Higher Critical Speed Research Articles

TECHNOLOGY EVALUATION OF STRUCTURAL AND VIBRATIONAL CHARACTERISTIC OF COMPOSITE DRIVE SHAFT FOR AUTOMOBILE USING FEM

In vehicle drive shaft is one of the most important component. It transmits torque from the engine to the differential gear of a rear wheel drive vehicle. Generally the drive shaft is made up of steel alloy but the use of conventional steel has disadvantages such as low specific stiffness and strength and high weight. Nowadays this steel drive shaft is replaced by composite material drive shaft. This advanced composite such as graphite, Kevlar, carbon, glass with suitable resin have advantage of higher specific strength, less weight, high damping capacity, longer life, high critical speed and greater torque carrying capacity and can results in considerable amount of weight reduction as compared to steel shaft. The main objective of this research work is to study the structural and vibrational behavior of composite material drive shaft assembly as compared to conventional steel drive shaft. Heavy duty vehicle transmission drive shaft has been used for the project. The conventional material steel SM45C and three composite materials HS carbon epoxy, E-glass epoxy, HM carbon epoxy have been used for drive shaft study so as to determine the suitable composite replacement in order to optimize the performance and design. The drive shaft was modelled using the CREO 3.0 cad software and finite element analysis were done using ansys 14.0 FEA as an analysis tool for numerical simulation to find the dynamic vibration response of composite material drive. The simulation result determines the total deformation, Equivalent Von misses stress, Maximum shear stress, natural frequencies and mode shapes under actual boundary conditions. The result concluded that HS carbon epoxy composite material is suited more for composite drive shaft application as compared to other composite materials.

New design of circular saw blade body and its influence on critical rotational speed

Oscillation is an unwelcome state as it has adverse effects not only on the work piece but also on the tool. This paper deals with the problem of circular saw blade oscillation and the effect of modification of the circular saw blade body on the natural frequency as well as on the critical rotational speed. The calculation and experimental investigation of the natural frequencies and node shapes on two types of circular saw blades were carried out. Two methods used to determine the natural frequencies are presented: the first, modal analysis (FEM), a theoretical method, and the second, experimental measurement. The results of the investigation were used to compare the FEM and experimental methods and to show which modification achieved a higher critical rotational speed. Both methods were conducted on two circular saw blades for continual cutting with 36 teeth and slots.

Cooperative and Competitive Dynamics Model for Information Propagation in Online Social Networks

Traditional empirical models of propagation consider individual contagion as an independent process, thus spreading in isolation manner. In this paper, we study how different contagions interact with each other as they spread through the network in order to propose an alternative dynamics model for information propagation. The proposed model is a novel combination of Lotka-Volterra cooperative model and competitive model. It is assumed that the interaction of one message on another is flexible instead of always negative. We prove that the impact of competition depends on the critical speed of the messages. By analyzing the differential equations, one or two stable equilibrium points can be found under certain conditions. Simulation results not only show the correctness of our theoretical analyses but also provide a more attractive conclusion. Different types of messages could coexist in the condition of high critical speed and intense competitive environment, or vice versa. The messages will benefit from the high critical speed when they are both competitive, and adopting a Tit-for-Tat strategy is necessary during the process of information propagation.

The Analysis of the Flutter Region of Wind Turbine Blade

As the wind turbine blade is becoming larger and larger, the flutter of the wind turbine blade has been paid great attention by many fields. The flutter region of the wind turbine blade airfoil was focused on. The equation of motion for the flutter of blade airfoil was established, based on the simplified aerodynamic force and torque. The flutter analysis of wind turbine blade was carried out with the four-order Runge-Kutta methods, and so the flutter region of the blade airfoil can be obtained. The results show that, there are two critical tip speed ratios for the given blade airfoil. When the tip speed ratio is below the low critical speed ratio, the blade airfoil is convergent. At the low tip speed ratio, the blade airfoil system will become divergent from convergent condition. When the tip speed ratio is between the low critical tip speed ratio and the high one, the blade airfoil system will diverge. At the high tip speed ratio, the system will become convergent from divergent condition. When the tip speed ratio is above the high critical tip speed ratio, the blade airfoil system will converge again. In addition, the torsional angular displacement and velocity always keep convergent, the flap velocity is slightly divergent, because they are not sensible to the change of the tip speed ratio, and they are difficult to cause flutter, so the torsional motion will be more stable than flap motion for the given blade airfoil. It can provide one of references for the determination of the blade airfoil.

