Science topic

# Hydrodynamics - Science topic

The motion of fluids, especially non-compressible liquids, under the influence of internal and external forces.

Questions related to Hydrodynamics

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.

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 ?

The question is about hydrodynamics and coastal water quality modeling.

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?

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 Its origin is obscure, may lie in the early unpublished reports of Los Alamos, Livermore, or Sandia Laboratories.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.

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

Will the aggregation affect the DLS analysis?

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!

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.

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

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?

We intend to model hydrodynamics and currents in oceans and seashores.

Hi everybody. I need to calculate hydrodynamic coefficient of Remus 100 AUV. Can you help me and give its m-file code to me?

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?

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.

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

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.

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?

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.

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?

It is required for the stability analysis of bearing.

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

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?

Hydrodynamic force on floating wind turbine

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

**, P-M etc) to RAO. A complete example from formulation to numerical evaluation.**

*JONSWAP spectrum* 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.

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

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.

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.

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.

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).

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.

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.

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.

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.

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?

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.

How to calculate the hydrodynamic forces with CFX ANSYS?

I need some tutorials or examples for hydrodynamic forces for offshore structures.

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.

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?

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.

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

It may be a binary black hole accretion disk or an AGN.

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.

studying hydrodynamic mechanism and sediment transport in coastal areas

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

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.

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.

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?

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.

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.

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.) ?

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?

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.

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)

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.

What are the design parameters for the hydrodynamic cavitation reactor for biodiesel production?

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?

Many thanks in advance.

Rh is hydrodynamic radius which is obtained from DLS and Rg is the radius of gyration which is obtained from SLS.

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.

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.

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?

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.

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)

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.

Please help me.

Thanks so much.

What is the influence of catalyst as it related to oil-alcohol inter phase toward maximizing the yield of biodiesel production in hydrodynamic reactor?

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)?

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?

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?

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?

please tell me about the books and papers of this issue.

I would greatly appreciate any help/clarification in this regard. Thanks in advance.

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.

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.

I really appreciate your contribution.

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?

We are looking at the effects of offshore wind farms on the hydrodynamics and sediment transport to assess the changes that a wind farm may induce in the Yucatan shelf. Our preliminary studies show that there is barely any effect and we would like to compare to other studies. We found some academic work, but it may be interesting to see reports from existing wind farms. Thanks! -Christian