Beijing Municipal Institute of Labour Protection

Beijing, China

Beijing Municipal Institute of Labour Protection

Beijing, China
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Li X.,Beijing Municipal Institute of Labour Protection
Journal of the Acoustical Society of America | Year: 2017

Microperforated panels (MPPs) are efficient sound absorbers featuring microperforations with low porosity. Sound absorption occurs inside the perforations and their vicinity as well, which is represented with an end correction in the transfer impedance of the MPPs. Many empirical models for the end correction were derived from experiment or numerical simulation data. In order to validate these models, this paper presents an analytical solution of the end correction for sharp-edged circular perforations using viscothermal wave theory. The perforations are assumed to be periodically distributed and each perforation is associated with a square duct resulting from a periodic spatial partition. The velocity profile and the temperature field in each perforation are derived from the low reduced frequency model, which pose the boundary conditions to determine the modal coefficients of the acoustic, entropy, and viscous waves in the duct. An impedance end correction model is derived from the asymptotic expansion of the modal solution. It improves the conventional model by introducing a static flow resistance term to describe the energy dissipation due to the acoustic flow distortion outside the perforations. Numerical and experimental examples validate that the proposed model offers better prediction for the transfer impedance and the sound absorption of the MPPs. © 2017 Acoustical Society of America.


Jonckheere S.,Catholic University of Leuven | Li X.,Beijing Municipal Institute of Labour Protection | Desmet W.,Catholic University of Leuven
Proceedings of ISMA 2016 - International Conference on Noise and Vibration Engineering and USD2016 - International Conference on Uncertainty in Structural Dynamics | Year: 2016

As the high computational cost hampers simulation over large frequency bands, the current generation of CAE tools, such as the Finite Element Method (FEM), struggles. This problem becomes even worse in the presence of damping treatments. Many Model Order Reduction (MOR) techniques have been developed to alleviate the overall computational load of numerical simulations. Most of them, however, struggle with the complex, and especially frequency dependent properties of typical damping materials. To overcome this problem, a matrix-free technique is proposed. This method is a rational Krylov approach as it uses forced responses to span the projection subspace to reduce the model. As its name ("matrix-free") suggests, it does not require explicit knowledge on the model matrices; the method works on any black-box transfer function between a given number of inputs and outputs. As such, it is a promising technique to speed up vibroacoustic calculations, even in the presence of damping materials with frequency dependent properties.


Li X.,Beijing Municipal Institute of Labour Protection
Proceedings of ISMA 2016 - International Conference on Noise and Vibration Engineering and USD2016 - International Conference on Uncertainty in Structural Dynamics | Year: 2016

Many engineering structures are subject to excitations with large amplitudes over a short time duration. These impulsive excitations can cause structural failure or unwanted noise especially in the high-frequency band. This paper presents a transient scaling approach to predict the high-frequency vibration of impulsively excited structures. General scaling laws are derived from the transient statistical energy analysis (TSEA). The similitude between the scaled model and the original system is demonstrated by the equivalence of the TSEA governing equations. Specific forms of the general scaling laws are formulated for a two-oscillator system and a coupled beam system. Computational speedup is achieved from both the reduced order of the original system and the accelerated energy evolution in the scaled model. Numerical validation demonstrates that time domain responses can be obtained efficiently by the transient scaling approach.


Li X.,Beijing Municipal Institute of Labour Protection
Proceedings of the INTER-NOISE 2016 - 45th International Congress and Exposition on Noise Control Engineering: Towards a Quieter Future | Year: 2016

The paper proposed a scaling approach to predict the local response of a complex structure in the mid- to high-frequency ranges. In the approach, the complex structure is reduced to a scaled model based on the reverberant field similitude. Since the scaled model is of reduced complexity, it can be solved efficiently with a finite element solver and the local response is available at a set of grid points. The finite element solution of the response involves contributions from both the direct and the reverberant fields. It is demonstrated that the reverberant field in the scaled model corresponds to that in the original structure. Hence the response of the original structure can be readily obtained from that of the scaled model modified by the difference between their direct fields which is obtained analytically. Numerical validation on flexural thin plate models shows that the scaling approach provides an accurate spatial description of vibrational fields when compared to the vibrational conductivity approach. © 2016, German Acoustical Society (DEGA). All rights reserved.


Tong D.Q.,National Oceanic and Atmospheric Administration | Tong D.Q.,Chinese Academy of Sciences | Dan M.,National Oceanic and Atmospheric Administration | Dan M.,Beijing Municipal Institute of Labour Protection | And 2 more authors.
Atmospheric Chemistry and Physics | Year: 2012

