bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Frequency Response of Primary Resonance of DWCNT and CNT Resonators Under Electrostatic Actuation
Authors: Caruntu Dumitru I. , Juarez Ezequiel
Published: November 2019

This paper deals with the frequency-amplitude response of primary resonance of electrostatically actuated Double-Walled Carbon Nanotubes (DWCNT) and Single-Walled Carbon Nanotubes (SWCNT) cantilever resonators. Their responses are compared. Both the DWCNT and SWCNT are modeled as Euler-Bernoulli cantilever beams. Electrostatic and damping forces are applied on both types of resonators. An AC voltage provides a soft electrostatic actuation. For the DWCNT, intertube van der Waals forces are present between the carbon nanotubes, coupling the deflections of the tubes and acting as a nonlinear spring between the two carbon nanotubes. Electrostatic (for SWCNT and DWCNT) and intertube van der Waals (for DWCNT) forces are nonlinear. Both resonators undergo nonlinear parametric excitation. The Method of Multiple Scales (MMS) is used to investigate the systems under soft excitations and weak nonlinearities. A 2-Term Reduced-Order-Model (ROM) is numerically solved for stability analysis using AUTO-07P, a continuation and bifurcation software. The coaxial vibrations of DWCNT are considered in this work, in order to draw comparisons between DWCNT and SWCNT. Effects of damping and voltage of the frequency-amplitude response are reported.
Interface Models for Multirate Co-Simulation of Nonsmooth Multibody Systems
Authors: Peiret Albert , Kövecses József , González Francisco , Teichmann Marek
Published: November 2019

Co-simulation techniques enable the coupling of physically diverse subsystems in an efficient and modular way. Complex engineering applications can be simulated in co-simulation setups, in which each subsystem is solved and integrated using numerical methods tailored to its physical behaviour. Co-simulation implies that the communication between subsystems takes place at discrete-time instants and is limited to a given set of coupling variables, while the internals of each subsystem are generally not accessible to the rest of the simulation environment. In non-iterative co-simulation schemes, this may lead to the instability of the integration. Increasingly demanding requirements in the simulation of machinery have led to the coupling, in real-time co-simulation setups, of multibody models of mechanical systems to computational representations of non-mechanical subsystems, such as hydraulics and electronics. Often, these feature faster dynamics than their mechanical counterparts, which leads to the use of multirate integration in non-iterative co-simulation environments. The stability of the integration in these cases can be enhanced using interface models, i.e., reduced representations of the multibody system, to provide meaningful input values to faster subsystems between communication points. This work describes such interface models that can be used to represent nonsmooth mechanical systems subjected to unilateral contact and friction.
Frequency Response of Parametric Resonance of Electrostatically Actuated Circular Plates Under Hard Excitations
Authors: Beatriz Julio , Caruntu Dumitru I.
Published: November 2019

In this paper, the Method of Multiple Scales, and the Reduced Order Model method of two modes of vibration are used to investigate the amplitude-frequency response of parametric resonance of electrostatically actuated circular plates under hard excitations. Results show that the Method of Multiple Scales is accurate for low voltages. However, it starts to separate from the Reduced Order Model results as the voltage values are larger. The Method of Multiple Scales is good for low amplitudes and weak non-linearities. Furthermore the Reduced Order Model running with AUTO 07p is validated and calibrated using the 2 Term ROM time responses.
Feasibility of Pairing a Low-Cost Positive Displacement Pump With Low-Energy Pressure Compensating Drip Irrigation Emitters for Smallholder Farms in Africa
Authors: Engelkemier Seiji , Grant Fiona , Landis Jordan , Sheline Carolyn , Varner Hannah , Zubajlo Rebecca E. , Sokol Julia , Winter Amos
Published: November 2019

In low income countries, existing drip irrigation systems are cost prohibitive to many smallholder farmers. Companies are working to develop efficient, low-cost irrigation systems by using technologies such as positive displacement (PD) pumps and pressure compensating (PC) emitters. However, these two technologies have not been paired in an efficient and cost-effective manner. Here we describe a proof-of-concept pump control algorithm that demonstrates the feasibility of exploiting the physical relationship between the input electrical power to a PD pump and the hydraulic behavior of a system of PC emitters in order to determine the optimal pump operating point. The development and validation of this control algorithm was conducted in partnership with the Kenya-based irrigation company SunCulture. This control method is expected to reduce cost, improve system efficiency, and increase accessibility of irrigation systems to smallholder farmers.
A Graph Coloring Technique for Identifying the Minimum Number of Parts for Physical Integration in Product Design
Authors: Gopalakrishnan Praveen Kumare , Cavallaro Jeffery , Jahanbekam Sogol , Behdad Sara
Published: November 2019

