Great video! But I can not see a difference in the boundary condition pictures between lower-constrained Unit Cell (7:20) and Fully Constrained Unit Cell (8:05).
Hello, thanks for the comment. Yes, your comment (i.e. the schematics I showed for the two types of RVEs) is the same but the idea behind them is actually different. The Fully Constrained unit cell has the upper and lower face sheets attached to the lattices and then as a result will constraint the behaviour of the lattice rigidly. For the lower-constrained, the idea is tha the lower face sheet will be there (holding the base like a built-in support system), while the top sheet allows for degrees of freedom displacement in one possible axis. I might not have reflected the ideas in my mind properly so thanks for the comment. I hope the clarification helps.
Thank you a lot for this channel. All videos are really helpful and you shed light to many crucial elements ( no pun indented ) that help us understand to a deeper level of the theory and the simulation itself. Wondering if you could do a video about the Interfacial thermal resistance of an 3D RVE ( single inclusion or even more ).
Dear Faidwn, I am glad you like them! Thanks for your interest in the channel. I will say I need to research into the question of your query and consider it for a future video. Do you have a specific paper that you are interested in so that I can take inspiration from it for the interfacial thermal resistance problem
@@MichaelOkereke thank you for your quick reply. I like the approach of this paper. onlinelibrary.wiley.com/doi/epdf/10.1002/pc.22859 Here they design the inclusion with an interphase, so with the use of the interphase they can model the not perfect contact and they set the thermal conductivity of the interphase with a value as low as 10e-13 which lowers the overall thermal performance of the RVE to the levels of the experimental results. thank you in advance.
Hi Michael! Thanks for your videos about the lattice structure. It's my research direction. And as I said before, I am very want to see a video about using PBC on lattice structure, even simple rectangular lattice. I would appreciate it very much if you are interested in doing this!
Thank you for this video. I have a question : the structure have been meshed using "beam" or "3D stress" elements ? wich type of elements is the most relevent for this kind of structure?
Good question. I used the 3D stress elements for this. Some people do use a beam element but that would treat the legs as struts but here I treated it as a full element hence able to generate all the terms of a stress tensor. So, yes, use 3D stress element, its more holistic but a beam element for some structural scale problems, with larger virtual domains will be okay. The use of a beam element will lead to a computationally efficient/less expensive solution whilst the 3d stress elements are fine for really small-scale (micromechanical) RVE based analysis.
Hi Dr. Okereke, Your tutorials have helped me immensely. I have one quick question regarding your loading step at @27:04 . Within the options to edit a step, there is an option to select NL geom. Is this ever applicable for lattices (particularly with very high levels of strains), or should this option be avoided? I was reading conflicting answers on the internet and was curious about your perspective. Thank you!
Hello, thanks for your comment and happy to hear these videos help you. NLGEOM means 'geometric nonlinearity' and it is a feature within ABAQUS allows the simulation to progress where the original geometry has changed significantly and becomes quite nonlinear. For example, the edge of a square model, following large deformation - temperature or displacement - may take a somewhat nonlinear profile. For the simulation to complete without aborting, the flag NLGEOM has to be set to on to make that happen. So back to your question, if you have high levels of strains (i.e. you expect this to be the case), then NLGEOM should be set to 'ON'. You can have large strains and the deformation remains still linear, then NLGEOM should be set to 'OFF'. However, in most cases where large plastic deformation exists, it is best to set this flag to 'ON'. In ABAQUS, by default, if you are using ABAQUS/Explicit solver, then it sets this term by default to 'ON' and this is by default the nature of how Explicit solver deals with solutions - it tries its best to find a solution even though the solution step might take a nonlinear time step sequence - hence it makes sense for the 'ON' status to be set. In ABAQUS/Standard, you have the option to set it to ON or OFF as you desire. It sounds in your case, you are working with the STandard Solver and hence this choice is yours to make. Hope the explanations help?
@@MichaelOkereke Thank you for your prompt reply and explaining this so clearly! For some reason, the simulation let me select NLgeom on or off, even for an explicit simulation (what I hope to use). I am also new to this, so I could be making a mistake or misreading something, but now I better understand how to configure this, thanks to your explanation. Also, one additional question if you have the time. Is there a good way to enable your simulation to detect itself during the compression and not merge through? I followed some of your tutorials but increased the strain level and noticed that the body would pass through itself rather than be altered by colliding with itself. Is it some surface-to-surface contact setting? Thank you!
