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To promote the combat capability of unmanned aerial vehicles (UAVs) in the future battlefield, the autonomous aerial refueling (AAR) technology becomes a challenging research issue. An accurate position relationship between the tanker and the receiver is significant for AAR. A novel drogue detection method is presented in this paper. The Adaptive boosting (Adaboost) and the convolutional neural networks (CNN) classifier with the improved focal loss (IFL) function are utilized to detect the drogue in complex environments. The sample imbalance during the training stage of the CNN classifier is solved by the IFL function. The PyTorch deep learning framework is employed to implement the software system with the graphics processing units (GPUs). Real scenario images with a mimetic drogue on the tanker are captured for training and testing dataset by the airborne camera on the receiver. The experimental results indicate that the presented algorithm can accelerate the detection speed and improve the detection accuracy. [ABSTRACT FROM AUTHOR]

Probe-and-drogue aerial refueling has been widely adopted because of its flexibility, but the drogue is susceptible to wind disturbances, especially the receiver forebody bow wave disturbance and the excessive contact on the drogue. The docking process must be accurate, and a submeter error may result in failure. Thus, it is important for the docking task to understand the dynamics of the drogue under wind disturbances and improve safety after excessive contact happens. In this article, based on the previous work on drogue dynamic modeling, an improved integrated model is proposed by adding the hose-drum unit to describe the behavior of the drogue under wind disturbances more accurately. For the convenience of docking controller design of the receiver aircraft, the simplified drogue dynamic model with the hose-drum unit is obtained through system identification. Finally, to avoid the hose whipping phenomenon after excessive contact on the drogue, a control method is proposed to monitor the state of the hose and control the hose length to stabilize the drogue movement. Simulations and comparisons indicate that the motion of the drogue generated by the proposed modeling method is in good agreement with the real experimental results, and the proposed control method can significantly reduce the effect of the hose whipping phenomenon and improve the safety of probe-and-drogue aerial refueling systems. [ABSTRACT FROM AUTHOR]

Air-to-air refueling for a fighter platform is a force multiplier in terms of increasing its combat radius and payload carrying ability. Adapting for such a facility especially for an aircraft under design and development is a challenging task. It requires rigorous ground and flight testing to meet the certification standards. One of important flight test parameter that needs to be validated for structural impact load calculations and certification needs is the closure velocity. The air-to-air refueller was equipped with a Ram-air-turbine powered drogue and chute system. An innovative methodology of estimating the closure velocity between the drogue of the mother aircraft and the in-flight refueling probe of the receiving aircraft was evolved. The method was employed and validated during the air-to-air refueling trials of a prototype fighter platform. The intention of this paper is to explain the methodology employed and deliberate the results obtained with respect to the air-to-air refueling certification. [ABSTRACT FROM AUTHOR]

In deep-towed multi-channel seismic systems, nonuniform mass distribution of seismic arrays results in a "W" shape, negatively impacting the exploration resolution. High towing speeds or use of large drogues can straighten the arrays; however, these approaches adversely affect the towing depth and maximum cable tension. Therefore, this study performed system optimization for drogue dimensions, towing speed, and towing cable length by employing an efficient surrogate model-based method. A surrogate model of the drogue that incorporates dimensional variation, along with another surrogate model that merely expresses the relationship between the drag forces and towed-vehicle motions, were used. These surrogate models were connected via nonuniform arrays modeled by an efficient quasi-static iteration method validated using the absolute nodal coordinate formulation. Finally, the drogue dimensions, towing speed, and towing cable length were optimized under constraints of limited towing depth and cable tension; the maximum vertical deviation of array shape was significantly reduced (from 3.0 m to 0.5 m). The quasi-static iteration and surrogate model-based approach affords an efficient means of optimizing the device dimensions and towing operations for marine towed systems. • An efficient quasi-static iteration method is proposed to determine nonuniform array shapes. • Surrogate models are generated to optimize drogue dimensions and towing operations. • The maximum vertical deviation of the array shape is < 0.5 m for 150-m long arrays. • System optimization affords quantized information for towing operations. [ABSTRACT FROM AUTHOR]

