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Updated: 18 hours 46 min ago

Got it

Thu, 2017-04-20 18:04

In reply to sequential Abaqus input change

Hello there, 

Did you solve it? 

Got it

Thu, 2017-04-20 18:04

In reply to sequential Abaqus input change

Hello there, 

Did you solve it? 

Same issue after 4 years..

Thu, 2017-04-20 10:26

In reply to residual stress and strain definitions (through-thickness) in ABAQUS/Explicit

I am trying to do the same with beam elements (B21). However, when I try to use the odb file of a static analysis, I get the warning:

"Initial stresses will be read from the output database. This type of initial conditions is supported only for continuum elements, and the initial conditions will be ignored for other element types."

 

Can anyone suggest a workaround for this?

Fixed typo

Wed, 2017-04-19 23:41

Apply some load, and plot the

Wed, 2017-04-19 22:43

In reply to Exact load to get a right mechanical properties

Apply some load, and plot the stress-strain curve. The shape of the curve and the maximum strain should give you an idea whether the load is enough, or you need to increase it.

 

Regards

an interesting new paper shows Guduru effect and then reduction

Mon, 2017-04-17 15:20

In reply to On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces

This interesting new paper shows for the first time some simulations of the Guduru increase of adhesion pull-off due to roughness, decaying then after reaching a maximum, also for random roughness (although the effect is small).

Needless to say, there is no reference to the strange result of Pastewka-Robbins, but rather pull-off is always shown to depend on rms roughness as most commonly expected.

This position has been filled

Sat, 2017-04-15 17:49

In reply to Postdoc position in soft tissue mechanics, Swansea University UK

This position has been filled

how to model the density as a function of the coordinates?

Sat, 2017-04-15 07:46

In reply to Using ABAQUS subroutine (UMAT,VUMAT) to modeling FGM plate

I want to model a 2D FGM cylinder. for this purpose, the young's modulus and poission's ratio were modeled by vumat. But I do not know how to model the density as a function of the coordinates(x,y).

Please help me.

Thanks,

 Reza Pourshab

Biswajit, yes, we met almost

Fri, 2017-04-14 14:40

In reply to Creating a multi-keyframe animation with d3.js.

Biswajit, yes, we met almost ten years ago. I moved to Purdue in 2013. Time flies.

You might be interested in trying a multiscale constituive modeling code on your ipad: https://cdmhub.org/resources/scstandard. 

 

 

re: cdmHub

Thu, 2017-04-13 22:29

In reply to Ajit, Biswajit and all, 

Hi Wenbin,

I think I met you once while you were at USU.  Looks like you've made a lot of progress in creating your platform.  Congratulations!  I will look at the evolution of the platform with interest.

-- Biswajit

Thank you very much for sharing your thoughts.

Thu, 2017-04-13 20:26

In reply to Many thanks for this review and perspective!

Dear Nick,

Thank you very much for sharing your thoughts. I agree with you that we need to consider fabrication constraints for design and optimization process. There are some efforts to do that as it's mentioned in the review paper by Jamie Guest (reference #3). I appreciate your kind encouragement and the helpful reference.

Ajit, Biswajit and all, 

Thu, 2017-04-13 15:08

In reply to Creating a multi-keyframe animation with d3.js.

Ajit, Biswajit and all, 

It is interesting to read the discussion. We are working on a platform called cdmHUB (cdmHUB.org) which makes cloud computing easy and free. As a matter of fact, I just published a blog here. Currently executables and scripts written in many languages can be directly uploaded and become apps launchable by others in the cloud. No change to the code. They can be connected to HPC if more computing resources are needed. 

Many thanks for this review and perspective!

