Unfortunately the old allegory of "it's like waiting for a bus to arrive; nothing for a while and then two turn up" didn't quite hold today. I was waiting for the X5 bus tonight (Cambridge -> Oxford) and ended up waiting for 2 hours before giving up and going back to college. They are supposed to be every 30 minutes from Cambridge to Milton Keynes - two turned up and drove straight past as they were full up! Not sure why it was full up, but it means that I now have to catch the crack-of-dawn bus tomorrow morning to MK or face an angry girlfriend, which is always very inadvisable.
Today we had a group meeting at the Magnetic Resonance Research Centre (http://www.cheng.cam.ac.uk/research/groups/mri/html/mrrc.htm) which is a fortnightly thing. Generally a couple of members present updates on their work and we discuss things about the site - usually which doesn't really concern me as I am based over in Engineering for the bulk of my work as my second (and arguably more important) supervisor is based there too. I find the others' work very interesting though - it feels as though they are doing "real" science whereas I just play with maths and computers all day! It can be a little overwhelming as the bulk of it is magnetic resonance imaging and catalysis, but I suppose that it's good for me to get a grip on the research going on and the techniques as it can serve me well. I'm collaborating with one third-year PhD student at the moment there as her work should provide some good insights into the two-phase models that I want to implement.
Sad to see the cloud back again though, it's been like a glimpse of summer here for the past couple of weeks! The ducks are all out and pestering the tourists for bread and other treats. The West Cambridge site is curious, as it's the only place where the University can actually build new buildings - good location for me (right next to Robinson College) but it's always very windy there! There is no protection from the natural Easterly breeze that rolls through Cambridge. There's a very nice pond and "garden" for the site though with a few picnic benches. Today when I was on my way back I saw a Chinese mum and her little daughter who was telling her mum "我要抱抱鸭子!" - "I want to hug the duck" - the duck though apparently didn't share the same want for physical contact. He did like the posh bread though!
Thursday, 28 April 2011
Wednesday, 20 April 2011
Delving into Multiphase Flow
Thought I would change the title from something weather-related to something more academic related. Although having said that, the weather is glorious here at the moment. Sunshine, 23 degrees - all in April in the UK (which for those not accustomed to UK weather, is typically the month when it rains fairly consistently - "April showers"). Cambridge is gorgeous in the spring, with blossoms everywhere and large old trees adorning the River Cam. I'll take some photos later to show that it's not just me being misty-eyed.
I started to delve into some two-phase flow stuff this week. I'm trying to decide on a model to implement into my CFD code, and this is more difficult than it sounds. On one hand, I want to choose a model that will converge nicely and give accurate answers for my test case, but on the other hand I want to make the code multi-functional as the idea is that other people can use it at the end. Unfortunately I don't have the time to implement all the models into my code (like in FLUENT for example) so it's really a toss-up between versatility/robustness, accuracy and ease of implementation at the moment.
The new code itself needs a bit of work on first as well. At the moment it can do multi-species modelling and combustion which is more than the old code, and it's also parallelised which helps out a lot. Problem is that it only models ideal gases at the moment, and only models a pressure inlet. Not really any use for me - I'm at the low-velocity end of the spectrum whereby the fluids are essentially incompressible, and I'd like to use liquids too.
Other problem is that the geometry definitions itself has changed. My old code was cell-vertex based, whereby all the fluid values (velocity, density, temperature . . .) are stored at the nodes of each tetrahedral cell. The values at the face (from which the appropriate fluxes are calculated) are then interpolated from these vertices by taking into account the appropriate contribution and the area of the face from the vector cross-product of the nodal distance vectors. The new code is cell-centred, whereby those values are stored at the centre of the cell and then interpolated out to the faces. This is (in the grand scheme of things) a better way of doing it. The only problem is that all my old meshes and case files are now not compatible!
That brings me into my current work - ICEM-CFD. I have my old geometry file which I can read in as co-ordinate point data to Ansys ICEM-CFD, and now I have to reconstruct the geometry, mesh the faces and volume and see if it works with PULSAR. (which it should - it just needs a lengthy conversion of uns (unstructured ICEM-CFD mesh) -> msh (FLUENT) -> mcv (NEWT) -> pcv (PULSAR) Once that is all done the code needs to be edited to cope with incompressible flows and a velocity inlet.
