Science topic

Hydrodynamics - Science topic

The motion of fluids, especially non-compressible liquids, under the influence of internal and external forces.
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Enhanced Oil Recovery: Wettability
1. Given the fact that the wetting process operates on a scale that extends from the macroscopic to the molecular-scale, while our observations usually involve only macroscopic quantities measured at resolutions no better than several micro-meters, is there a way, to validate the measured data on macroscopic contact angle?
Whether such measured macroscopic contact angle would remain to be the same as that of the nanoscopic local contact angles?
Whether the microscopic contact angle, deduced usually at a scale of nano-meters from the contact line – would remain to depend on the moving speed?
Can we deduce the interface profile for film thicknesses less than 100 nm – under “dynamic” fluid conditions – by using Environmental-SEM or wet-STEM or by using TEM?
2. How easy would it remain to have a control over capturing the contact line movement mechanism - associated with molecular jumping or interfacial rolling - at the junction of oil-brine-gas-phase interfaces - for a mixed/intermediate/fractional wet reservoir?
3. If (2) remains to be feasible @ laboratory-scale, then, how about capturing the regulation of the hydrodynamic singularity including slip, diffusion and disjoining pressure?
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These are insightful and intricate questions related to fluid dynamics, wetting phenomena, and experimental validation techniques. I'll address each point with the most relevant concepts and experimental techniques:
1. Validation of Measured Macroscopic Contact Angle
The macroscopic contact angle, which is often measured at the millimeter or micrometer scale, may not always reflect the behavior at the molecular scale. Here’s why:
  • Macroscopic vs. Nanoscopic Contact Angles: The macroscopic contact angle is influenced by the roughness and heterogeneity of the surface, as well as the underlying molecular interactions at the contact line. On the molecular scale, the contact angle can be much more variable due to factors like molecular orientation and interfacial forces that are averaged out in macroscopic measurements. Therefore, it's unlikely that the macroscopic contact angle would exactly match the nanoscopic contact angles.
  • Moving Speed and Microscopic Contact Angle: The microscopic contact angle, especially at the contact line, is often influenced by the speed of motion (in dynamic conditions), which can lead to hysteresis or changes in the angle due to kinetic effects. These effects become particularly relevant for high-speed spreading or moving droplets.
  • Measuring Thin Films and Interface Profiles (less than 100 nm): Techniques like Environmental-SEM (eSEM), wet-STEM, and TEM can indeed be used to observe the interface profiles at very small scales. These techniques allow for visualization of thin films, but capturing the dynamic nature of the fluid interface, especially under high-speed conditions or when molecular-scale interactions are involved, remains challenging. The resolution and imaging capabilities, especially under dynamic fluid conditions, are limited, but they are improving. Additionally, controlling environmental conditions (e.g., maintaining liquid films or wetting conditions in a vacuum or controlled atmosphere) is critical.
2. Capturing the Contact Line Movement in Oil-Brine-Gas Phases
The behavior at the contact line, especially when dealing with complex multi-phase systems like oil-brine-gas interfaces in a mixed or fractional wet reservoir, is indeed complex. Here are some challenges and opportunities:
  • Molecular Jumping and Interfacial Rolling: These mechanisms, which are linked to the motion of the contact line, can be influenced by the interfacial tension between the phases and the heterogeneity of the surface. In such systems, capturing these phenomena at the molecular scale can be difficult due to the roughness and the dynamic nature of the phases involved. However, with molecular dynamics simulations (MD) and high-resolution imaging techniques like atomic force microscopy (AFM) or high-speed video microscopy, it’s possible to observe and capture contact line movement mechanisms.
  • Control over Experimental Conditions: At the laboratory scale, controlling and capturing the contact line dynamics in oil-brine-gas systems may be feasible but requires specialized equipment. For instance, ensuring stable phase separation and controlling the interface under dynamic conditions (e.g., changing flow rates, applying external forces) would be necessary.
3. Regulation of Hydrodynamic Singularity (Slip, Diffusion, and Disjoining Pressure)
At the laboratory scale, capturing and controlling hydrodynamic singularities, such as slip lengths, diffusion, and disjoining pressures, is an advanced task that requires a deep understanding of interfacial physics and precise experimental techniques:
  • Slip and Diffusion: Slip at solid-liquid interfaces is often related to molecular interactions near the contact line and can be influenced by surface roughness and fluid properties. Experimental methods like rheometry, microfluidics, and AFM can be used to measure slip lengths and diffusion coefficients. However, capturing these phenomena at the molecular scale (especially in complex multi-phase systems) can be difficult.
  • Disjoining Pressure: Disjoining pressure refers to the pressure that arises between layers of a thin liquid film due to molecular interactions. It is particularly important in systems with thin films (e.g., less than 100 nm thick). This pressure can be influenced by surface forces and could potentially be measured using optical interferometry or atomic force microscopy (AFM), though measuring it under dynamic conditions remains a significant challenge.
In conclusion, while controlling and measuring these phenomena in complex, dynamic, multi-phase systems is challenging, it is not beyond the reach of current experimental techniques. Advances in imaging and molecular dynamics simulations, as well as specialized laboratory equipment, are making it increasingly possible to study such systems with higher precision. However, significant effort in controlling experimental conditions, resolution, and environmental constraints will be needed to extract meaningful data.
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My hydrodynamic simulation went from 0 to 100% immediately on Mike Coupled Model FM. And no results was generated afterwards. I don’t know what the problem is.
I forced the model with the tidal potential data and wind data.
What could the problem be?
I didn’t get an error message, which is another reason why I’m confused.
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Try to prepare the simulation file again and run
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People usually derive hydrodynamic equations from the Boltzmann equation. How to derive fluid mechanics equations from Heisenberg equation?
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The entire derivation is challenging, including quantum field theory, operator techniques, and statistical mechanics. It is not a frequent method since fluid mechanics is often developed from classical mechanics rather than quantum mechanics. However, in some high-energy or quantum fluid situations (such as superfluidity), such derivations can be useful.
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The aether as considered by lorentz, heaviside and others, seems to work fine with the relativity and general relativity, So has anyone worked on the thermodynamcis of the aether
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Branko V. Mišković , agreed but my question was not about can it be done, it was about has anyone done it, or else I have to do it from scratch
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Can DLS measurement distinguis the hydrodynamic size of particles with 250nm and 270 nm? what is the resolution of the method?
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No. If the 250 and 270 particles are mixed together you can't resolve them independently. It will be one broad peak. As a rule of thumb, DLS can't resolve nanoparticles whose sizes differ by less than a factor of three.
