Experimental Researches on Reducing the Critical Acceleration That Induces Sustainable Rotor Rubbing

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Wang Shimin ◽  
Zhang Xingye
Keyword(s):  
Phase Modulation ◽  
Vibration Amplitude ◽  
Critical Speed ◽  
Maximum Amplitude ◽  
Modulation Method ◽  
Constant Acceleration ◽  
Critical Acceleration ◽  
Driving System ◽  
Pass Through ◽  
Experimental Researches

When an imbalanced rotor is sped up to pass through the critical speed with a constant acceleration, sustainable rubbing can be induced if the maximum vibration amplitude of the rotor exceeds the gap. This is the so-called stiffness increase or stiffening phenomenon. The maximum vibration amplitude is dependent on the magnitude of the rotor’s acceleration: the smaller the acceleration, the larger the maximum amplitude. Thus, there exists a critical acceleration: for accelerations smaller than the critical one, the sustainable rubbing will be induced. To prevent such unwanted rubbing, the rotor acceleration or the gap must be large enough. Since the acceleration is limited by the power/torque of driving system while large gap decreases the efficiency of some rotating machines, smaller driving power and higher efficiency have to be content with the second best. In this paper, the phase modulation method is applied to reduce the critical acceleration, and experiments are conducted on a setup designed to test the phase of the imbalanced force. The method is to operate the rotor with a scheduled, not continuously increased speed: when accelerated to a given speed, the rotor is decelerated to an assigned speed, and then accelerated again. Numerical and experimental results show that the critical acceleration is reduced about 50% by this technique. A prerequisite for this method is that the rotor’s speed is controllable.

Reducing Lateral Vibration of a Rotor Passing Through Critical Speeds by Phase Modulating

2003 ◽  
Vol 125 (3) ◽  
pp. 766-771 ◽  
Author(s):  
S.-M. Wang ◽  
Q.-S. Lu ◽  
E. H. Twizell
Keyword(s):  
Vibration Amplitude ◽  
Critical Speed ◽  
Lateral Vibration ◽  
Constant Acceleration ◽  
Unbalanced Rotor ◽  
Acceleration Rate ◽  
Modulated Phase ◽  
Response Phase ◽  
Theoretical And Numerical Analysis ◽  
Rotor Model

A method is presented to reduce the lateral vibration amplitude of an unbalanced rotor accelerating or decelerating through its critical speed, by means of modulating the response phase with varying acceleration rate. Theoretical and numerical analysis on the amplitude and the phase characteristics of lateral vibration of a rotor model are made. Numerical results show that when the rotor passes through its critical speed with a modulated phase, the response amplitude can be reduced by 20% or so, compared with the nonmodulated (constant) acceleration case.

The Aerodynamic Characteristics of the Pantograph When the Train Passes Through the Tunnel

2017 ◽  
Author(s):  
Dilong Guo ◽  
Wen Liu ◽  
Junhao Song ◽  
Ye Zhang ◽  
Guowei Yang
Keyword(s):  
High Speed ◽  
Aerodynamic Force ◽  
Maximum Amplitude ◽  
Aerodynamic Characteristics ◽  
High Speed Train ◽  
Expansion Waves ◽  
Compression And Expansion ◽  
High Speed Trains ◽  
Current Characteristics ◽  
Pass Through

The aerodynamic force acting on the pantograph by the airflow is obviously unsteady and has a certain vibration frequency and amplitude, while the high-speed train passes through the tunnel. In addition to the unsteady behavior in the open-air operation, the compressive and expansion waves in the tunnel will be generated due to the influence of the blocking ratio. The propagation of the compression and expansion waves in the tunnel will affect the pantograph pressure distribution and cause the pantograph stress state to change significantly, which affects the current characteristics of the pantograph. In this paper, the aerodynamic force of the pantograph is studied with the method of the IDDES combined with overset grid technique when high speed train passes through the tunnel. The results show that the aerodynamic force of the pantograph is subjected to violent oscillations when the pantograph passes through the tunnel, especially at the entrance of the tunnel, the exit of the tunnel and the expansion wave passing through the pantograph. The changes of the pantograph aerodynamic force can reach a maximum amplitude of 106%. When high-speed trains pass through tunnels at different speeds, the aerodynamic coefficients of the pantographs are roughly the same.

