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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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.
For the kinetic description, a fluid can be considered a dense gas, since the liquids are not diluted intermolecular forces are much more complex, and according to several authors the Boltzman approach does not correspond.
In the case of hydrodynamics if the whole set of the equation is taken into account, still it describes an equilibrium process with fluid following Newton's laws since the main hydrodynamic equations follow in some sense Newton theory, of course, new equation appears such as the one for the entropy but all they can be treated by a more understood formalism, it is my guess.
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 ?
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.
Tecplot is a great tool to use in conjunction with EFDC. This is an EFDC model of a branched river system. http://dudleybenton.altervista.org/projects/Diffusers/export.gif
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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?
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.
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?
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?
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.
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 !
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.
Tejashwini Lnu Use electron microscopy or SAXS for the (metal/electron rich) core.
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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
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 current working on 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?
https://www.onshape.com/en/ CAD on cloud , very intuitive UI, also to store information
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We intend to model hydrodynamics and currents in oceans and seashores.
Hello Riza,
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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?
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?
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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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
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.
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?
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.
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?
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.
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.
Rajesh
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
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.
For simple PM, please check pages 6 to 8:
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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.
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
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.
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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To identify the most important fractional operator which is physically significant for the modeling of biological systems/processes (Viral dynamics, Fluid dynamics, Calcium dynamics and so on) to give better results.
Caputo fractional derivative, Caputo-Fabrizio, and Atangana-Baleanu with the application of Laplace approach...
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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.
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).
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.
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.
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.
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
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.
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?
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.
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.
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?
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.
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"
Detailed description in attached file
While no rotation is considered. Thank.
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It may be a binary black hole accretion disk or an AGN.
Thank you very much Sriram for the paper link you shared. The reported value of 33 G for V404 Cygni is significantly low. The paper itself mentions that the for other sources such as Cyg X-1, the range of magnetic field is ~10^5 to 10^7 G (My theoretical paper also suggests that this range of magnetic field can be acheived in a magnetically supported disc around a black hole. Ref: Sarkar B., Das S., 2018, JApA, 39, 3)
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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.
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
I suggest you try ERA5 data.
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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
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.
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.
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?
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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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.
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:
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.) ?
In addition to the very explicative answer by Prof. Alan F Rawle ,
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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I did experimental analysis of scale model ship to get RAO.(S.K chakrabarti text on hydrodynamics says,scaling up can be done.)
The question is if create model in software & prototype in software and run analysis,will the result be similar for both software simulation, will we get same RAO?
Usually it does not, although the solutions do not differ much.
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Hello,
I want to know whether or not the Zeta potential can give me an idea about the stirring degree in an electrochemical reactor, since i m dealing with a petroleum refinery wastewater.
The relation between these two parameters is what i m seeking indeed. During my research to chose the main parameters to study in the electrochemical reactor, the fact that i don't have an interesting idea about the stirring degree rang makes me wonder about finding the appropriate domain basing on the bulk proprieties to get an idea about the mass transfer in this later, and i ended up with the Zeta potential.
As you mentioned, i think the Zeta potential will be influenced by the hydrodynamic regime and so the mass transfer, thus, it will be interesting if we can express such relation.
Thank you for the clarification and your support.
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I am about to freeze dry carbon nano dots that have a hydrodynamic diameter profile of 2.5nm, I’m afraid they will dissipate with the water as it evaporates. Is this a legitimate concern and if so is there a safe way to do this or is my concern unfounded? (freeze drying is lyophilization)
Robert Micheal Miller Incidentally, is your middle name actually Micheal? Unusual if it is!
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We want to model hydrodynamics and currents in any sea and shallow water region. And also, we want to model rip currents and storm surges in shallow water.
I suggest SWAN+ADCIRC for storm surges
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What are the design parameters for the  hydrodynamic cavitation reactor for biodiesel production?
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Hello everyone,
I am researching three silver sulphide QDs that a collaborating group have synthesised - the cores are all the same size (around 3nm). One is coated in 2MPA, another coated in 2MPA and a targeting peptide, and the last one is conjugated to 2MPA and cetuximab on a PEG linker (probably 1 or 2 antibodies per QD). Hydrodynamic size from DLS suggests that the QD-2MPA is 4.2nm (which makes sense), the QD-2MPA-peptide is 4.8nm (still makes sense) but the QD-2MPA-cetuximab comes back as 5.9nm. On the presumption that an antibody is around 10nm, this must be an underestimate. The first two particles will be spherical, whereas two antibodies on a QD (or even one) will make a non-spherical object, that should be at least 10nm in size. However, I can't find a reference/paper online that explains why DLS might be underestimating the hydrodynamic diameter of a QD-antibody nanoconjugate. I presumed it was shape related, but cannot find published evidence confirming this. Can anyone explain this result, and ideally provide a reference?
Igree with Dr Peter Lawrence Zaki Labib
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Rh is hydrodynamic radius which is obtained from DLS and Rg is the radius of gyration which is obtained from SLS.
Rg/Rh = 1.6 consistent with an extended rod like shape in solution
Rg/Rh = 1.3 random coil structure
Rg/Rh = 0.77 for monodisperse compact spheres like globular proteins
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Hello CFD expertise!
I simulate hydrodynamic of single-phase water in a continuous stirred tank reactor with 45-degree pitch blades with the MRF approach in fluent. I recently noticed that the convergence of cfx is better than fluent in multiphase problems. but I don't know which software covers industrial needs for species transport and give insight into the efficiency of the leaching process.
Partially premixed is the name of a combustion modeling approach, not a mixture or multiphase flow approach.
I think species transport with an appropriately defined fluid mixture would be the approach to apply here.
