bluuebunny/crossref_metadata_2025 huggingface dataset:
A Survey of Control Systems for Offshore Well Service Pumps: State-of-the-Art, Challenges and Future Perspectives
Authors: Klis Pawel , Xing Yihan , Abd Abdalla H. , Ren Chao
Published: August 2024

Safety has become the most important value for many companies. This value is especially important in the offshore industry. Lately, there has been a trend to limit the number of people on a deck of platforms, production boats and other maintenance vessels. On the other hand, experts, operators, and technicians must be present during all offshore operations. Therefore, offshore companies are looking for a balance between safety and the number of personnel on decks. One of the solutions for that problem is a well-designed control system that allows one or more production units to operate remotely. The wireless connection between the machine and the operator’s computer located onshore gives an excellent opportunity to run the production device without physical presence. This solution enables the elimination of people from dangerous places. Furthermore, it will positively impact the environment because the transport of employees will be significantly reduced.

The main goal of this paper is to provide a general overview of the control systems used to operate offshore production units. The operation aspects of the control system are explained using the example of a topside Well Service Pump with a power of 725 HP. Firstly, the article provides the description, challenges and possibilities of the control system used to operate the pump unit. Next, the remote control using Human Machine Interface (HMI) and Supervisory Control and Data Acquisition (SCADA) are explained. Finally, the paper explores the artificial intelligence techniques, such as machine learning, and predictive maintenance. The study concludes with a summary of the findings.
Inspection Planning Optimisation for Offshore Energy Structures Using Digital Twin
Authors: Li Shen , Brennan Feargal
Published: August 2024

Inspection and maintenance are integral elements within the structural integrity management of offshore energy structures. This allows the identification and remediation of progressive structural degradation such as fatigue cracks, ensuring fitness-for-service of critical offshore assets throughout their service lifetime. In view of optimising the offshore retrieval/intervention and eventually reducing the life-cycle costs, risk-based inspection and maintenance planning is highly relevant. However, conducting a comprehensive risk assessment requires gaining a thorough knowledge of the as-built design and actual operational profile whereby accurately predicting its performance. Although design specifications and assumptions can serve as guidelines, a high degree of uncertainty may arise due to the disparity between the actual operational profile and the design assumptions. This paper studies the application of digital twin approach whose virtual monitoring feature coupled with fatigue load updating algorithm enables the derivation of more realistic loading spectrum. Probabilistic fracture mechanics-based model is utilised to simulate the fatigue crack growth. An optimisation of future inspections is performed with an objective to minimise the life cycle expected total cost due to fatigue failure, inspection and repair. For demonstration purpose, a case study using an offshore wind support structure is presented to illustrate this digital twin-enabled proposal. Furthermore, areas open future research in this field are discussed.
Estimation of Maximum Run-Up Heights on a Cylinder for Focused Waves Formed With Different Mechanisms
Authors: Zhang Huidong , Wang Tong , Xu Sheng , Zhou Xueqian
Published: August 2024

To evaluate the maximum run-up height on a fixed vertical column under the action of focused waves formed with different physical mechanisms, a 3D two-phase numerical wave tank is developed in this study. The influences of wave nonlinearity, column radius and water depth on the run-up heights are investigated in a series of tests. For focused waves with identical crest height and trough-to-trough period, the maximum run-up height is always larger in linear focused wave than in nonlinear focused one, due to their different hydrodynamic characteristics. The discrepancies become greater with the increased wave nonlinearity. Moreover, the maximum run-up height, less affected by water depth, is more sensitive to the variation of column radius in linear focused wave. Nevertheless, for both types of focused waves, their maximum run-up heights can be estimated reasonably well by the modified empirical function with the same parameters but different coefficients.
Oil-Based Vs Water-Based Fluids Behavior With Experimental Cuttings-Bed Erosion in Horizontal Wells
Authors: Pedrosa Camilo , Lund Bjørnar , Saasen Arild
Published: August 2024

Efficient removal of deposited cuttings-bed is a necessity during drilling operations. Nevertheless, it is a big challenge specially in horizontal wellbores as larger beds are formed and gravity tends to consolidate the formed beds. Poor cuttings cleaning might cause several problems such as, drill-pipe sticking, increased torque and drag, lower Rate of Penetration (ROP), excessive Equivalent Circulating Density (ECD), among others. Removal of the drilled cuttings is done by the drilling fluid flow thru the annulus and out to the surface.

