bluuebunny/crossref_metadata_2025 huggingface dataset:
Bio-Inspired Human Network Design: A Multi-Currency Robustness Metric Inspired by Ecological Network Analysis
Authors: Chatterjee Abheek , Layton Astrid
Published: November 2019

The Ecological Network Analysis (ENA) metric ecological robustness quantifies the unique balance that biological food webs have between their pathway efficiency and redundancy, enabling them to maximize their robustness to system disturbances. This robustness is a potentially desirable quality for human systems to mimic. Modeling the interactions between actors in human networks as predator-prey type exchanges (of a medium or currency rather than caloric exchanges) enables an ENA analysis. ENA has been shown to be a useful tool in improving the design of human networks because it allows the characteristics of biological networks to be mimicked. The application of these metrics is, however, limited to networks with only one flow type. Human networks are composed of many different types of flow interactions and thus a biologically-inspired indicator of total system robustness must take into account all of these interactions. This work further develops the traditional ENA ecological robustness metric to accommodate various flows between actors in multi-currency human networks. Two novel methods for quantifying multi-currency flow network robustness are introduced. The mathematical formulation for these new metrics is presented. The water network for the Kalundborg Eco-Industrial Park (EIP) is used as a case study to determine the benefits of the proposed robustness metrics. The results obtained using the single-currency robustness and the two multi-currency robustness metrics are compared using the case study. Based on the analysis of the results obtained at the system level, as well as at the sub-levels, both multi-currency metrics showed the ability to predict systems characteristics for the multi-currency Kalundborg EIP. While both of these are promising, more research regarding these metrics is needed in order to develop an elegant and comprehensive total system robustness metric.
Online Identification of Uncertain Fractional-Order Nonlinear Systems Using a Reinforced Differential Evolution Optimizer
Authors: Wei Jiamin , Yu Yongguang , Chen YangQuan
Published: November 2019

Parameter identification as known as a significant issue is investigated in this paper. The research focus on online identifying unknown parameters of uncertain fractional-order chaotic and hyperchaotic systems, which shows great potential in recent applications. Up to now, most of the existing online identification methods only focus on integer-order systems, thus, it’s necessary to expand these fundamental results to uncertain fractional-order nonlinear dynamic systems and adopt an effective optimizer to deal with the model uncertainties. Motivated by this consideration, this research introduces an efficient optimizer to offline and online parameter identification of the fractional-order chaotic and hyperchaotic systems through non-Lyapunov way. For problem formulation, a multi-dimensional optimization problem is converted into from the problem of parameter identification, where both systematic parameters and fractional derivative orders are considered as independent unknown parameters to be estimated. The experimental results illustrate that SHADE is significantly superior to the other compared approaches. In this case, online identification is conducted via SHADE, the simulation results further indicate that success-history based adaptive differential evolution (SHADE) algorithm is capable of detecting and determining the variations of parameters in uncertain fractional-order chaotic and hyperchaotic systems, and also is supposed to be a successful and potentially promising method for handling the online identification problems with high efficiency and effectiveness.
Designing Self-Organizing Systems With Deep Multi-Agent Reinforcement Learning
Authors: Ji Hao , Jin Yan
Published: November 2019

Self-organizing systems (SOS) are able to perform complex tasks in unforeseen situations with adaptability. Previous work has introduced field-based approaches and rule-based social structuring for individual agents to not only comprehend the task situations but also take advantage of the social rule-based agent relations in order to accomplish their overall tasks without a centralized controller. Although the task fields and social rules can be predefined for relatively simple task situations, when the task complexity increases and task environment changes, having a priori knowledge about these fields and the rules may not be feasible. In this paper, we propose a multi-agent reinforcement learning based model as a design approach to solving the rule generation problem with complex SOS tasks. A deep multi-agent reinforcement learning algorithm was devised as a mechanism to train SOS agents for acquisition of the task field and social rule knowledge, and the scalability property of this learning approach was investigated with respect to the changing team sizes and environmental noises. Through a set of simulation studies on a box-pushing problem, the results have shown that the SOS design based on deep multi-agent reinforcement learning can be generalizable with different individual settings when the training starts with larger number of agents, but if a SOS is trained with smaller team sizes, the learned neural network does not scale up to larger teams. Design of SOS with a deep reinforcement learning model should keep this in mind and training should be carried out with larger team sizes.
A Novel Variable Stiffness Compliant Robotic Gripper Based on Layer Jamming
Authors: Gao Yuan , Huang Xiguang , Mann Ishan Singh , Su Hai-Jun
Published: November 2019

In this paper, we present a novel compliant robotic gripper with three variable stiffness fingers. While the shape morphing of the grippers is cable-driven, the stiffness variation is enabled by layer jamming. The inherent flexibility makes compliant grippers suitable for tasks such as grasping soft and irregular objects. However, their relatively low load capacity due to low structural stiffness limits their applications. Variable stiffness robotic grippers have the potential to address this challenge as their stiffness can be tuned on demand based on the needs of tasks. Layer jamming is an emerging method for variable stiffness due to its advantages of light weight, simple and quick actuation. In our design, the compliant backbone of the fingers is made of 3d printed PLA material. Four thin film materials are attached to each side of the skeleton. The working process of the robotic gripper follows two basic steps. First, the compliant skeleton is bent to a desired shape by actuating a tension cable via a servo motor. Second, upon application of a negative pressure by a vacuum pump, the finger is stiffened up owing to the increasing of the friction between contact surfaces of layers preventing their relative movement.

