A study of a supersonic capsule/rigid disk-gap-band parachute system using large-eddy simulation

The aerodynamic performances and flow features of the capsule/rigid disk-gap-band(DGB)parachute system from the Mach number 1.8 to 2.2 are studied.We use the adaptive mesh refinement(AMR),the hybrid tuned center-difference and weighted essentially non-oscillatory(TCD-WENO)scheme,and the large-eddy simulation(LES)with the stretched-vortex subgrid model.The simulations reproduce complex interaction of the flow structures,including turbulent wakes and bow shocks,as well as bow shocks and expansion waves.The results show that the calculated aerodynamic drag coefficient agrees well with the previou simulation.Both the aerodynamic drag coefficient and the aerodynamic drag oscillation of the parachute system decrease with the increase of the initial Mach number of the fluid.It is found that the position and angle of the bow shock ahead of the canopy change as the Mach number increases,which makes the flow inside the canopy and the turbulent wake behind the canopy more complex and unstable.

Faster Than Sound, Daredevil Parachute Jumps from the Edge of the Space

This article discusses the kinematics of a parachutist making a very-high-altitude jump. The effect of altitude on the density of air, on the gravitational field strength of the Earth, and on the atmosphere’s temperature has been taken into account in our analysis. The well-known equations of classical mechanics governing the selected topic have been solved numerically by using the mathematical software Mathcad. Especially, the possibility of a person exceeding the speed of sound during their fall has been considered in our analysis. The effect of the sound barrier is taken into account so that the shape factor of the falling body is given as a speed-dependent function, which reaches its maximum value at Mach 1.0. The obtained results have been found to be highly consistent with the available experimental data on some high-altitude jumps. The data published on the famous jump of Captain Joseph Kittinger has been analyzed very carefully, and although our calculations reproduced the reported values for most parts, some interesting inconsistencies were also discovered. Kittinger jumped from a gondola attached to a helium-filled balloon from a record-high altitude of 102,800 ft, or 31,330 m, in August 1960. We also made numerical analysis on the high-altitude jump of Felix Baumgartner. He bailed out from his gondola at the record-high altitude of 39.0 km in October 2012.

改善缺血性心力衰竭的新选择——Parachute左心室重建术

近年来,心力衰竭（心衰）的患病率逐年增高,日渐成为严重的公共卫生问题,有临床症状患者的5年存活率与恶性肿瘤相仿。其病因众多,最常见的病因之一为急性心肌梗死[1]。临床上,尤其是前壁心肌梗死合并室壁瘤的患者更易发生缺血性心衰,左心室壁瘤可改变左室壁曲度和厚度,导致整个心脏的扩张和变形。

经皮左心室室壁瘤PARACHUTE封堵术治疗的护理

总结3例经皮左心室室壁瘤PARACHUTE封堵术治疗的护理体会。护理重点为术前规范化治疗基础疾病,改善心肾功能;术后严密监测生命体征,预防和积极处理异常情况,做好抗血小板抗凝治疗的护理,做好水化治疗护理,预防急性肾功能衰竭;治疗康复过程中重视患者主诉和心理护理,持续强化健康宣教。3例患者经治疗和护理,均治愈出院。

Study on transient aerodynamic characteristics of parachute opening process

In the research of parachute, canopy inflation process modeling is one of the most complicated tasks. As canopy often experiences the largest deformations and loa-dings during a very short time, it is of great difficulty for theoretical analysis and experimental measurements. In this paper, aerodynamic equations and structural dynamics equations were developed for describing parachute opening process, and an iterative coupling solving strategy incorpo- rating the above equations was proposed for a small-scale, flexible and flat-circular parachute. Then, analyses were carried out for canopy geometry, time-dependent pressure difference between the inside and outside of the canopy, transient vortex around the canopy and the flow field in the radial plane as a sequence in opening process. The mechanism of the canopy shape development was explained from perspective of transient flow fields during the inflation process. Experiments of the parachute opening process were conducted in a wind tunnel, in which instantaneous shape of the canopy was measured by high velocity camera and the opening loading was measured by dynamometer balance. The theoretical predictions were found in good agreement with the experimental results, validating the proposed approach. This numerical method can improve the situation of strong dependence of parachute research on wind tunnel tests, and is of significance to the understanding of the mechanics of parachute inflation process.

