Mother Ship Research Articles

Ship Forebody Optimization Based on Rankine Source Method

Abstract The shape of the ship’s forebody has a greater impact on the ship’s resistance, and a reasonable optimization of the forebody can play a role in reducing the propulsion power and optimizing the resistance performance. Under the premise of Rankine source method of potential flow wave theory as the theoretical basis, SHIPFLOW software is used as the calculation tool, and CAESES software is used as the optimization tool to study the optimal design of the ship with minimum wave resistance. In the optimization process, a real ship is taken as the object, and the optimal solution of the rising wave resistance coefficient is calculated with the rising wave resistance coefficient as the objective function and the ship speed and displacement as the constraints. The real ship is selected as the mother ship, the parameters of the hull shape are taken as the design variables, and the shape of the forebody is optimized by the Lackenby shift method, so as to obtain a ship shape with less wave resistance at the same speed and within the displacement limit. The results show that the improved ship shape has obvious effect of reducing the wave resistance, which verifies the effectiveness and feasibility of this method for ship shape optimization

Trajectory Planning of a Mother Ship Considering Seakeeping Indices to Enhance Launch and Recovery Operations of Autonomous Drones

Trajectory Planning of a Mother Ship Considering Seakeeping Indices to Enhance Launch and Recovery Operations of Autonomous Drones

Parallel activation of helicopter and ground transportation after dispatcher identification of suspected anterior large vessel occlusion stroke in rural areas: a proof-of-concept case with modeling from the LESTOR trial

BackgroundWhen stroke patients with suspected anterior large vessel occlusion (aLVO) happen to live in rural areas, two main options exist for prehospital transport: (i) the drip-and-ship (DnS) strategy, which ensures rapid access to intravenous thrombolysis (IVT) at the nearest primary stroke center but requires time-consuming interhospital transfer for endovascular thrombectomy (EVT) because the latter is only available at comprehensive stroke centers (CSC); and (ii) the mothership (MS) strategy, which entails direct transport to a CSC and allows for faster access to EVT but carries the risk of IVT being delayed or even the time window being missed completely. The use of a helicopter might shorten the transport time to the CSC in rural areas. However, if the aLVO stroke is only recognized by the emergency service on site, the helicopter must be requested in addition, which extends the prehospital time and partially negates the time advantage. We hypothesized that parallel activation of ground and helicopter transportation in case of aLVO suspicion by the dispatcher (aLVO-guided dispatch strategy) could shorten the prehospital time in rural areas and enable faster treatment with IVT and EVT.MethodsAs a proof-of-concept, we report a case from the LESTOR trial where the dispatcher suspected an aLVO stroke during the emergency call and dispatched EMS and HEMS in parallel. Based on this case, we compare the provided aLVO-guided dispatch strategy to the DnS and MS strategies regarding the times to IVT and EVT using a highly realistic modeling approach.ResultsWith the aLVO-guided dispatch strategy, the patient received IVT and EVT faster than with the DnS or MS strategies. IVT was administered 6 min faster than in the DnS strategy and 22 min faster than in the MS strategy, and EVT was started 47 min earlier than in the DnS strategy and 22 min earlier than in the MS strategy.ConclusionIn rural areas, parallel activation of ground and helicopter emergency services following dispatcher identification of stroke patients with suspected aLVO could provide rapid access to both IVT and EVT, thereby overcoming the limitations of the DnS and MS strategies.

Monocular Vision Guidance for Unmanned Surface Vehicle Recovery

The positioning error of the GPS method at close distances is relatively large, rendering it incapable of accurately guiding unmanned surface vehicles (USVs) back to the mother ship. Therefore, this study proposes a near-distance recovery method for USVs based on monocular vision. By deploying a monocular camera on the USV to identify artificial markers on the mother ship and subsequently leveraging the geometric relationships among these markers, precise distance and angle information can be extracted. This enables effective guidance for the USVs to return to the mother ship. The experimental results validate the effectiveness of this approach, with positioning distance errors of less than 40 mm within a 10 m range and positioning angle errors of less than 5 degrees within a range of ±60 degrees.

