Study on the Improvement in the One Dimensional Mathematical Model of the Air Drag in Melt Blowing Process

The one dimensional mathematical model of the air drag in melt blowing process, which had been put forward by Uyttendaele and Shambaugh is improved. The influence of the density and the specific heat capacity of polymer melt at constant pressure changing with polymer temperature on fiber diameter are studied. The power - law model is introduced as the constitutive equation. The influences of polymer volume flow rate, initial polymer temperature, initial air velocity and initial air temperature on fiber diameter are discussed.

Comparison of Microbubble and Air Layer Injection with Porous Media for Drag Reduction on a Self-propelled Barge Ship Model

Ship resistance issues are related to fuel economy,speed,and cost efficiency.Air lubrication is a promising technique for lowering hull frictional resistance as it is supposed to modify the energy in the turbulent boundary layer and thereby reduce hull friction.In this paper,the objective is to identify the optimum type of air lubrication using microbubble drag reduction(MBDR)and air layer drag reduction(ALDR)techniques to reduce the resistance of a 56-m Indonesian self-propelled barge(SPB).A model with the following dimensions was constructed:length L=2000 mm,breadth B=521.60 mm,and draft T=52.50 mm.The ship model was towed using standard towing tank experimental parameters.The speed was varied over the Froude number range 0.11–0.31.The air layer flow rate was varied at 80,85,and 90 standard liters per minute(SLPM)and the microbubble injection coefficient over the range 0.20–0.60.The results show that the ship model using the air layer had the highest drag reduction up to a maximum of 90%.Based on the characteristics of the SPB,which operates at low speed,the optimum air lubrication type to reduce resistance in this instance is ALDR.

Experimental Study of Air Layer Drag Reduction with Bottom Cavity for A Bulk Carrier Ship Model

Air lubrication by means of a bottom cavity is a promising method for ship drag reduction. The characteristics of the bottom cavity are sensitive to the flow field around the ship hull and the effect of drag reduction, especially the depth of the bottom cavity. In this study, a ship model experiment of a bulk carrier is conducted in a towing tank using the method of air layer drag reduction (ALDR) with different bottom cavity depths. The shape of the air layer is observed, and the changes in resistance are measured. The model experiments produce results of approximately 20% for the total drag reduction at the ship design speed for a 25-mm cavity continuously supplied with air at Cq = 0.224 in calm water, and the air layer covers the whole cavity when the air flow rate is suitable. In a regular head wave, the air layer is easily broken and reduces the drag reduction rate in short waves, particularly when λ/Lw1 is close to one;however, it still has a good drag reduction effect in the long waves.

基于大气阻力实时辨识的Drag-free卫星最优控制研究

研究了基于大气阻力实时辨识的Drag-free卫星最优控制。将Drag-free卫星和其内部的验证质量等效为两颗内、外编队卫星并建立动力学方程,推导了基于卫星和验证质量的相对运动状态观测值反演大气阻力的算法。建立了状态最优调节器模型,采用动态规划求解经典的二次型最优控制。对低轨圆轨道Drag-free卫星的仿真计算结果表明方法的求解精度较高,计算消耗较小。

95000 t大型船舶喷气节能及水翼导流技术

为探讨大型船舶喷气的节能效果以及分析水翼导流技术的可行性与关键问题,采用Mixture两相流模型和RANS k-ε湍流模型相结合,计入喷气消耗的功率,结合“净减阻率”的概念,构建大型平底气泡船粘性流场数值计算模型,探讨攻角、翼面到船底的距离、喷气口位置对导流效果的影响。数值计算结果表明,采用水翼导流可大幅降低喷气消耗功率,提高节能效果;距离与弦长之比d/C=0.3、攻角为6°~8°、喷气口至导缘的距离x/C=0.28时,水翼的综合导流效果最佳。直接向大型船舶底部喷气,能较大幅度降低船舶的航行阻力,但因喷气消耗的功率过大,节能效果不是特别明显。当采用水翼导流技术后,喷气的净减阻率大幅提高,由此可知,气层减阻技术应用于大型船舶的节能减排有效可行。

Damping of a Simple Pendulum Due to Drag on Its String

A basic classical example of simple harmonic motion is the simple pendulum, consisting of a small bob and a massless string. In a vacuum with zero air resistance, such a pendulum will continue to oscillate indefinitely with a constant amplitude. However, the amplitude of a simple pendulum oscillating in air continuously decreases as its mechanical energy is gradually lost due to air resistance. To this end, it is generally perceived that the main role in the dissipation of mechanical energy is played by the bob of the pendulum, and that the string’s contribution is negligible. The purpose of this research is to experimentally investigate the merit of this assumption. Thus, we experimentally investigate the damping of a simple pendulum as a function of its string diameter and compare that to the contribution from its bob. We find out that although in some cases the effect of the string might be small or even negligible, in general the string can play a significant role, and in some cases even a greater role on the damping of the pendulum than its bob.