Flow Field Characteristics for Parachute-projectile System

In the current research for parachute flow field nowadays,the size of parachutes in previous research are so large compared with their carriers that the effects of the carriers wake flow to parachute are always neglected.Different from such large parachutes,the parachute size in this paper is on the same magnitude with the carrier,thus,the carrier can obviously affect the parachute flow field.In this paper,flow field characteristics of small parachute for projectile decelerating are researched through two approaches,namely,computational fluid dynamics（CFD） simulation and wind tunnel tests.Three parachutes with various sizes are chosen for study.Firstly,the CFD simulation of flow field around these parachutes is carried out,and then the CFD simulation of parachute-projectile systems is executed.According to the simulation results,the phenomenon is observed that in the simulations of parachutes there are two vortex-rings at the wind shadow of parachutes,however,in the second simulations of parachute-projectile systems,two additional vortex-rings emerge inside the parachutes.Due to these two inner vortex-rings,the pressure inside parachutes decreases.As a result,the drag of parachute in simulation of parachute-projectile systems is about 20% smaller compared with the prior one.In order to verify the numerical results of CFD simulations,wind tunnel tests are employed.In terms of the data of the wind tunnel tests,the CFD simulation for flow field characteristics is reasonable and feasible.The results of both CFD simulation and wind tunnel tests demonstrated the influence of projectile wake flow to parachute drag can not be neglected if the parachute size is on the same magnitude with projectile.The influence to parachute drag from the ratio of projectile diameter to parachute diameter is also analyzed both in CFD simulations and wind tunnel tests.The approach combined CFD simulation and wind tunnel tests proposed can be used to guide the design of such parachute whose size is on the same magnitude with carrier.

Flow Characteristics of Double-Cruciform Parachute at Inflating and Inflated Conditions

The fluid-structure interaction (FSI) between the canopy and flow field on the inflating and inflated conditions is investigated based on the arbitrary Lagrange-Euler (ALE) method,in both a single-and double-cruciform parachute systems.The projection area of canopy is calculated in the inflation process.The flow field characteristics and the interaction between canopies are analyzed.Results showed that,with free stream velocity of 50m/s,overinflation phenomenon would not occur during the inflation process of the double-cruciform-parachute system,because the collision and extrusion of the two canopies during inflation obstructed the oscillation of the inner gores.Concurrently,compared with the single-cruciform parachute,the vortex motion in the wake of double-cruciform-parachute is more intense.Thus the double-cruciform parachute system oscillated at a velocity of 50 m/s with an angle of less than 6.8°.By comparison,the oscillation angle of the single-cruciform parachute was within 3.5° at the velocity of 50m/s.The results are consistent with those of the wind tunnel test.

Experimental investigation of the effect of Reynolds number on flow structures in the wake of a circular parachute canopy

In the present study, an experimental study was conducted to characterize the effect of Reynolds number on flow structures in the turbulent wake of a circular parachute canopy by utilizing stereoscopic particle image velocime- try （Stereo-PIV） technique. The parachute model tested in the present study was attached by 28 nylon suspension lines and placed horizontally at the test section center of the wind tunnel. The obtained results showed that with the in- crease of Reynolds number, the intensities of the vortices near the downstream region of the canopy skirt were found to increase accordingly. However, the increase of Reynolds number did not result in a significant change in ensemble- averaged normalized x-component of the velocity, ensembleaveraged normalized vorticity, normalized Reynolds stress, and normalized turbulent kinetic energy distributions in the turbulent wake of the circular parachute canopy. The obtained results are very useful to further our understanding about the unsteady aerodynamics in the wake of flexible circular parachute canopies and to constitute a reference for CFD computation.

