Bucket Tip Research Articles

Analysis of Brush Seal Interaction with Steam Turbine Rotor-Shafts

High-speed turbines are a major source for power production. They utilize high pressure and temperature fluid flow. Sealing of these machines to decrease the flow losses has been a major engineering challenge since the inception of steam turbines. From an engineering viewpoint, seals are used to introduce friction in the fluid flow path. This reduces the flow leakage. Improved seal performance offers substantial opportunities for turbine performance. Reduced leakages in steam turbines can lead to greater efficiency and power output. They can also allow tighter control of turbine secondary flows. However, sealing these machines is a major challenge. There are several seal locations on a steam turbine that have significant performance derivatives. These include the interstage shaft packing, the end packing, and the bucket tip seals. Brush seals are ideal for these locations because they can reduce the flow losses. This study analysed the efficiency of the steam turbine by using ANSYS APDL. It assessed the leakage performance of the brush seal for different cases and geometries. It also used porous medium modelling of the bristle pack to provide insight for designers. The outputs of interest were the rotor-shaft temperature and the efficiency of the entire turbine with the brush seal.

Microscopic insights into suction bucket installation in sand: Coupled coarse-grained CFD-DEM simulations

Suction bucket foundations are being used for a wide variety of offshore foundations. However, accurate modeling of its installation remains challenging due to the complexity of soil transportation, in which the soil is typically treated as a continuum and its discrete behavior is neglected. In this paper, the bucket foundation installation in the sand under different installation methods (i.e., jacked and suction-assisted installation) is investigated from a microscopic perspective (i.e., particle scale) based on the three-dimensional coupled computational fluid dynamics (CFD) and coarse-grained discrete element method (CGDEM). It is found that the CFD-CGDEM method can successfully simulate the bucket installation process. Suction-assisted installation results in a significant reduction in the inner skirt friction resistance and end resistance, while the outer skirt friction resistance shows only a minor decrease. During suction-assisted installation, soil loosening inside the bucket contributes more significantly to the soil plug formation compared to the inflow of external soil. Compared to jacked installation, the seepage induces a significant reduction in the effective stress of soil within the interior and below the bucket tip, while it increases the effective stress outside slightly under suction-assisted installation. The work provides an alternative research approach for the suction bucket installation.

Test and Analysis of Loading Resistance of Loader

In this paper, the resistance of the bucket and the change of the resistance during the loading process of the loader are studied. In the automatic shovel loading test, the bucket tip trajectory during shovel loading is planned reasonably by matching the shovel loading method (moving arm cylinder displacement and steering cylinder displacement with the linkage of the vehicle). The gravel material in the shovel loading test is analyzed. The shovel-loading process can be divided into the bucket insertion and shovel digging stages, and the resistance in the two stages was analyzed separately in terms of trajectory. It is obtained that the horizontal insertion resistance is proportional to the insertion depth of the shovel, the change of the resistance, the change of the resistance direction, and the trajectory of the shovel during the shovel excavation stage.

Operational Modal Analyses of Brush Seals and Seating Load Simulations

Abstract Brush seals are one of the most effective sealing technologies in turbomachinery since they enable contact-type operation for close clearance control. Brush seal bristles must interact under turbine conditions, and the minimum pressure load to initiate proper contact between fibers is called seating load. Seating load evaluation is essential for the durability and stability assessment of bristles since unseated fibers may flutter and cause seal failure. Even with proper seating, brush seal critical modes may still be excited by flow-induced fluctuations or bucket tip excitations. In this study, a finite element-based methodology was developed to determine the seating load and identify the critical modes of brush seals. Under pressure load, brush seal nonlinear contact simulations are followed by frequency-based analysis to determine bristle and seal pack critical modes. To determine the seating load of the brush seal, the change in modal response is examined. In this paper, the modeling methodology, parameter correction procedures, geometric inspection of test seals, correlation of transient analyses with dynamic tip force measurements, operational modes of brush seals and seating load evaluation methods are detailed.