Sensitivity Analysis of Air Gap Motion with Respect to Wind Load and Mooring System for Semi-Submersible Platform Design

A design of semi-submersible platform is mainly based on the extreme response analysis due to the forces experienced by the components during lifetime. The external loads can induce the extreme air gap response and potential deck impact to the semi-submersible platform. It is important to predict air gap response of platforms accurately in order to check the strength of local structures which withstand the wave slamming due to negative air gap. The wind load cannot be simulated easily by model test in towing tank whereas it can be simulated accurately in wind tunnel test. Furthermore, full scale simulation of the mooring system in model test is still a tuffwork especially the stiffness of the mooring system. Owing to the above mentioned problem, the model test results are not accurate enough for air gap evaluation. The aim of this paper is to present sensitivity analysis results of air gap motion with respect to the mooring system and wind load for the design of semi-submersible platform. Though the model test results are not suitable for the direct evaluation of air gap, they can be used as a good basis for tuning the radiation damping and viscous drag in numerical simulation. In the presented design example, a numerical model is tuned and validated by ANSYS AQWA based on the model test results with a simple 4 line symmetrical horizontal soft mooring system. According to the tuned numerical model, sensitivity analysis studies of air gap motion with respect to the mooring system and wind load are performed in time domain. Three mooring systems and five simulation cases about the presented platform are simulated based on the results of wind tunnel tests and sea-keeping tests. The sensitivity analysis results are valuable for the floating platform design.

Air Plasma Mitigation of Shock Wave

Shock wave is a detriment in the development of supersonic aircrafts;it increases flow drag as well as surface heating from additional friction;it also initiates sonic boom on the ground which precludes supersonic jetliner to fly overland. A shock wave mitigation technique is demonstrated by experiments conducted in a Mach 2.5 wind tunnel. Non-thermal air plasma generated symmetrically in front of a wind tunnel model and upstream of the shock, by on-board 60 Hz periodic electric arc discharge, works as a plasma deflector, it deflects incoming flow to transform the shock from a well-defined attached shock into a highly curved shock structure. In a sequence with increasing discharge intensity, the transformed curve shock increases shock angle and moves upstream to become detached with increasing standoff distance from the model. It becomes diffusive and disappears near the peak of the discharge. The flow deflection increases the equivalent cone angle of the model, which in essence, reduces the equivalent Mach number of the incoming flow, manifesting the reduction of the shock wave drag on the cone. When this equivalent cone angle exceeds a critical angle, the shock becomes detached and fades away. This shock wave mitigation technique helps drag reduction as well as eliminates sonic boom.

Computational Solution to the Problems of Projectile Motion under Significant Linear Drag Effect

This paper investigates the computational solution to the problem of projectile motion under a significant linear drag effect. The drag force acting on the particle within the medium of propagation is proportional to the cross-section area of the projectile, the velocity of the particle, and the medium’s density. From zero air resistance force (vacuum) the problems are well known with solutions, but with air resistance (drag force) the problems have no exact analytical solutions which lead to most of the significant scientific research works using numerical methods. Therefore, this study aims to present the analysis of the computational modelling of drag force exerted by the surrounding medium on the linear motion. However, the horizontal and vertical components of differential equations of motion were derived and characterized from the solutions governed by Newton’s 2nd law of motion. The baseball features were presented as the projectile (object) in this work. In addition, the numerical computational results were received from FreeMat. The results were discussed and compared with those from the vacuum. Moreover, the displacements, velocities, range, and trajectories of the projectile were all discussed and a conclusion was made.

