An Analysis of Automatic Closed-Loop Control of Rotary Drive Engines

With this automatic control system for use on rigs equipped with a mechanically driven rotary table, it is possible to eliminate rotary speed variation caused by torque in the drill pipe. When closed-loop control is used, low-frequency variations in rotary speed can be completely eliminated, and high-frequency variations can be significantly damped, depending upon the power available. Introduction In applying technology to a drilling operation, rotary speed is of prime importance. For example, the d exponent, formation drillability, roller-bit-bearing and tooth wear, as well as many other drilling relationships are functions of rotary speed. If rotary speed is to be used in any equations related to these, it must be measurable and fairly constant over the time interval of interest. The conventional method of controlling rotary speed on a rig with an independent and mechanically driven rotary table is to use a pneumatic regulator at the drawworks. The regulator pneumatic regulator at the drawworks. The regulator supplies air pressure to a diaphragm, which mechanically positions the engine throttle. This method does not positions the engine throttle. This method does not provide a constant rotary speed. Variations in rotary provide a constant rotary speed. Variations in rotary torque present a constantly changing load to the engine. Consequently, if the throttle is held constant, the angular speed of the rotary table will vary considerably. This effect is illustrated in Fig. 1 which is an actual recording of torque and rotary speed on a rig where the rotary speed was controlled in the manner described above. Note that the average value of rotary speed varied inversely with torque until the driller finally changed the throttle setting to bring the rotary speed back to its initial value. To keep rotary speed constant, the throttle would have to be continuously repositioned to compensate for the load changes. An automatic closed-loop control system can perform this operation. Such a control system has been designed and successfully used on several rigs to control rotary speed remotely. Our purpose is to describe that closed-loop control system and the results of simulation and field testing. Basic Control Theory A closed-loop control system is one that controls a variable by measuring it, comparing it with a desired value and correcting it if it is not equal to the desired value. It follows then that the system must perform two equally important functions: measurement and control. A simple illustration of this would be a man controlling the temperature of an oven by looking at a thermometer, noting that it reads lower than the desired temperature. and throwing a switch that causes an increase in heat flow to the oven. In the system to be discussed here the control is automatic. There are many theories on how to study the performance of closed-loop control systems. The most performance of closed-loop control systems. The most common method, and the one that will be discussed here, uses simplified block diagrams and mathematical models. Terms that will be used throughout the paper are defined here: Input A signal in engineering units, going into the control loop or any of its components. Output A signal in engineering units, coming outof the control loop or any of its components. JPT p. 1305

It has been established that rate of penetration (ROP) is directly related to rotational speed (RPM) of the drill bit in most formations. The Wembley area of northwest Alberta shows a proportionate increase in drilling rate with increases in rotary speed. Pan Canadian Petroleum Ltd. (PCP) optimized bit RPM by supplementing the rig's rotary capability with downhole motors. This paper will summarize the results of using downhole motors to Increase penetration rates in the Wembley field and will provide the drilling plan which PanCanadian uses to optimize vertical drilling with downhole motors. Introduction The relationship for soft and medium soft formations, between rate of penetration and rotational speed has been established as(1): (1) R = KWN a where: R = Rate of penetration K = Lithology factor N = Rotary speed W = Weight on bit a = exponent (equal to 1 for Wembley) For Wembley area this equation may be reduced to: (2) R = constant ( N ) Although the constant includes the bit weight, which is a variable, by drill off tests and manufacturer's recommendations bit weight has been optimized at a relatively constant value between 18 000 and 20 000 daN. Equation (2) suggests the rate of penetration can be enhanced through rotary speed increases. Factors which place an upper limit on rotary speed include:Drill string limitations.Drilling rig limitations on rotary speed.Drill bit limitations.Mechanical hole erosion.Casing wear. Drill string limitations include resonant vibration, joint strength, wear due to erosion and cyclic bending fatigue. Contractors limit rotary speed to 150 RPM or less and will not warrant the operational integrity of the string at higher rotary speeds. An excellent reference paper has been prepared by D. Dareing of Maurer Engineering Inc. (Ref. SPE 11228). Therefore most conventional drilling rigs are limited to rotary speeds of 150 RPM. Chain drive rotary tables are in common use and are usually coupled from the drawworks power take-off directly to the rotary drive pinion. Due to substructure space limitations it is not often possible to include a transmission on the rotary table. Chain sprockets also tend to be fixed by rotary torque requirements and chain speed limits. Torque tubes and electric drive rotaries have added flexibility to available RPM but these systems are not always available. Retrofit on existing rigs cannot be economically justified unless a long-term rig commitment is possible. Drill bit manufacturer's suggest RPM limits for their products but recent developments in premium sealed bearings have allowed greater flexibility. Also, insert bits have been improved in the bonding of carbide teeth to the cone matrix, allowing higher rotary speeds. Casing wear is a concern to all operators and, in some cases, optimum drilling performance has been sacrificed to limit wear. Non-rotating stabilizers have been used successfully but, again, stabilizer wear increases substantially when the drill string is rotated above 100 RPM.