The objective of this study is to develop a mathematical framework for determining the minimum number of parts required in a product to satisfy a list of functional requirements (FRs) given a set of connections between FRs. The problem is modeled as a graph coloring technique in which a graph G with n nodes (representing the FRs) and m edges (representing the connections between the FRs) is studied to determine the graph’s chromatic number χ(G), which is the minimum number of colors required to properly color the graph. The chromatic number of the graph represents the minimum number of parts needed to satisfy the list of FRs. In addition, the study calculates the computational efficiency of the proposed algorithm. Several examples are provided to show the application of the proposed algorithm.
Toward a Functional Failure Analysis Method of Identifying and Mitigating Spurious System Emissions in a System of Systems
Authors: Van Bossuyt Douglas L. , Arlitt Ryan M.
Published: November 2019

Increasingly tight coupling and heavy connectedness in systems of systems (SoS) presents new problems for systems designers and engineers. While the failure of one system within a SoS may produce little collateral damage beyond a loss in SoS capability, a highly interconnected SoS can experience significant damage when one member system fails in an unanticipated way. It is therefore important to develop systems that are “good neighbors” with the other systems in a SoS by failing in ways that do not further degrade a SoS’s ability to complete its mission.

This paper presents a method to (1) analyze a system for potential spurious emissions and (2) choose mitigation strategies that provide the best return on investment for the SoS. The method is suited for use during the system architecture phase of the system design process. A functional and flow approach to analyzing spurious emissions and developing mitigation strategies is used in the method. Use of the method may result in a system that causes less SoS damage during a failure event.
A Comparative Study of Formulations and Algorithms for Reliability-Based Co-Design Problems
Authors: Cui Tonghui , Allison James T. , Wang Pingfeng
Published: November 2019

Co-design, or integrated physical and control system design, has been demonstrated successfully for several engineering system design optimization applications, primarily in a deterministic manner. An opportunity exists to study non-deterministic co-design strategies, including incorporation of uncertainty-induced failures, into an integrated co-design framework. Reliability-based design optimization (RBDO) is one such method that can be used to increase the likelihood of having a feasible design that satisfies all reliability constraints. While significant recent advancements have been made in co-design and RBDO separately, limited work has been done where reliability-based dynamic system design and control design optimization are considered jointly. In this paper, the co-design problem is integrated with the RBDO framework to yield a system-optimal design and the corresponding control trajectory, which satisfy all reliability constraints in the presence of parameter variations. Different problem formulations and RBDO algorithms are compared through numerical examples. The design of a horizontal-axis wind turbine (HAWT) supported by a lattice tower (with parameter uncertainties) is presented to demonstrate the applicability of the proposed method.
Computing Poincaré-Lyapunov Constants via Carleman Linearization
Authors: Hubay Csanád Árpád , Kalmár-Nagy Tamás
Published: November 2019

Using Carleman linearization an approximation is given for the solution of a system at Hopf bifurcation. The values of the Poincaré-Lyapunov constants (whether they are zero or not) affect the linear algebraic properties of the Carleman matrix and they appear in solvability conditions (through the Fredholm alternative). We provide a linear algebra based algorithm to compute the Poincaré-Lyapunov constants.
Estimating the Value of Excess: A Case Study of Gaming Computers, Consoles and the Video Game Industry
Authors: Yadav Darshan , Long Daniel , Morkos Beshoy , Ferguson Scott
Published: November 2019

A widely held belief among design practitioners is that an ideal design solution is the one that meets all the requirements while minimizing surplus cost incurred by exceeding requirements. In this research, we challenge this notion by exploring if providing design “excess”, the ability of a solution to exceed certain requirements, can increase the value of a solution to its end users. A case study is performed in the video game industry to explore if design excess is prevalent and its impact on the industry. This study is performed by examining various PC builds (budget, mid-range, and high-end dream) and gaming consoles (Microsoft Xbox and Sony PlayStation) over an 18-year period. Based on a thorough investigation of video game requirements and capacity of different hardware, we find that design excess has existed in computer hardware and is intentionally used as a design property. The results indicate that mid-range solution provide the greatest value to its customers. Further, PC excess based value is adjusted during years when consoles are released. Using measurements of excess, this study also reveals a shift in technology push versus pull that occurs during the mid-2000s and is observable through the lens of system excess.
Using Semantic Fluency Models Improves Network Reconstruction Accuracy of Tacit Engineering Knowledge
Authors: Sexton Thurston , Fuge Mark
Published: November 2019

