Constructions and Applied Examinations of a Kind of Square-Conservative Schemes in High Precision in the Time Direction

In order to meet the needs of work in numerical weather forecast and in numerical simulations for climate change and ocean current, a kind of difference scheme in high precision in the time direction developed from the completely square-conservative difference scheme in explicit way is built by means of the Taylor expansion. A numerical test with 4-wave Rossby-Haurwitz waves on them and an application of them on the monthly mean current the of South China Sea are carried out, from which, it is found that not only do the new schemes have high harmony and approximate precision but also can the time step of the schemes be lengthened and can much computational time be saved. Therefore, they are worth generalizing and applying.

Research on Nonlinear Dynamic Characteristics ofStructures Supported on Slide-Limited Friction Base Isolation System

This paper presents a new type of base isolation system, i. e. , slide-limited friction (S-LF) base isolation system . Based on this system, the harmonic and subharmonic periodic response of S-LF subjected to harmonic motions is investigated by using Fourier-Galerkin-Newton (FGN) method with Flo-quet theory. The dynamic response of S-LF subjected to earthquake ground motions is calculated with a high order precision direct integration method, and the numerical results are presented in maximum acceleration response spectra of superstructure and maximum sliding displacement response spectrum form. The comparison of isolating effects of S-LF, pure-friction base isolation system (P-F) and resilient-friction base isolation system (R-FBI) shows that the isolating property of S-LF is superior to those of P-F and R-FBI. Finally, by analyzing an engineering example, it is observed that the distribution of the maximum shear between floors and absolute acceleration of S-LF to earthquake ground motion is very different from that of traditional structures.

Optimal Control of a Beam with Discontinuously Distributed Piezoelectric Sensors and Actuators

Because of its light weight, broadband, and adaptable properties, smart material has been widely applied in the active vibration control （AVC） of flexible structures. Based on a firstorder shear deformation theory, by coupling the electrical and mechanical operation, a 4-node quadrilateral piezoelectric composite element with 24 degrees of freedom for generalized displacements and one electrical potential degree of freedom per piezoelectric layer was derived. Dynamic characteristics of a beam with discontinuously distributed piezoelectric sensors and actuators were presented. A linear quadratic regulator （LQR） feedback controller was designed to suppress the vibration of the beam in the state space using the high precise direct （HPD） integration method.

Virtual simulation analysis and verification of seed-filling mechanism for dipper hill-drop precision direct rice seeder

In order to improve the seeder’seed-filling ability of the dipper hill-drop precision direct rice seeder,and to meet the mechanization requirement of high speed operation,the self-designed seeder was taken as the objective to explore its seed-filling mechanism and the movement status of rice seed in seed box from the perspective of mechanics.The force models of seed-filling process by dipper were established,and the influential regularity of its rotation speed to compressive resistance of seed population was analyzed as well.The image processing Module-Clipping of discrete element simulation software EDEM was used in the virtual simulation analysis for the process of the seed filling into the dipper,and the velocity relation curve and the force changing curve between rotation speed and seeds were obtained.According to the virtual experiment,the composite filling force of seeds,i.e.the qualified rate on filled rice seed amounts was the largest when rotation speed was at 40 r/min.The performance test bed of seeder was used to verify the simulation results,in which the qualified rate on scooped rice seed amounts was taken as the index,and six rotation speeds of seed-filling dipper were also selected for analysis of seed-filling ability of the device.The results are as follows:with the increase of working speed,the qualified rate on filled rice seed amounts fluctuated with a trend of cosine curve,the largest value was 94.16%occurred when the rotation speed of seed-filling dipper was at 40 r/min.The variation trend of simulation value was approximately consistent with that of verification value.The study can provide a reference for the research and development of mechanical seeder.

Surface texture formation in precision machining of direct laser deposited tungsten carbide

This paper focuses on an analysis of the surface texture formed during precision machining of tungsten carbide. The work material was fabricated using direct laser deposition （DLD） technology. The experiment included precision milling of tungsten carbide samples with a monolithic torus cubic boron nitride tool and grinding with diamond and alumina cup wheels. An optical surface profiler was applied to the measurements of surface textures and roughness profiles. In addition, the micro-geometry of the milling cutter was measured with the appli- cation of an optical device. The surface roughness height was also estimated with the application of a model, which included kinematic-geometric parameters and minimum uncut chip thickness. The research revealed the occurrence of micro-grooves on the machined surface. The surface roughness height calculated on the basis of the traditional kinematic-geometric model was incompatible with the measurements. However, better agreement between the theoretical and experimental values was observed for the minimum uncut chip thickness model.

A modified highly precise direct integration method for a class of linear time-varying systems

It is always a bottleneck to design an effective algorithm for linear time-varying systems in engineering applications.For a class of systems,whose coefficients matrix is based on time-varying polynomial,a modified highly precise direct integration(VHPD-T method)was presented.Through introducing new variables and expanding dimensions,the system can be transformed into a timeinvariant system,in which the transfer matrix can be computed for once and used forever with a highly precise direct integration method.The method attains higher precision than the common methods(e.g.RK4 and power series)and high efficiency in computation.Some numerical examples demonstrate the validity and efficiency of the method proposed.