Dynamic impedances and load carrying mechanism for skirted foundations

Dynamic impedances of foundations include dynamic stiffness and damping which have important effect on the internal forces in the structure. In some cases, such as offshore wind turbines, the influence of the foundation impedances on the system's natural frequency and overall damping could potentially have a significant effect on the fatigue life of the structure. The vertical, horizontal and rocking impedances of a skirted foundation (also termed bucket foundation in offshore wind industry) embedded in a fully saturated poroelastic seabed are addressed in this paper. The vertical impedance is most relevant for jacket foundations supported on three or four bucket foundations, while horizontal and rocking impedances are applicable for mono-bucket foundations. The dynamic vibration problems are solved semi-analytically with the help of dual integral equations and Green's functions. Numerical results for dynamic impedances are obtained; damping ratio are also obtained to show the importance of radiation damping for bucket foundations, even at very small excitation frequencies. The influence of length-to-radius ratio, Poisson's ratio, permeability of soil, excitation frequency and thickness-to-radius ratio on the impedances are also studied. Besides, the dynamic load sharing among the top plate, bucket shaft and bucket tip is obtained for vertical load, horizontal load and moment to shed light on the carrying mechanism of bucket foundation at dynamic working loads. It is found that for a rigid bucket foundation, even when the length-to-radius ratio is small (e.g. l/a = 1.0), most of the loads are carried by the shaft, while the top plate and tip of the bucket take only a small portion of the loads. The results of this study will be helpful for understanding the load-carrying mechanism of offshore bucket foundations for normal operation conditions.

Development of Integrative Methodologies for Effective Excavation Progress Monitoring.

Excavation is one of the primary projects in the construction industry. Introducing various technologies for full automation of the excavation can be a solution to improve sensing and productivity that are the ongoing issues in this area. This paper covers three aspects of effective excavation progress monitoring that include excavation volume estimation, occlusion area detection, and 5D mapping. The excavation volume estimation component enables estimating the bucket volume and ground excavation volume. To achieve mapping of the hidden or occluded ground areas, integration of proprioceptive and exteroceptive sensing data was adopted. Finally, we proposed the idea of 5D mapping that provides the info of the excavated ground in terms of geometric space and material type/properties using a 3D ground map with LiDAR intensity and a ground resistive index. Through experimental validations with a mini excavator, the accuracy of the two different volume estimation methods was compared. Finally, a reconstructed map for occlusion areas and a 5D map were created using the bucket tip’s trajectory and multiple sensory data with convolutional neural network techniques, respectively. The created 5D map would allow for the provision of extended ground information beyond a normal 3D ground map, which is indispensable to progress monitoring and control of autonomous excavation.

Oil Brush Seals in Turbomachinery: Flow Analyses and Closed-Form Solutions

Abstract Brush seals are one of the most important dynamic seals used in oil and oil mist applications in industrial turbines and aviation. Flexible bristle structure is the main structural superiority of brush seals, which enables precise clearance control and high performance in compensating rotor transients. The viscous medium between the high-speed rotor surface and brush seal bristles generates a hydrodynamic lifting force that determines seal clearance and leakage rate in oil sealing applications. Shear heating at moderate and high rotor surface speeds results in an increase in temperature and stabilization of lifting force, which is known as high-speed lift stabilization. Strong temperature–viscosity dependency of lube oils possesses the need for a detailed analysis and understanding of the effect of shear heat on hydrodynamic lift of brush seals in oil applications. To provide a better understanding about the critical balance of hydrodynamic lift force with rotor speed, temperature, and pressure, this work presents an analytical study to investigate pressure profile and shear heat temperature rise in liquid sealing medium within the hydrodynamic lift clearance. A closed-form solution to pressure and temperature distribution in axial and radial directions has been obtained by solving continuity, Navier–Stokes, and thermal energy equations for brush seals. The thermal and pressure functions are evaluated for linear and nonlinear pressure drop approaches, and the results are compared with each other. Deviation in nonlinear and linear pressure, resulting temperature level differences, and effect of rotor speed are detailed within the content of this study. The provided closed-form functions for pressure and temperature profiles are useful for designers since these can be utilized for turbine operation conditions. Dynamic test rig design for high-speed leakage performance measurement of turbomachinery seals is detailed, where the test rig can also be adopted for stiffness, frictional heat, power loss, torque loss, and bucket tip stability testing in oil and air environment. The test setup can also be used for testing dynamic seals other than brush seals.

Analysis of the Position Recognition of the Bucket Tip According to the Motion Measurement Method of Excavator Boom, Stick and Bucket.