This study introduces an observation-based dust identification approach and applies it to reconstruct long-term dust climatology in the western United States. Long-term dust climatology is important for quantifying the effects of atmospheric aerosols on regional and global climate. Although many routine aerosol monitoring networks exist, it is often difficult to obtain dust records from these networks, because these monitors are either deployed far away from dust active regions (most likely collocated with dense population) or contaminated by anthropogenic sources and other natural sources, such as wildfires and vegetation detritus. Here we propose an approach to identify local dust events relying solely on aerosol mass and composition from general-purpose aerosol measurements. Through analyzing the chemical and physical characteristics of aerosol observations during satellite-detected dust episodes, we select five indicators to be used to identify local dust records: (1) high PM10 concentrations; (2) low PM2.5/PM10 ratio; (3) higher concentrations and percentage of crustal elements; (4) lower percentage of anthropogenic pollutants; and (5) low enrichment factors of anthropogenic elements. After establishing these identification criteria, we conduct hierarchical cluster analysis for all validated aerosol measurement data over 68 IMPROVE sites in the western United States. A total of 182 local dust events were identified over 30 of the 68 locations from 2000 to 2007. These locations are either close to the four US Deserts, namely the Great Basin Desert, the Mojave Desert, the Sonoran Desert, and the Chihuahuan Desert, or in the high wind power region (Colorado). During the eight-year study period, the total number of dust events displays an interesting four-year activity cycle (one in 2000-2003 and the other in 2004-2007). The years of 2003, 2002 and 2007 are the three most active dust periods, with 46, 31 and 24 recorded dust events, respectively, while the years of 2000, 2004 and 2005 are the calmest periods, all with single digit dust records. Among these deserts, the Chihuahuan Desert (59 cases) and the Sonoran Desert (62 cases) are by far the most active source regions. In general, the Chihuahuan Desert dominates dust activities in the first half of the eight-year period while the Sonoran Desert in the second half. The monthly frequency of dust events shows a peak from March to July and a second peak in autumn from September to November. The large quantity of dust events occurring in summertime also suggests the prevailing impact of windblown dust across the year. This seasonal variation is consistent with previous model simulations over the United States. © 2012 Author(s).


Li X.,Beijing Municipal Institute of Labour Protection
Journal of the Acoustical Society of America | Year: 2010

This paper is concerned with the ensemble statistics of the dynamic responses of a random system subjected to harmonic excitations. Random point process theory is employed to derive general scaling laws with the Gaussian orthogonal ensemble assumption about the system natural frequencies. A scaled model is built to simulate the high-frequency vibrations of the original system. Specific forms of the scaling laws are presented for a mass-loaded plate regarding the scaling factors for the structural parameters. The ensemble statistics predicted from the scaled model are compared favorably with those obtained from the original system. © 2010 Acoustical Society of America.


Li X.,Beijing Municipal Institute of Labour Protection
Journal of the Acoustical Society of America | Year: 2010

This analysis presents a scaling approach to predict high-frequency mean responses of vibrating systems. The basis of the approach lies in the dynamic similitude between the original systems and the scaled models. A general scaling law is formulated using Skudrzyks mean-value theorem and its specific form is derived for the case of a flexural plate. Modal density is scaled down to reduce the computational cost in the high-frequency mean response prediction. Different scaling procedures are numerically experimented and some insights are given about the accuracy of the scaling approach as compared with a dense finite element analysis. © 2010 Acoustical Society of America.


Li X.,Beijing Municipal Institute of Labour Protection
Journal of Sound and Vibration | Year: 2013

A scaling approach is proposed for the vibration analysis of line-coupled plates at high frequencies. It extends earlier scaling approaches for an isolated system to coupled systems. Based on the power flow balance in the plate assembly, a general scaling law is derived and a scaled model is built accordingly. Due to the dynamic similitude in a statistical sense, the scaled model is able to simulate the dynamics of the original system at high frequencies. Numerical examples validate the efficiency of the approach and suggest the application of finite element methods in the high-frequency vibration analysis. © 2013 Elsevier B.V. All rights reserved.


Shusheng B.,Beihang University | Shanshan Z.,Beihang University | Xiaofeng Z.,Beijing Municipal Institute of Labour Protection
Precision Engineering | Year: 2010

An annulus-shaped flexure hinge is composed of three or more beam flexure elements distributed in an annulus suitable for rotational application, such as laser tracking system and cell operation system. The load-deflection property of annulus-shaped flexure hinges can be analyzed by traditional beam deformation expressions or pseudo-rigid-body method accurately and effectively, but methods are incapable to choose the type of hinge and the key parameters in a quick and exact way. In order to avoid laborious design steps, dimensionless design graphs for a novel annulus-shaped flexure hinge and another two types are presented which are based on finite element analysis. Using these graphs as a design tool, designers can determine the optimal geometry, based on the stiffness and demanded rotational properties of annulus-shaped flexure hinge. Between the analyzed flexure hinges, a comparison is made on the basis of equal hinge functionality: rotational properties for different hinges. The result describes the maximum stiffness properties from different hinges in identical situations. The straight-compliant annulus-shaped flexure hinge is preferred for radius stiffness and rotation stiffness. The curved-compliant annulus-shaped flexure hinge has the best axial stiffness. The instances of using dimensionless design graph are given and results indicate that the relative error between dimensionless graph and design demand is below 4%. Using the dimensionless design graph, design process can be reduced in both time and complexity. © 2010 Elsevier Inc. All rights reserved.


Song Y.,Capital Medical University | Tang S.,Beijing Municipal Institute of Labour Protection
TheScientificWorldJournal | Year: 2011

Accumulating studies in animals have shown that nanoparticles could cause unusual rapid lung injury and extrapulmonary toxicity. Whether exposure of workers to nanoparticles may result in some unexpected damage as seen in animals is still a big concern. We previously reported findings regarding a group of patients exposed to nanoparticles and presenting with an unusual disease. The reported disease was characterized by bilateral chest fluid, pulmonary fibrosis, pleural granuloma, and multiorgan damage and was highly associated with the nanoparticle exposure. To strengthen this association, further information on exposure and the disease was collected and discussed. Our studies show that some kinds of nanomaterials, such as silica nanoparticles and nanosilicates, may be very toxic and even fatal to occupational workers exposed to them without any effective personal protective equipment. More research and collaborative efforts on nanosafety are required in order to prevent and minimize the potential hazards of nanomaterials to humans and the environment. Copyright © 2011 Yuguo Song and Shichuan Tang.

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