This paper presents results from bench-top laboratory erosion tests as well as corresponding CFD simulations. The tests were conducted with two different oil fluids; a low-viscosity oil and an oil-based drilling fluids and compared against 2 fluids from previous work; pure water and water-based drilling fluid, flowing over a quartz sand particle bed wetted by different oil-based fluids. A bedload transport model was used to describe and analyze the motion forces imparted by the oil-based fluids into the sand grains from a consolidated cuttings-bed.

The results have shown that a cuttings-bed eroded with oil-based drilling fluid provide higher motion force than a cuttings-bed eroded with base oil fluid. But even with that higher energy to move the particles, to know the cohesive forces that cause agglomeration of particles in the bed may be important in order to design a fluid which can effectively erode a deposited bed.
Development of the Environmental Contour for Ice Drift Speed and Wind Speed
Authors: Sinsabvarodom Chana , Leira Bernt J. , Høyland Knut V. , Chai Wei , Jitpairod Kittikun , Nuntiyakul Waraporn , Seripienlert Achara
Published: August 2024

The purpose of this study is to develop environmental contours for ice drift speed and wind speed. The drift of sea ice is naturally influenced by various external forces, including wind stress at the air-ice boundary, water stress at the water-ice boundary, the Coriolis force, pressure gradients caused by sea surface tilting, and internal stress within the sea ice itself. Typically, sea ice drifts at a rate of approximately 2–3% of the wind speed (as measured at a height of 10 meters above the ocean surface) in the Arctic region. The Nansen number, which relates to the magnitude of the wind speed, can be used to estimate ice drift speed. This research investigates the relationship between wind speed and ice drift speed and applies it to generate environmental contours. Ice drift data for this study are collected through local subsurface measurements using acoustic Doppler current profilers (ADCP) in the Beaufort Sea. The distributions of wind speed and ice drift speed are studied, and the effects of the correlation between them are investigated. Subsequently, the environmental contours demonstrate the relationship between wind speed and ice drift speed. This provides valuable insights into the probabilistic nature of the relationship between wind speed and ice drift speed. The simultaneous values of the wind speed and ice drift speeds to be applied for design purposes can be obtained from the corresponding short term environmental condition along the derived environmental contour.
Digital Twin of Autonomous Surface Vessels for Safe Maritime Navigation Enabled Through Predictive Modeling and Reinforcement Learning
Authors: Menges Daniel , Von Brandis Andreas , Rasheed Adil
Published: August 2024

Autonomous surface vessels (ASVs) play an increasingly important role in the safety and sustainability of open sea operations. Since most maritime accidents are related to human failure, intelligent algorithms for autonomous collision avoidance and path following can drastically reduce the risk in the maritime sector. A DT is a virtual representative of a real physical system and can enhance the situational awareness (SITAW) of such an ASV to generate optimal decisions. This work builds on an existing DT framework for ASVs and demonstrates foundations for enabling predictive, prescriptive, and autonomous capabilities. In this context, sophisticated target tracking approaches are crucial for estimating and predicting the position and motion of other dynamic objects. The applied tracking method is enabled by real-time automatic identification system (AIS) data and synthetic light detection and ranging (LiDAR) measurements. To guarantee safety during autonomous operations, we applied a predictive safety filter to correct inputs from a reinforcement learning-based controller. The approaches are implemented into a DT built with the Unity game engine. As a result, this work demonstrates the potential of a DT capable of making predictions, playing through various what-if scenarios, and providing optimal control decisions according to its enhanced SITAW.
Assessing Hydrate Formation Risk in Infill CCS Wells
Authors: Skogestad Jan Ole , Feneuil Blandine , N'Gouamba Elie , Linga Harald , Aasen Ailo , Skår Gjertrud , Roggeband Serge M. , Nedrum Jack , Helgeland Stig
Published: August 2024

Carbon capture and storage (CCS) has been identified as a part of the solution to the climate crisis, but to play a major role, a massive scale-up is required. This will inevitably lead to a need for drilling wells into existing CO2 storage formations, and with that comes the risk of well control incidents where the influx from the formation into the well is dominated by CO2. A major concern regarding such incidents is the potential formation of hydrates caused by Joule-Thomson cooling when the CO2 loaded drilling fluid is forced through flow restrictions while being circulated out of the wellbore or when flowing through topside valves.