On modern construction sites, guidance and automation systems are increasingly applied to excavators. Recently, studies have been actively conducted to compare the estimation results of the bucket tip with the motion measurement method of the boom, stick, and bucket and the sensor selection. This study selected the method of measuring the cylinder length of boom, stick, and bucket, and the method of directly measuring the boom, arm, and bucket, which are commonly used in guidance and automation systems. A low-cost sensor that can be attached and detached to the excavator in modular form was selected to apply the above methods to commercial excavator. After the sensor selection, hardware and excavator simulation models for sensor measurements were constructed. Finally, the trajectory of the bucket tip was compared and analyzed through graphs and simulation results when the boom, stick, and bucket were independently rotated one by one, or together. The results gives a guideline on what kinds of sensors would be better in machine guidance or controlling an excavator according to given external environments.

Flexible virtual fixtures for human-excavator cooperative system

The coordination of human operation and automation of robotic excavators is a key problem in human-excavator interaction. To integrate the active decision of the operator and the accurate control of the machine system, flexible virtual fixtures are proposed to control trajectory of the robotic excavator. The flexible virtual fixtures rely on the current position at the bucket tip. The input signal of the restricted motion direction is weakened by introducing the flexibility coefficient kτ, and choosing kτ low imposes the additional constraint that the robotic excavator is stiffer in the restricted motion direction. In this way, a human-excavator cooperative system is built. Then, different tasks were designed to validate the performances of the proposed flexible virtual fixtures, and different operation ways were compared in terms of tracking accuracy, safety and operating time. The results have demonstrated that the flexible virtual fixtures in the trajectory tracking process not only guarantee the tracking precision, but also ensure a good obstacle avoidance ability. Also, the tele-operators can save a lot of time during the tele-operation process. In the future work, we will introduce the environmental identification results to assist the operator to choose a more reasonable kτ value.

Task space-based dynamic trajectory planning for digging process of a hydraulic excavator with the integration of soil–bucket interaction

In this paper, a task space-based methodology for dynamic trajectory planning for digging process of a hydraulic excavator is presented, with the integration of soil–bucket interaction. An extended soil–bucket interaction model, which adds the resistive moment compared to the previous models, is provided in this research. This improved model is validated by comparing with the measurement data taken from field experiments before integrating it into a dynamic model of an excavator. Further, Newton–Euler method is used for the derivation of the dynamics of each link of the excavator to determine the joint forces, which can cause the machine damage. The position and orientation trajectories of the bucket in the task space are parameterized by using the B-splines, so as to achieve the task-oriented operations and ensure the operation flexibility. The joint space motion characteristics are obtained by solving the inverse kinematics of the working mechanism of an excavator. Moreover, to avoid the operation uncertainty for a given bucket tip position trajectory and reduce the computational effort, the self-motion parameters are introduced when solving the inverse kinematics of the redundant working mechanism. All these self-motion parameters are taken as a set of design variables in the trajectory optimization problem. Also, the limits on the hydraulic driving forces, joint angles, angular velocities and accelerations, as well as bucket capacity are considered as the optimization constraints for the digging process. Finally, optimization examples of two typical digging categories (i.e. level digging work and slope digging work) are given to demonstrate and verify the capabilities of the new methodology proposed in this research. The results show that the proposed method can effectively generate the optimal trajectories satisfying the following criteria: time efficiency, energy efficiency, and least machine damage. This work lays a solid foundation for motion planning and autonomous control of an excavator.

Investigation of the load-bearing capacity of suction caissons used for offshore wind turbines

This paper presents the results of three-dimensional finite element analyses of the suction bucket foundation used for offshore wind turbines. The behavior of the bucket and the response of soil supporting the bucket in dense and medium dense sandy soils subjected to static horizontal load are investigated. Field tests results and a centrifuge model test are used to validate the numerical model. Dimensionless horizontal load-displacement and overturning moment-rotation relationships are derived utilizing the Power law and Buckingham’s theorem. The results show good agreement between the numerical analysis results and the straight lines obtained from the Power law until a specific value of horizontal load and overturning moment. Regarding stress behavior of soil supporting the bucket, due to soil densification and bucket movement, maximum stresses are seen near the bucket tip at the right inside of the bucket. The major part of the applied load is transferred by the bucket skirt. Numerical analysis modeling results show that the bucket rotation and displacement are highly dependent on the bucket geometry and soil properties in addition to loading conditions. Normalized equations and figures for the ultimate horizontal load and overturning-moment capacities are presented and can be used for the preliminary design of the bucket foundations in sandy soils.