Hopefully this will all result in some sort of code shoot-off. I have CFX and FLUENT to compare to, and my code (PULSAR) has a couple of options for determining the flow field. I'm thinking of some kind of shoot-out to test the effectiveness of each code by monitoring the residuals and velocity values at some point to see which one converges most quickly, and which gives the most accurate result in comparison to the available MRI data.
Of course, I won't publish the results if my code comes last! Or maybe I will, in true academic spirit. I'm about to send off a journal to (hopefully) be published in which I disseminate what's bad about CFD rather than highlighting what's good - I think that veracity and realising the short-comings of the method is more pertinent in some ways than just cherry-picking the best results and showing them off to the world.
All this rambling makes my stomach hungry . . . lunch time I think. Have a good week wherever you are!
I started to delve into some two-phase flow stuff this week. I'm trying to decide on a model to implement into my CFD code, and this is more difficult than it sounds. On one hand, I want to choose a model that will converge nicely and give accurate answers for my test case, but on the other hand I want to make the code multi-functional as the idea is that other people can use it at the end. Unfortunately I don't have the time to implement all the models into my code (like in FLUENT for example) so it's really a toss-up between versatility/robustness, accuracy and ease of implementation at the moment.
The new code itself needs a bit of work on first as well. At the moment it can do multi-species modelling and combustion which is more than the old code, and it's also parallelised which helps out a lot. Problem is that it only models ideal gases at the moment, and only models a pressure inlet. Not really any use for me - I'm at the low-velocity end of the spectrum whereby the fluids are essentially incompressible, and I'd like to use liquids too.
Other problem is that the geometry definitions itself has changed. My old code was cell-vertex based, whereby all the fluid values (velocity, density, temperature . . .) are stored at the nodes of each tetrahedral cell. The values at the face (from which the appropriate fluxes are calculated) are then interpolated from these vertices by taking into account the appropriate contribution and the area of the face from the vector cross-product of the nodal distance vectors. The new code is cell-centred, whereby those values are stored at the centre of the cell and then interpolated out to the faces. This is (in the grand scheme of things) a better way of doing it. The only problem is that all my old meshes and case files are now not compatible!
That brings me into my current work - ICEM-CFD. I have my old geometry file which I can read in as co-ordinate point data to Ansys ICEM-CFD, and now I have to reconstruct the geometry, mesh the faces and volume and see if it works with PULSAR. (which it should - it just needs a lengthy conversion of uns (unstructured ICEM-CFD mesh) -> msh (FLUENT) -> mcv (NEWT) -> pcv (PULSAR) Once that is all done the code needs to be edited to cope with incompressible flows and a velocity inlet.
Hopefully this will all result in some sort of code shoot-off. I have CFX and FLUENT to compare to, and my code (PULSAR) has a couple of options for determining the flow field. I'm thinking of some kind of shoot-out to test the effectiveness of each code by monitoring the residuals and velocity values at some point to see which one converges most quickly, and which gives the most accurate result in comparison to the available MRI data.
Of course, I won't publish the results if my code comes last! Or maybe I will, in true academic spirit. I'm about to send off a journal to (hopefully) be published in which I disseminate what's bad about CFD rather than highlighting what's good - I think that veracity and realising the short-comings of the method is more pertinent in some ways than just cherry-picking the best results and showing them off to the world.
All this rambling makes my stomach hungry . . . lunch time I think. Have a good week wherever you are!
Wednesday, 13 April 2011
End of the Sun
So it's been a glorious week here in the UK, and the weather has decided that it's about time to rain on that parade (quite literally). Cold and miserable! I need to go to the shops but I'm inside with a cup of tea instead.
The conference last week went well - mainly catalysis which is not really my area. (well, not at all) The talks were interesting and I met some people who gave me a good idea of how to focus my work a little more. To top it all off, when travelling to the conference we inadvertently met James May (of Top Gear fame) at Loughborough University when we got lost! Some excellent detective work from the other Chemical Engineers has shown that they were most likely filming an episode of something, and probably not Top Gear itself. He's going a bit grey now, it must be said.
Computing is as interesting as ever. I've tried to give myself a tiny push in the direction of time management by "allowing" myself to read in the morning and work after lunch; at the moment I'm getting through the book "Computational Fluid Dynamics: the Finite Volume Method" by the wonderfully-named W. Malalasekra. Very good book, pitched at this level as an introduction. I'm almost through it; once I am I will shuffle onto the 2-phase stuff which will be more relevant with my work. I want to go through the Blazek text on CFD as well but it looks like I want to read hundreds of books and I don't have hundreds of hours.