Thu, 2017-04-13 12:20

In reply to Journal Club for March 2017: Architected Materials

From fabrication and test point of view, I am particularly intrigued of the combinatorial design of tileable unit cells illustrated in Figure 4. It is desirable to consider fabrication constraints (such as, edge thickness and need of support structures for 3D printing) into the design and optimization process. A related work is from Denis Zorin group at NYU:

Elastic Textures
Julian Panetta, Qingnan Zhou, Luigi Malmo, Nico Pietroni, Paolo Cignoni, Denis Zorin
ACM Transactions on Graphics (TOG) vol. 34, 4, 2015 (Proceedings of SIGGRAPH 2015), 135

 

 

We are interested in

Thu, 2017-04-13 12:01

In reply to Computational inverse design of non-intuitive illumination patterns to maximize optical force or torque

We are interested in generalization of this approach to efficient all- optical manipulation of soft and flexible nanostructures. Look forward to inputs and related literature!

Figure 5. Model of path

Thu, 2017-04-13 03:58

In reply to Journal Club for April 2017: Multiscale and Multiphysics Simulation of Hydraulic Fracturing of Gas Tight Shale

Figure 5. Model of path choice of a hydraulic crack encountering a weak interface (left); It is revealed analytically that with increasing hydraulic pressure, a shale formation may sequentially undergo friction locking, mode II fracture, and mixed mode fracture, and in mode II fracture stage, crack-plane friction and crustal stress differences have no influence on the strain energy release rate ratio, i.e., crack deflection (right).

crack deflection in heterogeneous shale stratums

Thu, 2017-04-13 02:32

In reply to Journal Club for April 2017: Multiscale and Multiphysics Simulation of Hydraulic Fracturing of Gas Tight Shale

Very nice post on the influence of the weak layers on the mechanical properties of shales!

Hydraulic fracturing could form complex crack networks in the shale reservoirs mainly due to shale‘s mechanical heterogeneicty. These macroscale networks transport the encapsulated gas or oil just like the tree roots absorb water in the soil. Why and how the crack network develops in the sediment rocks is one of the most important questions in shale fracking work. It is well known that shale’s heterogeneity has a tremendous influence on its mechanical properties and fracture behavior. The discussion in IMechanica is indeed timely. As demonstrated in Figure 1 of the post, shales have complicated structures in different length scales, and the centimeter scale (intact rock specimen scale) and higher scales are of interest for shale fracking practical applications. In these scales, there are many natural cracks in the shale, sealed or unsealed. These cracks also have an important influence on shale’s mechanical properties (Gale et al., 2007 & 2014; Zeng and Wei, http://www.sciencedirect.com/science/article/pii/S0020768316301378). In a recently paper, we try to tackle the crack deflection in such heterogeneous media (Zeng and Wei, http://www.sciencedirect.com/science/article/pii/S0022509616306573) and we hope the discussion may be of the interest of IMechanica readers. By extending the energy release rate ratio criterion (He and Hutchinson, 1989) for cracking deflection, we give the critical conditions when the hydraulic crack kinks into the weak interface. The analysis also demonstrates how crack-surface friction and crustal stresses influence crack deflection from the matrix of higher fracture toughness to weak planes of lower resistance to crack propagation. It shows that Mode II fracture along the weak interfaces dominates the hydraulic fracturing process.

 References

Gale J F W, Laubach S E, Olson J E, Eichhubl P, Fall A. 2014. Natural fractures in shale: A review and new observations. AAPG Bulletin, 98: 2165-2216.

Gale J F W, Reed R M, Holder J. 2007. Natural fractures in the Barnett Shale and their importance for hydraulic fracture treatments. AAPG Bulletin, 91: 603-622.

He, M., Hutchinson, J.W., 1989. Crack deflection at an interface between dissimilar elastic materials. International Journal of Solids and Structures 25, 1053-1067.

Zeng X, Wei Y. 2016. The influence of crack orientation distribution on the mechanical properties of pre-cracked brittle media. International Journal of Solids and Structures, 96: 64-73.

Zeng X., Wei Y., 2017. Crack deflection in brittle media with heterogeneous interfaces and its application in shale fracking, Journal of the Mechanics and Physics of Solids 101, 235-249.

