72 research outputs found
Supplementary Materials: The Hidden Burden – Psychological Distress in Males with Substance Use Challenges
No full textThis OSF project contains supplementary materials associated with the manuscript “The Hidden Burden: Psychological Distress in Males with Substance Use Challenges” by Mainak Mitra. Materials may include manuscript versions, analysis notes, tables, and supporting documentation. The final published work is linked in the associated OSF preprint
Effects of contact mistuning on shrouded blisk dynamics
No full textMistuning commonly refers to non-cyclically symmetric variations in such an otherwise cyclically-symmetric structure. Mistuning in a blisk due to variations in blade materials and geometry have been studied extensively and are known to have a significant impact on the forced response of blisks. However, mistuning can also arise due to variations at contact interfaces within a blisk with friction damping mechanisms such as under platform dampers or shrouds. Past literature analyzing the effect of this source of contact mistuning is limited, particularly by the use of lumped or single-node contacts at each sector to shorten analysis times. In this paper, we aim to better understand the specific effects of parameter variations across contact interfaces on an otherwise tuned blisk. A blisk with shroud to shroud contacts is considered. Accurate representation of microslip phenomena are incorporated in the analysis by modeling multiple localized node to node contact models at contact surfaces on each blisk sector. Contact stiffnesses which dictate the friction damping dynamics of the shrouds are chosen as the mistuning parameters. The harmonic balance method is used to solve for forced responses. We analyze cases with random patterns of contact stiffnesses in different microslip regimes in the proximity of different modal regions. Probabilistic analysis of nonlinear contact responses are carried out close to a linear region where comparatively high amplification factors are observed. Statistics are also developed for linear cases and compared with the nonlinear case to qualify the dependence of amplification factors of nonlinear forced responses on the level of microslip and on the variance of contact parameters
Adaptive microslip projection (AMP) for reduction of frictional and contact non-linearities in shrouded blisks
No full textReduced order models (ROMs) of turbine bladed disks (blisks) are essential to quickly yet accurately characterize vibration characteristics and effectively design for high cycle fatigue. Modeling blisks with contacting shrouds at adjacent blades is especially challenging due to friction damping and localized non-linearities at the contact interfaces which can lead to complex stick-slip behavior. While well-known techniques such as the harmonic balance method and Craig-Bampton component mode synthesis have generally been employed to generate ROMs in the past, they do not reduce degrees of freedom (DoFs) at the interfaces themselves. In this paper we propose a novel method to obtain a set of reduction basis functions for the contact interface DoFs as well as the remaining DoFs called adaptive microslip projection (AMP). The method is based on analyzing a set of linear systems with specifically chosen boundary conditions on the contact interface. Simulated responses of full order baseline models and the novel ROMs under various conditions are studied. Results obtained from the ROMs compare very favorably with the baseline model. The AMP procedure is also easily generalizable to other dynamic systems with Coulomb friction contact
Dynamic model order reduction of blisks with nonlinear damping coatings using amplitude dependent mistuning
No full textIn this paper, a reduced order model is developed to simulate the dynamics of a bladed disk or blisk with nonlinear damping coatings adhered to its blades. The nonlinear forces exerted by these coatings on the underlying linear blisk structure are a function of the local strain. It is known that coatings modify the stiffness and damping of each blade depending on its amplitude. Blisks, which are designed as perfectly cyclic symmetric structures with identical blades, never behave as such in practice due to various uncertainties encountered during their manufacturing. This asymmetry in the structure is also referred to as mistuning. Mistuning in the linear blisk structure, which causes different blades to respond with non-identical amplitudes, interacts with the coating nonlinearity to yield a mistuning pattern which depends on the blade amplitudes. Additional stiffness and damping parameters that are dependent on the blade amplitude are introduced into a reduced linear model to formulate the nonlinear reduced order model. It is found that this model captures the nonlinear amplitude dependent mistuning effect and predicts the nonlinear coated blisk responses accurately near isolated blisk mode families in blade-dominated frequency regions where these coating effects are likely to be dominant. Significant reductions in the computational effort are achieved through this reduction
Adaptive Microslip Projection for Reduction of Frictional and Contact Nonlinearities in Shrouded Blisks
