Bridge vibration logarithmic decrement estimation at the presence of amplitude beat

Logarithmic decrement is one of the key dynamic parameters characterizing bridge status. It is usually estimated from vibration records applying digital signal processing. Among the processing procedures band-pass filtering is commonly used to extract spectral components of interest. We analyze the case when two very close spectral components are present in the acceleration records. We show that construction of the filter is non-trivial in such a situation and failing to choose optimal filter’s parameters leads to significant logarithmic decrement estimation errors. Therefore we propose a method that does not require band-pass filtering but utilizes knowledge of amplitude beat presence. Simulation of the method indicated errors by an order less than using filtering.     

Identification of the beat characteristics and damping ratios of the Hwacheon World Peace Bell using wavelet transform

In this paper, a new measurement technique is proposed to identify the beat characteristics and modal damping ratios of a Korean bell in the casting field. The beat response caused by the mutual interference of mode pair with very close doublet frequency is unique feature of the Korean bell and should be accurately measured in order to quantitatively estimate the bell sound. However, the conventional method based on a filtering concept such as the Fourier transform has difficulty in extracting the beat frequencies and modal damping ratios because the method should individually decompose the measured signal into each mode. The aim of this paper is to propose an effective measurement method to identify the beat frequencies, mode pairs and modal damping ratios using the continuous wavelet transform in a real striking condition. The proposed method is verified with the Hwacheon World Peace Bell cast in the year 2008, which is the largest bell in Korea. In the future, the proposed method can be applicable to the casting field of the Korean bell to effectively estimate its beat characteristics and damping characteristics.     

On the estimation of complex modulus and Poisson's ratio using longitudinal wave experiments

In this paper we consider different least-squares-based approaches for estimating the complex Young's modulus and the complex Poisson's ratio of a viscoelastic material using a longitudinal wave propagation experiment. We present a statistical analysis of different estimation approaches and compare their performances. The analytical covariance expressions are validated using experimental data.     

Damping identification from non-linear random responses using a multi-triggering random decrement technique

The concept of multi-triggering random decrement technique is introduced. Like the single triggering technique, it reduces multi-mode multi-measurement stationary random responses to free decay responses but has the advantage of increasing the apparent number of the resulting free decay time response functions. The maximum number of these free decay responses is equal to the square of the number of random measurements. These free decay responses are then used in a linear time domain modal identification algorithm to extract frequencies, damping factors and mode shapes of a structure under test. The quasi-linear modal approach is used to deal with non-linearities by repeating the linear identification process at different levels of inputs/responses. The procedure is applied to rectangular panels subjected to acoustic random input ranging from 130 to 157 dB. The changes in frequencies and damping factors with input level are reported. This application is part of a sonic fatigue research program.     

生化分析仪两种对数放大电路的设计

设计了两种用于生化分析仪器的对数放大电路,通过实验得出了对数放大电路的数学表达式。实验证明,两种电路都能很好地完成对数运算。但采用LOG102的对数放大电路具有更高的运算精度。     

An average inverse power ratio method for the damping estimation from a frequency response function

The well-known bandwidth method, especially the half-power bandwidth method [1], [3], [4] (Bishop and Gladwell, 1963; Nashif et al., 1985; Yin, 2008) is probably the simplest method for the damping estimation from a frequency response function (FRF). This method is quite efficient for simple model test cases when modes are well separated. However, the determination of the two frequencies corresponding to a given power ratio value requires numerical interpolations of experimental discrete data of frequency response functions. In this paper, an average inverse power ratio method is proposed. The average value is computed at two frequencies symmetrically located from a peak amplitude frequency. Then the damping ratio can be estimated by using a formula similar to that of the bandwidth method. In this way, the damping estimation becomes straightforward from the FRF data. This new method could be useful for engineers in practice due to its extreme simplicity.     