Re: Data Science, JScript, Cloud, Free

Mon, 2017-04-10 19:10

In reply to Data Science, JScript, Cloud, Free, Etc... Just a general chat

1) Data science: Data science is a broad field and needs several years of work to understand at a deep level. At present there is a lot of superficial interest in the subject because of hype.  Getting a deep understanding of statistics/probablity is non-trivial and that's just the starting point for a better understanding of data mining, machine learning, and statistical pattern recognition (which are the two main subfields of data science).  Because of these issues, typical data science specialists do not have an understanding of engineering problems and tend to provide solutions that defy common sense.  I've been trying to make progress in applying some machine learning to engineering problems without much success so far.  There are lots of questions that need research and I don't have the necessary funding.  But I'm encouraged that some mechanics experts are beginning to explore data science and are being funded.

2) Cloud computing:  Getting compute resources for free is not possible at this point even though some AWS resources are claimed to be "too cheap to meter" and therefore, essentially free.  You do have to provide your credit card number to get access to any of a number of providers.  My experience so far has been that the resources are typically not available when you want them unless you pay premium prices.  I don't have any contracts at this moment that require HPC; so the cloud computing aspect of my work is in the backburner for now.

3) Javascript:  Javascript is not Java.  The name was poorly chosen by Netscape.  But javascript makes truly OS-independent software possible.  If the word "Java" annoys you, just think of JS as ECMAScript, which turns out to be its current official name :)  JS has some nice functional programming features that I love.  Of course, it's also got some features that make debugging JS code and building complex software a nightmare.  Several frameworks have been developed to migitate those issues, e.g., Angular (Google), React (Facebook), Vue etc.  I've just Vue OK, but not the best for graphics heavy applications.  That's create the new nightmare of having to learn new ways of doing things every few months.  I hope things will stabilize in a few years.

4) Python:  I don't use Python much except for processing data.  But thanks for the suggestion. Will post something once I'm past the currently ongoing debugging nightmare for my MPI code.

5) MBAs etc:  The more I work on my own, the more I appreciate the need for division of labor.  Technical solutions are typically only part of the solution to a problem.  MBAs are needed for non-technical issues that people like me are not interested in and cannot do well.  

There are tons of articles that discuss generalities (you can find them on LinkedIn and Medium).  That's just entertainment as far as I am concerned.  My goal is to provide something more concrete in my articles.

-- Biswajit

 

Data Science, JScript, Cloud, Free, Etc... Just a general chat

Sun, 2017-04-09 16:11

In reply to Re: Interactive graphics and VR/AR

You know, Biswajit, I had turned really interested in Data Science for a while, some time last year...

OK, now, Data Science and the Cloud can, and do, go really well together. And I gather that you are working in these things. ... I really appreciate your providing scripts here and all. After all, unless someone actually codes, no output is ever produced... (Few MBAs profess to know this truth; all of them know it, through a direct knowledge of their particular incompetencies.  (OK, this is a Harvard-based blog. So what?))

But, as of today, I just can't find time for any of my personal research concerns.... Hopefully, things improve soon later...

But, frankly, I would really appreciate it if you could provide some code in Python rather than using JScript. ... It's been since mid-1990s that I have been actually hating anything to do with Java, even though such actually has never been one of my official positions. It's just that all my friends (and enemies) know me, including this opinion of mine... Rather too well, in fact.

Anyway, would be refreshing if you could please provide some Python scripts too...

Also, if you could let us know here if you have run into some way of making some CAE software work, for free, on the cloud. Like, say, OpenFOAM or something like that. (I don't mind creating free accounts...) ...

...OK, bye for now...

 

Best,

--Ajit

A bit late, but...

Sun, 2017-04-09 15:58

In reply to Huajian Gao Elected to German National Academy of Sciences

A bit late for that to happen, but, anyway, very well deserved.

Congrats!

--Ajit

 

Re: Interactive graphics and VR/AR

Sat, 2017-04-08 01:25

In reply to Re: Interactive graphics

It's hard to say how useful VR will be until the hardware and software catches up.  Latency is a big issue.

At this point I'm thinking more along the lines of providing richer sets of information in 2D data plots.  Think of an ordinary text document vs. a document with hyperlinks.  Except that the user will not have to do a HTTP request to get the data for each interaction.

 

-- Biswajit

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