Vortex- and Wake-Induced Vibrations of a Circular Cylinder Placed in the Proximity of Two Fixed Cylinders

Purpose This study aims to understand the vibratory response of a circular cylinder placed in proximity to other fixed bodies. Methods A circular cylinder model was placed in a circulating water channel and was supported elastically to vibrate in the water. Another two circular cylinders were fixed upstream of the vibrating cylinder. The temporal displacement variations of the vibrating cylinder were measured and processed by a frequency analysis. Results When the inline spacings were small, two amplitude peaks appeared in the reduced velocity range 3.0–13.0. When the inline spacings were large, the amplitude response showed a single peak. Conclusion For small inline spacings, the first peak was attributed to high-amplitude vibrations forced by Karman vortex streets shed from the upstream cylinders. The second peak arose from interactions of the wakes of the upstream cylinder with the vibrating cylinder. When the inline spacing increased, the vortex-induced vibrations resembled those of an isolated cylinder.

A novel electro-hydraulic servo steering system for Ackermann steering of heavy multi-axle vehicle

Ackermann steering is important for the steering performance of heavy multi-axle vehicle. When Ackermann steering condition is not satisfied, it will lead to abnormal tire wear. Traditional trapezoidal mechanism of heavy multi-axle vehicle is a single degree of freedom (DOF) mechanism, which is difficult to completely realize Ackermann steering. In this paper, a new two DOF electro-hydraulic servo steering system (TDEHSSS) by using a variable length tie rod is proposed for solving the issue. First, a complex nonlinear dynamic model of TDEHSSS is established. This model includes the two DOF mechanical model based on a Lagrange equation, the valve-controlled double steering power cylinders model and the valve-controlled tie rod cylinder model. Then, a simulation model is built through MATLAB/Simulink and the simulation results show that TDEHSSS can realize the proposed requirement. At last, a test bench is founded to verify model. It is indicated that the simulation and experimental curves are consistent, showing that mathematical model is in accordance with the experimental system. This research is valuable for analyzing TDEHSSS, designing advanced controllers, and finally realizing Ackermann steering for heavy multi-axle vehicles.

Intelligent Algorithms-Based CT Image Segmentation in Patients with Cardiovascular Diseases and Realization of Visualization Algorithms

The study focused on the intelligent algorithms-based segmentation of computed tomography (CT) images of patients with cardiovascular diseases (CVD) and the realization of visualization algorithms. The first step was to design a method for precise segmentation under the cylinder model based on the coronary body data of the coarse segmentation, and then the principles of different visualization algorithms were discussed. The results showed that the precise segmentation method can effectively eliminate most of the branches and calcified lesions; curved planar reformation (CPR) and straightened CPR can display the entire blood vessel on one image; and spherical CPR can display the complete coronary artery tree on an image, so that a problem with a certain blood vessel can be quickly found. In conclusion, the precise segmentation of CT images of CVD and visualization algorithm based on the cylinder model have clinical significance in the diagnosis of CVD.

Vertical-axis wind-turbine computations using a 2D hybrid wake actuator-cylinder model

The actuator-cylinder model was implemented in OpenFOAM by virtue of source terms in the Navier–Stokes equations. Since the stand-alone actuator cylinder is not able to properly model the wake of a vertical-axis wind turbine, the steady incompressible flow solver simpleFoam provided by OpenFOAM was used to resolve the entire flow and wakes of the turbines. The source terms are only applied inside a certain region of the computational domain, namely a finite-thickness cylinder which represents the flight path of the blades. One of the major advantages of this approach is its implicitness – that is, the velocities inside the hollow cylinder region feed the stand-alone actuator-cylinder model (AC); this in turn computes the volumetric forces and passes them to the OpenFOAM solver in order to be applied inside the hollow cylinder region. The process is repeated in each iteration of the solver until convergence is achieved. The model was compared against experimental works; wake deficits and power coefficients are used in order to assess the validity of the model. Overall, there is a good agreement of the pattern of the power coefficients according to the positions of the turbines in the array. The actual accuracy of the power coefficient depends strongly on the solidity of the turbine (actuator cylinder related) and both the inlet boundary turbulence intensity and turbulence length scale (RANS simulation related).

Fruit Detection and Pose Estimation for Grape Cluster–Harvesting Robot Using Binocular Imagery Based on Deep Neural Networks

Reliable and robust fruit-detection algorithms in nonstructural environments are essential for the efficient use of harvesting robots. The pose of fruits is crucial to guide robots to approach target fruits for collision-free picking. To achieve accurate picking, this study investigates an approach to detect fruit and estimate its pose. First, the state-of-the-art mask region convolutional neural network (Mask R-CNN) is deployed to segment binocular images to output the mask image of the target fruit. Next, a grape point cloud extracted from the images was filtered and denoised to obtain an accurate grape point cloud. Finally, the accurate grape point cloud was used with the RANSAC algorithm for grape cylinder model fitting, and the axis of the cylinder model was used to estimate the pose of the grape. A dataset was acquired in a vineyard to evaluate the performance of the proposed approach in a nonstructural environment. The fruit detection results of 210 test images show that the average precision, recall, and intersection over union (IOU) are 89.53, 95.33, and 82.00%, respectively. The detection and point cloud segmentation for each grape took approximately 1.7 s. The demonstrated performance of the developed method indicates that it can be applied to grape-harvesting robots.

