If the axis of the bit rotates in the same direction as the bit itself, the bit is said to undergo forward whirl. An efficient model of drillstring dynamics nasaads. The optidrill service detects whirl, bit bounce, and stickslip motions and their severity. Moreover, the instability of the backward whirl mode motion is only the primary physical mechanism for the partial rub transmitting into dry whip. In the case of the forward whirl, the orbital motion and the spin direction of the rotor are in same direction, whereas for the backward whirl they are opposite. Shaft whirling mechanical acousticsvibration engineering. A simple model of bit whirl for deep drilling applications. Dykstra 6 conducted tests on drill collars and studied the effects of lateral shocks and backward whirl. Whip velocity of backward whirl with slip in multipledegree. May 17, 2011 rotary whirl or bit whirl can occur downhole while rotary drilling oil wells etc.
Effects of forwardbackward whirl mechanism on nonlinear normal. The method assumes forward whirl and backward whirl and creates a plot for each then overlaps the plot which provides an accurate representation of the condition of the bottom hole assembly while drilling. Toggle navigation swansea universitys research repository. Differing from the forward whirl mode motion, the backward whirl mode motion can be unstable, since its modal damping may be less than zero in certain cases. The first two backward modes are overdamped real modes in this example and are not shown in this map. For the forward precessional modes, the gyroscopic effect contributes negative kinetic energy and tends to.
Vibration modes of rotating shafts mechanical acoustics. Oct 01, 2015 in this paper, the effects of forward and backward whirl mechanism on the existence and the stability of multiple nonlinear normal modes nnms in a four degreeoffreedom dof rotorstator rubbing system with crosscoupling stiffness and dry friction are investigated analytically. Instability of unbalance excited synchronous forward whirl at. Us6205851b1 method for determining drill collar whirl in a.
Forward and backward whirling of a rotor with gyroscopic. The following whirl speed map is generated for a typical rotor system with isotropic and constant bearing stiffness. Types of whirl conditions identifiable are forward and backward whirl with and without slip. Bhat and wenfang xie abstract the determination of whirling frequencies of high speed turbines is. Local blade whirl and global rotor whirl interaction osti. Forward and backward whirling of a rotor with gyroscopic effect ali fellah jahromi, rama b. In a discussion of elliptical orbits, kirk says, a major basic understanding required in the study of dynamics of rotors is the concept of forward and backward whirl. This motion is detected downhole by the optidrill services sub and i displayed in real time with a. There is a need for models of drillstring dynamics that can predict this variety of phenomena that are. Rotordynamics, also known as rotor dynamics, is a specialized branch of applied mechanics. The experimental system consists of a rotating shaft representing a section of the bottomhole assembly between two stabilizers. Experimental studies of forward and backward whirls of.
Method for determining drill collar whirl in a bottom hole. From system integration to autonomous systems proceedings of the 7th international workshop on structural health monitoring, iwshm 2009. As shown by calculations, for the time duration covered by simulation, the initial forward whirl changes into a transitory phase, in which the whirl direction continuously changes between forward and backward, and eventually settles into a backward. The tests were aimed at assessing the effects of the noted structural characteristics couplings on the whirl flutter of the proprotor during forward flight. In this paper, the effects of forward and backward whirl mechanism on the existence and the stability of multiple nonlinear normal modes nnms in a four degreeoffreedom dof rotorstator rubbing system with crosscoupling stiffness and dry friction are investigated analytically. Particularly, one can investigate the vibration phenomena of stickslip, forward whirl, backward whirl, and snaking. Rotary whirl or bit whirl can occur downhole while rotary drilling oil wells etc. Nelson essentially says that if one element of a rotor system has a large polar moment of inertia eg. Whirl definition and meaning collins english dictionary. It is quite well known that the lower branch corresponds to the backward whirl and the upper branch corresponds to forward whirl.
