Nonlinear dynamics of a circular curved cantilevered pipe conveying pulsating fluid based on the geometrically exact model

Due to the novel applications of flexible pipes conveying fluid in the field of soft robotics and biomedicine,the investigations on the mechanical responses of the pipes have attracted considerable attention.The fluid-structure interaction(FSI)between the pipe with a curved shape and the time-varying internal fluid flow brings a great challenge to the revelation of the dynamical behaviors of flexible pipes,especially when the pipe is highly flexible and usually undergoes large deformations.In this work,the geometrically exact model(GEM)for a curved cantilevered pipe conveying pulsating fluid is developed based on the extended Hamilton's principle.The stability of the curved pipe with three different subtended angles is examined with the consideration of steady fluid flow.Specific attention is concentrated on the large-deformation resonance of circular pipes conveying pulsating fluid,which is often encountered in practical engineering.By constructing bifurcation diagrams,oscillating shapes,phase portraits,time traces,and Poincarémaps,the dynamic responses of the curved pipe under various system parameters are revealed.The mean flow velocity of the pulsating fluid is chosen to be either subcritical or supercritical.The numerical results show that the curved pipe conveying pulsating fluid can exhibit rich dynamical behaviors,including periodic and quasi-periodic motions.It is also found that the preferred instability type of a cantilevered curved pipe conveying steady fluid is mainly in the flutter of the second mode.For a moderate value of the mass ratio,however,a third-mode flutter may occur,which is quite different from that of a straight pipe system.

Propagation characteristics of the Pc3 frequency range pulsations in the cusp latitudes

Two induction magnetometers have been installed at Zhongshan Station and Davis Station, Antarctica respectively. We adopt with cross-spectral analysis technique to analyze the data of the two induction magnetometers, in June, September,December 1996 and March 1997. to investigate the Pc3 frequency range pulsation occurrence and propagation characteristics in the cusp latitudes. The results are summarized as following:At Zhongshan-Davis Stations, the Pc3 frequency range pulsations occur mainly around the local noon/ local magnetic noon and local magnetic midnight respectively. In daytime, the pulsations have a seasonal variation in amplitude, occurrence and temporal range, all of them are sma1lest in winter. But in nighttime, the pulsations have no such a variation. The pu1sation amplitude in nighttime is much larger than the one in daytime all oveI the year. The pulsation propagating direction is mainly western in daytime and irregularly in nighttime. It can be thought that the different sources of the pulsation and the ionospheric electric conductivity are mainly responsible for these characteristics.

The characteristics of Pi2 pulsations at Zhongshan Station ofAntarctica

In this paper Pi2 pulsations at Zhongshan Station of Antarctica are analyzed from October 1 - 31, 1996. Their characteristics e. g. occurrence frequency,frequency, and polarization are studied. The characteristics of Pi2 pulsations are summerized as follows: (1 ) Pi2 pulsations at Zhongshan Station usually take place from 2000 MLT to 0200 MLT; the main frequencies are between 6. 79 mHz and 13. 58mHZ; (2 ) Pi2 pulsations with low frequencies are dominent. The range of main frequencies becomes narrow at midnight; (3) The Polarization of Pi2 pulsations are almost linear; (4) About the orientation of major axes the NW-SE direction is dominent before 2200 MLT and NE-SW is dominent after 2200 MLT. The generation mechanism of Pi2 pulsations at Zhongshan Station is discussed theoretically.

Polarization characteristics of Pc3 pulsations at Zhongshan Station of Antarctica

In this paper the data of geomagnetic pulsations at Zhongshan Station from February 3 to Novernber 30 in 1996 are analyzed in ordcr to study polarization characteristics of Zhongshan Station Pc3 pulsations which comprises the cusp Pc3 pulsation and the nightside Pc3 pulsation. For the cusp Pc3 pulsation. the right-handed polarization is always dominant. But their orientation of major axes of polarizations changes with season, NW-SE is dominant in summer and NE-SW in winter. For the nightside Pc3 pulsation,the right-handed with NE-SW is always dominant before midnight. But the left-handed with the mixing orientation of major axes is dominant in summer and the NE-SW with the mixing polarization sense is dominant in winter after midnight. It means that the two types of Zongshan Station Pc3 pulsations have different sources.

Characteristics of Pc3 pulsations at Great Wall Station,Antarctica

In this paper Pc3 pulsations at Great Wall Station of Antarctica are analyzed statistically from August 16 to November 20,1990.The occurrence frequency,frequency and polarization are studied for Pc3 pulsation events.The mechanisms of excitation and propagation of Pc3 pulsations at Great Wall Station are discussed theoretically.

