Towing Speed Research Articles

Damage assessment and survival estimates in the wedge clam (Donax trunculus) caught by mechanical dredging in the northern Alboran Sea

ABSTRACT This paper describes the impact of dredging on populations of the wedge clam (Donax trunculus) at two sites along the northern Alboran coast. Damage was assessed by quantifying shell and foot damage on commercial clams caught with mechanical dredges. Survival experiments were carried out to assess their survival capacity after 24 h purification treatment and 72 h cold storage, which represents an issue of great interest for fisheries research, management and marketing. Overall, 2.4% of wedge clams suffered any type of damage, including chipped edges and scratched valves. Higher proportions of shell-damaged individuals were positively correlated to bottom features (e.g. gravel content in sediment). Moreover, higher towing speed significantly increased shell damage. Analyses of shell damage areas revealed that the anterior dorsal and ventral parts of the shell are the most vulnerable to dredging. A total of 15.9% of individuals showed damage on the foot, which seems not to affect their survival. The incidence of foot damage was mostly linked to sublethal predation, reflected in a positive correlation between the proportion of foot-damaged individuals and biomass of decapod crustaceans in the fishing ground. Finally, D. trunculus exhibited very low mortality rates after 24 h purification treatment (0.2–0.4%) and 72 h cold storage (0.3–3.2%). The survival rate at the end of the experiment was high (>96%), with the highest mortality observed 96 h after the fishing day. No correlations were found between mortality rates and bottom type or towing speed.

Study of the effect of hull geometry on the towing resistance of motor ferries when overcoming water obstacles

Objective. The article studies the influence of the hull geometry on the towing resistance and speed of ferry vehicles on the water when overcoming water obstacles.Methods. 3D modeling methods are used in CAD and CAE packages to study the degree of influence of the hull geometry on the water resistance to the movement of the ferry vehicle, which makes it possible to accurately model the working processes occurring when flowing around motor ferries.Results. The analysis of the results of computer simulation of the movement of a ferry vehicle of the original design on the water is carried out. The advantages and disadvantages of the ferry bridge machine of the original design are determined, and various variants of design and layout schemes are proposed, the use of which allows increasing the speed and maneuvering characteristics of ferry vehicles.Conclusion. A variant of the design and layout scheme of a motor ferry is proposed, which allows improving the hydrodynamic characteristics of the ferry vehicle body by using modern technical solutions aimed at reducing towing resistance and increasing the speed of transportation when overcoming water obstacles.

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.

Specific Features of Using the Linearization Method for the Analysis of Low-Frequency Oscillations of a Towed System

The results of experiments and numerical calculations in the low-frequency range of oscillations of the power and geometric characteristics of a towed system (TS) are presented. The hypotheses used in the linear amplitude-frequency analysis are verified with the use of a discrete model. The limits of applicability of the finite-difference method for numerical TS simulation are determined on the basis of a continuous hyperbolic model that takes into account varying lengthwise tension and finite speed of longitudinal and transverse (configurational) waves. The total error of numerical simulation does not exceed 15–20%. There is a certain delay both in the angle of TS deflection from the vertical and in the maximum horizontal component of the tensile force at its root point. It may be one of the causes of breakage of TS in certain conditions of oscillations and at a certain towing speed, when the tugboat and the TS oscillate in antiphase.

Deep-sea <i>in-situ</i> laser Doppler velocity measurement system

A set of 4000-meter laser Doppler hydrothermal velocity measurement prototype suitable for deep sea <i>in-situ</i> measurement is developed in this work. In the system, an integrated design is adopted. The system is composed of a light source module, an optical module, and a Doppler signal processing module. The system is encapsulated in a pressure chamber with <i>L</i>500 mm × <i>Φ</i>205 mm to form an integrated optical measuring probe. An optical path of two-beam laser Doppler velocity measurement with strong local oscillator is proposed. The prototype is used to measure the simulated velocity in the laboratory. The measurement range is 0.01–10 m/s, and the flow velocity measurement resolution is 0.001 m/s. The experimental results preliminarily prove the feasibility of the laser Doppler velocity measurement system. After that, a withstanding voltage test on the system is conducted at the Qingdao Deep Sea Base, and the system obtains a normal signal under a high pressure of 40 MPa. A speed comparison measurement is carried out at the China Institute of Water Resources and Hydropower Research. In a low speed range from 0.01 m/s to 0.2 m/s, comparing with the acoustic Doppler velocity meter, the maximum measurement relative error is –9.43%. In a high speed range from 0.8 m/s to 9.6 m/s, comparing with the nozzle standard flow rate system, the maximum relative measurement error is –1.65%. The prototype system is tested in a shallow sea in Lingshui, Hainan. The sinking speed of the prototype system that sinks together with a crane down to a water depth of 50 m, and the towing speed of the system together with the ship at a depth of 2 m are tested. The test proves that the prototype system works normally in a shallow sea environment.