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I have 2 materials A and B. A has Particle size 15 nm and B has 34 nm. But the hydrodynamic radii of A comes to be 2400 nm and of B is 1700 nm.
How this has happened kindly anyone give the scientific explanation of it.
A is binary and B is ternary composite
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Your systems apparently relate to soft matter: surfactant micelles, polymer micelles... They are formed due to hydrophobic interaction or water-mediated interaction. The structure of water changes and is accompanied by quantum-thermal fluctuations of water. Fluctuations can be with slow diffusion, and, consequently, with a large size of water “clusters”. Look
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Surface textures is the intentional introduction of well defined features like micro dimples This helps to generate hydrodynamic lift between the parallel surface when they are in relative motion.
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I recommend you read some papers on this topic.
The above comments and explanations are not obvious and not always true. For example, partially textured and full textured surface configurations lead to different performances in terms of load carrying capacity.
Some explanations are given in this two papers:
DOI 10.1243/13506501JET433 : “About the Validity of Reynolds Equation and Inertia Effects in Textured Sliders of Infinite Width.”
DOI 10.1243/13506501JET673 :  “Optimizing surface texture for hydrodynamic lubricated contact using a mass-conserving numerical approach.”
Simple explanations with an analytical modeling are presented in:
DOI 10.1243/13506501JET470  : “Analytical investigation of a partially textured parallel slider.”
Experiments on parallel surface thrust bearings are presented in :
DOI 10.1177/1350650114537484  : "An experimental analysis of the hydrodynamic contribution of textured thrust bearings during steady state operation - Comparison with the untextured parallel surface configuration."
DOI 10.1016/j.triboint.2017.12.021  :  "Experimental analysis of the hydrodynamic effect during start-up of fixed geometry thrust bearings.”
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I want to analyze the noise and hydrodynamic performance of the propeller with OpenFOAM, but there is no relevant information here, I will express my thanks if you can help me +.
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You can use libAcoustics libary for noise prediction in OpenFOAM
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Can Matlab software modelate ship data like: propulsion force, ship resistance, hydrodynamic coefficients?
I need to software to easily verify and compute ship data. Any models for this?
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If you have the mathematical equations and the math model, yes it can be simulated.
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I have thus far been unable to get DLS characterizations of some ultrasmall iron oxide nanoparticles that I purchased commercially and I believe it is due to high rates of aggregration, especially as I have had a hard time getting a the nanoparticles fully solubilizzed in solution (water, PBS, DMSO). I'm thinking that maybe adding a surfactant could be effective at reducing aggregation just for the purpose of hydrodynamic diameter and zetapotential readings. Any suggestions for best surfactant options?
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Dorian Foster The stages in making a stable dispersion (as well-known by paints and ceramic experts) are:
  • Wetting
  • Separation
  • Stabilization
If your iron oxide (powder) particles do not wet in the liquid you're intending them to be dispersed in then this is the function of a surfactant (wetting agent). If your particles wet then you don't need a surfactant generally. Separation is achieved with input of energy, typically ultrasound in the wet. If the particles aggregate or agglomerate after separation then a stabilizer (charge/electrostatic or steric) is needed. IMHO, this is where your issues lie. I'd try sonicating in a 0.05wt% sodium hexametaphosphate solution as the phosphates are classic inorganic oxide stabilizers. Take a look at the following webinar (free registration required) for more details:
An acronym approach to laser diffraction method development: https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190815PST
I agree with John Francis Miller . If your particles are in the dry form it's going to be very difficult to disperse them. Try measuring the specific surface area of the powder by BET. It should be greater than 60 m2/cm3 for the particles to be considered less than 100 nm. Also see plenty of discussions on Research Gate on this topic.
2 quotes from those much greater than I:
'I think dry nanotechnology is probably a dead-end' Rudy Rucker Transhumanity Magazine (August 2002)
‘If the particles are agglomerated and sub-micron it may be impossible to adequately disperse the particle… ‘The energy barrier to redispersion is greater if the particles have been dried. Therefore, the primary particles must remain dispersed in water...’ J H Adair, E. Suvaci, J Sindel, “Surface and Colloid Chemistry” Encyclopedia of materials: Science and Technology pp 8996 - 9006 Elsevier Science Ltd. 2001 ISBN 0-08-0431526
See also a recent question:
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i have formulate a nano-emulsion as a drug carrier ,consist of oil,surfactant and co surf. , upon mixing different ratios of oil,SA,CoSA the hydrodynamic measurment is about 20-30nm (average of three readings) but have occured three peaks first one is matched to hydrodynamic diameter(20-30nm) but the other two are large ? so,how to make it unimodal (one peak) and if it impossible , whta is the size of my particle ?
Regards
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Your results are similar to our experiments with dodecyl sulfate solution
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I am a college student and just started to learn MIKE ZERO. Can I ask for help? I'm trying to run a flow model of the current hydrodynamic. I need to input discharge data into the boundary/domain, and the problem is I'm still confused about creating discharge data and how to input it into the boundary/domain. I will be very grateful if anyone can help and teach me, thankyou in advance.
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Hi,
Having the discharge data on Excel will make it easy for you to copy and paste it in a new time series file, following this on Mike zero:
File -> New File -> Time series -> .dfs0 ->Blank time series -> (fill the file properties according to the discharge data that you have; don't forget to specify the Data Type and the Unit) -> Paste the discharge values to the right column in the file you've created -> save.
Hope this help you :)
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min step=1e-3 max step=0.01 minstep=1e-5 increment =1.55 , models is hydrodynamic, math i have tried with default and also blocked and pardiso
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Okay, thanks will try that, also I am facing an error that interface "region_1/region_2" is not found in the grid file, is meshing at that interface a solution to this?
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What is the difference between MST and MPT and how to realize when to use MST and when to use MPT.... Isn't MST most appropriate to study the hydrodynamics of fluidized bed reactors as it represents fuel tracer particles unlike MPT where one can use only one magnetic particle and project its path (it will not undergo collisions with other fuel tracer particles)
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Magnetic Solid Tracing (MST) and Magnetic Particle Tracking (MPT) are two different techniques that use magnetic fields for fluid flow analysis.
MST involves introducing solid magnetic tracer particles into a fluid, and using magnetic sensors to track their movement. The magnetic tracer particles provide a direct measurement of the fluid velocity and allow for the visualization of complex flow patterns. MST is often used in industrial applications, such as flow analysis in pipelines and measurement of mixing in tanks.
MPT, on the other hand, involves suspending magnetic nanoparticles in a fluid and using magnetic sensors to detect their motion. MPT can provide high-resolution measurement of fluid velocity and can be used to study a wide range of fluid dynamics, including laminar and turbulent flows. MPT is commonly used in laboratory and research settings, where high accuracy and spatial resolution are important.