As mankind continues to exploit marine resources, there is a growing need to use unmanned surface vessel (USV) platforms for maritime security and surveillance of the operational environment at sea. Satellite remote sensing imagery is now the most common means used for maritime surface security surveillance. Satellite images are susceptible to cloud cover, while camera-equipped USVs can prevent the effects caused by cloud cover. However, there are virtually no vision-based target tracking solutions for the USV perspective. This paper proposes a tracking solution for multiple target tracking at sea named Sea-IouTracker. It can address the potential problems when the USVs are at sea, such as the target loss, anchor frame drift and even serious Re-ID phenomena due to wind and waves and other environmental effects. We chose Sort as the basic tracking framework and we picked Buffered-IoUs based on two different buffer scales instead of traditional IoUs for matching targets in neighbouring frames. And the innovation of the neighbouring frame matching mechanism lies on that the position of the Buffered-IoU is predicted using a motion prediction model and matched with the next detection frame because both matches are unsuccessful. This method increases the stability of the tracking model and reduces the phenomenon of re-ID. We have also developed a detector that adaptively fuses image features for the tracking scheme. The detector proposed is based on the ASFF (Adaptively Spatial Feature Fusion) detector head, CBAM (Convolutional Block Attention Module) and Yolov7 baseline for maritime target detection. This paper verifies that the Sea-IoUTracker can achieve MOTA = 77.5, ID SW = 1.5% when tracking multiple targets on the MOT17 dataset. We have also proved our detector proposed is superior to other SOTA detectors in accuracy when detecting sea surface targets in the Singapore Maritime Dataset (SMD). We have also verified that the target tracking scheme proposed in this paper outperforms to the current state-of-the-art(SOTA) tracker C-BIoU (Yang et al., 2022) Tracker and ByteTrack based on four tracking video sequences in SMD. In this case, the accuracy is improved by about 2% with respect to the latter, while the ID SW phenomenon is reduced by about 20%. • The target tracking scheme proposed in this paper is a maritime target tracking scheme for maritime security requirements. • After two failed B-IoU based matches, we add a re-matching mechanism between the predicted target anchor and the target detection frame based on the buffered area to increase the probability of re-matching the lost target and thus improve the tracking effect. • We propose a detector which outperforms than other SOTA detectors when detecting targets with multi-scale features at sea. [ABSTRACT FROM AUTHOR]

This paper aims to optimise the dimensions of Suction Embedded Anchors (SEAs) by investigating the opening mechanism through numerical large deformation finite element (LDFE) modelling. Consisting of two hinged half-cylindrical flukes, an SEA anchor uses a tactical design to allow the flukes to open under preloading to achieve more bearing area and, thus, a higher holding capacity. However, the applicability and practicability of this anchor depends on the opening process, where a critical dimension is the ratio of the anchor height relative to the diameter. A longer anchor increases both the forces prompting the opening process and the forces resisting it. The initial prompting force is the friction along the flukes and pressure on the wall annulus, while the initial resisting force is the soil pressure on the fluke faces. The LDFE results of this study demonstrate that these two components are in different orders of magnitude. Therefore, increasing the anchor height does not necessarily always increase the holding capacity but can have a detrimental effect on the holding capacity. The optimal anchor height is found to be ∼0.75 times the diameter. The detailed opening process and mechanism are demonstrated in the systematic LDFE analyses presented in this paper. • This paper investigates the practicability of a type of expandable anchor, i.e. Suction Embedded Anchor (SEA). • This paper employs LDFE modelling to rigorously explore the opening process of the expandable anchor SEA. • This paper demonstrates that the optimal SEA anchor height is ~0.75 times the diameter. [ABSTRACT FROM AUTHOR]

• The method of measuring 5-DOF pose parameters of drogue is proposed. • Drogue detection on the basis of arc-level constraint is proposed. • Pose estimation on the basis of the structure feature of drogue is proposed. This paper proposes a novel drogue measurement method based on monocular vision for autonomous aerial refueling task in unmanned aerial vehicles (UAV). Firstly, to solve the problem of detecting the drogue without artificial features, an arc-level drogue detection and recognition algorithm is proposed. Secondly, a pose estimation algorithm based on the structural features of the drogue is proposed measuring the pose of the drogue's 3D space. Finally, the proposed method is proved to be valid according to the real air refueling task data set, ground acquisition data, and simulation experiments. [ABSTRACT FROM AUTHOR]