Analysis on longitudinal vibration law of deep sea stepped mining pipe

In order to study the longitudinal vibration law of the deep sea stepped mining pipe, the pipe is regarded as the beam element and discrete by the finite element method and the mathematical model is established. Based on the Wilson-θ integration method, the numerical calculation is performed and the longitudinal vibration law under different pipe lengths, pipe thicknesses, and towing speeds is obtained. The research shows that the vibration is the irregular oscillating motion, and the law of the vibration amplitude from the top to the bottom is to decrease first and then to increase. Under the same working conditions, increasing the total length of the mining pipe, the pipe thickness, and the towing speed will reduce the amplitude of the longitudinal vibration, but only when the total length of the pipe changes, will the position of the minimum vibration amplitude be changed. The pipe thickness and the towing speed cannot change the vibration frequency, while the pipe length can change the vibration frequency. When the same external damping is added, reducing the pipe length, pipe thickness, and towing speed will increase the vibration intensity attenuation value and enhance the damping effect.

Mitigating seafloor disturbance of bottom trawl fisheries for North Sea sole Solea solea by replacing mechanical with electrical stimulation.

Ecosystem effects of bottom trawl fisheries are of major concern. Although it is prohibited to catch fish using electricity in European Union waters, a number of beam trawlers obtained a derogation and switched to pulse trawling to explore the potential to reduce impacts. Here we analyse whether using electrical rather than mechanical stimulation results in an overall reduction in physical disturbance of the seafloor in the beam-trawl fishery for sole Solea solea. We extend and apply a recently developed assessment framework to the Dutch beam-trawl fleet and show that the switch to pulse trawling substantially reduced benthic impacts when exploiting the total allowable catch of sole in the North Sea. Using Vessel Monitoring by Satellite and logbook data from 2009 to 2017, we estimate that the trawling footprint decreased by 23%, the precautionary impact indicator of the benthic community decreased by 39%, the impact on median longevity of the benthic community decreased by 20%, the impact on benthic biomass decreased by 61%, and the amount of sediment mobilised decreased by 39%. The decrease in impact is due to the replacement of tickler chains by electrode arrays, a lower towing speed and higher catch efficiency for sole. The effort and benthic physical disturbance of the beam-trawl fishery targeting plaice Pleuronectes platessa in the central North Sea increased with the recovery of the plaice stock. Our study illustrates the utility of a standardized methodological framework to assess the differences in time trends and physical disturbance between gears.

THE COMMERCIAL AND DISCARD CATCH RATES OF THE TRAWL FISHERY IN THE İSKENDERUN BAY (NORTHEASTERN LEVANTINE SEA)

The management of fishery is significant due to the sustainability of marine resources. Therefore, the fishing areas should be constantly monitored. In this study, the fishery data were collected from the Iskenderun Bay (Northeastern Levantine Sea) with a rented commercial trawl vessel. The fishery-dependent data was recorded during the 2012-2013 fishing season with the help of the crew. 33 tows were achieved using a trawl net (codend diamond mesh size of 44 mm) for 26 hours. Each tow was limited with 70 min and the towing speed varied between 2.5 to 3.0 knots. The depth contour ranged from 39 to 69 m. While 32 species were evaluated as discard, 35 species were included in the landed catch. The total catch consisted of 67.2% the landed and 32.8% of the discarded fish in terms of CPUEW (catch per unit effort by weight).