I'm just going through the code at the moment, getting used to how algorithms are implemented and trying to unravel the mysterious MPI commands. I'd like to get some simulations running but it's not that simple unfortunately - firstly the code itself is for a compressible gas so I need to do some alterations to get it going for an (incompressible) liquid and secondly the old geometry doesn't read into the new one. I need to go and re-draw and re-mesh the geometry, but the mesh conversion program doesn't work from GAMBIT files (which is what I use). It works from ICEM-CFD, but that doesn't work on my PC at the moment because of the licencing server going bottoms-up each time.
Pretty apt for a PhD really - what should be a fairly linear process ends up horribly truncated and dendritic. I suppose that's why time management just goes out of the window!
The conference last week went well - mainly catalysis which is not really my area. (well, not at all) The talks were interesting and I met some people who gave me a good idea of how to focus my work a little more. To top it all off, when travelling to the conference we inadvertently met James May (of Top Gear fame) at Loughborough University when we got lost! Some excellent detective work from the other Chemical Engineers has shown that they were most likely filming an episode of something, and probably not Top Gear itself. He's going a bit grey now, it must be said.
Computing is as interesting as ever. I've tried to give myself a tiny push in the direction of time management by "allowing" myself to read in the morning and work after lunch; at the moment I'm getting through the book "Computational Fluid Dynamics: the Finite Volume Method" by the wonderfully-named W. Malalasekra. Very good book, pitched at this level as an introduction. I'm almost through it; once I am I will shuffle onto the 2-phase stuff which will be more relevant with my work. I want to go through the Blazek text on CFD as well but it looks like I want to read hundreds of books and I don't have hundreds of hours.
I'm just going through the code at the moment, getting used to how algorithms are implemented and trying to unravel the mysterious MPI commands. I'd like to get some simulations running but it's not that simple unfortunately - firstly the code itself is for a compressible gas so I need to do some alterations to get it going for an (incompressible) liquid and secondly the old geometry doesn't read into the new one. I need to go and re-draw and re-mesh the geometry, but the mesh conversion program doesn't work from GAMBIT files (which is what I use). It works from ICEM-CFD, but that doesn't work on my PC at the moment because of the licencing server going bottoms-up each time.
Pretty apt for a PhD really - what should be a fairly linear process ends up horribly truncated and dendritic. I suppose that's why time management just goes out of the window!
Tuesday, 5 April 2011
Off to conference . . .
Tomorrow is the Johnson Matthey student conference, held in Loughborough. For those who don't know Loughborough, it's fairly close to Cambridge . . . yes, that's about it. Whilst we'd rather go to conferences in Hawaii or other exotic places, I'm sure it will be a great conference, with plenty to learn and lots to see. The idea is to bring together all the JM-sponsored students and see what else is going on in PhD studentships around the country, and to network and make connections with not only your peers, but also industrial contacts.
Since I'm a first year, I shall be presenting a poster there and that's it. I shall also be trying to avoid heckling or asking awkward questions to Oxford PhD students, as we don't want gang warfare on our hands. We even have an ex-Oxford'er on our side now for insider info. Maybe it all just stems down to individual jealousy as I was turned down from Oxford as a bright-eyed 17 year old all those years ago! Although as it turns out, Sheffield was a wonderful choice for an undergrad in Chemical Engineering. I made many good friends, met some brilliant academics and learnt an awful lot which I am subsequently doing my best to forget.
I suppose the next thing to think about is the hotel arrangements. Is it still au-fait to steal the hotel shampoo / shower gel? Having said that I'm feeling princely at the moment as I'm rocking the Radox shower gel - it was on BOGOF in Sainsbury's not too long ago so I stocked up to nuclear-war proportions. If the zombie apocalypse does come, and the zombies are afraid of jojoba oil shower cream (whatever jojoba oil is) then I am laughing. I'm also well stocked-up on Sainsbury's Basics Chocolate Digestive Biscuits, which for 38p (I think!) a pack are the world's greatest foodstock. My teeth might not live until the end of the apocalypse though.
Well anyway I shall spend the rest of my day decoding the new CFD code and writing a user guide for it. It might come in useful someday for someone else, but for now writing a user guide is more for clarifying everything to myself. Implementing two phase flow is going to be "a bitch", if you excuse my French.