Human- or expert-generated records that describe the behavior of engineered systems over a period of time can be useful for statistical learning techniques like pattern detection or output prediction. However, such data often assumes familiarity of a reader with the relationships between entities within the system — that is, knowledge of the system’s structure. This required, but unrecorded “tacit” knowledge makes it difficult to reliably learn patterns of system behavior using statistical modeling techniques on these written records. Part of this difficulty stems from a lack of good models for how engineers generate written records of a system, given their expertise, since they often create such records under time pressure using shorthand notation or internal jargon. In this paper, we model the process of maintenance work order creation as a modified semantic fluency task, to build a probabilistic generative model that can uncover underlying relationships between entities referenced within a complex system. Compared to more traditional similarity-metric-based methods for structure recovery, we directly model a possible cognitive process by which technicians may record work-orders. Mathematically, we represent this as a censored local random walk over a latent network structure representing tacit engineering knowledge. This allows us to recover implied engineering knowledge about system structure by processing written records. Additionally, we show that our model leads to improved generative capabilities for synthesizing plausible data.
Machine Learning Driven Individualized Gait Rehabilitation: Classification, Prediction, and Mechanism Design
Authors: Loya Amol , Deshpande Shrinath , Purwar Anurag
Published: November 2019

Design of mechanisms for human-machine interaction involves numerous subjective criteria and constraints in addition to the kinematic task. This is particularly important for the rehabilitation devices, where the size, complexity, weight, cost, and ease of use are critical factors. A large majority of the approaches towards the design of such devices, which are based on limited degree-of-freedom mechanisms start with finding numerically optimal solutions to the task path followed by pruning for feasible design concepts. Given the highly nonlinear nature of the problem, this approach discards a large proportion of numerically sub-optimal solutions, which could potentially be pragmatically optimal solutions if the subject criteria were applied from the start. To overcome this limitation, in this paper, we present an end-to-end computational approach for developing a device for individualized gait rehabilitation using machine learning techniques focusing on gait classification, prediction, and specialized device design. These models generate a distribution of linkage mechanisms, which strongly correlate to the distribution of target path variations. This way of formulating the problem results in a large variety of solutions to which subjective criteria can be applied to yield practically useful design concepts that would otherwise not be possible using traditional synthesis methods.
Establishing Baseline Performance for Off-the-Shelf Nitrile Seals for the India Mark II Hand Pump System
Authors: Ottosson Hans J. , Naylor Thomas A. , Johnson Oliver K. , Mattson Christopher A.
Published: November 2019

Accessing clean water is a persistent, and life threatening, challenge for millions of people in the world. Mechanical hand pumps have a long history of helping people access clean ground water for drinking and daily use. Among the most ubiquitous are the India Mark II and III pump systems, for which there are more than 4,000,000 installed across the world. These are estimated to serve between 600M and 1B people. All pumps degrade in performance over time, requiring service; many do not receive it causing pumps to become dysfunctional. The purpose of this paper is to establish a baseline for nitrile seal performance of India Mark II hand pump systems. Understanding off-the-shelf performance and using it as a baseline is an important step toward understanding degradation of performance over time, which is the focus of a much larger study to understand — mechanically and socially — how hand pumps perform, degrade, and ultimately meet human needs. In this paper, 110 off-the-shelf nitrile seals that were purchased in Uganda were tested and the following was characterized: (i) geometric variation, (ii) material variation, (iii) leak performance, and (iv) correlation between these. The seal leak performance was found to be very robust to variations in geometry and material at zero cycles. This important baseline supports our future work to understand how and to what degree seals become sensitive to geometric and material degradation during use.
Stress Field Prediction in Cantilevered Structures Using Convolutional Neural Networks
Authors: Nie Zhenguo , Jiang Haoliang , Kara Levent Burak
Published: November 2019

The demand for fast and accurate structural analysis is becoming increasingly more prevalent with the advance of generative design and topology optimization technologies. As one step toward accelerating structural analysis, this work explores a deep learning based approach for predicting the stress fields in 2D linear elastic cantilevered structures subjected to external static loads at its free end using convolutional neural networks (CNN). Two different architectures are implemented that take as input the structure geometry, external loads, and displacement boundary conditions, and output the predicted von Mises stress field. The first is a single input channel network called SCSNet as the baseline architecture, and the second is the multi-channel input network called StressNet. Accuracy analysis shows that StressNet results in significantly lower prediction errors than SCSNet on three loss functions, with a mean relative error of 2.04% for testing. These results suggest that deep learning models may offer a promising alternative to classical methods in structural design and topology optimization. Code and dataset are available at https://github.com/zhenguonie/stress_net.
Dynamic Analysis of Multiple Launch Rocket System Under the Action of Jet Flow
Authors: Li Shutian , Wang Guoping , Miao Yunfei , Rui Xiaoting
Published: November 2019

