Non-dominant Modes Research Articles

A simple method improving acoustic mode identification capability based on genetic algorithms

This letter develops a simple approach of duct mode identification and reconstruction based on genetic algorithms, which can extend the azimuthal mode order range compared to the conventional method based on the (spatial) discrete Fourier transform. The underlying principle is reconstructing the dominant mode from the modal identification forward model through optimization by exploiting the sparsity of the mode amplitude vector. The performance is experimentally demonstrated for detections of one and two azimuthal modes under noisy conditions with nondominant modes. Overall, the proposed genetic-algorithm-based framework for solving acoustic inverse problems is beneficial to duct acoustic testing, particularly design evaluations of fan blades and acoustic liners for aeroengines.

Design-oriented DC-side stability analysis of VSC-HVDC systems based on dominant frequency analysis

This paper derives analytical DC-side stabilizing conditions of voltage-source-converter-based high voltage DC (VSC-HVDC) links for control design. The case of a single modular multilevel converter (MMC) connected to an infinite DC bus system is first explored to determine the frequency of the dominant mode (dominant frequency) in the DC link. Then, the small-signal model of a generic two-terminal HVDC system is formulated. Since stability discrimination only focuses on the behaviors of the dominant mode, nondominant modes are collapsed in a way that leaves their dynamic properties nearby the dominant frequency intact. Accordingly, concise DC-side stabilizing conditions based on key parameters of physical systems and controllers can be derived, which indicates that the instability mechanism of VSC-HVDC links under DC-side perturbations is that the DC-voltage-controlled converter and the transmission line cannot provide sufficient positive damping to offset the negative damping induced by the power-controlled inverter. It is also interesting to find that increasing the proportional gain of the DC voltage control diminishes the damping of the converter, thereby endangering system stability. The maximum value of the proportional gain is further determined to guarantee sufficient system stability margins under various operating points. Finally, simulation studies validate the proposed DC-side stabilizing conditions for two-terminal VSC-HVDC systems.

Bi-regularization enhanced azimuthal mode analysis method for the aero-engine fan

Azimuthal mode analysis is regarded as an effective tool for aero-engine flow field investigation, where numerous microphones are evenly mounted as a ring to provide sufficient spatial resolution for azimuthal pressure acquisition. The current compressive sampling method enables azimuthal modes to be obtained from much fewer microphones, with dominant and non-dominant modes separately estimated by L1-norm regularization and spatial Fourier transform or least square method. Despite the effort of measurement system simplification, this classical compressive sampling method regularized by L1-norm inherently introduces accuracy loss in amplitude estimation for both dominant and non-dominant modes. With the aim of accuracy promotion and further measurement reduction, the Bi-regularization enhanced azimuthal mode analysis (BRAMA) method is devised to investigate the azimuthal modes of the aero-engine fan via limited acoustic measurements. The BRAMA method substitutes L1-norm regularization with Lp-norm (0<p<1) regularization to reach more accurate reconstruction of dominant modes. Meanwhile, the Tikhonov regularization based on L2-norm is introduced to estimate non-dominant modes. The effectiveness of the BRAMA method is verified in two cases, by operating a 2.5-stage aero-engine fan test rig at 50% and 90% of the nominal speed, respectively. Firstly, acoustic pressure signals are pre-processed to extract the dominant tonal component, which are used as the input of dominant mode estimation. Next, comparative realizations by L1-norm and Lp-norm are conducted to detect the dominant modes, meanwhile the amplitude accuracy with respect to p value and measurement number is discussed in both cases. Finally, non-dominant modes are estimated by using Tikhonov regularization in comparison to the classical approaches. Experimental results of both cases indicate that the BRAMA method outperforms the classical compressive sampling approach in accuracy improving, measurements reducing and interference proof capability.

Experimental Investigation of Vortex-Induced Vibrations on Yawed and Inclined Flexible Cylinders

Abstract An experimental setup was built to investigate the vortex-induced vibration (VIV) phenomenon on yawed and inclined flexible cylinders, in which five yaw angles θ = 0 deg, 10 deg, 20 deg, 30 deg, and 45 deg and five azimuth angles β = 0 deg, 45 deg, 90 deg, 135 deg, and 180 deg were combined. The experiments were carried out in a towing tank facility at Reynolds numbers from 1800 to 18,000, comprising vibrations up to the eighth natural mode. Time histories of displacements were recorded using a submerged optical system that tracks 17 reflective targets. A modal decomposition scheme based on Galerkin’s method was applied, aiming multimodal behavior investigations. Such an approach allowed the analysis of the modal amplitude throughout time, revealing interesting results for such a class of VIV tests. The flexible cylinder total response is generally a combination of two or more modes. Only for azimuths 0 deg, 90 deg, and 180 deg, a unimodal response was observed for the two first lock-in regimes. The frequency response showed that when the response was multimodal, non-dominant modes can follow the vibration frequency of the dominant one. Assuming a priori the independence principle (IP) valid to define the reduced velocities (Vr), it was observed that the resonance region was restricted to 3 ≤ Vr ≤ ~8 for the tested cases, indicating that the IP can be at least partially applied for flexible structures. As the literature scarcely explores the simultaneous yawed and inclined configurations, the present work may contribute to further code validation and improvements regarding the design of slender offshore structures.

Molecular etiology of non-dominant, non-syndromic, mild-to-moderate childhood hearing impairment in Chinese Hans.