Numerical prediction of flow noise levels on towed sonar array

Flow noise originating in the turbulent boundary layer (TBL) often severely limits the performance of towed sonar array. Therefore, it is necessary to predict this noise for the design of an efficient towed array. This paper presents large eddy simulation methodology to establish the TBL properties and wall pressure fluctuations on a 12 m long towed array with length to diameter ratio of 1200 in the operating tow speed range of 2 to 5 knots in water. The computed flow noise levels are compared with experimental measurements available in the literature successfully. The effectiveness of scaling the flow noise spectra with the diameter and tow speed is discussed, and non-dimensional wall pressure spectra presented with respect to non-dimensional frequency. The overall sound pressure levels are also compared with experimental data that show good accuracy achieved by the proposed numerical methodology.

Towing Test Data Set of the Kyushu University Kite System

Kites can be used to harvest wind energy with substantially lower material and environmental footprints and a higher capacity factor than conventional wind turbines. In this paper, we present measurement data from seven individual tow tests with the kite system developed by Kyushu University. This system was designed for 7 kW traction power and comprises an inflatable wing of 6 m2 surface area with a suspended kite control unit that is towed on a relatively short tether of 0.4 m by a truck driving at constant speed along a straight runway. To produce a controlled relative flow environment, the experiment was conducted only when the background wind speed was negligible. We recorded the time-series of 11 different sensor values acquired on the kite, the control unit and the truck. The measured data can be used to assess the effects of the towing speed, the flight mode and the lengths of the control lines on the tether force.

The Influence of a Method of Bracing a Fiber-Optical Seismic Streamer during Towing on the Parameters of Its Output Signal

The dependence of the noise density in a signal of a fiber-optic towed streamer in a frequency band of 10 Hz–1 kHz on the towing speed in a range of 1 to 5 knots, on the coefficient of relative elongation of its elastic section, its type, and on the type of attachment of the elastic section to the towed body have been studied. In addition, the dependence of the tensile load on the studied streamer on the towing speed is obtained. The experimental data obtained during field tests on the streamer noise level and their analysis are presented. The reduction of the towing noise level when using an elastic section occurred by a factor of up to 3 in a frequency range of 180 to 600 Hz depending on the type of elastic section when attaching it to a strength member of the towed body, and up to 2 in the entire studied frequency range.

Hardware in the Loop Simulation and Control Design for Autonomous Free Running Ship Models

This paper presents an hardware-in-the-loop (HIL) simulation system tool to test and validate an autonomous free running model system for ship hydrodynamic studies with a view to verification of the code, the control logic and system peripherals. The computer simulation of the plant model in real-time computer does not require the actual physical system and reduces the development cost and time for control design and testing purposes. The HIL system includes: the actual programmable embedded controller along with peripherals and a plant model virtually simulated in a real-time computer. With regard to ship controller design for ship model testing, this study describes a plant model for surge and a Nomoto first order steering dynamics, both implemented using Simulink software suit. The surge model captures a quasi-steady state relationship between surge speed and the propeller rpms, obtained from simple forward speed towing tank tests or derived analytically. The Nomoto first order steering dynamics is obtained by performing the standard turning circle test at model scale. The control logic obtained is embedded in a NI-cRIO based controller. The surge and steering dynamics models are used to design a proportional-derivative controller and an LQR controller. The controller runs a Linux based real-time operating system programmed using LabVIEW software. The HIL simulation tool allows for the emulation of standard ship hydrodynamic tests consisting of straight line, turning circle and zigzag to validate the combined system performance, prior to actual for use in the autonomous free-running tests.

An experiment revealing the ability of a side‐scan sonar to detect CO2 bubbles in shallow seas

AbstractWith the aim of using side‐scan sonar (SSS) in marine monitoring at offshore CO2 storage sites, an experiment was conducted in a bay with a flat seabed, approximately 32 m deep. CO2 bubbles released at regulated rates between 500 and 5000 mL min−1 were searched for with SSS to elucidate the detection limit, which depends on the towing speed and the altitude of SSS, and the horizontal distance between the release point and SSS. When the towing speed was less than 6 knots, SSS was able to detect CO2 bubbles released at 1000 mL min−1 (approximately 4 tonnes year−1), which is an extremely small rate compared with injection rates in commercial scale storage, O(106) tonnes year−1. The time required for searching an area of 1 km2 with SSS was estimated to be between 1.7 and 3.4 hours, assuming that SSS was towed at an altitude of 27 m. Thus, SSS was demonstrated to be serviceable for marine monitoring. pH measured at 5 m away from the release point dropped by larger than 0.05 four times during the experiment. Only one of them might have been due to the CO2 release, and the others were due to intrusion of water from deeper layers because temperature, salinity and dissolved oxygen simultaneously changed. This indicates that bubble searching with SSS could detect smaller‐scale CO2 leakages than locating anomalous carbonate values, although the latter is still important in case all or most of CO2 dissolve before the emission to the sea. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

