bluuebunny/crossref_metadata_2025_split huggingface dataset:
Twin-Skeg or Deadwood for Cutter Suction Dredgers? A Comparison of the Propulsive Efficiency
Authors: Wang Youjiang , Yang Jiantao , Huo Xueliang , Yu Xin , He Yanping 
Published: August 2024

Abstract
The cutter suction dredger (CSD) is a special type of engineering ship. It has normally a large breath-to-draught ratio, and openings are always necessary on the hull to install the cutter ladder and working spud. These openings affect the flow field around the hull significantly. For the positioning-bow CSDs, the cutter ladder is placed at the stern of the ship. Thus, a large slot for the cutter ladder is designed in the middle of the ship, and one propeller is arranged on each side of this slot. For such an arrangement, to improve the wake field quality and sailing stability, twin-skeg or deadwood are installed at the stern. Both setups have been found popular in the modern large self-propelled CSDs. However, detailed comparison between these two setups have never been reported. This poses a difficulty when designing new self-propelled CSDs. In the current work, we compared the propulsive efficiency of two CSD designs having twin-skeg and deadwood, respectively. The propulsive efficiency of each CSD is computed with help of the computational fluid dynamics technique. It is found that, the CSD with twin-skeg has a larger wake fraction and smaller thrust deduction, while the CSD with the deadwood has a higher relative rotative efficiency. When using the deadwood, the open-water efficiency of the propeller could be higher. As a total, the twin-skew has a little higher propulsive efficiency than the deadwood.
Cost-Benefit Analysis for Offshore Structures Under Structural Deterioration
Authors: Varela Gerardo , Flores Ricardo B. , Tolentino Dante 
Published: August 2024

Abstract
The partial or complete interruption of offshore facilities has a direct impact on the political, social, and economic sectors as well as on the environment. Then, these kinds of structures are considered as important systems. Periodic inspection and maintenance activities contribute to maintaining the structural system at satisfactory reliability levels. Based on the above, an approach to determine the optimal inspection interval that represents the minimum total cost using cost-benefit analysis (CBA) is proposed. The total cost involves inspection, repair, and failure cost. The size of crack due to fatigue in critical joints is considered as a damage condition. Demand exceedance rates are used to estimate demands that are involved in the cost of failure. The approach is exemplified on two structures located in different geographical areas of the Bay of Campeche, Mexico. The optimal time for maintenance is five and six years after installing the offshore platform located in Ku and Och area, respectively. The implementation of maintenance actions every five and six years reduces costs by 58% and 61% compared to the absence of maintenance. The proposed approach provides decision-makers with a strategic instrument to optimize the allocation of economic resources for maintenance.
Hydroelastic Responses of Submersible Modular Fish Pen With Different Lengths Under Wave and Current Actions
Authors: Qiao Yi Ping , Chu Yunil , Wang Chien Ming , Batra Mayank , Nguyen Huu Phu 
Published: August 2024

Abstract
This paper examines the hydroelastic responses of SeaFisher (a modular high-density polyethylene offshore fish pen) of different lengths, under wave and current actions, and at the water surface or at a submerged depth. The hydroelastic analysis of the SeaFisher with its single point mooring line system was performed by using the software package AquaSim that is specially tailored for hydroelastic analysis of aquaculture infrastructure. It is found that by lengthening the SeaFisher design, it becomes prone to failure by bending and buckling of structural members. Longer SeaFisher would require larger structural members for the frames or using stronger materials such as glass fibre reinforced HDPE pipes. The direction of the wave impacting the SeaFisher has a significant effect on the structural performance in general. When the incident wave direction is perpendicular to the SeaFisher, it experiences the least amount of force. When the wave and the current acts in the opposite directions, the SeaFisher is subjected to relatively higher compressive forces in structural members and the SeaFisher may fail by buckling, especially when it is long.
Dropped Object Simulation: Enhanced Safety and Risk Mitigation
Authors: Scales Derek , Hubbard Rex 
Published: August 2024