In summary, MST and MPT both use magnetic fields for fluid flow analysis, but MST uses solid magnetic tracer particles, while MPT uses magnetic nanoparticles suspended in fluid. Both techniques have their own advantages and applications, and the choice between them will depend on the specific requirements of the project.
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Hello Expert
Can Anyone suggest the subareal debris flow impact on oil and gas pipeline?
Hydrodynamic loading or debris flow hazard interaction with pipeline?
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You may refer to the article attached to this reply.
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Hello everyone,
I am trying to learn the fundamentals of breakage and coalescence modeling in bubble columns, specifically, for air-water systems when the water is at rest. I believe this is one of the most basic forms in bubble columns however, I am having a hard time finding good references on the topic.
Please let me know your recommendations for any good reference.
Thank you,
Erol.
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Thank you, Dr. Petr Stanovsky . I have the book of Jakobsen but I will investigate the second as well.
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In our last monograph "A new paradigm of formation of accumulative relief in shallow areas of oceans and seas" (Ukrainian), an endogenous theory of formation of underwater and above-water accumulative forms of bottom relief is proposed. The thesis that hydrodynamic barriers constantly exist in water over active tectonic faults is substantiated. The tectonic map of the Black and Azov Seas shows that all the accumulative forms of the bottom topography are formed over tectonic faults (map a). Look at the photo (on the map a large arrow) of the surface sandy accumulative form of the Black Sea (photo b). The structure has been eroded, and the hydrodynamic barrier over the tectonic fault continues to restore the sandy accumulative form. We confirmed this possibility by modeling (scheme c). Please comment and ask questions.
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I want to give a fragment from the discussion "The location of coral reefs in space most often has a linear shape. What is it connected with?". Here about the straightness of the bottom topography in the shallow areas of the tropical zone.
«It is generally accepted that for the formation of a coral reef, clear water is necessary (photosynthesis of zooxinela is impossible in muddy water) and warm water (in cold water, a polyp cannot form an external carbonate skeleton). In addition, it is desirable to have a solid substrate for fixing the polyp at the bottom and sea currents that bring food to the polyp are desirable.
In tropical seas, these conditions are everywhere, but coral reefs are not formed everywhere. The reason is that the tropical zone of the ocean is oligotrophic. For the first time, we have included in the list of necessary conditions a fluid dynamic process in tectonic faults of the earth's crust. You can see the link: https://magazine.neftegaz.ru/articles/geologorazvedka/443409-flyuidodinamicheskie-anomalii-kaspiyskogo-morya/.
This led to the need to formulate a new paradigm for the formation of coral reefs. We did this in the second volume (Spatial patterns of coral reef formation) of the monograph "A new paradigm of accumulative relief formation in shallow areas of oceans and seas" (2021).
It was shown for the first time that in the oligotrophic tropical zone of the ocean, solutions of phosphates and nitrates enter the bottom layer only along tectonic faults. Without these substances, phytoplankton cannot form. Without phytoplankton, zooplankton (polyp food) cannot arise. We used the theory of structure formation of the solid shell of the Earth.
Block sizes change discretely (… 35x35 km, 70x70 km, 140x140 km, 280x280 km, 560x560 km, 1120x1120 km …). The orientation of the block structure is discrete (0° and 270°; 17° and 287°; 35° and 305°; 45° and 315°; 62° and 332°; 77° and 347°).
Solutions of nitrogen and phosphorus enter the oligotrophic waters of the ocean only along straight faults. Linear fault directions can only have six azimuths. Coral reefs only form along faults. Let's apply a new coral reef formation paradigm to a coral reef in the Amazon Delta. I have attached a diagram of this reef and a satellite image of the Amazon Delta with our additions. (Scheme of a coral reef from an open Internet resource).
The grid of tectonic blocks is like a chessboard. The white squares are up and the adjacent black squares are down. On the satellite image, I put a yellow line (approximate position of the coral reef). To this line, I leaned a square with dimensions of 1120x1120 km with an azimuth of 35° and 305°. The line of the coral reef and the northeastern boundary of the tectonic block coincided.
The correctness of drawing a tectonic block on a satellite image has several practical confirmations. The arrow in the image shows a tectonic fault, which manifested itself in the configuration of the ocean coast. The bay has an azimuth of 35 degrees. In the north-west direction, at a distance of about 560 km, you can see a similar bay (tectonic fault). This is natural, since the tectonic block 1120x1120 km is divided into 4 blocks. The adjacent block is shown in red. It is shown in the terrain as an uplift. I think it's convincing.
If there are doubts about the theory of fluid dynamics, I will provide additional evidence. In the picture, I showed in blue a tectonic block, which has dimensions of 560x560 km. It has a different spatial orientation (77° and 347°). Along the northern and western borders of the block, you can see straight riverbeds. This can be explained only by the theory of fluid dynamics of the lithosphere. All riverbeds coincide with tectonic faults. Thank you for watching.
Sincerely, Boris.
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I am running an RSM simulation across a 2D structure in an open channel flow. When I try to plot the Reynolds stresses across the structure, I have two values for the same x value along the length of the structure. What do I do to solve this problem?
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Sorry but I don’t understand this issue, what is the link you stated between Reynolds stress (a tensor ) and the residual in the continuity equation?
Provide more details and some plot of your problem.
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Does anyone know any biocompitable gel that one could use (alone or mixed with agarose) that results in smaller pores (in the 2-10 nm range) to slow down the diffusion of 1 kDa molecules (0.5 nm hydrodynamic radi)?
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You can try it with HEMA gel.
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Hi,
Assuming the kinetic description is used for electron fluid and the hydrodynamic description for ion fluid. I am wondering what are the physical meaning and limits of such an approach.
Thanks.
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Prof. Johannes Gruenwald thank you for your instructive and clarifying answer.
Yes, both structures of equations are different, for example, the Boltzmann equation in the tao approximation is totally different from the equation for a viscous fluid, but the role of the Newton laws appears from the beginning say in the Navier–Stokes equations were what I meant was the conservation of linear momentum and mass for Newtonian fluids, meanwhile, for ions or charged particles in fluids, we cannot use that math approach directly. If there are charged particles we need the set of magnetohydrodynamic equations.
On the other hand, the kinetic equation always expresses the total evolution of time df /dt, which in one total derivative expression contains different physical phenomena: diffusion, collisions, and newton forces, I only mean that. To solve the kinetic equation we need non-linear integro-differential methods, quite difficult to follow sometimes and yes, we can try for 2 particles, 3 particles, or N particles the collision or scattering term (following for example the Bogoliubov approach
--> which is a method for asymptotic integration of non-linear differential equations), but equilibrium is not present, always the kinetic phenomena express out of equilibrium properties.
