State Key Laboratory of Fluid Power and Mechatronic Systems

Hangzhou, China

State Key Laboratory of Fluid Power and Mechatronic Systems

Hangzhou, China
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Qin S.,Zhejiang University | Chu N.,Zhejiang University | Yao Y.,Beijing Electromechanic Engineering Institute | Liu J.,Zhejiang University | And 3 more authors.
Physics of Fluids | Year: 2017

To investigate the stream-wise distribution of skin-friction drag reduction on a flat plate with bubble injection, both experiments and simulations of bubble drag reduction (BDR) have been conducted in this paper. Drag reductions at various flow speeds and air injection rates have been tested in cavitation tunnel experiments. Visualization of bubble flow pattern is implemented synchronously. The computational fluid dynamics (CFD) method, in the framework of Eulerian-Eulerian two fluid modeling, coupled with population balance model (PBM) is used to simulate the bubbly flowalong the flat plate. A wide range of bubble sizes considering bubble breakup and coalescence is modeled based on experimental bubble distribution images. Drag and lift forces are fully modeled based on applicable closure models. Both predicted drag reductions and bubble distributions are in reasonable concordance with experimental results. Stream-wise distribution ofBDRis revealed based on CFD-PBM numerical results. In particular, four distinct regions with different BDR characteristics are first identified and discussed in this study. Thresholds between regions are extracted and discussed. And it is highly necessary to fully understand the stream-wise distribution of BDR in order to establish a universal scaling law. Moreover, mechanism of stream-wise distribution of BDR is analysed based on the nearwall flow parameters. The local drag reduction is a direct result of near-wall max void fraction. And the near-wall velocity gradient modified by the presence of bubbles is considered as another important factor for bubble drag reduction.


Yang S.,Zhejiang University | Yang S.,State Key Laboratory of Fluid Power and Mechatronic Systems | Wu D.,Zhejiang University | Wu D.,State Key Laboratory of Fluid Power and Mechatronic Systems | And 4 more authors.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science | Year: 2017

In this study, three-dimensional computational fluid dynamics simulation was adopted to evaluate the valve-induced water hammer phenomena in a typical tank-pipeline-valve-tank system. Meanwhile, one-dimensional analysis based on method of characteristics was also used for comparison and reference. As for the computational fluid dynamics model, the water hammer event was successfully simulated by using the sliding mesh technology and considering water compressibility. The key factors affecting simulation results were investigated in detail. It is found that the size of time step has an obvious effect on the attenuation of the wave and there exists a best time step. The obtained simulation results have a good agreement with the experimental data, which shows an unquestionable advantage over the method of characteristics calculation in predicting valve-induced water hammer. In addition, the computational fluid dynamics simulation can also provide a visualization of the pressure and flow evolutions during the transient process. © Institution of Mechanical Engineers.


Dai Y.,Central South University | Dai Y.,State Key Laboratory of Fluid Power and Mechatronic Systems | Liu S.,Central South University
Huazhong Keji Daxue Xuebao (Ziran Kexue Ban)/Journal of Huazhong University of Science and Technology (Natural Science Edition) | Year: 2012

Taking the design scheme of China's deep ocean mining pilot system as the engineering background, the 3-dimensional dynamic model of the total deep ocean mining system was established based on the single-rigid-body of the seafloor tracked miner, the multi-body discrete element model of the pipeline and the kinematics model of the surface mining ship. A new integrated motion operation mode was proposed, which combines of longitudinal straight-line motion, turning motion and lateral straight-line motion. The dynamic simulation analysis of the new operation mode was achieved. Some critical dynamic characteristics results during the whole operation process were obtained, such as the motion trajectories of the main subsystems, the interaction forces between adjacent subsystems, the deflection angles of the rigid lift pipeline and etc. The dynamic simulation results show that the motion states of all the subsystems can keep stable within the permissible ranges during the whole operation process, which further prove the rationality and feasibility of the newly proposed integrated motion operation mode.


