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Статті в журналах з теми "Irregular air gap"
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Winterstein, Steven R., and Bert Sweetman. "Air Gap Response of Floating Structures: Statistical Predictions Versus Observed Behavior." Journal of Offshore Mechanics and Arctic Engineering 123, no. 3 (March 20, 2001): 118–23. http://dx.doi.org/10.1115/1.1377867.
Повний текст джерелаАнотація:
The air gap response of a specific semi-submersible platform subjected to irregular waves is considered. Detailed model tests for this structure are studied in depth. Using time-histories of both motions and air gap, statistical analyses both for the absolute near-structure wave elevation (with respect to a fixed observer), and the relative wave elevation (with respect to the moving structure) are performed. Statistics of wave crest amplification, due to diffraction, are established. Corresponding amplification factors are derived from linear diffraction theory, and the results of theory and observations are critically compared.
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Richmond, Owen, Louis G. Hector, and Joseph M. Fridy. "Growth Instability During Nonuniform Directional Solidification of Pure Metals." Journal of Applied Mechanics 57, no. 3 (September 1, 1990): 529–36. http://dx.doi.org/10.1115/1.2897055.
Повний текст джерелаАнотація:
Solidification of a pure metal against a flat mold surface is examined using a nonuniform thermohypoelastic beam. Heat is removed with a spatially periodic heat flux superimposed onto uniform cooling, which leads to irregular growth of the casting. The associated nonuniform temperature field also produces nonuniform deformation in the casting which in time may lead to air gap nucleation along the mold/casting interface. Air gap nucleation is defined as the circumstance where the local mold/casting interface pressure falls to zero. Unstable growth occurs when such air gaps nucleate beneath thickness minima, thus further reducing heat transfer at these positions, and dramatically amplifying the existing thickness nonuniformity. The time to onset of instability depends upon material properties such as density, latent heat, thermal conductivity, elastic constants, and coefficient of thermal expansion as well as upon process parameters such as cooling rate, fluid pressure, and wavelength of the periodic heat flux.
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Weidman, Patrick D., and Michael A. Sprague. "Steady and unsteady modelling of the float height of a rotating air hockey disk." Journal of Fluid Mechanics 778 (July 30, 2015): 39–59. http://dx.doi.org/10.1017/jfm.2015.374.
Повний текст джерелаАнотація:
A similarity reduction of the Navier–Stokes equations for the motion of an infinite rotating disk above an air-bearing table yields a coupled pair of ordinary differential equations governed by a Reynolds number $Re=Wh/{\it\nu}$ and a rotation parameter $S=\sqrt{2}h{\it\Omega}/W$, where $h$ is the float height, $W$ is the air levitation velocity, ${\it\Omega}$ is the disk rotation rate, and ${\it\nu}$ is the kinematic viscosity of air. After deriving the small- and large-Reynolds-number behaviour of solutions, the equations are numerically integrated over a wide range of $Re{-}S$ parameter space. Zero-lift boundaries are computed as well as the boundaries separating pure outward flow from counter-flow in the gap. The theory is used to model the steady float height of a finite-radius air hockey disk under the assumption that the float height is small relative to the diameter of the disk and the flow is everywhere laminar. The steady results are tested against direct numerical simulation (DNS) of the unsteady axisymmetric Navier–Stokes equations for the cases where the disk rotates at constant angular velocity but is either at a fixed height or free to move axially. While a constant shift in the gap pressure conforms closely to that found using steady theory, the interaction of the radial jet emanating from the gap with a vertical transpiration field produces vortex rings which themselves propagate around to interact with the jet. Although these structures diffuse as they propagate up and away from the gap, they induce a departure from the steady-flow assumption of atmospheric pressure at the gap exit, thus inducing small irregular axial oscillations of the floating disk.