气体润滑减阻研究综述

在我国“碳达峰、碳中和”战略背景下,气体润滑减阻作为一种流动控制节能与降碳方法,可有效降低船舶航行阻力,对我国船舶及航运业的低碳发展意义重大。本文介绍了气体润滑减阻研究的国内外背景及意义,阐述了气体润滑减阻的定义及分类方式,特别是提出了基于气液两相界面形态与减阻机理的离散气泡减阻和连续气层减阻分类方式,并在此基础上分别梳理了离散气泡减阻和连续气层减阻在减阻特性、减阻机理、两相流态及其影响因素等方面的进展情况,总结并展望了气体润滑减阻的研究现状和该领域的未来发展趋势。

Shock Wave Mitigation by Air Plasma Deflector

When the spacecraft flies much faster than the sound speed (~1200 km/h), the airflow disturbances deflected forward from the spacecraft cannot get away from the spacecraft and form a shock wave in front of it. Shock waves have been a detriment for the development of supersonic aircrafts, which have to overcome high wave drag and surface heating from additional friction. Shock wave also produces sonic booms. The noise issue raises environmental concerns, which have precluded routine supersonic flight over land. Therefore, mitigation of shock wave is essential to advance the development of supersonic aircrafts. A plasma mitigation technique is studied. A theory is presented to show that shock wave structure can be modified via flow deflection. Symmetrical deflection evades the need of exchanging the transverse momentum between the flow and the deflector. The analysis shows that the plasma generated in front of the model can effectively deflect the incoming flow. A non-thermal air plasma, generated by on-board 60 Hz periodic electric arc discharge in front of a wind tunnel model, was applied as a plasma deflector for shock wave mitigation technique. The experiment was conducted in a Mach 2.5 wind tunnel. The results show that the air plasma was generated symmetrically in front of the wind tunnel model. With increasing discharge intensity, the plasma deflector transforms the shock from a welldefined attached shock into a highly curved shock structure with increasing standoff distance from the model;this curved shock has increased shock angle and also appears in increasingly diffused form. In the decay of the discharge intensity, the shock front is first transformed back to a well-defined curve shock, which moves downstream to become a perturbed oblique shock;the baseline shock front then reappears as the discharge is reduced to low level again. The experimental observations confirm the theory. The steady of the incoming flow during the discharge cycle is manifested by the repeat of the baseline shock front.

大尺度自航模气层减阻试验研究

[目的]旨在研究气流量、航行倾角对船底凹槽内气层保持和节能效果的影响。[方法]以一艘肥大型散货船的较大尺度缩比模型为研究对象,通过设计气层减阻自航模系统和船底凹槽方案,开展开阔水域条件下自航模气层减阻试验,研究模型正浮状态下喷气减阻效果,以及模型一定纵倾角状态下对航速和轴功率的影响。[结果]结果表明:在主机转速一定时,喷气可以明显提高自航模的航速,停止喷气后,船底凹槽内的气体仍能维持较长时间;船体艉倾角为0°~0.25°时的气层减阻效果较好,较大艉倾角时气体从自航模艏部两侧溢出,气层无法对船底实现有效覆盖,减阻效果不佳。[结论]研究结果可对气层减阻技术在肥大型船舶上的工程应用提供一定参考。

船舶气层减阻技术研究综述

随着全球生态环境变化的要求以及我国“碳达峰、碳中和”目标的提出,船舶气层减阻技术作为船舶运输手段中一种有效的节能、降碳手段,近年来备受关注。文章阐述了气层减阻技术中气层的形成过程以及工作原理;从模型试验以及理论与数值计算方面分析了船舶气层减阻技术的发展和研究现状;列举分析了国内外部分研究单位的应用实例和实际效果;针对研究和应用现状,对船舶气层减阻技术面对的问题和未来发展方向进行了展望。

Realization of non HF air plasma cutting power source based on a complexisolated inverter

On the basis of analyzing and testing of common inverting circuits, a new type inverter, which has a special inverting circuit called complex isolated, has been put forward. In turn, an applicable air plasma cutting machine has also been put into use. Testing results show that this kind inverter has lots of properties as high reliability, high efficiency, good EMC(electromagnetic compatibility) and easy operating. The complex isolated inverting circuit can be considered as a quite valuable reference for the research of high power welding inverter.