Bifurcation\instability forms of high speed railway vehicles

The China high speed railway vehicles of type CRH2 and type CRH3, modeled on Japanese high speed Electric Multiple Units (EMU) E2 series and Euro high speed EMU ICE3 series possess different stability behaviors due to the different matching relations between bogie parameters and wheel profiles. It is known from the field tests and roller rig tests that, the former has a higher critical speed while large limit cycle oscillation appears if instability occurs, and the latter has lower critical speed while small limit cycle appears if instability occurs. The dynamic model of the vehicle system including a semi-carbody and a bogie is established in this paper. The bifurcation diagrams of the two types of high speed vehicles are extensively studied. By using the method of normal form of Hopf bifurcation, it is found that the subcritical and supercritical bifurcations exist in the two types of vehicle systems. The influence of parameter variation on the exported function Rec 1(0) in Hopf normal form is studied and numerical shooting method is also used for mutual verification. Furthermore, the bifurcation situation, subcritical or supercritical, is also discussed. The study shows that the sign of Re(λ) determinates the stability of linear system, and the sign of Rec 1(0) determines the property of Hopf bifurcation with Rec 1(0)>0 for supercritical and Rec 1(0)<0 for subcritical.

The effect of lubrication film thickness on thermoelastic instability under fluid lubricating condition

An idealized model consisting of a thermal conductor and a thermal insulator separated by a thin layer of lubricating fluid is developed to investigate thermoelastic instability with fluid lubrication. The governing equations are solved for the critical speed. A new dimensionless parameter H0 is defined to predict the critical speed. Furthermore, the effects of various materials and the wavelength of perturbations on thermoelastic instability are discussed. It has been found that the migration speed of hot spots is nonzero, but typically very slow compared with the sliding speed and the relation between the critical speed and the fluid film thickness is non-linear. In addition, a material with low elastic modulus, low thermal expansion coefficient and high thermal conductivity will experience a high critical speed.

Acceleration of Unbalanced Rotors

AbstractA lot of work in rotordynamics is done in the evaluation of the Laval rotor. By accelerating this type of rotor, described by a single rigid disc centred in the middle of a slim shaft modelled as spring, one can observe the sticking of the rotational speed at the first bending eigenfrequency of the system, also named critical speed. This phenomenon only appears when the rotor is unbalanced and a small external torque accelerates the rotor. Taking a look at higher critical speeds one will notice that the Laval rotor model is insufficient accurate to take this eigenfrequencies into account. Therefore the equations of motion are derived using the Projection Equation in subsystem representation leading to Partial Differential Equations (PDE). Using the Timoshenko beam theory enables one to include the discs not only as rigid body but as real elastic part of the beam system. Applying the Transfer-Matrix-Method (TMM) to the system's linearized equations delivers adequate shape functions for the nonlinear PDE. The advantage of using the TMM is the possibility to calculate multidisc rotors and systems where the border between disc and shaft related to the diameter to length ratio cannot be defined clearly. Furthermore, the excentricity which is responsible for the unbalance of the rotor, has to be taken into account. The modeling is again done with the Projection Equation. Numerical simulation solutions are presented and compared to experimental results.

824 磁気軸受型弾性ロータの高次危険速度通過技術に関する研究

824 磁気軸受型弾性ロータの高次危険速度通過技術に関する研究

1107 タイヤ稼働率を用いた電気自動車の車両運動制御の研究(OS3-2 車両運動制御,OS3 交通・物流システムの制御,オーガナイズド・セッション)

We propose new vehicle dynamics management of in-wheel electric motor vehicle based on tire force usage rate. In the vehicle dynamics management, we adopted non-linear optimizing controller using direct yaw-moment control, tire force usage rate and each tire force. In cornering performance test simulation of 3 degree freedom model, we confirmed that by using this vehicle dynamics management, saturating tire force could be avoided and higher critical speed also could be achieved. We did the simulation and the run test by the in-wheel electric motor vehicle. By these simulation and run test, it was confirmed that the 4 wheel drive in-wheel motor electric vehicle with the proposed vehicle dynamics management system could have higher stability performance comparing to the same vehicle without control.