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Lu, Wenyue, Wenhua Zhao, P. H. Taylor, Jianmin Yang, Longfei Xiao, and Xin Li. "Linearity and nonlinearity in wave run-up and air-gap response for a semi-submersible platform under irregular wave excitation." Applied Ocean Research 104 (November 2020): 102218. http://dx.doi.org/10.1016/j.apor.2020.102218.
Повний текст джерела
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Prevosto, Marc, and George Z. Forristall. "Statistics of Wave Crests From Models vs. Measurements." Journal of Offshore Mechanics and Arctic Engineering 126, no. 1 (February 1, 2004): 43–50. http://dx.doi.org/10.1115/1.1641795.
Повний текст джерелаАнотація:
The analysis phase of the Wave Crest Sensor Intercomparison Study (WACSIS) focussed on the interpretation of the wave data collected by the project during the winter of 1997–98. Many aspects of wave statistics have been studied, but the main emphasis has been on crest height distributions, and recommendations for crest heights to be used in air gap calculations. In this paper, we first describe comparisons of the crest height distributions derived from the sensors (radars, wave staffs, laser) and from simulations based on 3-D second-order irregular wave models. These comparisons permit us to make conclusions on the quality of these models and to qualify the ability of some sensors to measure the crest heights accurately. In the second part, two new parametric models of the crest height distributions are discussed and their superiority to standard parametric models is demonstrated.
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Abdussamie, Nagi, Roberto Ojeda, Giles Thomas, and Walid Amin. "Measurements of global and local effects of wave impact on a fixed platform deck." Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment 231, no. 1 (September 26, 2016): 212–33. http://dx.doi.org/10.1177/1475090216636410.
Повний текст джерелаАнотація:
This article describes a series of model tests conducted to examine extreme wave events associated with tropical cyclonic conditions and their impacts on an offshore deck structure. Extreme waves of a representative cyclonic sea state were examined in a towing tank within long-crested irregular wave trains. Experimental results presented include global forces and localised slamming pressures acting on a rigidly mounted box-shaped deck, which represents a simplified topside structure of a tension leg platform. The effect of static set-down on the still-water air gap was investigated by applying an equivalent reduction for the deck clearance. It was found that a small reduction of 20 mm (2.5 m full scale) in the original deck clearance can lead to a doubling of the magnitude of the horizontal force and the vertical upward-directed force components, as well as significantly increased slamming pressures in many locations on the deck underside.
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Evans, Alison, Tim Driscoll, Jonathan Livesey, David Fitzsimons, and Bronwen Ackermann. "Nasendoscopic Evaluation of Stress Velopharyngeal Insufficiency in Wind Musicians: A Pilot Study." Medical Problems of Performing Artists 30, no. 1 (March 1, 2015): 47–53. http://dx.doi.org/10.21091/mppa.2015.1007.
Повний текст джерелаАнотація:
OBJECTIVE: To investigate the anatomy and function of the velopharyngeal mechanism in musicians who experience symptoms of stress velopharyngeal insufficiency (VPI) compared to musicians who do not. METHODS: The velopharyngeal mechanism of 13 musicians, 8 with reported symptoms of stress VPI and 5 without, were evaluated using video nasendoscopy before and after 30 minutes of playing. All nasendoscopic recordings were rated by an external speech-language pathologist and ear, nose and throat surgeon for maintenance of velopharyngeal closure, type of velopharyngeal closure pattern, and velopharyngeal gap. RESULTS: Six out of 8 cases with stress VPI had nasal air leak during the assessment, 2 of whom had fatigue-related increased symptoms. Three controls had mild nasal air leak without affecting the consistency of soft palate seal nor quality of playing, suggesting that evidence of nasal air leak is not always symptomatic of stress VPI. All cases had unusual anatomical characteristics, such as the soft palate closing against an irregular surface on the posterior nasopharyngeal wall, which may cause insufficient velopharyngeal closure. Typically the soft palate contacted the nasopharyngeal wall higher when playing a wind instrument compared to during speech. CONCLUSION: Specific anatomical features and factors such as fatigue and stress may affect maintenance of velopharyngeal closure in persons with stress VPI. It is important that musicians with stress VPI are evaluated while playing their instrument. Future studies into stress VPI would benefit by including objective assessment components and some degree of quantifiable measurements.
