Anti-Disturbance Control for Tethered Aircraft System With Deferred Output Constraints

In this paper,we investigate the peaking issue of extended state observers and the anti-disturbance control problem of tethered aircraft systems subject to the unstable flight of the main aircraft,airflow disturbances and deferred output constraints.Independent of exact initial values,a modified extended state observer is constructed from a shifting function such that not only the peaking issue inherently in the observer is circumvented completely but also the accurate estimation of the lumped disturbance is guaranteed.Meanwhile,to deal with deferred output constraints,an improved output constrained controller is employed by integrating the shifting function into the barrier Lyapunov function.Then,by combining the modified observer and the improved controller,an anti-disturbance control scheme is presented,which ensures that the outputs with any bounded initial conditions satisfy the constraints after a pre-specified finite time,and the tethered aircraft tracks the desired trajectory accurately.Finally,both a theoretical proof and simulation results verify the effectiveness of the proposed control scheme.

Advances in dynamics and control of tethered satellite systems

The concept of tethered satellite system （TSS） promises to revolutionize many aspects of space exploration and exploitation. It provides not only numerous possible and valuable applications, but also challenging and interesting problems related to their dynamics, control, and physical implementation. Over the past decades, this exciting topic has attracted significant attention from many researchers and gained a vast number of analytical, numerical and experimental achievements with a focus on the two essential aspects of both dynamics and control. This review article presents the historic background and recent hot topics for the space tethers, and introduces the dynamics and control of TSSs in a progressive manner, from basic operating principles to the state-of-the-art achievements.

Review of deployment technology for tethered satellite systems

Tethered satellite systems（TSSs） have attracted significant attention due to their potential and valuable applications for scientific research. With the development of various launched on-orbit missions, the deployment of tethers is considered a crucial technology for operation of a TSS. Both past orbiting experiments and numerical results have shown that oscillations of the deployed tether due to the Coriolis force and environmental perturbations are inevitable and that the impact between the space tether and end-body at the end of the deployment process leads to complicated nonlinear phenomena. Hence, a set of suitable control methods plays a fundamental role in tether deployment. This review article summarizes previous work on aspects of the dynamics, control, and ground-based experiments of tether deployment. The relevant basic principles, analytical expressions, simulation cases, and experimental results are presented as well.

Nonlinear dynamics of flexible tethered satellite system subject to space environment

The paper studies the nonlinear dynamics of a flexible tethered satellite system subject to space environments, such as the J2 perturbation, the air drag force, the solar pressure, the heating effect, and the orbital eccentricity. The flexible tether is modeled as a series of lumped masses and viscoelastic dampers so that a finite multi- degree-of-freedom nonlinear system is obtained. The stability of equilibrium positions of the nonlinear system is then analyzed via a simplified two-degree-freedom model in an orbital reference frame. In-plane motions of the tethered satellite system are studied numerically, taking the space environments into account. A large number of numerical simulations show that the flexible tethered satellite system displays nonlinear dynamic characteristics, such as bifurcations, quasi-periodic oscillations, and chaotic motions.

An Integrated Hydrodynamics and Control Model of A Tethered Underwater Robot

An integrated hydrodynamics and control model to simulate tethered underwater robot system is proposed. The governing equation of the umbilical cable is based on a finite difference method, the hydrodynamic behaviors of the underwater robot are described by the six-degrees-of-freedom equations of motion for submarine simulations, and a controller based on the fuzzy sliding mode control(FSMC) algorithm is also incorporated. Fluid motion around the main body of moving robot with running control ducted propellers is governed by the Navier–Stokes equations and these nonlinear differential equations are solved numerically via computational fluid dynamics(CFD) technique. The hydrodynamics and control behaviors of the tethered underwater robot under certain designated trajectory and attitude control manipulation are then investigated based on the established hydrodynamics and control model. The results indicate that satisfactory control effect can be achieved and hydrodynamic behavior under the control operation can be observed with the model; much kinematic and dynamic information about tethered underwater robot system can be forecasted, including translational and angular motions of the robot, hydrodynamic loading on the robot, manipulation actions produced by the control propellers, the kinematic and dynamic behaviors of the umbilical cable. Since these hydrodynamic effects are fed into the proposed coupled model, the mutual hydrodynamic influences of different portions of the robot system as well as the hydrological factors of the undersea environment for the robot operation are incorporated in the model.