Highlights • A theoretical method is presented to analyze the 3D behavior of embedded anchor lines. • The 3D profile and tension transmitting properties both in clay and in sand can be obtained. • The efficiency of the method is confirmed by systematic comparative studies. • Examples of application of the embedded line under out-of-plane loading are analyzed. Abstract As key components of the mooring system, anchor lines connect the anchors and the floating moored platform. When the platform suffers extreme environmental loadings, the mooring system may partially fail, such as breaking of one or more anchor lines within the spread. Hence, the orientation of the intact lines may change dramatically and the anchor may even present a three-dimensional motion in the seabed, attributed to the long-distance drift of the floater. In such a scenario, both the anchor and the anchor line will experience out-of-plane loading. To evaluate the anchor capacity and the anchor behavior under out-of-plane loading, the three-dimensional behavior of embedded anchor lines should be fully understood in advance. In the present work, a theoretical method is developed to analyze the three-dimensional behavior of embedded anchor lines, including the three-dimensional profile and tension transmitting properties of the line both in clay and in sand. A systematic comparative study is performed to examine the efficiency of the proposed method. Then, two examples of application are designed to analyze the three-dimensional profile and tension transmitting properties of the embedded line under out-of-plane loading. The first corresponds to the partial failure of mooring systems, where an offset of the platform occurs with the anchor fixed at the original penetration. The second corresponds to an engineering case, where the anchor is motivated by the drifting platform and dives in the seabed. [ABSTRACT FROM AUTHOR]

Abstract Dynamic modeling and control system design for the hose–drogue system (HDS) in the docking stage of autonomous aerial refueling (AAR) are investigated in this paper. The dynamics and kinematics of hose are modeled via a finite-segment multi-body method, which describes the hose–drogue assembly as a link-connected system. A controllable drogue is connected to the hose for automatically stabilizing the drogue's relative position under the influences of tanker trailing vortex, receiver bow wave, atmospheric turbulence, gust, and wind shear. Thus, a drogue position control law based on fractional-order method is designed to resist the multi-wind disturbances. Noting that it is difficult to tune the parameters of fractional-order controller (FOC), a modified pigeon-inspired optimization (PIO), the hybrid of heterogeneous comprehensive learning strategy and PIO (HCLPIO), is carried out to optimize the parameters of FOC. The simulation results show that the proposed optimized fractional-order feedback controllers effectively stabilize the controllable drogue to swing within an acceptable range. [ABSTRACT FROM AUTHOR]

This paper reports the results from three-dimensional dynamic finite element analysis undertaken to provide insight into the behaviour of a novel dynamically installed anchor (DIA), termed as fish DIA, during dynamic installation and monotonic pullout in non-homogeneous clay and calcareous silt. The fish DIA has an elliptic-shaped shaft, which reduces hydrodynamic drag resistance. The shaft is shaped to be thicker near the head to lower the mass centroid, and increase its diving potential with a specialised padeye position. A series of large deformation finite element analyses have been carried out considering the relevant range of parameters in terms of soil undrained shear strength; impact velocity, padeye offset ratio and pullout angle. Considering the difference in soil undrained shear strength, and DIA dimensions and mass; overall anchor tip embedment depths of the fish DIA lied in the range of that of the OMNI-Max DIA. The tracked anchor trajectory confirmed that, compared to the OMNI-Max DIA, the fish DIA dove deeper and earlier for a wide range of padeye offset ratio. These are more critical and beneficial for calcareous silt where the achieved embedment depths are generally lower compared to those in clay. [ABSTRACT FROM AUTHOR]

This research assesses the reliability of floating offshore windfarms utilizing two different anchor configurations: a conventional single-line system in which each anchor is loaded by a single mooring line and a multiline system in which each anchor is loaded by three mooring lines. While there are advantages to adopting a multiline system for floating offshore wind farms, the interconnectedness of this concept introduces disadvantages, such as reduction of system reliability and the potential for cascading failures among multiple structures. The reduction in system reliability is investigated here by running Monte-Carlo simulations in which mooring line and anchor demands and capacities are sampled from probability distributions. Demand distributions are generated through dynamic simulations with environmental conditions corresponding to the 500-year storm. Failure of mooring lines or anchors are initiated when their capacity is exceeded by their demand. The results of this research show that the reliability of the multiline system degrades significantly when progressive failures are taken into consideration. This research also shows that design considerations, such as the sizing of mooring lines and anchors and designing for single-line or multiline loads, significantly influence the system reliability of a floating offshore wind farm. [ABSTRACT FROM AUTHOR]

