Towing Direction Research Articles

Spreading a demersal trawl without otter boards: A proof of concept using flexible foils

This manuscript documents an engineering proof of concept. We demonstrate that a deep-water demersal trawl targeting northern shrimp (Pandalus borealis) can be spread without otter boards using nothing more than flexible foils (i.e., kites) mounted near the wings of the trawl. A combination of numerical simulation, physical modeling in a flume tank, and full-scale sea trials were used to optimize the horizontal spreading of the demersal trawl. Spacing between the foils and the angle of attack to the direction of tow were found to be important parameters. To our knowledge this is the first successful attempt to spread a demersal trawl full-scale at-sea using nothing but flexible foils.

Characterising the shear resistance of a unidirectional non-crimp glass fabric using modified picture frame and uniaxial bias extension test methods

The forming behaviour of a unidirectional non-crimp fabric (UD-NCF) consisting of polyamide stitches with a tricot-chain stitching pattern is explored. Notably, there are no stabilising tows orientated transverse to the main tow direction in this fabric, a common feature in many ‘quasi’ UD-NCFs, this allows extension of the stitch in the transverse direction under certain loading conditions. The lack of stabilising tows introduces a possible low-energy deformation mode to the UD-NCF, which is absent in biaxial fabrics and to a large extent in ‘quasi’ UD-NCFs. The in-plane shear behaviour is initially investigated using both standard ‘tightly-clamped’ picture frame tests and uniaxial bias extension tests. Preliminary results show a dramatic difference in results produced by the two test methods. During the picture frame test, fibres can be subjected to unintended tension due to sample misalignment in the picture frame rig. To mitigate error arising from this effect, the picture frame test procedure is modified in two different ways: by using an intentional pre-displacement of the picture frame rig, and by changing the clamping condition of test specimen. Results show that the modified picture frame test data contain less error than the standard ‘tightly-clamped’ test but also that the shear stiffness of the UD-NCF is notably lower when measured in the bias extension test compared to the picture frame test, mainly due to the difference in loading conditions imposed during the two tests.

Study on Reducing Towing Drag by Varying the Shape and Arrangement of Floats and Gears

Many studies have been conducted with the aim of reducing fuel consumption by the fishing industry. We examined whether drag can be reduced by changing the arrangement of gears without requiring the development of new parts for the conventional float and ground gear. Ten differently shaped floats and ground gears were measured in a water flume tank. The float and ground gear were fixed to a steel rod to measure fluid drag according to attack angle, using a multi-component load cell. To estimate the frictional drag of ground gear on the seabed, five types of large ground gear were towed on flat land while changing attack angle using the load cell to measure tension. The fluid drag of the float and ground gear was highest at an attack angle of 60°, regardless of shape, size, and flow velocity. The resistance coefficients of the float and ground gear varied depending on the attack angle and tended to be lower at small attack angles. The frictional drag of the ground gear was greater when the axis of rotation had a small attack angle in the towing direction compared to other attack angles. We then investigated a method for designing bottom-towed gear that reduces drag while maintaining the size, buoyancy, and sinking force of conventional fishing gear parts. This gear design showed 1.2% drag reduction and an estimated 0.8% improvement in fuel efficiency per haul.

OrthoSpar, a novel substructure concept for floating offshore wind turbines: Physical model tests under towing conditions

An important condition of any port-assembled floating offshore wind turbine concept is the de-ballasted transport stage. As the hydrostatic and dynamic stability may vary greatly from the operational condition, it needs to be carefully investigated in early stages of the design-phase. In this work, physical modelling of the transport of the de-ballasted OrthoSpar device was carried out to determine roll and pitch RAOs, as well as load characteristics of the towing line. Towing was simulated with a stationary model being subjected to currents. To examine the influence of wave direction, a range of model orientations towards the incident waves were tested in still water and together with the simulated towing state. Roll and pitch motions were found to be highly dependent on the wave frequency and a result of a low damping ratio. The towing load amplitude was found to be influenced by the towing direction regarding the wave direction.