Abstract
Dropped objects from surface vessels and facilities pose a significant threat to subsea assets. DNV’s recommended practice is robust, however it over-estimates the likelihood of dropped object impacts on subsea equipment. This results in more costly subsea designs and potentially unnecessary production shutdowns during subsea interventions and well workovers.
This paper presents a case study of a refined dropped object assessment of a typical subsea drill center layout. The study utilizes the method in DNV-RP-F107 Risk Assessment of Pipeline Protection [1], and enhances the method to account for additional parameters, including the precise location from which a random object is dropped, and the precise location and orientation of a randomly dropped object as it strikes the seafloor. These enhancements significantly reduce the likelihood of an impact — for example a tubular dropped adjacent to a pipeline does not strike the pipeline if its orientation is parallel with the pipeline, but it does strike the pipeline if its orientation is perpendicular.
Use of automation allows for a large number of randomized cases to be analyzed rapidly, enabling Monte Carlo based risk modelling. This refined approach provides a more accurate and less conservative assessment of the calculated likelihood of impact compared to the DNV-RP-F107 methodology. If the refined assessment can demonstrate risk is reduced to an acceptable level, it can reduce the cost of subsea designs, and/or reduce or avoid production shutdowns during subsea interventions and well workovers.
Key aspects covered in this paper include:
1. Outline of DNV’s overall assessment process.
2. Use of a Monte Carlo based simulation to consider additional parameters, such as the precise location from which a random object is dropped, and the precise location and orientation of a random dropped object as it strikes the seafloor.
3. Techniques to rapidly generate the risk data and iterate design solutions through an interactive interface.
4. Comparison of Monte Carlo assessment outcomes with the outcomes from the standard DNV-RP-F107 methodology.
How Draft and Freeboard Affect Green Water: a Probabilistic Analysis of a Large Experimental Dataset
Authors: Boon Anna D. , Wellens Peter R. 
Published: August 2024

Abstract
Green water is a rare and complex wave impact event that can affect the safety of the ship and those aboard. During the design process, the risks that these events pose have to be mitigated, preferably by minimizing the probability of a high impact pressure. As green water events are rare and complex it is difficult to get a statistically representative dataset and thus previous work has mostly compared design variations through a limited number of events, instead of comparing the probabilities. The present study will use probabilities to compare design variations with different drafts and freeboards at the bow. A large set of green water events in irregular waves with forward velocity was experimentally obtained for six different bow designs. The dataset represents 57 hours of sailing per bow design and 3263 green water events. The data demonstrates that both freeboard and draft at the bow affect the probability of green water in a complex way. Increasing the draft at the bow increases the swell-up, reducing the effective freeboard and in turn, increasing the probability of green water. Increasing the freeboard results in a decrease in the probability of green water, as expected. However, the probability is not reduced equally for different green water impact pressures. The joint probability of green water occurrence and pressures shows that increasing the freeboard only decreases the probability of low-pressure events. Counter-intuitively, increasing the freeboard increases the probability of high-pressure events. These interesting results show the value of using statistically representative datasets when designing for green water.
Numerical Study on Seismic Performance of Jack-Up Platform for Operation Safety
Authors: Wang XueJun , Liu ZhuangJian , Lim Teck-Bin Arthur , Kang Chang Wei 
Published: August 2024

Abstract
Jack-up platform, as the mobile offshore structure, confronts the challenge of operating in seismically active regions due to growing demands of offshore activities. The operational safety of these platforms subjected to seismic events is critical to maintain uninterrupted operations and to minimize potential economic losses.
The research conducts a comprehensive parametric study to evaluate the seismic response of a mobile jack-up platform within sesmic regions, accounting for effects of variations of seabed soil condition, water depth, and hull elevated load. A detailed 3D finite element model of a typical jack-up platform is developed to accurately capture structural properties. The interaction between spud can foundation and soil is modeled using spring elements, guided by ISO 19905-1, to address the influence of seabed soil.
The parametric study employs parameter correlation analysis, DOE, and response surface method (RSM). Correlation analysis explores the impact of factors, such as seabed soil property, hull elevated mass and hull elevation on seismic response. The constructed response surface serves as a surrogate model and screening tool, enabling a rapid and efficient assessment of seismic response and platform safety, while circumventing the need for extensive seismic simulations. Moreover, it facilitates optimization for operation. In conclusion, this research contributes to enhance jack-up platform design and operation safety, particularly in seismic-prone regions.
Improving the Wave Energy Production Using Multi-Size WEC Arrays With Passive Control
Authors: Alday G. Matias , Raghavan Vaibhav , Lavidas George 
Published: August 2024