The characteristics of Pi2 pulsations at Great Wall Station,Antarctica

In this paper Pi2 pulsation events at Great Wall Station of Antarctica are analyzed from August 16,1990 to November 20,1990.Their main characteristics e. g.occurrence frequency, frequency,and polarizations are recognize. The mechanism of excitation for Pi2 pulsations at Great Wall Station is here discussed theoretically.

Analysis of periodic pulsating nanofluid flow and heat transfer through a parallel-plate channel in the presence of magnetic field

In this paper,we focus on the two-dimensional pulsating nanofluid flow through a parallel-plate channel in the presence of a magnetic field.The pulsating flow is produced by an applied pressure gradient that fluctuates with a small amplitude.A kind of proper transformation is used so that the governing equations describing the momentum and thermal energy are reduced to a set of non-dimensional equations.The analytical expressions of the pulsating velocity,temperature,and Nusselt number of nanofluids are obtained by the perturbation technique.In the present study,the effects of the Cu-H2O and Al_(2)O_(3)-H2O nanofluids on the flow and heat transfer in pulsating flow are compared and analyzed.The results show that the convective heat transfer effect of Cu-H2O nanofluids is better than that of Al_(2)O_(3)-H2O nanofluids.Also,the effects of the Hartmann number and pulsation amplitude on the velocity,temperature,and Nusselt number are examined and discussed in detail.The present work indicates that increasing the Hartmann number and pulsation amplitude can enhance the heat transfer of the pulsating flow.In addition,selecting an optimal pulsation frequency can maximize the convective heat transfer of the pulsating flow.Therefore,improved understanding of these fundamental mechanisms is conducive to the optimal design of thermal systems.

Mid-Latitude Pc1, 2 Pulsations Induced by Magnetospheric Compression in the Maximum and Early Recovery Phase of Geomagnetic Storms

We investigate the properties of interplanetary inhomogeneities generating long-lasting mid-latitude Pc1, 2 geomagnetic pulsations. The data from the Wind and IMP 8 spacecrafts, and from the Mondy and Borok midlatitude magnetic observatories are used in this study. The pulsations under investigation develop in the maximum and early recovery phase of magnetic storms. The pulsations have amplitudes from a few tens to several hundred pT and last more than seven hours. A close association of the increase (decrease) in solar wind dynamic pressure (Psw) with the onset or enhancement (attenuation or decay) of these pulsations has been established. Contrary to high-latitude phenomena, there is a distinctive feature of the interplanetary inhomogeneities that are responsible for generation of long-lasting mid-latitude Pc1,2. It is essential that the effect of the quasi-stationary negative Bz-component of the interplanetary magnetic field on the magnetosphere extends over 4 hours. Only then are the Psw pulses able to excite the above-mentioned type of mid-latitude geomagnetic pulsations. Model calculations show that in the cases under study the plasmapause can form in the vicinity of the magnetic observatory. This implies that the existence of an intense ring current resulting from the enhanced magnetospheric convection is necessary for the Pc1, 2 excitation. Further, the existence of the plasmapause above the observation point (as a waveguide) is necessary for long-lasting Pc1 waves to arrive at the ground.

Real-time observation of soliton pulsation in net normal-dispersion dissipative soliton fiber laser

We present experimental observations of soliton pulsations in the net normal-dispersion fiber laser by using the dispersive Fourier transform(DFT) technique. According to the pulsating characteristics, the soliton pulsations are classified as visible and invisible soliton pulsations. The visible soliton pulsation is converted from single-into dual-soliton pulsation with the common characteristics of energy oscillation and bandwidth breathing. The invisible soliton pulsation undergoes periodic variation in the spectral profile and peak power but remains invariable in pulse energy. The reason for invisible soliton pulsation behavior is periodic oscillation of the pulse inside the soliton molecule. These results could be helpful in deepening our understanding of the soliton pulsation phenomena.

Nonlinear Dynamics of Viscoelastic Pipe Conveying Pulsating Fluid Subjected to Base Excitation

Based on the Euler-Bernoulli beam theory and Kelvin-Voigt model,a nonlinear model for the transverse vibration of a pipe under the combined action of base motion and pulsating internal flow is established.The governing partial differential equation is transformed into a nonlinear system of fourth-order ordinary differential equations by using the generalized integral transform technique(GITT).The effects of the combined excitation of base motion and pulsating internal flow on the nonlinear dynamic behavior of the pipe are investigated using a bifurcation diagram,phase trajectory diagram,power spectrum diagram,time-domain diagram,and Poincare map.The results show that the base excitation amplitude and frequency significantly affect the dynamic behavior of the pipe system.Some new resonance phenomena can be observed,such as the period-1 motion under the base excitation or the pulsating internal flow alone becomes the multi-periodic motion,quasi-periodic motion or even chaotic motion due to the combined excitation action.

