Rotor Vibration Due to Collision With Annular Guard During Passage Through Critical Speed

1998 ◽  
Vol 120 (2) ◽  
pp. 544-550 ◽  
Author(s):  
S. Yanabe ◽  
S. Kaneko ◽  
Y. Kanemitsu ◽  
N. Tomi ◽  
K. Sugiyama
Keyword(s):  
Contact Force ◽  
Critical Speed ◽  
Angular Acceleration ◽  
Runge Kutta Method ◽  
Nonstationary Vibration ◽  
Backward Whirl ◽  
Before And After ◽  
Conservation Of Momentum ◽  
Pass Through ◽  
Two Bodies

This paper deals with a nonstationary vibration of a rotor due to its collision with a guard during passage through a critical speed. An unbalanced rigid rotor supported by springs and dampers is accelerated at a constant angular acceleration and collides with an annular guard supported by springs and dampers. This dynamic process is calculated by the Runge-Kutta method, and effects of system-parameters on the process are discussed. The collision phenomenon is analyzed through two different theories. In the collision theory, the law of conservation of momentum and the coefficient of restitution are used in order to obtain rotor and guard velocities after collision. The impulse of the force induced by collision is assumed to be equal to the momentum change before and after collision. In the contact force theory, the contact force is assumed to be proportional to the overlapped displacement of the two bodies. Few differences are observed between the calculated responses based on the two theories. In some cases, the rotor executes a diverging backward whirl due to the friction force that occurs during collision with the guard and can not pass through the critical speed. The criteria maps for nonoccurrence of the backward whirl are shown.

Backward Whirl and Its Suppression of a Squeeze Film Damper Mounted Rotor/Casing System in Passage through Critical Speed with Rubs

2004 ◽  
Vol 10 (4) ◽  
pp. 561-573 ◽  
Author(s):  
Qian Ding
Keyword(s):  
Critical Speed ◽  
Angular Acceleration ◽  
Squeeze Film ◽  
Squeeze Film Damper ◽  
Internal Support ◽  
Squeeze Film Dampers ◽  
Jeffcott Rotor ◽  
Backward Whirl ◽  
Pass Through ◽  
Second Peak

In this paper we consider a flexible Jeffcott rotor mounted at the ends by identical squeeze film dampers (SFDs). The rotative speed is supposed to increase at a constant angular acceleration. There can be one-peak and two-peak solutions for different values of SFD parameters during passage through the critical speed. Calculation shows that the rotor cannot pass through the critical speed due to the occurrence of diverging backward whirl in passage of the first or second peak, if the level of acceleration is lower than the critical ones. A flexible internal support, which can be activated or deactivated at a certain position along the rotor to change the stiffness of the system to suppress large vibration, is then applied to avoid the occurrence of backward whirl. The method is found to be effective if applied in a suitable way

Botzinger complex region role in phrenic-to-phrenic inhibitory reflex of cat

1989 ◽  
Vol 67 (4) ◽  
pp. 1364-1370 ◽  
Author(s):  
D. F. Speck
Keyword(s):  
Nerve Stimulation ◽  
Phrenic Nerve ◽  
Inhibitory Response ◽  
Phrenic Nerve Stimulation ◽  
Bötzinger Complex ◽  
Before And After ◽  
Pass Through ◽  
Bilateral Lesions ◽  
Decerebrate Cats ◽  
Inhibitory Reflex

Neuronal recordings, microstimulation, and electrolytic and chemical lesions were used to examine the involvement of the Botzinger Complex (BotC) in the bilateral phrenic-to-phrenic inhibitory reflex. Experiments were conducted in decerebrate cats that were paralyzed, ventilated, thoracotomized, and vagotomized. Microelectrode recordings within the BotC region revealed that some neurons were activated by phrenic nerve stimulation (15 of 69 expiratory units, 9 of 67 inspiratory units, and 19 nonrespiratory-modulated units) at average latencies similar to the onset latency of the phrenic-to-phrenic inhibition. In addition, microstimulation within the BotC caused a short latency transient inhibition of phrenic motor activity. In 17 cats phrenic neurogram responses to threshold and supramaximal (15 mA) stimulation of phrenic nerve afferents were recorded before and after electrolytic BotC lesions. In 15 animals the inhibitory reflex was attenuated by bilateral lesions. Because lesion of either BotC neurons or axons of passage could account for this attenuation, in eight experiments the phrenic-to-phrenic inhibitory responses were recorded before and after bilateral injections of 5 microM kainic acid (30–150 nl) into the BotC. After chemical lesions, the inhibitory response to phrenic nerve stimulation remained; however, neuronal activity typical of the BotC could not be located. These results suggest that axons important in producing the phrenic-to-phrenic reflex pass through the region of the BotC, but that BotC neurons themselves are not necessary for this reflex.

scholarly journals Dynamic Characteristics and Experimental Research of a Two-Span Rotor-Bearing System with Rub-Impact Fault

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Rui Zhu ◽  
Guang-chao Wang ◽  
Qing-peng Han ◽  
An-lei Zhao ◽  
Jian-xing Ren ◽  
...  
Keyword(s):  
Dynamic Characteristics ◽  
Critical Speed ◽  
Great Influence ◽  
Experimental Platform ◽  
Rotating Machine ◽  
Rotor Bearing ◽  
Before And After ◽  
Analysis System ◽  
The Stability ◽  
Bearing System

Rotor rub-impact has a great influence on the stability and safety of a rotating machine. This study develops a dynamic model of a two-span rotor-bearing system with rubbing faults, and numerical simulation is carried out. Moreover, frictional screws are used to simulate a rubbing state by establishing a set of experimental devices that can simulate rotor-stator friction in the rotor system. Through the experimental platform and its analysis system, the rubbing experiment was conducted, and the vibration of the rotor-bearing system before and after the critical speed is observed. Rotors running under normal condition, local slight rubbing, and severe rubbing throughout the entire cycle are simulated. Dynamic trajectories, frequency spectrum diagrams, chart of axis track, and Poincare maps are used to analyze the features of the rotor-bearing system with rub-impact faults under various parameters. The vibration characteristics of rub impact are obtained. Results show that the dynamic characteristics of the rotor-bearing system are affected by the change in velocity and degree of impact friction. The findings are helpful in further understanding the dynamic characteristics of the rub-impact fault of the two-span rotor-bearing system and provide reference for fault diagnosis.