In fluids we do not follow that complicated approach, we instead define the fluid from the beginning as something not statistical, I only mean that they are partial differential equations as we introduce them in a beginning fluid mechanics course. Of course, if we use a method such as smoothed particle hydrodynamics (SPH) what I said is not valid, since there is the kernel function that allows a statistical computational approach. And finally, yes, we can follow particle by particle in hydrodynamics as well and even include molecular forces, but it has a very high computational cost, I guess.
Thank you for the clarification.
PD The question about the inclusion of the entropy d S/d t = 0 in magnetohydrodynamics (fluid charged) and not in the kinetic equation approach is very subtle and I prefer not to discuss it here.
Best Regards.
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Can some tell me how to measure or calculate the aerodynamic diameter of TiO2 pigment powder ? Can the hydrodynamic diameter values be correlated with aerodynamic diameter ?
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Aerodynamic radius of TiO2 can be determined by Dustiness Test, EN 15051-2, rotating drum method (extend of TiO2 particles with aerodynamic diameter ≤ 10 μm). You can contact Carolyn McGonagle @ carolyn.mcgonagle@iom-world.org (- IOM UK - Lab Services) for conducting the evaluation.
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The question is about hydrodynamics and coastal water quality modeling.
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I forgot I had this overlay which shows the difference between rectangular and curvilinear grids better.
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In DLS there were 2 peaks major one centred at 113.9 nm and the other one was at 21.39nm.In DLS we are getting hydrodynamic size and in TEM the size will be real,right?
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Harsha Haridas e S One question for you to answer. What is the diameter of a hydrogen atom? Why is it relevant to this question?
DLS provides an intensity distribution proportion to r6 (or volume2) whereas TEM provides a number distribution (proportional to r1). TEM will examine the metallic core of the particle ignoring the essential protective and stabilizing layers (can't be seen) whereas DLS will consider the movement and interactions of the entire particle (core + protective layers). They are different but both are correct if the experiment has been conducted correctly. Understand the reasons for the differences and quote a reasonable number of decimal places.
Please explain your TEM sample preparation as artefacts are likely especially if microtoming is involved. Why?
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Area weighting is a technique used to preserve spherical symmetry in 2D simulations of hydrodynamics performed in cylindrical coordinates. Its origin is obscure, may lie in the early unpublished reports of Los Alamos, Livermore, or Sandia Laboratories. It is still used in many 2D hydrocodes and it would be nice to give proper credit.to its creator.
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The oldest paper that I found on an area-weighted 2D RZ Lagrangian hydro scheme is the following paper by Wilkins published in 1963. The numerical details on the scheme start on page 20. The oldestest 2D RZ scheme that I know of was a unique finite difference method by Bob Orr and published around 1956, it however did not use area weighting.
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Can anyone explain the relation between hydrodynamic size of a polymer with its adsorption capacity? Does a polymer with greater hydrodynamic size show better adsorption efficiency or vice versa?
Thanks in Advance
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For proteins, the hydrodynamic size refers to the diameter of a sphere with the same hydrodynamic properties as those possessed by the biomolecules
themselves. Thus the adsorption potential varies directly as the hydrodynamic size.
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Will the aggregation affect the DLS analysis?
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DLS - Dynamic light scattering technique used to obtain the hydrodynamic diameter based on the diffusion of the particles.
Vaibhav Raj Singh Parmar explained it well with the picture given
The hydrodynamic size shows how the particle behaves in a fluid.
As far as I read and understood, when a particle is dispersed in a liquid, it moves through a liquid medium with zigzag and random motion, a very thin or a thin electric dipole layer of the solvent used adheres to the surface of the particle. This layer on the surface plays a role in influencing the particle's movement or the path it travels in the liquid medium. Therefore, the HDD (hydrodynamic diameter) gives us information about the core particle along with any coated material on the particle and the solvent layer attached to the particle as it moves under the influence of Brownian motion.
The HDD is determined by using Stokes Einstein equation.
Please read these two articles given below for a better information.
TechniquesforAccurateSizingofGoldNanoparticlesUsingDynamic LightScatteringwithParticularApplicationtoChemicaland BiologicalSensingBasedonAggregateFormation
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I have trouble understanding why it is important to acknowledge hydrodynamic size in nanoparticle studies or in clinical applications.
I have read in some papers and posts that it ''helps the particles avoid clearance from circulation by the body's liver or kidneys, prolonging the drug's active lifetime and ultimately increasing the drug's efficacy'' and this was also used in the structure of some SARS-Cov-2 vaccines.
I did not fully understand how.
And does it affect interactions with cells for example?
Let's say two particles have the same core size but one has a larger hydrodynamic size than the other, how would it affect the particles characteristics (Aside from their diffusion speed/Brownian motion)?
Mind you, I do not work with nanoparticles or synthetic vesicles, my knowledge is very limited in those areas.
any answer or papers suggestions are welcome !
thank you in advance!
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Syrine Arif Simply, the hydrodynamic diametwe represents how particles interact with one another in suspension. Particles do not interact based on their core diameter but rather on the size represented by the core and the stabilization/protective shell layer.
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I am doing research on nano medicine. When I was measuring the size of NPs using DLS instrument, I could get hydrodynamic diameter. I wanna know if there's a way to calculate the core diameter using hydrodynamic diameter.
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Tejashwini Lnu Use electron microscopy or SAXS for the (metal/electron rich) core.
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Is anyone familiar with the natural period of the system of a floating structure in ANSYS AQWA after analyzing hydrodynamic diffraction & hydrodynamic time response?
I have modeled a Tension Leg Platform for a wind turbine in ANSYS AQWA and have analyzed the structure for hydrodynamic diffraction & hydrodynamic time response. Also I want to know which type out of the 4 types of mooring cables should I select ? Cable non-linear polynomial or non-linear steel wire ? How to select the stiffness and un-stretched length.
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To determine the natural period (in any DOF) of a system in AQWA. This test is called the free decay test and It is important to note that this type of analysis is conducted in calm water, i.e, by deactivating the wave, wind, and current tabs. By inserting the 'starting position' tab, the platform is displaced in a specific degree of freedom (eg x=15m for surge), after which a time series analysis is performed. The natural period is and corresponding damping rations in each DOF are computed from the free decay time series plot (detail of this computations can be referred to in any structural dynamics text book, eg Chopra).
Hope this help!
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I am working with a semi-submersible floating offshore wind turbine system and would like to find the frequency domain hydrodynamic coefficients. I am using Workbench to do it but and just learning so any assistance by way of tutorial or otherwise would be helpful.