Effect of Sealing Air on Oil Droplet and Oil Film Motions in Bearing Chamber

Beating chamber is one of important components that support aero-engine rotors and research on oil droplet and oil film motions is an important part of bearing chamber lubrication and heat transfer design. Consid- ering the pressure of sealing air is an important operating condition that affects the oil droplet and oil film mo- tions, the effect of sealing air pressure on airflow in bearing chamber is investigated in this paper firstly ; and then based on the air velocity and air/wall shear force, the oil droplet moving in core air, deposition of oil droplet im- pact on wall as well as velocity and thickness of oil film are analyzed secondly; the effect of sealing air pressure on oil droplet velocity and trajectory, deposition mass and momentum, as well as oil film velocity and thickness is discussed. The work presented in this paper is conducive to expose the oil/air two phase lubrication mechanism and has certain reference value to guide design of secondary air/oil system.

PSA装置C201-3一级右列做功差原因分析及处理措施

PSA装置解析气压缩机因发现振动大和异常声音而停机,检修完毕后出现一级右列做功差的现象,结合两次试机过程,并逐项排查各影响因素后,判断为气阀本身密封面失效导致吸入性能变差。结合本次检修的拆解情况,从工艺流程和气阀改型两方面提出应对措施,以期为相关研究提供参考。

汽车滑行试验道路阻力和风阻系数不确定度分析

对汽车滑行试验过程中滑行速度进行统计学分析,发现各个轮次的滑行车速偏差近似与平均滑行车速呈线性关系。基于滑行车速,分别利用v-F方法和v-t方法拟合得到汽车的滑行阻力和风阻系数,分析其对应优化问题的凸性和滑行阻力、风阻系数的不确定度;结果表明,v-F方法对应拟合问题是凸的,而v-t方法对应的拟合问题是非凸的。在拟合道路载荷时,需要选择泛化能力较强的迭代算法,同时需要根据参数的物理意义,设置合理的初始值和约束边界,以便得到合理的拟合参数值和道路阻力;而且相比v-F方法,v-t方法得到的风阻系数不确定度更小,置信区间也更窄。另外,基于车辆滑行速度的统计规律,进行蒙特卡洛模拟,分别应用v-F和v-t方法,得到道路阻力和风阻系数近似为正态分布;结果表明,v-F方法会放大随机因素的影响,v-t方法得到的道路阻力和风阻系数均更为稳定。

滚装船空气润滑减阻机理及性能数值研究

设计一种新型空气减阻装置,基于数值模拟法和理论分析法开展船舶空气减阻机理和空气减阻性能研究。通过分析船底喷气前后船体表面湍流粘度、动力粘度、剪切力分布等关键物理量的动态变化过程,揭示了空气减阻相关机理。对比船底通气前后船体总阻力的变化,探索了空气减阻的相关性能。研究结果表明,在船底持续释放空气后,船体表面流体密度降低、湍流粘度和动力粘度降低、雷诺应力减小,导致船体摩擦阻力减小。在设计航速、较低通气速率(3.92×10^(-4)kg/s)下空气减阻性能达到了9.53%,减阻效果明显,为绿色船舶设计提供了参考。

水下高压抗润湿V型槽分级铜纳米线簇超疏水表面的减阻研究

针对水下减阻超疏水表面气层稳定性差的问题,提出了在金属铜基底上使用两步电化学沉积法,制备了一种具有V型槽结构、区室化簇状结构和微纳分级结构的铜纳米线超疏水表面,进行了水下高压气层稳定性测试和减阻测试。结果表明,该表面最高可在0.45 MPa水压下维持76%的未润湿区域。同时,该表面在平板流变仪层流减阻测试中可取得高达56%的减阻率,具有优异的减阻性能。V型槽分级铜纳米线簇超疏水表面兼具水下高压气层稳定性和减阻效果,可应用到实际船舶航行领域,为解决超疏水表面减阻应用的瓶颈问题提供方案。

船舶气泡润滑技术对螺旋桨抽吸效应的影响

基于CFD软件STAR-CCM+,以KCS船模及KP505桨模为研究对象,考虑气泡与水的相互作用力,利用船体建模的方法,基于欧拉多相流,通过改变孔内通气量、通气孔的位置和螺旋桨转速对船桨耦合的船模气泡减阻进行数值模拟。结果表明,孔位置一定时,高通气量下,气泡对螺旋桨影响更显著,使得螺旋桨产生振动与噪声,推力减小;通过改变通气孔位置可以得出,通气孔排布在船尾位置时气泡对螺旋桨影响最小;通过改变螺旋桨转速得出,螺旋桨转速越大气泡对螺旋桨影响越小。