• Title/Summary/Keyword: out coupling

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Numerical simulation in time domain to study cross-flow VIV of catenary riser subject to vessel motion-induced oscillatory current

  • Liu, Kun;Wang, Kunpeng;Wang, Yihui;Li, Yulong
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.12 no.1
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    • pp.491-500
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    • 2020
  • The present study proposes a time domain model for the Vortex-induced Vibration (VIV) simulation of a catenary riser under the combination of the current and oscillatory flow induced by vessel motion. In this model, the hydrodynamic force of VIV comprises excitation force, hydrodynamic damping and added mass, which are taken as functions of the non-dimensional frequency and amplitude ratio. The non-dimensional frequency is related with the response frequency, natural frequency, lock-in range and the fluid velocity. The relatively oscillatory flow induced by vessel motion is taken into account in the fluid velocity. Considering that the added mass coefficient and the non-dimensional frequency can affect each other, an iterative analysis is conducted at each time step to update the added mass coefficient and the natural frequency. This model is in detail validated against the published test models. The results show that the model can reasonably reflect the effect of the added mass coefficient on the VIV, and can well predict the riser's VIV under stationary and oscillatory flow induced by vessel motion. Based on the model, this study carries out the VIV simulation of a catenary riser with harmonic vessel motion. By analyzing the bending moment near the touchdown point, it is found that under the combination of the ocean current and oscillatory flow the vessel motion may decrease the VIV response, while increase the excited frequencies. In addition, the decreasing rate of the VIV under vessel surge is larger than that under vessel heave at small vessel motion velocity, while the situation becomes opposite at large vessel motion velocity.

Preparation and application of silica-based coatings for corrosion protection of marine structures (해양구조물용 silica 기반 내해수성 코팅제의 제조 및 응용)

  • Lee, Byeong Woo
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.31 no.3
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    • pp.137-142
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    • 2021
  • In this study, the development of the room temperature curable silica-based coating compositions for anticorrosive and antifouling performance in marine environments was carried out. The marine (plant) structures with many exposed parts are operated in harsh marine environments such as strong ultraviolet rays, extreme temperature differences and salt water corrosion. Organic paints that are easily degraded under these environments and easily eroded by physical stimuli such as waves can not play a role properly. Dense ceramic coatings on marine structures provide careful protections even in saltwater environments due to their high hardness and rust resistance. Therefore, in the case of ceramic coatings, their use and application range in marine structures can be greatly improved due to their functional advantages. In the present study, silica-based coating compositions based on colloidal silica with silane coupling agents, curing salts, and ceramic fillers were developed, and their applications as protective coatings for corrosion protection and fouling prevention in seawater were also studied.

High-velocity ballistics of twisted bilayer graphene under stochastic disorder

  • Gupta, K.K.;Mukhopadhyay, T.;Roy, L.;Dey, S.
    • Advances in nano research
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    • v.12 no.5
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    • pp.529-547
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    • 2022
  • Graphene is one of the strongest, stiffest, and lightest nanoscale materials known to date, making it a potentially viable and attractive candidate for developing lightweight structural composites to prevent high-velocity ballistic impact, as commonly encountered in defense and space sectors. In-plane twist in bilayer graphene has recently revealed unprecedented electronic properties like superconductivity, which has now started attracting the attention for other multi-physical properties of such twisted structures. For example, the latest studies show that twisting can enhance the strength and stiffness of graphene by many folds, which in turn creates a strong rationale for their prospective exploitation in high-velocity impact. The present article investigates the ballistic performance of twisted bilayer graphene (tBLG) nanostructures. We have employed molecular dynamics (MD) simulations, augmented further by coupling gaussian process-based machine learning, for the nanoscale characterization of various tBLG structures with varying relative rotation angle (RRA). Spherical diamond impactors (with a diameter of 25Å) are enforced with high initial velocity (Vi) in the range of 1 km/s to 6.5 km/s to observe the ballistic performance of tBLG nanostructures. The specific penetration energy (Ep*) of the impacted nanostructures and residual velocity (Vr) of the impactor are considered as the quantities of interest, wherein the effect of stochastic system parameters is computationally captured based on an efficient Gaussian process regression (GPR) based Monte Carlo simulation approach. A data-driven sensitivity analysis is carried out to quantify the relative importance of different critical system parameters. As an integral part of this study, we have deterministically investigated the resonant behaviour of graphene nanostructures, wherein the high-velocity impact is used as the initial actuation mechanism. The comprehensive dynamic investigation of bilayer graphene under the ballistic impact, as presented in this paper including the effect of twisting and random disorder for their prospective exploitation, would lead to the development of improved impact-resistant lightweight materials.