Passive vibration damping enhancement of piezoelectric shunt damping system using optimization approach

Piezoelectric materials can be used for structural damping because of their ability to efficiently transform mechanical energy to electrical energy and vice versa. The electrical energy may be dissipated through a connected load resistance. In this paper, a new optimization technique for the optimal piezoelectric shunt damping system is investigated in order to search for the optimal shunt electrical components of the shunt damping circuit connected to the piezoelectric patch on a vibrating structure for the structural vibration suppression of several modes. The vibration suppression optimization technique is based on the idea of using the piezoelectric shunt damping system, the integrated p-version finite element method (p-version FEM), and the particle swarm optimization algorithm (PSOA). The optimal shunt electrical components for the piezoelectric shunt damping system are then determined by wholly minimizing the objective function, which is defined as the sum of the average vibration velocity over a frequency range of interest. Moreover, the optimization technique is performed by also taking into account the inherent mechanical damping of the controlled structure with the piezoelectric patch. To numerically evaluate the multiple-mode damping capability by the optimal shunting damper, an integrated p-version FEM for the beam with the shunt damping system is modeled and developed by MATLAB. Finally, the structural damping performance of the optimal shunt damping system is demonstrated numerically and experimentally with respect to the beam. The simulated result shows a good agreement with that of the experimental result. This paper was recommended for publication in revised form by Associate Editor Eung-Soo Shin Jin-Young Jeon received his Ph.D. degree in Mechanical and Aerospace Engineering from Tokyo Institute of Technology in 2005. Dr. Jeon is currently a senior engineer at Digital Printing Division, Digital Media & Communications Business at Samsung Electronics Co., Ltd., Korea. His research interests are the areas of structural-acoustic optimization, sound quality, motion quality, and vibration control.     

A method for the localization of damage in a CFRP plate using damping

In the past 25 years, the scientific and industrial communities have made great efforts on the fields of damage detection and structural health monitoring (SHM). However, no single approach has proven appropriate for all situations. Composite materials, which are receiving an increasing attention in the aeronautical industry, namely carbon fibre reinforced plastics (CFRP), are very sensitive to impacts of medium and low energy. Typically, barely visible impact damage (BVID) will occur, constituting an unsafe failure of difficult assessment. To assess (detect, locate and quantify) damage in this kind of material is still a challenge, especially if a huge amount of sensors or expensive equipments at hand are not used. In this work, a methodology that makes use of a reduced amount of conventional sensors is explored, with the aim of locating damage for a low cost on components that are subjected to impacts during service. This represents a considerable benefit, namely for the assessment of damage in aeronautical components, compared to most methods used today. This work can also give a major contribution to the research community since uncommon approaches will be used to model damage in composite materials, namely the modal damping factor as the main feature for damage localization.     

Measurement of ciliary beat frequency using high-speed video microscopy

Studies on the ciliary beat frequency (CBF) of frog palate epithelium are described. A high-speed video microscope system was used to record ciliary activity at 60 and 180 fields per second (fps). Temperature-controlled experiments were facilitated by a specially designed observation chamber. A total of 1150 measurements were performed on intact tissue (edge and surface observations) and single cells. The overall mean values of CBF at 60 fps (18.8 Hz) and 180 fps (19.1 Hz) were statistically indistinguishable (p less than 0.05). A temperature variation of 0.235 Hz/degree C was obtained for the range 24-27 degrees C. Comparison of results by two observers at both field rates indicated no statistical differences. The variation of CBF with time after collection was also not significant. It was determined that measurements obtained from the edge and single-cell recordings were preferable to those obtained from surface observations.     

振动模态固有频率和阻尼比的EMD识别方法

针对机械系统固有频率和阻尼比的识别问题,提出了基于经验模式分解(EMD)的模态参数识别方法.该方法首先对脉冲激励下机械系统的位移响应进行了EMD分解,确定与该系统的各阶模态对应的固有模式函数(IMF),分别对各阶IMF进行希尔伯特变换以得到各自的瞬时幅值和瞬时相位曲线,并对所得曲线进行线性拟合,最后根据拟合曲线的参数来...     

