Trajectory planning for multi-robot coordinated towing system based on stability

Given the unconstrained characteristics of the multi-robot coordinated towing system,the rope can only provide a unidirectional constraint force to the suspended object,which leads to the weak ability of the system to resist external disturbances and makes it difficult to control the trajectory of the suspended object.Based on the kinematics and statics of the multi-robot coordinated towing system with fixed base,the dynamic model of the system is established by using the Newton-Euler equations and the Udwadia-Kalaba equations.To plan the trajectories with high stability and strong control,trajectory planning is performed by combining the dynamics and stability of the towing system.Based on the dynamic stability of the motion trajectory of the suspended object,the stability of the suspended object is effectively improved through online real-time planning and offline manual adjustment.The effectiveness of the proposed method is verified by comparing the motion stability of the suspended object before and after planning.The results provide a foundation for the motion planning and coordinated control of the towing system.

Air-Floating Towing Behaviors of Multi-Bucket Foundation Platform

Air-floating towing beha viors of multi-bucket foundation plat form （MBFP） are investigated with the 1/20-scale model tests and hydrodynamic so ftware MOSES. MOSES numerical model was val idated by test results, and M OSES prototype model of MBFP can eliminate scale effect of model. The influences of towing factors of to wing speed, water depth, freeboard, and w ave direction on air-floating tow ing stability of MBFP were analyzed by model tests and validated MOSES prototype mod el. It is sho wn that the re duction of towing sp eed can effectively d ecrease the to wing force and surge acceleration to improve towing stability. Water depth is another f actor in towing s tability. Obvious shallow water effect will appear in shallow water with sma ll water depth-draft ratio and it w ill disappear gradually and air-floating towing becomes more stable with the increase of water depth. Accelerations of surge, s way and heave are small and they have modest changes when freeboard increases from 0.5 to 2 m. For MBFP, the freeboard is not suggested to be larger than 2 m in following wave. Wave direction has large influence on the towing stability, the surge acceleration and towing force are sensitive to the va riation of wave direction, the surge acceleration and towing force in following wave （0°） and counter wave （180°） are much larger than that in transverse sea （90°and 270°）.

Mechanical Analysis of Submarine Pipeline During off-Bottom Towing Operation

The off-bottom tow is an important method to lay pipeline for offshore oil and gas transportation in shallow water area. During the off-bottom towing operation, the actions such as sea current resistance, friction force of seabed, pontoon buoyancy, and tow force of tugboat can cause large deformation and fatigue damage to the pipeline. In order to keep the pipeline in safety, the lateral and vertical defomlations of pipeline must be controlled within an appropriate range. Theoretical study is carried out in the paper on the environmental forees acting on pipeline, pontoons and chaias, and the confimation of tow parameters including tow forces of tugboat, number of pontoons and length of chains. Then the pipeline in the off-bettom towing process may be simplified into a continuous beam with elastic supports under the concentrated and distributed forces. A finite element method is applied to achieve numerical solutions describing the distributions of deformation and stress along the pipeline. The results show that the lateral shape of the pipeline is like an arc with the maximal deformation appearing at the middle of the pipeline. The distributions of stress are similar between two arbitrary pontoons. Moreover, both deformation and stress have the inverse relation with the tow forces of tugboat.

Integrated Towing Transportation Technique for Offshore Wind Turbine with Composite Bucket Foundation

Composite bucket foundation and one-step installation technology for offshore wind turbine are the integration of foundation construction,transportation and whole installation at sea.The cost of offshore wind turbine construction and installation has been largely reduced.Foundation stability is the key technology in the process of towing transportation.Field observation data can reflect the real state of the foundation.In this paper,the influence of water depth and towing speed on liquid level,the compartment pressure,and the pitch angles during towing of composite bucket foundation are studied.These data are analyzed based on the field measurements data from a 3.3 MW offshore wind power project in China.The results show that with varied water depths and towing speeds,the compartment pressure changes are small during the bucket foundation towing process.The offshore wind turbine composite bucket foundation is stable while being towed in the ocean.