At the rotor speed of 5000 rpm, the first mode is a forward conical mode and the second mode is a forward translational mode. These studies predict a forward whirl before the first critical and after the second critical, whereas the rotor executes a backward whirl between the two criticals. When the propeller blades have flap hinges or are very flexible, however, an instability in the forward mode is possible. Numerical study of forward and backward whirling of drillstring marcin kapitaniak. Greenhill rotordynamicsseal research north highlands, ca guillermo a. However, friction between rotor and stator can cause the synchronous forward whirl to. It is capable of reproducing lateral drillstring vibrations with and without contact. Powell, structural technology corporation, zoar, ohio sorin weissman, alfa wasserman, inc. The purpose of this study is to analyse the steady backward whirl behaviour within the system which reduces the fatigue life of the drillstring. For the forward precessional modes, the gyroscopic effect contributes negative kinetic energy and tends to raise the corresponding forward whirl frequency. The influence of drillstringborehole interaction on backward. Whirl definition is to move in a circle or similar curve especially with force or speed. The interaction between the drillstring and borehole wall involves nonlinearities in the form of friction and contact.
Mode shapes versus bearing stiffness, shaft not rotating. Bit whirl is a lateral vibration of the drill bit during which the bit axis undergoes a circular motion. The drillstring borehole interaction induces whirling behaviour of the drillstring causing forward whirl, backward whirl or intermittent bouncing behaviour depending on the system parameters. Following this idea, unbalanced rotors were used to represent an eccentric drill pipe in the research by dykstra 6 and cmin liao et al. Local blade whirl and global rotor whirl interaction dtu orbit. A mathematic model of flexible rotor for the backward rolling with slipping on compliant stator and an exception concept for the contact forces are suggested. Whirl interaction of a drill bit with the borehole bottom. Usually lateral vibrations are classified into two types.
Apr 04, 2020 the backward whirl can cause cracks which can grow from the outside to the inside of the pipe body leading to a failure and result in washout or a twistoff. Meaning, pronunciation, translations and examples log in dictionary. Unsteady flow and whirlinducing forces in axialflow. In a 2dof rotorstator rubbing system, the nnm can be solved in closed form and used to reveal the physical reason for the onset of dry friction backward whirl. Drillstring vibrations and vibration modeling lateral vibrations are the most destructive type of vibration and can create large shocks as the bha impacts the wellbore wall. The natural frequencies of a jeffcott rotor are split in the presence of gyroscopic effect. If something or someone whirls around or if you whirl them around, they move around or. This is a destructive phenomena that can tear up your tools and hole. From system integration to autonomous systems proceedings of the 7th international. Particularly, one can investigate the vibration phenomena of. High amplitude vibration regimes can cause significant damage to oilwell drillstrings. Nonlinear dynamic analysis using the complex nonlinear modes. Hope was seemingly on the horizon some five years ago when the structure of the countrys apex league, the then nigeria premier league npl, later renamed nigeria professional football league npfl was overhauled under the immediate past administration of the nigeria football federation nff led. Numerical study of forward and backward whirling of drill.
Depending on the input, there are two types of whirl modes. A critical steady state behaviour within the system is the backward whirling of the drillstring, which reduces the fatigue life of the drillstring. If the axis of the bit rotates in the same opposite direction as the bit itself, the bit is said to undergo forward backward whirl see fig. Also, the simple rotor with only a single peak in its response is known to whirl in the forward direction at all speeds. Identification of the critical crack depths and locations of. Aug 15, 2014 the natural frequencies of a jeffcott rotor are split in the presence of gyroscopic effect. Elliptic motion may in fact be whirling in one of two directions. If the axis of the bit rotates in the direction opposite to that of the bit, the bit is said to undergo backward whirl. In a whirl frequency plot, it is always the case that forward whirl modes trend upward with rotor speed, and backward whirl modes trend downward. Critical speeds resulting from unbalance excitation of backward. As the speed increases, each vibration mode is split into two modes known asforward and backward precessional modes due to the gyroscopic effect. Cornejo power systems engineering division solar turbines san diego, ca abstract most rotordynamic analyses typically ignore the potential for.
