一种柱-锥盘荷波导的色散关系

导出了柱 锥盘荷波导的色散方程 ,并通过数值计算分析了这种慢波结构的几何参数对相对论行波管运行频率和通带的影响 ,与柱形盘荷波导相比 ,这种慢波结构的上截止频率高于柱形盘荷波导 ,因此 ,可以得到较高的运行频率和较大的通带 ,为设计这种慢波器件提供了依据。

X波段盘荷波导加速结构的模拟计算与实验测试

介绍了X波段盘荷波导行波加速结构研究的部分计算结果。给出了RF频率为 9 37GHz的X波段盘荷波导行波加速结构物理设计参数 ,研究了X波段盘荷波导的特征尺寸的微小变化与加速结构基本物理参数的关系。加工出一些模型腔 ,利用网络分析仪对其微波参数和测试条件的影响进行了测量分析。

一种高功率宽带回旋行波放大器

研究了一种X波段高功率宽带回旋行波放大器,它由改变了局部周期的矩形盘荷波导组成,并采用锥化引导磁场和盘的高度来提高增益和带宽。分析了器件的线性特性。利用全电磁(PIC)三维模拟程序EMC进行了数值模拟,结果表明:可以得到功率介于88～103kW,相对带宽介于16.63%～24.11%的不同微波输出。

Distribution of contact loads in crushed zone between tunnel boring machine disc cutter and rock

The construction efficiency and quality of tunnel boring machines(TBMs)is largely determined by the service life of cutting tools,which is the result of contact loads in the crushed zone between cutter ring and rock.In this paper,a series of rock breaking tests were conducted with a 216 mm diameter disc cutter and concrete samples.Based on the superposition principle,the distribution of contact loads between disc cutter and rock were obtained by using the truncated singular value decomposition(TSVD).The results show that both the peak value and the whole numerical distribution of the radial strains on the cutter ring increase with the increase of the penetration.The distribution curves of the contact loads show an approximate parabola going downwards,which indicates contact loads are more concentrated.The front non-loading area with a ratio from 1.8%to 5.4%shows an increasing trend with the increase of penetration.However,the change of rear non-loading area is not obvious.It is believed that the conclusions have guidance for the study of rock breaking mechanism and manufacturing process of the disc cutter.

Analytical solutions of simply supported magnetoelectroelastic circular plate under uniform loads

In this paper, the axisymmetric general solutions of transversely isotropic magnetoelectroelastic media are expressed with four harmonic displacement functions at first. Then, based on the solutions, the analytical three-dimensional solutions are provided for a simply supported magnetoelectroelastic circular plate subjected to uniform loads. Finally, the example of circular plate is presented.

Flexibility of the Lumbar Intervertebral Disc in Bending and Torsion： Experimental and Finite Element Study

Intervertebral disc flexibility is influenced by lifestyle, loading history, trauma, preexisting conditions, age and degeneration. With regard to degeneration, intervertebral discs become less flexible and stiffer. In this study, a testing protocol using bending and torsion loading was developed to gain the flexibility curves and stiffness often cadaveric lumbar discs. Measurements of rotation in the sagittal plane （flexion-extension）, coronal plane （right-lefl lateral bending） and transverse plane （torsion） due to a 5 N-m load are reported. Results show that overall normal discs are more flexible and behave in a nonlinear fashion. The testing results were used in a develop t＇mite element model of an intervertebral disc to investigate the stresses and strains in the disc components： annulus fibrosus and nucleus pulposus with regard to degeneration. Simulation of bending and torsion loadings show large strains in the annulus and nucleus from a normal disc, in contrast higher stresses develop in the annulus from a degenerated disc. The proposed methodology is novel, versatile, functional and economic with implications in bioengineering, medical sciences and the clinical field.

何晓晴作品

夏日 青青黍叶向天舒,霭霭闲云自在书。乱雨荷盘空舞后,珠含浓翠丽人梳。

The influence of the intervertebral disc on stress distribution of the thoracolumbar vertebrae under destructive load

Objective: To compare the influence of normal and degenerative discs on stress distribution of the thoracolumbar vertebrae under destructive load, explore the biomechanical background and clinical meaning and provide theoretical basis for clinical diagnosis and treatment. Methods: A mechanical model of thoracolumbar motion segment of normal and degenerative discs was built with a three dimensional finite element method and three stresses of vertical compression, compressive flexion and distractive flexion were comparatively analyzed. Results: With vertical compression and compressive flexion loads, the thoracolumbar motion segment of the normal disc showed that the central part of the upper and lower end plates of the vertebrae and the central part of the trabecular bone adjacent to the end plate were loaded with the most intensive stresses, meanwhile, the postero lateral part of the annulus fibrosus was concentrated with stresses. Degenerative disc showed that the stress distribution of the trabecular bone was relatively averaged, the stresses of the central part adjacent to the end plate were low, while at the same time, the stresses of the peripheral part were elevated relatively. With distraction flexion load, the stresses of the cortex bone, trabecular bone, end plate and annulus fibrosus of the thoracolumbar vertebrae of degenerative discs were low, meanwhile, the stresses of the posterior structure of the vertebral body were relatively elevated compared with that of normal discs. Conclusions: There is difference in influence between normal and degenerative discs on the stress distribution of the thoracolumbar vertebrae with destructive load. The transferring way of load is changed after disc degeneration.

Numerical investigation of disc heat transfer with a novel fin-like structure

Rotary disc is a key part in aero engine, HPT rotor disc due to its highest thermal load as well as mechanical load, always suffers from thermal or mechanical failure. In this paper, the authors initiate a new kind of novel fin-like structure which is presented on both surfaces of the rotating disc. The presence of the fin-like structure acts like a turbulence & vortex generator and hence increases the heat transfer effectiveness between the cooler cavity flow and the higher temperature disc surface. This paper deals with a numerical investigation of the new kind of fin-like structure which is tending to be applied on the high pressure turbine rotor's rotating disc. Numerical results revealed that with this novel structure thermal load of the disc reduced noticeably ranging from 10℃ to 20℃. This can be explained by the vortex structure generated by the disturbance of the cavity's cooling flow, thus enhancing the convective heat transfer rates between the disc surface and the cavity flow.

Determination of T-stress using finite element analysis

A method that uses finite element analysis to determine the non-singular stress （T-stress） at a crack tip is proposed in this study. T-stress includes two components： the Tx-stress parallel to the tangent of the crack at its tip and the Ty-stress perpendicular to this tangent. The effects of contact and friction on both the Tx- and Ty-stresses on the crack flanks are considered in the method. Because the method uses a single standard elastic finite element analysis derived directly from the equation of the stress fields around the crack tip and does not require any assumptions or simplification, it can be used to determine the T-stress for any given geometry and loading condition. Theoretical results are used to calibrate the results, which exhibited good agreement and to discuss the T-stress computational methodology. Furthermore, the Tx- and Ty-stresses in center-cracked Brazilian disc （CCBD） specimens subjected to diametrical or partially distributed compression were numerically computed, and the effects of contact and friction on the Tx- and Ty-stresses are discussed.