Since the structural stiffness of the fingers is increased, their load capacity will be increased proportionally. When the air pressure is sufficiently large, the morphed shape can even be locked (no slipping). Test for stiffness of individual finger and load capacity of the robotic gripper are conducted to validate capability of the design. The results showed a 69-fold increase in stiffness of individual finger and a 30-fold increase in gripper’s load capacity.
Reconstruction of Gap-Free Intersections for Trimmed NURBS Surfaces
Authors: Urick Benjamin , Crawford Richard H. , Hughes Thomas J. R. , Cohen Elaine , Riesenfeld Richard F.
Published: November 2019

The modern engineering technologies of Computer-Aided Design (CAD), Computer-Aided Engineering (CAE) and Computer-Aided Manufacturing (CAM) are ubiquitous in engineering design. They are focused on creating, analyzing, and fabricating objects represented as geometric models. Historically, these technologies developed independently, such that their geometric representations are customized to the needs of the technology. As a result, combined use of these technologies has led to differences in data structures, file formats, software constraints, and user knowledge and practice, requiring translation of representations between systems to support interoperability. Complicating this situation is the approximate nature of modeling operations in CAD systems, which can result in gaps at the boundary curves between mating trimmed surfaces of a model. The research presented here is aimed at removing the gaps between trimmed surfaces, resulting in a “watertight” model that is suitable for use directly by downstream applications. A three-step algorithm is presented that includes analysis of the parametric space of the trimming curves, reparameterization to create a global parameter space, and reconstruction of the intersecting surfaces to ensure continuity at the trimming curve.
Data-Driven Dynamic Network Modeling for Analyzing the Evolution of Product Competitions
Authors: Xie Jian , Bi Youyi , Sha Zhenghui , Wang Mingxian , Fu Yan , Contractor Noshir , Gong Lin , Chen Wei
Published: November 2019

Understanding the impact of engineering design on product competitions is imperative for product designers to better address customer needs and develop more competitive products. In this paper, we propose a dynamic network based approach to modeling and analyzing the evolution of product competitions using multi-year product survey data. We adopt Separate Temporal Exponential Random Graph Model (STERGM) as the statistical inference framework because it considers the evolution of dynamic networks as two separate processes: formation and dissolution. This treatment allows designers to investigate why two products enter into competition and why a competitive relationship preserves or dissolves over time. In an open market, the available products to customers are continuously changing over the time, posing challenges for conventional modeling methods concerning fixed product input. Consequently, we propose to leverage “structural zeros” in STERGM to tackle the problem of modeling varying product competitors as nodes in dynamic networks. We use China’s automotive market as a case study to illustrate the implementation of the proposed approach and its benefits compared to the static network modeling approach based on Exponential Random Graph Model (ERGM). The results show that our approach identifies the driving factors associated with product attributes and current market competition structures for the change of competition in both formation and dissolution processes. The insights gained from this paper can help designers better interpret the temporal changes of product competition relations and make product design decisions with the aid of dynamic network-based models.
Direct Energy Deposition 3D Printing of Thermoelectric Materials: Simulation and Experiments
Authors: Sun Kan , Wu Yongjia , Qi Huan , Wu Zhiwei , Zuo Lei
Published: November 2019

The thermoelectric material can directly convert energy between thermal and electric without involving any moving parts. Due to the limitation in geometry and efficiency of fabricating the thermoelectric modules in conventional methods, additive manufacturing is now becoming a promising solution. Direct Energy Deposition (DED) is superior for its large dimension limitation, fast processing speed, and independence from any powder bed. A physical model of DED fabrication with magnesium silicide (Mg2Si) powder was developed, and validation experiments were conducted. In the model and the experiments, a set of parameters and settings, including laser power, scanning speed, material feeding rate, and so on, were applied to investigate their influences on the products and to validate the simulation. The result of this research can give a reference for the further attempt of DED thermoelectric fabrication.
Factors Leading to Sustainable Social Impact on the Affected Communities of Engineering Service Learning Projects
Authors: Armstrong Andrew G. , Mattson Christopher A. , Lewis Randy S.
Published: November 2019