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Jreije, Antonio, Lalu Keshelava, Mindaugas Ilickas, Jurgita Laurikaitiene, Benas Gabrielis Urbonavicius, and Diana Adliene. "Development of Patient Specific Conformal 3D-Printed Devices for Dose Verification in Radiotherapy." Applied Sciences 11, no. 18 (September 17, 2021): 8657. http://dx.doi.org/10.3390/app11188657.
Повний текст джерелаАнотація:
In radiation therapy, a bolus is used to improve dose distribution in superficial tumors; however, commercial boluses lack conformity to patient surface leading to the formation of an air gap between the bolus and patient surface and suboptimal tumor control. The aim of this study was to explore 3D-printing technology for the development of patient-specific conformal 3D-printed devices, which can be used for the radiation treatment of superficial head and neck cancer (HNC). Two 3D boluses (0.5 and 1.0 cm thick) for surface dose build-up and patient-specific 3D phantom were printed based on reconstruction of computed tomography (CT) images of a patient with HNC. The 3D-printed patient-specific phantom indicated good tissue equivalency (HU = −32) and geometric accuracy (DSC = 0.957). Both boluses indicated high conformity to the irregular skin surface with minimal air gaps (0.4–2.1 mm for 0.5 cm bolus and 0.6–2.2 mm for 1.0 cm bolus). The performed dose assessment showed that boluses of both thicknesses have comparable effectiveness, increasing the dose that covers 99% of the target volume by 52% and 26% for single field and intensity modulated fields, respectively, when compared with no bolus case. The performed investigation showed the potential of 3D printing in development of cost effective, patient specific and patient friendly conformal devices for dose verification in radiotherapy.
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Yu, Peichang, Mengxiao Song, Qiang Chen, Lianchun Wang, Guang He, and Peng Leng. "Dynamic Response Analysis of Medium-Speed Maglev Train with Track Random Irregularities." Journal of Advanced Transportation 2021 (November 5, 2021): 1–16. http://dx.doi.org/10.1155/2021/1668496.
Повний текст джерелаАнотація:
In order to analyze the dynamic response of medium-speed maglev train in the speed range of 0–200 km/h, the suspension performance, suspended energy consumption, and riding comfort of the train stimulated by random track irregularities are discussed in this paper. Firstly, the model of medium-speed maglev train including car body, air spring vibration isolation system, and the suspension system is established. Then, a controller based on flux inner feedback loop and PID outer feedback loop is designed for the suspension system. The established model is stimulated by the actual track power spectrum in full speed range. The simulation results show that the fluctuation of suspension gap is less than ±4 mm. Furthermore, thanks to the adding of permanent magnet, the power consumption is significantly reduced, which is of benefit to the electromagnet heating problem and on-board levitation power supply system. The riding comfort of the train moving on the irregular track using Sperling index is assessed. The experimental results validate the effectiveness of the proposed analytical calculation model of medium-speed maglev train. It is shown that medium-speed maglev train achieved good performance, significant power reduction, and satisfactory riding comfort.
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Dziubak, T. "Material Properties Analysis with Addition of Nanofibres for Air Intake Filtration in Internal Combustion Engines." International Journal of Automotive and Mechanical Engineering 18, no. 1 (April 22, 2021): 8621–36. http://dx.doi.org/10.15282/ijame.18.1.2021.21.0656.