A large number of permanent magnet synchronous motors (PMSMs) are used to drive coal conveyer belts in coal enterprises. Sensorless energy conservation control has important economic value for these enterprises. The key problem of sensorless energy conservation control for PMSMs is how to decompose the stator current through estimating the rotor position and speed accurately. Then a double closed loop control for stator current and speed is formed to make the stator current drive the motor as an entire torque current. In this paper, the proposed startup estimation algorithm can utilize the current model of PMSM as reference model to estimate the rotor speed and position in the startup stages. It is not dependent on the back electromotive force (EMF) which is used by the general estimation algorithm. However, the resistance will change with the temperature shift of stator windings, and these changes will cause the reference current model to be inaccurate and influence the rotor speed and position estimation precision. Thus, startup estimation algorithm switches to the proposed operation estimation algorithm which is based on the robust sliding mode theory and is not dependent on the motor parameters. The advantages of startup estimation algorithm and operation estimation algorithm are combined to form a hybrid observer. This hybrid observer realizes the accurate estimation of the rotor speed and position from start-up to operation. The stator current is precisely decomposed. The excitation current is controlled to 0. Meanwhile, the double closed-loop control of current and speed is achieved. The stator current is as entire torque current to drive motor. The closed-loop control, which is based on the proposed rotor position and speed estimation algorithm, achieve the most efficient conversion of electrical energy.

A sensorless anti-windup speed control approach to axial gap bearingless motors with nonlinear lumped mismatched disturbance observers

Currently available techniques for optimizing weight-on-bit and rotary speed are somewhat limited in scope. Theydetermine optimum policy in. the light of a part of the drilling process, rather than in the light of the entire drilling process. The object of this two-part investigation was to develop techniques which are less limited in scope, and to demonstrate the importance of optimizing the drilling process as a whole, further than optimizing separate parts of that process. Three optimization methods have been developed. The methods differ primarily in the scope over which the optimization takes place. That is, the first method seeks to minimize the cost per foot drilled during a given bit run, the second method minimizes the cost of a selected interval and the third method minimizes the cost over a series of intervals. The methods are listed in order of increasing scope and complexity, the first two being examined in Part I, and the third treated in Part II. Results and conclusions regarding all three methods are to be found in Part II. It was found that each of the methods gave a worthwhile cost saving, and that the saving increased as the scope and complexity of the method increased. The need for better data also increases as the scope and complexity of the method increases. Hence, the method used should be chosen according to the amount and quality of the data available. Introduction Although many investigations have taken place over the years, in 1958 Speer(1) was the first to propose a comprehensive method for determining optimum drilling techniques. He demonstrated empirically the interelationships of penetration rate, weight-an-bit, rotary speed, hydraulic horsepower and formation drillability. Speer combined these five relationships into a chart for determining optimum drilling techniques from a minimum of field test data. Moore(2) was the first to suggest an analytical method for finding the optimum weight and speed. His equations for drilling rate and bearing wear were such that it was possible to calculate directly the optimum weight corresponding to a given rotary speed. The optimization technique suggested by Moore has been used extensively by other investigators on the more sophisticated drilling equations developed later. A graphical approach, together with more realistic drilling equations, was used by Graham and Muench(2) to calculate the optimum combinations of weight and speed to minimize drilling cost per foot. The cost per foot was computed versus weight for various depths at constant rotary speed. This procedure was repeated for various speeds until the optimum rotary speed was found for each depth. The next, and probably most significant, contribution to optimal drilling came in 1960 when Galle and Woods(4) presented a technique designed to minimize drilling costs by varying bit weight and rotary speed throughout a hit run. The authors established a set of empirical equations for drilling rate, dulling rate and bearing wear rate as functions of the drilling parameters. The calculus of variations was used to find the manner in which weight and rotary speed should be varied to minimize drilling cost.