University engineering programs across the USA engage in service learning projects. These projects involve student teams designing and implementing products or solutions for communities in need, often in developing nations. There has been much research done relating to pedagogy and the impact of these programs on student learning. However, less research has been done on measuring the impact of these programs on the affected communities. This paper examines factors that practitioners believe are related to successfully delivering a desirable and transferable solution to affected communities. The authors identified 46 distinct factors from the literature that implicitly or explicitly are suggested to contribute to successful project outcomes. Formed as postulates in this paper, these 46 factors have been separated into 5 categories to assist understanding and implementing these factors into service learning programs. Lastly, different methods of analyzing and measuring project success and impact are discussed. Future methods for proving the viability of the 46 postulates are discussed as well.
A Methodology for Determining Static Mode Shapes of a Compliant Mechanism Using the Pseudo-Rigid-Body Model (PRBM) Concept and the Degrees-of-Freedom Analysis
Authors: Bapat Sushrut G. , Bagivalu Prasanna Pratheek , Midha Ashok
Published: November 2019

Traditionally, the deflected configuration of compliant segments is determined through rigorous mathematical analysis using Newtonian mechanics. Application of these principles in evaluating the deformed configuration of compliant mechanisms, containing a variety of segment types, becomes cumbersome. This paper introduces a methodology to determine the expected deflected configuration(s) of a compliant mechanism, for a given set of load and/or displacement boundary conditions. The method utilizes the principle of minimum total potential energy, in conjunction with the degrees-of-freedom analysis and the pseudo-rigid-body model concept. The static mode shape(s) of compliant segments are integrated in identifying the possible functional configuration(s) of a given compliant mechanism’s structural configuration. The methodology, in turn, also facilitates the in situ determination of the deformed configuration of the constituent compliant segments. It thus assists in the identification of an appropriate pseudo-rigid-body model for design and analysis of a compliant mechanism.
Development of Novel Tooth-Matching Linear Piezoelectric Actuator
Authors: Huang Po-Lin , Chang Jen-Yuan (James)
Published: November 2019

This paper proposes a new concept of piezoelectric actuator. It is different from ordinary piezoelectric actuators which are actuated by friction, and wear becomes a major problem in long-term use. The main purpose of this research is to drive the motor without friction. Hence, the actuator driven by resonance force is proposed here. The foundation of the actuator is based on piezoelectric material which possess the inverse piezoelectric effect itself. The axial deformation of piezoelectric material is worked as excitation here, which makes the stator subjected to mutative equivalent force along the time. At the same time, the input frequency of sinusoidal voltage is controlled and applied to the stators which makes the stators resonated and in contact with motor for pushing the motor forward. In addition to proposing the preliminary design concept of linear piezoelectric actuator, the dynamic model of the piezoelectric actuator system is firstly studied by Hamilton’s Principle. Then, the finite element method is used to calculate the modal analysis of stator. Finally, the prototype is fabricated and experiment platform is established. The vibration response of stators is measured by laser Doppler vibration measuring system, which is able to verify reasonableness of the constructed finite element model and feasibility of linear piezoelectric actuator.
Optimization of Phase-Locked-Loop Based Correction Method for Linear Magnetic Encoding Signals
Authors: Shih Yi-Ting , Chang Jen-Yuan
Published: November 2019

A magnetic encoder is currently used in precision positioning system because it has many advantageous characteristics. The signals generated from magnetic sensor are always disturbed by noise, that is, these signals are not ideal. For the purpose of precise positioning and high resolution in many industrial control systems, this paper proposes an approach, which contains two parts: The first part is “eliminate the harmonic in the signals” by applying an adaptive notch filter. The second part is “the phase tracking and signal reconstruction” by applying software phase-locked loop (SPLL). Through this scheme of encoder signal processing, it could eliminate the noise and improve the accuracy of the system. The simulation results are provided to demonstrate the promotion of the resolution in positioning system.
Systematic Experimental Validation of High-Order Spectral Method for Deterministic Wave Prediction
Authors: Klein Marco , Dudek Matthias , Clauss Günther F. , Hoffmann Norbert , Behrendt Jasper , Ehlers Sören
Published: November 2019

The applicability of the High-Order Spectral Method (HOSM) as a very fast non-linear method for deterministic short-term wave prediction is discussed within this paper. The focus lies on the systematic experimental validation of the HOSM in order to identify and evaluate possible areas of application as well as limitations of use. For this purpose, irregular sea states with varying parameters such as wave steepness and underlying wave spectrum are addressed by numerical simulations and model tests in the controlled environment of a seakeeping basin. In addition, the influence of the propagation distance is discussed. For the evaluation of the accuracy of the HOSM prediction, the surface similarity parameter (SSP) is utilized, allowing a quantitative validation of the results. The results obtained are compared to linear wave prediction to discuss the pros and cons of a non-linear deterministic short-term wave prediction. In conclusion, this paper shows that the non-linear deterministic wave prediction based on HOSM leads to a substantial improvement of the prediction quality for moderate and steep irregular wave trains in terms of individual waves and prediction distance.
Failure Estimation of Offshore Renewable Energy Devices Based on Hierarchical Bayesian Approach
Authors: Abaei Mohammad Mahdi , Arini Nu Rhahida , Thies Philipp R. , Lars Johanning
Published: November 2019