A Systems Engineering Approach for Predicting NPP Response under Steam Generator Tube Rupture Conditions using Machine Learning

  • Tran Canh Hai, Nguyen;Aya, Diab
    • Journal of the Korean Society of Systems Engineering
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    • v.18 no.2
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    • pp.94-107
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    • 2022
  • Accidents prevention and mitigation is the highest priority of nuclear power plant (NPP) operation, particularly in the aftermath of the Fukushima Daiichi accident, which has reignited public anxieties and skepticism regarding nuclear energy usage. To deal with accident scenarios more effectively, operators must have ample and precise information about key safety parameters as well as their future trajectories. This work investigates the potential of machine learning in forecasting NPP response in real-time to provide an additional validation method and help reduce human error, especially in accident situations where operators are under a lot of stress. First, a base-case SGTR simulation is carried out by the best-estimate code RELAP5/MOD3.4 to confirm the validity of the model against results reported in the APR1400 Design Control Document (DCD). Then, uncertainty quantification is performed by coupling RELAP5/MOD3.4 and the statistical tool DAKOTA to generate a large enough dataset for the construction and training of neural-based machine learning (ML) models, namely LSTM, GRU, and hybrid CNN-LSTM. Finally, the accuracy and reliability of these models in forecasting system response are tested by their performance on fresh data. To facilitate and oversee the process of developing the ML models, a Systems Engineering (SE) methodology is used to ensure that the work is consistently in line with the originating mission statement and that the findings obtained at each subsequent phase are valid.

Ultrasonic Reflection Imaging for Discontinuity Detection of Rock Mass - Laboratory Study (암반 불연속면 탐측을 위한 초음파 반사 이미지 - 실내실험)

  • Lee, Jong-Sub;Kim, Seung-Sun;Kim, Dong-Hyun;Kim, Uk-Young;Lee, In-Mo
    • Journal of the Korean Geotechnical Society
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    • v.23 no.1
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    • pp.51-65
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    • 2007
  • The purpose of this study is the development and application of a high resolution ultrasonic wave imaging system to detect discontinuity plane in lab-scale rock models. This technique is based on received time series which capture the multiple reflections at interface. This study includes the fundamental aspects of ultrasonic wave propagation in rock mass, the selection of the optimal ultrasonic wave transducer, data gathering, a signal processing, imaging methods, and experiments. Experiments are carried out by the horizontal movement and rotation devices. Experimental studies show the discontinuity is well detected by the horizontal movement and rotation devices under water. Furthermore, the discontinuity and the cavity on the plaster block are identified by the rotation device. This study suggests that the new method may be an economical and effective tool for the detection of the discontinuity on rock mass.

Analysis of LBLOCA of APR1400 with 3D RPV model using TRACE

  • Yunseok Lee;Youngjae Lee;Ae Ju Chung;Taewan Kim
    • Nuclear Engineering and Technology
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    • v.55 no.5
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    • pp.1651-1664
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    • 2023
  • It is very difficult to capture the multi-dimensional phenomena such as asymmetric flow and temperature distributions with the one-dimensional (1D) model, obviously, due to its inherent limitation. In order to overcome such a limitation of the 1D representation, many state-of-the-art system codes have equipped a three-dimensional (3D) component for multi-dimensional analysis capability. In this study, a standard multi-dimensional analysis model of APR1400 (Advanced Power Reactor 1400) has been developed using TRACE (TRAC/RELAP Advanced Computational Engine). The entire reactor pressure vessel (RPV) of APR1400 has been modeled using a single 3D component. The fuels in the reactor core have been described with detailed and coarse representations, respectively, to figure out the impact of the fuel description. Using both 3D RPV models, a comparative analysis has been performed postulating a double-ended guillotine break at a cold leg. Based on the results of comparative analysis, it is revealed that both models show no significant difference in general plant behavior and the model with coarse fuel model could be used for faster transient analysis without reactor kinetics coupling. The analysis indicates that the asymmetric temperature and flow distributions are captured during the transient, and such nonuniform distributions contribute to asymmetric quenching behaviors during blowdown and reflood phases. Such asymmetries are directly connected to the figure of merits in the LBLOCA analysis. Therefore, it is recommended to employ a multi-dimensional RPV model with a detailed fuel description for a realistic safety analysis with the consideration of the spatial configuration of the reactor core.