Повний текст джерелаАнотація:
The aim of this study is to provide an experimental properties evaluation of a standard filter material (cellulose) and materials with fiber layer addition with small diameters (nanofibers). Filter media, including cellulose, used in the internal combustion engine inlet air filtration are made of high diameter fibres, approx. 15 µm. Significantly higher separation and filtration efficiency performance are obtained for materials with lower fibre diameters (nanofibres), however, at the expense of a significantly higher pressure drop, affecting the engine performance. Filter media manufacturers mainly specify the structure parameters (pore size, air permeability and thickness), without giving any information on the dust filtration performance and rate. The literature includes test results for models of different filter media structures. Filtration process modelling using polydisperse dust with particles of different shape and density and irregular filter media structure is possible using advanced computer techniques, however, the process is complex and requires many simplifications. Test results can be applied directly in the automotive industry. The data can be obtained by experimental tests on filter medium specimens, complete filter elements or air filters which are costly and time-consuming tests, however, those test methods are the most reliable. Conditions and testing methodology for intake air filter materials used in internal combustion engines were developed. Filtration and flow resistance efficiency and accuracy were done depending on test dust mass stopped per unit area. Tested materials filtration efficiency was assessed by a filtration quality factor, which includes experimentally determined efficiency and accuracy as well as flow resistance values. Much higher efficiency and filtration accuracy of dust grains below 5 µm in filtration materials with nanofibers addition compared to standard filtration material (filter paper) were demonstrated. For the same flow resistance values, filter materials with nanofibers addition accumulate smaller dust mass than standard filter paper. Usage of materials with nanofibers addition used in motor vehicles intake air filtration ensures their high efficiency and accuracy. It minimises its components wear, but at the expense of faster flow resistance increase, which shortens filter life and increases filter replacement frequency. Results obtained during the experimental research partly fill the gap when it comes to the basic material properties used in internal combustion engines intake air filter partitions production.
Дисертації з теми "Irregular air gap"
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Наний, Виталий Викторович. "Угол нагрузки двигателей с катящимся ротором". Thesis, Техническият университет – Габрово, 2012. http://repository.kpi.kharkov.ua/handle/KhPI-Press/24436.
Повний текст джерелаАнотація:
В статье приводиться методика определения реального угла нагрузки двигателя с катящимся ротором с помощью компьютерного моделирования магнитного поля двигателя. Дано сравнение 8- и 6-пазовой конструкции двигателя с катящимся ротором с учетом неравномерности его воздушного зазора и анализируется влияние этого зазора на реальный угол нагрузки машины. Приводятся результаты полученных исследований в графическом виде и сравниваются максимальные значения полученных углов для 6- и 8-пазовой модели двигателя.The article presents a comparison 8 - and 6-slot design of motor with a rolling rotor (MRR) subject to irregular air gap and analyzes the impact of this gap on the real machine load angle. The results of these researches are graphically presented and maximum values of load angles for 6 - and 8-slot motor models are compared.
Тези доповідей конференцій з теми "Irregular air gap"
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Prabhu, Vinit V., and Ehsan Mohseni Languri. "NUMERICAL MODELING OF BUOYANCY-DRIVEN AIR FLOW INSIDE IRREGULAR TENT AIR GAP." In First Thermal and Fluids Engineering Summer Conference. Connecticut: Begellhouse, 2016. http://dx.doi.org/10.1615/tfesc1.fnd.012749.
Повний текст джерела
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Kurniawan, Adi, Zhenhua Huang, Jing Li, Chunrong Liu, Xikun Wang, Zhiyong Hao, Soon Keat Tan, and Edwin Nah. "A Numerical Analysis of the Response and Air Gap Demand for Semi-Submersibles." In ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/omae2009-79163.
Повний текст джерелаАнотація:
This paper examines the effects of viscous damping on the prediction of air gap demand for semi-submersibles. This is illustrated by a case study of a typical six-column, double pontoon semi-submersible in irregular waves. Linear responses of the platform and free-surface elevations at selected locations are computed using WAMIT, in which viscous damping effects are included through the use of a linear damping matrix. The spectra of the platform’s response and of the relative free-surface elevation at the selected locations, as well as the probability distributions of air gap minima obtained using different damping matrices are compared. It is demonstrated that correct modelling of viscous damping is important for an accurate prediction of air gap demand of a floating platform, especially if the peak frequency of the wave spectrum is close to the heave, roll, and pitch natural frequencies of the platform.
