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Jan S. Ribberink - One of the best experts on this subject based on the ideXlab platform.
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measurements of sheet flow Transport in acceleration skewed oscillatory flow and comparison with practical formulations
Coastal Engineering, 2010Co-Authors: Dominic A Van Der A, Tom Odonoghue, Jan S. RibberinkAbstract:Near-bed oscillatory flows with acceleration skewness are characteristic of steep and breaking waves in shallow water. In order to isolate the effects of acceleration skewness on sheet flow sand Transport, new experiments are carried out in the Aberdeen Oscillatory Flow Tunnel. The experiments have produced a dataset of Net Transport rates for full-scale oscillatory flows with varying degrees of acceleration skewness and three sand sizes. The new data confirm previous research that Net Transport in acceleration-skewed flow is non-zero, is always in the direction of the largest acceleration and increases with increasing acceleration skewness. Large Transport rates for the fine sand conditions suggest that phase lag effects play an important role in augmenting positive Net Transport. A comparison of the new experimental data with a number of practical sand Transport formulations that incorporate acceleration skewness shows that none of the formulations performs well in predicting the measured Net Transport rates for both the fine and the coarser sands. The new experimental data can be used to further develop practical sand Transport formulations to better account for acceleration skewness.
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Modelling of sand Transport under wave-generated sheet flows with a RANS diffusion model
Coastal Engineering, 2010Co-Authors: Wael Hassan, Jan S. RibberinkAbstract:A 1DV-RANS diffusion model is used to study sand Transport processes in oscillatory flat-bed/sheet flow conditions. The central aim is the verification of the model with laboratory data and to identify processes controlling the magnitude and direction (‘onshore’/‘offshore’) of the Net time-averaged sand Transport. The model is verified with a large series of measured Net sand Transport rates, as collected in different wave tunnels for a range of wave-current conditions and grain sizes. Although not all sheet flow details are represented in the 1DV-model, it is shown that the model is able to give a correct representation of the observed trends in the data with respect to the influence of the velocity, wave period and grain diameter. Also detailed mean sediment flux profiles in the sheet flow layer are well reproduced by the model, including the direction change from ‘onshore’ to ‘offshore’ due to a difference in grain size from 0.34 mm (medium sand) to 0.13 mm (fine sand). A model sensitivity study with a selected series of Net Transport data shows that the stirring height of the suspended sediment es/ws strongly controls the magnitude and direction of the Net sediment Transport. Inclusion of both hindered settling and density stratification appears to be necessary to correctly represent the sand fluxes for waves alone and for waves + a superimposed current. The best agreement with a large dataset of Net Transport measurements is obtained with the 1DV-RANS model in its original settings using a Prandtl–Schmidt number σρ = 0.5.
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sand motion induced by oscillatory flows sheet flow and vortex ripples
Journal of Turbulence, 2008Co-Authors: Jan S. Ribberink, Jebbe J Van Der Werf, T O Donoghue, Wael HassanAbstract:A large series of field-scale experiments on turbulent sand-laden flows, conducted in preceding years in the LOWT and AOFT large oscillating water tunnels are reviewed and reanalysed. Using the combined experimental data sets, new insights are obtained on the detailed sand Transport processes occurring in sheet-flow and ripple regime conditions. For sheet flow (i) new equations are presented relating maximum erosion depth and sheet-flow layer thickness to the maximum Shields parameter; (ii) detailed analysis of sediment flux data shows the dominance of the current-related flux in the sheet-flow layer and the different characters of the current-related flux for fine and medium sands; (iii) a RANS-diffusion type model is shown to reproduce important trends in Net Transport rate related to grain size, velocity and wave period and to predict the magnitude of Net Transport rate to within a factor 2 of measured values. For the ripple regime it is shown that (i) asymmetric waves generate negative (‘offshore’) st...