Thank you.
Regards,
AOAW
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If you mean Ansys Workbench, you can use Aqwa. It does exactly what you are asking. I attached some tutorials, but since i have not been using Aqwa in a long time, i'm not sure if they are up to date.
An alternative is using open source software like Capytaine or HAMS:
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I am currently working on the settling tank design. All flow calculations and dimensions have been made I need to reproduce the drawing in the form of the attached file. What possible software can be used to achieve a similar drawing with the glossy flow description similar to the attached file?
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Thanks so much.
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We intend to model hydrodynamics and currents in oceans and seashores.
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Hello Riza,
Have you tried to download Delft-3d? It's open source and the company sends you a 1-year license which you can be renewed, download it from here:
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Hi everybody. I need to calculate hydrodynamic coefficient of Remus 100 AUV. Can you help me and give its m-file code to me?
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How will you calculate the hydrodynamic coefficient of Remus 100 AUV?
For more details read some recent work(especially thesis) on Remus and Please refer
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In physics, continuity equation often reads as ∂ρ/∂t+∇⋅(ρu)=0. Obviously, if velocity field u is solenoidal, the equation degenerates to dρ/dt=∂ρ/∂t+u⋅∇ρ=0. That is, the total derivative of density is zero. Then the question is arise. Two equations above both state that the density is independent of time, why can't that the total derivative vanishes imply continuity equation? Is it possible that there exists some real total derivative equivalent to that in the continuity equation?
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This interesting question was last touched in 2013, but like every time I do an answer on researchgate, scores of people will come in just to drown it and make it invisible.. which is sad...
Anyway, I just managed to find an answer to this while working in a different field and saw this question in my google search. The problem I was working on is if the Lorenz force is derivable from Maxwell equations or is an independent statement. I discovered that it can be derived by assuming the conservation of charge in motion or the continuity equation for a charge. It goes like this;
For any velocity v and vector A we have the material derivative;
D A/Dt =∂F/∂t + (v.grad)A =∂F/∂t +v div(A) + curl(Axv).
If A is the magnetic field B, then div(B)=0 and if the line of field are conserved(not changed inside a volume) the total derivative is zero and we get; ∂B/∂t =-curl(Bxv). From Maxwell Faraday equation we have; - ∂B/∂t =curl(E). Comparing the two we see that vxB is a term to be added to the static potential of the field to end up with F=q(E+vxB) which is the Lorenz force. So this force is a consequence of continuity and the rest of Maxwell equations.
In fluid mechanics we have div(v)=0 for incompressible fluids and div(ρv)=0 and the same vector identity can be used to show that the continuity of mass current implies the continuity equation too.
Note the material derivative is constructed to follow the conserved quantity as it moves in space with the control volume changing in shape but keeping the same conserved quantity inside. Hope this is useful. After the effort, I remembered I saw a long time ago a similar treatment in Panofski and Phillips book on Electromagnetism using volume integrals instead of the vector identity.
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When the proposed water-lubricated textured groove thrust bearing is under high speed, the initial cavitation number will increase, so the cavitation effect should be considered when modelling.
The previous research has established that cavitation obviously exists in the textured bearing, including thrust bearing under hydrodynamic lubrication and mechanical seals.
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Please go through the link and find your required answer.
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Hi all,
I'm planning to simulate flow past a floating body using CFD method with the main purpose of investigating its stability against hydrodynamic forces. A sketch of the problem is presented the the figure attached.
It seems that an accurate estimation of pressure field, and therefore hydrodynamic forces, is heavily dependent on correct prediction of flow topology, particularly separation and reattachment of the flow.
I'm wondering what turbulent models would best handle this problem. I would appreciate it if you provide details and specific reasoning.
Regards,
Armin
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The Reynolds Stress Model is the most complete turbulence model with regards to representing turbulent flow.
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Hi all,
I have investigated so much about the different fictitious domain and immersed boundary methods. The scope of the work contains a wide range of methods which most of the time seems complicated to me. BTW, Can you explain what the difference between these two types of methods is? To me, it seems that fictitious domain is a general category of the methods which contains immersed boundary methods. Hence, Can Distributed Lagrange Multipliers (DLM) be regarded as Fictitious Domain type? Thank you, in advance, for getting involved in this discussion.
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Fictitious domain method is a method to find the solution of a partial differential equations on a complicated domain.
IB methods impose momentum forcing on an Eulerian mesh to satisfy boundary conditions on the interface between fluid and structure
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CFD modelling is a useful tool to examine the performance of electrochemical cells for specific reactions over suitable catalysts. Currently, I am working on using CFD modelling framework to describe coupled mass transport, hydrodynamics of flow, chemical (homogeneous) and electrochemical (heterogeneous) reaction kinetics in an electrochemical flow cell for a specific oxidation reaction on an electrode.
As I plan to use Ansys Fluent, could anyone share very useful training resources (books, videos etc.) that can assist me to smoothly kick-start this project?
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check this link. This question has been already asked and answered on the research gate.
You can try learning from here as well. It starts from basics and has used common heat transfer examples
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I'm working on an industrial wastewater mainly composed by DMF and alcohols. I'm treating samples with hydrodynamic cavitation, hydrodynamic cavitation/H2O2 or hydrodynamic cavitation/O3 but at the end of each process the COD value is slightly higher than the wastewater one. I tried to remove excess of H2O2 by heating the samples at 90°C or adjusting pH to 10-11 and then heating at 45°C because of its interference, but also other samples have same problem Hannah Instrument COD kits are used to determine COD values.
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Hi Federico Verdini,
For the said industrial wastewater, determine or (repeat) the COD by varying dilution factors
(1:10, 1:50, 1:100, 1: 200). After that you may get average range of COD.First confirm intial value of given sample. For more accuracy you can correlate with BOD value.
However you can more details about interference and its limitations in APHA Standard method 5220, SECTION 5-11)
Reg
Prashant. B.B
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In 2010, Dr. Khmelnik has found the suitable method of resolving of the Navier-Stokes equations and published his results in a book. In 2021, already the sixth edition of his book was released that is attached to this question for downloading. Here it is worce to mention that the Clay Mathematics Institute has included this problem of resolving of the Navier-Stokes equations in the list of seven important millennium problems. Why the Navier-Stokes equations are very important?
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I finally could check the PDF, Prof. Aleksey Anatolievich Zakharenko
Dr. Khmelnik uses a variational principle to solve the NS equation, which is very powerful indeed.
He also discusses and gives examples & a reason for turbulence.
I know that the solution of NS is a non-linear problem that involves several modes and that it depends on the source.