Abstract
One of the key aspects to consider before large scale deployments of wave energy converters (WEC), is to optimize the devices’ characteristics to improve wave power absorption. Typically, devices with passive control are designed to have the highest efficiency in wave power absorption/production in the range of the most frequent wave conditions. In general, there is an intrinsic “trade-off” between the range of wave conditions where a WEC can operate and the operation efficiency which, in the end, is linked to the energy production yield. Outside the most frequent wave conditions, there is still a non-negligible percentage of occurrences of more energetic sea states carrying high energy flux values. Given the specific design characteristics of a WEC device, lower operation efficiency is expected during these stronger sea states, which is translated as a lower production compared to the available (usable) resource. In the present study, a multi-size point absorber WEC array, using passive internal control, is proposed to optimize wave power production at the array level. The main aim of this work is to verify the combined use of devices designed to work in the most frequent wave conditions, with WECs which mass and dimensions are defined to improve their response during stronger sea states. A comparison of the mean produced power is performed between a proposed multi-array and a single size one. This is done using 30 years of spectral wave data obtained from an implementation of the WAVEWATCH III model, while response of the wave energy converters array is simulated with the boundary element model HAMS-MREL. Preliminary results, using 10-devices arrays, show a promising increase in production from 60 to 140% when larger WECs are included.
An Efficient Full Long-Term Approach for Mooring Systems Extreme Response Estimation Using a Multi-Dimensional Joint Environmental Model
Authors: Simão Marina Leivas , Videiro Paulo Maurício , Volnei Sudati Sagrilo Luis , Costa de Oliveira Mauro 
Published: August 2024

Abstract
In the long-term scenario, the environmental actions to which floating offshore structures are subjected to, such as waves, wind and current, are non-stationary processes. However, this long-term behavior is usually modeled as a series of short-term stationary conditions. In a full long-term analysis approach (FLTA), an estimate of the N-year response can be obtained through an integration of short-term peaks probability distributions over all these short-term environmental conditions. This paper applies an innovative and more efficient full long-term integration method based on the Importance Sampling Monte Carlo Simulation (ISMCS) method, where the uniform distribution is used as the sampling function. In parallel, a multi-dimensional joint environmental model that statistically describes all relevant environmental parameters is developed, contemplating linear and directional variables, and treating wind sea and swell waves individually. The methodology is applied for two FPSO systems installed in Brazilian deep waters. It is shown through a Bootstrap procedure that ISMCS is a numerically stable procedure and provides reliable estimates for the long-term N-year response with a feasible number of required numerical simulations. It is also shown that it can be a powerful tool to account for the simultaneous occurrence of wind sea and swell waves in structural response evaluations and that its use can lead to more accurate extreme tension response estimates, without being overly conservative.
A Gradient Mesh Analysis of Numerical Ship Model With Two-Way Stiffened Plate Equivalence
Authors: Li Muzhi , Liu Xiaolei , Yuan Yuchao , Tang Wenyong , Duan Zhongdi , Xue Hongxiang , Liu Jun 
Published: August 2024

Abstract
With the development of ships in recent years, the ship size becomes larger and the hull structure becomes complicated. The entire ship should be modeled to study the dynamic responses as the key equipment may be located away from the loading area, leading to a dramatic increase in the number of numerical model elements. The stiffener, which is attached to the hull plate, may further make the numerical simulation time-consuming even difficult to converge and stabilize. Thus, it is necessary to reduce the element number of stiffened plates in the ship model. Current approaches may only consider the single in-plane or out-of-plane stiffness equivalence to smear the stiffener onto the plating. Besides, the applicability may be limited to the one-way stiffened plate. In this study, a simplified approach considered the coupling effect of in-plane and out-of-plane stiffnesses for two-way stiffened plate is proposed. Firstly, the equilibrium and compatibility equations are used to equal the stiffness of stiffened plate to the single plate with orthotropic material properties. Then the coupled load-deformation relationship of the equivalent single plate is derived based on the orthotropic material parameters and first-order shear deformation theory. Based on the mechanical property equivalence, the transverse stiffener and the longitudinal stringer of numerical ship model can be removed. Subsequently, the simplification of stiffener can amplify the maximum mesh size from stiffener spacing to web frame spacing, which can further reduce the number of elements. The fine mesh can be used for the loading and focus regions of the model, while the coarse mesh can be used for the rest region. Finally, the various dynamic evaluations are conducted to discuss the applicability of the approach. The results show that the equivalent single plate combined with the gradient mesh method can improve the computational efficiency and stability with high accuracy.
Study of a Top Tension Riser Using a 4-Node Shell Element Based on Vector Form Intrinsic Finite Element Method
Authors: Sun Hongwei , You Yunxiang , Han Panpan , Zhi Changhong 
Published: August 2024