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detailed measurements of velocities and suspended sand concentrations over full scale ripples in regular oscillatory flow
Journal of Geophysical Research, 2007Co-Authors: J J Van Der Werf, Tom Odonoghue, J S Doucette, Jan S. RibberinkAbstract:The knowledge and modeling of wave-induced sand Transport over rippled beds still has significant shortcomings, which is partly related to a lack of measurements of the detailed processes from controlled laboratory experiments. We have carried out new measurements of the detailed time-dependent velocity and suspended sand concentration field around vortex ripples for regular oscillatory flow conditions. The fact that the ripples were mobile and the flow conditions were full-scale makes these measurements unique. We made velocity measurements for 14 different flows and concentration measurements for three of these flows. The velocity and concentration field above ripples are dominated by the generation and ejection of vortices on the ripple flanks around the time of flow reversal. Vortex formation results in near-ripple flow reversals ahead of free-stream reversals and velocity maxima near the ripple crest that are much higher than the free-stream maxima. Asymmetry in the free stream produces steady circulation cells with dominant offshore mean flow up the ripple lee slope, balanced by weaker onshore streaming up the ripple stoss slope as well as higher up in the flow. The time- and bed-averaged horizontal velocity profile comprises an offshore streaming near the bed and an onshore drift higher up in the flow. The vortices are responsible for three main concentration peaks: one just after on-offshore flow reversal associated with the passage of a sand-laden vortex followed by two smaller peaks due to advected suspension clouds generated by vortex action at the neighboring onshore ripples. The sand flux field measured for one typical asymmetric flow condition is dominated by an offshore flux associated with the suspended sand cloud generated by vortex shedding from the ripple's lee slope around the time of on-offshore flow reversal. The Net (time-averaged) current-related and wave-related horizontal sand fluxes are generally offshore directed and mostly contained within 1.5 ripple heights above the ripple crest. The wave-related suspended Transport component is larger, but the contribution of the current-related suspended sand Transport cannot be neglected. In addition to the measured offshore Net Transport of suspended sand, there is an onshore-directed Transport very close to the ripple surface. The total Net Transport is in the offshore direction for this specific asymmetric flow condition.
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modelling of sand Transport with graded sands under oscillatory sheet flows
5th International Conference on Coastal Dynamics 2005, 2006Co-Authors: Wael Hassan, Jan S. RibberinkAbstract:The present study focuses at improving our basic understanding of size- graded sand Transport mechanisms under oscillatory sheet-flow conditions using different Transport models. Moreover, the study aims at improving the performance of different Transport model concepts for the description of both the rate and size- composition of the Transported sand. Quasi-steady and intermediate models are investigated, in combination with a large dataset of oscillatory sediment Transport measurements (sheet-flow conditions) as collected from two oscillatory water tunnels. A comparison is made between the measured Net Transport rates and Transport rates per size fraction and the results from various Transport formulas (Bailard 1981; Ribberink 1998; Dibajnia & Watanabe 1996; Dohmen-Janssen et al., 2002). First, the comparison is based on a 1-fraction approach i.e. the sand is modeled using D50 of the mixture. Second, a size-fraction approach is tested and developed further using the experimental dataset. Exposure corrections are proposed for fine and coarse size fractions in the sand mixture to improve model performance.
Eric H. Ledet - One of the best experts on this subject based on the ideXlab platform.
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ISSLS Prize Winner: Dynamic Loading-Induced Convective Transport Enhances Intervertebral Disc Nutrition.
Spine, 2015Co-Authors: Sarah E. Gullbrand, Joshua M. Peterson, Rosemarie Mastropolo, Timothy T. Roberts, James P. Lawrence, Joseph C. Glennon, Jenna Ahlborn, Arun Fricker, Mostafa Abousayed, Eric H. LedetAbstract:STUDY DESIGN: Experimental animal study of convective Transport in the intervertebral disc. OBJECTIVE: To quantify the effects of mechanical loading rate on Net Transport into the healthy and degenerative intervertebral disc in vivo. SUMMARY OF BACKGROUND DATA: Intervertebral disc degeneration is linked with a reduction in Transport to the avascular disc. Enhancing disc nutrition is, therefore, a potential strategy to slow or reverse the degenerative cascade. Convection induced by mechanical loading is a potential mechanism to augment diffusion of small molecules into the disc. METHODS: Skeletally mature New Zealand white rabbits with healthy discs and discs degenerated via needle puncture were subjected to low rate axial compression and distraction loading for 2.5, 5, 10, 15, or 20 minutes after a bolus administration of gadodiamide. Additional animals with healthy discs were subjected to high-rate loading for 10 minutes or no loading for 10 minutes. Transport into the disc for each loading regimen was quantified using post-contrast-enhanced magNetic resonance imaging. RESULTS: Low-rate loading resulted in the rapid uptake and clearance of gadodiamide in the disc. Low-rate loading increased Net Transport into the nucleus by a mean 16.8% and 12.6% in healthy and degenerative discs, respectively. The kiNetics of small molecule uptake and clearance were accelerated in both healthy and degenerative discs with low-rate loading. In contrast, high-rate loading reduced Transport into nucleus by a mean 16.8%. CONCLUSION: These results illustrate that trans-endplate diffusion can be enhanced by forced convection in both healthy and degenerative discs in vivo. Mechanical loading-induced convection could offer therapeutic benefit for degenerated discs by enhancing uptake of nutrients and clearance of by-products. LEVEL OF EVIDENCE: 4.
