I am a research associate in nonlinear structures at the University of Bristol and specialise in lightweight design of aerospace components. This means I try to make wings, fuselages, rocket shells, etc. as light as possible without them breaking, snapping, crushing … basically failing in service before they are meant to.

Why nonlinear? Because designing lightweight structures often entails optimising one aspect of the structure; the parameter that most influences the design.

Unfortunately, optimising for one parameter can make the structure quite fragile, and when the structure exceeds its design loading, failure can be sudden and dramatic. The ensuing large deformations in these collapse events can only be modelled accurately when nonlinearities are taken into account.

On the other hand, there are cases where we want structures to reliably undergo large deformations. For example, we can design structures that snap between two stable states and this can be used to optimise the performance under changing loading conditions. This approach is known as shape morphing and is generally how nature goes about optimising for changing environments.

You can find my contact details and a list of select publications below. To get in touch, please leave a comment and I will get back to you ASAP.

**Rainer Groh, PhD MEng**

**Postdoctoral Research Associate in Nonlinear Structures**

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Bristol Composites Institute (ACCIS)

Department of Aerospace Engineering, University of Bristol

Queen’s Building, University Walk, Bristol, BS8 1TR, UK

**PhD Thesis**

RMJ Groh (2015). Non-classical effects in straight-fibre and tow-steered composite beams and plates. University of Bristol. Bristol, UK.

**Teaching**

Advanced Materials & Structures 3 – Bending and Buckling of Plates, Department of Aerospace Engineering, University of Bristol.

**Publications**

G Arena, **RMJ Groh**, A Brinkmeyer, R Theunissen, PM Weaver, A Pirrera (2017). Adaptive compliant structures for flow regulation. Proceedings of the Royal Society A, 473:20170334. DOI: 10.1098/rspa.2017.0334.

**RMJ Groh**, A Tessler (2017). Computationally efficient beam elements for accurate stresses in sandwich laminates and laminated composites with delaminations. Computer Methods in Applied Mechanics and Engineering, 320, (pp. 369–395). DOI: 10.1016/j.cma.2017.03.035.

C Thurnherr, **RMJ Groh**, P Ermanni, PM Weaver (2017). Investigation of failure initiation in curved composite laminates using a higher-order beam model. Composite Structures, 168, (pp. 143–152). DOI: 10.1016/j.compstruct.2017.02.010.

A Madeo, **RMJ Groh**, G Zucco, PM Weaver, G Zagari, R Zinno (2017). Post-buckling analysis of variable-angle tow composite plates using Koiter’s approach and the finite element method. Thin-Walled Structures, 110, (pp. 1-13). DOI: 10.1016/j.tws.2016.10.012.

**RMJ Groh**, PM Weaver (2016). Deleterious localized stress fields: the effects of boundaries and stiffness tailoring in anisotropic laminated plates. Proceedings of the Royal Society A, 472:20160391. DOI: 10.1098/rspa.2016.0391.

C Thurnherr, **RMJ Groh**, P Ermanni, PM Weaver (2016). Higher-order beam model for stress predictions in curved beams made from anisotropic materials. International Journal of Solids and Structures, 97–98, (pp. 16–28). DOI: 10.1016/j.ijsolstr.2016.08.004.

G Zucco, **RMJ Groh**, A Madeo, PM Weaver (2016). Mixed shell element for static and buckling analysis of variable angle tow composite plates. Composite Structures, 152, (pp. 324–338). DOI: 10.1016/j.compstruct.2016.05.030.

**RMJ Groh**, PM Weaver (2016). A computationally efficient 2D model for inherently equilibrated 3D stress predictions in heterogeneous laminated plates. Part II: Model validation. Composite Structures, 156, (pp. 186-217). DOI: 10.1016/j.compstruct.2015.11.077.

**RMJ Groh**, PM Weaver (2016). A computationally efficient 2D model for inherently equilibrated 3D stress predictions in heterogeneous laminated plates. Part I: Model formulation. Composite Structures, 156, (pp. 171-185). DOI: 10.1016/j.compstruct.2015.11.078.

**RMJ Groh**, PM Weaver, A Tessler (2015). Application of the Refined Zigzag Theory to the modeling of delaminations in laminated composites. NASA/TM-2015-218808.

**RMJ Groh**, PM Weaver (2015). On displacement-based and mixed-variational equivalent single layer theories for modelling highly heterogeneous laminated beams. International Journal of Solids and Structures, 59, (pp. 147–170). DOI: 10.1016/j.ijsolstr.2015.01.020.

**RMJ Groh**, PM Weaver (2015). Static inconsistencies in certain axiomatic higher-order shear deformation theories for beams, plates and shells. Composite Structures, 120, (pp. 231–245). DOI: 10.1016/j.compstruct.2014.10.006.