Improving the reliability of marine renewable energy devices such as wave and tidal energy convertors is an important task, primarily to minimize the perceived risks and reduce the associated cost for operation and maintenance. Marine systems involve a wide range of uncertainties, due to the complexity of failure mechanism of the marine components, scarcity of data, human interactions and randomness of the sea environment. The fundamental element of a probabilistic risk analysis necessarily needs to rely on operational information and observation data to quantify the performance of the system. However, in reality it is difficult to ascertain observation of the precursor data according to the number of component failures that have occurred, mainly as a result of imprecision in the failure criterion, record keeping, or experimental and physical modelling of the process. Traditional reliability estimation approaches such as Fault Tree, Event Tree and Reliability Block Diagram analysis offer simplified, rarely realistic models of this complex reliability problem. The main reason is that they all rely on accurate prior information as a perquisite for performing reliability assessment. In this paper, a hierarchical Bayesian framework is developed for modelling marine renewable component failures encountered the uncertainty. The proposed approach is capable to incorporate the conditions, which lack reliable observation data (e.g. unknown/uncertain failure rate of a component). The hierarchical Bayesian framework provides a platform for the propagation of uncertainties through the reliability assessment of the system, via Markov Chain Monte Carlo (MCMC) sampling. The advantages of using MCMC sampling has proliferated Bayesian inference for conducting risk and reliability assessment of engineering system. It is able to use hyper-priors to represent prior parameters as a subjective observations for probability estimation of the failure events and enable an updating process for quantitative reasoning of interdependence between parameters. The developed framework will be an assistive tool for a better monitoring of the operation in terms of evaluating performance of marine renewable system under the risk of failure. The paper illustrates the approach using a tidal energy convertor as a case study for estimating components failure rates and representing the uncertainties of system reliability. The paper will be of interest to reliability practitioners and researchers, as well as tidal energy technology and project developers, seeking a more accurate reliability estimation framework.
CTOD Fracture Toughness Assessment Under Different Notch Type (Fatigue Pre-Cracking and EDM)
Authors: Marines-Garcia Israel , Aguilar Aaron , Carreon Kristian , Darcis Philippe
Published: November 2019

The standardization of any mechanical material characterization is aiming to get homogenization on the testing physical execution by independent laboratories and to drive for accurate material evaluation between different entities. However, from time to time, standard tests may be reconsidered in order to improve their efficacy, execution time and incorporate new testing techniques or technologies without compromising the testing results and consistency. In the present work, fracture toughness crack tip opening displacement (CTOD) testing is addressed and particularly the need to perform fatigue pre-cracking prior monotonic testing. Without the fatigue pre-cracking, CTOD testing time can be significantly reduced during the preparation of specimens, meaning that specimens can be tested as soon as they are machined.

Wire electro-discharge machining (EDM) technique allows generating sharp tip notches, and presents a good alternative to the standards specified fatigue pre-cracking [1–2]. In addition, this machining technology reduces the risk of rejecting the specimen testing, particularly when targeting weld heat affected zone/fusion line (HAZ/FL) microstructure on specimens with surface notch DNV-ST-F101 Figure B-9 [3], where it is specified that the crack tip shall be within a narrow distance (0.5 mm) from the fusion line (FL) or assess grain coarsened heat affected zone (GCHAZ) microstructure as indicated in DNV-ST-F101 section B.2.8.7 [3]. Herein, it is presented an assessment carried out in order to identify the notch type effect over the fracture toughness (CTOD) considering notches conditions as standard fatigue pre-crack and wire electro-discharge machining (EDM).

Fifteen (15) CTOD specimens were manufactured from plain pipe material (same pipe), 251.3 mm OD × 20.9 mm WT, SMLS 450PD and tested according to ISO 12135 recommendations [1], they were distributed as follow; five (5) specimens according to standard recommendations with fatigue pre-cracking length ≥ 1.3 mm or 2.5%W (whichever is bigger), five (5) specimens with a fatigue pre-cracking length < 1.3 mm (between 0.5 mm to 1 mm), and five (5) specimens without fatigue pre-cracking (EDM notch), additionally, results from five (5) specimens previously tested in a round robin (RR) testing performed internally by Tenaris using the same LP material and standard fatigue pre-crack length. The crack length target (a/W) was kept 0.5 for all cases.