State-Constrained Optimal Solutions for Safe Eco-Approach and Departure at Signalized Intersections

2020 ◽  
Author(s):  
Jihun Han ◽  
Dominik Karbowski ◽  
Aymeric Rousseau
Keyword(s):  
Analytical Solutions ◽  
Pure State ◽  
Energy Savings ◽  
Minimum Principle ◽  
Optimization Methods ◽  
Signalized Intersections ◽  
Constant Acceleration ◽  
Preceding Vehicle ◽  
Speed Change ◽  
Pass Through

Abstract This paper provides fundamentals of how to energy-efficiently pass through signalized intersections while avoiding any rear-end collisions with leading vehicles. In our previous works [1, 2], analytical solutions with and without second-order pure state constraints imposed by the preceding vehicle were presented; these showed significant energy saving potential for connected and automated vehicles (CAVs) compared to human-driven vehicles. However, these solutions were derived assuming that the desired distance headway policy does not include a speed change over a predictive horizon, and that the preceding vehicle has constant acceleration. We use the desired time headway policy that includes the speed change to define the first-order pure state constraint. We then derive analytical solutions using the direct adjoining method based on Pontryagin’s minimum principle. We also present a novel solver to compute energy-optimal and collision-free state trajectories by accounting for a piecewise constant acceleration of the preceding vehicle without using any numerical optimization methods that require initial guesses. For simple scenarios with one intersection, we analyze how the novel solver allows CAVs to smoothly pass through the signalized intersection and then reach a desired cruising speed. We also use a simulation framework based on high-fidelity powertrain models to validate its effectiveness based on energy savings when driving on real-world urban routes.

scholarly journals Active Elastic Support/Dry Friction Damper with Piezoelectric Ceramic Actuator

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Liao Mingfu ◽  
Song Mingbo ◽  
Wang Siji
Keyword(s):  
Dry Friction ◽  
Piezoelectric Ceramic ◽  
Vibration Amplitude ◽  
Critical Speed ◽  
Rotor System ◽  
Elastic Support ◽  
Basic Operation ◽  
Friction Damper ◽  
Rotor Vibration ◽  
Active Damper

The basic operation principle of elastic support/dry friction damper in rotor system was introduced and the unbalance response of the rotor with elastic support/dry friction damper was analyzed theoretically. Based on the previous structure using an electromagnet as actuator, an active elastic support/dry friction damper using piezoelectric ceramic actuator was designed and its effectiveness of reducing rotor vibration when rotor traverses its critical speed and blade-out event happened was experimentally verified. The experimental results show that the active elastic support/dry friction damper with piezoelectric ceramic actuator can significantly reduce vibration in rotor system; the vibration amplitude of the rotor in critical speed region decreased more than 2 times, and the active damper can protect the rotor when a blade-out event happened, so the rotor can traverse the critical speed and shut down smoothly. In addition, the structure is much simpler than the previous, the weight was reduced by half and the power consumption was only 5 W.

