用DCTT088对在线流量计的检测

本文叙述了用DCT7088便携式超声波流量计对在线流量计进行比对测试的方法，及对其测试中易出现的问题及对策进行了探讨。     

夹装式超声波流量计的发展与前景

本文综述了夹装式超声波流量计的发展过程，介绍了国外最新技术，展望了未来的发展方向，可供我国从事超声波流量计的研究人员参考。     

超声波流量计的测量原理及误差分析

超声波流量计是一种非接触式测量仪表，由一次传感元件和二次显示仪表组成。它具有安装方便，无须对管道进行机械加工，不影响被测介质的流态，节约能源等优点。从管壁外测量管道内流动液体的流量是其它测量方法所不能及的特点，在大流量测量时其优点尤为明显。本文就时差法超声波流量计的应用及误差分析做一介绍。1工作原理时差法超声波流量计测量流量是目前应用较为广泛的方法，其测量对象主要是自来水、地下水、海水、轻质油等单一均匀的介质。它是通过安装在管道外壁的两只传感器相互发射和接收超声波信号，根据超声波在顺流方向和逆流…     

用FLB便携式超声波流量计对在线流量计进行比对测试方法探讨

本文阐述了用FLB便携式超声波流量计，对在线流量计进行周期性比对测试的方法及问题探讨。     

超声波流量计现场标定方法

超声波流量计近年来在冶金行业得到了大范围的推广使用，收到了非常好的效果，受到了现场管理人员的欢迎。但目前普遍存在一个问题，超声波流量计在使用一段时间后如何校验及标定，以保证在线计量精度。来冶公司选用了唐山大方电子技术开发公司的LCZ—80型超声波流量计，对大管道供水系统进行在线计量，并在生产实践中总结出了一套行之有效的现场校验及标定方法（容积法），非常方便可行。1操作步骤（见图1）图1容积法标定贮水池示意图（1）标定前将贮水池充满水后停水泵，然后将所有进、排水通道关闭。（2）用皮尺或钢尺精确测量水泵抽水…     

超声波流量计中的数据处理

在超声波测量系统中，利用相关技术来处理采集所得数据信号是一种非常普遍的方法。本文采用了相关的直接法和快速法来处理数据，还提出了一种与相关类似的数据处理方法，最后给出了３种方法对超声流量测量的数据处理结果。     

超声波流量计在能源检测中的选型及应用

超声波流量计是一种利用超声波脉冲来测量流体的速度式流量仪表。文章主要讨论用于测量封闭管道液体流量的便携式超声波流量计,对时差式超声波流量计和多谱勒式超声波流量计进行了研究分析,结合多年的实际应用经验,系统阐述了超声波流量计的工作原理;从仪表性能、被测介质性质等方面总结了选用超声波流量计的原则,并对应中如何选择布置测点、安装、维护提出具体建议,为用户合理选择和应用超声波流量计提供了一些可以借鉴的经验和方法。     

用DCT7088对在线流量计的检测

本文叙述了超声波流量计的检测原理,用DCTT088便携式超声波流量计对在线流量计进行比对测试的方法,及对其测试中易出现的问题及对策进行了探讨.     

气体超声波流量计在长庆气田贸易计量中的应用

本文主要阐述了超声波流量计的测量原理、优点、以及在天然气计量上的具体应用效果,阐明了其维护方法,并对应用提出几点建议,总结说明气体超声波流量计用于贸易计量值得大力推广.     

超声波流量测量技术及发展

本文叙述了超声波流量测量的原理、基本测量方法以及传统的多普勒和时差法超声波流量计的缺陷和测量局限性，分析了超声波流量测量最新进展所采取的新的测量技术和方法，并介绍了超声波相关流量计的原理和技术特点．     