Influence of towing speed on effectiveness of rolling dynamic compaction

The influence of towing speed on the effectiveness of the 4-sided impact roller using earth pressure cells(EPCs)is investigated.Two field trials were undertaken;the first trial used three EPCs placed at varying depths between 0.5 m and 1.5 m with towing speeds of 9-12 km/h.The second used three EPCs placed at a uniform depth of 0.8 m,with towing speeds of 5-15 km/h.The findings from the two trials confirmed that towing speed influences the pressure imparted to the ground and hence compactive effort.This paper proposes that the energy imparted to the ground is best described in terms of work done,which is the sum of the change in both potential and kinetic energies.Current practice of using either kinetic energy or gravitational potential energy should be avoided as neither can accurately quantify rolling dynamic compaction(RDC)when towing speed is varied.

Test Research on Influence of Draft on Towing Behaviors of 3-Bucket Foundation Platform

To investigate the natural frequencies and towing behaviors of a 3-bucket foundation platform at different drafts, the decay and towing experiments were carried out in a towing tank on a scale of 1:20. The air pressure inside the bucket foundations, the water pressure at the bottom of the bucket foundations, the acceleration of the platform and the towing force were determined in the test process. The time-history curves of the measured parameters were obtained, and the frequency responses of the parameters at different drafts were analyzed by means of fast Fourier transform(FFT). The results showed that the platform natural frequency of heave decreased slightly with the rise of draft. The natural frequencies of roll and pitch are much lower than that of heave, and they increased slightly with the increase of draft. When towing in the following sea, the maximum acceleration of surge, sway and heave has downward trends with the increase of draft, but the change range decreased gradually with the increase of draft. When the draft is 5.0 m(the ratio of draft to bucket height is 0.56), the towing dynamic responses achieve the maximum, which is not conducive to the towing of the platform. When the draft is 6.0 m(the ratio of draft to bucket height is 0.67), the towing dynamic responses are the most stable.

Cooperative Multi-Agent Control for Autonomous Ship Towing Under Environmental Disturbances

Among the promising application of autonomous surface vessels(ASVs)is the utilization of multiple autonomous tugs for manipulating a floating object such as an oil platform,a broken ship,or a ship in port areas.Considering the real conditions and operations of maritime practice,this paper proposes a multi-agent control algorithm to manipulate a ship to a desired position with a desired heading and velocity under the environmental disturbances.The control architecture consists of a supervisory controller in the higher layer and tug controllers in the lower layer.The supervisory controller allocates the towing forces and angles between the tugs and the ship by minimizing the error in the position and velocity of the ship.The weight coefficients in the cost function are designed to be adaptive to guarantee that the towing system functions well under environmental disturbances,and to enhance the efficiency of the towing system.The tug controller provides the forces to tow the ship and tracks the reference trajectory that is computed online based on the towing angles calculated by the supervisory controller.Simulation results show that the proposed algorithm can make the two autonomous tugs cooperatively tow a ship to a desired position with a desired heading and velocity under the(even harsh)environmental disturbances.

Research on the Motion Track of Ocean Towing System

In this paper, a method for predicting the position of towline is presented. The location of the finite node is determined by installing fixed spaced attitude sensors in towline arrays, then the appropriate objective functions are selected for water depth profile and course profile respectively, and the interpolation fitting method is combined with the determined predicted positions. Through the hydrodynamic analysis of the existing towing cable’s underwater motion, the position of the towing cable under the steady state motion is obtained as the reference basis, and two methods are put forward, which are improved spline interpolation method, polynomial fitting method and multivariate nonlinear regression analysis. In the case of steady state motion, the two methods are compared and compared with the hydrodynamic simulation results. Finally, a more suitable method is selected as the basis of cable location inversion and applied to deep-sea towing operations.

