Selectively embedding multiple spatially steered fibers in polymer composite parts made using vat photopolymerization

Fiber-Reinforced Polymer Composite (FRPC) parts are mostly made as laminates, shells, or surfaces wound with 2D fiber patterns even after the emergence of additive manufacturing. Making FRPC parts with embedded continuous fibers in 3D is not reported previously even though topology optimization shows that such designs are optimal. Earlier attempts in 3D fiber reinforcement have demonstrated additively manufactured parts with channels into which fibers are inserted. In this paper, we present 3D printing techniques along with a printer developed for printing parts with continuous fibers that are spatially embedded inside the matrix using a variant of vat photopolymerization. Multiple continuous fibers are gradually steered as the part is built layer upon layer instead of placing them inside channels made in the part. We show examples of spatial fiber patterns and geometries built using the 3D printing techniques developed in this work. We also test the parts for strength and illustrate the importance of spatially embedding fibers in specific patterns.Comment: 9 pages and 8 figure

Modelling and control of a rotor supported by magnetic bearings

In this paper we develop a dynamical model of a rotor and the active magnetic bearings used to support the rotor. We use this model to develop a stable state feedback control of the magnetic bearing system. We present the development of a rigid body model of the rotor, utilizing both Rotation Matrices (Euler Angles) and Euler Parameters (Quaternions). In the latter half of the paper we develop a stable state feedback control of the actively controlled magnetic bearing to control the rotor position under inbalances. The control law developed takes into account the variation of the model with rotational speed. We show stability over the whole operating range of speeds for the magnetic bearing system. Simulation results are presented to demonstrate the closed loop system performance. We develop the model of the magnetic bearing, and present two schemes for the excitation of the poles of the actively controlled magnetic bearing. We also present a scheme for averaging multiple sensor measurements and splitting the actuation forces amongst redundant actuators

Nonlinear control of magnetic bearings

In this paper we present a variety of nonlinear controllers for the magnetic bearing that ensure both stability and robustness. We utilize techniques of discontinuous control to design novel control laws for the magnetic bearing. We present in particular sliding mode controllers, time optimal controllers, winding algorithm based controllers, nested switching controllers, fractional controllers, and synchronous switching controllers for the magnetic bearing. We show existence of solutions to systems governed by discontinuous control laws, and prove stability and robustness of the chosen control laws in a rigorous setting. We design sliding mode observers for the magnetic bearing and prove the convergence of the state estimates to their true values. We present simulation results of the performance of the magnetic bearing subject to the aforementioned control laws, and conclude with comments on design

Degenerate Kalman filter error covariances and their convergence onto the unstable subspace

The characteristics of the model dynamics are critical in the performance of (ensemble) Kalman filters. In particular, as emphasized in the seminal work of Anna Trevisan and coauthors, the error covariance matrix is asymptotically supported by the unstable-neutral subspace only, i.e., it is spanned by the backward Lyapunov vectors with nonnegative exponents. This behavior is at the core of algorithms known as assimilation in the unstable subspace, although a formal proof was still missing. This paper provides the analytical proof of the convergence of the Kalman filter covariance matrix onto the unstable-neutral subspace when the dynamics and the observation operator are linear and when the dynamical model is error free, for any, possibly rank-deficient, initial error covariance matrix. The rate of convergence is provided as well. The derivation is based on an expression that explicitly relates the error covariances at an arbitrary time to the initial ones. It is also shown that if the unstable and neutral directions of the model are sufficiently observed and if the column space of the initial covariance matrix has a nonzero projection onto all of the forward Lyapunov vectors associated with the unstable and neutral directions of the dynamics, the covariance matrix of the Kalman filter collapses onto an asymptotic sequence which is independent of the initial covariances. Numerical results are also shown to illustrate and support the theoretical findings

N-[4-(2-Morpholino­eth­oxy)phen­yl]acetamide monohydrate

In the title compound, C14H20N2O3·H2O, the geometry about the morpholine N atom implies sp 3 hybridization. In the crystal, symmetry-related mol­ecules are linked by inter­molecular N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds, forming infinite chains along the b axis. The chain structure is further stabilized by intra­molecular C—H⋯O inter­actions

Rank deficiency of Kalman error covariance matrices in linear time-varying system with deterministic evolution

We prove that for-linear, discrete, time-varying, deterministic system (perfect-model) with noisy outputs, the Riccati transformation in the Kalman filter asymptotically bounds the rank of the forecast and the analysis error covariance matrices to be less than or equal to the number of nonnegative Lyapunov exponents of the system. Further, the support of these error covariance matrices is shown to be confined to the space spanned by the unstable-neutral backward Lyapunov vectors, providing the theoretical justification for the methodology of the algorithms that perform assimilation only in the unstable-neutral subspace. The equivalent property of the autonomous system is investigated as a special case

Improvement of radar ice-thickness measurements of Greenland outlet glaciers using SAR processing

This is the published version, also available here: http://dx.doi.org/10.3189/172756402781816852.Extensive aircraft-based radar ice-thickness measurements over the interior and outlet-glacier regions of the Greenland ice sheet have been obtained by the University of Kansas since 1993, with the latest airborne surveys conducted in May 2001. The radar has evolved during this period to a highly versatile system capable of characterizing ice thickness over a wide variety of ice-sheet conditions. Before 1997, the digital system was limited, only capable of storing incoherent data or coherent data with a very large number of presumed signals at a low pulse-repetition frequency. In 1998, the radar was upgraded with modern components allowing coherent data to be stored with a small number of presumed returns for 1024 range cells at a high pulse-repetition frequency.The new data on ice thickness of Greenland outlet glaciers are archived and made available to the scientific community in the form of radar echograms and derived ice thickness at http://tornado.rsl.ukans.edu/Greenlanddata.htm. The U.S. National Snow and Ice Data Center (NSIDC) also provides a link to these data, and NSIDC will eventually serve as the permanent archive of these data. Improvements in radar sensitivity in outlet-glacier regions have been achieved by collecting coherent radar data and applying various signal-processing techniques. Deep outlet-glacier channels that were previously unresolved with incoherent data can now be mapped using a coherent signal, signal conditioning and synthetic aperture radar (SAR) processing

4-[2-(4-Meth­oxy­phen­yl)eth­yl]-3-(thio­phen-2-ylmeth­yl)-1H-1,2,4-triazol-5(4H)-one monohydrate

In the title compound, C16H17N3O2S·H2O, the triazole ring makes a dihedral angle of 34.63 (6)° with the benzene ring. The thio­phene ring is disordered over two orientations [occupancy ratio = 0.634 (4):0.366 (4)] which make dihedral angles of 54.61 (16) and 54.57 (31)° with the triazole ring. Inter­molecular N—H⋯O and O—H⋯O hydrogen bonds stabilize the crystal structure

4-[3-(1H-Imidazol-1-yl)prop­yl]-3-methyl-5-(thio­phen-2-ylmeth­yl)-4H-1,2,4-triazole monohydrate

In the title compound, C14H17N5S·H2O, the triazole ring makes dihedral angles of 48.15 (8) and 84.92 (8)° with the imidazole and thio­phenyl rings, respectively. The water mol­ecule is involved in inter­molecular O—H⋯N hydrogen bonding