Even if the sampling population is relatively small considering the three notch conditions, it seems that EDM might be an alternative to the standard specified fatigue pre-cracking. Thus, this experimental assessment aims to open the discussion on the use of EDM notch as alternative.
Application of Phase Decomposition to the Analysis of Random Time Series From Wave Basin Tests
Authors: Adcock Thomas A. A. , Feng Xingya , Tang Tianning , van den Bremer Ton S. , Day Sandy , Dai Saishuai , Li Ye , Lin Zhiliang , Xu Wentao , Taylor Paul H.
Published: November 2019

Many ocean engineering problems involve bound harmonics which are slaved to some underlying assumed close to linear time series. When analyzing signals we often want to remove the bound harmonics so as to “linearise” the data or to extract individual bound harmonic components so that they may be studied. For even moderately broadbanded systems filtering in the frequency domain is not sufficient to separate components as they overlap in frequency. One way to overcome this difficulty is to use input signals with the same linear envelope but with different phases and then use simple addition and subtraction of the resulting signals to extract different harmonics. This approach has been established for the analysis of wave groups. In this paper we examine whether this approach can be used on random time series as well. We analyse random wave time series of wave elevation from the towing tank in Shanghai Jiao Tong University and force measurements on a cylinder taken in the Kelvin tank at the University of Strathclyde.
Protection of Pipelines and Cables With a Combination of Soil and Rock Cover
Authors: Morrow Damian R. , Small Andrew A.
Published: November 2019

Soil cover, rock cover and a combination of soil and rock cover are common approaches to protecting pipelines, cables and umbilicals associated with offshore energy infrastructure. However, with the exception of a simplified rock cover case or a simplified sand cover case, there is limited published guidance with respect to this design consideration.

Based on a bearing capacity approach, geotechnical numerical analysis techniques have been used to investigate the protection provided by a range uniform and mixed cover scenario. Effects related to rock placement in a slot-shaped trench have also been investigated.

Relatively standard observations were noted with respect to the protection provided by uniform soil or rock cover cases, including noting the different behaviours associated with granular drained cover materials and cohesive undrained cover materials. Some significant observations were made concerning the mixed cover cases. Of particular note was the impact of very soft clay as a limitation on the protection provided by the rock material. The influence of adjacent soil conditions on the protection provided by a rock infilled slot-shaped trench was also noted from analysis results.
A Monte Carlo Based Simulation Method for Damage Stability Problems
Authors: Krüger Stefan , Dankowski Hendrik
Published: November 2019

To cope with future developments of the SOLAS 2009 B1, damage stability investigations must become a central part of the initial design phase. If damage stability calculations are performed in the classical way, they are very time consuming with respect to both modelling and computational time. To overcome this problem, damage stability can be treated as a stochastic process, where the probability of a damage case and the survivability of that particular damage case need to be determined. This task can be solved by direct numerical simulations based on the Monte Carlo principle. If statistical damage distributions are once known, the Monte Carlo simulation delivers a population of damages which can be automatically related to certain damage cases. These damage cases can then be investigated with respect to their survivability.

Applying this principle to SOLAS 2009 damage stability calculations leads to a number of implementation problems which must be solved to guarantee that the MC simulation delivers exactly the same results as the manual, zone based damaged stability calculation. If these problems are solved, the MC based damage stability calculations can be used during the initial design phase until the damage stability approval. The proposed method reduces the computational effort drastically which supports the initial design phase of the ship’s compartmentation. The method further leads to higher attained indices and consequently to a safer and more efficient design.
An Investigation Into the Effect of Biofouling on Full-Scale Propeller Performance Using CFD
Authors: Song Soonseok , Demirel Yigit Kemal , Atlar Mehmet
Published: November 2019

The negative effect of biofouling on ship resistance has been investigated since the early days of naval architecture. However, for more precise prediction of fuel consumption of ships, understanding the effect of biofouling on ship propulsion performance is also important. In this study, CFD simulations for the full-scale performance of KP505 propeller in open water, including the presence of marine biofouling, were conducted. To predict the effect of barnacle fouling on the propeller performance, experimentally obtained roughness functions of barnacle fouling were employed in the wall-function of the CFD software. The roughness effect of barnacles of varying sizes and coverages on the propeller open water performance was predicted for advance coefficients ranging from 0.2 to 0.8. From the simulations, drastic effects of barnacle fouling on the propeller open water performance were found. The result suggests that the thrust coefficient decreases while the torque coefficient increases with increasing level of surface fouling, which leads to a reduction of the open water efficiency of the propeller. Further investigations into the roughness effect on the pressure and velocity field, surface pressure and wall shear stress, and propeller vortices were examined.
Improved Fatigue Design of SCR Modified Miner’s Rule
Authors: Knagenhjelm Hans Olav , Hauge Mons , Nyhus Bård
Published: November 2019

The Aasta Hansteen floating production system is the first SPAR platform with steel catenary risers (SCR) at the Norwegian Continental Shelf (NCS). The water depth is 1300 msw. The weather conditions with respect to wave loading are more severe than any offshore installation completed so far. Under such environmental conditions, it is vital to verify the design of the SCR’s with respect to extreme loading and fatigue life.

