Transient behavior of towed cable systems during ship turning maneuvers

The dynamic behavior of a towed cable system that results from the tow ship changing course from a straight-tow trajectory to one involving steady circular turning at a constant radius is examined. For large-radius ship turns, the vehicle trajectory and vehicle depth assumed, monotonically and exponentially, the large-radius steady-state turning solution of Chapman [Chapman, D.A., 1984. The towed cable behavior during ship turning manoeuvers. Ocean Engineering 11, 327–361]. For small-radius ship turns, the vehicle trajectory initially followed a corkscrew pattern with the vehicle depth oscillating about and eventually decaying to the steady-state turning solution of Chapman (1984). The change between monotonic and oscillatory behavior in the time history of the vehicle depth was well defined and offered an alternate measure to Chapman's (1984) critical radius for the transition point between large-radius and small-radius behavior. For steady circular turning in the presence of current, there was no longer a steady-state turning solution. Instead, the vehicle depth oscillated with amplitude that was a function of the ship-turning radius and the ship speed. The dynamics of a single 360° turn and a 180° U-turn are discussed in terms of the transients of the steady turning maneuver. For a single 360° large-radius ship turn, the behavior was marked by the vehicle dropping to the steady-state turning depth predicted by Chapman (1984) and then rising back to the initial, straight-tow equilibrium depth once the turn was completed. For small ship-turning radius, the vehicle dropped to a depth corresponding to the first trough of the oscillatory time series of the steady turning maneuver before returning to the straight-tow equilibrium depth once the turn was completed. For some ship-turning radii, this resulted in a maximum vehicle depth that was greater than the steady-state turning depth. For a 180° turn and ship-turning radius less than the length of the tow cable, the vehicle never reached the steady-state turning depth.     

Nonlinear dynamics of an elastic cable during laying operations in rough sea

A numerical approach for predicting motion and tension of extensible marine cables during laying operations in a rough sea is presented here. The solution methodology consists of dividing the cable into straight elements, which must satisfy an equilibrium equation and compatibility relations. The system of nonlinear differential equations is solved by the Runge–Kutta method, taking the effect of regular and/or irregular waves into account explicitly.

Illustrative applications of the method are given for a typical cable laying ship. The results are presented as rms values of the cable dynamic tension and corresponding dynamic factor for two different types of cable and several values of cable stiffness. The effect of axial deformation on the maximum tension at the shipboard pulley location is highlighted.     

Dynamics and control of a towed underwater vehicle system, part I: model development

Autonomous vehicles are being developed to replace the conventional, manned surface vehicles that tow mine hunting towed platforms. While a wide body of work exists that describes numerical models of towed systems, they usually include relatively simple models of the towed bodies and neglect the dynamics of the towing vehicle. For systems in which the mass of the towing vehicle is comparable to that of the towed vehicle, it becomes important to consider the dynamics of both vehicles. In this work, we describe the development of a numerical model that accurately captures the dynamics of these new mine hunting systems. We use a lumped mass approximation for the towcable and couple this model to non-linear numerical models of an autonomous surface vehicle and an actively controlled towfish. Within the dynamics models of the two vehicles, we include non-linear controllers to allow accurate maneuvering of the towed system.     

Dynamics and control of towed underwater vehicle system, part II: model validation and turn maneuver optimization

This paper presents a validation of a three-dimensional dynamics model of a towed underwater vehicle system and discusses an application of the model to improve the performance of the system during a turn maneuver. The model was validated by comparing its results to experimental sea trial data, as well as to results from another independently developed simulation. The dynamics model was then imbedded in an optimization routine. This routine was used to vary turn radii in order to improve the U-turn performance. Significant improvements were obtained relative to a standard semicircular turn geometry.     