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Low rate loading-induced convection enhances Net Transport into the intervertebral disc in vivo
The spine journal : official journal of the North American Spine Society, 2014Co-Authors: Sarah E. Gullbrand, Joshua M. Peterson, Rosemarie Mastropolo, Timothy T. Roberts, James P. Lawrence, Joseph C. Glennon, Darryl J. Dirisio, Eric H. LedetAbstract:Abstract Background context The intervertebral disc primarily relies on trans-endplate diffusion for the uptake of nutrients and the clearance of byproducts. In degenerative discs, diffusion is often diminished by endplate sclerosis and reduced proteoglycan content. Mechanical loading-induced convection has the potential to augment diffusion and enhance Net Transport into the disc. The ability of convection to augment disc Transport is controversial and has not been demonstrated in vivo. Purpose To determine if loading-induced convection can enhance small molecule Transport into the intervertebral disc in vivo. Study design Net Transport was quantified via postcontrast enhanced magNetic resonance imaging (MRI) into the discs of the New Zealand white rabbit lumbar spine subjected to in vivo cyclic low rate loading. Methods Animals were administered the MRI contrast agent gadodiamide intravenously and subjected to in vivo low rate loading (0.5 Hz, 200 N) via a custom external loading apparatus for either 2.5, 5, 10, 15, or 20 minutes. Animals were then euthanized and the lumbar spines imaged using postcontrast enhanced MRI. The T1 constants in the nucleus, annulus, and cartilage endplates were quantified as a measure of gadodiamide Transport into the loaded discs compared with the adjacent unloaded discs. Microcomputed tomography was used to quantify subchondral bone density. Results Low rate loading caused the rapid uptake and clearance of gadodiamide in the nucleus compared with unloaded discs, which exhibited a slower rate of uptake. Relative to unloaded discs, low rate loading caused a maximum increase in Transport into the nucleus of 16.8% after 5 minutes of loading. Low rate loading increased the concentration of gadodiamide in the cartilage endplates at each time point compared with unloaded levels. Conclusions Results from this study indicate that forced convection accelerated small molecule uptake and clearance in the disc induced by low rate mechanical loading. Low rate loading may, therefore, be therapeutic to the disc as it may enhance the nutrient uptake and waste product clearance.
Jing Yuan - One of the best experts on this subject based on the ideXlab platform.
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an experimental study of Net sediment Transport rate due to acceleration skewed oscillatory flows over rippled seabeds
Coastal Engineering, 2020Co-Authors: Dongxu Wang, Jing YuanAbstract:Abstract Wave-driven near-bed oscillatory flows can be acceleration-skewed due to the onshore leaning of shoaling waves in shallow coastal waters. A full-scale experimental study was conducted to investigate the acceleration-skewness-induced Net sediment Transport rate over coarse-sand rippled beds. A dataset of ripple geometry, migration and Net sediment Transport rate has been produced for oscillatory flows with different degrees of acceleration skewness. The steepness of equilibrium ripples decreases due to the effect of acceleration skewness and a consistent onshore ripple migration with a very low speed was observed for all the tests involving acceleration-skewed flows. The measured ripple-averaged Net sediment Transport rate is always in the direction of highest-acceleration (onshore) and increases with acceleration skewness. The magnitude of Net Transport rate is comparable to that due to velocity skewness, highlighting the necessity of considering acceleration skewness in modeling coastal sediment Transport. The measurements can be well predicted by the formula of van der A et al. (2013), of which the calibration dataset does not cover such test conditions. The good model-data agreement suggests that sheet-flow and ripple-bed conditions share similar mechanisms by which acceleration skewness produces Net Transport rate.
