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Modelling Methods of Constrained Flexible Ropes in Capture Net System
LI Zhixiang, ZHANG Hanglan, SHI Junwei, YANG Wenmiao, ZHAO Zhen
Acta Scientiarum Naturalium Universitatis Pekinensis    2023, 59 (3): 359-364.   DOI: 10.13209/j.0479-8023.2023.014
Abstract448)   HTML    PDF(pc) (728KB)(192)       Save
Due to the difficulty of dynamical modelling of constrained flexible ropes for the closure process caused by the presence of non-smooth contacts and rigid-flexible coupling problem, a simplified model is provided. The contacts between the ropes and the rings or the separators are considered as slip joints, and the dynamical studies are conducted using the constraint method. Considering the collision of the slip joint, the contact stiffness is introduced and the contact dynamics equations of the slip joint are established. The absolute nodal coordinate formulation is used to describe the motion of rope element, and the dynamics model of which can then be established through the principle of virtual work. For rigid bodies such as separators, the quaternion description is used to establish the dynamics equations. The simulation of closure process is performed to obtain the motion law of the rope and the traction mass block, and the closure time and the degree of closure are compared under different numbers of rings. It is found that an increase in the number of rings will result in a more compact contraction of the rope, but considerable rings will prolong closure time and reduce closure efficiency.
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Effect of Interface Tangential Relative Motion Caused by Vibration on Friction
LU Jiandong, ZHAO Zhen
Acta Scientiarum Naturalium Universitatis Pekinensis    2020, 56 (5): 777-784.   DOI: 10.13209/j.0479-8023.2020.056
Abstract1186)   HTML    PDF(pc) (2073KB)(223)       Save
In order to study the effect of vibration on friction at contact interface, an experimental device was designed. The slider sliding at uniform speed on the vibrator was taken as the object. The mechanism of friction reduction caused by normal vibration and tangential vibration at interface was analyzed by means of experiment and theory. The experimental results show that normal vibration and tangential vibration often exist simultaneously. When the interface vibrates and the direction of the tangential relative velocity between the slider and the vibrator remains constant, the average sliding friction force of the slider is the same as that without vibration, and there is no friction reduction effect. When the interface vibrates and the tangential relative velocity direction changes periodically or stick-slip, there is an obvious friction reduction effect compared with that without vibration. Coulomb’s friction law was used to establish a dynamic model for simulation, and the simulation results are in good agreement with the experimental results, indicating that Coulomb’s friction model could reflect the friction between interfaces under the condition of known interface motion. The experimental and theoretical results show that the main reason for friction reduction is the periodic change of friction direction between interfaces or stick-slip caused by the tangential relative motion due to the vibration, when normal vibration and tangential vibration exist at the same time. 
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Obtaining Driving Torques of Space Manipulators Based on Ground Planar Experimental Data of the Manipulator with Air-bearing Support: Modeling and Experimental Verification
ZHANG Lei, CUI Zhiwu, CHEN Tao, YAO Hongxiang, ZHAO Zhen
Acta Scientiarum Naturalium Universitatis Pekinensis    2019, 55 (4): 597-602.   DOI: 10.13209/j.0479-8023.2019.006
Abstract1380)   HTML    PDF(pc) (1763KB)(191)       Save
In order to extract the true dynamics of a manipulator in space from the experimental data on ground, gap functions of the joints’ driving torques are deduced by Lagrangian equations between two manipulators with and without air-bearing support. The real driving torques can be predicted by the ground data minus the gap function. Verifying experiments are designed and carried out by a small manipulator with rigid arms.
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Accumulation Process and Control Factors of Jurassic-Cretaceous Distant-Source and Secondary-Filled Reservoirs in the Hinterland of Junggar Basin
MA Weijiao, WEI Yanzhao, LI Xia, TAO Shizhen, LI Yongguang, ZHAO Zhengya
Acta Scientiarum Naturalium Universitatis Pekinensis    2018, 54 (6): 1195-1204.   DOI: 10.13209/j.0479-8023.2018.073
Abstract922)   HTML    PDF(pc) (3206KB)(190)       Save

Homogenization temperature of fluid inclusions, stratigraphic burial-thermal history, paeleostructure of accumulation period, known reservoirs and geochemical index are analyzed. Hydrocarbon accumulation periods, hydrocarbon transport system, trap-forming conditions of the Jurassic-Cretaceous in the hinterland of Junggar Basin are discussed. Thus, the dynamic accumulation process of the distant sourced, secondary-accumulated reservoirs is revealed. Results show that there are two periods of oil and gas charging in the Jurassic and cretaceous reservoirs in the hinterland of Junggar Basin, which are primary reservoirs formed in the early Cretaceous and secondary-filled reservoirs formed in the late paleogene till now. Both the primary reservoirs and sencondary accumulated reservoirs are widely spread in the hinterland area. Faults-sand bodies-unconformities act as three dimensional transporting systems for hydrocarbon migration and accumulation. The formation of primary reservoirs is controlled by paleostructure of accumulation period. During the later dissolution of paleostructure, primary reservoirs are destroyed and oil and gas migrate towards the north. Reservoirs types are decided by trap conditions on the migration pathways. At present, low-amplitude anticline, fault block and litho-stratigraphic reservoirs are the most discovered.