Jet flow is one of the important factors affecting the vibration, initial disturbance and firing dispersion of Multiple Launch Rocket System (MLRS). In this research, based on the rocket gas jet dynamics, MLRS launch dynamics theory and transfer matrix method for multibody system, a physical model of jet flow model and a MLRS launch dynamics model considering the multiple launch rocket device and the launch of rocket are built. The launching dynamic process of rocket jet flow of MLRS is numerical simulated by using the technology of overset mesh and the Computational Fluid Dynamics (CFD) methods. The nephogram of mach number and contour map of velocity are obtained. The impact effect force on the air-facing surface of rocker launcher after the rocket slides and leaves the directional barrel is acquired. Regarding the calculated data of impact force to MLRS as external force, the MLRS launch dynamics equation is solved by using the transfer matrix method for multibody system. Finally, the dynamics response of MLRS under the effect of jet flow is analyzed.
Development and Experimental Evaluation of a Quad-Tilt-Wing Flying Robot Platform
Authors: Aihaitijiang A. , Onal Cagdas D.
Published: November 2019

In this paper, we present the mechanical design and control system of a new indoor and outdoor Quad-Tilt-Wing flying robot. The proposed flying robot can achieve vertical takeoff, hovering, and long duration horizontal high-speed flight. All of these flight modes can be achieved by simply changing the angle of the rotors and wings by a tilt mechanism. We present the details on design and prototyping, the attitude control system, and experimental results, including wind-tunnel experiments, full flight tests, and performance tests. The experimental results show that our Quad-Tilt-Wing flying robot successfully achieves full conversion flight: vertical and rapid takeoff, high-speed cruise, and vertical landing. Performance test results show that during horizontal flight, the wings generate lift and effectively reduce energy use compared to a fixed quad rotor architecture. Consequently, the proposed platform combines unique features of multi-rotor and fixed wing systems to achieve long-duration flight with low-energy compared to a conventional multi-rotor UAV.
On Quality Factor Improvement in a NEMS Resonator With Nonlinear Damping
Authors: Ramakrishnan Subramanian , Shougat Md Raf E Ul
Published: November 2019

Nonlinear damping effects have been reported in experiments on nanoelectromechanical (NEMS) resonators and suggested as a pathway to improve the quality (Q) factors of the resonators. In particular, in a nonlinearly damped Duffing NEMS resonator operating in the hardening regime, it has been shown that white noise excitation can shrink the hysteresis region resulting in higher Q factors. In this paper the authors: (1) find that an analytical expression they previously derived using the method of harmonic balance for the frequency-amplitude relationship of a weakly-excited, nonlinearly damped Duffing NEMS resonator is valid for strong excitation, (2) show analytically and verify numerically that for constant values of the nonlinear damping coefficient, higher amplitude of forcing leads to increase in the resonant frequency, (3) find that white-noise induced stochastic parametric excitation can lead to enhanced Q factors and (4) show that decreasing the nonlinear damping coefficient leads to higher Q-factor. The results, in addition to being theoretically significant, are expected to be important in sensing applications using NEMS resonators.
3D Shape Synthesis for Conceptual Design and Optimization Using Variational Autoencoders
Authors: Zhang Wentai , Yang Zhangsihao , Jiang Haoliang , Nigam Suyash , Yamakawa Soji , Furuhata Tomotake , Shimada Kenji , Kara Levent Burak
Published: November 2019

We propose a data-driven 3D shape design method that can learn a generative model from a corpus of existing designs, and use this model to produce a wide range of new designs. The approach learns an encoding of the samples in the training corpus using an unsupervised variational autoencoder-decoder architecture, without the need for an explicit parametric representation of the original designs. To facilitate the generation of smooth final surfaces, we develop a 3D shape representation based on a distance transformation of the original 3D data, rather than using the commonly utilized binary voxel representation. Once established, the generator maps the latent space representations to the high-dimensional distance transformation fields, which are then automatically surfaced to produce 3D representations amenable to physics simulations or other objective function evaluation modules. We demonstrate our approach for the computational design of gliders that are optimized to attain prescribed performance scores. Our results show that when combined with genetic optimization, the proposed approach can generate a rich set of candidate concept designs that achieve prescribed functional goals, even when the original dataset has only a few or no solutions that achieve these goals.
Cost Effective On-Site Fault Diagnosis Home Appliance Using a Smart Phone and Support Vector Machine
Authors: Baek Ji Min , Lee Kyeong Ha , Lee Seung Ho , Koo Ja Choon
Published: November 2019

One of the common rotating machines of the consumer electronics might be a washing machine. The rotating machinery normally suffers mechanical failures even during daily operations that results in poor performance or shortening lifetime of the machine. Therefore, engineers have been interested in the earliest fault diagnosis of the rotating machine. Existing fault diagnosis methods for rotating machines have used fast fourier transform (FFT) method in frequency domain to detect abnormal frequency. However, it is difficult to diagnose using the FFT method if the normal frequency components of the rotating machines overlaps with the fault frequencies. In this paper, sets of acoustic signals generated by the washing machines are collected by using a smart phone in which an inexpensive microphone is equipped, and collected data are analyzed using a new algorithm, which combining the skewness, kurtosis, A-weighting filter, high-pass filter (HPF), and FFT. The analyzed data is applied to support vector machine (SVM) to determine defect existence. The proposed algorithm solves the disadvantages of the existing method and is accurate enough to discriminate the data collected by the cheap microphone of the smart phone.
Numerical and Experimental Investigation of Nanoscale Heat Transfer in the Head-Media Interface During Static Touchdown
Authors: Sakhalkar Siddhesh V. , Cheng Qilong , Ma Yuan , Ghafari Amin , Bogy David B.
Published: November 2019

