Higher mode effects in hinged wall with BRBsin base-frame structures using distributed parameter models

To investigate the effect of higher modes on the displacement and inner forces in HWBB(hinged wall with buckling-restrained braces in base)-frame structure,distributed parameter models for both the HWBB-hinged frame structure and the HWBB-MRF(moment resisting frame)structure are built.The hinged wall is simplified as a flexural beam.BRBs(bucking-restrained braces)are simplified to a rotational spring.MRF is simplified to a shear beam.Vibration equations of distributed parameter models are derived.Natural periods,natural modes of vibration,inner forces and displacements of the distributed parameter models are derived based on the vibration equations using numerical methods.The effect of the relative stiffness ratio and the rotational stiffness ratio on the higher mode effects is investigated.For elastic structures,the global displacement and shear in MRF are predominantly controlled by the first mode,while the shear and bending moment in the wall are significantly affected by higher mode effects.The effect of the yielding of BRB on the inner forces distribution in the HWBB-hinged frame is investigated.The results indicate that the first mode will no longer contribute to the inner forces and the contribution from higher modes to inner forces increases after the BRBs yield.Displacement is not sensitive to higher mode effects and it is controlled by the first mode after the BRBs yield.Parameter analysis demonstrates that the displacement amplitudes are reduced with the increase in the flexural stiffness of the wall before the flexural stiffness reaches a certain value.The first three periods decrease with the increase in the rotational stiffness.With the increase in the rotational stiffness ratio,the contribution from the first mode decreases while contributions from both the second mode and third mode increase.

Noise reduction and signal to noise ratio improvement in magneto-optical polarization rotation measurement

The measurement of an extremely small magneto-optical polarization rotation angle with high sensitivity is integral to many scientific and technological applications. In this Letter, we have presented a technique based on Faraday modulation combined with the optical differential method to measure an extremely small polari- zation rotation angle with high sensitivity. The theoretical and experimental results show that common mode noise is reduced appreciably and signal to noise ratio is enhanced. The effectiveness of this technique has been demonstrated by measuring the Verdet constant of terbium gallium garnet glass and measuring the small polari- zation rotation angle. A sensitivity of enhancement of one order of magnitude has been achieved using differ- ential detection based on Faraday modulation.

Numerical and Experimental Analysis of the Hydrodynamic Performance of a Three-Dimensional Finite-Length Rotating Cylinder

The hydrodynamic performance of a three-dimensional finite-length rotating cylinder is studied by means of a physical tank and numerical simulation.First,according to the identified influencing factors,a hydrodynamic performance test of the rotating cylinder was carried out in a circulating water tank.In order to explore the changing law of hydrodynamic performance with these factors,a particle image velocimetry device was used to monitor the flow field.Subsequently,a computational field dynamics numerical simulation method was used to simulate the flow field,followed by an analysis of the effects of speed ratio,Reynolds number,and aspect ratio on the flow field.The results show that the lift coefficient and drag coefficient of the cylinder increase first and then decrease with the increase of the rotational speed ratio.The trend of numerical simulation and experimental results is similar.

弹性转动约束边界组合梁高腹板加劲肋设置

通过构建组合梁腹板的转动约束边界计算模型,采用里兹能量法推导了弹性转动约束边界刚性加劲和柔性加劲状态下加劲板的屈曲应力计算公式.在此基础上,获得组合梁受边界约束影响的纵向加劲肋临界刚度和最优位置的计算公式.理论推导结果与有限元分析结果符合良好,证明本分析方法正确.结合算例对本方法和现行规范进行对比分析,结果表明:采用本方法设计钢-混组合梁高腹板纵向加劲肋,相比现行规范可以显著提高腹板屈曲荷载,有效降低材料消耗,更具经济性和合理性.