Thermoelastic Modeling of Rotor Response With Shaft Rub

2010 ◽  
Vol 77 (6) ◽  
Author(s):  
S. Ziaei-Rad ◽  
E. Kouchaki ◽  
M. Imregun
Keyword(s):  
Friction Coefficient ◽  
Critical Speed ◽  
Normal Force ◽  
Contact Point ◽  
Tangential Force ◽  
Bending Moment ◽  
Contact Forces ◽  
Mass Unbalance ◽  
Deceleration Rate ◽  
The Time Domain

This paper studies the effects of shaft rub on a rotating system’s vibration response with emphasis on heat generation at the contact point. A 3D heat transfer code, coupled to a 3D vibration code, was developed to predict the dynamic response of a rotor in the time domain. The shaft bow is represented by an equivalent bending moment and the contact forces by rotating external forces. The seal ring is modeled as a linear spring, which exerts a normal force to the rotor. The tangential force is then calculated as the product of the normal force with the friction coefficient. Stable or unstable spiraling and oscillating modes were seen to occur in well defined shaft speed zones. In the main, for the configurations studied, the shaft vibration was found to be unstable for speeds below the first critical speed and stable for speeds above the first critical speed. Limit cycle behavior was observed when the phase angle between the unbalance force and the response was around 90 deg. The vibration behavior with rub during startup and shutdown was studied by considering the effects of acceleration/deceleration rate, friction coefficient, and mass unbalance. It was found that friction coefficient and increasing mass unbalance amplified the rub effects while acceleration/deceleration rate reduced it.

scholarly journals Application of Nadal Limit for the Prediction of Wheel Climb Derailment

2011 ◽  
Author(s):  
Brian Marquis ◽  
Robert Greif
Keyword(s):  
Alternative Explanation ◽  
Normal Force ◽  
Contact Point ◽  
Angle Of Attack ◽  
Steady Motion ◽  
Critical Value ◽  
Contact Forces ◽  
Creep Force ◽  
Rigid Body Mechanics ◽  
Tangential Friction

Application of the Nadal Limit to the prediction of wheel climb derailment is presented along with the effect of pertinent geometric and material parameters. Conditions which contribute to this climb include wheelset angle of attack, contact angle, friction and saturation surface properties, and lateral and vertical wheel loads. The Nadal limit is accurate for high angle of attack conditions, as the wheelset rolls forward in quasi-static steady motion leading to a flange climbing scenario. A detailed study is made of the effect of flange contact forces Ftan and N, the tangential friction force due to creep and the normal force, respectively. Both of these forces vary as a function of lateral load L. It is shown that until a critical value of L/V is reached, climb does not occur with increasing L since Ftan is saturated and the flange contact point slides down the rail. However, for a certain critical value of L/V (i.e. the Nadal limit) Ftan is about to drop below its saturated value and flange climb (rolling without sliding) up the rail occurs. Additionally, an alternative explanation of climb is given based on a comparison of force resultants in track and contact coordinates. The effects of longitudinal creep force Flong and angle of attack are also investigated. Using a saturated creep resultant based on both (Ftan, Flong) produces a climb prediction L/V larger (less conservative) than the Nadal limit. Additionally, for smaller angle of attack the standard Nadal assumption of Ftan = μN may lead to an overly conservative prediction for the onset of wheel climb. Finally, a useful analogy for investigating conditions for sliding and/or rolling of a wheelset is given from a study of a disk in rigid body mechanics.

Friction Coefficient of Nano-Ceramic Polished by Oxide Film on ELID Grinding Wheel

2013 ◽  
Vol 669 ◽  
pp. 91-94 ◽  
Author(s):  
Ji Cai Kuai
Keyword(s):  
Friction Coefficient ◽  
Oxide Film ◽  
Normal Force ◽  
Tangential Force ◽  
Grinding Wheel ◽  
Nano Materials ◽  
Dynamic Changes ◽  
Bonding Agents ◽  
Elid Grinding ◽  
Feeding Speed

The dynamic changes of the friction properties of the oxide film are characterized by the dynamic changes of the ELID grinding force. The tangential force and normal force are used to represent the friction coefficient in order to obtain the accurate real-time friction coefficient of oxide film. Therefore, the friction coefficient of various grinding wheels with different bonding agents, various grinding parameters, various grinding materials (nano- Al2O3 ceramic, nano ZrO2 ceramic and ordinary ZrO2 ceramic), and ELID grinding and ordinary grinding can be further studied. The results show that: the friction coefficient of the oxide film on the bronze-based grinding wheel is greater than that composed by iron; the friction coefficient of the oxide film decreases with the increase in grinding depth and feeding speed; the friction coefficient of the oxide film and nano-materials is smaller than that of the oxide film and ordinary materials; the transformation from γ-Fe2O3 to α-Fe2O3 in oxide film and the elastic deformation of the oxide film caused by the high-temperature of grinding may make the friction coefficient of ELID grinding greater than that of ordinary grinding, so the oxide film contains better property of friction and polishing. Therefore, excellent surface quality is easier to be obtained by it compared with the ordinary grinding technology.

