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PhD positions at Purdue – Computational biomechanics and CFD

Wed, 2020-09-23 10:28

In reply to PhD positions at Purdue – Computational biomechanics and fluid dynamics

We have several openings for a PhD positions. The successful candidate will conduct original research on biomechanics and fluid dynamics and develop numerical methods to model coupled processes on high-performance computing platforms. This position is in the Gomez Research Group ( in the Department of Mechanical Engineering at Purdue.



Please send an email expressing your interest, together with a CV to Prof. Hector Gomez ( Reviews of applications will start on October 7, 2020 and continue until the position is filled.


Fri, 2020-09-18 17:04

In reply to Re: Plates and Shells

Dear Arash,

Thank you for you comment. I am looking for the definition of the p.d.e in (r,s) natural coordinates (or r,s,t) of the curved shell midsurface. You have cited the p.d.e in (x,y) cartesian coordinate of a plane plate which is developed in its plane. There are envelopes theory and cylindric envelopes theory where these domains are known as shells in finite elements. The finite elements is an efficient method which uses interpolations functions and different methods are used to program plates and shells where curved domains can be approximated with several plane plates or with curved shells but this is a numerical method. In this method a plate with membrane effects (quadrilateral element) + bending effects (plate element) is equivalent to a shell elemnt with five to six degrees of freedom.

Mohammed Lamine

Re: Plates and Shells

Thu, 2020-09-17 15:50

In reply to Plates and Shells

Dear Mohammed:

In Kirchhoff-Love plate theory shear deformations are ignored (this is a theory of thin plates). Assuming that energy of a shell depends on the first and the second fundamental forms of its mid surface one is implicitly ignoring shear deformations. To take into account shear deformations one would need to consider director fields at each point of the mid surface. Mindin (or Mindlin-Reissner) plate theory would be a special case of plates with director fields.


Plates and Shells

Thu, 2020-09-17 13:50

In reply to Transformation Cloaking in Elastic Plates

Dear Arash Yavari,

Golgoon is using in your cited paper plate elements and after he call them shell elements. The partial differential equation of plates is shown. 

There are two theories for plates elements Kirchoff theory and Mindlin theory which includes the shear deformation energy effect. When the plate element has a great thickness, the Mindlin theory is used. The plate element is considered as a shell element when it has a small thickness and the theory of shell elements can also be used. Shell theory is developed with the midplane of the elements. Is there a relation between these two names in the cited developments ?

Re: Scholarship in mechanics, Twitter

Thu, 2020-09-17 09:31

In reply to Scholarship in mechanics

This iMechanica thread links to a Twitter thread:

Re: Scholarship in mechanics

Wed, 2020-09-16 15:34

In reply to Re: Scholarship in mechanics

The motivation for writing books I would guess is pretty personal.  For me, my first book was written for two reasons (1) the book I was following (Popov) had gotten to wordy and dense with extraneous material (further the publisher ruined the book by forcing Egor to revise it when he was nearly 88, which introduced many typos), and (2) all the other books were similar and nearing +$200 for a strength of materials book.  Thus I wrote my own to be slimmer and less expensive.  Plus I needed a book for juniors and based on calculus not algebra -- of which there were few.

My next book was a translation project (German to English); so there it was to help out some good friends in Germany that wanted to bring their book (undergraduate dynamics) to English speakers.  So this was really just for the fun of it.

My most recent book, Continuum Mechanics of Solids with Lallit Anand and the companion problems book , were written to fill a void in comprehensive modern introductory text books for graduate students.  If I look around my desk right now at the books that really matter to me, most fall into this latter category -- books written to fill a void at the time they were written.  Put another way, people wanted to fill a void that they saw, whether for their own needs or those of the wider profession.

These days it seems that there is less drive to do that from our top colleagues -- perhaps because the rewards system.  But I think having a well adopted book is its own special type of award -- the appreciation of students and the feeling that comes from knowing that you have really helped someone else achieve one of their goals -- being a teacher in addition to being a researcher.  I even make educational YouTube videos on mechanics, which will never gain me any traditional rewards, but it is nice to know that many students world wide appreciate them.  Hidden however is a type of monetary reward, but not from book sales! (Never write a book to make royalties, as you will find your hourly wage to be something quite laughable in a sadistic kind of way.)  In the traditional promotion system like we have at Berkeley, the campus wide promotions/salary advancements committee seats many professors from the liberal arts where books are the major stepping stones to promotion.  So indirectly, when you are advanced far enough in your career, there is a monetary reward.  But for engineers this is only later in a career (past tenure and full professor) since your promotion at the department and college level will hinge 90% on your research.


This is one of those things

Wed, 2020-09-16 14:02

In reply to Scholarship in mechanics

This is one of those things that comes with experience, which I guess is one of the reasons that many books are written by faculty in the latter-half of their careers. But the process of writing a book – not the compilation of ideas – but the process of building a cohesive story is what is lacking in a piecewise collection of papers. Also, too many grad students take a piecewise appraoch to their dissertations... but that is another story. Mastery of a subject comes through in such works, such as those by Timoshenko - not too many my age (and I'm getting older) are picking up these rare tomes, but they were critical resources for me when I used to teach.

This is also the difference between a good review article and a great one – they may have all the same information, but a great review pulls it together in a more synergistic (and hopefully appealing) manner. A text gives you the room to flesh out ideas, motivate them and meander around them.