Software tools incorporating mathematical models for hydraulics and flow in the well play an important role in risk assessment related to drilling operations. To evaluate the risk of hydrate formation and subsequent plugging of valves and flow restrictions, a tool that sufficiently well captures the relevant thermodynamics and flow physics may be of crucial importance. By combining existing hydraulic flow models for drilling and well control operations developed for petroleum wells with new sub-models describing Joule-Thomson cooling and hydrate formation risk in the presence of CO2, such a tool can be built. To achieve accurate models, laboratory experiments of hydrate formation in drilling muds loaded with CO2 are required.

In order to enable a software tool for evaluating and handling risks related to hydrate formation during CO2 well control incidents, researchers and industry actors here work together to close knowledge gaps and provide the understanding of the physics involved that is required. We present experimental methods and lab results on hydrate formation in drilling fluids loaded with CO2 along with considerations on modelling aspects. This includes thermodynamical sub-models, integrated hydraulic models and the development of a software tool for use in operations planning and execution. Finally, the impact from such a tool for contributing to reducing the risk for hydrate formation related to drilling of CO2 infill wells is discussed.
Understanding the Role of Buoyancy on Jet Flows Within Viscoplastic Medium: Insights for Plug and Abandonment of Wells
Authors: Hafezi Mohammad , Hassanzadeh Hossein , Akbari Soheil , Faramarzi Mohsen , Taghavi Seyed Mohammad
Published: August 2024

Plug and abandonment (P&A) operation refers to the final stage of the oil and gas well’s operational life-cycle. The successful implementation of a P&A operation ensures the secure sealing of the well to prevent fluid movement and eliminate leakage between different layers. The key steps of a P&A operation entail three processes: (1) accessing the annulus section, (2) cleaning the target area (i.e., inside and outside the casing), and (3) installing cement plug barriers. The proper cleaning helps to enhance the cement-casing bonding while mitigating the risk of cement contamination. Jet cleaning, known as an efficient technique in the second step of P&A operations, displaces undesirable fluids and materials by injecting a cleaning fluid into the target area. Fluid properties, including density difference between injected and ambient fluids and the fluids’ rheological parameters, stand as key variables that directly influence the cleaning efficiency. Hence, a comprehensive understanding of how these parameters affect the jet flow is crucial for optimizing efficiency in well-cleaning procedures. In this study, we experimentally examine the miscible jet flow dynamics for two distinct scenarios: positively buoyant jets, where momentum and buoyancy act in the same direction, and negatively buoyant jets, where they act in opposite directions. The jet flow is formed by introducing a Newtonian fluid vertically downward, through a circular nozzle, into a transparent tank containing a viscoplastic fluid. We assume a “free jet” condition in our experiments, as the large tank dimensions render the wall effect negligible on the jet behavior. We use high-speed imaging to study the effects of the injection velocity, the density difference, and the rheological parameters (in particular, the yield stress) on the jet flow dynamics. The penetration length (indicating the evolution of the jet length over time) is the primary jet feature addressed in this study, which is investigated in both positively and negatively buoyant jets. Our findings show that the yield stress of the ambient fluid resists the jet evolution, leading to a decrease in the jet penetration length.
Study on Practical Control Force Decision to Improve Facility Utilization of PA-WEC
Authors: Murai Motohiko , Kakimoto Shinnosuke , Kawagishi Tatsuki , Han Jialin
Published: August 2024

The Japanese government has set a goal of increasing the share of renewable energy to 36–38% by 2030. Wave energy is one of the sources of renewable energy from the ocean. In this study, we focused on a floating point-absorber wave energy converter (PA-WEC), which has a simple structure like a traditional buoy can be farmed relatively easily to ensure safety. The PA-WEC generates energy by utilizing the heave motion of the floating part. We analytically obtain the control force that maximizes the average power output of the PA-WEC in understood irregular waves, which are defined as the superposition of regular waves.