Pulsation Analysis of High-AmplitudeδScuti Stars with TESS

In this work,the pulsation analysis is performed on 83 high-amplitudeδScuti stars(HADS),which have been observed by the Transiting Exoplanet Survey Satellite.The results show that 49 of these HADS show single-mode pulsation,27 of them show radial double-modes pulsation(in which 22 of them pulsate with the fundamental and first overtone modes and five of them pulsate with the first and second overtone modes),and seven of them show radial triple-modes pulsation(three of which are newly confirmed triple-mode HADS).The histogram of the fundamental periods and the ratios between the fundamental and first overtone periods show bimodal structures,which might be caused by the stellar evolution in this specific phase.Most of the radial triple-mode HADS have a fundamental amplitude of 41-54 mmag,and 50%of them have similar amplitudes of the fundamental and first overtone pulsation modes.All these hints require further confirmation not only in observations with more HADS samples,but also in theoretical models with suitable treatments of stellar evolution and pulsation.

Assessment of the Implementation of Energy Conservation Opportunities Arising from Energy Audits;A Study of Four-Star and Five-Star Hotels in Nairobi Kenya

This study assesses the implementation of energy conservation opportunities in four-star and five-star hotels in Nairobi. The Covid-19 pandemic had a significant impact on the Hospitality Industry. Currently, there is a growing inclination to furnish guests with superior and sustainable services in an energy-efficient and eco-friendly way. Comprehensive research was conducted from energy audits gathered from the establishments and contracted auditing companies, on top of this, hotel staff were given digital questionnaires. To add to the data, the researcher surveyed the hotels with engineering managers. The Energy Audits found that all 10 hotels had adopted Energy Conservation Opportunities (ECOs). After further analysis, the mean adoption rate of Energy Conservation Opportunities (ECOs) during the past three years was 55.83%, which was below the aim of 100%. According to studies, hotel staff manages energy to cut costs. The researcher found that hotels use up a lot of energy. However, they have conservation potential, depending on government policies, costs, ease of implementation, and management commitment to sustainable practices. Essentially, Energy Conservation Opportunities (ECOs) reduce energy expenditures and boost reliable revenues, especially during high energy prices and uncertainty.

单分散Al-4.5wt%Cu合金粒子的制备与凝固过程模拟

使用脉冲微孔喷射法制备了粒径可控的单分散Al-4.5wt%Cu液滴,对液滴凝固成的粒子进行分析表征。结果表明:该粒子具有粒径均一、高球形度、热履历一致的优点。随着粒径的增长,粒子的内部微观结构由胞状晶变为树枝晶。建立了粒子凝固过程的传热数值计算模型,分析了粒子下落中温度、温度梯度变化及冷却速率与粒子微观组织形貌的关系。在本实验条件下,310.0μm粒子内部凝固组织为胞状晶,冷却速率为771.71 K/s;485.1μm粒子内部凝固组织为树枝晶,冷却速率为382.40 K/s。

基于多目标遗传算法的斜盘式轴向柱塞泵低脉动结构优化设计

由于轴向柱塞泵的非对称结构特性,其输出压力和输出流量存在脉动特性,对液压系统的输出稳定性和可靠性造成影响,因此提出了一种基于多目标遗传算法的斜盘式轴向柱塞泵低脉动结构优化设计方法。首先,通过CFD(computational fluid dynamics,计算流体动力学)仿真分析方法,对轴向柱塞泵上/下死点位的压力-流量脉动的产生机理进行了分析;其次,对阻尼槽结构参数对轴向柱塞泵输出压力-流量脉动的影响规律进行了分析,构建了阻尼槽结构的多目标优化模型;最后,求解了低脉动阻尼槽结构。优化后的结构参数:阻尼槽半径为2.21 mm,阻尼槽长度为10.32 mm,阻尼槽错配角为16.54°。优化后压力脉动率为0.59%,相比于优化前的0.75%降低了0.16%,脉动幅值为0.25 MPa;优化后流量脉动率为12.02%,相比于优化前的5.61%降低了43.59%。研究结果为轴向柱塞泵低脉动结构的优化设计提供了有效的理论支持和实践指导。

叶片数对无轴泵喷推进器性能的影响

为丰富无轴泵喷推进器噪声性能优化理论,研究了叶片数对无轴泵喷推进器性能的影响,重点探究了不同叶片数下无轴泵喷推进器内的压力脉动变化规律。基于计算流体力学中的有限体积法离散RANS方程,应用RNG k-ε湍流模型封闭计算模型,采用SIMPLEC进行压力-速度耦合,对不同叶片数下的无轴泵喷推进器内部流场进行了非定常数值模拟计算,并对计算结果进行了详细的对比分析。研究结果表明:随叶片数的增加,无轴泵喷推进器模型的扬程、效率和推力均逐渐增大,叶片表面压力分布更加均匀,叶轮轮缘和中部的压力脉动均明显降低,叶轮进出口主频处的压力脉动幅值从轮缘向中心逐渐减小。

