More Like this

1. Enigmatic surface rolls of the Ellesmere Ice Shelf

   https://doi.org/10.1017/jog.2022.3  

   Coffey, Niall B.; MacAyeal, Douglas R.; Copland, Luke; Mueller, Derek R.; Sergienko, Olga V.; Banwell, Alison F.; Lai, Ching-Yao (January 2022, Journal of Glaciology)

   Abstract The once-contiguous Ellesmere Ice Shelf, first reported in writing by European explorers in 1876, and now almost completely disintegrated, has rolling, wave-like surface topography, the origin of which we investigate using a viscous buckling instability analysis. We show that rolls can develop during a winter season (~ 100 d) if sea-ice pressure (depth-integrated horizontal stress applied to the seaward front of the Ellesmere Ice Shelf) is sufficiently large (1 MPa m) and ice thickness sufficiently low (1–10 m). Roll wavelength initially depends only on sea-ice pressure, but evolves over time depending on amplitude growth rate. This implies that a thinner ice shelf, with its faster amplitude growth rate, will have a shorter wavelength compared to a thicker ice shelf when sea-ice pressure is equal. A drawback of the viscous buckling mechanism is that roll amplitude decays once sea-ice pressure is removed. However, non-Newtonian ice rheology, where effective viscosity, and thus roll change rate, depends on total applied stress may constrain roll decay rate to be much slower than growth rate and allow roll persistence from year to year. Whether the viscous-buckling mechanism we explore here ultimately can be confirmed as the origin of the Ellesmere Ice Shelf rolls remains for future research. 

   more » « less
2. Assessing Wound Roll Quality using Measured Stiffness and Models

   Markum, R.; Good, J.K. (June 2019, Proceedings of the Fifteenth International Conference on Web Handling)

   For those concerned with roll quality it is difficult to suppress the urge to compress the outer surface of a wound roll with your thumb to sense how tightly the roll was wound and how large the internal pressures might be. If several rolls of a given web are wound at unique tensions a human could often arrange these rolls in order of ascending winding tension using their thumb test. The thumb senses the relative conforming deformation of the roll surface. A soft roll would deform more and have greater contact area with our thumb than a hard roll for a given load. The thumb test is most useful on softer rolls wound from nonwovens, tissues, some grades of paper and polymer films but less so on metal coils that deform little in comparison to our thumb. The physics define stiffness as the extent to which an object resists deformation in response to an applied force. This publication reports the results of research where the stiffness of the outer surface of a wound roll is used to characterize the internal residual stresses throughout the roll due to winding. Measurements of stiffness of the outer surface of wound rolls will be demonstrated using commercially available devices along with a proposed handheld device all having greater resolution than the thumb. These measurements will be coupled with models to allow the exploration of internal residual stresses in the wound roll that can be used to investigate winding defects and roll quality. 

   more » « less
3. Active head rolls enhance sonar-based auditory localization performance

   https://doi.org/10.1371/journal.pcbi.1008973  

   Wijesinghe, Lakshitha P.; Wohlgemuth, Melville J.; So, Richard H.; Triesch, Jochen; Moss, Cynthia F.; Shi, Bertram E. (May 2021, PLOS Computational Biology)

   Thaler, Lore (Ed.)

   Animals utilize a variety of active sensing mechanisms to perceive the world around them. Echolocating bats are an excellent model for the study of active auditory localization. The big brown bat ( Eptesicus fuscus ), for instance, employs active head roll movements during sonar prey tracking. The function of head rolls in sound source localization is not well understood. Here, we propose an echolocation model with multi-axis head rotation to investigate the effect of active head roll movements on sound localization performance. The model autonomously learns to align the bat’s head direction towards the target. We show that a model with active head roll movements better localizes targets than a model without head rolls. Furthermore, we demonstrate that active head rolls also reduce the time required for localization in elevation. Finally, our model offers key insights to sound localization cues used by echolocating bats employing active head movements during echolocation. 

   more » « less
4. Quasistatic strain fields in normally- and tangentially-loaded elastomeric rollers under impending slip

   https://doi.org/10.1016/j.ijsolstr.2024.112739  

   Mork, Nehemiah; Rajchel, Milosz K; Varenberg, Michael; Antoniou, Antonia; Leamy, Michael J (April 2024, International Journal of Solids and Structures)

   Elastomeric rollers are important components in applications such as printing and roll-to-roll manufacturing. To gain insight into roller mechanics and provide a basis for further investigations into dynamic rolling problems where rolling instabilities and rolling friction arise, we employ a specially designed apparatus to obtain displacement and strain fields via digital image correlation (DIC) under applied loads.We test loading scenarios leading to impending slip of an elastomeric roller, mounted on a steel hub, and in contact with a glass (rigid) substrate. We first examine strain fields under normal loading and compare them with the closest analytical predictions. We also analyze the strain fields under normal and tangential loading for which limited analytical predictions exist. For each loading scenario, we discuss the displacement and strain fields of the roller sidewall and contact interface. We implement a conceptual string model to demonstrate how stick and slip zones develop within the contact area as well as how memory effects arise during cyclic loading. This memory effect is then verified experimentally using the DIC strain fields. Additionally, we demonstrate a means for identifying the stick zone area between the roller and substrate using the experimentally-obtained displacement fields. We believe the apparatus, and the ability to obtain experimental displacement and strain fields, will prove valuable in understanding roller mechanics and associated instabilities. 

   more » « less
5. Web Length Creep in Wound Rolls

   Mollamahmutoglu, C.; Gajjalla, A.; Markum, R.; Azoug, A.; Good, J.K. (June 2019, Proceedings of the Fifteenth International Conference on Web Handling)

   For convenience, webs are stored in wound rolls. The available web length in a wound roll is one mark of roll quality and a concern for many who process and convert webs. Elastic winding models have proven very precise at estimating the number of layers, the web length wound into a roll, and the residual stresses in the roll at the time of winding. Wound rolls can spend long periods of time in storage, where controlling the environment is cost-prohibitive. As many webs are viscoelastic on some time scale, the residual stresses due to winding will result in creep during storage. The changes in web length due to creep result in web process errors and quality loss, including registration errors and camber webs for example. This publication will focus on the development of a viscoelastic winding model to predict these changes in web length due to creep in a wound roll. The viscoelastic model predicts the tangential stress relaxation and radial creep due to winding residual stresses from a fully viscoelastic orthotropic material behavior. A spunned-meltblown-spunned (SMS) web and a low-density polyethylene (LDPE) web are taken as examples of viscoelastic webs. Their viscoelastic properties are systematically characterized using creep experiments. The results of the model show good agreement with winding and storage experiments for both webs. Finally, webs often do not creep uniformly across their width. An example of this non-uniform creep will be explored. 

   more » « less