Dynamic modeling of cable towed body using nodal position finite element method

This paper analyses nonlinear dynamics of cable towed body system. The cable has been modeled and analyzed using a new nodal position finite element method, which calculates the position of the cable directly instead of the displacement by the existing finite element method. The newly derived nodal position finite element method eliminates the need of decoupling the rigid body motion from the total motion, where numerical errors arise in the existing nonlinear finite element method, and the limitation of small rotation in each time step in the existing nonlinear finite element method. The towed body is modeled as a rigid body with six degrees of freedom while the tow ship motion is treated as a moving boundary to the system. A special procedure has been developed to couple the cable element with the towed body. The current approach can be used as design tool for achieving improved directional stability, maneuverability, safety and control characteristics with the cable towed body. The analysis results show the elegance and robustness of the proposed approach by comparing with the sea trial data.     

Evaluation of the effects of the communication cable on the dynamics of an underwater flight vehicle

This paper presents a numerical scheme to evaluate the effects of the communication cable attached to an underwater flight vehicle. Both simulation and model validation results show that the numerical scheme is effective and provides a means for developing a feed-forward controller to compensate for the cable effects when developing an autopilot for the tethered vehicle. Moreover, the numerical scheme can also be applied to predict the effects of the ROVs umbilical during its deployment.     

An experimental investigation into the influence of the damage openings on ship response

Ship motions after damage are difficult to evaluate since they are affected by complex phenomena regarding fluid and structures interactions. The possibility to better understand how ship behavior in damage is influenced by these phenomena is important for improving ship safety, especially for passenger vessel.In this paper an experimental campaign is carried out on a passenger ferry hull, to show the effects of the water dynamics across damage openings on ship motions. Novel aspects of this research include the study of the effects of the damage position on the ship roll response. The study is carried out for still water and for beam regular waves at zero speed.Results from the experiments carried out underline that the roll behavior of a damaged ship is affected by the position of damage opening and not only by its size. Assuming the same final equilibrium conditions after flooding but characterized by different damage openings it is possible to observe how motions RAOs and roll decay characteristics modify according to the opening locations.     

The influence of long tides on ecosystem dynamics in the Barents Sea

The Barents Sea ecosystem has been associated with large biomass fluctuations. If there is a hidden deterministic process behind the Barents Sea ecosystem, we may forecast the biomass in order to control it. This presentation concludes, for the first time, investigations of a long data series from North Atlantic water and the Barents Sea ecosystem. The analysis is based on a wavelet spectrum analysis from the data series of annual mean Atlantic sea level, North Atlantic water temperature, the Kola section water temperature, and species from the Barents Sea ecosystem.The investigation has identified dominant fluctuations correlated with the 9.3-yr phase tide, the 18.6-yr amplitude tide, and a 74-yr superharmonic cycle in the North Atlantic water, Barents Sea water, and Arctic data series. The correlation between the tidal cycles and dominant Barents Sea ecosystem cycles is estimated to be R=0.6 or better. The long-term mean fluctuations correlate with the 74-yr superharmonic cycle. The wavelets analysis shows that the long-term 74-yr cycle may introduce a phase reversal in the identified 18-yr periods of temperature and salinity. The present analysis suggests that forced vertical and horizontal nodal tides influence the ocean's thermohaline circulation, and that they behave as a coupled non-linear oscillation system.The Barents Sea ecosystem analysis shows that the biomass life cycle and the long-term fluctuations correlate better than R=0.5 to the lunar nodal tide spectrum. Barents Sea capelin has a life cycle related to a third harmonic of the 9.3-yr tide. The life cycles of shrimp, cod, herring, and haddock are related to a third harmonic of the 18.6-yr tide. Biomass growth was synchronized to the lunar nodal tide. The biomass growth of zooplankton and shrimp correlates with the current aspect of lunar nodal tidal inflow to the Barents Sea. The long-term biomass fluctuation of cod and herring is correlated with a cycle period of about 3×18.6=55.8 yr. This analysis suggests that we may understand the Barents Sea ecosystem dynamic as a free-coupled oscillating system to the forced lunar nodal tides. This free-coupled oscillating system has a resonance related to the oscillating long tides and the third harmonic and superharmonic cycles.     