Rock-Cut Slipways and Slipping Techniques at Dana Island Shipyard

One of the great recent discoveries in maritime archaeology was the discovery, in 2015, of a hitherto unknown shipyard in the Cilicia Region. Approximately 294 slipways/shipsheds were found on Dana Island (Pitusu-Pityoussa) in eastern Rough Cilicia (Cilicia Trachea), on the Mediterranean coast of Turkey. Recent studies carried out in 2023 on the island have added to our knowledge of the techniques of landing and servicing vessels, while also uncovering an additional small slipway at this location. Some of the rock-cut slipways for the ships have modestly sized rock-cut constructions behind or between them, and these have been interpreted as service areas for the tenders to the mother ships. These features may indicate that maintenance of both the ship and tender was carried out simultaneously. The rock-cut slipways on Dana Island have different characteristics and range considerably in type and size, implying the use of different slipping techniques at various periods. A number of these features are present on other known ancient slipways in the Mediterranean, such as Rhtymna, Eulimna and Matalon (Crete), Tell Dor (Israel), and Apollonia (Cyrenaica-Libya).

Motion characteristics and T-foil based optimization of marine towed-cage in swell

Unmanned surface vehicles (USVs) are widely used in variety of ocean operations and are typically launched and recovered from a mother ship. However, their recovery can be challenging, especially when they encounter ocean swells. In this paper, the main research objective is to analyze the performance of a cage-type davit launch and recovery system, with a specific focus on the marine towed-cage used in this process. The study utilizes Computational Fluid Dynamics (CFD) to conduct a detailed analysis of the longitudinal motion characteristics of the marine towed-cage during towing conditions. It has been observed that while encountering ocean swell, the marine towed-cage, as a hollow-out surface towed vehicle, faces difficulties such as stern trimming, oscillations, and an unstable attitude. This instability is mainly attributed to an insufficient pitch restoring moment. In order to address these issues and to optimize the longitudinal motion of the marine towed-cage, the study proposes two aspects of optimization: geometric optimization and cable length selection. This involves designing a modified marine towed-cage equipped with a T-foil and using a constant and sufficiently long cable. Subsequent to implementation of the proposed optimization scheme, the modified marine towed-cage exhibits significant improvements such that high-frequency oscillations are reduced, large-amplitude trim by the bow is minimized, especially at high towing speeds, and the system becomes more adaptable to changes in towing speed. The research presented in this paper provides a better understanding of the seakeeping performance of the marine towed-cage under towing condition and contribute to the safer and more efficient recovery of USVs.

Man-in-the-Loop Control and Mission Planning for Unmanned Underwater Vehicles

UUVs (unmanned underwater vehicles) perform tasks in the marine environment under direction from a commander through a mother ship control system. In cases where communication is available, a UUV task re-planning system was designed to ensure task completion despite uncertain events faced by UUVs. First, the XML language standardizes the expression of UUV task elements. Second, considering the time sequence and spatial path planning requirements of human-supervised UUV control tasks, time sequence planning based on a genetic algorithm and spatial path planning based on an improved genetic algorithm were designed to plan near-optimal approximate spatial paths for control tasks. Third, uncertainties encountered during UUV task execution were classified so that the commander could adjust according to the situation or invoke the control task re-planning algorithm to re-plan. Finally, a simulation platform was built using the QT development environment to simulate human-supervised UUV control task planning and re-planning, verifying the algorithm’s design effectiveness.

Equivalent Minimum Hydrogen Consumption of Fuzzy Control-Based Fuel Cells: Exploration of Energy Management Strategies for Ships

Aiming to solve the problems of insufficient dynamic responses, the large loss of energy storage life of a single power cell, and the large fluctuation in DC (direct current) bus voltage in fuel cell vessels, this study takes a certain type of fuel cell ferry as the research object and proposes an improved equivalent minimum hydrogen consumption energy management strategy, based on fuzzy logic control. First, a hybrid power system including a fuel cell, a lithium–iron–phosphate battery, and a supercapacitor is proposed, with the simulation of the power system of the modified mother ship. Second, a power system simulation model and a double-closed-loop PI (proportion integration) control model are established in MATLAB/Simulink to design the equivalent hydrogen consumption model and fuzzy logic control strategy. The simulation results show that, under the premise of meeting the load requirements, the control strategy designed in this paper improves the Li-ion battery’s power, the Li-ion battery’s SOC (state of charge), the bus voltage stability, and the equivalent hydrogen consumption significantly, compared with those before optimization, which improves the stability and economy of the power system and has certain practical engineering value.