Abstract
The top tension riser plays a pivotal role in deep sea oil and gas extraction, operating within a complex environment influenced by flows, waves, and the top buoyancy module. Accurately simulating its dynamic response in such intricate marine conditions is paramount. Current research predominantly involves modeling full-scale, large aspect ratio top tension riser using beam elements. In contrast, shell elements offer distinct advantages, presenting a superior representation of the pipeline’s shape and more precise reflection of the flexural and torsional stress distribution in top tension riser. However, employing shell elements for top tension riser studies introduces several challenges. Notably, the requisite number of shell elements is considerably higher than that of beam elements for the same model. In traditional finite element nonlinear structural dynamics computations, an increased element count exponentially intensifies computational difficulty. Consequently, modeling and computing the dynamic response of large aspect ratio top tension riser with shell elements pose formidable research challenges. To address these issues, we develop a four-node shell element based on the vector form intrinsic finite element method, utilizing parallel computing to enhance computational efficiency for top tension riser. This study applies the developed method to compute the dynamic response of top tension riser, employing parallel computing for efficient calculations. The dynamic response under the influence of uniform flow and top buoyancy module motion is investigated. The program is further utilized for the analysis of pipeline stress in top tension riser, validating the precision of the computational method. This research presented innovative methods for the study of the tension risers.
Numerical Study on Ice-Induced Loads on Ship Hulls in Ice Floe Regions
Authors: Zhong Kai , Li Zhiyuan , Ni Bao-Yu , Xue Yanzhuo 
Published: August 2024

Abstract
The reduction in polar ice coverage as a consequence of global warming has led to an increase in commercial ship traffic in the Arctic and the Antarctic waters. The floating ice region has gradually become an important ice condition in polar navigation under the long-term trend of global warming. In addition to causing a surge in ship resistance, the ice load acting in the normal direction of the hull will also pose a threat to the structural safety of the ship. Ice floes can have irregular shapes due to wind, waves, currents, and thermodynamics, which leads to differences in their interaction patterns with the ship hull. Ice-induced load characteristics are closely related to the type of ice floe and operating speeds of the ship. In this study, the authors use a viable analysis procedure to predict the ice-induced hull pressure characteristics for ships navigating in floe ice fields. Based on the CFD-DEM approach, a numerical tool verified by previous experiments is applied to explore the impacts of ice floe shapes, sizes and ship speeds on hull pressure characteristics, which also considers the water-ice effects on the hull. The Statistical analysis procedure is also applied to get the probability distributions of the ice pressure from numerical simulation and their characteristics are analyzed.
Design of a Towing Carriage for Measuring Forces on a Submerged Model in a Hydraulic Channel
Authors: Barrera Daniel , Encarnación Ángel , Leon Jose , Moreira Daniel , Silva-Leon Jorge 
Published: August 2024

Abstract
The design of a towing carriage for measuring forces in a hydraulic channel is presented as a means of conducting experimental research on the quantitative and qualitative analysis of drag forces between dynamic flows in stationary bodies and static flows in moving bodies. The principle of inertial reference frames is well-known and widely applied in the development of scale models for the study of fluid flow phenomena. In this sense, the literature is based on the equivalence of an object in motion with the surrounding fluid at rest compared to the fluid in motion with the object at rest. A project is currently being developed to empirically verify CFD simulations and evaluate differences between cases of stationary and mobile submerged models. This project aims to generate experimental evidence that enriches the literature in this regard. An experimental setup is proposed to test the situations mentioned above. The design was carried out as part of the graduation work of mechanical engineering students, the selection process was based on an analysis of various options through the formal design process. The prototype consists of a mobile cart that will tow a submerged model in a hydraulic channel. This channel is designed to create a stable flow of water, allowing for testing a submerged. The mechanical and hydrodynamic forces involved were considered for analysis in detail.
Underactuated Unmanned Ship Trajectory Tracking Control Based on LSTM and DDPG Under Environmental Disturbance
Authors: Wang Ziming , Chen Shunhuai 
Published: August 2024

Abstract
To solve the trajectory tracking problem of low-speed small unmanned ships with unknown environmental disturbances, and enhance the computational performance of trajectory tracking. This article is based on LSTM neural network and reinforcement learning DDPG algorithm to establish an unmanned ship trajectory tracking control model considering event triggering mechanism. Firstly, establish a kinematic and dynamic model of three degree of freedom unmanned ships, and design a trajectory tracking controller through feedback linearization method. Secondly, the LSTM network is used as the actor network of the DDPG algorithm, and an LSPG model is established to adapt the control parameters of the trajectory tracking controller. Subsequently, event triggering conditions are set based on trajectory tracking errors. When the event is triggered, the trajectory tracking controller outputs control force to achieve trajectory tracking of unmanned ships. Finally, numerical simulation experiments are conducted, which verified the effectiveness of the trajectory tracking control algorithm and demonstrated that the trajectory tracking model considering event triggering mechanism can effectively enhance computational performance while achieving trajectory tracking objectives.