No full textReduced order models (ROMs) of turbine bladed disks (blisks) are essential to quickly yet accurately characterize vibration characteristics and effectively design for high cycle fatigue. Modeling blisks with contacting shrouds at adjacent blades is especially challenging due to friction damping and localized nonlinearities at the contact interfaces which can lead to complex stick-slip behavior. While well-known techniques such as the harmonic balance method (HBM) and Craig-Bampton component mode synthesis (CB-CMS) have generally been employed to generate ROMs in the past, they do not reduce degrees-of-freedom (DoFs) at the interfaces themselves. In this paper, we propose a novel method to obtain a set of reduction basis functions for the ontact interface DoFs as well as the remaining DoFs called "adaptive microslip projection" (AMP). The method is based on analyzing a set of linear systems with specifically chosen boundary conditions on the contact interface. Simulated responses of full order baseline models and the novel ROMs under various conditions are studied. Results obtained from the ROMs compare very favorably with the baseline model. This study addresses the case of a shrouded blisk in microslip close to stick. The AMP procedure may be possibly applied to other systems with Coulomb friction contacts, but its accuracy and effectiveness will need to be evaluated separatel
A sensitivity based heuristic for optimal blade arrangement in a linear mistuned rotor
No full textThis paper investigates methodologies for finding optimal or near-optimal blade arrangements in a bladed disk with inserted blades for minimizing or maximizing blade response amplification due to mistuning in material properties of the blades. The mistuning in the blades is considered to be known, and only their arrangement is modifiable. Hence, this is a problem in discrete optimization, particularly combinatorial optimization where the objective of response amplification is a nonlinear function of the blade arrangement. Previous studies have treated mistuning as a continuous parameter to analyze its effects on the response amplification. Sensitivity metrics have proven to be an important tool in quantifying the effects of mistuning. One such sensitivity metric is used here to formulate an iterative heuristic approach to solve the optimization problem. A component mode mistuning reduced order model is used for fast evaluations of the dynamic responses of a bladed disk with a given blade arrangement. At any iteration the sensitivity of the maximum response of the current rotor design to changes in blade stiffnesses due to changes in the blade arrangement is used to predict the arrangement for the following iteration. In addition to the proposed sensitivity-based approach, we use genetic algorithms to find optimal arrangements and compare results with the heuristic approach
CCDC 1418388: Experimental Crystal Structure Determination
No full textRelated Article: Mainak Mitra , Hassan Nimir , Serhiy Demeshko , Satish S. Bhat , Sergey O. Malinkin , Matti Haukka , Julio Lloret-Fillol , George C. Lisensky , Franc Meyer , Albert A. Shteinman , Wesley R. Browne , David A. Hrovat , Michael G.Richmond , Miquel Costas , Ebbe Nordlander|2015|Inorg.Chem.|54|7152|doi:10.1021/ic5029564,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
CCDC 994961: Experimental Crystal Structure Determination
No full textRelated Article: Mainak Mitra , Hassan Nimir , Serhiy Demeshko , Satish S. Bhat , Sergey O. Malinkin , Matti Haukka , Julio Lloret-Fillol , George C. Lisensky , Franc Meyer , Albert A. Shteinman , Wesley R. Browne , David A. Hrovat , Michael G.Richmond , Miquel Costas , Ebbe Nordlander|2015|Inorg.Chem.|54|7152|doi:10.1021/ic5029564,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
CCDC 1033835: Experimental Crystal Structure Determination
No full textRelated Article: Mainak Mitra , Hassan Nimir , Serhiy Demeshko , Satish S. Bhat , Sergey O. Malinkin , Matti Haukka , Julio Lloret-Fillol , George C. Lisensky , Franc Meyer , Albert A. Shteinman , Wesley R. Browne , David A. Hrovat , Michael G.Richmond , Miquel Costas , Ebbe Nordlander|2015|Inorg.Chem.|54|7152|doi:10.1021/ic5029564,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Functional Models for Non-heme Mononuclear Iron Oxygenases
No full textNon-heme mononuclear iron oxygenases catalyze a large number of oxidation reactions in biological systems. The reactions are often proposed to proceed via the intermediacy of high valent Fe(IV) oxo (ferryl) or, Fe(V) oxo (perferryl) intermediates. Therefore, in order to mimic the high valent Fe(IV) oxo chemistry as well as the catalytic processes exhibited by those enzymes, new functional model complexes have been prepared and their reactivities have been studied both experimentally and theoretically. In order to prepare high valent Fe(IV) oxo complexes, two new pentadenate nitrogen donor-based ligands have been synthesized and their Fe(II) complexes have been synthesized and characterized. The Fe(II) complexes have been converted into the corresponding Fe(IV) oxo complexes using suitable oxidant. The Fe(IV) oxo complexes have been characterized by several spectroscopic techniques and their reactivities in C-H activation and the O-atom transfer reaction have been investigated. Theoretical studies have been carried out to investigate the H-atom transfer reaction. The Fe(II) complexes have also been employed in alkane oxidation catalysis using hydrogen peroxide and peracids. To make functional models for Rieske oxygenases, three tetradentate nitrogen-donor based ligands have been prepared. The corresponding Fe(II) complexes have been prepared and characterized. The C-H hydroxylation and C=C oxidation reactions have been studied using these complexes as catalyst and hydrogen peroxide as oxidant. Isotope labeling studies and computational studies have been performed to investigate the reaction mechanisms. A Fe(II) complex of a tetradentate chiral nitrogen-donor based ligand has also been prepared to investigate the asymmetric epoxidation of olefins, using hydrogen peroxide as oxidant
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