佩戴头盔模拟飞行8h的飞行耐力试验

目的:测定飞行员长时间(8h)模拟飞行时,佩戴飞行头盔对其飞行耐力的影响,为飞行头盔设计改进和使用提供依据。方法:按受试者佩戴头盔的重量(1.7 kg与2.0 kg)和任务负荷(仅提供影视音乐节目与模拟航线飞行)的不同将试验分为3组,观察记录受试者的主诉和表现。结果:受试者反映的问题,主要是闷热和压痛。为减轻闷热和压痛,受试者不断地调整头盔。闷热、压痛和调整头盔频次与时间进程相关,闷热出现在1h-3h,压痛出现在4-7h。因头盔重量和任务负荷不同,各组受试者的主诉和调整头盔频次有显著性差异。结论:头盔重量以及任务负荷等对飞行耐受能力有重大影响:头盔增重、任务负荷增加,加快了闷热和压痛的生成。频繁地调整头盔是缓解闷热和压痛的主要行为表现。相关测量结果为飞行头盔设计改进和使用提供了重要依据。     

The evolution of darker wings in seabirds in relation to temperature-dependent flight efficiency

Seabirds have evolved numerous adaptations that allow them to thrive under hostile conditions. Many seabirds share similar colour patterns, often with dark wings, suggesting that their coloration might be adaptive. Interestingly, these darker wings become hotter when birds fly under high solar irradiance, and previous studies on aerofoils have provided evidence that aerofoil surface heating can affect the ratio between lift and drag, i.e. flight efficiency. However, whether this effect benefits birds remains unknown. Here, we first used phylogenetic analyses to show that strictly oceanic seabirds with a higher glide performance (optimized by reduced sink rates, i.e. the altitude lost over time) have evolved darker wings, potentially as an additional adaptation to improve flight. Using wind tunnel experiments, we then showed that radiative heating of bird wings indeed improves their flight efficiency. These results illustrate that seabirds may have evolved wing pigmentation in part through selection for flight performance under extreme ocean conditions. We suggest that other bird clades, particularly long-distance migrants, might also benefit from this effect and therefore might show similar evolutionary trajectories. These findings may also serve as a guide for bioinspired innovations in aerospace and aviation, especially in low-speed regimes.     

Active and passive stabilization of body pitch in insect flight

Flying insects have evolved sophisticated sensory–motor systems, and here we argue that such systems are used to keep upright against intrinsic flight instabilities. We describe a theory that predicts the instability growth rate in body pitch from flapping-wing aerodynamics and reveals two ways of achieving balanced flight: active control with sufficiently rapid reactions and passive stabilization with high body drag. By glueing magnets to fruit flies and perturbing their flight using magnetic impulses, we show that these insects employ active control that is indeed fast relative to the instability. Moreover, we find that fruit flies with their control sensors disabled can keep upright if high-drag fibres are also attached to their bodies, an observation consistent with our prediction for the passive stability condition. Finally, we extend this framework to unify the control strategies used by hovering animals and also furnish criteria for achieving pitch stability in flapping-wing robots.     

Controlling roll perturbations in fruit flies

Owing to aerodynamic instabilities, stable flapping flight requires ever-present fast corrective actions. Here, we investigate how flies control perturbations along their body roll angle, which is unstable and their most sensitive degree of freedom. We glue a magnet to each fly and apply a short magnetic pulse that rolls it in mid-air. Fast video shows flies correct perturbations up to 100° within 30 ± 7 ms by applying a stroke-amplitude asymmetry that is well described by a linear proportional–integral controller. For more aggressive perturbations, we show evidence for nonlinear and hierarchical control mechanisms. Flies respond to roll perturbations within 5 ms, making this correction reflex one of the fastest in the animal kingdom.     

Lift enhancement by bats' dynamically changing wingspan

This paper elucidates the aerodynamic role of the dynamically changing wingspan in bat flight. Based on direct numerical simulations of the flow over a slow-flying bat, it is found that the dynamically changing wingspan can significantly enhance the lift. Further, an analysis of flow structures and lift decomposition reveal that the elevated vortex lift associated with the leading-edge vortices intensified by the dynamically changing wingspan considerably contributed to enhancement of the time-averaged lift. The nonlinear interaction between the dynamically changing wing and the vortical structures plays an important role in the lift enhancement of a flying bat in addition to the geometrical effect of changing the lifting-surface area in a flapping cycle. In addition, the dynamically changing wingspan leads to the higher efficiency in terms of generating lift for a given amount of the mechanical energy consumed in flight.     