Hydrodynamic characteristics of a full-scale kelp model for aquaculture applications

Hydrodynamic characteristics are needed to optimize the design of kelp aquaculture systems. To support this need, the objective of this study was to resolve both the normal and tangential drag forces acting on a dense aggregate of kelp blades using full-scale physical model tests. The physical model was designed to match the exposed length, individual blade flexural rigidity, the number of blades per unit width, the mass/length of biomass, and the aggregate mass density of kelp cultured at the University of New England experimental aquaculture lease site in Saco Bay, Maine USA. Tow tests were conducted at the United States Naval Academy in a tank with the dimensions of 116m × 7.9m × 4.9 m. The large tank size enabled the use of the full-scale physical model, minimizing dynamic similarity issues. In a series of tests, the model was towed in orientations both aligned and perpendicular to the tow direction. Horizontal and vertical reaction forces were measured for five tow speeds, along with the deflection of the dense kelp aggregate. With these datasets and the wet weight biomass per length of the model, normal and tangential drag forces were calculated. Drag components were processed into corresponding normal and tangential drag-area values. The drag-area representation was chosen since reference areas were ambiguous for both the actual kelp and model. At the higher speeds, the total horizontal drag in the aligned configuration were slightly lower than for the perpendicular orientation. Normal drag-areas as a function of tow speed ranged from 2.36 m2/m to 1.39 m2/m for the aligned case and from 2.49 to 1.88 m2/m for the perpendicular case. Tangential drag-areas as a function of tow speed ranged from 0.264 m2/m to 0.0325 m2/m for the aligned case and from 0.213 to 0.0415 m2/m for the perpendicular case. A transition from a bluff body to a streamlined body occurred as the tow speeds increased. To investigate this transition, horizontal components of the normal and tangential drag forces were reconstructed with the results of the tow tests. The reconstructed forces were obtained using a force balance system of equations with drag-area values for tow speeds less than 0.25 m/s extrapolated from the experimental datasets. For both aligned and perpendicular orientations, the model-aggregate reconfigured at a threshold of 0.25 m/s. We defined the threshold for reconfiguration as the tow speed at which the horizontal component of tangential drag equaled or exceeded the horizontal component of the normal drag. The drag-area results from this study can be incorporated into a dynamic fluid-structure interaction model representing kelp aggregates as a finite element beam prescribed with in-situ values of length, volume, mass density and flexural-rigidity of kelp material.

Identification and Removal of Non-acoustic Noise in Towed Array Sonar Using F-Κ Transform for Enhanced Torpedo Detection

Low frequency passive towed array sonar is an essential component in a torpedo detection system for surface ships. Compact towed arrays are used for torpedo detection and they will be towed at higher towing speeds compared to conventional towed array sonars used for surveillance. Presence of non-acoustic noise in towed array sensors at higher towing speeds degrades torpedo detection capability at lower frequencies. High wavenumber mechanical vibrations are induced in the array by vortex shedding associated with hydrodynamic flow over the array body and cable scope. These vibrations are known to couple into the hydrophone array as nonacoustic noise sources and can impair acoustic detection performance, particularly in the forward end fire direction. Lengthy mechanical vibration isolation modules can isolate vibration induced noise in towed arrays, but this is not recommended in a towed array which is towed at high speeds as it will increase the drag and system complexity. An algorithm for decomposing acoustic and non-acoustic components of signals received at sensor level using well known frequency-wavenumber transform (F-K transform) is presented here. Frequency-wavenumber diagrams can be used for differentiating between acoustic and non-acoustic signals. An area of V shape is identified within the F-K spectrum where acoustic energy is confined. Energy outside this V will highlight non-acoustic energy. Enhanced simultaneous spatio-temporal and spatio-amplitude detection is possible with this algorithm. Performance of this algorithm is validated through simulation and experimental data.