However, my knowledge of the foundations of NS is very limited to a few linear/non-linear problems on non-equilibrium gas dynamics& MHD solved by the method, Prof. Miguel Hernando Ibanez had.
Thank you for sharing the link. I recovered my account.
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It is required for the stability analysis of bearing.
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Thanks for suggesting the books.
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I would like to make a operating window for a bioreactor process where I want to incorporate data such as impeller speed, gas flow rate, hydrodynamic shear, mass transfer efficiency, power consumption and other engineering parameters which define bioreactors' optimum performance.
Currently struggling to make a comprehensive operating window, therefore your suggestion on it will be highly appreciated. please suggest which tool (excel or any software) will be suitable for this task.
thanks in advance
Rajesh
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The recursive least squares algorithm (RLS) allows for (real-time) dynamical application of least squares regression to time series. Years ago, while investigating adaptive control and energetic optimization of aerobic fermenters, I have applied the RLS algorithm with forgetting factor (RLS-FF) to estimate the parameters from the KLa correlation, used to predict the O2 gas-liquid mass-transfer, while giving increased weight to most recent data. Estimates were improved by imposing sinusoidal disturbance to air flow and agitation speed (manipulated variables). The power dissipated by agitation was accessed by a torque meter. Simulations were carried in Excel 5.0 with Visual Basic for Applications (VBA) macros.The proposed (adaptive) control algorithm compared favourably with PID. This investigation was reported at (MSc Thesis):
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As briefly information, I got the data of hydrodynamic size, and it revealed the high diameter (let us say this is more than 1000 nm). However, another way, I found out the pore size from TEM that was around 23 nm. Why are these different? Can anybody explain the difference between hydrodynamic size with TEM? Could hydrodynamic diameter be considered as the particle size or pore size and why?
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Hydrodynamic force on floating wind turbine
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It depends on the wave regime... in the Inertia regime forces are assumed to be consisted of pressure and acceleration components as follows
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I am interested to perform spectral analysis of a structure under random waves. could anyone suggest me a book or an example that starts from wave spectrum (such as
JONSWAP spectrum , P-M etc) to RAO. A complete example from formulation to numerical evaluation.
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Hi everyone,
I want to use CFX to simulate the transient 2D flow past a stationary rectangular cylinder crossing the free surface (see Figure attached). The main objective is to accurately predict the lift and drag. Assuming that the free surface dynamics would probably have a minor effect, I want to treat the free surface as a free-slip wall (rather than take an involved multiphase approach), thereby speeding up the simulation and avoiding convergence issues associated with the explicit modelling of the free surface. With this in mind, (1) What is the best practice for the boundary conditions here? Particularly, how can I impose zero pressure on the free surface in order to get accurate force prediction? (2) Is it possible to have a more efficient boundary conditions arrangement whereby the free surface dynamics could be resolved only over a small distance upstream and downstream of the cylinder? Note the fact that the inlet and outlet must be far away from the cylinder leads to a long narrow domain; so the free surface dynamics is absolutely of no interest over the major part of its span.
I would appreciate any comments.
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Dear Armin,
I do not know how did you conclude that the free surface dynamics would have a minor effect? If you want to avoid calculation of the free surface, consider a "double body approach" which is convenient in the measuring of ship viscous resistance in a free stream. In such an approach, the free surface becomes a symmetry plane. Best regards, Zdravko Virag.
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Hello everybody, I would like to simulate a three phase reactor and study its hydrodynamics. I would like to know which type of software is better? I have a good command of ANSYS Fluent and I am really convenient with it but i have no experience of working with OPEN FOAM or CFX ...
Do you recommend to use another one? please let me know your opinion.
Thanks
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Agreed with Hanane, ANSYS Fluent could be sufficient for your hydrodynamic simulation of your 3 phase reactor.
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It seems a 6dof UDF containing vehicle characteristics such as mass and moments of inertia can be used for specifying a boundary as reprentative of ocean vehicle. It is required to have hydrodynamic loads on every part of the vehicle though. Although, definition of each part is possible individually, definition of differnt boundaries in dynamic mesh as a unique body seems not acceptable by the solver. Does anyone face similar issue? I appreciate any help.
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I am afraid if this question has some issue in foundation, because if one wants to do so how is she going to manage mass COG and gyration radius?!
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I am looking for an approved method of hydrochemistry using only and quite simply the major hydrochemical elements, to find a possible hydrodynamic relationship between two superimposed aquifers.
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Interesting
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Residence time distribution for a tubular reactor follows semi empirical model, I want to know how can I use this RTD for predicting conversion of my system using mass balance equation for the tubular reactor( like axial dispersion model which consider reaction happening in the system as well as axial dispersion).
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Prajakta Gajbhiye, In my opinion, you cannot "incorperate" E(t) into any mass balance equation. However, you can try to modify the mass balance taking into account, apart from longitudinal dispersion, e.g. radial dispersion. The model can also be extended with the dynamics of the catalyst grain. But that's just a guess.
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I am using the same sea water as autoclaved as well as non-autoclaved after adding the nanoparticle. I am getting different Hydrodynamic size for the same nanoparticle.
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The possible variable charge of the seawater being tested can influence the hydrodynamic diameter of the nanoparticles.
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I am doing a time based study and at the initial hours , i am getting considerable high values of hydrodynamic size. The concentration is very low in the range of 3-10ppm and the nanoparticles are phosphorus based and the dispersing medium is the Deionised Water or MQ.
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Anurag Nath It depends on the nature of the material used. Also, if the concentration is too low, maybe the DLS is returning a false-positive result. To check that, please see the kcps value. It should be ideally more than 100 which means it has enough particles to scatter the light. It might also be possible that in the initial hours, the dispersion is not effective and what you are getting are the aggregates or clumps of nanoparticles and not actual single particles. For this please check the polydispersity index. It should ideally be less than 0.1. A value above 0.1 indicates the aggregation of particles and the presence of multiple species.
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I am about to start my research work related to hydrodynamic parameters' effects on froth flotation. Any suggestions both in terms of good research articles and experiences are more than welcome.
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Hydrodynamic can be divided into perfect mixing condition in mechanical flotation and plug flow condition in column flotation. This, usually relatively coarse particles are separated using mechanical flotation and fine particles are separated using column flotation.
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Sedimentology, Geology 
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May be it's too late but the answer is you need to create the chart so that one of the axes is of probability scale. You can do it by calculating z-scores for your cumulative distribution function, which is calculated by NORM.S.INV function in Excel. Put z scores on one axis and the random variable (whatever it is) on the other. The random variable's axis should be of logarithmic scale. That's how you obtain a log-probability chart.