An on-site computer system to control bit weight and rotary speed has been developed and successfully installed on a South Louisiana well. Early field tests indicate that the system could be invaluable in reducing drilling costs. Introduction Previous laboratory and field experimentation has Previous laboratory and field experimentation has demonstrated the effect of several variables on drilling rate. These results have been incorporated into optimization theories for the purpose of reducing drilling cost. Minimum-cost drilling theories rely on a combination of historical data and empirical prediction techniques for selecting optimum bit weight and rotary speed. Past solutions have required extensive use of computing equipment because of both the complexity of the mathematical formulations and the large number of parameters involved. Field attempts to apply these computed results have frequently failed because of the uncertainty of input data requirements. Humble has developed an on-site computer system to control bit weight and rotary speed and thereby implement the concepts of minimum-cost drilling. This system can perform short interval drilling rate tests for formation evaluation, use the results of these tests as input information to solve minimum-cost drilling formulas, and control bit weight and rotary speed in accordance with these computed solutions. The purpose of this paper is to describe the computer control system and present results of initial field testing. Theoretical Considerations Minimum-cost drilling (MCD) requires a quantitative evaluation of the variables involved. Several forms of a basic mathematical model have been suggested. The relationships reported here form the basis for the solution programmed in this work. Four equations are used, expressing drilling rate, bit bearing wear, bit tooth wear, and cost. A solution for minimum-cost drilling assuming constant bit weight and rotary speed over the entire bit life has been programmed for use in computing MCD schedules. This solution is subject to certain limiting assumptions such as those discussed by Graham et al.: Drilling cost is the summation of bit cost, rotating cost, connection cost and hoisting cost. Diamond bits are excluded. Bit life is limited by either bearing failure or tooth wear, or by a combination of operational factors that make it cheaper to pull an incompletely consumed bit. Circulating hydraulics are adequate and do not limit drilling rate. Bit weight considerations exclude hole deviation. Drilling rate is a function of only bit weight, rotary speed, and degree of tooth dullness; that is, the effects of pressure, lithology, fluid property, hydraulics and drill string dynamics are ignored. JPT P. 483

This critical collision damage force of millet and sweet buckwheat grain and the shelling force of shelled granular materials are important basic data for research of threshing and shelling technology and equipment. In order to master the linear velocity and collision force of grain with different moisture content when collision damage occurs, a centrifugal collision test device is designed. Based on the dynamic and kinematic analysis of grain in the centrifugal rotary table, the collision force between grain and steel plate was measured by PVDF piezoelectric pressure sensor and data acquisition system. The results showed that: under the same moisture content, the higher the rotational speed, the higher the grain crushing rate; at the same rotational speed, with the increase of moisture content, the crushing rate first decreased and then increased. When the moisture content of Jingu-21 and Yuqiao-4 is 19.7% and 17.8%, respectively, the grain crushing rate was the lowest. In terms of the anti-collision ability of grain, the optimum moisture content of threshing is between 19.7% and 21% for millet. For sweet buckwheat, the optimum moisture content of threshing is 17.8% ~19%, while the optimum moisture content of shelling by centrifugal sheller is about 11%. The faster the rotational speed of centrifugal rotary table is, the greater the linear speed of grain is, and the greater the collision force is. When the linear velocity of grain was 8.32 m/s and 11.30 m/s respectively, the millet grain moisture content was 11.1% and 20.9% respectively, damage began to appear, and the corresponding collision force was about 5.51 N and 10.6 N, respectively. When the linear velocity of grain was 8.32 m/s and 11.30m/s respectively, and the moisture content was 11.1% and 22.8% of the sweet buckwheat grain respectively, damage began to appear, the corresponding collision force was about 8.92 N and 12.79 N, respectively. When the rotating speed of rotary table was 910 r/min, the linear speed of grain was 27.05 m/s, the crushing rate of millet and sweet buckwheat grain in harvest period were 56.30% and 63.76%, respectively, and the crushing rate of millet and buckwheat grain with 11.1% moisture content were 86.27% and 89.4%, respectively. The research results can provide theoretical basis for design and optimization of millet and sweet buckwheat combine harvester, threshing device and shelling device.