If the float’s range of motion were infinite, the maximum power generation possible based on linear theory can be achieved. However, increasing the range of motion would result in higher construction and operation costs, while reducing the range would limit the operable wave conditions and decrease facility utilization.

Therefore, it is very important to improve equipment utilization while keeping the range of motion small. This study proposes a practical control strategy with the objective of enhancing the facility utilization of the PA-WEC while ensuring that the heave motion remains within physical constraints. The effectiveness of the control strategy in suppressing the range of float motion and consequently improving facility utilization without being care about the optimal solution in linear theory is discussed.
Experimental Investigation on Vortex Induced Vibration of a Rigidly Coupled Twin-Tube Model
Authors: Shen Jiawei , Fu Shixiao , Zhang Mengmeng , Niu Zhibo , Hua Yilong , Xu Yuwang , Chu Yaopeng , Bin Song
Published: August 2024

The objective of this experimental study is to reveal the features of vortex-induced vibration (VIV) for a tandem rigidly coupled twin-tube model. A series of self-oscillation model tests were carried out under uniform flow with a range of reduced velocity from 3 to 20, and Reynolds numbers from 2 × 103 to 1.5 × 104. The spacing ratio, defined as the center-to-center distance divided by the cylinder’s diameter, varied within a range of 1.5–5. The cross-flow VIV response amplitudes and frequencies of the twin-tube model were studied under different spacing ratio compared with a single-tube model. The results reveal that the VIV response amplitude of the twin-tube structure follows a different trend from that of conventional single-tube structures or two free cylinders. The response characteristic of the twin-tube model shows a separated VIV-galloping at the spacing of 1.5D. The most suitable spacing ratio for a submerged floating tunnel (SFT) is 1.5, as it exhibits the lowest response amplitude. The spacing ratio has a significant influence on the response amplitude and frequency, 3D is a transition spacing of the vortex shedding modes, an amplitude modulation phenomenon is observed at the spacing ratio of 3. When the spacing ratio is larger than 4, the response tends to be similar.
Symbolic Regression Equations to Predict the Maximum Stress Concentration Factors in Flexible Pipes With Damaged Tensile Armors
Authors: Mendes de Sousa José Renato , Cunha dos Santos Anderson
Published: August 2024

Flexible pipes are fundamental in various offshore oil and gas exploration applications, such as production, gas injection, gas lift, or water injection lines. However, such structures can be damaged infield, reducing their structural capacity and leading to costs associated with replacements, production loss, or oil leakage. Among the various failure modes of flexible pipes, the rupture of the tensile armors is critical, as these armors withstand the axial loads imposed on the pipe. In this context, this work aims to contribute to evaluating the structural integrity of damaged flexible pipes subjected to tensile loads. Given the limitations of analytical models and the high computational cost of models based on the finite element (FE) method in assessing the structural behavior of damaged flexible pipelines, this work proposes an empirical-analytical equation obtained through Symbolic Regression (SR) as an expedited alternative for determining the maximum stresses in the tensile armors of damaged flexible pipes. Firstly, several flexible pipes were analyzed using a previously proposed FE model. Several tensile armors in their outer layers were considered broken in these analyses. The maximum stress concentration factors (SCF) in the remaining tensile armors were calculated and, together with nondimensional parameters selected to represent the pipe’s mechanical response adequately, formed a dataset analyzed with an SR tool. Finally, a closed-form equation (SR equation) was obtained to analyze other damaged flexible pipes. The proposed equation was verified against FE model results and experimental tests, and good agreement was shown.
Modeling Emissions of Shipping Operations in Sea Ice
Authors: Veber Joshua , Brown Jeffrey , Wang Jungyong , Browne Thomas , Veitch Brian , Molyneux David
Published: August 2024

