zones for three on-cam conditions oriented in high flow rates are also presented. The ACF is shown to be effective in decreasing the cavitation intensity at the leading edge without altering the turbine hydraulic performance. A modification of ACF shape at the trailing edge is suggested to avoid damage to the turbine blade and the ACF.
•Installing a fin on a Kaplan turbine suction side tip weakens leakage cavitation intensity.•The anti-cavity fin attachment does not affect the turbine hydraulic performance.•The fin proves to be advantageous at the leading edge and unfavorable at the trailing edge.•Trimming of the fin is suggested for large clearance gap at trailing edge.
In the low-flow rates of off-design conditions in the pump–turbines, complicated flows can develop with vortices in the flow passages, which significantly increase the vibrations and noise, resulting ...in destabilizing the pump–turbine system. Under low-flow-rate conditions, an appropriate Thoma number is the most essential requirement for stable operation in turbine mode of the pump–turbine. Thus, this study elucidated to examine the internal flow and unsteady pressure phenomena in a laboratory-scale pump–turbine model operated in turbine mode with different Thoma numbers. The experimental investigations were conducted under 70% of the flow rate at the best efficiency point with different Thoma number to observe the unsteady pressures and vortex rope behavior. Then, the numerical validations were conducted by three-dimensional unsteady-state RANS analyses in a SAS–SST model. The Thoma number did not significantly affect the performance of the pump–turbine model or the unsteady flow phenomena in the vaneless and runner regions. However, the Thoma number affected the draft tube region at low flow rate condition. At low Thoma numbers, the irregular flow phenomena along the flow direction enhanced the unsteady pressure characteristics.
•Internal flow phenomena by Thoma number of a pump-turbine model were presented.•Experimental and numerical investigations were conducted by different Thoma number.•The Thoma number effects were investigated under low-flow-rate condition.•The performance was independent of the Thoma number under low-flow-rate condition.•The Thoma number affected the draft tube region with a visible vortex rope.
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