The rotary table vibration of the spin coater directly impacts the quality of the spin coating film. In view of the unclear vibration characteristics of the rotary table during operation, the rotary table vibration characteristics and its influencing factors considering the spindle system are studied. Based on the elastic contact theory and multi-body system theory, the rotary table vibration characteristics of the rotary table when the parts of the rotary table are flexible are analyzed by establishing the rotary table multi-rigid body and flexible coupling dynamics models, respectively. By comparing with the rotary table vibration measurement results, it is found that the flexible treatment of the load tray is more consistent with the actual vibration characteristics. The study further analyzes the effects of the unbalance of the rotary table, the rotary table speed, the coaxiality of the load tray and the spindle, and the perpendicularity of the load tray and the spindle on the vibration characteristics. The results show that the influence of the spin coater rotary table under the actual working conditions is from the highest to the lowest degree of influence on the unbalance of the load tray, the coaxiality of the load tray and the spindle, the perpendicularity of load tray and the spindle, and the rotational speed of the rotary table. This study provides a reliable theoretical and experimental basis for the vibration characteristics analysis and structural design of the spin coater rotary table.

The investigation of passive cyclic pitch variation using an automatic yaw control system made use of the test equipment and of the results of an earlier study. The atmospheric test equipment consisted of a horizontal axis wind turbine with vane controlled upwind two-bladed rotor of 7.6 m (25 ft) diameter having passive cyclic pitch variation. An automatically triggered electric furl actuator prevented over-speeds and over-torques by furling the rotor which means yawing the rotor out of the winds. The atmospheric test equipment was modified to accept two alternative fully automatic yaw or furl control systems. The first system was of the active type and included a hydraulic single acting constant speed governor as it is used for aircraft propeller controls. Upon reaching the rotor speed limit, the governor delivered pressurized oil to a hydraulic furl actuator which then overcame the unfurling spring force and furled the rotor. When the rotor speed fell below the set value, the governor admitted oil flow from the hydraulic actuator into the oil reservoir and the rotor was unfurled by the spring. The second automatic control system was of a purely mechanical passive type. The rotor thrust, which was laterally off-set from the yaw axis, in combination with a yawing component of the rotor torque due to uptilt of the rotor axis overcame at rated power the unfurling spring and furled the rotor. The analytically predicted and experimentally substantiated negative rotor yaw damping would cause excessive furling rates unless alleviated by a furl damper. The tests were supported by a specially developed dynamic yawing analysis. Both analysis and tests indicated that the two-bladed passive cyclic pitch wind rotor can be effectively torque or speed limited by rotor yaw control systems which are less costly and more reliable than the conventional blade feathering control systems.

ABSTRACTThe coaxial compound helicopter with lift-offset rotors has been proposed as a concept for future high-performance rotorcraft. This helicopter usually utilizes a variable-speed rotor system to improve the high-speed performance and the cruise efficiency. A flight dynamics model of this helicopter associated with rotor speed governor/engine model is used in this article to investigate the effect of the rotor speed change and to study the variable rotor speed strategy. Firstly, the power-required results at various rotor rotational speeds are calculated. This comparison indicates that choice of rotor speed can reduce the power consumption, and the rotor speed has to be reduced in high-speed flight due to the compressibility effects at the blade tip region. Furthermore, the rotor speed strategy in trim is obtained by optimizing the power required. It is demonstrated that the variable rotor speed successfully improves the performance across the flight range, but especially in the mid-speed range, where the rotor speed strategy can reduce the overall power consumption by around 15%. To investigate the impact of the rotor speed strategy on the flight dynamics properties, the trim characteristics, the bandwidth and phase delay, and eigenvalues are investigated. It is shown that the reduction of the rotor speed alters the flight dynamics characteristics as it affects the stability, damping, and control power provided by the coaxial rotor. However, the handling qualities requirements are still satisfied with different rotor speed strategies. Finally, a rotor speed strategy associated with the collective pitch is designed for maneuvering flight considering the normal load factor. Inverse simulation is used to investigate this strategy on maneuverability in the Push-up & Pull-over Mission-Task-Element (MTE). It is shown that the helicopter can achieve Level 1 ratings with this rotor speed strategy. In addition, the rotor speed strategy could further reduce the power consumption and pilot workload during the maneuver.