Incidence and risk factors associated with injuries during static line parachute training in Royal Thai Army

Background:Incidence and risk factors of parachute injuries has been studied in developed countries,but not in trainees of the airborne forces in the Royal Thailand Army.Methods:A prospective cohort study was conducted among 992 military personnel who attended the basic airborne training program from February to July 2018.Information sheets were used to collect data about(a)personal demographics;(b)environmental conditions surrounding the parachute practice;and(c)parachute-related injuries.The incidence rate of injury was then calculated.Risk factors were examined using multilevel Poisson regression analysis and presented as incidence rate ratio(IRR)and 95%confidence interval(95%CI).Results:A total of 166 parachute-related injuries occurred in 4677 jumps.The incidence rate of injury was 35.50 per 1000 jumps(95%CI 30.04–41.21).Factors significantly related to parachute injury included:jumping with equipment versus without equipment[adjusted IRR(95%CI):1.28(0.88–1.87)],higher wind speed[1.54(1.27–1.87)per knot],airplane versus helicopter exit[1.75(0.68–4.55)],side versus rear exit[2.13(1.43–3.23)],night versus day jumping[2.19(0.81–5.90)],and presence of motion sickness[3.43(1.93–6.92)].Conclusions:To prevent military static line parachute injuries,the following factors should be taken into consideration:type of aircraft,aircraft exit,time of the day,equipment,motion sickness and wind speed.Trial registration:The project was certified by the Research Ethics Committee,Faculty of Medicine,Chulalongkorn University(IRB No.697/60).

Numerical Study of Parachute-Payload Land Site Distribution with Randomize Wind Gust Model

A parachute-payload model with randomize wind gust is developed to study the landing accuracy of the parachute decelerator system,which can be exactly described by the landing site distribution.The research focuses on the steady descent phase of the parachute descent process,so the parachute and the payload suspension formulation during the phase are mainly discussed.In addition,since the wind effects have a significant impact on the land site distribution of the passive decelerator system and it is difficult to obtain the exact wind profile in practice,major features of parachute-payload system are studied via the randomized wind gust formulation.As the randomized wind gust formulation is adopted,the wind effect can be considered without the exact wind gust profile and the parachute aerodynamic simulation can be fulfilled with uncertainties.Finally,the model is validated and discussed,and the parachute land site distributions with different wind randomize profiles are presented for comparison.The results show that when parachute is less stable,the land site tends to have a larger variance.

Measurement of the flow structures in the wakes of different types of parachute canopies

We measured flow structures with stereoscopic particle image velocimetry(stereo-PIV) in the turbulent wakes of three parachute canopies, which had the same surface area, but different geometries. The tested parachute canopies included ribbon canopy, 8-branches canopy, and cross canopy. The obtained results showed that the geometry of the parachute canopies had significant influences on the flow structures in the wakes of these three canopies. In addition, the variation of Reynolds number did not lead to a dramatic change in the distributions of velocity, vorticity,Reynolds stress, and turbulent kinetic energy.

Study of velocity effects on parachute inflation performance based on fluid-structure interaction method

The inflation of a five-ring cone parachute with the airflow velocity of 18 m/s is studied based on the simplified arbitrary Lagrange Euler （SALE）/fluid-structure interaction （FSI） method. The numerical results of the canopy shape, stability, opening load, and drag area are obtained, and they are well consistent with the experimental data gained from wind tunnel tests. The method is then used to simulate the opening process under different velocities. It is found that the first load shock affected by the velocity often occurs at the end of the initial inflation stage. For the first time, the phenomena that the inflation distance proportion coefficient increases and the dynamic load coefficient decreases, respectively, with the increase in the velocity are revealed. The above proposed method is competent to solve the large deformation problem without empirial coefficients, and can collect more space-time details of fluid-structure-motion information when it is compared with the traditional method.

