Browsing by Subject "Perturbation"

Now showing 1 - 3 of 3

Analysis of soil-structure system response with adjustments to soil properties by perturbation method
(2014-05) Patta, Sang Putra Pasca Rante; Tassoulas, John Lambros
The research described in this dissertation undertakes a computational study of wave motion due to ground excitation in layered soil media. Adjustments of soil properties consistent with the level of deformation is applied using an equivalent linear approach. The finite element method provides the basis of the numerical procedure for soil-structure system response calculation in conjunction with a first-order perturbation scheme. Available experimental data are employed for shear-modulus and damping adjustments. The findings of the research are expected to lead to efficient calculation of structural response to earthquake ground motion.
Fourth-order vibrational perturbation theory(VPT4) : analytic expressions and applications
(2018-10-08) Gong, Justin.; Henkelman, Graeme; Stanton, John; Makarov, Dmitrii; Anslyn, Eric; Heinzen, Daniel
An analytic derivation of fourth order vibrational perturbation theory (VPT4) based on the Watson Hamiltonian in rectilinear coordinates is presented along with equations for [two different] anharmonic constants that appear in the expression for the vibrational energy. The framework and procedure involved in calculating these anharmonic constants is detailed, and the various numerical checks for the equations are described. This method is then used to calculate vibrational energy levels of water and formaldehyde with VPT4 at the CCSD(T)/ANO1 level. VPT4 vibrational levels are shown to be closer to exact variational results than VPT2 for the examples studied.
The influence of cognitive load on balance control during walking
(2021-04-19) Small, Gabriella Hodges; Neptune, Richard R.
Maintaining dynamic balance is essential during walking, with foot-placement playing a critical role. Situations requiring increased cognitive attention may impair an individual’s ability to actively control their balance. While dual-task studies have analyzed walking-while-talking conditions, few studies have focused on how cognitive loads impact balance control during steady-state walking and more difficult motor tasks, such as walking with foot-placement perturbations. Individuals recover from a loss of balance using an ankle or hip strategy, but how cognitive loads effect these recovery strategies remains unknown. The overall goal of this research was to investigate the influence of cognitive loads on balance control using two aims. The first aim assessed how individuals prioritize cognitive resources and control balance during steady-state walking with increasing cognitive loads. Aim 2 investigated how individuals prioritize cognitive resources to control their balance during dual-task walking while experiencing foot-placement perturbations. Fifteen young healthy adults performed a cognitive single-task condition (spelling-while-standing) and four treadmill walking conditions (no cognitive load, attentive listening, spelling short words backwards and spelling long words backwards), each performed during steady-state (Aim 1) and perturbed conditions (Aim 2). No specific task-prioritization instructions were given. During the perturbed trials, medial and lateral foot-placement perturbations were applied before heel-strike during random steps. Aim 1 showed that cognitive performance did not change between single- and dual-task conditions, but balance control decreased during the spelling dual-tasks. Aim 2 found that cognitive performance decreased between unperturbed and perturbed conditions. While balance control decreased during perturbed relative to unperturbed walking, the additional cognitive load had little effect during the perturbations. Lastly, the balance recovery strategy was unaffected by the addition of a cognitive load. The results from Aim 1 highlight that in steady-state walking, balance control decreases during treadmill walking with increased cognitive loads, but cognitive performance does not change, suggesting that participants prioritized cognitive performance over balance control. In contrast to steady-state walking, Aim 2 found that individuals prioritize their balance over cognitive task performance when faced with foot-placement perturbations. Overall, these results emphasize the flexibility of task-prioritization in young adults and provide a foundation for future studies analyzing neurologically impaired populations