Cheng J.,State Key Laboratory of Fluid Power and Mechatronic Systems | Liu Z.,State Key Laboratory of Fluid Power and Mechatronic Systems | Wu Z.,State Key Laboratory of Fluid Power and Mechatronic Systems | Tang M.,State Key Laboratory of Fluid Power and Mechatronic Systems | Tan J.,State Key Laboratory of Fluid Power and Mechatronic Systems
Computers and Structures | Year: 2016

A constrained interval optimization model is proposed for the optimization of uncertain structures with their mechanical performance indices described as the objective and constraint functions of the design vector and interval uncertain parameters. Present indirect approaches for solving such interval optimization models by converting them into deterministic ones will result in the loss of uncertainty information and deviate from the original intention of realistically modeling engineering optimization problems. To overcome these shortcomings, a novel optimization algorithm is proposed for directly solving the nonlinear constrained interval optimization models based on a novel concept of the degree of interval constraint violation (DICV) and the DICV-based preferential guidelines. A nested genetic algorithm (GA) is developed to realize the direct interval ranking of various design vectors. The outer layer GA locates the optimal solution based on direct interval ranking. The inner layer GAs integrated with Kriging technique compute the intervals of the mechanical performance indices of every design vector in the current population of the outer layer GA. The validity and superiority of the proposed direct interval optimization algorithm was verified by three numerical examples. Finally, the proposed direct interval optimization method was applied to the optimization of the cone ring fixture with uncertain material properties in a large turbo generator aimed at moving its natural frequencies away from the exciting one. The results demonstrated its feasibility and effectiveness in optimizing practical engineering structures under uncertainties. © 2015 Elsevier Ltd. All rights reserved.


Cao Y.,Jiangnan University | Cao Y.,State Key Laboratory of Fluid Power and Mechatronic Systems | Wu M.,Jiangnan University | Zhou H.,Jiangnan University
International Journal of Robotics and Automation | Year: 2013

For a special class of the Stewart parallel mechanism whose moving platform and the base are two dissimilar semi-symmetrical hexagons, the position-singularity of the mechanism for a constant orientation is analysed systematically. After expanding the determinant of the Jacobian matrix, a cubic symbolic polynomial representing the threedimensional (3D) position-singularity locus of the mechanism is derived and graphical representations of the 3-D position-singularity locus are illustrated. Based on this cubic polynomial, a quadratic polynomial that represents the position-singularity locus of the mechanism in the characteristic plane is derived. It is shown that the characteristic of the position-singularity loci in parallel characteristic planes includes infinity many sets of hyperbolas, four pairs of intersecting lines, a parabola and even two lines or one line for some special orientations.


Li B.,Jiangnan University | Li B.,Anhui University of Science and Technology | Cao Y.,Jiangnan University | Cao Y.,State Key Laboratory of Fluid Power and Mechatronic Systems | And 2 more authors.
Robotica | Year: 2013

In this paper, for a special class of the Stewart parallel mechanism, whose moving platform and base one are two dissimilar semi-symmetrical hexagons, the position-singularity of the mechanism for a constant-orientation is analyzed systematically. The force Jacobian matrix [J]T is constructed based on the principle of static equilibrium and the screw theory. After expanding the determinant of the simplified matrix [D], whose rank is the same as the rank of the matrix [J]T, a cubic symbolic expression that represents the 3D position-singularity locus of the mechanism for a constant-orientation is derived and graphically represented. Further research shows that the 3D position-singularity surface is extremely complicated, and the geometric characteristics of the position-singularity locus lying in a general oblique plane are very difficult to be identified. However, the position-singularity locus lying in the series of characteristic planes, where the moving platform coincides, are all quadratic curves compromised of infinite many sets of hyperbolas, four pairs of intersecting lines and a parabola. For some special orientations, the quadratic curve can degenerate into two lines or even one line, all of which are parallel to the ridgeline. Two theorems are presented and proved for the first time when the geometric characteristics of the position-singularity curves in the characteristic plane are analyzed. Moreover, the kinematic property of the position-singularity curves is obtained using the Grassmann line geometry and the screw theory. The theoretical results are demonstrated with several numeric examples. Copyright © 2012 Cambridge University Press.


Zhou H.,Jiangnan University | Zhou H.,State Key Laboratory of Fluid Power and Mechatronic Systems | Cao Y.,Jiangnan University | Cao Y.,State Key Laboratory of Fluid Power and Mechatronic Systems | And 5 more authors.
International Journal of Advanced Robotic Systems | Year: 2012