Comparison of Mothership Versus Drip‐and‐Ship Models for Endovascular Treatment of Basilar Artery Occlusion in the London Metropolitan Area

Background To date it is uncertain whether the drip‐and‐ship (DS) model (transport to the nearest primary stroke centers) or the mothership (MS) model (direct transportation to the comprehensive stroke center) is the best prehospital stroke system of care to deliver endovascular thrombectomy in patients with basilar artery occlusion. In the present analysis, we aim to investigate the impact of MS versus DS model in patients with basilar artery occlusion treated with endovascular thrombectomy in the London metropolitan area. Methods This is a multicenter observational, investigator‐initiated, retrospective study comparing outcomes (functional independence, defined as modified Rankin scale scores of 0 through 2, the rate of successful reperfusion, and the rate of complications postprocedure) in DS versus MS stroke patients with basilar artery occlusion admitted in 5 thrombectomy capable centers in London (United Kingdom). Results Of 113 patients, 38 (33.6%) patients were MS and 75 (66.4%) were DS. Between the 2 groups we did not observe statistically significant differences for most of the clinical characteristics. There was a significant difference regarding the rate of functional independence at 3 months between the MS and DS groups, respectively 47.4% versus 36% ( P = 0.047). Rates of complications postprocedure and successful recanalization did not differ between the 2 groups. Multivariable regression analysis demonstrated that MS model was an independent predictor of functional independence at 90 days (odds ratio [OR] 1.17; [95% CI, 1.11–1.26]; P = 0.003 and independent negative predictor of postoperative complications (OR, 0.39; [95% CI, 0.16–0.98]; P = 0.045). Conclusion Our study showed that MS model was a predictor of functional independence at 3 months and reduced risk of postoperative complications post‐endovascular thrombectomy in patients with basilar artery occlusion in a metropolitan area.

Research on the Heterogeneous Autonomous Underwater Vehicle Cluster Scheduling Problem Based on Underwater Docking Chambers

The onboard energy supply of Autonomous Underwater Vehicles (AUVs) is one of the main limiting factors for their development. The existing methods of deploying and retrieving AUVs from mother ships consume a significant amount of energy during submerging and surfacing, resulting in a small percentage of actual working time. Underwater docking chambers provide support to AUVs underwater, saving their precious energy and addressing this issue. When an AUV cluster is assigned multiple tasks, scheduling the cluster becomes essential, and task allocation and path planning are among the core problems in AUV cluster scheduling research. In this paper, based on the underwater docking chamber, an Improved Genetic Local Search Algorithm with Prior Knowledge (IGLSAPK) is proposed to simultaneously solve the task allocation and path planning problems. Under constraints such as onboard energy supply, AUV quantity, and AUV type, the algorithm groups AUVs, assigns tasks, and plans paths to accomplish tasks at different locations, aiming to achieve overall efficiency. The algorithm first generates an initial population using prior knowledge to improve its search efficiency. It then combines an improved local search algorithm to efficiently solve large-scale, complex, and highly coupled problems. The algorithm has been evaluated through simulation experiments and comparative experiments, and the results demonstrate that the proposed algorithm outperforms other algorithms in terms of speed and optimality. The algorithm presented in this paper addresses the grouping, task allocation, and path planning problems in heterogeneous AUV clusters. Its practical significance lies in its ability to handle tasks executed by a heterogeneous AUV group, making it more practical compared to previous algorithms.

Implementation of an Efficient Image Transmission Algorithm for Unmanned Surface Vehicles Based on Semantic Communication

With the increasingly maturing technology of unmanned surface vehicles (USVs), their applications are becoming more and more widespread. In order to meet operational requirements in complex scenarios, the real-time interaction and linkage of a large amount of information is required between USVs, between USVs and mother ships, and between USVs and shore-based monitoring systems. Visual images are the main perceptual information gathered from USVs, and their efficient transmission and recognition directly affect the real-time performance of information exchange. However, poor maritime communication signals, strong channel interference, and low bandwidth pose great challenges to efficient image transmission. Traditional image transmission methods have difficulty meeting the real-time and image quality requirements of visual image transmissions from USVs. Therefore, this paper proposes an efficient method for visual image transmission from USVs based on semantic communication. A self-encoder network for semantic encoding which compresses the image into low-dimensional latent semantics through the encoding end, thereby preserving semantic information while greatly reducing the amount of data transmitted, is designed. On the other hand, a generative adversarial network is designed for semantic decoding. The decoding end decodes and reconstructs high-quality images from the semantic information transmitted through the channel, thereby improving the efficiency of image transmission. The experimental results show that the performance of the algorithm is significantly superior to traditional image transmission methods, achieving the best image quality while transmitting the minimum amount of data. Compared with the typical BPG algorithm, when the compression ratio of the proposed algorithm is 51.6% of that of the BPG algorithm, the PSNR and SSIM values are 7.6% and 5.7% higher than the BPG algorithm, respectively. And the average total time of the proposed algorithm is only 59.4% of that of the BPG algorithm.