A fatigue verification program has been executed for ground OD welds of both clad and carbon steel riser materials. The objective was to determine the effect of weld defects in combination with the effect of variable amplitude loading using the actual fatigue stress distribution experienced by critical parts of the SCR. The stress distribution is based on the local wave spectrum and estimated from hydrodynamic analysis of the riser and the long-term wave statistics.

Two clad pipes and one carbon steel pipe was exposed to rotation bending fatigue testing with artificially imposed defects. One clad pipes gave fracture after more than 1.0 × 109 cycles. The carbon steel pipe gave fracture after 4.56 × 108 cycles.

A modified Miner’s summation rule is proposed for variable amplitude fatigue design. The procedure is based on a verification of variable amplitude testing against constant amplitude testing. The results indicate that load amplitudes below a fatigue limit defined at 107 cycles are not contributing significantly to fatigue crack initiation and growth from a weld defect. The proposed method suggests an engineering approach to this by a modification of the Miner’s rule for VA loading.
Design Methodology and Development of an Independently Rotating Multi-Hull Vessel
Authors: Nihei Yasunori , Srinivasamurthy Sharath , Sakamoto Hiroshi , Masuda Norikazu , Hara Naoyuki
Published: November 2019

Aquaculture farms play a vital role for food security in Japan. The cultivation potential is directly related to the quality of the marine environment. Water quality parameters such as dissolved oxygen and temperature need to be measured and monitored regularly throughout the cultivation period. Energy efficiency and ease of navigation are the prime requirements for environmental survey vessels. In this paper, a new and novel automated vessel is introduced and design methodology is explained. Multi-hull innovative vessel is named as ‘Quadmaran’ and developed particularly for carrying out environmental surveys. The vessel consists of four hulls each capable of rotating independently thereby leading to better sailing performance and excellent stability. It is equipped with devices to measure quality parameters at various water depths and includes a dynamic positioning system aiding for the environment data collection. The basic design criteria of the Quadmaran is derived and understood in this study. Scaled model (1/3 scale) is fabricated for tank tests and resistance tests are carried out in a circulating water tank at Osaka Prefecture University, Osaka, Japan. With the knowledge gained from tank tests, multi-hull phenomenon of the Quadmaran is studied and interaction between the hulls is investigated. It is found that wave interference due to hull orientation becomes significant for Froude number greater than 0.5 and resistance of Quadmaran is found to be less than two times the twin hull resistance for same water draft. Further, an attempt is made to understand how the configuration arrangement affects the resistance of the vessel.
Prediction of Internal Pressure of Flexible Pipe
Authors: Shao Qiangqiang , Liu Ting , Yuan Shuai , Han Peihua , Bai Yong
Published: November 2019

The flexible pipes are widely used in the oil and gas industry to transport petroleum products. The pipe might burst fails when a large internal fluid pressure acts on the pipe, and the consequences are disastrous. In order to ensure the security and reliability of flexible pipes in the application, the mechanical responses of the pipe subjected to high pressure loads should be carefully estimated. The main purpose of this paper is to investigate the burst pressure of the pipe. Based on the principle of virtual work, a theoretical model for stress and deformations of the pipe is established, which takes the material plasticity into consideration. In addition, a finite element model is developed by ABAQUS to verify the feasibility of the theoretical model. According to the verified model, it is efficient to predict the burst pressure and design its cross-section economically with its serving conditions.
Irregular Frequency Removal and Convergence in Higher-Order BEM for Wave Diffraction/Radiation Analysis
Authors: Utsunomiya Tomoaki
Published: November 2019

Higher-order boundary element method (HOBEM) for wave diffraction/radiation analysis is a powerful tool for its applicability to a general (curved) geometry. Inspired by the paper which examined the convergence of BIE code with constant panels (Martic, et al., 2018; OMAE2018-77999), the convergence characteristics of HOBEM with quadrilateral panels have been examined. Here, the effect of removal of irregular frequencies is particularly focused as discussed by Martic, et al. (2018). The irregular frequency removal has been made by the rigid-lid method which is applicable to HOBEM, where the intersection line between the body-surface and the free-surface should be carefully handled. The results show that for first order quantities the convergence is quite good for both cases with/without irregular frequency removal (except where the irregular frequencies affect for the case without irregular frequency removal). For mean drift forces, the convergence becomes poor particularly for the case without irregular frequency removal. The convergence characteristics are examined and some discussions are made.
Four-Point Bending of Metallic I-Core Sandwich Beams With Longitudinal Girder
Authors: Hu Wenwei , Liu Jun , Zhang Pan , Cheng Yuansheng
Published: November 2019