Analysis on location of maximum vibration amplitude in panel flutter

2019 ◽  
Vol 234 (2) ◽  
pp. 457-469 ◽  
Author(s):  
Xianzong Meng ◽  
Zhengyin Ye ◽  
Kun Ye ◽  
Cheng Liu
Keyword(s):  
Theoretical Basis ◽  
Vibration Amplitude ◽  
Dynamic Pressure ◽  
Maximum Amplitude ◽  
Displacement Function ◽  
Limit Cycle Oscillation ◽  
Panel Flutter ◽  
Mathematical Basis ◽  
Critical Dynamic ◽  
Cycle Oscillation

When the panel is under limit cycle oscillation, the location of maximum vibration amplitude always locates at 0.75 of panel length under different dynamic pressure. However, this conclusion is drawn from engineer practice without further investigations on its theoretical basis. Thus, the current study focuses on the theoretical and mathematical basis of this problem. The pattern of the location of maximum amplitude is verified at first by using three numerical methods. Then, based on the law of energy conservation, the displacement function of linear panel oscillation is derived for theoretical investigation. The linear panel consists of two structural modes. Theoretical analysis shows that, under critical dynamic pressure, the generalized displacement responses of two structural modes have opposite phase, the same vibration amplitude and the same vibration frequency. As a result, the superposition of displacement function of two structural modes, which is the displacement function of panel, leads to the occurrence of maximum vibration amplitude at 0.7 of panel length. With more structural modes considered, the location of maximum moves to 0.75 of panel length.

scholarly journals Experimental Study of a Signal Modulation Method to Improve eLORAN Data Channel Communications

Sensors ◽  
2020 ◽  
Vol 20 (22) ◽  
pp. 6504
Author(s):  
Chaozhong Yang ◽  
Yulin Wang ◽  
Shifeng Li ◽  
Wenhe Yan
Keyword(s):  
Phase Modulation ◽  
Service System ◽  
Modulation Method ◽  
Pulse Modulation ◽  
Digital Modulation ◽  
Typical Application ◽  
Time Service ◽  
Data Channel ◽  
Modulation Coding ◽  
Modulation Methods

There are mainly two types of data modulation methods used for enhanced LOng-RAnge Navigation (eLORAN) systems: pulse position modulation (PPM) and supernumerary interpulse modulation (SIM). The typical application for PPM is tri-state PPM (3S-PPM), also known as Eurofix. The typical application for SIM is ninth pulse modulation. Both of these methods are phase modulation methods. Phase modulation coding, a very mature technology, is used at present. To achieve a better demodulation success rate of eLORAN digital modulation signals at longer distances, a method of using the transmitting station duplex mode to transmit a digital modulation pulse group after LORAN-C transmitting a pulse group is proposed to realize modulation pulse on–off modulation. In this method, a broadcasting experiment was performed on the BPL (The call sign of eLORAN time service system in China) broadcaster station. After monitoring, a good receiving demodulation effect was initially obtained.

Communication Periodic Phase Modulation Method for Fast Diagnosis of Phased Array

2020 ◽  
pp. 1-1
Author(s):  
Chong He ◽  
Bai Lin ◽  
Qun Chen ◽  
Anjie Cao ◽  
Jingfeng Chen ◽  
...  
Keyword(s):  
Phase Modulation ◽  
Phased Array ◽  
Modulation Method

scholarly journals II. Experimental researches on the strength of pillars of cast iron

1857 ◽  
Vol 8 ◽  
pp. 318-321
Keyword(s):  
Cast Iron ◽  
The Third ◽  
Pass Through ◽  
Experimental Researches

In a previous paper on this subject (Philosophical Transactions, 1840), I had shown,—1st, that a long circular pillar, with its ends flat, was about three times as strong as a pillar of the same length and diameter with its ends rounded in such a manner that the pressure would pass through the axis, the ends being made to turn easily, but not so small as to be crushed by the weight; 2nd, that if a pillar of the same length and diameter as the preceding had one end rounded and one flat, the strength would be twice as great as that of one with both ends rounded; 3rd, if, therefore, three pillars be taken, differing only in the form of their ends, the first having both ends rounded, the second one end rounded and one flat, and the third both ends flat, the strength of these pillars will be as 1—2—3 nearly. The preceding properties having been arrived at experimentally, are here attempted to be demonstrated, at least approximately.

Sign in / Sign up

Export Citation Format

Share Document