Hello,I am not sure about the on-and-off issue. I think you can still switch it off in ABAQUS Explicit but by default it is always turned on. I think you will need to have a true reason why it should be off and you need to do a parametric study for this case, to quantify the effect of such choice, before choosing to turn it off. On your additional question, it might be a surface-to-surface contact requirement. However, as you stated here, at large strains, it seems the body is merging/cutting into itself. It might not truly be doing so. It is just not able to resolve the right deformation profile at those large strains. If it was truly cutting into itself (mechanically), then you will see a force transfer at the contacting surfaces. What I think is that due to poor meshing, the deformation is not as smooth as required and that amorphous/bad deformation profile will overcompensate looking like it cuts into the body: this is just a suggestion but it might not be the reason. Good luck.
Thank you sir for this video. Would you please do the same modelling but with two layers of different material in a BCC lattice structure. I want to learn simulation of biphasic bcc lattice and assigning contact between two layers of different materials to calculate effective modulus of composite unit cell. Kindly make video illustrating above problem it will be very helpful to understand simulation of composite lattice in Abaqus.
Hello @Ankit Jain, thanks for your interest in the channel. I will need some information on what you mean here by biphasic BCC. Do you mean having two BCCs with the upper layer made say from ABS and a lower-layer BCC made from say PLA. With that, then we can undertake simulation of say compressive response. What happens at the interface between them? Are they bonded together, following say a 3D printing implementation? Or do you introduce an interphase plate to separate them? Why do you expect a contact to be in place for such biphasic system? If you have any publication or reference material about this, then share with me and I will consider making a relevant video. It does sound an interesting project to investigate.
Hello sir, finally I got to see the analysis of lattice structures. Thanks for putting effort in making this video sir. I have a question, Can you please compare the experimental results with numerical results? Or can you give me your suggestions here!!. Thank you
@Santosh b, what I will say is that you just need to get some experiments, of probably a unit cell of the structure (and if not possible) a few stacks of lattice unit cell. Then, you can manufacture it (say by 3D printing), and test it. Using same model, you can run a simulation say compression and then compare the results.
Sir, I am Research scholar working on 3D printed cellular structure (Re-entrant honeycomb). I have performed the experiments and trying to compare the results with Ansys (Static structural-Nonlinear) But I am not able to get the matching results in Ansys.
HELLO SIR. YOUR LESSON IS SO HELPFULLY TO US COULD YOU PLEASE PREPARE A SUBJECT ON HOW TO IMPLEMENT NOVEL ASYMPTOTIC HOMOGENIZATION AND MAKE COMPARISON WITH RVE AND TRADITIONAL AH.... THANK YOU VERY MUCH FOR THE LESSON.
Hi, thank you for the video! please I have a question Dr Michael, how we can calculate the effective young modulus and porosity of a material using the lattice structure?
@@MichaelOkereke Please If i duplicate the unit cell and make top and down plate, to determine the effective young modulus and plot the stress-strain value, what loading settings should be for the tensile test please Dr Michael?
Thank you for all your videos. It will be very helpful if you upload video on simulation of BCC unit cell lattice made up of two material (composite bcc unit cell). I mean BCC lattice struts made up of two concentric cylinders of different materials. For illustration related paper is already sent to your email
Hello @gaurav jain, thanks for your interest in the channel. I am not sure which email you used but I didn't get it. Please check again and resend or put here the title and doi of the paper.
Very interesting video but really I get confused between unit cell model and RVE model, could you tell me the difference between them. Thanks in advance
Hello John, thanks for your interest in the channel. Indeed, I understand the confusion. But here is it: 1. RVE is a representative geometric domain that can be used to substitute the whole structure. It should show the same mechanics as the whole structure. As a result, you need to run the models to show a response of the RVE that is comparable to the big structure. 2. Unit cell on the other hand is a repeating geometric sub-domain of the structure. It is always a sub-domain. It is used when you find a structure has a lot of repeating segments and you want to isolate the smallest sub-section that can be used as a unit cell. Unit cells can be RVEs but RVEs cannot be unit cells. RVEs are used in many micromechanical analysis and it is the common virtual domain. However, on the other hand, unit cells tend to be used when you have structures that you want to isolate a sub-domain of it. It would work mainly when you have structures with homogeneous distribution of microstructural components or crystalline systems. If you cannot always have a repeating microstructural representation, then you should not use a unit cell. Instead RVEs are preferred. I hope this explanation makes sense.