Numerical analysis of wave energy dissipation by damping treatments in a plate with acoustic black holes

The reduction of vibration by acoustic black holes (ABHs) with damping treatments can be achieved in two stages: energy focalization and energy dissipation. The energy focalization is mainly due to changes of the local thickness by slowing down the flexural wave speed and energy dissipation can be achieved by using viscoelastic damping materials. In structures with embedded ABHs, the damping effectiveness can depend significantly on the types of damping treatments. In this paper, 4 different damping treatments according to the types of attached region are considered in order to estimate the effectiveness of damping treatments as 1) a fully-covered unconstrained damping treatment, 2) a fully-covered constrained damping treatment, 3) a partially-covered unconstrained damping treatment and 4) a partially- covered constrained damping treatment as well as no damping treatment as reference data. In this study, the performance of damping treatments is explored using numerical simulations of three-dimensional thin plate embedded truncated ABH(s). The wave energy in the ABH, the normalized total energy and the focalization ratio are introduced to compare the effectiveness of the damping treatments. The numerical results show that the fully-covered constrained damping treatment provides the most effective configuration in terms of the wave energy in ABH and the normalized total energy.     

Estimation of the saw-tooth shock wave using a lead shock programmer

Structure durability under shock load is evaluated by performing a shock resistance test. Saw-tooth shock wave is generated in a specific environment and transmitted to the structure. The saw-tooth shock wave is generated using a specific impact test system. In general, the impact test system is generally composed of three types: Drop, lateral and rotational. Each type of impact test system has different detail parts. This study applies the drop-type impact test system. A test table, a fixed table, and a shock programmer compose comprise the drop-type impact test system. The drop-type impact test system uses the initial height of the test table, where the specimen is mounted on. The impact velocity in the drop-type impact test is determined by the initial height of the test table. The shock programmer generates the shock wave transmitted to the specimen mounted on the test table, which is then. The shock wave transmitted to the specimen is then generated by the shock programmer material. Parameter research of the parameter testing on the shock programmer has to be performed using the drop-type impact test system to generate the saw-tooth shock wave with non-linear characteristics. This study generates the saw-tooth shock wave by designing and simulating the lead shock programmer. Lead is considered as the shock programmer material. The accuracy of the simulation program (i.e., LS-Dyna) is verified by performing the drop shock test of theon the three types of lead shock programmer with three types. The results of the time history on the test table acceleration between the simulation and the test are compared with those of the shock test and the simulation. The shock test and simulation results are plotted using the tolerance range of the saw-tooth shock wave presented in MIL-STD-810G. The saw-tooth shock wave generated using the lead shock programmer with conical and truncated conical shape is estimated using the verified simulation program. The aspect ratio of the conical and truncated conical lead shock programmer is presented to generate the saw-tooth shock wave is also presented.

     

Non-obstructive particle damping using principles of gas-solid flows

Non-obstructive particle damping is a type of nonlinear damping related to the velocity amplitude of a vibrating structure. Many scholars have spent considerable time researching the damping and energy dissipation mechanism due to interparticle collision and friction, and they achieved corresponding results by using the principles of gas-solid flows and discrete element method. However, the damping mechanism due to kinetic dissipation between particles and gas has been entirely ignored. In this paper, a mathematical evaluation of the damping mechanisms due to kinetic dissipation is performed by using the principles of gas-solid flows. For systematic research into the application of non-obstructive particle damping technology in engineering practice, the improved model is perfectly embedded into finite element software by using co-simulation technology, in which MATLAB invokes a COMSOL file and controls the calculation process. A frequency analysis of the experiment verifies that the prediction accuracy of the improved model is obviously increased. Moreover, energy dissipation was explored by using the principles of gas-solid flows. Results indicate that particle damping technology can effectively control the structure vibration at a higher-order frequency. However, the energy dissipation mechanism takes effect at a lowerorder frequency.     

Analysing the natural resting aspect of a component for automated assembly using the energy envelope method

This paper presents a new approach for analysing the natural resting behaviour of a non-rotational component. The method employs the energy envelope concept to analyse the natural resting of a component. The resultant curves for all the prisms agree well with Boothroyd's theoretical curve and Boothroyd's experimental data.     

Three-dimensional filtering of engineering surfaces using envelope system

With the advent of cheap and powerful computers, three-dimensional evaluation of surfaces is possible. This article deals with the development of a computational method for three-dimensional filtering of surface using the envelope system (E-System, a dialation using a sphere) concept. The shape of the envelope surface is dependent only on the prominent peak points on the surface. The computational method developed uses this set of prominent points to facilitate fast evaluation of the envelope surface. Roughness values obtained by two, two-and-a-half, and three-dimensional evaluation of typical surfaces are also given. This procedure of waviness filtering gives a strong base for an integrated approach for surface and form measurements.     