I-core sandwich structure has great potential in the application of hull structure construction due to its high specific strength and relatively simple manufacturing process. The topic on the study of mechanical properties of I-core sandwich structure under bending loads is of interest to structural designers since the structure is often subjected to bending loads in engineering applications. In this paper, a metallic I-core sandwich beam with longitudinal girder was designed and manufactured using laser welding technique, and finally tested under four-point bend loading. The elastic-plastic behaviors and the ultimate load carrying capacity of this novel beam structure were obtained. A numerical model was developed to investigate the mechanical properties of this novel beam structure by finite element method. The results of the numerical model were compared with experimental data. Stress components of the front face and back face in the failure process were analyzed and discussed to investigate the failure of them. Results showed that the huge local bending stresses of plate caused the failure of the front face and back face. Finally, an improved scheme for the test was proposed to provide a pure bending load, which was proved by finite element simulation. All the findings aim to guide the engineering application of this structure.
CFD Modelling of an Electrically Trace Heated Blanket
Authors: Le Toux Vincent , Harchambois Stéphanie , Guindeuil Geoffrey , Vivet Romain , Pasquet François-Xavier , Tosi Guillaume , Palermo Thierry , Herrera Gilbert , T'Joen Christophe
Published: November 2019

The Electrically Trace Heated Blanket (ETH-Blanket) is a new offshore intervention/remediation system currently in development by TechnipFMC for the efficient remediation of plugs due to hydrates or wax in subsea production and injection flowlines. The ETH-Blanket consists of a network of heating cables placed underneath an insulation layer which is laid onto the seabed above the plugged flowline. By applying electrical power to the cables, heat is generated by Joule effect which warms up the flowline content until hydrate dissociation or wax plug remediation through softening or complete melting.

As part of a Joint Industry Project (JIP) between TechnipFMC, Shell and Total, full-scale thermal testing of an ETH-Blanket prototype was carried out in Artelia facilities (Grenoble, France). This testing was performed to verify the capability of the ETH-Blanket system to increase the temperature of the fluid inside a pipe sample above a target temperature (hydrate dissociation temperature or wax disappearance temperature) for various conditions. The impact of lateral misalignment of the ETH-blanket on the pipe and of the pipe burial depth were studied. Moreover, the tests were carried out on two pipe samples, with different designs and insulation properties.

CFD models of the test set-up have been built to replicate the thermal behaviour of the ETH-Blanket prototype. Once validated against the test results, the final aim of CFD modelling is to be able to calculate the performances of the system in real subsea conditions. The modelling of the prototype includes a 3D geometry of the system including the soil, natural convection of water between the ETH-blanket and the pipe sample and natural convection of fluid in the pipe sample.

The present paper focuses on the CFD work performed to match the full-scale thermal test results and to predict the ETH-Blanket performances for real subsea operating conditions. It will describe the various CFD models used, the sensitivities and findings in terms of local and global heat transfer and flow effects and the comparison to the experimental data.
Subsea Rigid Jumper Design Optimization for Sour Service Application
Authors: Toleman Benjamin , Huang Chaojun , Sonawane Mahesh , Shankaran Rohit , Foster Danny
Published: November 2019

Subsea rigid jumpers are designed to meet numerous criteria including thermal and pressure effects, environmental and riser / pipeline interaction loads, slugging, and other field specific requirements. Jumper VIV can be a concern in fields with strong bottom currents. Without the benefit of detailed VIV fatigue analysis, designers must rely on experience and engineering judgement on placement of strakes if VIV is identified as a concern. VIV mitigation is even more challenging because the jumpers can contain numerous long and short design options to accommodate tolerances for subsea well locations and installation tolerances of subsea PLETS and manifolds.

This paper will discuss a case study on optimization of 12 M-shaped jumpers designed for a sour service application in Gulf of Mexico. VIV fatigue assessment of the preliminary jumper design and the methodology adopted to optimize the jumper design and placement of VIV suppression will be discussed. Challenges in meeting high target fatigue life due to sour service application will be discussed. The key challenges whilst optimizing an acceptable VIV suppression solution are the assumed effectiveness of strakes, cost / available inventory of strakes, and physical limitations for placement of strakes.

This paper will highlight the trade-offs that are required to strike a balance between strength and fatigue design requirements when using straked buoyancy modules vs. regular strakes. The paper will also highlight the current limitations in design code that relies on standards developed for pipeline application. An alternative method / modification to the DNV F105 approach used to calculate the cross-flow induced in-line VIV fatigue damage is also discussed.
Towards Implementing Condition-Based Maintenance (CBM) Policy for Offshore Blowout Preventer (BOP) System
Authors: Elusakin Tobiloba , Shafiee Mahmood , Adedipe Tosin
Published: November 2019