Vision-based flight control in the hawkmoth Hyles lineata

Vision is a key sensory modality for flying insects, playing an important role in guidance, navigation and control. Here, we use a virtual-reality flight simulator to measure the optomotor responses of the hawkmoth Hyles lineata, and use a published linear-time invariant model of the flight dynamics to interpret the function of the measured responses in flight stabilization and control. We recorded the forces and moments produced during oscillation of the visual field in roll, pitch and yaw, varying the temporal frequency, amplitude or spatial frequency of the stimulus. The moths’ responses were strongly dependent upon contrast frequency, as expected if the optomotor system uses correlation-type motion detectors to sense self-motion. The flight dynamics model predicts that roll angle feedback is needed to stabilize the lateral dynamics, and that a combination of pitch angle and pitch rate feedback is most effective in stabilizing the longitudinal dynamics. The moths’ responses to roll and pitch stimuli coincided qualitatively with these functional predictions. The moths produced coupled roll and yaw moments in response to yaw stimuli, which could help to reduce the energetic cost of correcting heading. Our results emphasize the close relationship between physics and physiology in the stabilization of insect flight.     

The influence of sensory delay on the yaw dynamics of a flapping insect

In closed-loop systems, sensor feedback delays may have disastrous implications for performance and stability. Flies have evolved multiple specializations to reduce this latency, but the fastest feedback during flight involves a delay that is still significant on the timescale of body dynamics. We explored the effect of sensor delay on flight stability and performance for yaw turns using a dynamically scaled robotic model of the fruitfly, Drosophila. The robot was equipped with a real-time feedback system that performed active turns in response to measured torque about the functional yaw axis. We performed system response experiments for a proportional controller in yaw velocity for a range of feedback delays, similar in dimensionless timescale to those experienced by a fly. The results show a fundamental trade-off between sensor delay and permissible feedback gain, and suggest that fast mechanosensory feedback in flies, and most probably in other insects, provide a source of active damping which compliments that contributed by passive effects. Presented in the context of these findings, a control architecture whereby a haltere-mediated inner-loop proportional controller provides damping for slower visually mediated feedback is consistent with tethered-flight measurements, free-flight observations and engineering design principles.     

Stable hovering of a jellyfish-like flying machine

Ornithopters, or flapping-wing aircraft, offer an alternative to helicopters in achieving manoeuvrability at small scales, although stabilizing such aerial vehicles remains a key challenge. Here, we present a hovering machine that achieves self-righting flight using flapping wings alone, without relying on additional aerodynamic surfaces and without feedback control. We design, construct and test-fly a prototype that opens and closes four wings, resembling the motions of swimming jellyfish more so than any insect or bird. Measurements of lift show the benefits of wing flexing and the importance of selecting a wing size appropriate to the motor. Furthermore, we use high-speed video and motion tracking to show that the body orientation is stable during ascending, forward and hovering flight modes. Our experimental measurements are used to inform an aerodynamic model of stability that reveals the importance of centre-of-mass location and the coupling of body translation and rotation. These results show the promise of flapping-flight strategies beyond those that directly mimic the wing motions of flying animals.     

Elytra boost lift,but reduce aerodynamic efficiency in flying beetles

Flying insects typically possess two pairs of wings. In beetles, the front pair has evolved into short, hardened structures, the elytra, which protect the second pair of wings and the abdomen. This allows beetles to exploit habitats that would otherwise cause damage to the wings and body. Many beetles fly with the elytra extended, suggesting that they influence aerodynamic performance, but little is known about their role in flight. Using quantitative measurements of the beetle''s wake, we show that the presence of the elytra increases vertical force production by approximately 40 per cent, indicating that they contribute to weight support. The wing-elytra combination creates a complex wake compared with previously studied animal wakes. At mid-downstroke, multiple vortices are visible behind each wing. These include a wingtip and an elytron vortex with the same sense of rotation, a body vortex and an additional vortex of the opposite sense of rotation. This latter vortex reflects a negative interaction between the wing and the elytron, resulting in a single wing span efficiency of approximately 0.77 at mid downstroke. This is lower than that found in birds and bats, suggesting that the extra weight support of the elytra comes at the price of reduced efficiency.