The illimited LAB

Permanent URI for this collectionhttps://digital.lib.washington.edu/handle/1773/48358

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Detecting hidden transient events in noisy nonlinear time-series
(2022) Montoya, A.; Habtour, E.; Moreu, F.
The information impulse function (IIF), running Variance, and local Hölder Exponent are three conceptually different time-series evaluation techniques. These techniques examine time-series for local changes in information content, statistical variation, and point-wise smoothness, respectively. Using simulated data emulating a randomly excited nonlinear dynamical system, this study interrogates the utility of each method to correctly differentiate a transient event from the background while simultaneously locating it in time. Computational experiments are designed and conducted to evaluate the efficacy of each technique by varying pulse size, time location, and noise level in time-series. Our findings reveal that, in most cases, the first instance of a transient event is more easily observed with the information-based approach of IIF than with the Variance and local Hölder Exponent methods. While our study highlights the unique strengths of each technique, the results suggest that very robust and reliable event detection for nonlinear systems producing noisy time-series data can be obtained by incorporating the IIF into the analysis.
Directional DIC method with automatic feature selection
(Mechanical Systems and Signal Processing, 2025) Masmeijer, T.; Zaletelj, K.; Slavič, J.; Habtour, E.
Using displacement identification via high-speed cameras is a non-contact, full-field technique for characterizing the dynamic properties of engineered structures. Achieving reliable measurements of structural deformation through conventional Digital Image Correlation (DIC) requires a well-defined spatial gradient in two orthogonal directions within an image subset of pixels. However, DIC is susceptible to the aperture problem, which leads to an ill-conditioned optimization problem. An example of such a case is cable systems on which no speckle patterns can be applied. This study proposes Directional DIC (D-DIC) as an alternative technique to overcome the limitations posed by the aperture problem in conventional DIC methods. Directional DIC assumes the local direction of motion, which is often a valid assumption in structural vibration tests, as individual vibration shapes are often unidirectional at localized parts of the structure. This alleviates some restrictions on trackable image subsets, enabling more trackable locations. A parameter for quantifying expected tracking performance for D-DIC is introduced. The parameter enables automatic feature selection for D-DIC, making optical methods more accessible for displacement identification on structures where no speckle patterns can be applied. Experimental modal tests are conducted using a flexible spider web-like structure to validate the D-DIC method and compare it to conventional DIC. The experimental findings show that the Directional DIC method allows for measuring displacements at significantly more locations than conventional DIC. Additionally, D-DIC provided less noisy frequency response functions, more retrieved stable poles, and more fitted vibrational modes. Lastly, the findings show that D-DIC is especially superior to DIC when using small subsets since D-DIC is less inhibited by the aperture problem.
Programming tension in 3D-printed networks inspired by spiderwebs
(Materials & Design, 2026-01) Masmeijer, T.C.P.; Swain, C.C.; Hill, J.R.; Habtour, E.
Each element in tensioned structural networks—e.g., tensegrity or architectural fabrics—requires a specific tension to achieve the desired shape and stability. These structures are challenging to manufacture, 3D print, or assemble because flattening them during fabrication introduces multiplicative inaccuracies in the final tension gradients. We overcome this challenge by offering an algorithm for direct 3D printing of such networks with programmed tension gradients, analogous to the spinning of spiderwebs. The algorithm: (i) defines the desired network and prescribes its tension gradients; (ii) converts it into an unstretched counterpart by optimizing element lengths and converting straight elements into arcs; and (iii) decomposes the network into printable toolpaths; with the option to: (iv) flatten curved 2/3D networks to ensure printing compatibility; and (v) automatically resolve unwanted crossings introduced by flattening. Experimental validation is achieved using 2D unit cells with <1.0 % strain error in the tension gradients. The method remains effective for networks with a minimum element length of 5.8 mm and a maximum stress of 7.3 MPa. Fabricating complex cases is demonstrated for flat spiderweb, curved mesh, and tensegrity networks. The method represents a stepping-stone toward developing compact, integrated cable networks and orthotic devices with programmable moment-exerting structures.
Technology-forcing to reduce environmental noise pollution: a prospectus
(Nature, 2024-06-10) Kuehne, Lauren M.; Echenagucia, Tomás Méndez; Orfield, Steven J.; Habtour, Ed
BACKGROUND: Environmental movements of the late 20th century resulted in sweeping legislation and regulatory actions to reduce the prevalence of diverse pollutants. Although the consequences of noise pollution to public health, environment, and the economy have been recognized over the same time period, noise has received far less policy attention. Correspondingly, even while evidence of the diverse and detrimental effects of noise pollution on human health has grown, solutions and actual reductions in environmental noise remain seemingly out of reach. OBJECTIVE: To address this shortcoming, we developed a prospectus for environmental noise reduction through technology forcing policies. Technology-forcing describes intent to encourage technological solutions for pollution control through policy and regulations, and has been a critical component of national and global progress in reducing environmental pollutants. METHODS: We take advantage of the unique policy history for noise in the United States - which initially enacted, but then abandoned federal noise regulation. We compare this history against outcomes from contemporaneous environmental legislation for air, water, and occupational pollution control, to demonstrate the potential for technology-forcing to reduce noise pollution. Our review then identifies promising solutions, in the form of existing technologies suitable for innovation and diffusion through technology-forcing regulations and incentives. RESULTS: Based on this review, we outline a program for noise policy development to support efforts to reduce environmental noise pollution worldwide. The proposed program consists of three steps, which are to (i) identify dominant sources of noise pollution, (ii) combine legislative or regulatory provisions with suitable systems of enforcement and incentives, and (iii) anticipate and prepare for stages of technological change. IMPACT STATEMENT: Analysis of noise policy often focuses on justifying the need to reduce noise pollution. In this article, we demonstrate how technology-forcing regulations could also promote much-needed innovation and diffusion of technologies to reduce environmental noise pollution. We first establish the potential for technology-forcing by comparing technology outcomes from environmental legislation passed contemporaneously to the inactive US Noise Control Act. We next review promising innovations available for diffusion in multiple sectors to reduce environmental noise. Lastly, we recommend a program to support development of technology-forcing noise policies, to help ensure that the benefits of reduced noise pollution are distributed equitably.

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