Papers are like a date – could be fun, could be very attractive, might even arrange a second date, but you’re not committed. A book is like a marriage – a commitment to an idea, good and bad, and so much more rewarding.

Now, if you have a book in mind (i.e., marriage), you might even improve your individual papers (i.e., dates), because you know what you are looking for – you see the bigger picture.

The same thought process doesn’t have to be applied to research either – there are many creative ways to deliver course material, for example, which have resulted in very unique texts that are much more valuable, inspiring and motivational than a collection of the lectures and problem sets. 

In terms of academic social media, that is like Tindr – a quick glance to move on to the date. :) 

Abolish h-index

Wed, 2020-09-16 13:57

In reply to Scholarship in mechanics

 Nowadays, in many places, the h-index is used to measure researchers' productivity and impact. Many people even split one paper into multiple small papers to increase citation and h-index. 

 Here are some important discussions on the negative impact of h-index :

    Why the h-index is a bogus measure of academic impact

    h-index and how academic publishing has changed: Feynman and Einstein just aren't that impressive anymore

 Four great reasons to stop caring so much about the h-index

 Is it time to bury the h-index?

 Why the h-index is little use?


Zhigang: it may be useful to

Wed, 2020-09-16 13:55

In reply to Re: Scholarship in mechanics

Zhigang: it may be useful to quantify this. But I would expect (or as I sometimes say, be willing to bet a quarter), that a larger fraction of the top researchers wrote books many decades ago than today. Think about who you believe is at the top of the field, in terms of their excellent research, deep understanding of mechanics, etc.. And then see how many of them have written a book or a monograph. I have personally asked a few of these individuals why they don't write books, and they were honest in their replies by stating that they are too busy to do so. Of course I respect their decision, but at the same time it is a shame. As pointed out, we are still reading the classic texts from as far back as 100 years ago. Would it not be great for learners if, say, Timoshenko's of Love's classics in elasticity are augmented by a book or books on modern topics and applications of elasticity, to which you have greatly contributed (hint hint). 


Wed, 2020-09-16 13:40

In reply to Scholarship in mechanics


Re: Scholarship in mechanics

Wed, 2020-09-16 13:06

In reply to Scholarship in mechanics

To write papers or to write books, that is the question. Gibbs wrote his book-length paper to define thermodyanmics as a branch of physical chemistry. This act was tough to follow even in his day. Timoshenko wrote books that are still read today. Also a tough act to follow, but one would think that some people could. It is puzzeling that why many superb reserchers do not write books today. Has this always been the case that only a tiny fractions of reserchers write books? Or are we moving from books to papers and shorter papers? I have not looked at the numbers myself. Even if the trend is real, I am uncertain of its cause. Let's see if other people have comments.


Wed, 2020-09-16 11:49

In reply to How is this multiaxial relationship derived in this paper?

Solved. Simple chain rule.

I uoploaded my recent paper

Wed, 2020-09-09 13:13

In reply to Timoshenko and Ehrenfest

I uoploaded my recent paper titled "Who Developed the So-Called Timoshenko Beam Theory?"

File has been uploaded.Please

Wed, 2020-09-09 13:09

In reply to Unfortunately, I can't open

File has been uploaded.Please check again. 

Thank you so much, Prof. Suo.

Tue, 2020-09-08 10:18

In reply to A crosslink between iMechanica and Twitter

Thank you so much, Prof. Suo.  Following your "To Read Is Human, to Watch Divine", I am trying to get into the first stage, and further for the second one.  Such a foresight with pioneering endeavors is impressive, enlightening, and exciting. I wish and pursue to contribute to this.

The positions are still

Mon, 2020-08-31 22:53

In reply to Postdoc Positions at Jiangsu University, Zhenjiang, China

The positions are still avaiable.

First trial a breakouts

Mon, 2020-08-31 19:07

In reply to Re: poling

Thanks Matt.  Today I tried breakout groups.  I attempted to flip my class by having them read particular sections of the book before hand.  I then started the lecture with a 10-15 summary of a few highlights of the reading.  Then I launched into working with material.  Periodically (4 times during the hour) I posed a question and sent them to breakout rooms.  When they returned (3 to 4 minutes), I took a couple of suggestions on the answer either by calling on a particular group or taking volunteers.  After that I detailed either a suggested method or just gave a version I felt was more instructive.

I asked a student later about the experience and they said it actually worked (eventually).  The first time they had no idea how to interact in the groups but they figured it out pretty quickly.

I think I will try this for another week and then take the pulse of the class to see if they prefer moving forward this way or returning to the 'usual' lecture format.

Abaqus mailing list

Mon, 2020-08-31 14:46

In reply to Stress intensity factor from Abaqus


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Our Answer

Mon, 2020-08-31 13:28

In reply to Discussion of fracture paper #26 - Cracks and anisotropic materials

Dear Per,

Thank you for your comment. Yes, exactly, once the general series solution in obtained, the BCM can be used to determine the coefficients of the truncated series. The article below has used the BCM to determine the stress intensity factor for an edge-cracked plate of an anisotropic material. 

Zhang Heng, D.M. Cammond, B. Tabarrok,  Stress determination in edge-cracked anisotropic plates by an extension of boundary-collocation method, Computer Methods in Applied Mechanics and Engineering 54, 187-195 (1986).

A crosslink between iMechanica and Twitter

Mon, 2020-08-31 11:29

In reply to keep reading-13

I have just tweeted your reading notes:


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