With minimum fly height of less than 10 nm in contemporary hard-disk drives, understanding nanoscale heat transfer at the head-media interface is crucial for developing reliable head and media designs. Particularly, with the emergence of Heat-Assisted Magnetic Recording (HAMR) and Microwave-Assisted Magnetic Recording (MAMR), head failure due to overheating has become an increasing concern. There is a need to develop a methodology to use theoretical curves for spacing-dependent nanoscale heat transfer coefficient to predict head and media temperatures in actual hard disk drives. In this study, we present a numerical model to simulate the head and media temperature profiles during static touchdown and compare our results with experiments performed with a magnetic head on a silicon wafer. As the head approaches touchdown with increasing TFC power, the phonon conduction heat transfer coefficient between the head and the substrate increases exponentially, causing a drop in the head temperature vs TFC power curve. Our model shows that the introduction of van der Waals forces between the head and the substrate causes a steeper drop in the head temperature curve and ensures a good quantitative match with experimental results.
Optimizing Production Facilities Using a Transient Multiphase Flow Simulator
Authors: Al-Qasim Abdulaziz S. , Almudairis Fahad , Bin Omar Abdulrahman , Omair Abdullatif
Published: November 2019

This paper discusses a method for optimizing production facilities design for onshore/offshore wells during new field development. Optimizing the development of new oil and gas fields necessitates the use of accurate predication techniques to minimize uncertainties associated with day-to-day operational challenges related to wells, pipelines and surface facilities. It involves the use of a transient multiphase flow simulator (TMFS) for designing new oil and gas production systems to determine the feasibility of its economic development.

A synthetic offshore oil field that covers a wide range of subsurface and surface facility data is considered in this paper. 32 wells and two reservoirs are considered to evaluate the effect of varying sizes of tubing, wellhead choke, flowline, riser, and transport line. A detailed investigation of the scenario of emergency shutdowns to study its effect on the system is performed using TMFS. Other scenarios are also evaluated such as startup, depressurization, pigging, wax deposition, and hydrate formation.

This paper provides a method to minimize the cost by selecting the optimum pipelines sizes and diameters, and investigating the requirements of insulation, risk of pipeline corrosions and other related flow assurance parameters. Different facility design scenarios are considered using TMFS tool to achieve operational flexibility and eliminate associated risks. Pressure and temperature conditions are evaluated under several parametric scenarios to determine the best dimensions of the production system. This paper will also provide insight into factors affecting the flow assurance of oil and gas reservoirs.
Flow-Induced Vibration Analysis of a Water Injection System at Elevated Flow Rates of an FPSO
Authors: González Díez Néstor , Pontaza Juan P. , Awe Oluwaseun M. , van Beek Pieter , Tümer Can
Published: November 2019

The water injection system of an FPSO active in the Gulf of Guinea is to increase injection capacity to levels that are threatening from a flow-induced vibration perspective, such that hydrocarbon recovery can be accelerated. A three-tier method based on the internal guidelines of the system operator has been employed to assess the level of FIV threat expected from the increase in flow rate. A high-level screening analysis is followed by a more detailed approach, modified in this case by introducing knowledge obtained from field data gathered during a comprehensive measurement campaign aboard the FPSO. In particular, the data has been used to calibrate the finite element model of the mechanical layout of the pipework and associated supporting by making use of an optimization technique. The PSD of the flow excitation has been calibrated to match the measured response of the system, with descriptions of the turbulent excitation introduced in elbows by means of PSD functions available in the open literature. The PSDs, once calibrated, are further scaled to the future flow-rates so that they can be used as input to the mechanical response analysis. Though the high-level screening analysis delivers the conclusion that flow rates should be limited, the detailed analysis proves that the expected vibrations will be acceptable.
Thorough Verification and Validation of CFD Simulation for FPSO Roll Damping
Authors: Lee Donghwan , Huang Zhenjia (Jerry)
Published: November 2019

For floating production platform such as FPSO and FLNG, it is important to use confidently estimated roll damping coefficients in the prediction of its motions in waves since in many cases the roll response is mainly contributed from resonance. Traditionally roll damping prediction was made through model tests or empirical formulas. As computing power and numerical modeling techniques have been improved during last a few decades, offshore industry starts to consider CFD as an alternative engineering and design tool complementary and/or supplementary to physical model tests. This paper presents our verification and validation work of modeling practices with commercially available CFD software for engineering applications for FPSO roll decay damping in calm water. The numerical modeling followed a recommended modeling practice developed by a Joint Development Project – TESK JDP [1].
Challenges and Lessons Learnt From the Design, Fabrication and Installation of Rigid Tie-in Spools
Authors: Curti Gianbattista , Pavone Diego , Pirinu Gianluigi , Qin Jianjun
Published: November 2019

This paper is based on the experience made during the engineering, fabrication and installation of rigid spools used to tie-in production lines (10”) to manifolds, in 650m max water depth, on a project recently completed in West Africa.