Design of variable stiffness composites for maximum fundamental frequency considering manufacturing constraints of tow steering

In this study, an in-house finite element approach is developed to optimize fundamental frequency of variable stiffness composites considering manufacturing constraints of tow steering process. The method uses the lamination parameters as the design variables. Tow angles or fiber angles and their stacking sequence are computed from the optimum lamination parameters by direct search method. The Least-Squares and Continuity (LSC) method is applied to maintain the fiber or tow continuity within a prescribed curvature limit for manufacturability. Finally the discrete fiber angles or tow directions were converted into paths by using stream functions to have continuous manufacturable paths. The results of the method were compared to various literature findings for constant, balanced variable, and general variable stiffness designs for different boundary conditions, aspect ratios, and material properties. The optimum lamination parameter distributions were in good agreement with literature findings. The fundamental frequency improvements up to 11.9% and 10.2% were computed by the LSC method with respect to the optimum constant stiffness results for fully simply-supported and fully clamped cases, respectively.

Experimental study on elastic behaviors of two tandem risers in constant flow

Multiple pipes bundled with a certain distance are used for deep ocean development for such as lifting seafloor massive sulfides (SMS), pumping up a large amount of cooling water for onboard natural gas liquefaction, and production of oil/gas. To understand the vortex-induced phenomenon of fluids and the structural mutual interference among pipes in a steady flow, a towing tank test using a model of two vertical elastic pipes in tandem is performed. The parameters of this test are: the distance between the two pipes, the incident angle of crossflow with the inline direction of the pipes, the flow velocity (towing speed), and the boundary conditions of the tops of the pipes. The two horizontal accelerations of the towing direction and perpendicular direction are measured with synchronization. Then, the motion of the two pipes in each direction was measured, and the influence of the distance between the two pipes on the motion from the amplitude and phase information was analyzed. The results are investigated relatively in detail about the tandem arrangements of the two pipes to the incident flow. It is found that the major motion pattern of the two pipes in the tandem case is a rotational motion around the midpoint of two pipes.

Endoscopic Submucosal Dissection Using EndoTrac, a Novel Traction Device

Background: Endoscopic submucosal dissection (ESD) is recognized as a minimally invasive and curative treatment for superficial gastrointestinal (GI) cancers. However, ESD is still challenging and time-consuming with a high risk of adverse events such as bleeding and perforation. Various traction methods have been explored for maintaining good visualization of the submucosal layer during ESD. We developed a novel traction device (the EndoTrac) which can easily tie the thread and has the ability to change the towing direction. The aim of this study is to evaluate safety and feasibility of ESD using the EndoTrac for GI neoplasms. Patients and Methods: We retrospectively analyzed 44 patients (45 lesions) with esophageal, gastric, duodenal, and colorectal neoplasms who had undergone ESD using the EndoTrac device between June 2018 and May 2019. Primary outcome measures were preparation time, procedural success using the EndoTrac device, and ease of ability to change towing direction. Results: Mean preparation time was 2 (2–5) min in esophagus, 3 (1–5) min in stomach, 6 (5–9) min in duodenum, and 4 (2–8) min in colorectum. The procedural success rate was 100% (8/8) in esophagus, 100% (21/21) in stomach, 100% (4/4) in duodenum, and 100% (12/12) in colorectum. The rate of successful towing to both proximal and distal sides was 100% (8/8) in esophagus, 100% (21/21) in stomach, 0% (0/4) in duodenum, and 100% (12/12) in colorectum. Conclusions: Use of the EndoTrac device appears to be a feasible approach to ESD for GI neoplasms.