A Pilot Study Exploring Temporal Development of Gut Microbiome/Metabolome in Breastfed Neonates during the First Week of Life

  • Imad Awan;Emily Schultz;John D. Sterrett;Lamya'a M. Dawud;Lyanna R. Kessler;Deborah Schoch;Christopher A. Lowry;Lori Feldman-Winter;Sangita Phadtare
    • Pediatric Gastroenterology, Hepatology & Nutrition
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    • v.26 no.2
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    • pp.99-115
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    • 2023
  • Purpose: Exclusive breastfeeding promotes gut microbial compositions associated with lower rates of metabolic and autoimmune diseases. Its cessation is implicated in increased microbiome-metabolome discordance, suggesting a vulnerability to dietary changes. Formula supplementation is common within our low-income, ethnic-minority community. We studied exclusively breastfed (EBF) neonates' early microbiome-metabolome coupling in efforts to build foundational knowledge needed to target this inequality. Methods: Maternal surveys and stool samples from seven EBF neonates at first transitional stool (0-24 hours), discharge (30-48 hours), and at first appointment (days 3-5) were collected. Survey included demographics, feeding method, medications, medical history and tobacco and alcohol use. Stool samples were processed for 16S rRNA gene sequencing and lipid analysis by gas chromatography-mass spectrometry. Alpha and beta diversity analyses and Procrustes randomization for associations were carried out. Results: Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria were the most abundant taxa. Variation in microbiome composition was greater between individuals than within (p=0.001). Palmitic, oleic, stearic, and linoleic acids were the most abundant lipids. Variation in lipid composition was greater between individuals than within (p=0.040). Multivariate composition of the metabolome, but not microbiome, correlated with time (p=0.030). Total lipids, saturated lipids, and unsaturated lipids concentrations increased over time (p=0.012, p=0.008, p=0.023). Alpha diversity did not correlate with time (p=0.403). Microbiome composition was not associated with each samples' metabolome (p=0.450). Conclusion: Neonate gut microbiomes were unique to each neonate; respective metabolome profiles demonstrated generalizable temporal developments. The overall variability suggests potential interplay between influences including maternal breastmilk composition, amount consumed and living environment.

Difference analysis of the collapse behaviors of the single-story beam-column assembly and multi-story planar frame

  • Zheng Tan;Wei-Hui Zhong;Bao Meng;Xing-You Yao;Yu-Hui Zheng;Yao Gao;Shi-Chao Duan
    • Steel and Composite Structures
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    • v.50 no.3
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    • pp.265-280
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    • 2024
  • The collapse behavior observed in single-story beam-column assembly (SSBCA) do not accurately represent the actual overall stress characteristic of multi-story frame structure (MSFS) under column loss scenario owing to ignoring the interaction action among different stories, leading to a disconnection between the anti-collapse behaviors of "components" and "overall structures", that is, the anti-collapse performance of frame structures with two different structural scales has not yet formed a combined force. This paper conducts a numerical and theoretical study to explore the difference of the collapse behaviors of the SSBCA and MSFS, and further to reveal the internal force relationships and boundary constraints at beam ends of models SSBCA and MSFS. Based on the previous experimental tests, the corresponding refined numerical simulation models were established and verified, and comparative analysis on the resistant-collapse performance was carried out, based on the validated modeling methods with considering the actual boundary constraints, and the results illustrates that the collapse behaviors of the SSBCA and MSFS is not a simple multiple relationship. Through numerical simulation and theoretical analysis, the development laws of internal force in each story beam under different boundary constraints was clarified, and the coupling relationship between the bending moment at the most unfavorable section and axial force in the composite beam of different stories of multi story frames with weld cover-plated flange connections was obtained. In addition, considering the effect of the yield performance of adjacent columns on the anti-collapse bearing capacities of the SSBCA and MSFS during the large deformation stages, the calculation formula for the equivalent axial stiffness at the beam ends of each story were provided.