With the steadily growing demand for energy in the world, oil and gas companies are finding themselves facing increasing capital and operating costs. To ensure the economic viability of investments and improve the safety of operations, oil and gas companies are promoting their asset integrity management (AIM) systems. In the past, the oil and gas industry adopted reactive maintenance regimes, which involved recertification, testing and repair of faulty equipment while trying to achieve minimum downtime. As technology becomes more affordable, operators have been able to carry out improved fault diagnosis, prognosis and maintenance optimisation. As a result of this, condition-based maintenance (CBM) is being adopted more and more as the preeminent maintenance regime for oil and gas equipment. The blowout preventer (BOP) is one of the most expensive and safety critical drilling equipment in the oil and gas industry. However, there have been very few studies and best practices about how to develop a CBM policy and what specific monitoring techniques and devices will be required to implement it for the BOP system. This paper proposes a V-model based architecture for designing a CBM policy in BOP systems. As a result of the model proposed, gaps in implementation are identified and all the hardware, software and training requirements for implementing the CBM solution in BOP systems will be outlined in detail. Our proposed CBM framework will help BOP operators and maintenance personnel make cost savings through less repairs and replacements and minimal downtime.
Non-Linearly Restoring Performance and its Hysteresis Behavior of Dynamic Catenary
Authors: Li Yilun , Guo Shuangxi , Kong Yue , Li Min , Chen Weimin
Published: November 2019

Catenary is increasingly used as mooring-line and riser system as the water depth gets larger due to its lower cost and easier installment. Its dynamic response and restoring performance become more complicated, as the length of the mooring-line become larger, and the structural and fluid dynamics the mooring-line become consequently more obvious. Compared to the quasi-static method where the static restoring force is mainly involved, the dynamic behaviors and its hysteresis of the catenary mooring-line are considered here so as to comprehensively examine the non-linearly restoring performance of mooring-lines. Based on the 3d dynamic vector equations along with the modified FEM simulations, the hysteresis character of the restoring stiffness and the influences of the catenary dynamics on its restoring performance are presented and discussed.

It is found that, principally owing to the damping and inertial effect coming from the fluid and structural dynamics, the restoring force of the mooring-line depends on both the structural displacement and velocity. Moreover, the dynamic stiffness behaves as a hysteresis loop, instead of a curve. Our numerical results show that the energy consumption during one period rises nonlinearly with the increase of the body frequency ωd and amplitude A0. And, the influence of nonlinear restoring stiffness on the structural response along with the slack-taut phenomenon caused by structural /hydrodynamic inertia and damping is discussed.
Fate of Hydrocarbon Leaks From Plugged and Abandoned Wells Compared to Natural Seepages
Authors: Tveit Mari R. , Khalifeh Mahmoud , Nordam Tor , Saasen Arild
Published: November 2019

As the hydrocarbon fields mature and reach the end of their productive lives, their Permanent Plug and Abandonment (PP&A) become inevitable. Even though new technology and verification methods are being researched, it is evident that operational, barrier material and qualification challenges together contribute to a risk of leaks from abandoned wells. Well integrity standard NORSOK D-010 constitutes zero leak acceptance criteria to protect the environment; however, natural hydrocarbon seepages are occurring all over the world on a daily basis. In this study, we introduce the comparison between leaking wells and natural seeps and suggest conducting a fate analysis is appropriate to provide necessary data for evaluating environmental implications of leaking wells. Two case studies were analyzed using SINTEF Ocean’s OSCAR (Oil Spill Contingency And Response) software; one historical gas leak (Field A) and a theoretical oil leak (Field B). It is found that for releases of natural gas at 70 m water depth, 95 to 99 % dissolve in the ocean, and the fraction of gas reaching the atmosphere is dependent on the initial gas bubble size. Fate of oil is more complex than gas, but evaporation, sedimentation and biodegradation are the main contributing mechanisms in the fate analysis.
CFD Analysis on Hydrodynamic Characteristics for Optimizing Torpedo Anchors
Authors: Sun Jing , Liu Haixiao
Published: November 2019

Compared with other types of anchors, gravity-installed anchors (GIAs) have several main advantages such as simple structure, convenient installation way and cost reduction. The torpedo anchor is one type of GIAs. The geometric configurations have a direct influence on the hydrodynamic characteristics of the anchor, and thus affect its installation performance in water. The present work aimed to put forward some new aspects for optimizing the existing geometries of torpedo anchors by comprehensively improving the hydrodynamic characteristics of the anchor during installation in water. A computational fluid dynamics (CFD) model was established and numerical simulations were carried out using the software of ANSYS FLUENT. The hydrodynamic characteristics concerned involved the drag coefficient, the terminal velocity and the directional stability. The present study paid more attention to the fin’s design. By changing the fin parameters, including the aspect ratio and the area of the fin, the optimum design method of the fin was proposed, which would make sure of a higher terminal velocity as well as good directional stability. Besides, effects of the mass distribution on the hydrodynamic characteristics were investigated. The present work provides a design reference for torpedo anchors and is also beneficial to the research and development of new types of GIAs.