A towed magnetic gradiometer array for rapid, detailed imaging of utility, geological, and archaeological targets

Efficient and accurate acquisition of magnetic field and gradient data have applications over a large range of environmental, archaeological, engineering, and geologic investigations. Developments in new systems and improvements in existing platforms have progressed to the point where magnetic surveying is a heavily used and trusted technique. However, there is still ample room to improve accuracy and coverage efficiency and to include reliable vector information. We have developed a vector magnetic gradiometer array capable of recording high-resolution field and gradient data over tens of hectares per day at 50 cm sensor spacing. Towed by an all-terrain vehicle, the system consists of eight vertical gradiometer sensor packages and incorporates differential GPS and an inertial measurement system. With a noise floor of around 6 nT at 15 km/h towing speed and 230 Hz sample rates, large areas can be mapped efficiently and precisely. Data are processed using a straightforward workflow, using both standard and newly developed methodologies. The system described here has been used successfully in Denmark to efficiently map buried structures and objects. We give two examples from such applications highlighting the system's capabilities in archaeological and geological applications.

INCREASING THE EFFICIENCY OF WATER TRANSPORT OF THE FOREST TO INCREASE THE HYDRODYNAMIC PROPERTIES OF THE RAFT

Of all the known modern types of water transport of the forest, the most promising is timber rafting, which, when used, has both positive and negative properties. Negative indicators include such indicators as: seasonality of work, since use in the winter period is impossible, loss of wood when unloading logs onto water and a raft, large dimensions, complexity of management, the need to unload a raft when unloading it. Passes through non-standard sections of the river bed and subsequent formations, special requirements for the dimensions of the waterway, speed limits and others. One of the most acute problems caused by huge hydrodynamic resistance to movement, which increases with an increase in towing speed, is the limitation of the speed of movement of the raft in the water area. In this regard, the maximum speed of the raft in calm weather reaches no more than 1 1.2 m / s, while two or more powerful tugs are involved. The limited time frame for rafting on wooden rafts is due to the flood period during the spring floods and floods, and they have fallen on hard times. Increasing the raft’s allowable towing speed will shorten the raft’s transport time. A decrease in hydrodynamic resistance when the raft is moving will increase the maximum allowable speed of its towing, which will have a positive effect on the efficiency of timber rafting. Based on the analysis of existing known designs of modern rafts, as well as methods of influencing the reduction of hydrodynamic resistance in the field of shipbuilding, a number of methods have been proposed for reducing the hydrodynamic resistance to the movement of the raft. Methods of reducing the resistance to the movement of the raft by changing the features of its formation by placing separate sections or beams in the streamlined material, the introduction of hydrodynamic fairings are considered. The proposed methods for reducing the hydrodynamic resistance can significantly increase the efficiency of timber rafting.

Multi-Agent Simulation of Iceberg Mass Loss during Its Energy-Efficient Towing for Freshwater Supply

The problem of freshwater deficit in the last decade has progressed, not only in Africa or Asia, but also in European countries. One of the possible solutions is to obtain freshwater from drifting icebergs. The towing of large icebergs is the topic analyzed in various freshwater supply projects conducted in different zone-specific regions of the world. These projects show general effects of iceberg transport efficiency but do not present a detailed methodology for the calculation of their mass losses. The aim of this article is to develop the methodology to calculate the mass losses of icebergs transported on a selected route. A multi-agent simulation was used, and the numerical model to estimate the melting rate of the iceberg during its energy-efficient towing was developed. Moreover, the effect of towing speed on the iceberg’s mass loss was determined. It was stated that the maximum use of ocean currents, despite longer route and increased transport time, allows for energy-efficient transport of the iceberg. The optimal towing speed of the iceberg on the selected route was recommended at the range of 0.4–1 m/s. The achieved results may be of interest to institutions responsible for sustainable development and dealing with water resources and freshwater supply.