Dynamics and rebound behavior analysis of flexible tethered satellite system in deployment and station-keeping phases

The tether deployment of a tethered satellite system involves the consideration of complex dynamic properties of the tether,such as large deformation,slack,and even rebound,and therefore,the dynamic modelling of the tether is necessary for performing a dynamic analysis of the system.For a variablelength tether element,the absolute nodal coordinate formulation(ANCF)in the framework of the arbitrary Lagrange-Euler(ALE)description was used to develop a precise dynamic model of a tethered satellite.The model considered the gravitational gradient force and Coriolis force in the orbital coordinate frame,and it was validated through numerical simulation.In the presence of dynamic constraints,a deployment velocity of the tether was obtained by an optimal procedure.In the simulation,rebound behavior of the tethered satellite system was observed when the ANCF-ALE model was employed.Notably,the rebound behavior cannot be predicted by the traditional dumbbell model.Furthermore,an improved optimal deployment velocity was developed.Simulation results indicated that the rebound phenomenon was eliminated,and smooth deployment as well as a stable state of the station-keeping process were achieved.Additionally,the swing amplitude in the station-keeping phase decreased when a deployment strategy based on the improved optimal deployment velocity was used.

Structure and switching of single-stranded DNA tethered to a charged nanoparticle surface

Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA（ss DNA）tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DNA are taken into account. The main results are as follows： i） when the temperature is lower than the critical switching temperature, the ss DNA will collapse due to the existence of electrostatic interaction between ss DNA and charged nanoparticle surface; ii）for the short ss DNA chains with the number of bases less than 10, the switching of ss DNA cannot happen, and the critical temperature does not exist; iii） when the temperature increases, the electrostatic attractive interaction between ss DNA and charged nanoparticle surface becomes weak dramatically, and ss DNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ss DNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ss DNA will not happen if the grafting densities are too high.

Equilibrium configurations of the tethered three-body formation system and their nonlinear dynamics

This paper considers nonlinear dynamics of teth- ered three-body formation system with their centre of mass staying on a circular orbit around the Earth, and applies the theory of space manifold dynamics to deal with the nonlinear dynamical behaviors of the equilibrium configurations of the system. Compared with the classical circular restricted three body system, sixteen equilibrium configurations are obtained globally from the geometry of pseudo-potential energy sur- face, four of which were omitted in the previous research. The periodic Lyapunov orbits and their invariant manifolds near the hyperbolic equilibria are presented, and an iteration procedure for identifying Lyapunov orbit is proposed based on the differential correction algorithm. The non-transversal intersections between invariant manifolds are addressed to generate homoclinic and heteroclinic trajectories between the Lyapunov orbits. （3,3）- and （2,1）-heteroclinic trajecto- ries from the neighborhood of one collinear equilibrium to that of another one, and （3,6）- and （2,1）-homoclinic trajecto- ries from and to the neighborhood of the same equilibrium, are obtained based on the Poincar6 mapping technique.