Hello @Abhinav Siliveru, I am sure this is possible. We can import an ABAQUS *.inp file directly into ABAQUS CAE environment and use it for our modelling. The only problem with such imported *.inp files are that they do not allow for modifications of certain of the geometric and mesh properties (once imported). The best bet is always to get the original ABAQUS CAE file and make your modelling from that but from your question, it does sound you only have the volume mesh. You can use still it but you do need to recognize the limitations especially the geometric and mesh changes limitations. It does not matter what study style you go on to do next (explicit, dynamic, implicit), it should still work. The volume mesh file is simply a geometric file which you start off with, and once imported, you can then start applying the necessary boundary conditions, step files, material models, etc and then progress to run the simulation. Let me know if this makes sense and you have further questions. Good luck with this.
Hello @209 Nitin Joshee, I have looked into this in the past and has not got around to doing it. It is something I am thinking about doing when I get the time. Watch this space please.
Thankyou for the video sir! I exactly tried the same... When I try to apply the mesh, the abaqus software is closing automatically. I'm using a cracked version and is that the reason??
Hello @Sushanth, I am not sure why you are having this problem. It could be due to the version of ABAQUS you have but I cannot say definitely it is. Good luck with the work.
Thank you sir for this video. Would you please do the same modelling but with a composite material such as IM7/977-2 or maybe running a buckling test with a grid stiffened cylindrical shell again with a composite material. Actually, my main problem is with assigning the composite material to lattice structure beams.
Thanks Sina for your comment. Please can you share with me any publication that captures what you are suggesting here. I am trying to understand it. I will then review and see if I can make a video about it. I have plans on making videos about lattice composites so please watch out for those videos when they become available.
@@MichaelOkereke Thank you so much for responding. I already sent an email including the related article for you sir. The article is "Optimization for buckling loads of grid stiffened composite panels" by Wodesenbet et al, published in composite structure in the year 2003. I will look forward to your next amazing videos.
I saw the paper @sina academy buts it's such an old paper I wondered if you didn't want to find something more recent. Some of those ideas in the paper are a bit obsolete.
@@MichaelOkereke Thanks again sir, would you mind checking another article written by Wang and Abdalla in 2015 named "Global and local buckling analysis of grid-stiffened composite panels". I am mostly concerned with the buckling of stiffened shells, not rectangular pannels. Also, there are more relevant papers by the same author.
@@MichaelOkereke Actually, I just remembered you have been reviewed an article by an Italian researcher named Vasiliev. He has been done some researches on the subject with his Co-worker Mr Tottaro.
Hello Amit, its a variable quantity depending on the method of manufacture and composition. Typically its about 0.4 being a polymer but thats just a start. I suggest for a heterogeneous system composition you csn use the approach of my recent video on Numerical determination of Poisson Ratio to obtain it.
Hello @irem, it is not easy to mesh this BCC structure with hexahedral (Hex) meshes, due mainly to the complexity of the central joints of the trusses. There could be other ways of meshing with hex elements but that means having to partition the domain a multiple number of times.
thank you very much, this is a subject I have been working on for a while. ( Un grand MERCI !!!)
Hello Ahmed, I am glad you find the videos helpful. Merci!
Thank you so much, Dr. Michael Okereke.
Since it is much helpful, could you please keep it up. Thanks.
I will try to do so Solomon. Thanks for your interest in the videos.
Hello . Thank you very much for your videos. Please also post a video about the implementation of periodic boundary conditions for 3D lattices.
Yes indeed, this is for the future.
Great video!
But I can not see a difference in the boundary condition pictures between lower-constrained Unit Cell (7:20) and Fully Constrained Unit Cell (8:05).
Hello, thanks for the comment. Yes, your comment (i.e. the schematics I showed for the two types of RVEs) is the same but the idea behind them is actually different. The Fully Constrained unit cell has the upper and lower face sheets attached to the lattices and then as a result will constraint the behaviour of the lattice rigidly. For the lower-constrained, the idea is tha the lower face sheet will be there (holding the base like a built-in support system), while the top sheet allows for degrees of freedom displacement in one possible axis.