The current work is focused on lateral vibrations, which are characterized by a circular motion of the bit axis. The forward whirl mode of the rotor has been observed experimentally, however, the backward whirl has not been observed. The forward whirl mode of the rotor has been observed. A total of 26 backward whirl flutter states and 50 forward whirl flutter states were found.
The drillstring borehole interaction induces whirling behaviour of the drillstring causing forward whirl, backward whirl or intermittent bouncing behaviour depending. In the example below, a largehole bha is crossing a formation boundary and experiencing severe backward whirl. Natural frequencies of forward and backward whirling mode of blades. Natural frequencies of forward and backward whirling mode of. Forward and backward whirling of a rotor with gyroscopic effect. The whirl velocity can be calculated accurately, not only in case of a clear rolling when it is determined by the rotary velocity and a ratio of rotor. Pdf forward and backward whirling of a rotor with gyroscopic. Significance of forward whirl and backward whirl frequency. The backward whirl can cause cracks which can grow from the outside to the inside of the pipe body leading to a failure and result in washout or a twistoff. Experimental studies of forward and backward whirls of drill. Critical speeds resulting from unbalance excitation of backward whirl modes lyn m.
The sketches on the righthand side of figure 2 give an example of the manner in which the system would respond in the backward whirl mode following a disturbance such as a gust. Dynamic characteristics for the rotor whirling are determined by the matrix methods. The campbell diagram, also known as whirl speed map or a frequency interference diagram, of a simple rotor system is shown on the right. Backward whirl of unbalanced shaft at elastically constrained journal bearings and floating seals due to mechanical contact 236 fundamental work principle of floating ring is a performance of the selfcentering. Global rotor whirl interaction j0rgen thirstrup petersen, kenneth thomsen. Maybe i am missing something, but a forward whirl is a whirl orbit in the direction of rotation and a backward whirl is an orbit in the opposite direction to rotation. The interaction between bha and drillstring contact points may, in certain circumstances, drive. Effects of forwardbackward whirl mechanism on nonlinear. Predicting the stability of rotor systems with the comsol.
Investigation of reverse whirl of a flexible rotor adolf lingener1 rakenteiden mekaniikka, vol. Can someone explain to me gyroscopic stiffening and softening. Critical speeds resulting from unbalance excitation of. From those two, the backward whirl is a bigger threat to the drilling. During the chaotic or intermittent whirl, the bha may repeatedly impact the borehole wall, this behavior can generate high lateral shocks and damage down hole tools such as mwd. A major concern within the oil drilling industry remains the interaction between the drillstring and borehole.
Recent experimental studies include the work performed by rand and peyran. Jan 30, 2017 a major concern within the oil drilling industry remains the interaction between the drillstring and borehole. The pink and blue curves show the backward whirl bw and forward whirl fw modes, respectively, which diverge as the spin speed increases. By this definition then there cannot be whirl at zero speed. He identified that whirl frequency is same as transverse vibration frequency of a stationary shaft and showed the existence of critical speeds of a. This synchronous forward whirl has to be stable in order to avoid destructive self. A flexible rotor can have stations that whirl either forward or backward along the rotor, at the same time. The method assumes forward whirl and backward whirl and creates a plot for each then overlaps the plot which provides an accurate representation of the condition of. The following whirl speed map is generated for a rotor system supported by fluid film bearings. Identification of the critical crack depths and locations of rotordynamic systems in backward whirl. This motion is detected downhole by the optidrill services sub and i displayed in real time with a recommended e.
402 1185 423 160 6 1308 1056 1536 627 1323 1089 155 1455 243 599 558 338 888 190 1051 984 1392 166 430 1518 1436 227 691 220 1240 1174 169 1427 1283 189 942