“深海一号”半潜式生产储油平台长距离湿拖方案论证

针对“深海一号”半潜式生产储油平台拖航方案设计及工程实施面临拖航距离远、拖航路径环境恶劣、拖船资源选择少,以及作业风险高等众多技术难题,通过对比分析平台干拖和湿拖方案,重点分析湿拖过程中的拖航路线、平台吃水、湿拖阻力、拖船配置等关键技术问题,通过水池模型试验验证该方案的可行性,顺利实施了“深海一号”平台的长距离湿拖工作。

飞机高速牵引滑行制动模式分析

在传统牵引车牵引飞机的运动过程中,其制动行为是通过牵引车独立制动来完成的,主要用于低速推出牵引和轻载中速维护牵引工况。针对未来飞机牵引滑行的高速重载新特征,仅靠牵引车实施制动能否满足牵引系统制动性能需要重新评估。为此,文中考虑了由飞机和牵引车联合制动的新模式,即由飞机主起落架机轮刹车系统和牵引车轮刹车系统同时制动,通过分配制动力来实现牵引车-飞机系统的制动行为。建立了飞机牵引滑行时制动过程的动力学模型,并以B737-200型飞机和TBL-180型牵引车为例,分析对比了牵引车单独制动和牵引车-飞机联合制动两种模式下的系统制动性能和制动安全性。结果表明:牵引车-飞机联合制动时的制动性能远优于牵引车单独制动时的制动性能,是飞机高速牵引滑行时紧急制动的优选模式;在安全性方面,牵引车-飞机联合制动时的前起落架横向载荷也远小于牵引车单独制动,会为飞机前起落架结构保留更大的横向冲击安全裕度。

基于LightGBM的拖曳系统动力响应预报方法

针对传统数值仿真计算方法耗时长、占用计算机资源多等缺点,提出基于LightGBM算法的拖曳系统动力响应进行评估的回归预测模型,以已有的OrcaFlex数值模拟得到的数据为样本,以拖曳系统上的海洋环境条件、拖船航速和下放缆长为特征,以动力响应为目标,引入LightGBM算法,对拖曳缆顶端张力最大值等动力响应进行预测分析。与传统数值模拟方法相比,LightGBM算法在保证结果准确性的同时大幅度提高了计算效率。通过与随机森林(RF)、极限梯度提升(XGBoost)算法相比,其准确度和计算效率的表现更好。最后提出了贝叶斯参数优化的LightGBM算法,准确度进一步提高,为提前采取措施保障拖曳系统的作业安全提供了一条高效的技术途径,同时为建立拖曳系统数字孪生体提供了有力的技术支撑。

基于遗传算法的不等间距阵优化方法

阵元数一定情况下,针对不等间距拖线阵高频信号处理存在的空间增益和无栅瓣兼容问题,提出一种基于遗传算法的不等间距拖线阵阵型优化方法。该方法以频带交互下最大旁瓣级最小作为约束因子,通过模拟生物自然进化过程搜索全局最优解,得到优化后的阵元位置。优化后阵型在保证低频信号处理空间增益不变情况下,实现对高频信号高空间增益、无栅瓣处理。计算机仿真结果表明:相比未优化阵型,在高频信号处理方面,优化后阵型在无栅瓣情况下,空间增益提升值近似理论值提升值;在低频信号处理方面,优化后阵型具有相同的空间增益。为实际不等间距拖线阵阵型优化和应用提供了一种思路。

泰和县钟埠村"拖龙船"仪式音声的建构及象征

仪式音声是近二十年来出现的一个重要学术概念,它从仪式整体的语境中分析音声对于仪式作为一种人类学意义上的"文化表演"过程的重要意义。文章以泰和"拖龙船"仪式为研究对象,结合传统的发明、象征人类学的理论与方法,从"音声"切入,置"音声"于仪式或信仰的共生环境中探寻其内涵和意义。对于"拖龙船"仪式而言,执仪人"文化表演"所形成的"音声声谱"有着从"象"到"意"的隐喻,形成一个"符号(基本单位)一仪式(聚集体)一象征(意义)"的动力循环圈。音声在保持仪式进行有效性的同时,不但赋予娱人娱己双重功能,还在不同的仪轨环节中,具有不同的象征意义。