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bottom slope induced Net sheet flow sediment Transport rate under sinusoidal oscillatory flows
Journal of Geophysical Research, 2017Co-Authors: Jing Yuan, Ole Secher MadsenAbstract:It is generally believed that the slope of beaches can lead to a Net downslope (usually offshore) sediment Transport rate under shoaling waves, but very few high-quality measurements have been reported for a quantitative understanding of this phenomenon. In this study, full-scale (1:1) experiments of bottom-slope-induced Net sheet-flow sediment Transport rate under sinusoidal oscillatory flows are conducted using a tilting oscillatory water tunnel. The tests cover a variety of flow-sediment conditions on bottom slopes up to 2.6°. A laser-based bottom profiler system is developed for measuring Net Transport rate based on the principle of mass conservation. Experimental results suggest that for a given flow-sediment condition the Net Transport rate is in the downslope direction and increases linearly with bottom slope. A conceptual model is presented based on the idea that gravity helps bottom shear stress drive bedload Transport and consequently enhances (reduces) bedload Transport and suspension when the flow is in the downslope (up-slope) direction. The model predicts both the measured Net sediment Transport rates and the experimental linear relationship between Net Transport rates and bottom slope with an accuracy generally better than a factor of 2. Some measured Net Transport rates in this study are comparable to those due to flow skewness obtained in similar sheet-flow studies, despite that our maximum slope could be milder than the actual bottom slope in surf zones, where sheet-flow conditions usually occur. This shows that the slope effect may be as important as wave nonlinearity in producing Net cross-shore sheet-flow sediment Transport. This article is protected by copyright. All rights reserved.
Sarah E. Gullbrand - One of the best experts on this subject based on the ideXlab platform.
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ISSLS Prize Winner: Dynamic Loading-Induced Convective Transport Enhances Intervertebral Disc Nutrition.
Spine, 2015Co-Authors: Sarah E. Gullbrand, Joshua M. Peterson, Rosemarie Mastropolo, Timothy T. Roberts, James P. Lawrence, Joseph C. Glennon, Jenna Ahlborn, Arun Fricker, Mostafa Abousayed, Eric H. LedetAbstract:STUDY DESIGN: Experimental animal study of convective Transport in the intervertebral disc. OBJECTIVE: To quantify the effects of mechanical loading rate on Net Transport into the healthy and degenerative intervertebral disc in vivo. SUMMARY OF BACKGROUND DATA: Intervertebral disc degeneration is linked with a reduction in Transport to the avascular disc. Enhancing disc nutrition is, therefore, a potential strategy to slow or reverse the degenerative cascade. Convection induced by mechanical loading is a potential mechanism to augment diffusion of small molecules into the disc. METHODS: Skeletally mature New Zealand white rabbits with healthy discs and discs degenerated via needle puncture were subjected to low rate axial compression and distraction loading for 2.5, 5, 10, 15, or 20 minutes after a bolus administration of gadodiamide. Additional animals with healthy discs were subjected to high-rate loading for 10 minutes or no loading for 10 minutes. Transport into the disc for each loading regimen was quantified using post-contrast-enhanced magNetic resonance imaging. RESULTS: Low-rate loading resulted in the rapid uptake and clearance of gadodiamide in the disc. Low-rate loading increased Net Transport into the nucleus by a mean 16.8% and 12.6% in healthy and degenerative discs, respectively. The kiNetics of small molecule uptake and clearance were accelerated in both healthy and degenerative discs with low-rate loading. In contrast, high-rate loading reduced Transport into nucleus by a mean 16.8%. CONCLUSION: These results illustrate that trans-endplate diffusion can be enhanced by forced convection in both healthy and degenerative discs in vivo. Mechanical loading-induced convection could offer therapeutic benefit for degenerated discs by enhancing uptake of nutrients and clearance of by-products. LEVEL OF EVIDENCE: 4.