Out with the old and in with the new: T90 codends improve size selectivity in the Canadian redfish (Sebastes mentella) trawl fishery

The size selectivity of four codends were compared in the Gulf of St. Lawrence, Canada, redfish fishery (Sebastes mentella), including the regulated diamond mesh codend with a mesh opening of 90 mm (T0) and three experimental codends of different mesh openings (90, 100, 110 mm) in which the netting is turned 90° to the direction of tow (T90). Results for the regulated codend showed that there was little size selection, catching greater than 97% of redfish over all of the length classes observed. Considering the fished population, the smallest T90 codend would catch 30% fewer redfish under the minimum landing size (MLS) of 22 cm compared with the T0 codend, but would also lose 16% of catch above 22 cm. The T90 codend with 100 mm mesh opening had the same size selectivity as the smallest T90 codend. The 110 mm T90 codend would catch 50% less redfish below MLS but lose 40% of redfish above MLS. Overall, results show that T90 codends improve size selectivity in which large proportions of undersized fish are successfully released.

Computational model for oxidation-assisted rupture of ceramic matrix composites

The manuscript presents a novel reduced order homogenization model for oxidation-assisted rupture in SiC/SiC composites at intermediate temperatures. Starting with a one-dimensional model based on the slow crack growth model originally proposed by Iyengar and Curtin, which is subsequently generalized to three dimensions focusing on the woven composite architecture. The proposed oxidation-assisted rupture model is developed within the framework of continuum damage mechanics where the constitutive equation in the axial tow direction is governed by the continuum damage mechanics variant of the slow crack-growth model and the availability of oxygen to fibers, which in turn depends on the initial matrix pores and subsequent matrix cracking. The constitutive model in the transverse tow directions as well as in the matrix phase outside the tows is assumed to obey a time-independent orthotropic continuum damage mechanics model, but the time-dependent nature of the axial tow model, inevitably causes the time-dependent redistribution of damage in all directions and phases. The reduced order homogenization approach that provides an efficient framework for computing overall composite behavior is employed for model reduction. Numerical validation studies are conducted on the eight-harness weave architecture.

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.

Analysis of tow architecture variability in biaxially braided composite tubes

Spatial deviations in composite braid unit cell dimensions limit mechanical performance and are challenging to model. Full-field measurements of the irregular tow placement in biaxially braided composite tubes were obtained by digital image correlation. Analysis of the reconstructed tow paths showed long-range defects along the hoop direction with short-range defects dominating the biased tow direction. A route toward numerical simulation of the composite response is established by developing a 3D model of the composite using the measured tow trajectories. Finally, a comparison to previously-published triaxial braid results indicates axial tows work to constrain unit cells dimensions along the hoop direction.

Optimization of Process Parameters for Robotic Fibre Placement

Compared with labour-intensive and time-consuming processing of conventional fabrication methods, the robotic fiber placement process greatly improves the flexibility of the fiber placement process and allows for the construction of more complex structures. Based on the study of the placement process, the intimate contact process and healing process were analysed theoretically. The key process parameters for affecting the quality of the composite component were put forward:hot gas torch temperature, compaction force and laying velocity. In order to analyse the fabrication process for laying the cylindrical parts with 0-degree tow direction, the model of the process parameters coupling affected the interlaminar bond strength was established, according to the design of the response surface method. The reliability and validity of the model were verified by the analysis of variance. The optimal process parameters of fiber placement were obtained. The results show that the model is effective and the optimum peeling force of the laying products is 24.1 N under the optimum process parameters.

Shear and drape behavior of non-crimp fabrics based on stitching geometry

Non-crimp fabrics (NCFs) enable relatively high mechanical properties by keeping the reinforcement tows straight. Handling of those fabrics is improved by stitching the reinforcement tows together. While the stitching has little structural influence on the final part, it highly affects the NCFs capability to shear and drape over a mold during preforming. High tensile strain in the stitching yarn has been correlated to the NCF resistance to shearing and even adverse drape defects such as tow undulations. Furthermore, stitching causes the shear behavior of the fabric to be anisotropic, with different behavior in positive and negative shear. In the current study, a model based on the stitching geometry and reinforcement tow directions has been created to find the tensile strain in the stitching yarn as the NCF is being sheared. It was found that the stitch angle was the main driving stitching parameter, and that this angle could be selected so that shearing in both positive and negative directions produces no tensile strain in the stitching yarn. The model showed good correlation with uniaxial bias-extension and drape tests for NCFs with different stitching parameters. Finally, design charts are displayed which can be used to select the stitching parameters of standard industrial NCF-machines which results in NCFs with near-symmetric shear behavior and thus good shear and draping performance.