The design of tie-in spools needs to accommodate the operation and environmental loads, and the installation, fabrication, metrology and, if applicable, also stack up tolerances.

This may require spools of large sizes/weights and complex geometries, with associated fabrication and installation costs that significantly contribute to the overall costs of a project.

This paper is focused on the process that was followed during the execution of the RFI (Risers Flowlines Installation) EPCI (Engineering Procurement Construction Installation) contract.

To find workable configurations of the spools, such not to compromise the execution of the project, was a major challenge.

Horizontal connection systems were to be used.

Configurations of the spools, initially designed to be in contact with the seabed (“seabed-supported” design) turned to be by far more complex than the geometries estimated before the start of the detailed engineering, and which had been the basis for laying down the execution schedule of the project.

Spools suspended between the horizontal hubs (“free-spanning” design) were finally chosen, which significantly simplified the fabrication and the installation.

A key driver of the design was to keep the interface loads within the maximum permissible values specified for the connectors.

The feedbacks from the fabrication and the installation are included in the paper, and the lessons learned are provided.

Alternative solutions — based on use of flexible pipes — are also discussed.
A Multi-Level Approach to the Prediction of the Added Resistance and Powering of Ships in Waves
Authors: Liu Shukui , Papanikolaou Apostolos , Feng Peiyuan , Fan Sheming
Published: November 2019

In this paper, we present a multi-level fidelity approach and associated computational tools for the prediction of the added resistance of various types of ships in waves. Employed methods include a fully empirical formula, a semi-empirical asymptotic formula, a potential flow, 3D panel method and a CFD code. Each of them requires a different level of detail for the hull form and this enables the application to various practical scenarios. The developed software tools are here validated against recently obtained model experiments data from MARIC. Developed tools are now integrated in the design software platform of MARIC and are used in the optimisation of ship design.
Second Order Wave Propagating Along VLFS
Authors: Iijima Kazuhiro , Ma Chong
Published: November 2019

This paper addresses the nonlinear deflection wave which propagates along a Very Large Floating Structure (VLFS). The whole VLFS is modeled as a one-dimensional beam afloat on the water surface in a vertical two-dimensional plane. It is assumed that the deflection of the wave propagating along the VLFS has a finite amplitude. The nonlinear wave propagating along the VLFS is investigated by extending the propagation theory of the linear wave along the VLFS. The kinetic and kinematic conditions at the boundary surface between the water and VLFS are considered rigorously up to the 2nd order. The 2nd order wave is obtained as a wave associated with the 1st order wave. The characteristics of the nonlinear wave along the VLFS are elucidated by the mathematical solution. The nonlinear wave along the VLFS has characteristics slightly different from the nonlinear free surface wave, known as Stokes wave. The positive peak of the wave along the VLFS is higher than the negative peak due to the nonlinearity in some frequency range while it is the opposite in the other frequency range. The amplitude of the 2nd order wave increases divergently at the frequency range between the two frequency regimes.
Lean Global Analysis of Marine Slender Structures With Machine Learning
Authors: Ribeiro Machado da Silva Vinicius , Santos Matheus Costa dos , Vignoles Mario Alfredo
Published: November 2019

The new age of oil and gas industry is being driven by cost effective solutions, aiming to provide cheaper, faster and better products/services. The industry 4.0 brings an opportunity to transform systems and processes to be more efficient, making use of digitalization and new technologies, including the use of artificial intelligence algorithms applied to engineering problems.

In Brazilian offshore fields, the operating conditions for flexible riser applications (deep-water, mean wave frequencies, floating units and corrosive fluids) make the metallic layer’s fatigue failure mode one of the drivers in its design. In a daily basis, nonlinear dynamic finite element analysis uses regular wave scatter diagrams as an equivalent way to model the wave elevation, avoiding the time consuming irregular wave representation. The analysis performed with regular waves are faster but carries conservatisms with it. In a deep-water scenario, the wave height and period ranges of the wave scatter diagram can be refined to improve the fatigue results obtained, leading to a considerable increase in the total amount of wave classes that need to be evaluated.

Great part of the wave classes has a very low participation in the total fatigue damage, spending an unnecessary time to analyze them. Helped by a robust design of simulation experiment (DoSE) and machine learning regressors, a lean representation of the regular wave scatter can be done, where some of them are simulated and the rest of the results can be accurately predicted.