In log-probability chart, they say that a straight line is formed if the random variable is log-normally distributed, and the standard deviation is equal to the the ratio of the values of random variables at CDF= 84.1% and 50%.
My question is where 84.1% comes from.
Also, I wrote an Excel VBA routine that uses Gradient algorithm and iteratively finds the mean and the standard deviation of a log-normally distributed sample once the random variable and corresponding cumulative probabilities are given. I need that 84.1% issue to be solved before I conclude my software and publish it.
Any help is appreciated.
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In the past, I mostly used WAMIT and NEMOH to compute the hydrodynamic coefficients of floating bodies. Now, due to licensing reasons, I had to switch to ANSYS Aqwa.
The added mass terms for the rotational degrees of freedom are expressed in N.m2/°. I would be expecting the units to be kg.m2. Is the added mass value returned by Aqwa as a function of circular wave frequency? Where in the guide can I find this information? I have checked, but unsuccessfully.
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As an alternative, just because you've mentioned licensing of WAMIT, you can try HAMS. It has a simple input format and writes out WAMIT type output files. It has also recently been made open source.
I've tested it on complex geometries against WAMIT with very dependable results and decided to switch to HAMS.
Here is the background info and access:
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I want to use standard sandpapers of different grit sizes to impart flow resistance to a surface. I am wondering how to convert the roughness of sandpaper to an equivalent sand-grain roughness. Is there any established correlation between grit size and equivalent sand-grain roughness?
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Hello everyone. I have a question about microfluidic-based methods. In this article, "Microflidic-Based Approaches in Targeted Cell/ParticleSeparation Based on Physical Properties: Fundamentalsand Applications", It has been mentioned that flow rate in methods with external force fields such as electric field, optical field,etc. are relatively low compared to fluid dynamics-based microfulidic separation methods such as Pinched Flow Fractionation, Deterministic Lateral Displacement, Inertial Method, etc.
My question is that why the flow rate in methods with externally applied forces is relatively low compared to fluid dynamics-based microfulidic separation methods?
Thank you for your time.
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External forces are usually proportional to the volume of the cell (or particle) and thus very small. In order to effectively separate cells you want them to be displaced by that force meaningfully. So the tiny force must be applied to the cells for enough long time. This means fluid velocity must be small. On the other hand in fluid dynamics-based methods separation is done by cells following local fluid patterns. These fluid patterns are stronger at higher flow rates, so separation is more effective with higher velocities.
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How to calculate the hydrodynamic forces with CFX ANSYS?
I need some tutorials or examples for hydrodynamic forces for offshore structures.
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It shows at 23 minutes how to calculate the hydrodynamic force.
You should use Function Calculator.
Function - Force
Location - Solid Surface where the force is calculated.
Kind regards
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I am trying to calculate some hydrodynamic properties from MD results. Part of the process in to calculate the transvers current correlation function which is formulated as C(q,t)=⟨J∗(0)J(t)⟩
. The issue is that this formula is regarded as canonical ensemble average in literature which should be calculated based on parameter $\Beta$. However my intuition is that this should be a form of autocorrelation or cross correlation of a rolling window. This is confusing to me and I would like to ask if anyone can provide me a pseudo code example for this calculation.
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I think your intuition is correct.
First of all, in equilibrium the ensembles should be equivalent so whether you have a canonical ensemble (fixed temperature) or a microcanonical ensemble (fixed energy, easier in MD) should not matter to zeroth order (apart from subtle finite size effects that you may worry about much later).
Then the average is, as you say, just an average over snapshots of the simulation. You need to be careful about the 'rolling window' because ideally you do not want to average over correlated snapshots so you should wait between snapshots until correlations have decayed. Which is a bit of a chicken and egg problem as you want to measure the correlations exactly to figure out how long they persist. So this probably needs some iterations to figure out good parameters. Or, alternatively, you do not reuse simulations at all and start from fresh, random initial conditions for every t=0.
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Dynamic light scattering method is used to determine the distribution of particles in solutions and suspensions.
This method uses the Stoke-Einstein equation.However, this formula uses a hydrodynamic diameter, which limits the use of this method to obtain the diameter and length of rod particles.
Do you suggest a method or coefficient for using this method to obtain the length and diameter of rod particles?
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DLS doesn't actually measure the size distribution of particles in suspension. It measures a diffusion coefficient which can be related to size by means of a mathematical engine with assumptions (Stokes-Einstein). An analogous situation exists with sedimentation where Stokes' Law is the mathematical engine used to convert terminal/settling velocity to size.
You've highlighted the conundrum in particle size measurement for irregular particles - more than one number is needed to correctly define an irregular particle, so there are 3 consequences:
  • Equivalent diameters are needed if we are to compare on the basis of a single number. See attached
  • Visualization is essential. This means electron microscopy
  • There is a shape distribution (or, more correctly, many shape distributions) as well as a size distribution
In certain circumstances we can derive fractal information from light scattering but this only provides a single number related to particle geometry. The theoretical history has many examples of work related to the flow and movement of cylindrical and other irregularly shaped particles. See the following webinar (registration needed):
The importance of the measurement of diffusion in 2-phase systems
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The user manuals for WAMIT and NEMOH are not quite clear, at least to my understanding. Is there any article/chapter/video description or web link, explaining the calculation of hydrodynamic coefficients including; Impulse Response Function (IRF) of the radiation force, damping coefficient, added mass etc. in context of wave energy conversion systems?
Copious of literature is using these, but rarely anyone gives detailed insight to it.
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From the theoretical side, you may need to refer to Marine Hydrodynamics by J.N. Newman, Sea loads on ship and offshore structures by O.M. Faltinsen for details on the explanation of hydrodynamic coefficient. The calculation of IRF can be found in many papers.
If you are asking how to use Nemoh or WAMIT to model a WEC system, the answer is they cannot be directly applied for WEC simulation. You must establish your hydrodynamic model in these code, and build up you own WEC model in other place.
The WAMIT manual has very rich explanantions on both theoretical introduction and how to use it. Also, there are plenty of examples. I would disagree with you that the manual is not clear. I would suggest you to take some time to read the manual.
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Dear Colleagues!
I ask you for cooperation in the implementation of the project
"Numerical calculation of the counterintuitive behavior of an underwater cylinder of infinite length under hydrodynamic loading"
Thank you in advance
Detailed description in attached file
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While no rotation is considered. Thank.
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It may be a binary black hole accretion disk or an AGN.