I might not have reflected the ideas in my mind properly so thanks for the comment. I hope the clarification helps.
Thank you a lot for this channel. All videos are really helpful and you shed light to many crucial elements ( no pun indented ) that help us understand to a deeper level of the theory and the simulation itself. Wondering if you could do a video about the Interfacial thermal resistance of an 3D RVE ( single inclusion or even more ).
Dear Faidwn, I am glad you like them! Thanks for your interest in the channel. I will say I need to research into the question of your query and consider it for a future video. Do you have a specific paper that you are interested in so that I can take inspiration from it for the interfacial thermal resistance problem
@@MichaelOkereke thank you for your quick reply. I like the approach of this paper. onlinelibrary.wiley.com/doi/epdf/10.1002/pc.22859 Here they design the inclusion with an interphase, so with the use of the interphase they can model the not perfect contact and they set the thermal conductivity of the interphase with a value as low as 10e-13 which lowers the overall thermal performance of the RVE to the levels of the experimental results. thank you in advance.
Okay Faidwn, I will look at the paper and consider if I can make a video to illustrate the points and support your work. Take care.
@@MichaelOkereke thank you for your reply and for even considering making a video.
Hi Michael! Thanks for your videos about the lattice structure. It's my research direction. And as I said before, I am very want to see a video about using PBC on lattice structure, even simple rectangular lattice. I would appreciate it very much if you are interested in doing this!
Great suggestion Jerry! In future, once I show how PBCs can be implemented on non-periodic meshes, I believe we can then attend to this question.
Thank you for this video. I have a question : the structure have been meshed using "beam" or "3D stress" elements ? wich type of elements is the most relevent for this kind of structure?
Good question. I used the 3D stress elements for this. Some people do use a beam element but that would treat the legs as struts but here I treated it as a full element hence able to generate all the terms of a stress tensor. So, yes, use 3D stress element, its more holistic but a beam element for some structural scale problems, with larger virtual domains will be okay. The use of a beam element will lead to a computationally efficient/less expensive solution whilst the 3d stress elements are fine for really small-scale (micromechanical) RVE based analysis.
Hi Dr. Okereke,
Your tutorials have helped me immensely. I have one quick question regarding your loading step at @27:04 . Within the options to edit a step, there is an option to select NL geom. Is this ever applicable for lattices (particularly with very high levels of strains), or should this option be avoided? I was reading conflicting answers on the internet and was curious about your perspective.
Thank you!
Hello, thanks for your comment and happy to hear these videos help you. NLGEOM means 'geometric nonlinearity' and it is a feature within ABAQUS allows the simulation to progress where the original geometry has changed significantly and becomes quite nonlinear. For example, the edge of a square model, following large deformation - temperature or displacement - may take a somewhat nonlinear profile. For the simulation to complete without aborting, the flag NLGEOM has to be set to on to make that happen.
So back to your question, if you have high levels of strains (i.e. you expect this to be the case), then NLGEOM should be set to 'ON'. You can have large strains and the deformation remains still linear, then NLGEOM should be set to 'OFF'. However, in most cases where large plastic deformation exists, it is best to set this flag to 'ON'.
In ABAQUS, by default, if you are using ABAQUS/Explicit solver, then it sets this term by default to 'ON' and this is by default the nature of how Explicit solver deals with solutions - it tries its best to find a solution even though the solution step might take a nonlinear time step sequence - hence it makes sense for the 'ON' status to be set.
In ABAQUS/Standard, you have the option to set it to ON or OFF as you desire. It sounds in your case, you are working with the STandard Solver and hence this choice is yours to make.
Hope the explanations help?
@@MichaelOkereke Thank you for your prompt reply and explaining this so clearly! For some reason, the simulation let me select NLgeom on or off, even for an explicit simulation (what I hope to use). I am also new to this, so I could be making a mistake or misreading something, but now I better understand how to configure this, thanks to your explanation.
Also, one additional question if you have the time. Is there a good way to enable your simulation to detect itself during the compression and not merge through? I followed some of your tutorials but increased the strain level and noticed that the body would pass through itself rather than be altered by colliding with itself. Is it some surface-to-surface contact setting?
Thank you!