The marine industry is a large contributor to overall global emissions and must mitigate its environmental impacts through innovation. These improvements can be achieved through combinations of design fundamentals, such as more efficient hull forms, technical innovations, such as wind-assisted propulsion, and operational transformations, such as switching to alternative fuels. Adopting various decarbonization measures will be expensive and must be informed by a detailed understanding of ship performance. In this paper, a method to predict carbon emissions is presented and applied to the case of a medium icebreaker. The emissions predictions are based on a model of ship resistance and propulsion in ice and open water, and they constitute an essential part of a general ship performance model. Route optimization can be informed by such ship performance models in combination with routing algorithms and rewards functions. Our goal is to incorporate a detailed emissions prediction method in a route optimization framework explicitly aimed at transits involving sea ice. The paper includes a description of a full-scale field trial through which we evaluate the accuracy of the predictions and develop a profile of emissions for tactical maneuvers to broaden the prediction capabilities. The results of the trials will be presented at the OMAE conference in Singapore.
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

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

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

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

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

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

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

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

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

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

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

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

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

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.
A Method to Establish Characteristic Load Effect and Capacity Check During Installation Design for Marine Operations
Authors: Gullaksen Joannes
Published: August 2024

This paper will present a methodology for establishing characteristic load effect and capacity check while performing installation design as part of the modelling and analysis scope of marine operation in order to establish operational parameters and limit weather criteria. The purpose of installation design is to ensure safety in terms of personnel, equipment and environment, as well as the structural integrity of the product during installation. This is achieved by analyzing the different steps of an operation in order to establish operating parameters and limit weather conditions based on a comparison of extreme and characteristic load effects and relevant limit state criteria. The methodology is customized for product design codes that require products to be verified with respect to applicable installation loads, including design formats for capacity check for combined loads on rigid pipe, umbilical and power cables, as well as capacity check for single response quantities for flexible pipes directly from the time domain analyses. The extreme value is modelled with a probability distribution of the largest response, where the extreme value is a given percentile in the extreme response distribution. The Gumbel distribution is used as a model for the extreme value distribution to fit the largest response from each simulation realization. Alternatively, a more efficient procedure may be used, including establishing response time series, establishing time series for the load effect, fitting a 3-parameter Weibull distribution of individual maxima, establishing the associated Gumbel extreme value distribution for the largest individual maxima, and finally estimating extreme value as the appropriate percentile in the Gumbel distribution. The method is implemented in a software application to be able to automate the process and which can also be used as a postprocessing tool along with a non-linear time domain analysis solver. Nonlinear time domain analysis is required to handle nonlinearities in geometric stiffness, hydrodynamic loading, material nonlinearities and contact problems. Nonlinear properties and hydrodynamic load mechanism are transforming the wave frequency of Gaussian excitation into non-Gaussian global responses. Assessment of extreme load effect for non-Gaussian response processes is required to perform capacity checks based on an irregular wave representation. In present context, the meteorological and oceanographic data analysis involves manipulating, transforming, and visualizing data based on data analysis results using descriptive and inferential statistics.
Assessment of the Technical Potential of the Ocean Thermal Energy Conversion in the Brazilian Equatorial Margin
Authors: Corrêa Daniela , Shadman Milad , Almeida Jeferson , Estefen Segen Farid
Published: August 2024

This study investigates the potential of the Ocean Thermal Energy Conversion (OTEC) technology in the Potiguar Basin, that is part of the Equatorial Margin of the Brazilian coastline. OTEC is based on the Rankine thermodynamic cycle, which uses the temperature difference between the ocean’s surface and deep waters to generate electricity. The methodology employed in this study is based on the development of computer algorithms for processing temperature results from a three-dimensional global numerical model. Data in situ from Argo was used to correlate with HYCOM, validating the model to analyze ocean temperature. The temperature measurements from HYCOM are acquired in the research area considering 40 vertical layers (with a maximum depth of up to 6366 meters), with a daily temporal resolution between January 1, 2000, and December 31, 2020. The installation of an OTEC plant requires the presence of a thermal gradient of at least 20°C. This operational threshold was highlighted and considered in the context of this research. Calculations of gross and net energy power were done to analyze the warm-water and cold-water flow rates necessary for available energy. The technical potential of the OTEC is addressed considering the Pitu Oeste, that is an exploratory area from Potiguar, showing the possibility of decarbonizing the oil and gas activities.