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Kvaleid, Jørgen, Volkert Oosterlaak, and Tor Kvillum. "Non-Linear Air Gap Analyses of a Semi-Submersible Compared With Linear Analyses and Model Tests." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-24044.
Повний текст джерелаАнотація:
For semi-submersible units, the magnitude of air gap or local wave impact in the survival condition is a key design driver. Linear analyses are widely used in the industry to predict survival air gap for semi-subs. Large relative motions, leading to large changes in shape of the submerged hull and large changes in water plane area make this approach questionable. In this paper, the GG5000 [1], a twin pontoon four legged semi-sub is considered. Both linear analyses and model tests had been performed, but the results were diverging. It was decided to investigate further, using non-linear hydrodynamic analyses. Initially, the model test setup is reproduced in the numerical model. The simulation model is verified for both response power spectra and extreme response distributions. In the non-linear simulations, the wetted surface of the hull is updated for each time step. Both excitation and restoring forces are based on the instantaneous wetted surface. This proves essential for the prediction of large motions. Later, the verified simulation model is run with realistic full scale setup including elastic catenary moorings with coupled cable dynamics, thruster assist, irregular waves and irregular wind. Highly non-linear effects proven to be vital to accurate air gap prediction are investigated and their representation in the non-linear analyses is validated against model tests.
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Liang, Xiufeng, Jianmin Yang, Longfei Xiao, Xin Li, and Jun Li. "Numerical Study of Air Gap Response and Wave Impact Load on a Moored Semi-Submersible Platform in Predetermined Irregular Wave Train." In ASME 2010 29th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2010. http://dx.doi.org/10.1115/omae2010-20260.
Повний текст джерелаАнотація:
The importance of understanding air gap response and potential deck impact is well-known in the design stage of semi-submersible platform. The highly non-linear nature of wave elevation around large structures in steep waves makes it difficult to accurately predict wave field under the deck and wave run up along the columns. Present engineering tools for the prediction of air gap response generally based on simplified models. Even the models accounting for nonlinear wave diffraction is not free of uncertainties. A method adopted here couples a Navier-Stokes solver, VOF technique capturing violent free surface and DNV/Seasam predicting motions of moored semi-submersible platform. Air gap response at different locations of the hull was evaluated in predetermined irregular wave train. Wave run up was also measured by wave probes near the columns. Load cells were mounted under the deck of the platform to trace potential deck impact. The predetermined irregular wave train was simulated in a numerical wave tank and verified against physical tank results. Analysis of the air gap response, wave run up and impact loads on the semi-submersible platform were conducted.
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Stansberg, Carl Trygve. "Slow-Drift Pitch Motions and Air-Gap Observed From Model Testing With Moored Semisubmersibles." In ASME 2007 26th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2007. http://dx.doi.org/10.1115/omae2007-29536.
Повний текст джерелаАнотація:
Low-frequency pitch motions of a moored semisubmersible in irregular sea states are analyzed. Physical mechanisms and significance to air-gap problems are addressed. Excitation from wave drift and from moorings/risers is primarily considered, Effects from current and wind are also addressed. Related challenges in deepwater model testing of semis with truncated moorings are discussed. Motion and air-gap data from two previously performed model tests are analysed. Catenary moorings in 335m water depth and in 1100m water depth, respectively, are considered. Model scales are 1:55 and 1:150, respectively. Observed slow-drift pitch components are of the same magnitude level as the wave-frequency components. Comparisons to coupled numerical analysis models are made. Wave drift moment coefficients calibrated empirically according to experiments were used, since the original coefficients gave too low results. The final comparisons show good agreement for the 1:55 case. For the 1:150 case, fairly good agreement is found, but some deviations are observed and believed to be due to poorer wave repeatablity. Tests with truncated moorings at half of the two actual depths were also included, for a check of methods for deepwater model tests performed at reduced depths and combine with numerical analysis (hybrid verification). The importance of proper experimental reproduction at reduced depths, of full-depth pitch and air-gap, is addressed. The results show that with the actual truncation designs, reasonable agreements are obtained, but use of the scale 1:150 seems to give too large uncertainties due to the poorer wave repeatability.