This paper addresses the problem of identifying the property of the singularity loci of a class of 3/6- Cough-Stewart manipulators for general orientations in which the moving platform is an equilateral triangle and the base is a semiregular hexagon. After constructing the Jacobian matrix of this class of 3/6-Cough-Stewart manipulators according to the screw theory, a cubic polynomial expression in the moving platform position parameters that represents the position-singularity locus of the manipulator in a three-dimensional space is derived. Graphical representations of the position- singularity locus for different orientations are given so as to demonstrate the results. Based on the singularity kinematics principle, a novel method referred to as 'singularity-equivalent-mechanism' is proposed, by which the complicated singularity analysis of the parallel manipulator is transformed into a simpler direct position analysis of the planar singularity-equivalent-mechanism. The property of the position-singularity locus of this class of parallel manipulators for general orientations in the principal-section, where the moving platform lies, is identified. It shows that the position-singularity loci of this class of 3/6-Cough-Stewart manipulators for general orientations in parallel principal-sections are all quadratic expressions, including a parabola, four pairs of intersecting lines and infinite hyperbolas. Finally, the properties of the position-singularity loci of this class of 3/6-Cough-Stewart parallel manipulators in a three- dimensional space for all orientations are presented. © 2012 Zhou et al.


Li Y.,Chang'an University | Li Y.,State Key Laboratory of Fluid Power and Mechatronic Systems | Zhu T.,Chang'an University | Liu Y.,Chang'an University | And 2 more authors.
Water Science and Technology | Year: 2012

Bubble behavior is fundamental to the performance of froth flotation operations used in wastewater treatment processes. To fully understand and characterize bubble behavior under flotation-related conditions in wastewater, the high-speed photographic method has been employed to examine the motion of single bubbles and size distribution of bubble swarms with intermediate sizes ranging from 1 to 4 mm in the presence of surfactants in a laboratory scale flotation column. Both distilled water and synthetic municipal wastewater have been used to make solutions as well as two types of common surfactants. The instantaneous bubble motion has been recorded by a high speed camera. Subsequently, bubble trajectory, dimensions, velocity and distribution have been determined from the recorded frames using the image analysis software. The experimental results show that the addition of surfactant into wastewater has similar effects on bubble hydrodynamic behavior as in pure water (e.g., improving trajectory stabilization, dampening bubble deformation, slowing down terminal velocity, reducing bubble size and increasing the specific surface area of bubble swarm) due to the Marangoni effect. However, it is interesting to note that surfactant effects on single bubble hydrodynamics in wastewater are slightly stronger than those in pure water while surfactant effects on size parameters of bubble swarms in wastewater are significantly stronger than those in pure water. This finding suggests that besides surfactant, inorganic salts present in synthetic wastewater have an important influence on bubble dispersion. © IWA Publishing 2012.


Ai C.,Hebei Province Key Laboratory of Heavy Machinery Fluid Power Transmission and Control | Ai C.,State Key Laboratory of Fluid Power and Mechatronic Systems | Lin J.,Hebei Province Key Laboratory of Heavy Machinery Fluid Power Transmission and Control | Kong X.,Hebei Province Key Laboratory of Heavy Machinery Fluid Power Transmission and Control | And 2 more authors.
Gaojishu Tongxin/Chinese High Technology Letters | Year: 2016

In the view of the problem that the flow in the pressure compensation valve of the LUDV multi-way valve of a constant hydraulic pump system is low, a new large flow energy-saving pressure compensation valve was designed by theoretical calculation. The valve contains a main channel and two overflow channels. Through the AMESim simulation and experiments, the good unloading pressure characteristic and the good pressure compensation characteristic in large flow working conditions of the new large flow three-way pressure compensation valve were verified. The flow of the new valve can reach 400 L/min and the unloading pressure can be reduced to 3MPa.Thus, the new valve meets the requirements of LUDV multi-way valves in quantitative pump hydraulic systems of construction machinery. The new large flow three-way pressure compensation valve makes an important contribution to the further research on multi-way valves. © 2016, Inst. of Scientific and Technical Information of China. All right reserved.


Bao J.,State Key Laboratory of Fluid Power and Mechatronic Systems | Lin Y.,State Key Laboratory of Fluid Power and Mechatronic Systems | Li W.,State Key Laboratory of Fluid Power and Mechatronic Systems | Liu H.,State Key Laboratory of Fluid Power and Mechatronic Systems
Taiyangneng Xuebao/Acta Energiae Solaris Sinica | Year: 2016

A scheme of digital controlled hydraulic cylinder group (DCHCG) of inverse pendulum wave energy converter was proposed. The working principle of DCHCG was introduced. The mathematic model was built and the united simulation analysis of the whole wave energy converter based on AMESim and Matlab/Simulink was done to verify that DCHCG can adjust pressure, and can improve the energy capture efficiency of pendulum wave energy converter. Furthermore, a prototype of DCHCG and a testing system were built and tested. The test results verify the feasibility and simulation conclusion of DCHCG. © 2016, Editorial Board of Acta Energiae Solaris Sinica. All right reserved.

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