Climate variance influence on the non-stationary plankton dynamics

We examined plankton responses to climate variance by using high temporal resolution data from 1988 to 2007 in the Western English Channel. Climate variability modified both the magnitude and length of the seasonal signal of sea surface temperature, as well as the timing and depth of the thermocline. These changes permeated the pelagic system yielding conspicuous modifications in the phenology of autotroph communities and zooplankton. The climate variance envelope, thus far little considered in climate-plankton studies, is closely coupled with the non-stationary dynamics of plankton, and sheds light on impending ecological shifts and plankton structural changes. Our study calls for the integration of the non-stationary relationship between climate and plankton in prognostic models on the productivity of marine ecosystems.     

Recent sediment dynamics in hadal trenches: Evidence for the influence of higher-frequency (tidal,near-inertial) fluid dynamics

In addition to high hydrostatic pressure, scarcity of food is viewed as a factor that limits the abundance and activity of heterotrophic organisms at great ocean depths, including hadal trenches. Supply of nutritious food largely relies on the flux of organic-rich particulate matter from the surface ocean. It has been speculated that the shape of hadal trenches helps to ‘funnel’ particulate matter into the deeper parts of the trench, leading to sediment ‘focussing’ and improved benthic food supply. Here we investigate for five Northwest Pacific trenches the efficiency of sediment focussing by evaluating ratios of measured (sediment-derived) and expected (water-column-derived) sedimentary inventories of the naturally occurring and radioactive particulate-matter tracer ²¹⁰Pb_xs. The sites comprise a broad range of surface-ocean productivity and physical-oceanographic regimes. Across the five trench-axis settings the inventory ratio varies between 0.5 and 4.1, with four trench-axis settings having ratios>1 (sediment focussing) and one trench-axis setting a ratio<1 (sediment winnowing). Although the fluid- and sediment-dynamical forcing behind sediment focussing remains unclear, this study finds evidence for another mechanism that is superimposed on, and counteracts, the focussing mechanism. This superimposed mechanism is related to higher-frequency (tidal, near-inertial) fluid dynamics. In particular, there is evidence for a strong and negative relation between the intensity of propagating internal tides and the extent of sediment focussing in the trench-axis. The relation can be approximated by a power function and the most intense drop in sediment focussing already occurs at moderate internal-tide intensities. This suggests that propagating internal tides may have a subtle but significant influence on particulate-matter dynamics and food supply in hadal trenches in particular, but possibly also in the deep seas in general. A mechanism for the influence of internal tides on sediment dynamics is proposed.     

水下拖曳升沉补偿系统水动力数学模型研究

建立变缆长的水下拖曳升沉补偿系统水动力学偏微分方程组和边界条件.拖缆动力学模型基于Ablow and Schechter模型,拖体采用水下运载体六自由度方程模拟,运用有限差分法离散偏微分方程组和牛顿迭代法计算变缆长情况下拖体深度与拖缆各点张力的动态取值.数值计算结果表明采用收放拖缆的升沉补偿方法能够有效削弱母船升沉运动对拖体深度和拖缆张力的影响.     

水下机器人光纤微缆动力学研究

讨论了水下机器人远程通信光纤微缆的动力学问题,研究分析了在海洋层流条件下水下机器人的运动对光纤微缆张力的影响,在仿真分析的基础上提出了对光纤微缆收放系统的设计要求并给出了概念设计方案。     

The motion of a deep-sea remotely operated vehicle system: Part 1: Motion observations

Rapid and high-resolution motion and tension measurements were made of a caged deep-sea remotely operated vehicle (ROV) system. Simultaneous measurements were made of all six components of motion at the cage and ship A-frame and of the tension in the tether at the ship. Data were collected for cage depths of 0–1765 m. The most significant forcing was in the wave-frequency band (0.1–0.25 Hz) and accounted for over 90% of the variance of vertical acceleration. The vertical acceleration of the cage lagged the acceleration of the A-frame by up to 1.9 s and its variance was larger by up to a factor 2.2. For moderate displacements of the A-frame (≤2 m), the system is only weakly non-linear because the harmonics (3rd and 5th) of the vertical acceleration of the cage account for less than 2% of the total variance. The system is essentially one-dimensional because only the vertical motion of the cage and the vertical motion of the A-frame were coherent, while horizontal motions of the cage were weak and incoherent with any component of motion of the A-frame. The natural frequency of the system is 0.22 Hz at 1730 m, and we estimate that it is within the waveband for depths between 1450 m and the full operating depth of 5000 m.Large vertical excursions of the A-frame produce momentary slack in the tether near the cage. Retensioning results in snap loads with vertical accelerations of 0.5 gravity. Large rates of change of tension and vertical acceleration first occur at the cage during its downward motion and propagate to the surface with the characteristic speed (3870 m s⁻¹) of tensile waves for the tether. Six echoes are clearly detectable at both ends of the tether, and their pattern is extremely repeatable in different snap loads. Due to misalignment of the tether termination with the centres of mass and buoyancy, the cage pitches by up 14° during a snap. The resulting small radius of curvature poses the greatest stress on the tether.     

