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1.
Biomechanical behaviors of dragonfly wing: relationship between configuration and deformation 下载免费PDF全文
In this paper, the natural structures of a dragonfly wing, including the corrugation of the chordwise cross-section, the sandwich microstructure veins, and the junctions between the vein and the membrane, have been investigated with experimental observations, and the morphological parameters of these structural features are measured. The experimental result indicates that the corrugated angle among the longitudinal veins ranges from 80° to 150°, and the sandwiched microstructure vein mainly consists of chitin and protein layers. Meanwhile, different finite element models, which include models I and I* for the planar forewings, models II and II* for the corrugated forewings, and a submodel with solid veins and membranes, are created to investigate the effects of these structural features on the natural frequency/modal, the dynamical behaviors of the flapping flight, and the deformation mechanism of the forewings. The numerical results indicate that the corrugated forewing has a more reasonable natural frequency/modal, and the first order up-down flapping frequency of the corrugated wing is closer to the experimental result (about 27.00 Hz), which is significantly larger than that of the planar forewing (10.94 Hz). For the dynamical responses, the corrugated forewing has a larger torsional angle than the planar forewing, but a lower flapping angle. In addition, the sandwich microstructure veins can induce larger amplitudes of torsion deformation, because of the decreasing stiffness of the whole forewing. For the submodel of the forewing, the average stress of the chitin layer is much larger than that of the protein layer in the longitudinal veins. These simulative methods assist us to explain the flapping flight mechanism of the dragonfly and to design a micro aerial vehicle by automatically adjusting the corrugated behavior of the wing. 相似文献
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双带频率选择表面设计 总被引:2,自引:0,他引:2
为了实现频率选择表面(FSS)的双带特性,设计了由矩形栅格和三圆环组合单元FSS。对FSS的谱域求解方法进行了详细的描述。采用谱域法分析了不同角度和极化入射波下FSS的频率响应性能。结果表明,所设计的FSS对于不同入射角度和极化电磁波具有稳定的双带、平顶传输及陡峭下降边缘特性。双带特性大致表现为1.8~5.4GHz的阻带和5.4~20.0GHz的通带。阻带谐振频率稳定在3.1GHz左右,而通带在-4dB的平顶传输带宽达14.3GHz以上。其陡峭下降边缘特性表现为S波段信号强烈反射,而其他波段信号通过,从而实现多波段通讯。该结构FSS可应用于卫星通信、雷达罩及其他相关领域。 相似文献
3.
The thermal effect and the heat generation in diode-end-pumped continuous-wave 914-nm Nd:YVO4 lasers are investigated in detail. A theoretical model of a diode end-pumped solid-state laser is constructed to analyse the influence of fractional thermal loading on the thermal effect in the Nd:YVO4 laser based on finite element analysis. The thermal focal lengths and the end-surface deformations of laser rods in Nd:YVO4 quasi-three-level and four-level lasers are measured and compared with the results obtained by ordinary interferometry for the demonstration of higher thermal loading in 914-nm laser. Finally the fractional thermal loading in the Nd:YVO4 quasi-three-level laser is calculated by matching the experimental and the simulated end deformations. 相似文献
4.
Several kinds of models have already been proposed to explain the photoemission process. The exact photoemission theory of the semiconductor photocathode was not well established after decades of research. In this paper an integral equation of quantum efficiency (QE) is constructed to describe the photoemission of positive electron affinity (PEA) of the semiconductor photocathode based on the three-step photoemission model. Various factors (e.g., forbidden band gap, electron affinity, photon energy, incident angle, degree of polarization, refractive index, extinction coefficient, initial and final electron energy, relaxation time, external electric field and so on) have an impact on the QE of the PEA semiconductor photocathode, which are entirely expressed in the QE equation. In addition, a simulation code is also programmed to calculate the QE of the K2CsSb photocathode theoretically at 532 nm wavelength. By and large, the result is in line with the expected experimental value. The reasons leading to the distinction between the experimental and theoretical QE are discussed. 相似文献
5.
