Institute of Fundamental Technological Research

Many mode decomposition methods suffer from aliasing effects and modal distortion. This paper proposes a constrained mode decomposition (CMD) method that directly addresses these problems. The CMD is based on a linear combination of structural-free responses. The decomposed response is thus ensured to have a physical meaning and to satisfy the structural equation of motion, which improves the accuracy of mode decomposition and identification. The decomposition aim is to obtain a single-mode response. The CMD defines the corresponding natural frequency as the target frequency, while other natural frequencies are defined as constrained frequencies. The proposed method combines the measured physical responses in such a way that the constrained frequency components are selectively suppressed, while the amplitude of the target frequency component is selectively retained above a predefined level. The result is the intended single-mode free response, which can be used to clearly extract the corresponding modal parameters. For well-separated modes, the criterion for selective suppression is based on the fast Fourier transform (FFT) peak amplitude. For separation of closely spaced modes, a criterion based on FFT derivative is proposed to avoid modal distortion. The accuracy and applicability of the CMD method is tested in a numerical simulation and using a four-story lab frame structure. The experimental data are used to verify the effectiveness of the proposed CMD method and to compare it with two other widely used mode decomposition methods.

frequency-domain response, linear combination, mode decomposition, peak characteristics, structural health monitoring (SHM)

Adhesive and stretchable nanofibrous hydrogels have attracted extensive attraction in wound dressings, especially for joint wound treatment. However, adhesive hydrogels tend to display poor stretchable behavior. It is still a significant challenge to integrate excellent adhesiveness and stretchability in a nanofibrous hydrogel. Herein, a highly adhesive, stretchable, and breathable nanofibrous hydrogel was developed via an in situ hybrid cross-linking strategy of electrospun nanofibers comprising dopamine (DA) and gelatin methacryloyl (GelMA). Benefiting from the balance of cohesion and adhesion based on photocross-linking of methacryloyl (MA) groups in GelMA and the chemical/physical reaction between GelMA and DA, the nanofibrous hydrogels exhibited tunable adhesive and mechanical properties through varying MA substitution degrees of GelMA. The optimized GelMA60-DA exhibited 2.0 times larger tensile strength (2.4 MPa) with an elongation of about 200%, 2.3 times greater adhesive strength (9.1 kPa) on porcine skin, and 3.1 times higher water vapor transmission rate (10.9 kg m–2 d–1) compared with gelatin nanofibrous hydrogels. In parallel, the GelMA60-DA nanofibrous hydrogels could facilitate cell growth and accelerate wound healing. This work presented a type of breathable nanofibrous hydrogels with excellent adhesive and stretchable capacities, showing great promise as wound dressings.

nanofibrous hydrogels, hybrid cross-linking, adhesivity, stretchability, breathable capability

In this article we report on a study of the near-wall dynamics of suspended colloidal hard spheres over a broad range of volume fractions. We present a thorough comparison of experimental data with predictions based on a virial approximation and simulation results. We find that the virial approach describes the experimental data reasonably well up to a volume fraction of ϕ ≈ 0.25 which provides us with a fast and non-costly tool for the analysis and prediction of evanescent wave DLS data. Based on this we propose a new method to assess the near-wall self-diffusion at elevated density. Here, we qualitatively confirm earlier results [Michailidou, et al., Phys. Rev. Lett., 2009, 102, 068302], which indicate that many-particle hydrodynamic interactions are diminished by the presence of the wall at increasing volume fractions as compared to bulk dynamics. Beyond this finding we show that this diminishment is different for the particle motion normal and parallel to the wall.

This contribution presents, discusses and illustrates the constrained mode decomposition (CMD) method. The CMD is a recently proposed method that extracts single mode components from measured multimodal free structural responses. These components can be then processed, in time domain or in frequency domain, for identification of modal parameters, and ultimately, for structural health monitoring. The aim of the CMD is thus similar to the aims of other well-known mode decomposition approaches, such as the empirical mode decomposition (EMD) or the variational mode decomposition (VMD). However, in contrast to the EMD, the CMD-processed responses retain the characteristics of the free response (satisfy the equation of motion of the same structure) and they have thus a clear, well-defined physical meaning. In comparison to the VMD, the formulation of the CMD is much simpler: the CMD combines linearly recorded structural responses in a way that simultaneously (1) amplifies the selected modal component and (2) constrains/suppresses other components. The amplification/suppression process is quantified in terms of the FRF peaks or, in case of closely spaced modes, in terms of FRF derivatives.

mode decomposition, frequency domain, linear combination, FRF peak, structural health monitoring, modal identification