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Low rate loading-induced convection enhances Net Transport into the intervertebral disc in vivo
The spine journal : official journal of the North American Spine Society, 2014Co-Authors: Sarah E. Gullbrand, Joshua M. Peterson, Rosemarie Mastropolo, Timothy T. Roberts, James P. Lawrence, Joseph C. Glennon, Darryl J. Dirisio, Eric H. LedetAbstract:Abstract Background context The intervertebral disc primarily relies on trans-endplate diffusion for the uptake of nutrients and the clearance of byproducts. In degenerative discs, diffusion is often diminished by endplate sclerosis and reduced proteoglycan content. Mechanical loading-induced convection has the potential to augment diffusion and enhance Net Transport into the disc. The ability of convection to augment disc Transport is controversial and has not been demonstrated in vivo. Purpose To determine if loading-induced convection can enhance small molecule Transport into the intervertebral disc in vivo. Study design Net Transport was quantified via postcontrast enhanced magNetic resonance imaging (MRI) into the discs of the New Zealand white rabbit lumbar spine subjected to in vivo cyclic low rate loading. Methods Animals were administered the MRI contrast agent gadodiamide intravenously and subjected to in vivo low rate loading (0.5 Hz, 200 N) via a custom external loading apparatus for either 2.5, 5, 10, 15, or 20 minutes. Animals were then euthanized and the lumbar spines imaged using postcontrast enhanced MRI. The T1 constants in the nucleus, annulus, and cartilage endplates were quantified as a measure of gadodiamide Transport into the loaded discs compared with the adjacent unloaded discs. Microcomputed tomography was used to quantify subchondral bone density. Results Low rate loading caused the rapid uptake and clearance of gadodiamide in the nucleus compared with unloaded discs, which exhibited a slower rate of uptake. Relative to unloaded discs, low rate loading caused a maximum increase in Transport into the nucleus of 16.8% after 5 minutes of loading. Low rate loading increased the concentration of gadodiamide in the cartilage endplates at each time point compared with unloaded levels. Conclusions Results from this study indicate that forced convection accelerated small molecule uptake and clearance in the disc induced by low rate mechanical loading. Low rate loading may, therefore, be therapeutic to the disc as it may enhance the nutrient uptake and waste product clearance.
Fusao Tomita - One of the best experts on this subject based on the ideXlab platform.
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indigestible disaccharides open tight junctions and enhance Net calcium magnesium and zinc absorption in isolated rat small and large intestinal epithelium
Digestive Diseases and Sciences, 2004Co-Authors: Hitoshi Mineo, Fusao Tomita, Midori Amano, Hideyuki Chiji, Norihiro Shigematsu, Hiroshi HaraAbstract:The effects of three indigestible disaccharides on Net calcium (Ca), magnesium (Mg), and zinc (Zn) Transport in isolated rat jejunal, ileal, cecal, and colonic epithelium were determined. Permeability of fluorescein isothiocynate–dextran-4 (FD4) and transepithelial electrical resistance (TEER), which vary according to tight junction (TJ) activity in the intestinal mucosa, were also determined. The addition of 1–100 mM melibiose, difructose anhydride (DFA) III, or DFA IV to the mucosal medium increased the Net absorption of the three minerals and FD4 permeability, while decreasing TEER dose dependently in the four intestinal portions. Positive linear relations were found between the Net Transport of the three minerals and FD4 passage in all portions of the intestine, whereas negative linear relations were observed between Net absorption of the three minerals and TEER. We concluded that the three indigestible saccharides directly affect the epithelial tissue and open TJs, thereby promoting Ca, Mg, and Zn absorption in the small and large intestine in vitro.
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sugar alcohols enhance calcium Transport from rat small and large intestine epithelium in vitro
Digestive Diseases and Sciences, 2002Co-Authors: Hitoshi Mineo, Hiroshi Hara, Fusao TomitaAbstract:We compared the effect of a variety of sugar alcohols on calcium absorption from the rat small and large intestine in vitro. An Ussing chamber technique was used to determine the Net Transport of Ca across the epithelium isolated from the jejunum, ileum, cecum, and colon of rats. The concentration of Ca in the serosal and mucosal Tris buffer solution was 1.25 mM and 10 mM, respectively. The Ca concentration in the serosal medium was determined after incubation for 30 min and the Net Ca absorption was evaluated. The addition of 0.1–200 mM erythritol, xylitol, sorbitol, maltitol, palatinit, or lactitol to the mucosal medium affected Net Ca absorption in the intestinal preparations. Differences in Ca Transport were observed between portions of the intestine, but not between sugar alcohols tested. We concluded that sugar alcohols directly affect the epithelial tissue and promote Ca absorption from the small and large intestine in vitro.