Coupled gas-particulate discharge from a bucket elevator

The vertical conveying of bulk materials is often performed using bucket elevators. Such devices use conveyor belts to drag a series of buckets in a circuit, up, around and then down within an enclosure. They are typically used for upward transport of fine granular materials. The speed at which these buckets travel can displace a large volume of air. Interaction between this air and the bucket contents can modify the discharge dynamics of the granular load. A coupled gas-particulate numerical model is presented using Finite Differences to solve for the gas flow with an Immersed Boundary Method (IBM) to represent the complex bucket and enclosure geometry in the model. The Discrete Element Method (DEM) is used for particulate flow. The combined method is used to investigate the effect of gas flow on particulate behavior, particularly at the time of discharge from the buckets. The bucket elevator design used is based on an existing installation with known operational issues. The presence of gas flow is shown to alter the preferential ejection of particles from the bucket, influence the shape of the trajectory of the ejected particle stream, and reduce the efficiency of particles exiting the elevator by 10–14%. These effects are also shown to be strongly size dependent with finer particles being much more susceptible to drag forces from the air flow. The retention of material inside the machine was found to consist of roughly 50% of material centrifugally ejected from near the bucket tip and roughly 70% of material located closer to the conveyor belt side of the bucket that spills off the splitter during the final stage of emptying and falls back down to the boot.

Digging Soil Experiments for Micro Hydraulic Excavators based on Model Predictive Tracking Control

Recently, the increase of burden to operators and lack of skilled operators are the issue in the work of the hydraulic excavator. These problems are expected to be improved by autonomous control. In this paper, we present experimental results of hydraulic excavators using model predictive control (MPC) which incorporates servo mechanism. MPC optimizes digging operations by the optimal control input which is calculated by predicting the future states and satisfying the constraints. However, it is difficult for MPC to cope with the reaction force from soil when a hydraulic excavator performs excavation. Servo mechanism suppresses the influence of the constant disturbance using the error integration. However, the bucket tip deviates from a specified shape by the sudden change of the disturbance. We can expect that the tracking performance is improved by combining MPC and servo mechanism. Path-tracking controls of the bucket tip are performed using the optimal control input. We apply the proposed method to the Komatsu- made micro hydraulic excavator PC01 by experiments. We show the effectiveness of the proposed method through the experiment of digging soil by comparing servo mechanism and pure MPC with the proposed method.

Research on Superimposed Terrain Model for Teleoperation Work Efficiency

[abstFig src='/00280002/08.jpg' width=""300"" text='Superimposed terrain model in operator's view image' ]In recent years, unmanned construction based on the teleoperation of construction equipment has increasingly been used in disaster sites or mines. However, operations based on teleoperation are based on 2D images, in which the lack of perspective results in considerably lower efficiency when compared with on-board operations. Previous studies employed multi-viewpoint images or binocular stereo, which resulted in problems, such as lower efficiency, caused by the operator's need to evaluate distances by shifting his or her line of sight, or eye fatigue due to binocular stereo. Thus, the present study aims to improve the work efficiency of teleoperation by superimposing a 3D model of the terrain on the on-board operator's view image. The surrounding terrain is measured by a depth image sensor and represented as a digital terrain model, which is generated and updated in real time. The terrain model is transformed into the on-board operator's view, on which an artificial shadow of the bucket tip and an evenly spaced grid projected to the ground surface are superimposed. This allows the operator to visually evaluate the bucket tip position from the artificial shadow and the distance between the excavation point and bucket tip from the terrain grid. An experiment was conducted investigating the positioning of the bucket tip by teleoperation using a miniature excavator and the terrain model superimposed display. The results showed that the standard deviations of the positioning errors measured with the superimposed display were lower by 30% or more than those obtained without the superimposed display, while they were approximately equal to those acquired using binocular stereo. We thus demonstrated the effectiveness of the superimposed display in improving work efficiency in teleoperation.

