Sean Palmer

A laser study of transient Lamb waves in thin materials

A method is described by which transient ultrasonic Lamb waves may be generated and detected within thin materials, using laser techniques. The material is thin enough that only the two lowest‐order modes of Lamb waves need be considered. These are the a0 mode, which is dispersive in the thin plate limit, and the s0 mode, which is not. Signal processing techniques were used to determine the dispersion characteristics of the a0 mode, and the velocity of the s0 mode, in both aluminum and metallic glass samples. From these measurements, it was possible to estimate both the thickness of the samples and their elastic constants. The errors involved in such a measurement are discussed.

Laser‐generated ultrasonic pulses at free metal surfaces

Longitudinal, shear, and surface acoustic pulses have been generated by irradiation of free metal surfaces with a Q‐switched Nd:YAG laser. Laser energies as low as 3u2009mJ are sufficient to generate ultrasonic pulses, in various metals, that are readily detected by conventional piezoelectric transducers, without the need for laser focusing. The generation efficiency of longitudinal, shear, and Rayleigh modes has been studied in both the presence and absence of a plasma. Experimental data in graphical form highlight several features of the acoustic source, from which a qualitative model is proposed.

Rigging the oceans of Disney's "Moana"

Disneys Moana was set in an environment inspired by the Pacific Islands, which made the ocean a prominent setting throughout the film. For much of the film, we found it necessary to treat our oceans like we would our hero characters, and so we developed three ocean rigs that formed the basis of all our ocean variants. Using a unified workflow that our artists were already familiar with, these rigs gave them the ability to easily portray and dial in a wide variety of ocean types such as open seas, calm seas, stormy seas, lagoons, shorelines, and wide ocean vistas, some which spanned hundreds of kilometers out to the horizon. This paper describes the techniques we used and some of the challenges we faced in developing these ocean rigs.

Some Applications of Laser-Generated Ultrasound in Metals

A Q-switched Nd:YAG laser has been used by the authors to generate elastic waves at metal surfaces. As a result of this work, various applications have been highlighted, and are described. These include use as a remote method of acoustic generation for nondestructive evaluation, as a standard acoustic source with excellent repeatibility, and as a method for liquid depth estimation.

Laser‐generated ultrasonic waveforms in metals

A Q‐switched, Nd:YAG laser has been used to generate elastic waves within aluminum and mild steel disks. A single 24‐ns pulse from the laser irradiated one face of each disk, and acoustic displacements were detected at the other face following propagation through the substrate. A capacitance transducer was used as the detector, providing undistorted displacement waveforms over a wide bandwidth. The displacement waveform depended markedly on the irradiation conditions. At low laser power densities, such that generation occurred primarily by thermoelastic expansion, a common waveform was produced whose amplitude varied linearly with optical energy. At higher power densities in the presence of material ablation, the longitudinal amplitude increased substantially whereas that of the shear decreased. Wave propagation theory in a plate has been applied to the problem, and theoretical waveforms in good agreement with experiment have been produced; this leads to conclusions concerning the nature of the acoustic s...

Countless characters and clovers: interpreting Dr. Seuss' style with 3D fur

Translating Dr. Seuss Horton Hears a Who! from the printed page to an animated feature presented stylistic and technical challenges for Blue Sky’s ray-traced voxelized fur technology. The directors embraced our fur tools to interpret Seuss brush strokes, challenging us to address the scope of our furriest feature film to date. We furred and feathered jungle animals, groomed clothing for Whos in Whoville, emulated Seuss’ swooshes for trees and bushes, and created landscapes with windswept grasses and clovers.

EXPERIMENTAL STUDIES INTO ULTRASONIC MODE CONVERSION

Two experimental techniques have been investigated, for the practical application of mode conversion techniques to the detection of surface-breaking defects. Both are based upon ultrasonic generation by pulsed lasers. In the first, the laser generates a Rayleigh wave, which results in shear radiation from the defect; this signal is then detected by an EMAT. In the second technique, an immersion transducer detects signals arising from longitudinal to shear mode conversion.

Building moana's kakamora barge

In Walt Disney Animation Studios Moana, a key moment in the story calls for the protagonists to confront a floating island barge crewed by coconut-clad pirates: the Kakamora. Combining a large moving set on an animated ocean with active crowds, sails, ropes and effects simulations required coordination across multiple departments and some on-the-fly innovations. To handle the challenges the sequence presented, we made extensive use of automation and procedural tools along with some creative design decisions to save artist time and allow for greater reuse.

The ocean and water pipeline of Disney's Moana

Disneys Moana was the largest and most complex water project the studio had ever undertaken. Over 900 shots required ocean interaction, which included boat wakes, splashes, shorelines, walls of water, and highly art-directed sentient water. Our previous films water techniques would not scale to address the complexity and volume of work required by Moana and staffing and time constraints necessitated automating large parts of the process. We redesigned our pipeline to provide a flexible authoring process for a lightweight implicit ocean representation. This new workflow allowed artists to visualize and edit specific parts of the water setup and easily share their updates with other departments.

State and future of hair in feature film and visual effects

Computer generated hair has historically been a challenging element in the feature film and visual effects industry. Technology and workflow challenges in authoring, animation, simulation, shading, lighting and rendering have motivated studios and software companies to invest in tools and techniques to address the evergrowing creative appetite for hair to deliver captivating stylized and/or realistic characters. To deliver on the creative demand, some feature production studios have specialized hair production across multiple workflows-visual development, rigging, simulation, and lighting to name a few. Has this divided approach to solving a visually holistic challenge affected the tools choices and the way we invest in our toolsets? This panel will bring together engineers and artists representing various areas of expertise to provide a summary of their day to day relationship with hair. They will describe some of the big challenges and their solutions, as well as any issues still outstanding. From there we will dive into some of the commonalities and outliers to better understand how we have arrived at our current state and ultimately what the future is for CG hair, from a technology, workflow, and organizational points of view.