We consider an inverse problem for the nonlinear Boltzmann equation with a time-dependent kernel in dimensions n \geq 2. We establish a logarithm-type stability result for the collision kernel from measurements under certain additional conditions. A uniqueness result is derived as an immediate consequence of the stability result. Our approach relies on second-order linearization and multivariate finite differences, as well as the stability of the light-ray transform.
more »
« less
One-period stability analysis of polygonal sweeping processes with application to an elastoplastic model
We offer a finite-time stability result for Moreau sweeping processes on the plane with periodically moving polyhedron. The result is used to establish the convergence of stress evolution of a simple network of elastoplastic springs to a unique cyclic response in just one cycle of the external displacement-controlled cyclic loading. The paper concludes with an example showing that smoothing the vertices of the polyhedron makes finite-time stability impossible.
more »
« less
- Award ID(s):
- 1916876
- PAR ID:
- 10151263
- Date Published:
- Journal Name:
- Mathematical Modelling of Natural Phenomena
- Volume:
- 15
- ISSN:
- 0973-5348
- Page Range / eLocation ID:
- 25
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Holder-Brascamp-Lieb inequalities provide upper bounds for a class of multilinear expressions, in terms of L^p norms of the functions involved. They have been extensively studied for functions defined on Euclidean spaces. Bennett-Carbery-Christ-Tao have initiated the study of these inequalities for discrete Abelian groups and, in terms of suitable data, have characterized the set of all tuples of exponents for which such an inequality holds for specified data, as the convex polyhedron defined by a particular finite set of affine inequalities. In this paper we advance the theory of such inequalities for torsion-free discrete Abelian groups in three respects.The optimal constant in any such inequality is shown to equal 1 whenever it is finite.An algorithm that computes the admissible polyhedron of exponents is developed. It is shown that nonetheless, existence of an algorithm that computes the full list of inequalitiesin the Bennett-Carbery-Christ-Tao description of the admissible polyhedron for all data,is equivalent to an affirmative solution of Hilbert's Tenth Problem over the rationals.That problem remains open.more » « less
-
null (Ed.)This paper develops an analytic framework to design both stress-controlled and displacement-controlled T -periodic loadings which make the quasistatic evolution of a one-dimensional network of elastoplastic springs converging to a unique periodic regime. The solution of such an evolution problem is a function t ↦( e ( t ), p ( t )), where e i ( t ) is the elastic elongation and p i ( t ) is the relaxed length of spring i , defined on [ t 0 , ∞ ) by the initial condition ( e ( t 0 ), p ( t 0 )). After we rigorously convert the problem into a Moreau sweeping process with a moving polyhedron C ( t ) in a vector space E of dimension d , it becomes natural to expect (based on a result by Krejci) that the elastic component t ↦ e ( t ) always converges to a T -periodic function as t → ∞ . The achievement of this paper is in spotting a class of loadings where the Krejci’s limit doesn’t depend on the initial condition ( e ( t 0 ), p ( t 0 )) and so all the trajectories approach the same T -periodic regime. The proposed class of sweeping processes is the one for which the normals of any d different facets of the moving polyhedron C ( t ) are linearly independent. We further link this geometric condition to mechanical properties of the given network of springs. We discover that the normals of any d different facets of the moving polyhedron C ( t ) are linearly independent, if the number of displacement-controlled loadings is two less the number of nodes of the given network of springs and when the magnitude of the stress-controlled loading is sufficiently large (but admissible). The result can be viewed as an analogue of the high-gain control method for elastoplastic systems. In continuum theory of plasticity, the respective result is known as Frederick-Armstrong theorem.more » « less
-
Abstract Moist static energy (MSE) budgets and gross moist stability (GMS) have been widely used as a diagnostic tool to study the evolution of moisture and convection at different time scales. However, use of GMS is limited at shorter time scales because many points in the tropics have close-to-zero large-scale vertical motion at a given time. This is particularly true in the case of convective life cycles, which have been shown to exist with noise-like ubiquity throughout the tropics at intraseasonal time scales. This study proposes a novel phase angle–based framework as a process-level diagnostic tool to study the MSE budgets during these cycles. Using the GMS phase plane, a phase angle parameter is defined, which converts the unbound GMS into a finite ranged variable. The study finds that the convective life cycles are closely linked to evolution of moisture and effectively behave as moisture recharge–discharge cycles. Convective cycles in different datasets are studied using TOGA COARE, a mix of different satellite products and ERA-Interim. Analysis of the MSE budget reveals that the cyclic behavior is a result of transitions between wet and dry equilibrium states and is similar across different regions. Further, vertical and horizontal advection of MSE are found to act as the primary drivers behind this variability. In contrast, nonlinearities in the radiative and surface flux feedbacks are found to resist the convective evolution. A linearized model consistent with moisture mode dynamics is able to replicate the recharge–discharge cycle variability in TOGA COARE data. Significance Statement In the tropics, variability of moisture and rainfall are closely linked to each other. Through this study we aim to better understand the evolution of moisture in observed daily time series data. We present a novel phase angle–based diagnostic tool to represent and study the energy budget of the system at this time resolution. Our results suggest that similar processes and mechanisms are relevant across different regions and at different scales in the tropics with moisture dynamics being important for these processes. Further, a key role is played by the energy transport associated with the large-scale circulation that drives moisture evolution in a cyclic pattern.more » « less
-
Earthquake-related failure modes for embankment dams are commonly evaluated through numerical simulations using finite element or finite difference approaches. This is especially true for liquefaction triggering or cyclic softening of fine-grained materials where advanced constitutive models are used to capture the dynamic response of the dam and the nonlinear behavior of the soil. Both liquefaction and cyclic softening can lead to significant strength loss, which can lead to large deformations within the dam, but these numerical tools often cannot capture these large deformations due to excessive mesh distortion and subsequent numerical errors. This leads to significant uncertainties in estimating potential crest settlement, which is often a critical value for risk assessments of dams. Hybrid numerical methods like the material point method (MPM) offer a promising alternative to model large deformations, but their application to dams is still limited and relatively little validation has been done on using MPM for post-earthquake stability analyses. This study focuses on applying MPM simulations to evaluate the post-earthquake stability of a hypothetical embankment dam and to examine potential deformations of a flowslide that occurred in Palu, Indonesia in 2018. The MPM program Anura3D is used for the analyses with modifications to allow for assigning residual strengths. The results from the Palu flowslide are compared with observations from the field to show that the MPM analyses are able to capture the extent of the slide, but underpredict the measured displacements in the central portion of the flowslide. The analyses for the embankment dam are compared with post-earthquake stability results from finite difference analyses using FLAC. The MPM analyses are able to capture the full deformation of the flowslide, while the FLAC analyses are halted due to excessive mesh deformation. These results demonstrate the potential of MPM to be used as a complement to existing numerical tools for evaluating the seismic response of dams, but additional work is needed to validate this approach using case histories with both large and small deformations.more » « less
An official website of the United States government

