An optimum multimode interference coupler as an all-optical switch based on nonlinear modal propagation analysis

Since the noise generated by mechanical structures affects the merchantability, it is important to predict the noise and vibratory characteristics at the first design stage. The frames and panels or trim parts in automobiles are coupled systems of the rigid and flexible substructure. In these systems, vibration of the flexible structures often becomes one of the major noise sources when the excitation force is applied to the rigid structure. FEM and modal analysis technique are not sufficient to carry out the effective low noise design in higher frequency because of high modal density and complexity of mode shape. Modal energy propagation method, proposed in this paper, is based on the mode synthesis method and the vibration power flow between the eigen modes of the rigid and flexible structures. Previous studies have verified that the vibration level can be reduced by extracting modes that contribute highly to the vibration power flow between subsystems and changing their characteristics. In this report, we present the results of applying this method to a coupled system of a body and panel structures in automobiles and verifying its validity. The structural modifications obtained from this analysis method were verified for their effectiveness in decreasing vibration.

A nonlinear modal analysis procedure is presented for the forced response of nonlinear structural systems. It utilizes the notion of invariant manifolds in the phase space, which was recently used to define nonlinear normal modes and the corresponding nonlinear modal analysis for unforced vibratory systems. For harmonic forcing, a similar procedure could be formulated, simply by augmenting the size of the free vibration problem. However, in order to accommodate general, nonharmonic external excitations, the invariant manifolds associated with the unforced system are used herein for the forced response analysis. The procedure allows one to generate reduced-order models for the forced analysis of structural systems. Although strictly speaking the invariance property is violated, good results are obtained for the case study considered. In particular, it is found that fewer nonlinear modes than linear modes are needed to perform a forced modal analysis with the same accuracy. For systems with small and/or diagonal damping, approximate invariant manifolds are determined, which are shown to yield good results for both the unforced and forced responses. (Author)

This paper presents a rigorous field theoretical analysis of slow wave mode propagation in coplanar waveguide (CPW) metal-insulator-semiconductor (MIS) transmission lines with a laterally confined doping profile. Two types of transmission line structures are investigated-bulk silicon and semiconductor-on-insulator (SOI). In both cases a Gaussian profile of the doping depth is assumed. It was found that an optimum lateral width of the doping region exists for which both structures exhibit a much better slow wave factor at lower losses than traditional thin-film MIS transmission lines. The abrupt transition between MIS, CPW, and CPW on a normal insulating substrate was investigated as well. It was found that the reflection coefficient increases significantly with frequency and when the lateral width of the doping region is extended over the whole cross section of the CPW. The investigation was carried out using the frequency-domain transmission line modeling (TLM) (FDTLM) method.

Modal analysis is a well-established method for analysis of linear dynamic structures, but its extension to non-linear structures has proven to be much more problematic. A number of viewpoints on non-linear modal analysis as well as a range of different non-linear system identification techniques have emerged in the past, each of which tries to preserve a subset of properties of the original linear theory. The objective of this paper is to discuss how the Hilbert-Huang transform can be used for detection and characterization of non-linearity, and to present an optimization framework which combines the Hilbert-Huang transform and complex non-linear modal analysis for quantification of the selected model. It is argued that the complex non-linear modes relate to the intrinsic mode functions through the reduced order model of slow-flow dynamics. The method is demonstrated on simulated data from a system with cubic non-linearity.

Wave propagation in thin pretwisted composite strips with an embedded delamination

The design and development of a wing for a completely brand-new aircraft represents, in aeronautics, one of the highest challenges from an engineering point of view. The present work describes a novel methodology devoted to execute numeric simulation in a non-linear post-buckling regime to verify the composite wing compliance under the design load conditions. The procedure was developed as part of a wing design and research activity and was motivated by the need to have more realistic results, without standard conservatisms like the no-buckling up to ultimate load, to be of use for achieving further weight savings. To carry this out, it was obviously necessary to ensure that the structural integrity was also guaranteed in the post-buckling regime, above the limit load, and therefore in a highly non-linear regime. The present work illustrates a numerical approach based on non-linear finite element analysis which uses the inertia relief option in order to have a more realistic representation of the structural response of the wing in its real context. All that represents a novelty since, at present, the commercial FE codes allow us to use the inertia relief option exclusively for linear analysis. Obviously, the approach can be applied to any other structural component with similar needs. The obtained results show that the differences between linear and non-linear regime are not negligible and, above all, that it is possible to design a wing (or other structural components) considering, at the same time, the large deformation due to the post-buckling regime, the material non-linearities due to the failures and any other non-linearities in order to achieve the challenging weight requirement of the new aircraft generation.