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Matsumoto, Fabio Tadao, Joa˜o Vicente Sparano, Rafael de Andrade Watai, Alexandre Nicolaos Simos, and Marcos Donato A. S. Ferreira. "A Design Procedure for Evaluating the Air Gap on a Large-Volume Semi-Submersible Platform." In ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2011. http://dx.doi.org/10.1115/omae2011-49256.
Повний текст джерелаАнотація:
This paper presents a design procedure for the evaluation of the air-gap response on semi-submersible platforms subjected to irregular sea conditions. The suggested procedure takes into account both first and second order (low frequency) effects on hull motions when evaluating the air gap. As a first step of the procedure, a large range of sea conditions with different returning periods and directions of incidence are simulated using a frequency domain model. This first step is intended to determine the critical sea conditions regarding the air gap response of that particular floating unit. For those conditions, it is suggested to be performed a more complete analysis of the problem, including time-domain CFD simulations, in order to improve the results, especially for areas that may be susceptible to intense wave run-up effects. Experimental results for some typical sea states of Campos Basin have been employed to validate the procedure using as an example a large displacement four column semi-submersible platform operating at Campos Basin, Brazil. Results have confirmed that the sea state with the highest significant wave height, or peak period, may not lead to the worst air-gap situation. It’s also shown that, although for the critical sea conditions the first order effects were dominant in the air gap response, at many non-critical sea states the second order effects presented magnitudes comparable to those of first order, indicating that the resonant response of the unit should not be disregarded a priori when dimensioning the air-gap of similar deep-draft semi-submersibles.
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Yan, Fasuo, Hui Yang, Pengfei Shen, Dagang Zhang, and Liping Sun. "A Probability Distribution of Air-Gap and Wave Run-Up by Model Tests of a Horizontal Moored Semi-Submersible Platform." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-23021.
Повний текст джерелаАнотація:
Design of a floating structure is supposed to be based on the extreme responses experienced by the components of the structure during its lifetime. The airgap response and potential deck impact of ocean structures under sea waves is of considerable interest. Non-linear diffraction models are usually called for a more consistent evaluation of the wave field under the deck and the wave run-up upon the columns, but even second-order analysis is not free of uncertainties. Therefore, air gap evaluation still relies heavily on experimental analysis. This paper presents some deep-tank results performed for the evaluation of the dynamic airgap of a large-volume semisubmersible platform. A series of model tests were carried out for the scale model of a horizontal moored semi in regular and extreme irregular wave conditions. Airgap response combined with run-up close to columns at total 11 locations on the deck was evaluated under oblique wave status. Motions and elevation data are analyzed by statistical treatment. Weibull-tail fitting procedure is realized to determine the extreme response levels.
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Kota, Ravikiran S., and Torgeir Moan. "An Experimental Study of Wave Loads on Deck in Irregular Waves." In ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/omae2012-84000.
Повний текст джерелаАнотація:
Global loads on deck-structures due to air-gap loss in irregular seas are discussed. Estimation of such loads is important in structural integrity verification of fixed and floating platforms. The current study presents results from wave-tank experiments in which global forces and wetted lengths arising from wave impact on a rigid deck-box from several pseudo-random realizations of long-crested waves of moderate steepness are recorded. Short-term statistics and distributions of these quantities are estimated and compared against estimates from semi-analytical results previously reported by the authors for von Karman-type impact events in Gaussian waves. The scope of work presented here does not address wave loads on decks in extreme seas where the waves are steep and predominantly non-Gaussian.