A towed magnetic gradiometer array for rapid, detailed imaging of utility, geological, and archaeological targets

Efficient and accurate acquisition of magnetic field and gradient data have applications over a large range of environmental, archaeological, engineering, and geologic investigations. Developments in new systems and improvements in existing platforms have progressed to the point where magnetic surveying is a heavily used and trusted technique. However, there is still ample room to improve accuracy, coverage efficiency, and to include reliable vector information. We have developed a vector magnetic gradiometer array capable of recording high resolution field and gradient data over tens of hectares per day at 50 cm sensor spacing. Towed by an all-terrain vehicle, the system consists of 8 vertical gradiometer sensor packages, and incorporates differential GPS and an inertial measurement system. With a noise floor of around 6 nT at 15 km/h towing speed and 230 Hz sample rates, large areas can be mapped efficiently and precisely. Data are processed using a straightforward workflow, using both standard and newly developed methodologies. The system described here has been used successfully in Denmark to efficiently map buried structures and objects. We give two examples from such applications highlighting the system’s capabilities in archaeological and geological applications.

Towfish Attitude Control: A Consideration of Towing Point, Center of Gravity, and Towing Speed

This paper deals with the attitude control of a towfish (underwater towed vehicle) with two elevators and a single rudder to improve the image quality of an attached sound navigation ranging (sonar) system. Image distortion can occur if the towfish shakes excessively. Since a towfish is connected to the mother ship through a towing cable and the motion of the towfish is affected not only by the motion of the cable, but also by the position of the center of gravity, towing point, and towing speed, it is necessary to analyze how these factors affect the towfish to appropriately control its attitude. In this study, a method for obtaining a feasible region of the towing point in accordance with the variations in the center of gravity and towing speed is proposed, and the feasible region obtained can ensure that pitch control can be achieved using the installed elevators. In addition, the allowable range of disturbances for yaw control was also investigated. Simulations were conducted using the dynamic models of the towfish and cable to check the obtained feasible region/range, and it was confirmed that there is a region/range where the attitude control can be carried out with relative ease.

Maneuverability and Hydrodynamics of a Tethered Underwater Robot Based on Mixing Grid Technique

The maneuverability and hydrodynamic performance of the tethered underwater robot in a uniform flow field is investigated. In this research, a tethered underwater robot symmetrically installed with NACA66 hydrofoils and Ka 4-70/19A ducted propellers around its main body is first constructed. The method of overlapping grid combined with sliding mesh is applied in the numerical simulations, and the principle of relative motion is adopted to describe the hydrodynamic responses of the tethered underwater robot during the robot manipulation. The reliability of the CFD methods applied in this research is verified by experimental results, and the comparison between numerical and experimental ones shows that there is very little difference being found. The numerical results indicate that computational cost due to the research’s large-scale domain can be effectively reduced by the adopted numerical methods, hydrofoils’ control effect is greatly influenced by the towing speeds, and thrusts issued from the ducted propellers are related to the tethered underwater robot’s position and towing speed.

Cooperative Maneuvering Mathematical Modeling for Multi-tugs Towing a Ship in the Port Environment

The towing operation of multi-tug-assisted ship navigation mainly relies on the experience of the captain, and there is no set of effective operation methods. Therefore, it is difficult to achieve accurate assisted navigation when multiple tugboats work in coordination. The calculation method of maneuverability of the towing system with multi-tug-assisted navigation is proposed in this paper. In view of the complexity of multi-tug-assisted large ship maneuvering, this article focuses on solving the problems of force analysis and maneuvering modeling between the multi-tug and ship systems. Firstly, a maneuvering mathematic model for towing ships is established, and the hydrodynamic force of the hull, rope force of the tugs, and force of wind interference are analyzed. The thrust and moment of the ducted azimuthal propeller are calculated, and the mathematical model of the tug’s cable tension is discussed. Then, the fourth-order Runge–Kutta method is used to solve the differential equations of the maneuvering motion of the ships and each tug. Based on the ship-towing process by multiple tugs, a multi-tug-assisted ship towing simulation platform was built by using the Visual Studio development tool. Finally, on the simulation platform, multi-tug longitudinal-towing-simulation experiments at different speeds were carried out, and the simulation of turning towing maneuvers under the influence of wind was done. The simulation results showed that as the towing speed increases, the initial towing speed fluctuates greatly. There is a significant drift effect on the ships by the wind force. And the wind will cause a fluctuation in the tug’s rope force. The simulation of the multi-tugs towing a ship entering the port was carried out in the port environment. The results showed that the multi-tug towing system and simulation platform may be used for the safety training of the tug’s crew.