굴삭기의 버킷 끝단 위치인식에 관한 연구

The accurate calculation of bucket tip position has a large influence on showing the motion of an excavator on the display device of the excavator and controlling the excavator automatically. It is generally known that Inertial Measurement Unit (IMU) sensors are more accurate than accelerometer-based sensors while the boom, arm or bucket moves because additional forces beyond gravity add additional acceleration to the sensors. To prove the accuracy difference between the two types of sensors, a position recognition system using an accelerometer-based sensor and an IMU sensor is implemented on the excavator. The experimental results show that the system using the IMU sensor significantly reduces the position recognition error while bucket moves and additional force beyond gravity exists.

B209 パワーショベルによるモデル予測軌道追従制御(OS3 フルードパワーの基礎と応用1)

In this paper, we propose a trajectory tracking method for hydraulic excavators considering constraint of attitude angle of the bucket by model predictive control. The digging operation becomes possible by tracking the reference trajectory keeping the constraint for the attitude angle of the bucket. Target input is decided by the inverse kinematics for the finished shape. Then, we perform the trajectory tracking control on the bucket tip by MPC. The efficacy of the proposed method is shown through comparing with a servo mechanism in simulations.

Contour control for leveling work with robotic excavator

This paper presents electro-hydraulic servo systems of a robotic excavator with a contour control algorithm. It is very important to precisely move the bucket tip of the excavator to a desired trajectory. There have been many studies to accurately control the bucket dealing with the non-linearity in the hydraulic boom, arm, and bucket cylinders. Beginning with these conventional methods, a new method that focuses on keeping contours rather than just following position commands is presented. In the leveling work, for example, it is more important to maintain linear contour than chasing a position goal. The contour control shares the control effort to make the bucket stay on the path, while slightly sacrificing the position tracking accuracy. After the kinematics of the excavator system were analyzed, the contour control algorithm was developed. The algorithm was applied to leveling work with a real excavator. The experiments showed better performance than using position control alone.

Markov modulated Poisson process models incorporating covariates for rainfall intensity

Time series of rainfall bucket tip times at the Beaufort Park station, Bracknell, in the UK are modelled by a class of Markov modulated Poisson processes (MMPP) which may be thought of as a generalization of the Poisson process. Our main focus in this paper is to investigate the effects of including covariate information into the MMPP model framework on statistical properties. In particular, we look at three types of time-varying covariates namely temperature, sea level pressure, and relative humidity that are thought to be affecting the rainfall arrival process. Maximum likelihood estimation is used to obtain the parameter estimates, and likelihood ratio tests are employed in model comparison. Simulated data from the fitted model are used to make statistical inferences about the accumulated rainfall in the discrete time interval. Variability of the daily Poisson arrival rates is studied.

Kinematics of mini hydraulic backhoe excavator - part II

An excavator is a typical hydraulic heavy-duty construction machine used in hazardous, worst working conditions, severe weather, and dirty areas where it is very difficult to operate machine by human operator. The excavator operations require coordinated movement of boom, arm and bucket in order to control the bucket tip position to follow a desired trajectory. This can be achieved through the implementation of automatic control system for excavation task and it required understanding of kinematics of backhoe excavator. This paper focuses on the mathematical kinematic modelling of the backhoe excavator attachment to understand relations between the position and orientation of the bucket and spatial positions of joint-links, helpful for improving the operating performance of the backhoe excavation machine. This paper covers the inverse kinematics, differential motions, inverse Jacobian, and static model of backhoe excavator. The kinematic model developed for autonomous excavation of light duty construction work can be applied for heavy duty or all types of backhoe excavators.

Real-Time GPU-Based Visualization of Dynamic Terrain in Excavator Simulator

This paper presents a real-time GPU-based visualization of dynamic terrain in excavator simulator, which is an interactive system for the purpose of training human operators and corresponding researches. Firstly, we establish the kinematic model of excavator, so as to trans-fer the bucket tip's reference trajectories to corresponding, required reference angle sequence for each joint and to control motion sequences of articulated hierarchies. Then, our method use GPU to create the DDHM and digging offset map, with which we can perform the terrain de-formation entirely in the GPU. In order to improve the visual quality, we also present a method of procedural texture for deformation terrain. Finally, the Real-Time Optimally Adapting Meshes (ROAM) algorithm is used to render the dynamic terrain effectively.