Internal gravity wave radiation from a stratified turbulent wake

The near-field energetics and directional properties of internal gravity waves (IGWs) radiated from the turbulent wake of a sphere towed through a linearly stratified fluid are investigated using a series numerical experiments. Simulations have been performed for an initial Reynolds number and internal Froude number , defined using body-based scales – , the sphere diameter; , the tow speed; and , the Brunt–Vaisala frequency. Snapshots of temporally evolving wake flow fields are sampled over the full wake evolution. The energy extracted from the wake through internal wave radiation is quantified by computing the total wave power emitted through a wake-following elliptic cylinder. The total time-integrated wave energy radiated is found to increase with and decrease with . The peak radiated wave power occurs at early times, near to the onset of buoyancy control, and is found to be approximately unchanged in magnitude as is increased. For the two higher considered, at late times, IGWs continue to be emitted – accounting for a distinct increase in total radiated wave energy. The most powerful IGWs are radiated out of the wake at a wide range of angles for , at to the horizontal for , and nearly parallel to the horizontal late in the non-equilibrium regime of wake evolution. Internal wave radiation is found to be an important sink for wake kinetic energy after , suggesting wave radiation cannot be neglected when modelling stratified turbulent wakes in geophysical and ocean engineering applications.

Numerical Prediction of Wall Pressure Fluctuations in a Turbulent Boundary Layer on a Cylinder in Axial Flow

Flow noise originating in the turbulent boundary layer (TBL) often severely limits the performance of towed sonar cylinder and therefore it is necessary to predict this noise for the design of efficient towed cylinder. This paper presents large eddy simulation methodology to establish the TBL properties and wall pressure fluctuations on a 3 m long cylinder with length to diameter ratio of 315 in the operating speed of 11.4 m/s in air. The computed flow induced sound is compared with experimental measurement available in the literature successfully. The effectiveness of scaling the flow noise spectra with diameter and tow speed is discussed and non-dimensional wall pressure spectra presented with respect to non-dimensional frequency. The overall sound pressure levels are also compared with experimental data that show good accuracy achieved by the proposed numerical methodology.

Influence of towing speed on effectiveness of rolling dynamic compaction

Abstract 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.

Towed underwater PIV measurement of propeller wake in self-propelled condition

A series of particle image velocimetry measurements was conducted in a towing tank to analyze the propeller wake dynamics of a fully appended very large crude oil carrier model. The Froude number and the Reynolds number of the test condition based on the model length and towing speed were 0.142 and 2.32 × 106, respectively. The propeller wake dynamics was investigated in terms of vortical structure and wake acceleration. It was found that the propeller loading on the starboard side was larger than that on the port side, as upward component of the propeller inflow resulted in a higher inflow speed on that side. The different propeller loading deformed the wake structure and bent it towards the port side. Between neighboring tip vortices, the local maxima of the turbulence kinetic energy and corresponding local turbulence structure were found. The rudder effects on the propeller wake were also investigated, proving that the rudder blocked the progress of the hub vortex and straightened the propeller wake.

Experimental and Numerical Model Investigations of the Underwater Towing of a Subsea Module

In underwater towing operations, the drag force and vertical offset angle of towropes are important considerations when choosing and setting up towing equipment. The aim of this paper is to study the variation in drag force, vertical offset angle, resistance, and attitude for towing operations with a view to optimizing these operations. An underwater experiment was conducted using a 1:8 scale physical model of a subsea module. A comprehensive series of viscous Computational Fluid Dynamics (CFD) simulations were carried out based on Reynolds-averaged Navier–Stokes equations for uniform velocity towing. The results of the simulation were compared with experimental data and showed good agreement. Numerical results of the vorticity field and streamlines at the towing speeds were presented to analyze the distribution of vortexes and flow patterns. The resistance components were analyzed based on the numerical result. It was found that the lateral direction was a better direction for towing operations because of the smaller drag force, resistance, and offset angle. Similar patterns and locations of streamlines and vortexes were present in both the longitudinal and lateral directions, the total resistance coefficient decreases at a Reynolds number greater than that of a cylinder.