Calculation of Orbital Elements for Released Tethered Satellite

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基于TCP流RTT测量的Tethering行为检测架构

Tethering行为是一种移动设备通过自身传输介质共享其互联网连接服务的行为,其不仅对移动互联网造成运营压力和收益影响,还对移动互联网隐藏其内部网络结构,造成网络安全隐患。由于Tethering存在诸多混淆和规避方法,现有Tethering行为检测技术难以有效检测。鉴于此,分析了移动互联网通信基站中,Tethering行为终端在数据流量的处理、转发等特征,以及移动互联网用户流量中传输控制协议(TCP)流往返时延(RTT)的相关特性,提出一种基于TCP流RTT测量的Tethering检测架构,构建了所提架构的测试网络环境。实验结果表明:所提架构在检测Tethering行为中具有有效性,实现了利用无监督学习和被动监测网络流量对移动互联网中Tethering行为的有效检测,对Tethering行为检测的准确率达到97.50%。

Numerical investigation of dynamical behavior of tethered rigid spheres in supersonic flow

The dynamical behavior of two tethered rigid spheres in a supersonic flow is numerically investigated. The tethered lengths and radius ratios of the two spheres are different. The two spheres, which are centroid axially aligned initially, are held stationary first, then released, and subsequently let fly freely in a supersonic flow. The mean qualities of the system and the qualities of the bigger sphere are considered and compared with the situations without the tether. In the separation process, six types of motion caused by the spheres, tether, and fluid interaction are found. The results show that the mean x-velocity of the system changes in a different manner for different radius ratios, and the x-velocity of the bigger sphere is uniformly reduced but through different mechanisms.

Dynamic analysis of tethered space system deployment process

Discusses in detail the deploying strategies and feature of the motion of the Tethered Space System and the effects of some parameters, such as the property and initial length of the tether, the perturbation of the atmosphere, the ellipse of the orbit and the mass distribution of the system and points out the deploying strategy is based on the controlling of tension and the length of tether. And concludes from the computer simulation results of a tethered atmosphere probing satellite deployment that the deploying strategy presented does work well.

Microsurgical efficacy in 326 children with tethered cord syndrome: a retrospective analysis

Tethered cord syndrome is a progressive disease with a typically insidious onset in infants and children, and which can lead to persistent progress of neurological deficits and a high rate of disability without timely intervention. The purpose of this study was to investigate the curative effect of microsurgery in children with different types of tethered cord syndrome. In this study, we analyzed 326 patients with tethered cord syndrome, aged from 2 months to 14 years old, who were followed for 3–36 months after microscopic surgery. Based on clinical manifestations and imaging findings, these patients were classified into five types: tight filum terminale(53 cases), lipomyelomeningocele(55 cases), lipomatous malformation(124 cases), postoperative adhesions(56 cases), and split cord malformation(38 cases). All patients underwent microsurgery. Curative effects were measured before and 3 months after surgery by Spina Bifida Neurological Scale based on sensory and motor functions, reflexes, and bladder and bowel function. The results showed that Spina Bifida Neurological Scale scores improved in all five types after surgery. Overall effective rates in these patients were 75%. Effective rates were 91% in tight filum terminale, 84% in lipomyelomeningocele, 65% in lipomatous malformation, 75% in postoperative adhesion, and 79% in split cord malformation. Binary logistic regression analysis revealed that types of tethered cord syndrome(lipoma-type or not) and symptom duration before surgery were independent influencing factors of surgical outcome. These results show that therapeutic effect is markedly different in patients with different types of tethered cord syndrome. Suitable clinical classification for tethered cord syndrome will be helpful in predicting prognosis and guiding treatment.

Association between chromosomal aberration of COX8C and tethered spinal cord syndrome:array-based comparative genomic hybridization analysis

Copy number variations have been found in patients with neural tube abnormalities.In this study,we performed genome-wide screening using high-resolution array-based comparative genomic hybridization in three children with tethered spinal cord syndrome and two healthy parents.Of eight copy number variations,four were non-polymorphic.These non-polymorphic copy number variations were associated with Angelman and Prader-Willi syndromes,and microcephaly.Gene function enrichment analysis revealed that COX8 C,a gene associated with metabolic disorders of the nervous system,was located in the copy number variation region of Patient 1.Our results indicate that array-based comparative genomic hybridization can be used to diagnose tethered spinal cord syndrome.Our results may help determine the pathogenesis of tethered spinal cord syndrome and prevent occurrence of this disease.