Perturbation Dynamics and Its Application for Parachute-Munition System

The nine-degree-freedom dynamic model of the parachute-munition system is developed by the theories and the analysis methods of parachute dynamics and multibody dynamics.On the basis of the above model,a linear five-degree-of-freedom dynamic model is developed by linearization at the steady state.A new algorithm,which can be fused with submunition kinematics and used in target identification,is developed by the principle of parachute dynamics.The simulation program is developed and used to remove the influence of wind gust on hitting accuracy.The successful airdrop test demonstrates that the new method can be used in the guidance of smart munition.

Numerical Simulation of ATPS Parachute Transient Dynamics Using Fluid-Structure Interaction Method

In order to simulate and analyze the dynamic characteristics of the parachute from advanced tactical parachute system(ATPS),a nonlinear finite element algorithm and a preconditioning finite volume method are employed and developed to construct three dimensional parachute fluid-structure interaction(FSI)model.Parachute fabric material is represented by membrane-cable elements,and geometrical nonlinear algorithm is employed with wrinkling technique embedded to simulate the large deformations of parachute structure by applying the NewtonRaphson iteration method.On the other hand,the time-dependent flow surrounding parachute canopy is simulated using preconditioned lower-upper symmetric Gauss-Seidel(LU-SGS)method.The pseudo solid dynamic mesh algorithm is employed to update the flow-field mesh based on the complex and arbitrary motion of parachute canopy.Due to the large amount of computation during the FSI simulation,massage passing interface(MPI)parallel computation technique is used for all those three modules to improve the performance of the FSI code.The FSI method is tested to simulate one kind of ATPS parachutes to predict the parachute configuration and anticipate the parachute descent speeds.The comparison of results between the proposed method and those in literatures demonstrates the method to be a useful tool for parachute designers.

Transcatheter Decompression of the Left Atrium in an Adolescent with a Double Inlet Left Ventricle, Severe Parachute Mitral Valve Stenosis and Pulmonary Hypertension

A 17-year-old adolescent with non-operated double inlet left-ventricle and severe stenosed parachute mitral valve is reported. He was admitted with repetitive syncope related to intermittent atrial fibrillation. Life-threatening syncope combined with pre- and post-capillary pulmonary hypertension together with his single ventricle pathophysiology led to the decision for left atrial decompression by percutaneous static atrial septum ballooning after transseptal needle perforation. Aiming to create a restrictive atrial septum defect, unloading of the left atrium without disturbing the balanced hemodynamics was directed for a long-term palliation or as a basis for a further surgical follow-up approach.

面向空投的青藏高原风场大涡模拟研究

青藏高原地形复杂且气候恶劣,对高原空投伞降和航空安全是巨大的挑战;本文基于数值模拟方法,研究一套适用于高原复杂地形的风场精确模拟方法。本研究首先基于WRF(Weather Research and Forecasting)模式的大涡模拟LES(Large Eddy Simulation)方案,研究青藏高原大涡模拟方法,构建一套降尺度至40 m水平分辨率的WRF-LES系统。然后,基于青藏高原大风个例,通过敏感性试验研究,评估LES方案和地形高程数据对风场模拟影响。其外,对LES方案的标准亚格子湍流应力模型中参数进行分析,得到青藏高原风场模拟的最优方案组。最后,进行批量试验,检验该方案对高原风场模拟的适用性。试验结果表明:(1)40 m分辨率的WRF-LES系统可模拟得到更精细和准确的风场信息,模拟风速平均绝对误差MAE(Mean Absolute Error)较ACM2方案减小1.4 m·s^(-1)且均方根误差RMSE(Root Mean Square Error)减小1.81 m·s^(-1);(2)高精度地形资料ASTER的接入可以改善模式对风场模拟的效果,各项误差较模式默认地形模拟结果均存在约0.2 m·s^(-1)的改善;(3)LES方案采用基于1.5阶湍流动能方案且常数项系数为0.1时模拟效果最佳,MAE为1.56 m·s^(-1)且RMSE为2.06 m·s^(-1)。批量试验验证了大涡模拟方案对于青藏高原边界层风场模拟具有较强的适用性,40 m分辨率区域风场模拟效果明显优于中尺度模拟效果,可为高原空投伞降提供准确的风场信息。