Analysis of Subwavelength Metal Hole Array Structure for the Enhancement of Quantum Dot Infrared Photodetectors

  • Ha, Jae-Du;Hwang, Jeong-U;Gang, Sang-U;No, Sam-Gyu;Lee, Sang-Jun;Kim, Jong-Su;Krishna, Sanjay;Urbas, Augustine;Ku, Zahyun
    • Proceedings of the Korean Vacuum Society Conference
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    • 2013.02a
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    • pp.334-334
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    • 2013
  • In the past decade, the infrared detectors based on intersubband transition in quantum dots (QDs) have attracted much attention due to lower dark currents and increased lifetimes, which are in turn due a three-dimensional confinement and a reduction of scattering, respectively. In parallel, focal plane array development for infrared imaging has proceeded from the first to third generations (linear arrays, 2D arrays for staring systems, and large format with enhanced capabilities, respectively). For a step further towards the next generation of FPAs, it is envisioned that a two-dimensional metal hole array (2D-MHA) structures will improve the FPA structure by enhancing the coupling to photodetectors via local field engineering, and will enable wavelength filtering. In regard to the improved performance at certain wavelengths, it is worth pointing out the structural difference between previous 2D-MHA integrated front-illuminated single pixel devices and back-illuminated devices. Apart from the pixel linear dimension, it is a distinct difference that there is a metal cladding (composed of a number of metals for ohmic contact and the read-out integrated circuit hybridization) in the FPA between the heavily doped gallium arsenide used as the contact layer and the ROIC; on the contrary, the front-illuminated single pixel device consists of two heavily doped contact layers separated by the QD-absorber on a semi-infinite GaAs substrate. This paper is focused on analyzing the impact of a two dimensional metal hole array structure integrated to the back-illuminated quantum dots-in-a-well (DWELL) infrared photodetectors. The metal hole array consisting of subwavelength-circular holes penetrating gold layer (2DAu-CHA) provides the enhanced responsivity of DWELL infrared photodetector at certain wavelengths. The performance of 2D-Au-CHA is investigated by calculating the absorption of active layer in the DWELL structure using a finite integration technique. Simulation results show the enhanced electric fields (thereby increasing the absorption in the active layer) resulting from a surface plasmon, a guided mode, and Fabry-Perot resonances. Simulation method accomplished in this paper provides a generalized approach to optimize the design of any type of couplers integrated to infrared photodetectors.

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Traveling-wave Ti:LiNbO3 optical modulator capable of complete switching (완전 스위칭이 가능한 Ti:LiNbO3 진행파 광변조기)

  • 곽재곤;김경암;김영문;정은주;피중호;박권동;김창민
    • Korean Journal of Optics and Photonics
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    • v.14 no.5
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    • pp.545-554
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    • 2003
  • Design of the optical modulator composed of a three-waveguide coupler and CPW traveling-wave electrodes was carried out. Switching phenomena of three-waveguide couplers were analyzed by using the coupled mode theory, and the coupling-lengths of the devices were calculated by means of the FDM. CPW traveling-wave electrodes were analysed by the CMM and SOR simulation technique in order to find the conditions of phase-velocity and impedance matching. Traveling-wave modulators were fabricated on z-cut LiNbO$_3$ substrate. Ti was in-diffused in LiNbO$_3$ to make waveguides and Au electrodes were built on the waveguides by the electrolyte technique. The fabricated modulator chip was end-polished, pig-tailed and packaged in a brass mount with K-connector. The insertion loss and the switching voltage of the optical modulator were about 4㏈ and 19V, respectively. Network analyzer was used to obtain the S parameter and the corresponding RF response. From the measurement, parameters of the traveling-wave electrodes were extracted to be Z$_{c}$= 45 Ω, N$_{eff}$=2.20, and $\alpha$$_{0}$=0.055/cm√GHZ. The measured optical response R($\omega$) was compared with the theoretically estimated one, showing both responses agree well. The measurement results revealed that 3㏈ bandwidth turned out to be about 13 GHz.