Electrodynamic Tethered Deorbit System Dynamics and Performance Analysis

Electrodynamic tethered deorbit technology is a novel way to remove abandoned spacecrafts like upper stages or unusable satellites. This paper investigates and analyses the deorbit performance and mission applicability of the electrodynamic tethered system. To do so, the electrodynamic tethered deorbit dynamics with multi-perturbation is firstly formulated, where the Earth magnetic field, the atmospheric drag, and the Earth oblateness effect are considered. Then, the key system parameters, including payload mass, tether length and tether type, are analyzed by numerical simulations to investigate their influences on the deorbit performance and to give the setting principles for choosing system parameters. Based on this and given an appropriate group of system parameters, numerical simulations are undertaken to study the impact of the mission parameters, including orbit height and orbit inclination, and thus to investigate the mission applicability of the electrodynamic tethered deorbit technology.

Thoracolumbar surgery for degenerative spine diseases complicated with tethered cord syndrome:A case report

BACKGROUND Tethered cord syndrome(TCS) secondary to split cord malformation(SCM) is rare in adulthood.There is as yet no consensus about the optimal treatment method for adult patients with SCMs and degenerative spine diseases such as lumbar stenosis,spondylolisthesis and ossification of the ligamentum flavum(OLF).The tethered cord poses a great challenge to the decompression and fusion procedures for the intraoperative stretching of the spinal cord,which might lead to deteriorated neural deficits.Here,we report on a case to add our treatment experience to the medical literature.CASE SUMMARY We treated a 67-year-old female patient with type II SCM suffering from lumbar disc herniation,degenerative lumbar spondylolisthesis and thoracic OLF.The patient underwent thoracolumbar spinal fusion and decompression surgery for severe lower back pain,extensive left lower limb muscle weakness and intermittent claudication.After the thoracolumbar surgery,without stretching the tethered cord,the patient achieved complete relief of pain and lower extremity weakness at final follow-up.CONCLUSION For adult patients with underlying TCS secondary to SCM coupled with thoracic OLF and lumbar spondylolisthesis,a thoracolumbar fusion surgery could be safe and effective with the tethered cord untreated.It is critical to design individualized surgical protocols to reduce the stretch of the low-lying spinal cord.

Nonlinear dynamics and coupling effect of libration and vibration of tethered space robot in deorbiting process

In order to control the growth of space debris,a novel tethered space robot(TSR) was put forward.After capture,the platform,tether,and target constituted a tethered combination system.General nonlinear dynamics of the tethered combination system in the post-capture phase was established with the consideration of the attitudes of two spacecrafts and the quadratic nonlinear elasticity of the tether.The motion law of the tethered combination in the deorbiting process with different disturbances was simulated and discussed on the premise that the platform was only controlled by a constant thrust force.It is known that the four motion freedoms of the tethered combination are coupled with each other in the deorbiting process from the simulation results.A noticeable phenomenon is that the tether longitudinal vibration does not decay to vanish even under the large tether damping with initial attitude disturbances due to the coupling effect.The approximate analytical solutions of the dynamics for a simplified model are obtained through the perturbation method.The condition of the inter resonance phenomenon is the frequency ratio λ_1=2.The case study shows good accordance between the analytical solutions and numerical results,indicating the effectiveness and correctness of approximate analytical solutions.

Anterior sacral Meningocele Associated with Tethered Cord Syndrome Presenting with Constipation:US,CT,MRI and X-Ray Findings

Anterior sacral meningocele is characterized by the herniation of the thecal sac into the retroperitoneal space. A 33-year-old man was referred to our hospital with the complaints of a longlasting constipation and nonspecific lower abdominal pain. At ultrasound, a cystic mass was detected at the presacral space. Computed Tomography revealed a defect at the anterior aspect of the sacrum, together with a presacral cystic mass which showed a connection with the dural sac. At Magnetic Resonance Imaging, it was demonstrated that the cystic mass made an impression on the rectum, and did not possess any solid components. An anteroposterior pelvis radiogram demonstrated a sacral deformity and the scimitar sign. Upon these imaging findings, the patient got the diagnosis of an anterior sacral meningocele. The possibility of an anterior sacral meningocele must always be kept in mind in the differential diagnosis of a pelvic cystic mass.