N(2,2,0)代数的稳定化子与同余分解 总被引:1,自引:1,他引:0
李旭东 《纯粹数学与应用数学》2011,27(1):123-128
为了深入研究N(2,2,0)代数的代数结构,首先利用代数的推理方法进一步研究了N(2,2,0)代数的稳定化子,改进了以前学者的部分结果,然后利用稳定化子建立了一种同余关系,给出了N(2,2,0)代数的同余分解,证明了其商代数仍是N(2,2,0)代数,并获得了自然同态下一类逆像的代数结构和性质. 相似文献
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We present a high power and efficient operation of the ^4F3/2 → ^4I9/2 transition in Nd:GdVO4 at 912nm. In the cw mode, the maximum output power of 8.6 W is achieved when the incident pump power is 40.3 W, leading to a slope efficiency of 33.3% and an optical-optical efficiency of 21.3%. To the best of our knowledge, this is the highest cw laser power at 912nm obtained with the conventional Nd:GdVO4 crystal. Pulsed operation of 912nm laser has also been realized by inserting a small aeousto-optie (A-O) Q-Switch inside the resonator. As a result, the minimal pulse width of 20ns and the average laser power 1.43 W at the repetition rate of lOkHz are obtained, corresponding to 7.1 kW peak power. We believe that this is the highest laser peak power at 912nm. Furthermore, duration of 65ns has also been acquired when the repetition rate is 100 kHz. 相似文献
8.
对红外热像仪参数双黑体测量装置的工作原理进行了介绍。装置采用双黑体及反射型靶标为温差辐射源,可实现黑体温度温差准直辐射的定期校准和红外热像仪参数测量量值的溯源,也可实现红外热像仪参数的可控性,以及对它进行稳定的、可复现的精确测量。推导出利用红外热像仪参数双黑体测量装置测量信号传递函数SiTF数学模型,分析了红外热像仪参数测量装置的客观因素——仪器常数,针对仪器常数对SiTF测量的影响进行了试验。试验结果表明,仪器常数对红外热像仪SiTF参数测量精度影响较大,并同时影响时域与空域NETD及3D噪声的准确测量。 相似文献
9.
研究了胶原纤维固化黑荆树单宁对V(V)的吸附。采用不同温度、pH值等条件进行吸附研究,并进一步探讨了固化黑荆树单宁的吸附动力学和吸附柱动力学及其吸附机理。结果表明,该材料对V(V)的吸附平衡符合Freund lich方程,温度对吸附平衡的影响不明显;吸附动力学可用拟二级速度方程来描述,该材料同时具有良好的柱动力学特性;V(V)的吸附过程可能存在三个反应,即V(V)与吸附剂之间发生氧化还原反应生成V(IV),V(IV)和-COOH之间发生离子交换反应,以及V(IV)与单宁的邻位羟基发生螯合。 相似文献
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利用流固耦合算法,模拟了不同药量TNT内爆下大尺寸多舱室结构的毁伤效应。将各舱室划分为爆炸舱、共面邻舱、共边界邻舱和共点邻舱,再划分内爆下多舱室结构的毁伤等级。通过量纲分析,研究了内爆载荷下舱壁的变形失效规律,推导了内爆下多舱室结构的无量纲毁伤数,该毁伤数考虑了内爆载荷、材料性能和作用空间等因素,最后给出快速毁伤预测方法。研究结果表明:(1)内爆下多舱室结构的毁伤特点主要表现为舱壁挠曲变形、舱壁中心冲切失效、舱壁边界撕裂;(2)舱壁挠曲变形的挠厚比δ/H和固定边界撕裂的裂缝长厚比l/H均与药量-单舱室容积比m/V有明显线性关系;(3)提出的无量纲毁伤数和快速预测方法能够反映内爆下多舱室结构的毁伤情况,可为舰船毁伤研究提供参考。 相似文献