An improved in-plane displacement model for the stability analysis of laminated composites with general lamination configurations

This paper describes how the derivatives of lateral displacement are eliminated in the general displacement field of the global–local higher-order theory for stability analysis of laminated composite and sandwich plates with general lamination configurations. In contrast to previous models, the present model is applicable not only to the cross-ply but also to the angle-ply laminated composite and sandwich plates. Based on known traction forces on the surface boundaries, the derivatives of transverse displacement have been taken out from the general displacement field, so that C⁰ interpolation functions are only required for the finite element implementation. To verify the proposed theory, the classical quadratic six-node C⁰ triangular element is employed for the interpolation of all the displacement parameters defined at each nodal point on the composite plate. Numerical results show that following the proposed theory simple C⁰ finite elements could accurately predict the critical loads of sandwich plate with soft core, which has long been a difficult case for the other global higher-order theories.     

Thermomechanical buckling of laminated composite and sandwich plates using global–local higher order theory

In this paper, a global–local higher order theory has been used to study buckling response of the laminated composite and sandwich plates subjected to thermal/mechanical compressive loads. The present global–local theory satisfies the free surface conditions and the geometric and stress continuity conditions at interfaces, and the number of unknowns is independent of the layer numbers of the laminate. Based on this higher-order theory, a refined three-noded triangular element satisfying C¹ weak-continuity conditions has been also proposed. The present theory not only predicts accurately the buckling response of general laminated composite plates but also calculates the critical buckling loads of the soft-core sandwich plates. However, numerical results show that the global higher-order theories as well as first order theories encounter some difficulties and overestimate the critical buckling loads for the sandwich plates with a soft core.     

An accurate higher-order theory and C finite element for free vibration analysis of laminated composite and sandwich plates

At present, it is difficult to accurately predict natural frequencies of sandwich plates with soft core by using the C⁰ plate bending elements. Thus, the C¹ plate bending elements have to be employed to predict accurately dynamic response of such structures. This paper proposes an accurate higher-order C⁰ theory which is very different from other published higher-order theory satisfying the interlaminar stress continuity, as the first derivative of transverse displacement has been taken out from the in-plane displacement fields of the present theory. Therefore, the C⁰ interpolation functions is only required during its finite element implementation. Based on the Hamilton’s principle and Navier’s technique, analytical solutions to the natural frequency analysis of simply-supported laminated plates have been presented. To further extend the ranges of application of the proposed theory, an eight-node C⁰ continuous isoparametric element is used to model the proposed theory. Numerical results show the present C⁰ finite element can accurately predict the natural frequencies of sandwich plate with soft core, whereas other global higher-order theories are unsuitable for free vibration analysis of such soft-core structures.     

An assessment of several displacement-based theories for the vibration and stability analysis of laminated composite and sandwich beams

Several displacement-based theories are assessed by analyzing the free vibration and the buckling behaviors of laminated beams with arbitrary layouts as well as soft-core sandwich beams. The equations governing the dynamic response of laminated structures are derived by using Hamilton’s principle. However, equations of equilibrium for buckling problems are given by employing the principle of virtual displacements. Moreover, using Navier’s technique and solving the eigenvalue equations, analytical solutions based on the global–local higher-order theory used in this paper are first presented in present study. At the same time, the effect of the order number of higher-order shear deformation as well as interlaminar continuity of transverse shear stress on the global response of both laminated beams and soft-core sandwiches has been also studied. Numerical results show that by increasing the order number of in-plane and transverse displacement components, the global higher-order theories can reasonably predict the natural frequencies and the critical loads of laminated beams with arbitrary layouts and soft-core sandwich beams whereas these global higher-order theories are still less accurate compared to the global–local higher-order theory and the zig-zag theory used herein.     

基于Nios II软核的遥感图像实时压缩系统

针对在空间遥感探测领域,大量遥感图像传输和对图像实时处理的需求,提出一种基于Nios II 软核的遥感图像实时压缩系统的设计方法.该方法基于先进的JPEG2000图像压缩标准,使用专用协议芯片,结合嵌入式处理器和可编程逻辑器件,搭建了硬件压缩系统,并在基于Nios II软核的遥感图像实时压缩系统工控机终端建立软件解码单元,实现了大量遥感数据的实时传输压缩与解码显示.测试证明,该遥感图像压缩系统能够实时连续压缩数据,图像压缩效果达到应用要求.通过测试结果分析,并结合具体的工程任务,指出了该图像压缩系统下一步的改进方向.     

40Gb/s交换IP软核验证和测试

研究40Gb／s交换IP软核的验证和测试方法。通过建立SDH芯片验证平台和SDH芯片测试平台,实现IP软核的功能仿真、时序仿真和芯片性能测试。使得IP软核质量优良、性能稳定，适应性强，达到了交换IP软核的设计要求。形成了具有自主知识产权的40Gb／s交换IP软核。     

Buckling Analysis of Angle-ply Composite and Sandwich Plates by Combination of Geometric Stiffness Matrix

Buckling response of angle-ply laminated composite and sandwich plates are analyzed using the global-local higher order theory with combination of geometric stiffness matrix in this paper. This global-local theory completely fulfills the free surface conditions and the displacement and stress continuity conditions at interfaces. Moreover, the number of unknowns in this theory is independent of the number of layers in the laminate. Based on this global-local theory, a three-noded triangular element satisfying C¹ continuity conditions has also been proposed. The bending part of this element is constructed from the concept of DKT element. In order to improve the accuracy of the analysis, a method of modified geometric stiffness matrix has been introduced. Numerical results show that the present theory not only computes accurately the buckling response of general laminated composite plates but also predicts the critical buckling loads of soft-core sandwiches. However, the global higher-order theories as well as first order theories might encounter some difficulties and overestimate the critical buckling loads for soft-core sandwich plates.     

The design and implementation of the IEEE 802.11 MAC based on soft-core processor and RTOS

The implementation method of the IEEE 802.11 Medium Access Control （MAC） protocol is mainly based on DSP （Digital Signal Processor）/ARM （Advanced Reduced instruction set computer Machine） processor or DSP/ARM IP （Intellectual Property） core. This paper presents a method based on Nios II soft-core processor embedded in Altera＇s Cyclone FPGA （Field Programmable Gate Array） and MicroC/OS-II RTOS （Real-Time Operation System）. The benefits and drawbacks of above methods are compared, and then the method presented in this paper is described. The hardware and software partitioning are discussed; the hardware architecture is also illustrated and the MAC software programming is described in detail. The presented method has some advantages, such as low cost, easy-implementation and very suitable for the implementation of IEEE 802.11 MAC in research stage.     

NEW APPROACH TO EMULATE SEU FAULTS ON SRAM BASED FPGAS简

Field Programmable Gate Arrays （FPGAs） offer high capability in implementing of com- plex systems, and currently are an attractive solution for space system electronics. However, FPGAs are susceptible to radiation induced Single-Event Upsets （SEUs）. To insure reliable operation of FPGA based systems in a harsh radiation environment, various SEU mitigation techniques have been provided In this paper we propose a system based on dynamic partial reconfiguration capability of the modern devices to evaluate the SEU fault effect in FPGA. The proposed approach combines the fault injection controller with the host FPGA, and therefore the hardware complexity is minimized. All of the SEU injection and evaluation requirements are performed by a soft-core which realized inside the host FPGA Experimental results on some standard benchmark circuits reveal that the proposed system is able to speed up the fault injection campaign 50 times in compared to conventional method.