Signing off from a somewhat cloudy Cambridge,
Dave
Since I'm a first year, I shall be presenting a poster there and that's it. I shall also be trying to avoid heckling or asking awkward questions to Oxford PhD students, as we don't want gang warfare on our hands. We even have an ex-Oxford'er on our side now for insider info. Maybe it all just stems down to individual jealousy as I was turned down from Oxford as a bright-eyed 17 year old all those years ago! Although as it turns out, Sheffield was a wonderful choice for an undergrad in Chemical Engineering. I made many good friends, met some brilliant academics and learnt an awful lot which I am subsequently doing my best to forget.
I suppose the next thing to think about is the hotel arrangements. Is it still au-fait to steal the hotel shampoo / shower gel? Having said that I'm feeling princely at the moment as I'm rocking the Radox shower gel - it was on BOGOF in Sainsbury's not too long ago so I stocked up to nuclear-war proportions. If the zombie apocalypse does come, and the zombies are afraid of jojoba oil shower cream (whatever jojoba oil is) then I am laughing. I'm also well stocked-up on Sainsbury's Basics Chocolate Digestive Biscuits, which for 38p (I think!) a pack are the world's greatest foodstock. My teeth might not live until the end of the apocalypse though.
Well anyway I shall spend the rest of my day decoding the new CFD code and writing a user guide for it. It might come in useful someday for someone else, but for now writing a user guide is more for clarifying everything to myself. Implementing two phase flow is going to be "a bitch", if you excuse my French.
Signing off from a somewhat cloudy Cambridge,
Dave
Monday, 4 April 2011
First post!
Thought it was about time to join a blog, many years after the inception of them. I hope that one day this can be useful or entertaining to people - I shall try to blog regularly about what is going on here.
Seeing at this is the first post I figure that I should first of all introduce myself! My name is Dave and I am a first year PhD student at the Department of Chemical Engineering and Biotechnology at the University of Cambridge. I graduated in 2010 with an undergraduate masters (MEng) degree in Chemical Engineering from the University of Sheffield. I wanted to pursue further studies, and what better place in the UK (or even the world) than the University of Cambridge?
I was very late in applying for a PhD - around June/July time. I was whisked down to Cambridge for an "informal interview" (which I still wore a suit to - this is Cambridge after all!) and met the (then) Head of Department, (now Pro-Vice Chancellor) Professor Lynn Gladden. I was very interested in what they do down here and she seemed to think that I wasn't quite as daft as a brush (closer to a comb I think) and very generously offered to supervise me and gave me a stipend to carry out my PhD here, entitled Development of CFD Codes to Predict Two-Phase Flows and Reaction in Trickle-Bed Reactors. This involves developing software to predict the way that fluids flow and interact with each other - very challenging and demanding, and just what I need to kick my work up a notch.
At the start of my tenure I met Professor Stewart Cant, who is a world-renowned expert in the field of computational engineering, who is my second supervisor. Stewart has many years of experience in the field of CFD and computational engineering, with his SENGA code for direct numerical simulation of combustion chemistry an international standard. On top of it all, he is a very amiable chap - I think best summed up by a description of him (by a person who shall remain unnamed!) as "the supervisor who makes me smile at difficult problems, and whose office I leave with a sense of purpose and determination instead of dejection and confusion." I meet Stewart every Wednesday, and always feel energised and ready for more hard work afterwards. Probably a useful time in the week to have the meeting too!
In the first half of this year I have been getting to grips with the CFD code NEWT, which is an in-house code used at the Department of Engineering. I've been using it to compute some single-phase flows (i.e. just liquid flowing through a column) and have achieved some good results with it. I've got a hold of some MRI data from the Chem. Eng connections and compared it, finding remarkably good agreement in the region of 2-9% accuracy. I'm coming to the end of drafting an academic manuscript on the work and hope to submit it soon.
Doing a PhD, in my very brief experience, feels very much like climbing a lighthouse where the stairs are all huge. You start at the bottom and slowly work your way up the winding stairs, and inevitably you run into problems. These are both external (waiting for someone else to do something that you need) and internal, and perhaps it is the latter of these that defines the difference between a postgrad programme and a PhD one. If I encounter some problem here it is really up to me to sort it out, whether it is software-related, maths-related or science-related. Of course there is help, but no-one can just spoon-feed you the information any more; you've got to kick up to a higher gear in order to manage to jump to the next step. Unfortunately though there are hundreds of steps left to go!