Vehicle Dynamics Management of Electric Vehicle Based on Tire Force Usage (1st Report, Examination of Tire Force Usage Control for In Wheel Motors)

We propose new vehicle dynamics management of in-wheel electric motor vehicle based on tire force usage rate. In the vehicle dynamics management, we adopted non-linear optimizing controller using direct yaw-moment control, tire force usage rate and each tire force. In cornering performance test simulation of 3 degree freedom model, we confirmed that by using this vehicle dynamics management, saturating tire force could be avoided and higher critical speed also could be achieved. We also conducted pylon course slalom test simulation. By this simulation, it was confirmed that the 4 wheel drive in-wheel motor electric vehicle with the proposed vehicle dynamics management system could have higher stability performance comparing to the same vehicle without control.

Zero Bias Backstepping Control of Magnetic Bearing System with Gyroscopic Effect (Consideration Based on Rigid Model and Flexible Model)

This paper deals with a large flywheel magnetic bearing system. A simple rigid model was derived based on overlapping principle. A servo system backstepping controller taking into consideration of the gyroscopic effect was designed. The switching method for the control current was chosen to avoid the use of bias current. Through simulation and experiments, the effectiveness of rigid model and stability of the controller was verified. Meanwhile, the power consumption using the proposed controller is reduced by half compared to bias current control. Faced with the problem that the rotor cannot overcome a high critical rotational speed, a flexible model based on finite-element method was derived and used in place of the rigid model, applying the same controller. From the result of root locus analysis of closed-loop system, a conclusion can be drawn that it is important to the magnetic bearing system to design a controller considering the gyroscopic effect based on a flexible model which includes two rigid modes and a first flexible back mode.

1005 磁気軸受支持弾性ロータの研究(OS-6 運動と振動の制御)

In the active magnetic bearing system, it is difficult to control stably flexible rotor which cause spillover instability. In this research, as a part of the work for this problem, it was tried to build a control system for the flexible rotor with 10 disks on the active magnetic bearing, to levitate it stably and pass high order critical speed stably.

Compatibility of Curving Performance and Hunting Stability of Railway Bogie

SUMMARYThe curving performance and high speed hunting stability are important for railway bogies, but generally they are contrary to each other. In this paper we report methods which can realize the compatibility between curving performance and hunting stability. The methods that we adopt are 1) Optimized worn tread profile of wheel, 2) Independently rotating wheels in rear axle and 3) Asymmetric arrangement of longitudinal primary stiffness. For validation of the effects of these methods, we carried out numerical simulation by multi-body dynamics software, full scale stand tests and partly field running tests. According to the results the curving performance of proposed bogie is improved remarkably, for example the lateral force between wheel and rail is 50% reduced, keeping high critical speed against hunting. So we have successfully developed brand new bogies which have not only excellent curving performance but also good hunting stability.

Laboratory-based measurements of swimming performance and related metabolic rates of field-sampled smallmouth buffalo (Ictiobus bubalus): a study of seasonal changes.

Numerous studies have demonstrated how the performance physiology of fish may change when they are acclimated to designated laboratory temperatures, but few researchers have examined naturally occurring seasonal effects on several physiological parameters associated with swimming performance. Using field-acclimatized smallmouth buffalo (Ictiobus bubalus) collected each season, we report significant seasonal effects in the following variables: critical swimming speed (modified), metabolic rate (standard, active, and scope for activity), and swimming efficiency (total and net cost of transport). Underlying seasonal changes in performance was the reproductive cycle of buffalo, particularly the period of fall gonadal recrudescence. Compared with spring, fall buffalo had a significantly lower mean critical swimming speed (72%) and lower active metabolic rate (53%), even when tested at similar temperatures. During spring, buffalo had a high mean critical swimming speed and low net cost of transport in comparison with other seasons. Buffalo are known to participate in a spring migration and spawning that may require the increased performance and efficiency observed during that season. In addition, significant sex effects were detected in winter measurements of standard metabolic rate and net cost of transport, with females the more efficient swimmers.