**RMJ Groh**, PM Weaver (2014). Buckling analysis of variable angle tow, variable thickness panels with transverse shear effects. Composite Structures, 107, (pp. 482–493). DOI: 10.1016/j.compstruct.2013.08.025.

**RMJ Groh**, PM Weaver, S White, G Raju, Z Wu. (2013). A 2D equivalent single-layer formulation for the effect of transverse shear on laminated plates with curvilinear fibres. Composite Structures, 100, (pp. 464–478). DOI: 10.1016/j.compstruct.2013.01.014.

**Conference Papers and Presentations**

**RMJ Groh**, A Pirrera (2017). A general computational framework for designing morphing structures*.* IN: Proceedings of the 21st International Conference on Composite Materials. Xi’an, China.

**RMJ Groh**, A Pirrera (2017). Numerical continuation—a robust approach for nonlinear stability analysis of composite shell structures. 3rd International Conference on Mechanics of Composites. University of Bologna, Italy.

G Arena, **RMJ Groh**, R Theunissen, PM Weaver, A Pirrera (2016). Adaptive Nonlinear Structures for Flow Regulation: Modelling Fluid-Structure Interactions with Coupled Eulerian-Lagrangian Meshes. IN: 2016 SIMULIA UK Regional User Meeting. Manchester, UK.

A Madeo, G Zagari, G Zucco, **RMJ Groh**, PM Weaver, R Zinno (2016). Koiter asymptotic analysis of Variable Angle Tow composite plates. ECCOMAS Congress 2016. Crete, Greece.

**RMJ Groh**, PM Weaver (2015). A mixed-variational, higher-order zig-zag theory for highly heterogeneous layered structures. 18th International Conference on Composite Structures. Lisbon, Portugal.

**RMJ Groh**, PM Weaver (2015). Full-field stress tailoring of composite laminates*.* IN: Proceedings of the 20th International Conference on Composite Materials. Copenhagen, Denmark.

**RMJ Groh**, PM Weaver (2015). Mass Optimization of Variable Angle Tow, Variable Thickness Panels with Static Failure and Buckling Constraints. IN: Proceedings of AIAA SciTech: 56th AIAA/ASME/ASCE/AHS/ASC Structures, structural dynamics and materials conference. Kissimmee, FL, USA.

**RMJ Groh**, PM Weaver (2014). Post-buckling analysis of variable angle, variable thickness panels manufactured by Continuous Tow Shearing. 1st International Conference on Mechanics of Composites. Stony Brook University, USA.

**RMJ Groh**, PM Weaver (2013). Buckling analysis of variable angle tow, variable thickness panels with transverse shear effects. IN: Proceedings of the International Conference on Composite Materials 19. Montreal, Canada.

**RMJ Groh**, PM Weaver (2013). Buckling analysis of variable angle tow, variable thickness panelswith transverse shear effects. 17th International Conference on Composite Structures. Porto, Portugal.

**Awards**

Collier Research HyperSizer/AIAA Structures Best Paper Award at AIAA SciTech: 56th AIAA/ASME/ASCE/AHS/ASC Structures, structural dynamics and materials conference. Kissimmee, FL, USA.

Ian Marshall’s Award for Best Student Paper at the 17th International Conference on Composite Structures, Porto, 2013.

Hello, Rainer! I’m a pilot in the U.S., flying a Boeing 737. I’ve always been interested in the hows and whys of aircraft design (not all pilots are so interested, though). I’ve always wondered: the 737 cockpit is rather noisy in flight, especially above 250 knots indicated airspeed. Why are some nose designs so different, and how do they affect aerodynamic efficiency and cockpit noise? For instance, the de Havilland Comet used a completely faired nose. But, the 707/727/737 use a stepped nose design, with considerable sharp corners and angles. The 757 nose is much more streamlined (at least it looks that way), and I’ve wondered if it results in less drag than the 707/727/737 nose. Also, all the new-generation aircraft (Boeing 787, Bombarier C-Series, Embraer 170/190) use a completely faired nose section, like the Comet. Could you do an article discussing these traits, and particularly, addressing if the 737 nose section is particularly “draggy?” With the 737MAX on the horizon, I’d like to know if Boeing missed an opportunity to do away with the old 1950’s-era nose section. Thanks! I enjoy your blog.