Hello,I am not sure about the on-and-off issue. I think you can still switch it off in ABAQUS Explicit but by default it is always turned on. I think you will need to have a true reason why it should be off and you need to do a parametric study for this case, to quantify the effect of such choice, before choosing to turn it off.
On your additional question, it might be a surface-to-surface contact requirement. However, as you stated here, at large strains, it seems the body is merging/cutting into itself. It might not truly be doing so. It is just not able to resolve the right deformation profile at those large strains.
If it was truly cutting into itself (mechanically), then you will see a force transfer at the contacting surfaces. What I think is that due to poor meshing, the deformation is not as smooth as required and that amorphous/bad deformation profile will overcompensate looking like it cuts into the body: this is just a suggestion but it might not be the reason.
Good luck.
Thank you sir for this video. Would you please do the same modelling but with two layers of different material in a BCC lattice structure. I want to learn simulation of biphasic bcc lattice and assigning contact between two layers of different materials to calculate effective modulus of composite unit cell. Kindly make video illustrating above problem it will be very helpful to understand simulation of composite lattice in Abaqus.
Hello @Ankit Jain, thanks for your interest in the channel. I will need some information on what you mean here by biphasic BCC. Do you mean having two BCCs with the upper layer made say from ABS and a lower-layer BCC made from say PLA. With that, then we can undertake simulation of say compressive response. What happens at the interface between them? Are they bonded together, following say a 3D printing implementation? Or do you introduce an interphase plate to separate them? Why do you expect a contact to be in place for such biphasic system? If you have any publication or reference material about this, then share with me and I will consider making a relevant video. It does sound an interesting project to investigate.
Hello sir, finally I got to see the analysis of lattice structures. Thanks for putting effort in making this video sir. I have a question, Can you please compare the experimental results with numerical results? Or can you give me your suggestions here!!. Thank you
@Santosh b, what I will say is that you just need to get some experiments, of probably a unit cell of the structure (and if not possible) a few stacks of lattice unit cell. Then, you can manufacture it (say by 3D printing), and test it. Using same model, you can run a simulation say compression and then compare the results.
Sir, I am Research scholar working on 3D printed cellular structure (Re-entrant honeycomb). I have performed the experiments and trying to compare the results with Ansys (Static structural-Nonlinear) But I am not able to get the matching results in Ansys.
HELLO SIR. YOUR LESSON IS SO HELPFULLY TO US COULD YOU PLEASE PREPARE A SUBJECT ON HOW TO IMPLEMENT NOVEL ASYMPTOTIC HOMOGENIZATION AND MAKE COMPARISON WITH RVE AND TRADITIONAL AH.... THANK YOU VERY MUCH FOR THE LESSON.
Hello @Fikirini Jr, thanks for this. It is a good suggestion but I am not looking to make this type of video now. Thank you.
Thanks a lot. it really amazing
Thanks too Samer.
Hi, thank you for the video! please I have a question Dr Michael, how we can calculate the effective young modulus and porosity of a material using the lattice structure?
Hi @Bika Giro, the video did not cover the modulus and porosities, maybe that could be in a future video.
@@MichaelOkereke Thanks
@@MichaelOkereke Please If i duplicate the unit cell and make top and down plate, to determine the effective young modulus and plot the stress-strain value, what loading settings should be for the tensile test please Dr Michael?
Thank you for all your videos. It will be very helpful if you upload video on simulation of BCC unit cell lattice made up of two material (composite bcc unit cell). I mean BCC lattice struts made up of two concentric cylinders of different materials. For illustration related paper is already sent to your email
Hello @gaurav jain, thanks for your interest in the channel. I am not sure which email you used but I didn't get it. Please check again and resend or put here the title and doi of the paper.
@@MichaelOkereke Sir please share your email id
Very interesting video but really I get confused between unit cell model and RVE model, could you tell me the difference between them. Thanks in advance
Hello John, thanks for your interest in the channel. Indeed, I understand the confusion. But here is it:
1. RVE is a representative geometric domain that can be used to substitute the whole structure. It should show the same mechanics as the whole structure. As a result, you need to run the models to show a response of the RVE that is comparable to the big structure.
2. Unit cell on the other hand is a repeating geometric sub-domain of the structure. It is always a sub-domain. It is used when you find a structure has a lot of repeating segments and you want to isolate the smallest sub-section that can be used as a unit cell.