scholarly journals Contact Forces in a Screw Feeding Process

2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Yunfei Shi ◽  
Xiliang Zhang ◽  
Shoujuan Cui ◽  
Kui Ma
Keyword(s):  
Contact Force ◽  
Normal Force ◽  
Bulk Material ◽  
Distinct Element ◽  
Tangential Force ◽  
Particle Diameter ◽  
Contact Forces ◽  
Slip Model ◽  
Screw Feeder ◽  
Feeding Process

The contact force between particles is analysed in this paper. Firstly, theoretical analysis is carried out based on the Hertz–Mindlin (no slip) model. Secondly, the normal force and tangential force are, respectively, simulated in single/double-flight screw feeders with the discharging device at three rotating speeds (60 rpm, 90 rpm, and 120 rpm) using different diameter particles (3 mm,  5 mm, and 7 mm) by the extended distinct element method (EDEM) software. Finally, the simulation results show that the particle diameter has the biggest impact on average contact force in the feeding process. This research provides theoretical basis for the study of the rule of bulk material movement in the screw feeder and the development of the high-precision feeding machine.

Elastic Contact of Rough Surfaces Subject to Combined Force and Moment

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Ali Sepehri ◽  
Kambiz Farhang
Keyword(s):  
Half Plane ◽  
Normal Force ◽  
Rough Surfaces ◽  
Tangential Force ◽  
Contact Forces ◽  
Elastic Contact ◽  
Force Component ◽  
Angular Misalignment ◽  
Tangential Contact ◽  
Applied Forces

In this paper we consider the contact between two rectangular rough surfaces that provide normal and tangential contact forces, as well as contact moment, to counteract the net moment imposed by the applied forces. The surfaces are permitted to develop a slight angular misalignment, and thereby contact moment is derived. Through this scheme it is possible to also define elastic contribution to friction, since the half-plane tangential contact force on one side of an asperity is no longer balanced by the half-plane tangential force component on the opposite side. The elastic friction force, however, is shown to be of a much smaller order than the contact normal force.

scholarly journals Numerical Parametric Study on the Effectiveness of the Contact-Point Response of a Stationary Vehicle for Bridge Health Monitoring

2021 ◽  
Vol 11 (15) ◽  
pp. 7028
Author(s):  
Ibrahim Hashlamon ◽  
Ehsan Nikbakht ◽  
Ameen Topa ◽  
Ahmed Elhattab
Keyword(s):  
Numerical Model ◽  
Health Monitoring ◽  
Contact Point ◽  
Response Spectra ◽  
Roughness Effects ◽  
Moving Vehicle ◽  
Bridge Health Monitoring ◽  
Vehicle Response ◽  
Instrumented Vehicle ◽  
The Time Domain

Indirect bridge health monitoring is conducted by running an instrumented vehicle over a bridge, where the vehicle serves as a source of excitation and as a signal receiver; however, it is also important to investigate the response of the instrumented vehicle while it is in a stationary position while the bridge is excited by other source of excitation. In this paper, a numerical model of a stationary vehicle parked on a bridge excited by another moving vehicle is developed. Both stationary and moving vehicles are modeled as spring–mass single-degree-of-freedom systems. The bridges are simply supported and are modeled as 1D beam elements. It is known that the stationary vehicle response is different from the true bridge response at the same location. This paper investigates the effectiveness of contact-point response in reflecting the true response of the bridge. The stationary vehicle response is obtained from the numerical model, and its contact-point response is calculated by MATLAB. The contact-point response of the stationary vehicle is investigated under various conditions. These conditions include different vehicle frequencies, damped and undamped conditions, different locations of the stationary vehicle, road roughness effects, different moving vehicle speeds and masses, and a longer span for the bridge. In the time domain, the discrepancy of the stationary vehicle response with the true bridge response is clear, while the contact-point response agrees well with the true bridge response. The contact-point response could detect the first, second, and third modes of frequency clearly, unlike the stationary vehicle response spectra.

scholarly journals Slipping–rolling transitions of a body with two contact points

2021 ◽  
Author(s):  
Mate Antali ◽  
Gabor Stepan
Keyword(s):  
Rigid Body ◽  
Contact Point ◽  
Static Friction ◽  
Rigid Body Dynamics ◽  
Contact Forces ◽  
Friction Forces ◽  
Contact Points ◽  
Body Dynamics ◽  
Coulomb Model ◽  
Rigid Surfaces

AbstractIn this paper, the general kinematics and dynamics of a rigid body is analysed, which is in contact with two rigid surfaces in the presence of dry friction. Due to the rolling or slipping state at each contact point, four kinematic scenarios occur. In the two-point rolling case, the contact forces are undetermined; consequently, the condition of the static friction forces cannot be checked from the Coulomb model to decide whether two-point rolling is possible. However, this issue can be resolved within the scope of rigid body dynamics by analysing the nonsmooth vector field of the system at the possible transitions between slipping and rolling. Based on the concept of limit directions of codimension-2 discontinuities, a method is presented to determine the conditions when the two-point rolling is realizable without slipping.