The plate shaped gravity installed anchor (GIA) provides a potential alternative to deepwater mooring systems as its dynamic installation and diving behavior. However, the anchor final penetration depth in seabed soils, especially in soils with high strength gradient, is relatively shallow due to the limited impact velocity and large contact area between the anchor and the surrounding soil. An innovative booster concept is put forward in this study to increase the anchor final penetration depth by increasing the kinetic energy during free fall in water and gravitational energy during dynamic penetration within seabed. The booster is attached to the rear of the anchor during installation and can be retrieved after installation for reuse. The present study performed model tests with the aim of investigating the working efficiency of booster on the impact velocity of the GIA during free fall in the water column. A mini motion tracing device (MTD) is developed to record the anchor free fall history in water. The hydrodynamic characteristics, including the terminal velocity, drag coefficient and directional stability, for the GIA were studied. A series of experimental cases were subsequently conducted to study the effects of the adding booster on the impact velocity and directional stability of the GIA. The testing results demonstrated that both the directional stability and the release height can be improved for the GIA with a booster, thus the anchor impact velocity is increased. The anchor kinetic energy is significantly increased due to the additional mass and increased impact velocity by the booster, which ensures the anchor to be embedded deeper within seabed. [ABSTRACT FROM AUTHOR]

An editorial is presented the transformation of the Quaderns de l'Institut Català d'Antropologia journal from a printed publication to a digital open-access format, continuing to serve as a platform for discussions among anthropologists. It mentions this issue, Volume 39, advocates for interdisciplinary dialogue and includes a section dedicated to the debate between anthropology and architecture, as well as articles covering topics such as political extremism.

The risk of vessel capsizing is inherent to anchor handling operations (AHOs). Lessons learned from the Bourbon Dolphin accident reveal that the large static heeling angle could not be prevented due to the lack of awareness of the vessel's stability status, which can be improved with the help of a suitable on-board monitoring system. Therefore, an on-board monitoring system is proposed for assessing stability in terms of the static heeling angle. However, a complete mathematical model is not available for estimating a static heeling angle as a function of operational parameters. Therefore, an artificial neural network (ANN)-based functional relationship has been established between the operational parameters and the static heeling angle. Furthermore, a parametric study has been performed to investigate the effect of neural network topology on network performance. The results show that an ANN topology that contains one hidden-layer is efficient enough to predict a static heeling angle. The correlation coefficient between the ANN model predictions and the target values is 0.999. This result shows that the ANN provides an accurate estimate of the static heeling angle as a function of the operational parameters. Therefore, the proposed mathematical model can be used for assessing a vessel's stability during AHOs. [ABSTRACT FROM AUTHOR]

In the design of floating breakwaters, assessment of the extreme wave-induced loads on the connections, their weakest element, is required to ensure structure survival. This case study provides guidelines for estimating the extreme wave-induced forces on the connections of a floating breakwater. A Boundary Element Method (BEM) solver was applied to obtain the time-domain response of an array of five pontoons anchored to the sea bottom with elastic mooring lines. The hydrodynamic behaviour of the structure was assessed for short-duration sea states with different wave peak periods and oblique wave directions. Two peak selection criteria were applied to obtain force distributions, and several different probability density functions (PDF) were fitted to the resulting data. The extreme wave-induced forces on every connection and sea state were estimated for two different exceedance levels during a typical 3-h sea state. Based on the results, combination of the Peaks Over Threshold (POT) method and generalized Pareto distribution results is proposed for estimating the wave-induced design forces on the connections of floating pontoon breakwaters. • Extreme tensile forces on the connections of a floating breakwater are estimated. • The interaction of the structure with irregular waves is solved in the time domain. • Short-term distributions of tensile forces on the connections are analysed. • 2 peak selection criteria and 7 PDF are used to fit the force data of 9 sea-states. • Combining the POT method with the Generalized Pareto distribution is recommended. [ABSTRACT FROM AUTHOR]

The Imago Mundi journal has awarded the tenth biennial Prize to Šima Krtalić for their article titled 'Anchoring the Image of the Sea: Copying Coastlines on Manuscript Nautical Charts from the Late Middle Ages and the Early Modern Period'. The article was judged to have made the most significant contribution to the discipline. The judges, who were drawn from the Directors of Imago Mundi, considered articles published in volumes 73 and 74 of the journal. The winner received a prize of $2,000. The Imago Mundi Prize is sponsored by Jossy Nebenzahl on behalf of the late Kenneth Nebenzahl. The article is available for free on the Taylor & Francis website for six months. [Extracted from the article]