Use the technique of three layers suspension to lift the mid-low face

Objective To explore an ideal surgical method for mid-low face lifting. Methods In this procedure, the first surgical step was subcutaneous undermining that was performed through the incision along temporal hairline, anteriorear, and mastoideae. It extended distally beyond the furthest skin fold and along the mandibular border or the midline of the neck if nacessary. Then three layers suspension were performed, which included three procedures: first, SMAS was purse string sutured in certain direction; secondly, the malar fat pad was suspended to tow directions backward and upward and anchored in the periosteum of zygoma and SMAS too; lastly, through traction suture of reducing tension step-by-step, lots of the tension was relieved from the incision; at the same time, new retaining ligaments between flap and SMAS were reestablished. And redundant skin was removed in incision at the end of the procedure. Results A total of 22 cases received this operation. 16 cases were followed up from 3 months to 24 months after operation. The results of operation were divided into three degrees: excellent, acceptable and poor; and those were evaluated by patients themselves. 14 cases obtained excellent result (87.5%) , 2 cases regarded that their results were acceptable (12.5%). The total satisfactory rate was 100%. None serious complication occurred in those cases except some slight complications, such as local edema, skin numbness and small hematoma which relieved in 3 to 6 months after operation. Scar was inconspicuous. Conclusions This technique can correct the posies of lower tow-third face better, especially for mitigating the nasolabial fold and enhancing the elastic of face skin. Simultaneously, it is an effective, safe and simple technique. Key words: Face lift; Superficial musculoaponeurotic system; Malar fat pad

Variation in snow crab entry ratio among sections of footrope and its effect on trawl net catching efficiency

When evaluating catching efficiency of trawl nets for snow crabs, assessing crab behavior around the footrope is crucial. Using two underwater video cameras, we captured footage at three sections of footrope with different thicknesses and attack angles in relation to the towing direction: the belly, the lower wing gusset, and the wing sections. Based on the footage, we calculated the entry ratio (ratio of snow crabs entering the trawl net to the overall number of snow crabs in contact with the footrope). Our results indicated that the entry ratio was 0.122 at both the belly and the lower wing gusset sections and 0.530 at the wing section, suggesting that footrope thickness and/or attack angle in relation to towing direction affects the entry ratio. The total number of crabs that entered was estimated using these entry ratios and corresponded well to the number of individuals captured at the cod end. Considering the variation among entry sections, the catching efficiency of the trawl net used was estimated to range from 0.311 to 0.361. These results demonstrate that calculating the entry ratio at each section of the footrope separately allows for a more accurate estimation of catching efficiency.

Path instability on a sphere towed at constant speed

The dynamics of towed objects in a fluid environment is of interest for many practical situations. In this paper we report results for wake instabilities of spheres towed in a water tank. Six particles of different diameter and/or density ratio have been investigated, towed at 5 different constant velocities. The explored density ratios lay within Γ∈[1.06;2.56], with particle Reynolds numbers Rep∈[100;1200], corresponding to Galileo numbers in the range Ga∈[1300;8000]. We introduce a surrogate Galileo number Ga⁎ that, by taking into account the towing force applied to the particle, allows a comparison with the case of free falling/ascending spheres. Using innovative 3D tracking techniques, the three-dimensional trajectory of each particle is reconstructed. The wake instability for the studied particles is found to be associated to a 3D helicoidal motion with an elliptical cross section in the plane perpendicular to the towing direction. The 3D oscillatory motion was found independent of the particle density ratio, with a threshold of the order of Repc~355 (or Ga⁎c~245). This threshold is slightly larger than the one found for the free falling particles’ transition to 3D chaotic motions (Repc~310 or Gac~225).