Structural frame analysis of an electrically powered robotic subsea dredging crawler under static loading conditions

Robotic subsea dredging crawlers are dynamically and remotely controlled vehicles that are used for deep sea mining and recovery operations. These exploration machines are released from a mother ship and move around on the ocean floor using tracks. Current ocean crawlers such as the MK3 ROST are hydraulically powered. In this paper we develop a scaled-down model for simulating and performing static loading analysis of an electrically powered robotic subsea dredging crawler (EPRSDC). The modeling, simulation, and analysis were carried out using modelling software from Solidworks. The structural frame was assembled using the Tetrix max robotics kit. The kit's structural components were produced from 1050 aircraft-grade aluminum. The results were used in optimizing and for considering other materials, and the to identify specific areas to be reinforced in future crawler designs.

Book Review: Mother Ship

Book Review: Mother Ship

Arctic naval launch and recovery operations, under ice impact interactions

This study analyses dynamic influence of stochastic vibro-impact ship behaviour on the ship's launch and recovery capability. To deliver cargo and people to the Arctic regions, ships must withstand harsh environmental conditions and interact with large floating ice pieces. This interaction may result in impact-type loading of a ship hull by ice, preventing planned navigation and even causing to abort of some routine launch and recovery operations of delivering cargo or other equipment. The major safety concern is the risk of collision between the payload and the mother ship hull. The ship-based crane, which served for conducting launch and recovery operations, was assumed to be rigid, mimicking the ship dynamics, whereas the payload is modelled as a single-degree-of-freedom pendulum. This study advocates practical engineering approach, applicable to various scenarios with vessels operating in relevant in situ environmental sea and ice conditions. The proposed study intends to contribute to improving launch and recovery operational reliability, as well as motion control, especially in Arctic aquatic regions. When mentioning Arctic and defence technologies, launch and recovery systems have significant relevance for unmanned vehicles onboard ships.

Design of an improved adaptive slide controller in UUV dynamic base recovery

This paper addressed the problems in UUV dynamic base recovery, such as limited mission time, high control accuracy requirements and many uncertainties. The entire recycling process has been designed in sections to address these issues. A new sliding mode surface with predictive ideas based on the original fast terminal sliding mode control is designed for each phase, and a neural network (RBF) is introduced to compensate for the deviation between the actuator output and the controller command in practice. A new sliding-mode surface based on the compensated sliding-mode surface can be used to compensate for the failure of the original actuator due to faults and other factors, and a corresponding adaptive controller is derived. Simulation and experimental verification show that the designed controller not only has good convergence quality, but also can quickly adjust the position to the recovery mother ship after the original actuator failure, meeting the requirements of dynamic base recovery, and the feasibility in practice has been effectively proved.

Comparison between different referral strategies for acute ischemic stroke patients in a hub-spoke emergency stroke network: a real-world experience in south-east Lazio.

To describe different referral strategies for acute ischemic stroke (AIS) patients in a Hub-Spoke emergency stroke network with their incidence, time metrics and related outcomes. Referral paradigms were defined as follows: primary transfer to the comprehensive stroke center (CSC) from a remote region, called mothership (MS); secondary transfer to the CSC from a primary stroke center where intravenous thrombolysis was available, called drip and ship (DS); secondary transfer to the CSC from a community hospital where no reperfusion therapy was available, called ship and drip (SD); primary transfer to the CSC from its catchment area, called direct CSC (dCSC). Among 517 anterior circulation AIS patients treated with mechanical thrombectomy between 2015 and 2020, 16.6% of them were SD, in addition to the well-known referral paradigms of MS (21.8%) and DS (18.1%). This rate grew to 30% when only patients whose place of onset was outside the CSC catchment area were considered. In the SD group, onset to CSC and onset to groin were significantly longer (178±80 min vs. 102±60 min, p<0.001, and 277±77 min vs. 211±61 min, p<0.001, respectively), and the risk of any intracranial hemorrhage (ICH) was significantly higher (OR: 2.514; 95%CI: 1.18-5.35, p=0.017) compared to MS. In this hub-spoke stroke network, a high proportion of SD paradigm was found, which was associated with longer times to treatment and higher rates of any ICH. A closer cooperation between hospital stroke physicians, national health system staff, and paramedics is warranted to identify the most appropriate referral strategy for each patient.