收放伞绳对十字型伞静态气动特性影响的数值模拟研究

为研究十字型降落伞作为主动控制装置时,其可控性与气动特性的规律,建立了不同伞绳收缩比δ为0、10.0%、12.5%、15.0%、20.0%、25.0%时十字型伞无限质量充气的有限元模型,基于任意拉格朗日-欧拉方法进行数值模拟,分析了十字型降落伞收缩伞绳,引起伞面几何构型不对称对气动特性的影响.结果表明:不同攻角为0°、5°、10°时,十字型降落伞的平均阻力系数随伞绳收缩比δ的增大而减小;十字型伞的瞬时升力峰值随着伞绳收缩比δ的增加而增大,方向始终由伞绳收缩一侧指向另一侧,具有较强的时变特性.

返回器飞行管道的快速预测算法

针对返回器回收任务中对安全空域和期望落点的计算需求,提出了基于Koopman算子的飞行管道快速预测算法,给出了搜救直升机安全飞行空域的判定流程。建立了物伞动力学模型,利用Halton采样方法从随机空间中均匀采点,计算得到多条可能弹道;采用Koopman算子的后拉机制,将初始概率密度值与当前状态关联,得到不确定条件下返回器及其分离部件的飞行管道和期望弹道。仿真结果表明,基于Koopman算子的飞行管道快速预测算法在收敛速度和精度上都要显著优于Monte Carlo方法;利用飞行管道计算结果对搜救直升机飞行路线进行规划后,碰撞风险最大降低54%且搜索时间减少70%。飞行管道预测算法已成功应用到嫦娥五号的回收任务中。

降落伞用新型伞绳与伞带连接方式的试验研究

文章介绍了一种探测器回收降落伞伞绳和伞带的新型连接方式,测试了其连接强力,掌握了该新型连接产品的制作工艺及部分材质和规格与连接强力之间的变化规律,为该产品在探测器回收降落伞上的应用提供了数据支撑。

基于动态嵌套网格技术的载荷出舱过程研究

针对内装载荷在空中分离出舱过程中存在的安全性和姿态稳定性问题,文章采用动态嵌套网格结合罚函数的研究方法对载荷在考虑适配器碰撞下的出舱分离过程进行了数值模拟。相较于以往的研究,该方法将分离过程中的气动特性由离散的稳态计算转变为连续的瞬态计算,将适配器碰撞由特征点法估算转变为节点-面法精细计算,实现了非定常流场与多体碰撞的耦合求解,拥有更好的保真性。文章首先通过与美国空军Arnolds工程发展中心风洞实验室的标模试验进行对比,验证了所采用的数值方法的准确性;随后建立了载荷出舱系统仿真模型并分析了标准工况下的出舱特性以及初始速度、初始攻角对载荷在牵引伞作用下出舱过程的影响。结果表明:标准工况下载荷能够安全平稳出舱;初始速度越低,分离过程越平稳,适配器受压缩程度越低,马赫数Ma=0.5时运载器与载荷的最小间距相较于Ma=0.8时增大了1 mm;初始攻角较大对分离时的安全性和稳定性有不利影响,攻角ɑ=15°时适配器摩擦力是ɑ=5°时的2.67倍。该方法适用于采用适配器作为安全保护措施的载荷出舱系统的数值模拟研究,所得结论可为研究载荷出舱系统分离过程提供一定参考。