陆岛互通工程对海岛产业用地时空格局影响分析——以舟山市为例

陆岛联动发展对提升海岛综合价值和推进陆海统筹战略具有重要意义.以舟山市为例,基于多源遥感影像、POI数据、景观格局梯度分析和相关性分析,探讨了陆岛连通工程对海岛产业用地演变的影响及其时空格局特征.主要结论如下:(1) 2010-2018年期间,舟山市陆域用地面积总体扩张,其中第一产业用地递减,第二、三产业用地迅速增加,产业用地转换频繁复杂.(2)海岛产业用地演变呈显著时空差异性.第一产业用地分布逐渐分散化、破碎化,重心向东北方向转移.第二产业用地集中于本岛沿岸并向外围邻近小岛辐射,其重心转移最为明显,趋向西北方.第三产业用地呈现双核多点分布特征,其中本岛南部城市核心区集聚扩张,在外围涌现零星增加点,其重心持续向西北方转移.(3)样带梯度分析表明2010-2015年间舟山海岛产业用地景观指数变化更高,而市中心产业用地景观格局变化较少,随着离市中心距离增加景观指数变化增强,在两端的金塘岛和朱家尖岛出现明显波动.海岛沿岸第二、三产业用地景观格局变化剧烈.(4)舟山海岛产业用地景观变化与跨海大桥建设、岛内交通网络、距离海岸线等地理因素呈现显著相关性和时空差异性,跨海大桥对第一产业用地的影响逐渐减弱,后期第二、三产业用地格局变化更多受到岛内交通网络、岸线资源、本底产业基础等因素影响.     

2004-2015年夏季渤海湾生态监控区网采浮游植物变化研究

基于2004-2015年12年的夏季渤海湾生态监控区浮游植物网样数据,开展浮游植物群落及96种定种的多年变化研究。结果表明:12年共鉴定出5门120种,硅藻占绝对优势,甲藻次之,赤潮生物种类占定种的59%;各年份物种数变化范围为23~61种,年平均细胞丰度范围为（7~87 731）×104个/m3,物种多样性指数范围为1.13~3.04,丰富度指数范围0.36~1.12,均匀度指数范围0.31~0.72;12年中生物种类数、细胞丰度总体呈上升趋势,多样性指数、丰富度指数在波动中呈上升趋势,均匀度指数呈略有下降趋势;样品中几乎每年都出现的物种有10种,只检出1年的物种有23种;站位检出率不小于50%的物种只有4种,小于0.01%的有57种;星脐圆筛藻（Coscinodiscus asteromphalus）、中肋骨条藻（Skeletonema costatum）、格氏圆筛藻（Coscinodiscus granii）、叉角藻（Ceratium furca）和旋链角毛藻（Chaetoceros curvisetus）为该区域的优势种;近5年细胞丰度水平普遍比2010年前高,格氏圆筛藻（C.granii）、中肋骨条藻（S.costatum）、夜光藻（Noctiluca scintillans）等10种常见种密度呈增长趋势,较常见种长菱形藻（Nitzschia longissima）、星脐圆筛藻（C.asteromphalus）和北方角毛藻（Chaetoceros borealis）多年呈下降趋势。本研究有助于掌握该区域浮游植物物种的本底情况及演变趋势。