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Grabenstein, Volker, and Stephan Kabelac. "Experimental Investigations and Modelling of Condensation in Plate Heat Exchangers." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22385.
Повний текст джерелаАнотація:
The use of Plate Heat Exchanger (PHE) as condensers and evaporators increases every year. The easy and modular construction and the high thermal performance at very compact size make the PHE to an ideal heat exchanger for a wide range of applications. Due to the missing of authoritative models for the design of PHEs used as condensers or as evaporators they will typically be constructed larger than needed. For a physically based model more detailed knowledge is needed to take into account the flow and heat interactions during the condensation or evaporation process inside a PHE. In this work the two-phase flow in a PHE is analysed. For this purpose one gap of a PHE was built with two transparent polyurethane plates with the same geometrical parameter than the stainless steel plates of a commercial used PHE. Demineralized-water and air are used to define an exact 2-phase-flow. Measurements of the contact angles and surface energies of the stainless steel plates and the transparent polyurethane plates with different working fluids have been made to show the relation between the wettability and the surface energies of the plates. These measurements show a significant influence of the surface energies on the wettability of the steel and polyurethane plates and therefore it is necassary to take into account the plate material properties for the visualization experiments. A flow pattern map is developed and the typical flow patterns are presented and explained. The defined flow regimes converge with comparable data from the literature. The flow pattern of bubbly flow, irregular bubbly flow, film flow and slug flow can be identified. The film flow occurs over the whole range of the air flow rate and at superficial liquid velocities below 0.1 m/s. Above this limit at low flow rates of the gaseous phase a bubbly flow occurs and with increasing air flow rate the flow pattern changes at a superficial air velocity of 1.5 m/s to an irregular bubbly flow. With further rising of the gas phase fraction the irregular bubbly flow shifts at gas velocities nearly 4 m/s into a transition regime, which is marked by the mixed behaviour of the irregular bubbly and the slug flow regime. Slug flow can be identified when the superficial velocity of the air rises up to 7 m/s.
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Lu, Xin, Pankaj Kumar, Anand Bahuguni, and Yanling Wu. "A CFD Study of Focused Extreme Wave Impact on Decks of Offshore Structures." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-23804.
Повний текст джерелаАнотація:
The design of offshore structures for extreme/abnormal waves assumes that there is sufficient air gap such that waves will not hit the platform deck. Due to inaccuracies in the predictions of extreme wave crests in addition to settlement or sea-level increases, the required air gap between the crest of the extreme wave and the deck is often inadequate in existing platforms and therefore wave-in-deck loads need to be considered when assessing the integrity of such platforms. The problem of wave-in-deck loading involves very complex physics and demands intensive study. In the Computational Fluid Mechanics (CFD) approach, two critical issues must be addressed, namely the efficient, realistic numerical wave maker and the accurate free surface capturing methodology. Most reported CFD research on wave-in-deck loads consider regular waves only, for instance the Stokes fifth-order waves. They are, however, recognized by designers as approximate approaches since “real world” sea states consist of random irregular waves. In our work, we report a recently developed focused extreme wave maker based on the NewWave theory. This model can better approximate the “real world” conditions, and is more efficient than conventional random wave makers. It is able to efficiently generate targeted waves at a prescribed time and location. The work is implemented and integrated with OpenFOAM, an open source platform that receives more and more attention in a wide range of industrial applications. We will describe the developed numerical method of predicting highly non-linear wave-in-deck loads in the time domain. The model’s capability is firstly demonstrated against 3D model testing experiments on a fixed block with various deck orientations under random waves. A detailed loading analysis is conducted and compared with available numerical and measurement data. It is then applied to an extreme wave loading test on a selected bridge with multiple under-deck girders. The waves are focused extreme irregular waves derived from NewWave theory and JONSWAP spectra.