Unit cells can be RVEs but RVEs cannot be unit cells. RVEs are used in many micromechanical analysis and it is the common virtual domain. However, on the other hand, unit cells tend to be used when you have structures that you want to isolate a sub-domain of it. It would work mainly when you have structures with homogeneous distribution of microstructural components or crystalline systems. If you cannot always have a repeating microstructural representation, then you should not use a unit cell. Instead RVEs are preferred. I hope this explanation makes sense.
Really thanks a lot Dr. Michael for your kind detailed clear explanations
Can we import .inp (Volume mesh file) to do tensile testing? Dynamic explicit study. As Iam facing this problem past a month.
Hello @Abhinav Siliveru, I am sure this is possible. We can import an ABAQUS *.inp file directly into ABAQUS CAE environment and use it for our modelling. The only problem with such imported *.inp files are that they do not allow for modifications of certain of the geometric and mesh properties (once imported). The best bet is always to get the original ABAQUS CAE file and make your modelling from that but from your question, it does sound you only have the volume mesh. You can use still it but you do need to recognize the limitations especially the geometric and mesh changes limitations. It does not matter what study style you go on to do next (explicit, dynamic, implicit), it should still work. The volume mesh file is simply a geometric file which you start off with, and once imported, you can then start applying the necessary boundary conditions, step files, material models, etc and then progress to run the simulation. Let me know if this makes sense and you have further questions. Good luck with this.
@@MichaelOkereke Thanks for replying. I will try to replicate your input. If any doughts, I will come again.
Hi sir I would like to know how to design unit cell. Please make a video on that.
Using TPMS
Hello @209 Nitin Joshee, I have looked into this in the past and has not got around to doing it. It is something I am thinking about doing when I get the time. Watch this space please.
Thankyou for the video sir! I exactly tried the same... When I try to apply the mesh, the abaqus software is closing automatically. I'm using a cracked version and is that the reason??
Hello @Sushanth, I am not sure why you are having this problem. It could be due to the version of ABAQUS you have but I cannot say definitely it is. Good luck with the work.
@@MichaelOkereke thankyou sir 🙌
Thank you sir for this video. Would you please do the same modelling but with a composite material such as IM7/977-2 or maybe running a buckling test with a grid stiffened cylindrical shell again with a composite material. Actually, my main problem is with assigning the composite material to lattice structure beams.
Thanks Sina for your comment. Please can you share with me any publication that captures what you are suggesting here. I am trying to understand it. I will then review and see if I can make a video about it. I have plans on making videos about lattice composites so please watch out for those videos when they become available.
@@MichaelOkereke Thank you so much for responding. I already sent an email including the related article for you sir. The article is "Optimization for buckling loads of grid stiffened composite panels" by Wodesenbet et al, published in composite structure in the year 2003. I will look forward to your next amazing videos.
I saw the paper @sina academy buts it's such an old paper I wondered if you didn't want to find something more recent. Some of those ideas in the paper are a bit obsolete.
@@MichaelOkereke Thanks again sir, would you mind checking another article written by Wang and Abdalla in 2015 named "Global and local buckling analysis of grid-stiffened composite panels". I am mostly concerned with the buckling of stiffened shells, not rectangular pannels. Also, there are more relevant papers by the same author.
@@MichaelOkereke Actually, I just remembered you have been reviewed an article by an Italian researcher named Vasiliev. He has been done some researches on the subject with his Co-worker Mr Tottaro.
thank u sir
You are welcome.
thank you for the video, but how can i design other structures like gyroid or primitive (TPMS) in abaqus?
Hello Huynh, this is an interesting challenge. I will consider it and see if I can make a video about such structures.
@@MichaelOkereke Thank you, Iam waiting for ur instruction
sir ,how much we will take poisson'sratio in case of polyvinyl alcohol(pva)
Hello Amit, its a variable quantity depending on the method of manufacture and composition. Typically its about 0.4 being a polymer but thats just a start. I suggest for a heterogeneous system composition you csn use the approach of my recent video on Numerical determination of Poisson Ratio to obtain it.
Hello Sir, i want to form hexa mesh for BCC in Abaqus ? How can i do this ?
Hello @irem, it is not easy to mesh this BCC structure with hexahedral (Hex) meshes, due mainly to the complexity of the central joints of the trusses. There could be other ways of meshing with hex elements but that means having to partition the domain a multiple number of times.