基于声振传递的飞行器噪声振动环境预示方法研究

针对高速飞行器飞行条件下的噪声、振动环境恶劣、复杂、难预示的问题,提出了基于声振传递的飞行器飞行条件下的噪声、振动环境预示方法。采用数值仿真、脉动压力风洞试验或工程分析等方法,获取飞行器在典型工况下的舱外脉动压力场;通过噪声试验或声振耦合仿真分析的方法,得到飞行器声振传递特性;根据获得的舱外脉动压力和声振能量传递特性,结合具体飞行参数得到实际飞行条件下的飞行器声振预示环境。采用该方法对某飞行器开展了振动环境预示研究,经地面及飞行试验验证振动环境量级预示精度可达1.6 dB。提出的基于声振传递的飞行声振环境预示方法可以广泛应用在导弹、火箭等飞行器的精细化环境设计中,对于提高飞行器总体性能、环境适应性和飞行可靠性具有重要的工程意义。

灯泡贯流式水轮机增减负荷动态特性分析

水轮机频繁经历变负荷工况转换过程,使得机组在较短时间内工作参数急剧变化,严重影响电站稳定运行。该研究以某贯流式水轮机为研究对象,在考虑自由液面和水体重力的情况下,采用动网格技术对贯流式水轮机相同出力范围下的减、增负荷过渡过程的动态特性进行分析。研究结果表明:由于增负荷和减负荷过渡过程的起始工况导致起始流动状态不同,因此在相同出力时,机组内的流动分布不同,减负荷过程尾水管内的涡流面积及强度明显小于增负荷工况,且尾水管涡带尺度也明显小于增负荷过程;相比于增负荷过程,减负荷过程中转轮叶片大范围的低压区极易引发空化;机组内的水压力脉动主要以尾水管涡带引起的0.1f_n(f_n为转频)低频压力脉动和转轮的旋转引起3f_n的高频压力脉动为主,增负荷过程的压力脉动幅值明显大于减负荷过程,两种压力脉动共同作用,使得贯流式水轮机主要振动区域集中于转轮。研究结果对贯流式水轮机的设计与运行具有一定的指导意义。

航行体水下发射过程气幕降载特性

水下发射过程中在筒口附近形成气幕通道,可有效降低航行体出筒过程中表面高频脉动载荷.基于流体体积(VOF)均质多相流理论、标准的RNG k-ε湍流模型及重叠网格技术,研究筒口气幕对航行体表面脉动载荷的影响规律,分析气幕环境下的流场结构及流体动力演变特性,对比不同横流强度、燃气质量流率下气幕流场结构演变和出筒降载效果.结果表明,航行体出筒过程中,喷嘴喷出的高速燃气近似覆盖了航行体表面,并逐渐在发射筒口周围形成一个气体通道,显著降低了航形体表面载荷;有气幕条件下,航行体所受力矩与表面载荷均出现明显降低,其中所受力矩峰值降低了80.3%,航行体表面压力峰值最大降低了81.2%;提高横流速度,航行体表面压力峰值最大增加了56.7%;在质量流率由2 kg/s提高到16 kg/s时,航行体所受力矩降低了80.8%,表面压力峰值最大降低了82.8%.

基于能量守恒定律对涡轮流量计的脉动误差上限的估算

在管道输运当中,非稳态流会使涡轮流量计的计量结果产生偏差。为了指导脉动流工况下的涡轮流量计选型和修正,需估算脉动工况对涡轮流量计产生的最大脉动误差。忽略流体压力和温度变化影响,基于涡轮流量计的动态特性和能量守恒定律,在一个脉动周期内计算脉动流和定常流对叶轮的做功比值,推导得出正弦脉动流误差上限公式。基于6DOF模型和UDF建立了涡轮流量计CFD仿真模型,搭建了空气流实验平台,以工作级流量标准装置作为标准表,被校表和标准表间采用内置整流器的管段相连。对比定常流下的流量值,计算各脉动工况下的误差限值。综合各脉动工况点,上限公式与CFD仿真所得脉动误差上限的最大差值为0.281%,与空气流实验所得脉动误差上限的最大差值为0.224%。经CFD仿真和空气流实验结果对比验证,脉动误差上限公式较为准确,可以直接用于脉动频率大于10 Hz的工况下误差值的估计和修正。