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°）.

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.

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.

Regulated emission characteristics of in-use LNG and diesel semi-trailer towing vehicles under real driving conditions using PEMS

On-road driving emissions of six liquefied natural gas(LNG) and diesel semi-trailer towing vehicles(STTVs) which met China Emission Standard IV and V were tested using Portable Emission Measurement System(PEMS) in northern China.Emission characteristics of these vehicles under real driving conditions were analyzed and proved that on-road emissions of heavy-duty vehicles(HDVs) were underestimated in the past.There were large differences among LNG and diesel vehicles, which also existed between China V vehicles and China IV vehicles.Emission factors showed the highest level under real driving conditions, which probably be caused by frequent acceleration, deceleration, and start-stop.NOx emission factors ranged from 2.855 to 20.939 g/km based on distance-traveled and 6.719–90.557 g/kg based on fuel consumption during whole tests, which were much higher than previous researches on chassis dynamometer.It was inferred from tests that the fuel consumption rate of the test vehicles had a strong correlation with NOx emission, and the exhaust temperature also affected the efficiency of Selected Catalytic Reduction(SCR) aftertreatment system, thus changing the NOx emission greatly.THC emission factors of LNG vehicles were 2.012–10.636 g/km, which were much higher than that of diesel vehicles(0.029–0.185 g/km).Unburned CH4 may be an important reason for this phenomenon.Further on-road emission tests, especially CH4 emission test should be carried out in subsequent research.In addition, the Particulate Number(PN) emission factors of diesel vehicles were at a very high level during whole tests, and Diesel Particulate Filter(DPF)should be installed to reduce PN emission.

Dynamic Behavior of Two Part Towing Cable System During Turning

An improved numerical method is used to simulate the dynamic behavior of a two part towing cable systems during turnings. In U turns and full turns, periodical heave motions are found both for the towed vehicle and for the depressor. Periodic motions of the subsea units and of the cable surface tension are closely related to the turning parameters, such as turning velocity and turning radius. System parameters, such as length of the second cable and the vehicle hydrodynamics, also damp turning instability.

The Numerical Simulation of a Towing Cylinder Based on Immersed Body Boundary Method

An immersed body boundary method is adopted to track the motions of a towing cylinder, and a homogenous multiphase Eulerian-Eulerian fluid approach is used to capture the free surface. The Reynolds average Navier-Stockes(RANS) solver is applied to all gird nodes to deal with different velocities of the nodes that are in the body boundary, near the boundary and out of the boundary and their effect on the fluid. The towing cylinder resistance at different submerged depths in the tank is presented. The simulation results are compared with the experimental data, and the method is verified and validated. Finally, the hydrodynamic characters of the cylinder are discussed further. The numerical and experimental results show that at high speeds, the deeper the cylinder submerges, the lower resistance it suffers. The resistance coefficient trough is obtained at Froude number in the range of 0.3 < F r < 0.4. These phenomena can provide some suggestions on the small waterplane area twin hull(SWATH) design.

武夷山朱子文化旅游发展与路径

随着观光发展与旅游型态的进化,乡贤文化旅游已成为国人选择旅游方式之一,亦是全国旅游发展的重点领域。透过乡贤文化传播,不仅可起到乡贤文化资源保护与传承,还可运用其乡贤话题发展旅游观光,提升城市知名度,达到文化传承、资源共享,更能带动地方经济的发展。本研究之目的在找出武夷山朱熹文化旅游发展与创新的策略,透过对文献、案例的探讨与SWOT分析,再以TOWS矩阵匹配战略掌握竞争优势,形成最适合武夷山朱子文化旅游的建设路径。研究结果提出以下四个方面:朱子文化推进文旅合作发展;跨区域性的策略联盟;产业发展定位,形塑特色的区域产业;推动朱子文创园区,打造武夷优质城市。

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。

One-Step-Installation of Offshore Wind Turbine on Large-Scale Bucket-Top-Bearing Bucket Foundation

In 2010,the first offshore wind turbine with integrated installation was established in Qidong sea area of Jiangsu Province,China,which led to the implementation phase of one-step-installation technique based on the design and construction of large-scale bucket-top-bearing (LSBTB) bucket foundation.The critical technique of LSBTB bucket foundation included self-floating towing,penetration with adjustment of horizontal levelness,removability and one-step-installation.The process of one-step-installation included the prefabrication of LSBTB bucket foundation in onshore construction base,installation and debugging of wind power,overall water transportation of foundation and wind power system,and installation of foundation and offshore wind turbine on the appointed sea area.The cost of one-step-installation technique was about 5 000 Yuan/kW,which was 30%-50% lower than that of the existing technique.The prefabrication of LSBTB bucket foundation took about two months.During the one-step-installation process,the installation and debugging of wind power and overall water transportation need about one to two days in sea area within 35 m depth.After the proposed technique is industrialized,the cost will be further reduced,and the installation capacity is expected to be up to 500 wind turbines per year.

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.

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"。

Use of Helical Strakes for FIV Suppression of Two Inclined Flexible Cylinders in A Side-by-Side Arrangement

The experimental studies on flow-induced vibrations(FIV) reduction of two side-by-side flexible cylinders inclined at 45° by using the helical strakes were carried out in a towing tank. The main aim of the experiment is to check whether the helical strakes with a pitch of 17.5 D and a height of 0.25 D, which is considered as the most effective vibration suppression device for the isolated cylinder undergoing vortex-shedding, still perform very well to reduce FIV of two inclined flexible cylinders in a side-by-side arrangement. The vibration of two identical inclined cylinders with a mass ratio of 1.90 and an aspect ratio of 350 was tested in the experiment. The center-to-center distance between the two cylinders was 3.0 D. The uniform flow was simulated by towing the cylinder models along the tank.The towing velocity varied from 0.05 to 1.0 m/s with an interval of 0.05 m/s. The maximum Reynolds number can be up to 1.6×104. Three cases were experimentally studied in this paper, including two side-by-side inclined smooth cylinders, only one smooth cylinder fitted with helical strakes in the two side-by-side inclined cylinders system and both two cylinders attached with helical strakes. The variations of displacement amplitude, dominant frequency, FIV suppression efficiency and dominant mode for the two side-by-side inclined cylinders with reduced velocity were shown and discussed.