I'm not aware of a limitation regarding the max. number of species in a fluid mixture. In combustion people sometimes track very large number of species, i.e. in the order of 40-50 species.
Regards,
Dr. Th. Frank.
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Does anyone know of any literatures where the hydrodynamic size range of cellulose nanocrystals and nanofibers would fall within? The literature I have seen indicates actual lengths and diameters, however I am going to be using a zetasizer and obviously this gives the hydrodynamic diameter so I am trying to see what size the transition from nanocrystal to nanofiber would occur.
The DLS method gives the average hydrodynamic size of nanoparticles. If you measure the size of a nanoparticle in the shape of a ball, then you get the exact diameter. If you measure the size of a nanoparticle in the shape of a tube, then you get the average size between the size of the diameter of the tube and the length of the tube. The average fiber diameter you will not get. You need to use an optical microscope.
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I want to do a numerical study of ship propeller. I can make a random 3D propeller model using CAD softwares. But is there any recomended propeller models or detail information of any propeller geometry - blade shapes, angles, dimensions etc?
AS I know the propeller blades are designed according to the NACA profiles. every cross section pf the blade is a NACA profile. however, the size of the profiles are different.
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During my current study I figure out that hydrodynamic co-efficient value decrease with increase in Froude number. The results also matched with the Cui et al 2015 and Faug 2015 reference lines. However, I am intended to explore the insights of the trends. Anyone please illustrate! The results are enclosed with the query for reference.
well it is naturak,increase in Froude number means increase in hydodynamic resistance or in other word uncrease in frictional forces compared to inertial forces...so increase in resstance will reduce impct force from debris on structures in the flow.
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I am trying to calibrate the focal volume of FCS setup by using Alexa 488 dye. The experiments is being carried out at room temperature (25 degrees). I have to take the diffusion coefficient of Alexa to find out the volume. But in some papers it is 465 and in some literature values it is taken as 220. If I take the hydrodynamic radius of Alexa to be 5.7 A and calculate it then the value is 430.
Now I am confused as to which value to actually consider.
Any help is appreciated.
(I have 488nm laser, hence using Alexa 488)
Thanks a lot Marcia Levitus and
Irem Nasir
for the information.
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Hello, I tried to simulate a spouted fluidized bed with a draft tube by use of the following article information; but it did not work properly.
Thanks so much.
Hi
Depending on how much volume of particles in your reactor, there are two general methods for simulating the gas-solid system as:
1. If the total volume of solid particles is less than about 10% (number of particles is not too big), you can try an approach named as Eulerian-Lagrangian (EL) where the gas phase is considered as continuous phase, and the solid particles are calculated by discrete phase model (DPM). You can choose several models among EL approach such two-way turbulence coupling DPM, discrete element method (DEM), etc.
2. If the total volume of solid particle is higher than 10%, the EL approach is not efficiency. You can try the Eulerian-Eulerian (EE) approach, also called two-fluid model (TFM). In EL approach, both gas and solid are considered as continuous phases. Note that the primary phase should be gas and secondary phase is solid. The dispersed phase should be checked in turbulence model. In EE approach, the drag model is one of the most important for getting good prediction. To my experience, the Gidaspow drag model is suitable to medium fluidized velocity (<10u_mf), while the EMMS drag model is suitable for fast fluidization.
Good luck,
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What is the influence of catalyst as it related to oil-alcohol inter phase toward maximizing the yield of biodiesel production in hydrodynamic reactor?
Since the reactants mixture have interaction in hydrodynamic reactor, catalyst definitely increase the reaction rate...
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Compact astro-objects (like white dwarfs and neutron stars) are non-Newtonian in the sense that they are governed by relativistic effects. Under such circumstances, in the hydrodynamic approach to study them, is it possible to take gravitational Poisson equation (Newtonian gravity)?
Dear Sayanti Dasgupta,
The gravitational Poisson equation (Newtonian gravity) of the hydrodynamic approach cannot be used well in the study of compact astro-objects… In case of your example ‘white dwarfs and neutron stars’ it can be used because the mentioned objects by you are not totally compact objects in reality… I hope that the next totally easily understandable theory of gravity will help you:
Regards,
Laszlo
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I have this PM from @Tahani Aldhafeeri
dear Sir
what is the difference between Peak , z avarage , and hydrodynamic diameter in DLS results??
which one can I use if i want to have the diameter of the nanparticles?
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I know that a way to establish the lubrication regime in a pin on disk test is by measure the resistance between the pin and the disc. Some papers say that if the resistance is of 2 ohm, the lubrication regime is hydrodynamic. Can some of you explain me this value, please?
No Sir.
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Dear all,
I want to know about the hydrodynamic equations for junction of pipes with non-uniform cross section.
how about the Hagen-poisueille equation for these type of junctions?
how could derive the friction coefficient in this junctions?
I would greatly appreciate any help/clarification in this regard. Thanks in advance.
Thankful dear, Sa Ja
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I am searching a best method to measure water surface level in a experimental flume(channel) with some obstacles which is located in the centerline of it.
Here is some interesting literature to consult with...
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I am about to do a research in one of Iran's dams , but i need to modify W2 for my project. how can I modify this model?! Any suggestions will do.
@ Saber Aradpour, You can visit http://www.ce.pdx.edu/w2/
The source code is available in online
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Hi all, i'm oppening a discussion related to lubrication during cold rolling process and its effects on surface quality.
Firstly, i would like to present a defect i'm studying. It's like this, (image credits shall be given to scientific.net).
I suppose that more than a metalic particle falling on strip surface its also related to friction condiction. Anyone else has any comentary about this?