Childhood hearing impairment (HI) is genetically heterogeneous. Compared with the severe-to-profound HI, the molecular etiology of mild-to-moderate HI in children has been less well characterized, especially for those not inherited in the dominant mode. In this study, we recruited 114 probands with non-dominant, non-syndromic, mild-to-moderate childhood HI. Sequencing of GJB2, SLC26A4, and MTRNR1 identified causative mutations in 30.7% (35/114), 4.4% (5/114), and 4.4% (5/114) of subjects, respectively. A majority (62.9%) of bi-allelic GJB2 mutations have non-truncating mutations in at least one allele. In 10 multiplex probands with no GJB2, SLC26A4, and MTRNR1 mutations identified, targeted next-generation sequencing (NGS) of 79 known deafness genes did not identify any additional causes. Our data showed that the molecular etiology of mild-to-moderate childhood HI is considerably different from what reported for severe-to-profound HI and far from complete for those inherited in non-dominant modes.

O moderno arcaísmo nacional: investimento estrangeiro direto e expropriação territorial no agronegócio canavieiro

Este trabalho visa compreender as reconfigurações territoriais desencadeadas no meio rural brasileiro a partir do início dos anos 2000 em decorrência da expansão dos monocultivos de cana destinados à produção de agrocombustíveis, bem como analisa a origem e montante dos investimentos estrangeiros diretos aplicados na produção brasileira de etanol. Para tanto, utiliza uma abordagem teórica que considera a existência de conflitos ambientais e territoriais associados à lógica operatória de exploração capitalista da natureza, e busca elucidar a presença de discursos hegemônicos direcionados a invisibilizar modos distintos e não dominantes de uso e apropriação dos recursos naturais. Ademais, inspirada nas contribuições de intelectuais latino-americanos aglutinados no que se denominou chamar paradigma modernidade-colonialidade, irá propor que a apropriação assimétrica dos recursos naturais tem sido parte integrante de uma condição de colonialidade na apropriação da natureza. Para sustentar essas análises, o artigo se vale da realização de dois trabalhos de campo conduzidos em áreas de expansão da monocultura de cana nos estados de Minas Gerais, São Paulo e Mato Grosso do Sul e do uso de estatísticas oficiais cotejadas pelo IBGE e pelo Banco Central.

Pieced Together: Collage as an Artist's Method for Interdisciplinary Research

As a visual artist undertaking doctoral studies in education, the author required a research method that integrated her studio practice into her research process, giving equal weight to the visual and the linguistic. Her process of finding such a method is outlined in this article, which touches on arts-based research and practice-led research, and her ultimate approach of choice, collage. Collage, a versatile art form that accommodates multiple texts and visuals in a single work, has been proposed as a model for a “borderlands epistemology”: one that values multiple distinctive understandings and that deliberately incorporates nondominant modes of knowing, such as visual arts. As such, collage is particularly suited to a feminist, postmodern, postcolonial inquiry. This article offers a preliminary theorizing of collage as a method and is illustrated with images from the author's research/visual practice.

Discrete two-time-scale systems

In this paper reduced-order modelling and control analysis of linear, discrete-time systems having dominant and non-dominant modes are presented. Decoupling of modes is achieved using an explicitly invertible linear transformation. A matrix norm condition is derived, the satisfaction of which enables approximate expressions for the block-diagonalizing matrices, eigenvalue distribution and state trajectories to be obtained. Design of stabilizing feedback controllers is developed and it is shown that two gain matrices are needed for separate assignment of dominant and non-dominant eigenvalues. The theoretical analysis is illustrated by control system examples.

On the use of reduced-order models in output feedback design of discrete systems

The problem of designing output feedback controllers for discrete systems using reduced-order models is investigated in this paper. It is shown that neglecting nondominant modes does not generally guarantee the stability of the closed-loop system. Certain special structures have been identified for which the use of static and dynamic feedback controllers can provide a stabilizing effect. Examples are presented to illustrate these structures.

Radial excitations ofp- and π-mesons and their strong decays

Radial (L=0) excitations ofp- and π-mesons are considered in the framework of the quark model. The experimentally observed statesρ′ (1220) andρ″ (1560) are identified with the first and second radial excitations of thep-meson. Within the relativistically generalized model of spontaneous production of a $$q\bar q$$ pair from vacuum we explain the dominant (ρ′ →ωπ;ρ″ →ω2π) modes of strong decays of these resonances and find nondominant modes (ρ ′ 2π;ρ″ →ωπ) to be suppressed. An estimation is given for masses of analogous excitations of the pion and partial widths of their decays.

Order Reduction of Linear State-Space Models Via Optimal Approximation of the Nondominant Modes

A new method of high order system simplification is proposed that yields stationary exact models of lower order. Using the Jordan-transform of the original system, first the notion ‘dominant eigenvalue’ is clarified by a dominance measure for each eigenvalue. By the aid of these dominance measures the dominant eigenvalues can be chosen as well as the order that the reduced system should have. After chosing the dominant eigenvalues the dominant modes are retained in the reduced model. Furthermore the lost nondominant modes are expressed as optimal linear combinations of the existing dominant motions and then they are reintroduced in the model of lower order. The optimization yields a directly programmable formula for the system matrices of the reduced model. The usefulness of the proposed method is demonstrated in detail by the application to the practical problem of a processing line whose original model is of 51th order.