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On Nonholonomic Constraints about the Pure Rolling of Point Contact
ZHAO Zhen, LIU Caishan, LU Jiandong
Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (4): 713-716.   DOI: 10.13209/j.0479-8023.2016.084
Abstract3044)   HTML    PDF(pc) (312KB)(749)       Save

Nonholomonic constraints are involved for 3D point-contact problems. The virtual displacements restricted by the constraints are usually given by Appell-Chetaev’s rule. It has not been very clear of the geometric meaning in configuration space for Appell-Chetaev’s rule of nonholonomic constraints. The authors investigate point contact with pure rolling by two rigid bodies in a multibody system to discover its geometric sense. First, the sufficient and necessary conditions of point contact are given. A ball-plane system is presented to demonstrate the validation of the conditions by deducing the system’s obvious contact constraint originating from them. Two geometric restrictions for pure rolling are obtained by the nonholonomic constraints of pure rolling as well as the contact constraint in velocity level. It proves that the virtual displacements of the two restrictions are same as those of the constraints of point contact with pure rolling obtained by Appell-Chetaev’s rule. So, it is thought that the constraints of pure rolling are constructed by the two geometric restrictions.

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Variable Structural Dynamics for a Two-Dimension Rod
CAI Huiping,ZHAO Zhen
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract487)            Save
Contact, impact and friction may induce none-smooth behaviors on velocity level for multi-rigid-body system. Variable structural dynamics can deal with them by loading and uploading constraints on the system. Variable structural dynamics for two dimensional dynamic system including contact, impact and friction is introduced. A 2D rod is presented to achieve the final dynamic simulation.
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Stepping-Forward Impulse Method
ZHAO Zhen,LIU Caishan,CHEN Bin
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract843)            Save
The complexity of tangential movements during impact is one of main characteristics for multi-rigid-body systems. A general numerical method for impulse problems of 2D rigid body systems is introduced. The method inherits the invariance of configuration of dynamic system during impact. It discretizes impact process into multi-steps. A little impuse increment is permitted in each step and the mode of sticking or sliding must be judged before every step increment. This method can solve the impact problems properly and efficiently due to collision or inconsistency for multi-rigid-body systems.
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Dynamics of Discrete System with Friction and Multiple-Point Impact
YAO Wenli,CHEN Bin,ZHAO Zhen,YU Lixiao
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract622)            Save
The purpose is to study the solution of impulsive dynamics of planar discrete system with friction and multiple-point impact. When impact applies on a discrete system in which one of constraints is a constant with coulomb friction, the phenomenon of slip-stick at the point can cause the change of friction and the integration for frictional force during infinitesimal impulsive interval becomes impossible according to traditional impulsive dynamics of discrete systems. By introducing a new dimensional time parameter, first-order momentum-impulse differential equations are obtained and the discussion over infinitesimal impulsive interval is transformed into a piece-wise study on the finite region of impulse. An algorithm for response of impact and an example are given.
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Ideal Load of Bilateral Constraint
ZHAO Zhen,JIN Hai,CHEN Bin
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract841)            Save
One of ideal methods that deal with variable structure system is treating variable structure problem as load or relieving of constraints. The simplest instance is ideal load of bilateral constraints, which means that there is only ideal constraint force during load. From the point of view of analytical mechanics, the theory of ideal load of bilateral constraint is given. The advantage of the theory is that it reveals mechanical mechanism of ideal load of bilateral constraint and it is more convenient for extension.
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The Effect of Adsorption of Surfactants on Stability of Suspension of Alumina Powders
WANG Shun,ZHAO Zhenguo,LIU Yingqing,QIAN Cheng
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract942)            Save
The adsorption of sodium dodecyl sulfonate (SDBS), tetradecyl pyridinechloride (TPC) and Triton X-100 (TX-100) onto the alumina powders at various pH was studied. The ξ-potential of the particles and the stability of the suspension in water were determined. The main results are as follows. (1) At suitable pH, the adsorption isotherms are LS type for SDBS and TPC. At higher concentration of surfactants, association on the surface occurs to form a close-packed monolayer. The orientation of hydrophilic group to water phase was inferred from values of adsorption limit, surface area and molecular dimensions. The sign of ξ-potential of alumina powder was opposite to the original one in lower concentration of SDBS or TPC, and the values of ξ-potential increased with increasing concentration. The stability of suspension of alumina powders is a function of SDBS or TPC concentration and displays an V-shaped curve with increasing concentration at lower concentration. (2) At pH 6.9 and higher concentration, monolayer on the surface of alumina was formed by adsorption of TX-100. In the monolayer the hydrophilic EO group interact with the hydroxy of surface and the hydrophilic group is in water phase. Then the stability of the suspension of alumina powders is lower than that of the suspension at lower concentration of TX-100.
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Preparation of Spherical CaCO3 Powers
ZHAO Zhenguo,DING Ding
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract634)            Save
The pure spherical CaCO3 powders have been prepared by decomposition of chelates. The experimental results show that the spherical CaCO3 powders were obtained when the ethylenediaminetetraacetic acid(H 4edta)as chelating agent was applied and it concentration was suitable. The large increase in partical size occurs as ageing at higher temperature.
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Preparation of ZnO Powders by Decomposition of Chelates
ZHAO Zhenguo,DING Ding,CHENG Humin,MA Jiming,QI Limin
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract607)            Save
The zinc oxide powders have been prepared by decomposition of zinc ammine and zinc chelates. The NH4OH as complexing agent and the ethylenediaminetetraacetic acid disodium salt, L-Cysteine as chelating agent were used. The experimental results show that the nanometresize ZnO powders were obtained when the metal chelates have a medium stability constant.
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