Experimental Study on the End Effect and the Effect Due to the Difference in End Shape of the Fluid Force Acting on a Rotating Cylinder in a Uniform Flow

When investigating the characteristics of the fluid force acting on a rotating cylinder in a flow, three-dimensional effects such as edge shape and walls become a problem. In this paper, we investigated the fluid force characteristics of the rotating cylinder, as well as the effect of the flow under the end of the cylinder and the shape of the cylinder end in the water tank experiment. There are three types of experimental conditions: No end flow condition, end flow condition, and condition with end plate. There are five disk-shaped end plates with different diameters, and the changes in fluid force are quantitatively summarized for each ratio between the diameter of the cylinder model and the end plate. By generating a flow under the end of the cylinder, the fluid force is significantly reduced compared to the no end flow condition. By attaching the end plate, the fluid force does not decrease even when a flow is generated under the end of the cylinder. The fluid force increases until the ratio DE/D of the diameter D of the cylinder model and the diameter DE of the end plate is around 3, but after that, it shows a constant value.

An innovative heat source model for calculating wheel/rail contact temperature

Modeling an accurate and effective heat source is a challenge when describing the thermal behavior of wheel/rail contact, conventionally modeled using Goldak’s heat source. This Gaussian distributed model transplanted directly from the welding field is quite different from the ellipsoidal heat source on the contact patch. An innovative heat source model which reflects the shape and size of contact patch was created based on the energy equivalence in this study. The thermal behavior of the wheel/rail contact was described by using this heat source moving along the rail. Numerical simulations based on a three-dimensional (3-D) finite element (FE) model validate that the proposed heat source model is valid as the relative errors of the peak temperature between the proposed and previously published heat source model are less than 4.45%. The distribution of the contact temperature on the rail surface reflects the shape and size of the contact patch. The semi-ellipsoidal distributed temperature obtained by the proposed elliptic cylinder model is more precise than the Gaussian distributed temperature obtained by the conventionally used Goldak’s model. The proposed elliptic cylinder model has the advantages of simple structure and flexible model variables than the ready-made Goldak’s model in commercial software.

Vertical-axis wind-turbine computations using a 2D hybrid wake actuator-cylinder model

The actuator-cylinder model was implemented in OpenFOAM by virtue of source terms in the Navier-Stokes equations. Since the stand-alone actuator cylinder is not able to properly model the wake of a vertical-axis wind turbine, the steady incompressible flow solver SimpleFoam provided by OpenFOAM was used to resolve the entire flow and wakes of the turbines. The source terms are only applied inside a certain region of the computational domain, namely a finite thickness cylinder which represents the flight path of the blades. One of the major advantages of this approach is its implicitness, that is, the velocities inside the hollow cylinder region feed the actuator-cylinder model, this in turn computes the volumetric forces and passes them to the OpenFOAM solver in order to be applied inside the hollow cylinder region. The process is repeated in each iteration of the solver until convergence is achieved. The hybrid RANS actuator-cylinder can be used to model a wind farm since a turbine is now able to take into account the effect of other wakes. The model was compared against numerical and experimental works, wake deficits and power coefficients are used in order to assess the validity of the model. Overall, there is a good agreement of the pattern of the power coefficients according to the positions of the turbines in the array. Wake patterns are also similar at certain distances downwind. The actual accuracy of the power coefficient depends strongly on the solidity of the turbine (actuator-cylinder related) and the inlet boundary turbulence intensity (RANS simulation related); a heuristic approach to correct the results of high-solidity turbines is presented for the case of a wind farm made of small-scale turbines. Thus this method can be used to quickly compute the power coefficients of low-solidity vertical-axis wind farms.

STRESS SENSITIVITY ANALYSIS OF FRACTAL POROUS MEDIA BASED ON THE ELASTO-PLASTIC THICK-WALLED CYLINDER MODEL

The stress-dependent flow and transport behaviors of porous media are ubiquitous in various scientific and engineering applications. It has been shown that the change of effective stress has important effects on the permeability and porosity of porous media. In this paper, a new stress sensitivity model for porous media is developed based on the fractal theory and the elasto-plastic thick-walled cylinder model. The proposed model is able to predict the elasto-plastic deformation of the fractal porous media under loading–unloading stress cycles, which plays a crucial role on the permanent variations of the permeability and porosity. It is found that the permeability of stress-sensitivity porous media is related to the capillary fractal dimension, capillary fractal tortuosity dimension, minimum and maximum capillary diameters, Young’s modulus and Poisson’s ratio of capillary. Each parameter has a clear physical meaning. The validity of the developed fractal model is verified by comparing the model predictions with the available experimental data.