Structural Design and Hydrodynamic Coefficient Calculation of Observation-class ROVs

Remote Operated Vehicle (ROV) can replace humans in inspecting and maintaining water facilities such as reservoirs and dams. Connected to surface support equipment through umbilical cables, the umbilical cable allows the operator to control the ROV's operations remotely from a mother ship or shore. Using the ROV as an underwater operational platform, precise and efficient underwater inspection and repair operations for hydraulic structures can be achieved by mounting underwater mechanical arms, pan-tilt cameras, cleaning and cutting devices, etc. This paper designs an observation-class ROV, carries out structural design of the ROV body, selects and models sensors and actuators according to actual needs, and provides a method for using the FLUENT software to perform hydrodynamic calculations and obtain hydrodynamic coefficients based on the model.

An underwater docking system based on UUV and recovery mother ship: design and experiment

The research focuses on the autonomous docking of unmanned underwater vehicles (UUV) to a recovery mother ship. Firstly, a novel fork-pole docking station was designed, which could operate independently or be transported onboard a recovery mother ship. Subsequently, a docking guidance scheme combining long-range acoustic guidance and short-range opti-acoustic guidance was proposed. Acoustic guidance employed ultra-short baseline sonar and acoustic beacons to measure relative position information, while optical guidance utilized camera and L-shaped light arrays to obtain relative pose information. Then, an opti-acoustic complementary recovery control strategy was developed to address the instability of acoustic signals. Finally, experimental tests were conducted in a pool to evaluate the performance of the proposed recovery docking system in both static and dynamic docking scenarios, which demonstrated that the docking system was capable of achieving fully autonomous recovery of UUV. Furthermore, the experimental data analysis shows that the presented recovery control strategy is effective and feasible.

Uncrewed surface systems facilitating a new era of global ocean exploration

There is growing recognition that key to addressing critical issues like climate change, global sea level rise and the long-term sustainability of humankind is a more complete understanding of our oceans and processes within them that account for the distribution of global heat, CO2 and provide sustenance to so many. Yet, despite years of effort, less than 25% of the global ocean seafloor has been mapped and less than 5% of the ocean volume explored, likely due to the cost and inefficiency of traditional ocean mapping and exploration techniques using large, very expensive, crewed research vessels. Recent advances in the development of uncrewed surface vessels offer the possibility to reduce costs and increase efficiency of ocean mapping and exploration. Such efficiencies can be gained by using small mother ship-deployed uncrewed vessels acting as relatively inexpensive mapping and sampling force multipliers or the use of small uncrewed vessels launched to from a mother ship to monitor and control autonomous underwater vehicles, allowing multiple operations simultaneously and “verified, directed sampling”, all while freeing the mother ship for independent operations. We are also seeing the development of larger uncrewed vessels launched from shore with long-endurance and range, capable of carrying a full suite of deep ocean mapping and exploration tools. All of these systems and approaches offer great hope but it is very early in our understanding of their full capabilities, costs and limitations and we must be careful not to overpromise, leading to disappointments and early abandonment of a potentially innovative approach, while at the same time maintaining the patience required to continue the research, investment and innovation that will hopefully bring us to a new world of efficient and effective ocean mapping and exploration that will allow us to meet our goal of complete coverage of the ocean.

Dynamic Analysis of Active Heave Compensation System for Marine Winch under the Impact of Irregular Waves

The six-degree-of-freedom (6 DOF) motion of the mother ship, especially the heave motion, brings difficulties to offshore operations and even causes safety accidents. To ensure the reliability of the launch and recovery system when the active heave compensation (AHC) function works, its dynamic characteristics are analyzed. Firstly, the dynamic model of the launch and recovery system with a rigid rope is constructed, and the mathematical simulation of the launch and recovery system without the AHC function under the excitation of irregular waves is completed. Secondly, a flexible rope based on the finite element method is established, and the dynamic responses of the launch and recovery system with AHC function under different conditions are compared with those without AHC function. The simulation results demonstrate that the dynamic responses of the system are related to the load, the underwater penetration, and the sea condition. In detail, the increase of the load leads to an increase in the dynamic response of the system. In essence, the underwater penetration affects the dynamic response of the system by affecting the activity of load acceleration. Therefore, a short rope is preferred in the maritime operations. Moreover, the harsh sea condition usually causes an undesirable effect of AHC function. In summary, the overall work is conductive to the modeling of the launch and recovery system, as well as the development of AHC technology so as to improve the quality of offshore operations in the future.