The support that you have is key, and Cambridge is a wonderful place in this regard. Whether the support is from fellow PhD students, supervisors or other academics working in your department, I've always received very insightful and positive criticism from whomever I've spoken to. Without wishing to present my old University as the opposite, I've always felt at Sheffield that the faculty was somewhat split by "factions" and that it wouldn't have been the best place to pursue a PhD. Here in Cambridge everyone is at the top of their games, and there's a lot of collaboration - you can really see why the University of Cambridge continues to be a world-leader today.
I've gone on too long here so I shall sign off now on an increasingly-cloudy April day - hopefully it will rain a little later on as the Robinson College gardens smell incredibly good after a blanket of rain. The squirrels don't like the wet weather too much though!
Dave
Seeing at this is the first post I figure that I should first of all introduce myself! My name is Dave and I am a first year PhD student at the Department of Chemical Engineering and Biotechnology at the University of Cambridge. I graduated in 2010 with an undergraduate masters (MEng) degree in Chemical Engineering from the University of Sheffield. I wanted to pursue further studies, and what better place in the UK (or even the world) than the University of Cambridge?
I was very late in applying for a PhD - around June/July time. I was whisked down to Cambridge for an "informal interview" (which I still wore a suit to - this is Cambridge after all!) and met the (then) Head of Department, (now Pro-Vice Chancellor) Professor Lynn Gladden. I was very interested in what they do down here and she seemed to think that I wasn't quite as daft as a brush (closer to a comb I think) and very generously offered to supervise me and gave me a stipend to carry out my PhD here, entitled Development of CFD Codes to Predict Two-Phase Flows and Reaction in Trickle-Bed Reactors. This involves developing software to predict the way that fluids flow and interact with each other - very challenging and demanding, and just what I need to kick my work up a notch.
At the start of my tenure I met Professor Stewart Cant, who is a world-renowned expert in the field of computational engineering, who is my second supervisor. Stewart has many years of experience in the field of CFD and computational engineering, with his SENGA code for direct numerical simulation of combustion chemistry an international standard. On top of it all, he is a very amiable chap - I think best summed up by a description of him (by a person who shall remain unnamed!) as "the supervisor who makes me smile at difficult problems, and whose office I leave with a sense of purpose and determination instead of dejection and confusion." I meet Stewart every Wednesday, and always feel energised and ready for more hard work afterwards. Probably a useful time in the week to have the meeting too!
In the first half of this year I have been getting to grips with the CFD code NEWT, which is an in-house code used at the Department of Engineering. I've been using it to compute some single-phase flows (i.e. just liquid flowing through a column) and have achieved some good results with it. I've got a hold of some MRI data from the Chem. Eng connections and compared it, finding remarkably good agreement in the region of 2-9% accuracy. I'm coming to the end of drafting an academic manuscript on the work and hope to submit it soon.
Doing a PhD, in my very brief experience, feels very much like climbing a lighthouse where the stairs are all huge. You start at the bottom and slowly work your way up the winding stairs, and inevitably you run into problems. These are both external (waiting for someone else to do something that you need) and internal, and perhaps it is the latter of these that defines the difference between a postgrad programme and a PhD one. If I encounter some problem here it is really up to me to sort it out, whether it is software-related, maths-related or science-related. Of course there is help, but no-one can just spoon-feed you the information any more; you've got to kick up to a higher gear in order to manage to jump to the next step. Unfortunately though there are hundreds of steps left to go!
The support that you have is key, and Cambridge is a wonderful place in this regard. Whether the support is from fellow PhD students, supervisors or other academics working in your department, I've always received very insightful and positive criticism from whomever I've spoken to. Without wishing to present my old University as the opposite, I've always felt at Sheffield that the faculty was somewhat split by "factions" and that it wouldn't have been the best place to pursue a PhD. Here in Cambridge everyone is at the top of their games, and there's a lot of collaboration - you can really see why the University of Cambridge continues to be a world-leader today.
I've gone on too long here so I shall sign off now on an increasingly-cloudy April day - hopefully it will rain a little later on as the Robinson College gardens smell incredibly good after a blanket of rain. The squirrels don't like the wet weather too much though!
Dave
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