This paper presents the application of supervised learners that are used to predict riser fatigue damage at different riser locations, given partial simulations of a regular wave scatter diagram. The techniques support the strategy to reduce the total amount of fatigue analysis required within a project design phase. The focus stays on the evaluation of the fatigue of metallic layers at two main critical regions, bend stiffener and touch down zone. Hidden patterns inside each scatter diagram are discovered, minimizing the total number of finite element analysis (FEA) required. The amount of the wave class reduction starts from 50% going up to 75%, maintaining a good level of accuracy on the predicted damage values.
Numerical Analysis of Nonlinear Wave Loads on an Offshore Wind Turbine Monopile
Authors: Feng Xingya , Willden Richard H. J. , Zhou Binzhen , Adcock Thomas A. A.
Published: November 2019

Highly nonlinear extreme waves are the major, often the dominant, environmental load on offshore wind turbines. The higher-order ‘ringing’ loads associated with the nonlinear waves can cause unexpected resonance of the monopile. Hydrodynamic analysis of these harmonic loads remains a challenge due to the difficulty in extracting the bound harmonics from the force spectrum in an extreme wave event. A phase manipulation approach (four-phase combination) has been recently demonstrated to be able to separate the higher harmonic components of the wave loads in tank tests. In this work, we employ a fully nonlinear potential flow based Numerical Wave Tank (NWT) to simulate the wave diffraction by a fixed vertical column. We present a detailed study of our checks on the numerical accuracy of our model. Phase control is implemented for the wavemaker to manipulate the phase of each wave component. Focused wave groups are generated to represent the incoming extreme waves. With the four-phase decomposition, the higher harmonics of the wave loads are shown to be clearly separated. Comparisons with the existing test results show fairly good agreement at higher harmonics. The structure of the harmonic forces and moments are analysed and we reconstruct the higher harmonics based on the Stokes expansion assumption using the linear force. In addition, the effects of wave steepness on the harmonic components are discussed.
Plug and Abandonment Environment in British Columbia
Authors: Bizhani Majid , Trudel Élizabeth , Frigaard Ian
Published: November 2019

British Columbia (BC) has a significant oil & gas industry, with approximately 25,000 wells drilled in the province since the early 1900s. In the past few decades, the industry has changed from a balanced oil & gas production to activities dominated by unconventional gas production which is recovered by hydraulic fracturing. Concurrently, since 2000 there has been a shift from isolated vertical wells to pad-drilled horizontal wells. The older well stock at end-of-life combines with horizontal production wells and fractured reservoirs, the consequence of which is a growing wave of abandonment in BC, building over the next decade. This paper reviews the existing data on BC wells, as it is relevant to well abandonment operations. This includes the well architectures, trajectories, depths, testing procedures, etc.
Emergency Disconnect and Storm Hang-Off: Reducing Risk for Drilling Risers in Harsh Environments
Authors: Gallagher Conor , Williams Dara
Published: November 2019

As the search for oil and gas moves to deeper waters and more challenging environments such as the Atlantic margin and South America, the operational risks and consequences of equipment failure increase significantly.

Industry guidelines, such as API RP 16Q [1] and ISO 13624-1 [2], define standard scenarios to include in a riser analysis that cover many of the various phases of installation and operation of drilling risers. These scenarios include assessments of the riser in both connected and disconnected modes such as storm hang-off. It is industry practice, as per API RP 16Q/ISO 13624-1, to assess these scenarios independently. Unplanned disconnect of the drilling riser in a storm involves transitioning through intermediate stages to get to the final hang-off configuration. While recoil analysis (assessment of riser disconnect phase) of the riser is commonly addressed, standard industry approaches fail to address other key intermediate and transitional phases of operation required to position the riser into the storm hang-off configuration.

This paper presents a study that highlights the importance of analyzing all pertinent stages of drilling riser disconnect and hang-off operations. The study demonstrates that these intermediate phases of operation are often limiting and, if not assessed adequately, have the potential to be catastrophic in harsh environments. A detailed set of revised riser analysis requirements are generated along with the development of a comprehensive harsh environment WSOG (Well Specific Operating Guideline) that optimizes operational performance and improves safety for harsh environment drilling. These revised analysis guidelines and associated modelling that are necessary for harsh environment locations represent a level of pre-drilling assessment that is ahead of that typically undertaken by the industry today.
Experimental and Numerical Investigation of Gas-Yield Power-Law Fluids in a Horizontal Pipe
Authors: Ihmoudah Abdalsalam , Awad Mohamed M. , Rahman Mohammad Azizur , Butt Stephen D.
Published: November 2019