Active damping of forced vibrations in a two-mass system using force and parametric effects

A linear dynamic model of two masses sequentially connected with linear elastic links is considered. The masses are under the effect of external harmonic perturbations that have the same frequency but differ by amplitude; there is also a phase difference between the forces. To decrease the intensity of forced vibrations, two vibration-damping factors are activated: a force applied to one of the mass and a parametric factor corresponding to periodic changes in rigidity of the mass fixing. The structure of quasi-optimal vibration-suppression laws ensuring the minimal amplitude of steady-state vibration is determined in a closed form.     

Exit wave reconstruction using a conventional transmission electron microscope

Exit wave reconstruction of a focus series of Ge in [110] using the PAMMAL algorithm was performed on a conventional electron microscope. The simulated images using the reconstructed object wave match very well with those obtained experimentally. Amplitudes from the complex wave function were extracted by means of local Fourier transformation. Crystal thickness and tilt were determined locally by quantitative comparison of the reconstructed amplitudes with amplitudes from multislice calculations. Detailed analysis yields the quasicoherent imaging approach used in the PAMMAL algorithm to produce the largest error in the analysis. For the Ge crystal specimen parameters were quantified to spatial frequencies of 5 nm¹. In the case of an object producing strong diffracted beams, the reconstruction may fail because the quasicoherent approximation will not describe correctly the nonlinear image formation.     

On-line block pulse implementation of a sine wave using microprocessor

The present work uses a microprocessor and relevant hardware to express an integrable time-varying function, e.g., a sine wave, received as an on-line signal, in terms of equivalent block pulse functions (BPFs). The BPF coefficients, determined via experiments are employed for reconstruction of the original time signal. Two alternative methods have been adopted for practical implementation: (i) method of integration and (ii) method of sampling. BPF coefficients, determined experimentally, are compared with those obtained via exact computation. From the computed BPF coefficients, Haar spectral coefficients are determined using similarity transformation. Again, the average values, RMS values and form factors are calculated for exact and BPF approximated sine waves for comparison and relative accuracy. Relevant tables are presented to assess comparative usefulness of the work.     

Measurement of in-cylinder equivalence ratio during starting using a fast FID

In spite of the importance of the mixture preparation process during starting in affecting HC emissions, it has been poorly understood because the process is highly complicated by the multi component fuel, transient thermal environment, and two-phase mass transfer. For better understanding of the process, measurement of the equivalence ratio in the cylinder was attempted using a fast FID (Flame lonization Detector). Although extensive research has been made on the measurement using the fast FID, the method is not yet straightforward and needs careful operation. In this paper, the current status of the method is described. And within the limitations of the method the in-cylinder sampling test was conducted under the engine operating condition of 900 rpm, 0,527 bar intake pressure with gasoline injceted. The test results show that 15 to 20% of the injected fuel evaporates in the first cycle regardless of the amount of fuel injected. The lean limit of the equivalence ratio for engine firing was about 0.6. For secure firing in the first cycle, 5 to 6 times the stoichiometric fuel amount had to be injected. The contribution of the left-over fuel in the previous cycles to the mixture formation in the present cycle was found to be substantial.     

The nature of the logarithmic traction gradient

Great significance has been attached to the logarithmic traction gradient in elastohydrodynamic lubrication. It has been used to justify the assumption of logarithmic constitutive behavior.We have calculated viscous traction curves from the viscous shear response that is observable by simulation or experiment out of contact. This response includes Newtonian, shear-thinning of the ordinary power-law type, and rate independent behavior. The calculated traction curves can be reasonably described by a sinh law using fictitious viscosity and Newtonian limit. These system model parameters behave as expected from cases where the same system model was applied to measured traction.We conclude that for point contact, the logarithmic gradient results from rate-independent (limiting stress) behavior combined with greater than exponential pressure-viscosity behavior. Shear-thinning has little effect on this gradient in point contact. On the other hand for line contact, shear-thinning of the ordinary type (Carreau) is essential for the appearance of a logarithmic gradient.