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Their study shows that B is around for 33 G for V404 Cygni
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As shown in the figure attached, the turbulent fluid flow around a floating (i.e. partially submerged) cylinder with a rectangular cross-section is to be modelled. Clearly, the forces and torques acting on the cylinder are oscillatory due to the vortex shedding phenomenon. The ultimate goal is to study the cylinder stability on the surface. The question is then how to characterize the fluid forces. Particularly, I have no idea if such a stability analysis could be based on the time-averaged forces or the instantaneous values may play a dominant role. How to characterize and quantify the significance of time-averaged values versus instantaneous values in this specific application?
I would appreciate any comment.
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Dear Prof. Armin Hajighasem Kashani, I suppose the following document could give some ideas on how the question posed by you might be addressed. Let's hope for the participation of a vortex specialist in fluid mechanics in this thread.
Instantaneous and time-averaged flow fields of multiple vortices in the tip region of a ducted propulsor by G. Oweis y S. Ceccio.
The mentioned authors emphasize, I unquote then, that "...an identification procedure is used to characterize multiple regions of compact vorticity in the flow fields as series of Gaussian vortices. Significant differences are found between the vortex properties from the time-averaged flow fields and the average vortex properties identified in the instantaneous flow fields....".
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studying hydrodynamic mechanism and sediment transport in coastal areas
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I want to know that is it possible to model the Bingham lubrication in Hydrodynamic module or thin fluid film module? or mabey I should use another module?
#nonnewtonian lubrication
#Comsol multiphysics
#lubrication
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In COSMOL it is possible. But the tutorials are not available. you need patience in convergence issue
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I'm trying to develop a code to solve the stream function-vorticity equations using the Finite Element Method in order to simulate a 2D incompressible flow problem. I was wondering what the pros and cons are, whether coupling a turbulence model is possible, whether formulating the boundary conditions may face difficulty and whether the evaluation of the pressure field is flawed possibly due to decoupling of the pressure variable from the governing equations. Note an accurate evaluation of the pressure field is particularly important for my case of study.
I very much appreciate helping me out.
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Dear
Tapan K. Sengupta
I have included the link mainly to show the importance of the vorticity equation in the actual meteorological applications.
Concerning the questions: “ If possible, then please explain how one can link vorticity equation with energy transfer. Is it via enstrophy? Wouldn't that be indirect based on some model in mind?”
We work with three theoretical models to describe energy transfer: 2-D turbulence, 3-D turbulence and QG (quasi-geostrophic) turbulence.
In 2-D turbulence we have conservation of both (kinetic) energy and enstrophy. According to Fjørtoft (1953) there is only transfer of energy from small to large scales. The opposite situation is observed in 3-D turbulence with the well known downscale direction of the energy transfer. In atmospheric large scale problems the quasi-geostrophic turbulence exhibits characteristics of both regimes because the vortex stretching mechanism is present in a QG vorticity equation. This fact is not always acknowledged and it often wrongly assumed that the large scale atmospheric turbulence is described by a 2-D model.
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I seek quick publication option for one review article written by me on tsunami hydrodynamics. I wish to find guidance from fellow researchers working on similar topics.
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1-Natural Hazards and Earth System Sciences (NHESS)
2- Pure and Applied Geophysics
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I made some UF membrane which had bigger mean pore diameter than that of hydrodynamic diameter of BSA. We know that if the mean pore dimeter of membrane is less than hydrodynamic diameter the protein can be separate by membrane otherwise no rejection will happen. The interesting result happened for me. Although the membrane has bigger pore size diameter than that of BSA hydrodynamic diameter , I have more rejection of BSA solution in performance . How I can explain this finding and discuss about the membrane?
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There are many factors that affect your final BSA rejection. I assume your membranes experience instantaneous fouling at the first seconds of BSA solution filtration. Therefore, the surface of the membranes would cover with BSA chains and create the cake layer that can play the role of a good barrier to prevent passing other BSA chains. Moreover, it is proven that, the big surface pores are susceptible for pore-clogging by BSA chains. In fact, the BSA chains can easily enter these pores and would be trapped. This process can be confirmed by very low BSA flux during BSA solution filtration. Therefore, membranes having larger surface pores can show higher BSA rejection.
Hope you the best!
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This is the link to the video(https://youtu.be/mNHp8iyyIjo)
He says, it is similar to Magnus effect and no coanda effect is involved. My thoughts are starting friction which rotates the disc + coanda effect + Magnus effect which keeps the ball in equilibrium position ?
This is my explanation to this phenomenon:
" Firstly, the ball starts to rotate because of the friction between water and ball surface which is just like a Tesla turbine. As the ball is being hit by the water on one side (not centre), it will push the ball to the other side because it comes in the way of the water. Once the ball starts rotating, the fluid following the surface don't adhere to the surface much longer and drift apart tangentially.
This is where the 'Magnus effect' kicks in. The magnus effect creates a force perpendicular to the jet direction. This force pushes back the ball to remain in contact with the jet on one side. So, the weight of the rotating ball is born by the jet completely.
The magnus force is proportional to the speed of rotation of the ball which is proportional to the velocity of the jet of water. So, the ball levitates in air as long as the jet discharge is kept constant."
Let me know what is the right reason for this phenomenon. Please correct if I'm wrong.
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Good Answer Tomas Melin
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In fluid dynamics, Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy. According to this principle, can we say that the density of a fluid (i.e. incompressible and flows at low Mach number) is lower compare to the hydrostatic density? Roughly speaking, is there a difference between the density of a fluid and static liquid (for the same matter)? If "yes", What is the method of fluid density (let say dynamic density) measurement? I am not an expert in this field. Thak you very much for your answers in advance.
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There is no difference between the density of the fluid in the flow and in a static condition. Density is the property of the fluids. If the fluid is compressible, it can change its density which depends on the pressure, temperature, etc. Both for simple compressible fluids, the density depends on the two other properties.
There are several assumptions for Bernoulli's equation as following:
1) the flow is steady
2) adiabatic and no shaft work
3) it is valid for a streamline
4) the fluid is inviscid
5) the flow is incompressible
We might modify Bernoulli's equation for other situations such as viscous and compressible flow with heat transfer and shaft work.
Thank you.
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I want to understand how can two spheres of different materials but the same hydrodynamic size and in the same solution have identical diffusion coefficients? Like shouldn't it also depend on the material the spheres are made of? Or at least the molecular weight, i.e., what if one of the spheres is hollow or a nanocomposite? Does none of this change D (as defined in the S-E eqn.) ?
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In addition to the very explicative answer by Prof. Alan F Rawle ,
I would like to add to this thread, the following link powered by Comsol.:
The link shortly gives a review about the D dependence on several physical variables for different physical situations. In the case of the stokes Einstein eq. will inversely depend on μ---the solvent viscosity.
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