Two-phase flow of gas/yield power-law (YPL) fluids in pipes can be found in a wide range of practical and industrial applications. To improve the understanding of the effects of rheological parameters of non-Newtonian liquids in a two-phase model, experimental and Computational Fluid Dynamics (CFD) investigations of gas/yield power-law fluids in a horizontal pipe were carried out. Two Xanthan gum (XG) solutions at concentrations of (0.05% and 0.10% by weight) were used as the working liquids. The experiments were conducted in a flow loop in a 65-m open-cycle system. The horizontal test section had a diameter of 3 inches (76.2 mm). The transient calculations were conducted using a Volume of Fluid (VOF) model in ANSYS Fluent version 17.2. Slug flow characteristics were recorded and observed by a high-speed digital camera in different operating conditions. The slug velocity and slug frequency were investigated experimentally and numerically, and a comparison of results with empirical relationships found in the literature was performed. We observed that the rheological properties of non-Newtonian phase influence the flow behavior in two-phase flow with increasing XG concentrations. The results of the empirical correlation to measure the slug frequency of a gas/non-Newtonian with considered the rheology of the shear-thinning behaver gave acceptable agreement with numerical measurements at low polymer concentration. The effect of liquid superficial velocity on slug translational velocity at low gas superficial velocity was relatively high.
Coupled Numerical Analysis of a Concept TLB Type Floating Offshore Wind Turbine
Authors: Ramzanpoor Iman , Nuernberg Martin , Tao Longbin
Published: November 2019

The main drivers for the continued decarbonisation of the global energy market are renewable energy sources. Moreover, the leading technological solutions to achieve this are offshore wind turbines. As installed capacity has been increasing rapidly and shallow water near shore sites are exhausted, projects will need to be developed further from shore and often in deeper waters, which will pose greater technical challenges and constrain efforts to reduce costs.

Current floating platform solutions such as the spar and semi-submersible rely on large amounts of ballast and complex structural designs with active stabilisation systems for stability of the floating offshore wind turbine platform (FOWT).

The primary focus of this study is to present a design concept and mooring arrangement for an alternative floating platform solution that places emphasis on the mooring system to achieve stability for a FOWT. The tension leg buoy (TLB) is designed to support future 10MW offshore wind turbine generators.

This paper presents the numerical methodology used for a coupled hydro-elastic analysis of the floater and mooring system under combined wind, wave and current effects.

A concept TLB design is presented and its platform motion and mooring line tension characteristics are analysed for a three-hour time domain simulation representing operating and survival conditions in the northern North Sea with water depths of 110 metres. The importance of wave drift forces and the other non-linear excitation forces in the concept design stage are evaluated by comparing the motion and tension responses of three different numerical simulation cases with increasing numerical complexity.

The preliminary TLB system design demonstrated satisfactory motion response for the operation of a FOWT and survival in a 100-year storm condition. The results show that accounting for second-order effect is vital in terms of having a clear understanding of the full behaviour of the system and the detailed response characteristics in operational and survival conditions. Extreme loads are significantly reduced when accounting for the second-order effects. This can be a key aspect to not overdesign the system and consequently achieve significant cost savings.
Experimental and Numerical Investigation on Planar Motion Responses of a Single Point Moored Shuttle Tanker in Waves
Authors: He Ning , Zhang Cheng , Kang Zhuang , Kang Youwei , Wang Changhong
Published: November 2019

In order to ensure the safety of the single point moored shuttle tanker in waves, the numerical model of a shuttle tanker moored with a fixed point was established on the basis of radiation / diffraction theory and pressure integral method in this paper, which was further checked by a series of model tests. Then the plane motion characteristics of the tanker like fishtailing oscillation were analyzed by applying the combined approach of numerical simulation and model test. On this basis, the effects of wave and ballast conditions as well as mooring line length and stiffness on the plane motion of the single point moored tanker were investigated by means of model test. Overall, the research can provide a reference for the design and safety assessment of deep-water offloading system, and give the technical support for the engineering development of deep-water oil and gas projects.
A Closed-Form SIF Determination and Fatigue Life Investigation on Ship Construction Model
Authors: Lou Benqiang
Published: November 2019

Stress intensity factors (SIFs) are important parameters in brittle fracture assessment of marine notched components; in respecting of previous researches, it has found that there are several ways for SIF solutions. Following outline of LEFM based fatigue analysis; the paper has proposed a closed-form SIF solution as an alternative way for ship structural details prediction. It has shown that the stress intensity factors (SIFs) can be solved revealing the effect of the geometric parameters. Numerical tool has offered an evaluation as convergence behavior of relative SIF results between CCT (central crack) and DENT (double edge notch). Then the proposed methodology is applied onto the construction similar to HHI #1 and #2 specimens. It has be concluded in results that the SIFs and fatigue lives by the proposed method have good agreement with those by FEA calculations, furthermore, these key parameters can be expressed in formula format. For real engineering application, the main advantage of the proposed method will be useful for fatigue prediction rapidly and conveniently.