scholarly journals Effect of Water-Based Nanolubricants in Ultrasonic Vibration Assisted Grinding

2018 ◽  
Vol 2 (4) ◽  
pp. 80 ◽  
Author(s):  
Mir Molaie ◽  
Ali Zahedi ◽  
Javad Akbari
Keyword(s):  
Surface Roughness ◽  
Specific Energy ◽  
Material Removal ◽  
Normal Force ◽  
Tangential Force ◽  
Process Efficiency ◽  
Multiwall Carbon Nanotube ◽  
Ultrasonic Vibrations ◽  
Mql Grinding ◽  
Water Based

Currently, because of stricter environmental standards and highly competitive markets, machining operations, as the main part of the manufacturing cycle, need to be rigorously optimized. In order to simultaneously maximize the production quality and minimize the environmental issues related to the grinding process, this research study evaluates the performance of minimum quantity lubrication (MQL) grinding using water-based nanofluids in the presence of horizontal ultrasonic vibrations (UV). In spite of the positive impacts of MQL using nanofluids and UV which are extensively reported in the literature, there is only a handful of studies on concurrent utilization of these two techniques. To this end, for this paper, five kinds of water-based nanofluids including multiwall carbon nanotube (MWCNT), graphite, Al2O3, graphene oxide (GO) nanoparticles, and hybrid Al2O3/graphite were employed as MQL coolants, and the workpiece was oscillated along the feed direction with 21.9 kHz frequency and 10 µm amplitude. Machining forces, specific energy, and surface quality were measured for determining the process efficiency. As specified by experimental results, the variation in the material removal nature made by ultrasonic vibrations resulted in a drastic reduction of the grinding normal force and surface roughness. In addition, the type of nanoparticles dispersed in water had a strong effect on the grinding tangential force. Hybrid Al2O3/graphite nanofluid through two different kinds of lubrication mechanisms—third body and slider layers—generated better lubrication than the other coolants, thereby having the lowest grinding forces and specific energy (40.13 J/mm3). It was also found that chemically exfoliating the graphene layers via oxidation and then purification prior to dispersion in water promoted their effectiveness. In conclusion, UV assisted MQL grinding increases operation efficiency by facilitating the material removal and reducing the use of coolants, frictional losses, and energy consumption in the grinding zone. Improvements up to 52%, 47%, and 61%, respectively, can be achieved in grinding normal force, specific energy, and surface roughness compared with conventional dry grinding.

An optimal wheel-torque control on a compliant modular robot for wheel-slip minimization

Robotica ◽  
2015 ◽  
Vol 35 (2) ◽  
pp. 463-482 ◽  
Author(s):  
Avinash Siravuru ◽  
Suril V. Shah ◽  
K. Madhava Krishna
Keyword(s):  
Friction Coefficient ◽  
Normal Force ◽  
Experimental Studies ◽  
Traction Force ◽  
Static Stability ◽  
Wheel Speed ◽  
Torque Control ◽  
Modular Robot ◽  
Wheel Slip ◽  
Wheel Torque

SUMMARYThis paper discusses the development of an optimal wheel-torque controller for a compliant modular robot. The wheel actuators are the only actively controllable elements in this robot. For this type of robots, wheel-slip could offer a lot of hindrance while traversing on uneven terrains. Therefore, an effective wheel-torque controller is desired that will also improve the wheel-odometry and minimize power consumption. In this work, an optimal wheel-torque controller is proposed that minimizes the traction-to-normal force ratios of all the wheels at every instant of its motion. This ensures that, at every wheel, the least traction force per unit normal force is applied to maintain static stability and desired wheel speed. The lower this is, in comparison to the actual friction coefficient of the wheel-ground interface, the more margin of slip-free motion the robot can have. This formalism best exploits the redundancy offered by a modularly designed robot. This is the key novelty of this work. Extensive numerical and experimental studies were carried out to validate this controller. The robot was tested on four different surfaces and we report an overall average slip reduction of 44% and mean wheel-torque reduction by 16%.

Wheel-Rail Multi-Point Contact Method for Railway Turnouts

2011 ◽  
Vol 97-98 ◽  
pp. 378-381
Author(s):  
Zhi Wei Chen ◽  
Linan Li ◽  
Shi Gang Sun ◽  
Jun Long Zhou
Keyword(s):  
Calculation Method ◽  
Normal Force ◽  
Contact Point ◽  
Point Contact ◽  
Contact Model ◽  
Contact Method ◽  
Elastic Contact ◽  
Simulation Calculation ◽  
Acute Change

A calculation method of wheel-rail multi-point contact based on the elastic contact model is introduced. Moreover, the simulation calculation of vehicles passing through branch lines of No.18 turnouts is carried out. The result showed that the acute change of wheel-rail normal force caused by the transfers of wheel-rail contact point between two rails can be avoid by wheel-rail multi-point contact method, and the transfers of wheel-rail normal force between two rails is smoother. The validity of wheel-rail multi-point contact method is verified.

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