基于TOWS理论审视我国体育旅游发展战略——以河南省体育旅游开发为例

将战略规划的系统方法——TWOS分析引入河南省体育旅游发展战略规划实践。研究认为,区域体育旅游的发展战略关系到体育旅游发展的全局性、根本性问题,是区域体育旅游取得持续发展的决定性因素。据此认为,河南省体育旅游的开发应围绕特色文化、区域合作、体制创新、产品整合、相对优势、品牌和形象主导制定战略规划。

基于TOWS分析的区域旅游发展战略规划——以辽宁鞍山为例

发展战略在区域旅游开发和规划中至关重要,它关系到旅游发展的全局性和战略性问题,是区域旅游业取得长期绩效的决定性因素。目前,区域旅游发展战略规划,基本上依赖于专家的经验和直觉,随意性和主观性较强,给区域旅游发展系统带来莫大的风险。为此,本文以辽宁鞍山为实例,将TOWS分析方法引入旅游发展战略的制定过程,以增强区域旅游发展战略规划的客观性、系统性和可靠性,降低旅游系统所面临的风险,旨在促进区域旅游持续发展。

大同市旅游发展战略的TOWS分析

利用TOWS分析法对大同市旅游发展的优势、劣势、机遇与威胁进行了综合分析评价,得到以云冈石窟为代表的人文旅游资源优势明显、旅游产品结构单一、旅游交通的极大改善为旅游业发展提供了机遇、对重点文物和环境保护的压力大等关键的内外部因素,最后提出了如特色文化、完善交通、区域联合等适合大同市旅游发展的六个战略.

基于SWOT-TOWS分析区域竞技体育发展的战略规划——以辽宁省竞技体育发展为例

运用文献资料、数理统计、逻辑分析、SWOT分析等方法,对辽宁竞技体育发展过程中所面临的内外部环境进行探讨,进而引入战略规划的系统研究方法—TWOS分析对未来辽宁竞技体育发展的战略规划进行研究。表明:区域竞技体育发展的战略规划是关系到竞技体育发展的全局性和根本性的问题,是区域竞技体育取得可持续发展的决定性因素。因此,辽宁竞技体育的发展应以特色文化战略、相对优势战略、区域联盟战略、体制创新战略和整合发展战略为重点制定战略规划。

TOWS分析方法在公路交通发展战略制定中的应用

从公路交通与企业发展所而临的环境的相似性出发,将社会经济系统作为公路交通发展的外部环境,用TOWS分析方法对公路交通与经济发展的适应性进行了分析,提出了与之相适应的发展战略.

拖曳系统中瑞利阻尼系数变化在回转过程中对拖缆动力学振动响应的影响

海洋拖曳系统是典型的刚柔多体系统。需要指出的是,到目前为止,绝大多数的关于海洋拖曳缆体系统的动力学问题研究都没有非常充分地考虑到阻尼的作用。但在海洋拖曳系统的结构动力学分析中,特别是拖缆回转过程中的动态响应分析中,阻尼的作用是不可忽略的。且由于阻尼的存在,拖缆的模态特性也会呈现出高度的复杂性。为探究瑞利阻尼在拖缆回转过程中的影响,基于凝集质量法对瑞利阻尼的在拖缆系统中的表达形式进行了进一步的整理与分解,并对各个阻尼分量的影响进行了归纳总结,得到了一些较为通用性的结论,对于实际海上拖曳作业有一定的指导意义。

高校发展战略选择的影响因素--兼论TOWS矩阵和博弈论的应用

本文借助波特的产业分析思想,全面分析了高校所面临的竞争环境,指出了与高校发展密切相关的五种作用力,探讨影响高校发展战略选择的相关因素,并给出战略选择的一般流程。本文另运用TOWS矩阵分析方法以实例分析了高校所面临的外部威胁和机遇,内部的弱势和优势,从而做出具体的战略选择。继而,本文还论述了博弈论的思想在制定高校发展战略时的价值,指出高校盲目扩张策略的"囚徒困境"。