气层减阻技术关键因素影响研究

气层减阻技术可显著降低船舶阻力、减少燃料消耗和提高船舶航速,是极具潜力的新型船舶节能减排技术。在大型低速船上应用这项技术时,由于航速低的原因,气层难以在船舶底部生成并稳定保持。针对气层减阻技术在低速船上的应用难点,以平板为研究对象,进行气层生成和稳定保持的试验研究,探讨低速状态下气层能稳定保持的关键因素。对喷气方式、喷口形式、气流量等因素展开了系列研究,获得了低速状态下具有较高减阻节能效果的喷气模式(喷气方式+喷口形式)和关键设计参数。以此为设计依据,对船模、百吨级原理样船以及沿海实船等为多种尺度的研究对象进行气层减阻方案设计,获得了较好的减阻节能效果,船模减阻率达47%,百吨级原理样船净节能11%,沿海实船净节能7%以上,验证了寻获的气层减阻关键因素的合理性和有效性,为气层减阻技术在低速船上应用提供技术支撑。

挠性卫星姿态快速机动控制

挠性卫星在快速机动中既要满足快速性要求,又要抑制挠性附件产生的振动。本文提出了一种基于非约束模态方程的方波序列控制方法,并给出了最小机动时间的方波规划方法。该方法不仅保证机动后无余振,而且满足最快机动的要求,此外,由于控制输出为方波,因而适合卫星上的喷气推力器控制模式和飞轮控制模式。最后通过数字仿真验证了方波序列控制的有效性。

Effects of different combustion modes on the thermal efficiency and emissions of a diesel pilot-ignited natural gas engine under low-medium loads

Research on dual-fuel(DF)engines has become increasingly important as engine manufacturers seek to reduce carbon dioxide emissions.There are significant advantages of using diesel pilot-ignited natural gas engines as DF engines.However,different combustion modes exist due to variations in the formation of the mixture.This research used a simulation model and numerical simulations to explore the combustion characteristics of high-pressure direct injection(HPDI),partially premixed compression ignition(PPCI),and double pilot injection premixed compression ignition(DPPCI)combustion modes under a low-medium load.The results revealed that the DPPCI combustion mode provides higher gross indicated thermal efficiency and more acceptable total hydrocarbon(THC)emission levels than the other modes.Due to its relatively good performance,an experimental study was conducted on the DPPCI mode engine to evaluate the impact of the diesel dual-injection strategy on the combustion process.In the DPPCI mode,a delay in the second pilot ignition injection time increased THC emissions(a maximum value of 4.27g/(kW·h)),decreased the emission of nitrogen oxides(a maximum value of 7.64 g/(kW·h)),increased and then subsequently decreased the gross indicated thermal efficiency values,which reached 50.4%under low-medium loads.

Rarefied planar jets into vacuum

This paper presents a fundamental gaskinetic study on high speed rarefied jets expanding into vacuum from a cluster of planar exits.Based on the corresponding exact expressions for one planar jet,this paper straightforwardly derives the combined multiple jet flowfield solutions of density and velocity components,however,for the combined temperature and pressure solutions,extra attention shall be practiced.Several direct simulation Monte Carlo simulation results are provided and they validate these analytical solutions of rarefied planar jet flows.

Novel consistency control strategy for jet dispensing

A new consistency control method for jet dispensing is proposed. First, the working parameters, namely, viscosity, supply pressure and supply time, are experimentally investigated. Then, the glue viscosity is approximated by a polynomial model using the least square method. Based on this model and temperatme control implemented using the Dahlin principle, the viscosity of the glue can be maintained at a constant value. Then, the viscosity model of the glue is applied to deriving the droplet mass as the nominal model of the temperature controller. The robustness of the temperature controller is analyzed by applying the small gain theory. The glue supply pressure controller is designed using the consistency control strategy, and the robustness is analyzed. Finall）, simulations and experiments are conducted using a jet dispensing control system. The results show that the proposed control strategy can significantly improve the droplet consistency.

TEXTOR—94中不同约束状态下的氖辐射效率

对于氖种籽放电，线性地取决于有效氖冷却率并能够被看作是氖辐射效率的一个量度的量[Δrad/ΔZeff(0)]/neo^2对于给出的装置不是一个常量，当按照运行模式[ΔPrad/ΔZeff(0)]no^2大时，在低Zeff下可有效地实现辐射功率排出，这个比值我们称作氖冷却品质，发现它不仅与等离子体边缘温度相关而且甚至更强地与放电的约束性能相关，已比较了TEXTOR－94中两种不同的离约束辐射状态：辐射改善（RI）模式（最高约束）和喷气／纯射频模式（略低约束），尽管由于输入功率水平的反馈控制使得电子温度分布在两种状态下是相似的，但是实验上已现现氖冷却品质在RI模式下比在喷气／纯射频模式下低，在用独立的诊断设备和方法确定的剩余固有碳的冷却品质中已观察到类似的特性，用自洽RITM牟模拟证明，粒子输运，尤其是边缘垂直扩散率，是在等离子体芯部给定的杂质浓度下确定边缘辐射功率水平的一个关键参数。