肛门直肠畸形合并先天性脊髓栓系综合征的发生情况及治疗探讨

目的探讨肛门直肠畸形(anorectal malformation,ARM)合并先天性脊髓栓系综合征(tethered cord syndrome,TCS)的发生情况及相关治疗。方法回顾性分析2018年2月至2022年2月福建省儿童医院(上海儿童医学中心福建医院)收治的105例ARM患儿病史和影像学资料。按照Wingspread分类法分型,将ARM患儿分为中高位和低位两类;按照Krickenbeck分类法分型,将ARM患儿分为伴瘘管和不伴瘘管两类;根据MRI检查结果,将患儿分为TCS组和无TCS组。统计分析TCS与年龄、ARM分型及合并其他畸形的相关性及相关治疗意义。结果105例ARM患儿中,29例(27.6%)存在TCS,76例(72.4%)无TCS。55例(52.4%)合并其他畸形,其中37例合并1种畸形,18例合并两种及以上畸形。Wingspread分型及合并其他畸形是ARM患儿合并TCS的独立影响因素,中高位ARM合并TCS的概率是低位ARM的3.223倍(OR=3.223,95%CI:1.128~9.210,P=0.029),合并2种及以上其他畸形的患儿患TCS的概率是合并1种其他畸形的10.120倍(OR=10.120,95%CI:2.715~37.729,P=0.001)。无TCS的ARM患儿与合并TCS的ARM患儿比较,两组在切口感染发生率、住院时间、有效率、病死率及术后2个月排便功能上比较,差异无统计学意义(P>0.05)。经治疗后,两组患儿在排便功能改善上差异无统计学意义(P>0.05)。结论中高位ARM患儿及合并多系统畸形的患儿TCS发生率较高。建议ARM患儿常规行腰骶部MRI检查,以尽早发现TCS的类型和严重程度。治疗上,ARM患儿合并TCS应先治疗ARM,建议行脊髓栓系松解术,以防止脊髓损伤进一步加重带来的严重后果。

经胸实时三维超声心动图评估特发性肺动脉高压患者三尖瓣几何构型的价值

目的:研究经胸实时三维超声心动图在评估特发性肺动脉高压(IPAH)患者的三尖瓣几何构型中的应用价值。方法:前瞻性入选2017年9月至2018年12月在中国医学科学院阜外医院就诊的IPAH患者30例(为IPAH组),健康志愿者15例为对照组。所有研究对象均行经胸二维及三维超声心动图检查,并使用四维自动三尖瓣定量(4D Auto-TVQ)在聚焦右心室切面分析三尖瓣结构。肺动脉高压患者均在超声心动图检查后48 h内采用右心导管检查确诊。结果:IPAH组的三尖瓣形态学参数瓣环面积、瓣环周长、四腔心直径、瓣叶结合点高度、幕状区最大高度和幕状区容积均显著大于对照组(P均<0.05)。与对照组相比,IPAH组瓣环收缩期位移明显更小(P<0.05)。两组的瓣环面积变化率和两腔心直径差异均无统计学意义(P均>0.05)。IPAH患者的三尖瓣幕状区最大高度和瓣叶接合点高度均与右心室舒张末期容积具有良好相关性(r=0.710、0.515,P均<0.05);瓣环周长、四腔心直径和瓣环面积均与右心房收缩末期容积具有良好相关性(r=0.712、0.558、0.545,P均<0.05)。结论:IPAH患者三尖瓣幕状区最大高度、瓣叶接合点高度和幕状区容积明显增大,三尖瓣环扩张主要体现在四腔心切面直径。三尖瓣幕状区高度与右心室容积相关,而三尖瓣环尺寸与右心房容积相关。