Study on the Dynamic Responses of a Large Caisson during Wet-Towing Transportation

Large caissons are extensively applied as deep-water foundations in marine engineering. In fact, caissons are generally prefabricated and transported to project site by wet towing. Motion responses of large caissons and those occurring during the towing process were investigated, and CO2 emissions under various conditions were calculated. These are all considered to ensure towing safety and environmental protection. The caisson resistance coefficient was simulated via Ansys Fluent software. The effects of towrope length, towing speed, and drift depth on the motion responses of caissons under the combined action of wind and wave were evaluated via Ansys AQWA software. Maximum heave value was dominantly affected by rope length and draft depth, and its fluctuation was highly influenced by towing speed and draft depth. However, all of the above mentioned factors had insignificant influences on pitch response. When towing existed, rope tension was rapidly increased from zero to a constant value that depended on towing speed and drift depth. However, the speed of achieving this stable phase depended on the length of the towrope.

Simulation of changes in the length and tension of the cable during the towing operation

При разработке систем автоматического управления буксирной системой следует предварительно определить те её параметры, которые могут быть подвергнуты регулированию в процессе выполнения буксирной операции. Представляется возможным, что в числе таких регулируемых параметров можно рассматривать натяжение буксирного троса и (или) его длину. Причём регулирование указанных параметров может осуществляться как изменением скорости буксировки, так и работой буксирной лебёдки в приделах её технических возможностей. В качестве управляющего параметра можно выбирать любой из тех, которые характеризуют состояние движения буксируемого судна, в частности, угол отклонения буксирного троса от диаметральной плоскости (ДП) буксируемого судна, угловую скорость буксируемого судна или угол его дрейфа. Однако практическая сторона реализации этой идеи должна исходить из возможности получения управляющего сигнала, т.е. из того, какой из этих параметров измеряется с меньшими трудностями и большей точностью. После этого не составляет труда сформировать управляющий сигнал для буксирной лебедки буксирующего судна или для его двигателя как механизма, выполняющего исполнительную функцию. Существующие на данный момент автоматические судовые буксирные лебедки решают не задачу управления, а задачу безопасности, уменьшая натяжение в тросе при превышении им некоторого заданного предельного значения или подбирая трос при снятии напряжения в нём. When developing automatic control systems for the towing system, it is necessary to determine beforehand the parameters that can be regulated during the towing operation. It is possible that among these adjustable parameters, we can consider the tension of the tow rope and (or) its length. Moreover, the regulation of these parameters can be carried out both by changing the towing speed, and by working the tow winch in the limits of its technical capabilities. As a control parameter, you can select any of those that characterize the state of movement of the towed vessel, in particular, the angle of deviation of the tow rope from the diametrical plane (DP) of the towed vessel, the angular speed of the towed vessel or the angle of its drift. However, the practical side of implementing this idea should be based on the possibility of obtaining a control signal, i.e., which of these parameters is measured with less difficulty and greater accuracy. After this, it is not difficult to generate a control signal for the towing winch of the towing vessel or for its engine as a mechanism that performs an executive function. Currently existing automatic ship towing winches solve the problem of safety rather than control, reducing the tension in the cable when it exceeds a certain set limit value or selecting the cable when the tension in it is removed.

Experimental and numerical study of the resonant feature of internal gravity waves in the case of ‘dead water’ phenomenon

<p> ‘Dead water’ phenomenon, which is essentially a ship-wave in a stratified fluid is studied experimentally in a laboratory tank. Interfacial waves are excited by a moving ship model in a quasi-two-layer fluid, which leads to the development of a drag force that reaches the maximum at the largest wave amplitude in a critical ‘resonant’ towing speed, whose value depends on the structure of the vertical density profile. We utilize five ships of different lengths but of the same width and wet depth. The experimental analysis focuses on the variability of the interfacial wave amplitudes and wavelengths as a function of towing speed in different stratifications. Data evaluation is based on linear two- and three-layer theories of freely propagating interfacial waves and lee waves. We observe that although the internal waves have considerable amplitude, linear theory still gives a surprisingly adequate description of subcritical to supercritical transition and the associated amplification of internal waves.</p>