A series of tests was conducted to provide data for an economic evaluation of percussion drilling in geothermal reservoirs. Penetration rate, operation on aqueous foam, and high temperature vulnerabilities of downhole percussion tools are described.

Numerical investigation of the vorticity transportation and energy dissipation in a variable speed pump-turbine

There are various secondary flow types in turbodrill’s blade cascades, and all kinds of secondary flow have a significant effect on flow loss. In this paper, the stator cascade of φ160 mm turbodrill is taken as the research object, and the CFD method is used to analyze the secondary flow and its evolution. The origin and evolution mechanism of secondary flow is explained from the flow mechanism. The results show that when the working rotary speed is lower than the design rotary speed, the secondary flows are composed of suction surface separation vortex, horseshoe vortex, and passage vortex coexisting. The intensity of secondary flows increases with the decrease of rotary speed. When the working rotary speed is near the design rotary speed, the secondary flows include horseshoe vortex, passage vortex, and corner vortex. When the working rotary speed is higher than the design rotary speed, the secondary flows consist of pressure surface separation vortex and suction surface trailing edge separation vortex. Regardless of rotary speed, secondary flow intensity in the shroud region is greater than the hub region, which has a greater influence on the mainstream. In addition, compared with high rotary speeds, secondary flow intensity is greater at low rotary speeds, resulting in greater flow losses.

Current Rotorcraft Developments like under the Future Vertical Lift Program in the USA (e.g. Bell V-280, see figure 1) respectively RACER (Airbus Helicopters, see figure 2) and NextGENCivil Tiltrotor (Leonardo, see figure 3) in Europe deal with High-Speed Rotorcraft or Tiltrotor-/Tiltwing Aircraft. They can expand and optimize their performance by using a variable rotor speed either to adopt the rotor speed to high forward speed or to meet the different requirements of a rotor in Hover and Aircraft Mode of a Tiltrotor-/Tiltwing Aircraft. As the required speed range can not be covered by the turbine, TU Munich (Germany), TU Wien (Vienna, Austria), ADT - Advanced Drivetrain Technologies (Austria) and Zoerkler Gears (Austria) work in the transnational project "VARI-SPEED II" on a rotor system that can change the rotor speed via change of the ratio of the transmission (variable rotor speed with constant turbine speed). The project is based on the results of "VARI-SPEED" and the direct follow-up project. VARI-SPEED showed that a rotor speed variation performed by a transmission system is possible. The efficiency and the flight envelope of the rotorcraft can be improved by this technology. Furthermore, a method for rotor blade design in a RPM range was invented. VARI-SPEED II now has built up a model of the complete dynamic system from engine to rotor of a helicopter with a variable speed rotor. This model is used for dynamic simulations of the components and the whole system. A scaled model of the module that changes the speed will be developed and pilot studies in a simulator are planned to find out the characteristics of such a system. Aim of the project is to reach TRL 3 as basis for further development of the technology with interested OEM's. This paper deals with the dynamic behaviour of the components and the whole drive train. The Bell V-280 is in the flight testing phase, RACER has recently conducted its maiden sortie and for the NextGENCtr the first flight is announced for the first half of 2024. All mentioned aircraft use transmission systems with a fixed gearbox ratio; this is feasible as a new technology like Vari-Speed normally is not added to completely new rotorcraft. However as the OEM's rate Vari-Speed positive, variable rotor speed can be integrated in a later development stage of the rotorcraft and thus development timelines of the rotorcrafts and Vari-Speed match quite well.

Current helicopter flight and propulsion controls are typically designed with the assumption that rotor speed will be held to a constant setpoint. A new flight and propulsion control system using a continuously variable rotor speed command is proposed to improve the maneuverability and agility of helicopter systems. In this new approach, the flight control system generates an optimal variable rotor speed command in addition to conventional control commands in a framework of integrated flight/propulsion control. The benefits (i.e. improved maneuverability and agility) of varying rotor speed during transient maneuvers are demonstrated using a bob-up maneuver as an example. In particular, two types of benefits are identified in different maneuver conditions. One comes from a thrust augmentation, while the other comes from an exchange of rotational and translational energy. In the example, a simple linear dynamic hover model is used with an optimal control design method to generate the optimal rotor speed command.