Hi Steve, as you pointed out the shape of the nose is heavily influenced by attempts to reduce drag and thereby maximise aerodynamic performance. The optimum shape of the nose is often determined by the desired flight velocity and therefore the type of flow that passes over the nose section. For commercial subsonic flight pressure-drag due to boundary layer separation is largely non-existent, so most of the drag is a result of skin-friction drag. The shear stresses that cause skin friction are also directly responsible for the noise levels within the cockpit. Skin-friction drag depends on the wetted area and type of flow (laminar or turbulent). For minimum friction and noise you ideally want laminar flow over the nose, which is really difficult to maintain due irregularities in the surface (bugs, scratches, dents) and the presence of any discontinuities in the shape that may trip the boundary layer. So for your 737 you ideally want a short, blunt and smooth elliptical shape. However, the shape of the nose is of course also influenced by packaging constraints for electronic and hydraulic actuating systems etc. and effectively channeling the flow to the rear parts of the aircraft where most of the lift is generated. So as is typically the case, some sort compromise has to be struck in order to maximise the overall performance. I am by no means an expert on the detail design of noses though, so I will do some research and then write an article about the findings. Cheers for reading the blog!

Regards,

Rainer

The 737 nose was copied from the 707, and both use large, flat window panes. The smaller panes used in the Comet and the Caravelle made their noses easier to shape. Modern designs use curved panes, and they produce no sharp edges which contribute noise.

Hello Rainer, I’m a high school student about to apply to Engineering. I was wondering whether you thought applying for general engineering and then specializing in aeronautics in the third and fourth year would be a waste of time compared to a 4 years solid aeronautics degree. I’m fascinated by the articles in this blog, but still unsure about whether I’d prefer getting to know all the different disciplines better before making a clear choice (especially because I’ve very intrigued by Mechanical engineering)or just throwing myself into aeronautics and hope for the best. Sorry for this confused comment! Love the blog though!

Hi Rainer, my name is Jorge Gerardo Aragón Villarreal, I´m mexican and currently live in Monterrey, México. I´m in the International Baccalaurete 2 year program and as part of it I need to make a research paper. Mine is about airfoils and I constructed a wind tunnel to make the experimentation. I´m lost in one aspect, however very important.

How I´m supposed to quantitatively visualize the critical angle of attack in an airfoil? is there any guide or criteria I could use to do it ? how can I determine if the angle of attack in a particular airfoil is , if i just have an wind tunel with smoke visualising ?

c

Hey George

http://www.dept.aoe.vt.edu/~aborgolt/aoe3054/manual/expt1/fig7.jpg is a good demonstration of how to get the quantative angle of attack. To be more precise you could think of a weighing system to calculate the lift and use Xfoil or just the airfoil data to correlate the lift and the angle

Hope you find this useful

Shrey

I stumbled onto your blog while looking for Aeronautical Engineering blogs and am very much enjoying it.

Hi Rainer,

Can you explain horizontal tail dihedral (or anhedral sometimes); what are the main drivers for rigging dihedral in a tailplane?

Hi Stephen, thanks for your comment. Sure, I’ll try to write a post about that soon. Cheers, Rainer

Hey Rainer! Awesome blog, congratulations!

Your aerospace hall of fame is great, I am here just to make sure you will remember aviation pioneer Santos-Dumont. He’s not so famous outside of Brazil, but certainly a great contributor to the beginning of aviation.

https://en.wikipedia.org/wiki/Alberto_Santos-Dumont

Hi George,

thank you for your comment, and I am glad that you enjoyed the post. Thank you also for the tip on Santos-Dumont. I will keep him in mind when I get to surnames starting with S 🙂

Rainer

Hi there, I will be starting a glider project university and am pre reading on lift, could you explain what this means as I am struggling to understand what it means:

“Bernoulli’s principle, i.e. along a streamline an increasing pressure gradient causes the flow speed to decrease and vice versa, is then invoked to deduce that the speed differential creates a pressure differential between the top and bottom surfaces, which invariable pushes the wing up.”

From your page on how to increase lift. Thank you!

Hi, thank you for your comment. What I am referring to in this comment is that Bernoulli’s principle is often invoked to explain why wings create lift. Bernoulli’s principle is derived from the conservation of energy along a streamline and states that , where is the fluid flow speed at a point on a streamline, is the gravitational constant, is the vertical distance with respect to a reference plane, is the fluid pressure, and the fluid density. So the combination of these parameters between two different points along a streamline have to give the same result when plugged into Bernoulli’s equation. If you look at the equation and assume that the streamline is horizontal (so does not change), then a decrease in pressure means that to keep the equation constant we need an increase in velocity . So the bottom line is that if pressure falls between two points then the velocity must increase, and if the pressure increases between the two points then velocity must decrease. What I was referring to in that comment is that the (faulty) argument is often made that the flow over the top surface of an aircraft wing is faster because this surface is longer due to curvature, and for equal transit times the flow over the top surface must be faster than over the bottom. It is certainly true that the flow over the top surface is often faster than over the bottom surface (and hence from Bernoulli the pressure on the top surface must be lower than on the bottom surface, which creates a pressure differential that sucks the wing in the direction of the top surface) but this is not due to the argument of equal transit times but rather due to centripetal forces induced by curved streamlines as a argue in the article. Let me know if this clarifies the above point…