Using a novel design approach, high-performance large-port-count switches based on cascaded multimode interference (MMI) couplers are shown to be feasible in low-index-contrast materials. This approach combines the transfer matrix method, optimization of the MMI dimensions, and mode propagation analysis (MPA) for calculation of phase shifts. 1/spl times/4, 1/spl times/8, 1/spl times/16, and 1/spl times/32 switches are designed, with insertion losses of 1 dB and crosstalk as low as -31.7 dB. Also, it is shown that this approach can balance the losses for different switch states.

Equivalent linear modal parameter estimation for a nonlinear aeroelastic system

In this article, we derive a mechanical distributed parameter model for the annular sector plate segments of the Extremely Large Telescope’s deformable mirror M4. Additionally, we modally analyse the derived model via analytical and numerical approaches. The deformable mirror M4 is used to reject wavefront disturbances and enhance the optical imaging quality. We present a control oriented annular sector Kirchhoff–Love plate model featuring an elastic boundary condition and its modal analysis for one of the six identical M4 segments. Subsequently, we show that the well-known method of separation of variables is incompatible with the modal analysis of the presented distributed parameter model in cylindrical coordinates. Moreover, we successfully modally analyse the model using a finite difference approximation and a realistic construction of an M4 segment via a finite element approximation to compare the results. The modal analyses provide consistent results and therefore, both models underlying the analyses are consistent.

2DH numerical model of nonlinear wave propagation based on a hybrid finite-volume and finite-difference scheme

A general method for calculating the solution of the scalar wave equation for the field propagating through integrated optical devices is presented. The method is capable of a three-dimensional description and of treating problems with reflected waves. It consists of dividing the device into a series of sections of axially uniform waveguides. The modes in each section are found by expansion of the field in a two-dimensional Fourier series and solving the associated matrix eigenvalue problem. Propagation is then described by relating the mode amplitudes of each section to the previous one. The amplitudes are related by a matrix that is the product of the eigenvector matrices of the two sections. The method is illustrated by the analysis of an adiabatic mode transformer, the coupling of light from a semiconductor laser through free space to a waveguide, and the propagation through an adiabatic 3 dB coupler and Y branch.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper presents an evaluation study of the performance of reinforced concrete arch bridge structures under earthquake load. The study is aimed to investigate the seismic performance of Wreksodiningrat Bridge, located in the province of Yogyakarta, Indonesia. This bridge is a three spans reinforced concrete arch bridge with a main span length of 75 m and two side spans with a length of 35 m, respectively. This study is a part of a large project carried out by the Ministry of Public Works to study the impact of the new 2016 Indonesia Seismic Design Code for Bridges (SNI 2833:2016). The main objective of this paper is to determine the displacement demands due to earthquake load based on the new seismic code design for bridges, SNI 2833:2016. In addition, demand capacity ratios (D/C) of the main structural components, such as the compression arch and main column (pier) at the fixed support, are also reviewed in this paper. The analysis was carried out using nonlinear modal pushover analysis. The arch bridge modeling is three dimensional, where structural elements such as beams, columns, and compression arches are modeled as frame elements. The plastic hinges are modeled as fiber hinges with unconfined and confined concrete material stress-strain relationship following Mander formula. The analysis result shows that the displacement demands of the bridge are 2.9 cm and 20 cm in the longitudinal and transverse direction, respectively. The D/C ratios of the compression arch due to demand earthquake load are 0.74 and 0.95 in the longitudinal and transverse direction of the bridge, while the D/C ratios of the pier are 0.15 and 0.80 in the longitudinal and transverse direction. Based on the above results, it is concluded that the studied bridge is able to withstand the seismic load requirements in the new Indonesia Seismic Design Code.

Hydroelastic response of a floating plate on the falling film: A stability analysis

Nonlinear modal analysis of interaction between torsional modes and SVC controllers

Bridge structure condition assessments are critical for decision-making for bridge operation and maintenance. The natural frequencies of a structure depend on its global stiffness and weight. Therefore, the decrease in the natural frequency can be a global indication of structural damage conditions. However, the criteria for establishing a natural frequency threshold for judging the structure damage condition are still in question for engineers. In this paper, a method is proposed to find reference thresholds of frequency decline for the evaluation of bridge structural damage conditions using nonlinear incremental modal pushover analysis. The natural frequency thresholds obtained by the proposed method can be used in the system to automatically evaluate the damage and produce reports after each detected seismic event or at predetermined periods. The accuracy of the proposed method was verified by Eigenvalue analysis and nonlinear dynamic response analysis. In addition, this paper presents an integrated digital transformation system for bridge damage assessment. The system includes a wireless accelerometer, cloud integration, and edge computing to allow users to set up various damage assessment thresholds for warning and reporting when it detects damage or anomalies in structures.