Effects of diel period and diurnal cloud cover on the species selection of short and long penaeid trawls

Diel period and diurnal cloud cover (i.e. ambient light) were tested for their importance in explaining variability in the relative selectivity of two penaeid trawls that differed only in their side tapers (1N3B or ‘long’ and ∼28̊ to the tow direction vs 1N5B or ‘short’ and ∼35̊). The trawls were tested in an Australian estuarine fishery during paired deployments (n=44) across replicate nights and during days with variable cloud cover (categorized as <50 and >50%). Catches were dominated by the targeted school prawns, Metapenaeus macleayi and seven teleosts. Only two teleosts (southern herring, Herklotsichthys castelnaui and Australian anchovy, Engraulis australis) along with the school prawns were significantly affected by trawl side taper, with all retained in lower numbers by the short trawl. For school prawns and Australian anchovy, their catch reductions mostly remained consistent irrespective of diel phase and diurnal cloud cover, but southern herring (mostly smaller individuals) only escaped from the short trawl during diurnal deployments and with <50% cloud; possibly through anterior meshes in response to more available ambient light. The results highlight the importance of environmental parameters for affecting the selectivity of penaeid trawls, and have implications for their ongoing refinement and use as survey tools.

Study of composite plate in water with transient and steady state motions

Hydrodynamic loading and dynamic response of a composite plate were measured inside a tow tank while the speed of the plate increased from zero to various steady-state values and remained at the steady state values. Strain responses of the plate were recorded using strain gages. To determine the effect of the composite plate with fluid–structure interaction, a stiffer and heavier aluminum plate was compared to the composite plate. The composite plate was tested under various setting angles relative to the towing direction. Some experimental data were compared to numerical results at steady state motions, and they agreed well each other. The study showed that the hydrodynamic loading was greater on the polymer composite plate than on the aluminum plate of the same size. Furthermore, the hydrodynamic force was much greater during the transient period of the increasing speed than at the final steady state speed. The ratio of the peak strain in the composite plate during the transient period to the strain at the steady state motion depended on the plate speed and the setting angles significantly. Therefore, design and analysis of composite structures moving in water should consider the hydrodynamic loading during the transient motion including fluid–structure interaction.

사고선박의 다양한 예인계획에 따른 예인상태 추정 프로그램 개발

해상에서 사고선박을 예인하기 위해서는, 예상되는 바람과 조류 등의 해상상태에서, 선정된 예인선들의 예인력과 예인방향을 이용하여 피예인선의 선속과 방향을 추정하여야 한다. 본 논문에서는 사고선박의 다양한 예인계획에 따른 예인상태 추정 방법을 연구하였다. 기존 전산 프로그램을 사용하여 계산된 피예인선의 정면방향 선속과 저항을 가져오는 방법과, 초기 예인상태에서 선정된 예인선들에 의한 피예인선의 전진방향 선속과 저항을 계산하는 방법, 그리고 안정된 예인상태에서 피예인선의 전진방향 선속과 저항을 계산하는 방법을 제안하였다. 이들 계산 방법은 전산 프로그램으로 구현되었으며, 이 프로그램은 피예인선의 상태를 적절히 추정할 수 있는 유용한 프로그램으로 확인되었다.

Numerical modelling of bottom trawling ground gear element on the seabed

This paper focuses on the numerical modelling of the interaction between gear components, rockhoppers, in particular and the seabed. This interaction is developed by using the Coupled Eulerian Lagrangian Method (CEL). To demonstrate the rate effect, a 2D finite element model is developed to analyse the pore pressure distribution and soil deformation. In situ soil conditions of the seabed with large deformations require multiphase simulation which is very expensive to investigate numerically. However, fully drained conditions were considered and the results obtained were deemed acceptable for this study. Validation of the numerical model was achieved by means of laboratory experiments undertaken on a 1:5 scaled model. Good agreement between the experimental tests and numerical simulations is found which provides the basis for investigation of the effect of the size of the rockhoppers, their position with respect to the towing direction and the number of discs modelled. A unique expression for the towing force of the segment of rockhopper gear is expressed as a function of the drag force of a single disc, the diameter, thickness, and angle of attack.