RheoCube .18 latest features

RheoCube .18 latest features

13 October 2021

The latest release notes from RheoCube highlight several new features for users. There are improvements for everything from basic user functionality to better modeling features such as surfactant physics, an experimental feature in microscale, and some touch ups in Data Visualization and Analysis. Let’s take a look at RheoCube Version 0.18.

RheoCube 

Improvements to RheoCube overall target a better user experience with improved error messages and new tabs. 

In Fig. 1, you can see that the left panel has been organized into Specification, Process, and Preview (where applicable). The  Process tab allows you to control the processing of the object (previously handled within the Specification tab), and will display messages from the simulation engine. 

Fig. 1 Information about an error that caused the simulation to fail

Moving on, now we have simplified specifications for homogenous States by hiding the domains and the button to create additional domains in the specification form and pre-filling the volume fractions with the values from Formulation and disabling the inputs. (Check Fig. 2)

(Fig. 2. Example of a simplified State form)

Models

Improved Surfactant Physics

Surfactant physics have been largely improved. Strong fluid interfaces are nanoscale in width, which are often smaller than the size of SPH blobs (the basic volume element used in the mesoscale SPH model). We use the local mixing thermodynamics to infer the presence of sharp interfaces and feed this into the surfactant physics model. In RheoCube 0.18, we enhanced the interface detection in the cases where interfaces are strongly curved. For example, you can see this in colloidal droplets. 

Mesoscale Ionics

Who’s up for some experimentation? These next few features described are experimental. The behavior of these new features is expected to change as refinements are made during the next release cycle(s).

Dissolved Salts

Monovalent salt (e.g. sodium chloride, NaCl) can now be included when creating a fluid by specifying that fluid’s dissolved monovalent salt concentration. The salt undergoes thermodynamic transport during the simulation. The presence of salt in the mesoscale simulation leads to a concentration-dependent screening of electrostatic interactions (higher salt concentration leads to weakening of electrostatic interactions). The relative permittivity also has to be added to the Fluid. Check Fig. 3 below.

(Fig. 3)

Electrostatics-based interactions between particles

One common technique for stabilizing particulate suspensions is through electrostatic interactions. Particles with the appropriate surface chemistry develop surface charges in certain solvents. Since like particles develop like charges, particles are repelled from each other. When the repulsion is sufficiently strong to overcome the innate tendency for aggregation, the outcome is a stable suspension. In the movies below we can see 2 suspensions under shear. On the left, without electrostatics, we see that clusters are formed when particles come in contact. On the right, with electrostatics turned on, we see that no clusters are formed.

Interactions between particles carrying surface charges were developed based on Gouy-Chapman theory. The level of charge is controlled by a user-specified zeta potential, which can often be determined experimentally. The electrostatic interaction is screened by the presence of salt. The zeta potential (Fig 4.) for a fluid-particle pair can be defined in Composition under Fluid-Particle interactions and has units of volts. The electrostatics model is enabled by checking the Enable electrostatic interactions toggle in Experiment. It requires all Fluids in the experiment to have a Relative permittivity.

(Fig. 4. Zeta potential for fluid-particle pairs in a Composition)

Microscale Updates 

Random initialization procedure

The microscale simulation is now initialized in a random configuration, as opposed to the previous lattice configuration. The new initialization allows for a more efficient route to obtaining a properly equilibrated simulation.

Non-equilibrium shear simulations (Experimental feature)

Non-zero shear rates can now be specified in the experiment card for microscale simulations. This will trigger a sheared non-equilibrium molecular dynamics simulation, where the equilibrium “Production” stage of the simulation is replaced with a non-equilibrium “Shear” stage. Other settings such as run time are kept the same.

Data Visualization and Analysis

Experiment merging

Two or more mesoscale experiments can now be merged if the latter is derived from the former using the ‘state from snapshot‘ feature. Merged experiments are seamlessly combined and can be treated as a singular experiment in all other widgets, except for the ‘versus parameter‘ tab of the Material Properties widget and the Oscillatory Shear Viscosity widget.

Microscale modeling clustering analysis

Micro data is now accepted by the clustering widget, giving the ability to cluster droplet or micelle structures and get information on size distributions, cluster shapes and spatial distribution.

(Fig 5. Visualization of clusters based on molecule id (left), a histogram of cluster sizes (middle) and a distribution of distances between cluster pairs (right)

Per-component isosurface creation

We’ve added the ability to quickly generate isosurfaces for any component in the simulation, as well as the ability to quickly hide fluid and/or particle blobs.

(Fig. 6 A simulation preview using isosurfaces for each component)

Volume fraction for color mixing

The color mixing of blobs in the visualization is now based on the volume fractions of the different components, instead of their mass fractions.

Fixer Uppers and Solved Issues

Data Visualization and Analysis sessions leading to 400 error: Opening a session might lead to a page with a 400 error. This can be solved by clearing the site data in browser settings or working in an incognito browser. If you need assistance with this please contact your Scientific Consultant.

Applying widget presets during calculation may cause issues: Applying a previously saved widget preset while a widget is performing a calculation may result in an error. To prevent this, only apply a preset when the widget is performing a calculation. Widgets that are stuck can be refreshed from the preset menu.

Resolved: For now, we’ve resolved an issue where the number of periods in the oscillatory shear analysis widget is not automatically updated. When a running oscillatory shear experiment is loaded in the oscillatory shear analysis widget, periods that are completed afterwards are not automatically updated. To get the correct number of periods, deselect and select the experiment.

Again, for users who can still use some help troubleshooting, please contact your scientific consultant. 

Find out more

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