Effect of Angular Acceleration and Unbalance Force Orientation on the Backward Whirl in Cracked Rotors

2018 ◽  
Author(s):  
Fatima K. Alhammadi ◽  
Mohammad A. AL-Shudeifat ◽  
Oleg Shiryayev
Keyword(s):  
Experimental Testing ◽  
Crack Opening ◽  
Real Life ◽  
Angular Acceleration ◽  
Sharp Drop ◽  
Rotating Systems ◽  
Start Up ◽  
Backward Whirl ◽  
Unbalance Force ◽  
Vector Orientation

Rotors have wide applications in several aerospace and industrial heavy-duty systems. In most of these applications, the rotating system reaches its steady state operational speed after the passage through at least one of its critical rotational speeds. In real-life applications, the probable appearance of a residual slight unbalance in the system could cause an elevation in vibration amplitudes at the critical rotational speeds. Accordingly, propagation of cracks in rotating shafts usually influences the level of these vibration amplitudes during start-up and cost-down operations. For such rotating systems, the critical whirl speeds are usually associated with forward and backward whirl responses where it has been always assumed that the backward whirl zone should precede the forward whirl zone. Here, two configurations of cracked rotor-disk systems are considered to study the effect of the angular acceleration and the unbalance force vector orientation with respect to the crack opening direction on the whirl response at the backward whirl zone of rotational speeds. The obtained numerical simulation results are verified through a robust experimental testing for system startup operations. The backward whirl zone is found here to appear immediately after the passage through the critical forward whirl rotational speed. The onset of the backward whirl is also found to be associated with a sharp drop in vibration whirl amplitudes. This backward whirl zone is found to be significantly affected by the unbalance force angle vector orientation and the shaft angular acceleration. More importantly, this zone of backward whirl orbits is not found to be preceding the critical forward whirl zone for the considered cracked shaft-disk configurations.

scholarly journals Eliminate the Queuing Time in the New Suez Canal: Predicting Adjustment on Ships’ Arrival Time under Optimal Non-Queuing Toll Scheme

2021 ◽  
Vol 9 (1) ◽  
pp. 70
Author(s):  
Pey-Yuan Sun ◽  
Chen-Hsiu Laih
Keyword(s):  
Arrival Time ◽  
Suez Canal ◽  
Management Decision ◽  
Large Size ◽  
Ship Owner ◽  
Entry Time ◽  
Before And After ◽  
Pass Through ◽  
New Suez Canal ◽  
Scheduled Time

In 2016, the construction of the New Suez Canal was completed, enabling most large-size vessels to pass through and causing more ships to queue into the canal. As the queueing problem at the entrance of the canal was anticipated to be serious, an optimal non-queueing toll scheme was previously established to eliminate the queueing phenomenon at the anchorage of the canal. However, no information about each ship’s arrival time adjustment under the optimal non-queueing toll scheme is available from the previous literature. To solve this problem, we derive a series of mathematical formulae for each ship’s arrival time, length of queuing time and entry time before, and after, implementing the optimal non-queueing toll scheme. The arrival time adjustments, which enable ships to enter the canal without queueing, could then be obtained. These results enable the Suez Canal authorities to draw up the ship’s arrival timetable under the optimal non-queueing toll scheme, so that the captain could follow to enter the canal. The above information that we provide would be conducive to the management decision for the canal authorities to implement such a toll scheme. Once a tolled ship could enter the canal at the scheduled time without queueing, the ship owner could accurately control the sailing schedule, and the use of the ship could be more efficient.

scholarly journals Characterization of the Resistance and Force of a Carbon Nanotube/Metal Side Contact by Nanomanipulation

Scanning ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Ning Yu ◽  
Masahiro Nakajima ◽  
Qing Shi ◽  
Zhan Yang ◽  
Huaping Wang ◽  
...  
Keyword(s):  
Contact Resistance ◽  
Contact Force ◽  
Contact Area ◽  
Field Effect Transistors ◽  
Influence Factors ◽  
Contact Length ◽  
Before And After ◽  
Negative Exponential ◽  
Good Agreement

A high contact resistance restricts the application of carbon nanotubes (CNTs) in fabrication of field-effect transistors (FETs). Thus, it is important to decrease the contact resistance and investigate the critical influence factors such as the contact length and contact force. This study uses nanomanipulation to characterize both the resistance and the force at a CNT/Au side-contact interface inside a scanning electron microscopy (SEM). Two-terminal CNT manipulation methods, and models for calculating the resistance and force at contact area, are proposed to guide the measurement experiments of a total resistance and a cantilever’s elastic deformation. The experimental results suggest that the contact resistance of CNT/Au interface is large (189.5 kΩ) when the van der Waals force (282.1 nN) dominates the contact force at the interface. Electron-beam-induced deposition (EBID) is then carried out to decrease the contact resistance. After depositing seven EBID points, the resistance is decreased to 7.5 kΩ, and the force increases to 1339.8 nN at least. The resistance and force at the contact area where CNT was fixed exhibit a negative exponential correlation before and after EBID. The good agreement of this correlation with previous reports validates the proposed robotic system and methods for characterizing the contact resistance and force.

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