Industrial application of position sensorless active magnetic bearings

AbstractActive magnetic bearings (AMBs) are applied to turbomolecular pumps (TMPs) and milling spindles. However, their application areas are limited because they are costlier and require larger space than conventional mechanical bearings. Omitting position sensors from AMBs is one of the promising methods to solve such problems. An additional merit is that rotors can be shortened to have a higher critical speed by removing sensor targets from the rotor. The sensorless operation of AMBs has already been achieved in several instruments developed for experimental study. In this research, the sensorless magnetic suspension method is applied to a TMP manufactured as an industrial product, and it is demonstrated that sensorless AMBs can suspend a high‐speed rotor.

Critical Speeds of Turbomachinery: Computer Predictions vs. Experimental Measurements—Part I: The Rotor Mass—Elastic Model

This is the first part (Part I) of two papers describing results of a research program directed at verifying computer programs used to calculate critical speeds of turbomachinery. This research program was undertaken since questions existed about the accuracy of calculations for the second and higher critical speeds. Part I describes improvements in computer programs and data modeling that resulted from comparing measured and calculated “free-free” natural frequencies of several shafts and rotors. Program modifications to improve accuracy include consideration of the effect of disk/shaft attachment stiffness, revised treatment of the end masses, and an improved convergence. Modifications resulting from the study are applicable to many other damped and undamped critical speed computer programs.

Formation of Standing Waves in Radial Tires

Abstract Radial tires for automobiles were subjected to high speed rolling under load on a testing wheel to determine the critical speeds at which standing waves started to form. Tires of different makes had significantly different critical speeds. The damping coefficient and mass per unit length of the tire wall were measured and a correlation between these properties and the observed critical speed of standing wave formation was sought through use of a circular membrane model. As expected from the model, desirably high critical speed calls for a high damping coefficient and a low mass per unit length of the tire wall. The damping coefficient is particularly important. Surprisingly, those tire walls that were reinforced with steel cord had higher damping coefficients than did those reinforced with polymeric cord. Although the individual steel filaments are elastic, the interfilament friction is higher in the steel cords than in the polymeric cords. A steel-reinforced tire wall also has a higher density per unit length. The damping coefficient is directly related to the mechanical loss in cyclic deformation and, hence, to the rolling resistance of a tire. The study shows that, in principle, it is more difficult to design a tire that is both fuel-efficient and free from standing waves when steel cord is used than when polymeric cords are used.

A Comparison of the Stability and Curving Performance of Radial and Conventional Rail Vehicle Trucks

This paper compares the lateral stability and steady-state curving performance of radial and conventional rail vehicle trucks. The radial truck has two unique features, it allows direct elastic coupling between the wheelsets and it allows greater total truck shear stiffness for a given bending stiffness. It is shown that the first property allows the radial truck to achieve up to a 40 percent higher critical speed than the conventional truck for equivalent truck total shear and bending stiffness since the direct coupling between the wheelsets allows decoupling of the truck mass from the hunting wheelset masses. The second feature, i.e., greater shear stiffness capability, allows the radial truck to have improved wear properties during the negotiation of tight curves. It is shown that the high shear stiffness property combined with a low bending stiffness reduces the lateral flange force and wheelset angle of attack during flange contact. It is concluded that for routes where the majority of curves are less than 4 deg (greater than 400 m radius) the truck optimized for off-flange performance should have intermediate values of shear stiffness, bending stiffness, and conicity. On the other hand, for routes where the majority of curves are greater than 4 deg, the truck optimized for on-flange performance should have a high shear stiffness and low values of bending stiffness and conicity.

Mixed Lubrication of “Parallel” Plane Sliders

A theoretical model for the friction coefficient indicates two critical speeds of sliding. The lower critical speed corresponds to a change-over from boundary to mixed lubrication conditions, the higher critical speed a transition to full fluid-film lubrication at angles of inclination less than 0.01 deg. The first critical speed appears to be associated with the “stick-slip” phenomenon.

Mechanical Design Concept for 1000-MVA Superconducting Turboalternator

A design concept for the construction of a 1000-mva superconducting alternator is determined by consideration of (a) electrical requirements, (b) thermal isolation requirements, (c) mechanical strength, and (d) structural rigidity. The alternator consists of a rotating superconducting field winding and stationary water cooled stator. This study indicates that a superconducting machine will have lower specific weight and smaller physical size, higher critical speed, increased efficiency, lower synchronous reactance, increased I22t, and higher terminal voltage than conventional machines.