Estimation Of Dynamic Characteristics Research Articles

Research on Dynamic Characteristics Estimation Method for Predicting Ship Structural Health

Research on Dynamic Characteristics Estimation Method for Predicting Ship Structural Health

Формування математичної моделі турбовального двигуна

The subject of the study is the process of forming a mathematical model (MM) of a turboshaft gas turbine engine and a twin-engine helicopter power plant, which provides the determination of parameters of the working process in steady and transient operating modes for use in the estimation of dynamic characteristics, in the analysis and synthesis of engine and helicopter automatic control systems. The goal is to substantiate the structure and methodology of MM formation intended for use in real and accelerated time scale systems. Tasks: implementation of the previously proposed MM structure taking into account the turboshaft engine performances, development of a methodology for determining the MM coefficients based on known information about the static and dynamic properties of the engine, and formation of the MM structure of a two-engine helicopter power plant. For this, the methods of the theory of airjet engines and the theory of linear dynamic systems are used. The following results were obtained: the structure of a multimode high-speed MM of a turboshaft engine and a two-engine power plant was formed and tested. The scientific and practical novelty of the obtained results is as follows: the structure of the multimode linearized MM of the turboshaft engine is formed, which consists of static and dynamic submodels implemented in corrected parameters; the modeling technique was worked out on a simplified model, compiled considering expert information about the static and dynamic properties of the engine in the considered operation area. Formulas were obtained that relate the coefficients of the linear dynamic model to the values of the time constants of the rotors and the sensitivities obtained from the static characteristics; transient characteristics of the engine based on changes in fuel consumption and load power are determined, which correspond to physical knowledge about the engine; the modeling methodology and MM structure of a two-engine power plant were formed, which is distinguished by the combination of individual static and linear dynamic models of two engines with a single nonlinear dynamic model of the helicopter rotor; a simplified MM load necessary for testing the MM of the engine installation is proposed, which provides the calculation of the power consumed by the rotor, depending on the angular position of the blades.

Estimation of Dynamic Characteristics of Vibration Protection Systems of a New Type for Water Transport Vessels

The use of traditional means of vibration isolation of ship power plants does not always give the desired effect, which predetermines the need to search for and use fundamentally new devices to improve the efficiency of vibration isolation of a ship engine. This can be achieved by installing active-passive vibration isolators in the elastic mounts of the engine, such as electromagnetic hydraulic vibration isolators (EHVO) for auxiliary engines and other marine equipment. Despite the seeming simplicity of the design and principle of operation, the calculation of EHVO is a rather complex problem, the solution of which is associated with a number of difficulties due to the specific features of electromagnetic devices, since their calculation is associated with a large number of factors and limitations. The known functions of time obtained by solving the equations were used to calculate the dynamic parameters of the EHVO: vibration energy, periodicity, overheating of the coils and efficiency

Evaluation of Site Effects Using HVSR Microtremor Measurements in Vishakhapatnam (India)

Dynamic soil properties form an important base for estimation of strains and deformations due to dynamic loading. Frequency, amplitude and time period are the prominent parameters that define a strong ground motion. When the frequency of the soil and strong ground motion reaches to same value during a seismic event, it results in resonance effect leading to huge damage of the structures. Therefore, it is required to estimate the predominant frequency of the soil and amplitude of vibration. Invasive and non-invasive techniques can be employed to determine the dynamic soil properties. Invasive methods, including SPT, DCPT, downhole, cross hole, etc., contain source located either on the surface or in a downhole. The non-invasive methods can be classified as single station and multiple source methods. Microtremor method has been gaining a lot of importance due to its feasibility to perform test in densely populated areas and the speed of processing the information. The instrument works on the principle of recording micro-vibrations in the ground of specific amplitude termed as microtremors. Therefore, evaluation of site effects has been attempted using microtremor testing in Vishakhapatnam (India). The city of Visakhapatnam is one among the prominent and largest functional port cities of India. Site effects due to sand and clay soil layers are characteristic of the whole city area. Seismic hazard studies of the study area are required as per the survey by Disaster Management Authority of India (NDMA 2012). The microtremor horizontal-to-vertical spectral ratio (HVSR) method was therefore applied for measuring the free-field response in the city to assess the peak frequency and amplitude of the soil sediments. Nakamura (A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface. Railway Technical Research Institute/Tetsudo Gijutsu Kenkyujo, Tokyo, 1989) method has been used to analyses the recorded data as it simplifies the recording process and provides accurate results. It has been evident from the results that clear H/V spectral ratio peaks were observed in the entire central parts of the city, whereas in the eastern and western parts lower site response has been observed due to low impedance contrast of gravel with the rock. The predominant frequency hazard map shows frequency distribution of 0.43–10 Hz throughout the city. Frequency is considerably higher in the central part (> 4 Hz) than in the eastern and western parts (> 1 Hz) in the north eastern and south western locations.

Customised active monitoring system for structural control and maintenance optimisation

The paper illustrates the development and the application of an active monitoring system, and analyzes the investigated dynamic behaviour of the structure where the system is applied. The system is installed on a 250 m suspended arch steel bridge that has been instrumented with sensors of different type. This work focuses on the employed methodologies and obtained results related to the dynamic monitoring of the bridge. The use of the Operational Modal Analysis techniques with data-driven stochastic subspace identification algorithms allows the extraction of the structural dynamic characteristics: natural frequencies, damping ratios, and mode shapes. These data are in overall accordance with those calculated through the computational model utilized by the active monitoring system. Besides, the definition of a range of scattering of modal parameters, under specific conditions, has been obtained. The bridge has very low vibration frequencies, below 1 Hz for all significant modes. The outcomes indicate that the estimation of dynamic characteristics and the corresponding accuracy is influenced by several factors, including the length of the accelerometric acquisitions and the followed specific procedures. The impact of environmental factors, with particular reference to the temperature, is examined. Compared to the damping ratio, the natural frequency shows higher estimation accuracy and marked sensitivity to the environmental factor. Consequently, in the selection of benchmark for damage detection, it should be taken into account that the two modal parameters have specific criticalities. Once that the modal parameter has been chosen, values outside the estimated uncertainty range can be considered as alarm triggers.

Reliability verification of a vision-based dynamic displacement measurement for system identification

In this paper, dynamic experiments of various amplitudes with a broad band of frequencies were carried out using a shaking table in order to validate the wide-range reliability of a vision-based displacement measurement system. In addition, the dynamic characteristics of a multiple-degree-of-freedom model structures were estimated using the vision-based measurement method. As a result of error analysis through comparison with a laser displacement sensor (LDS), it was determined that the accuracy of dynamic displacement measurement by the camcorder in the vision-based system is affected by the frequency of the measurement object. From these results, it is judged that the CMOS sensor type has the rolling shutter effect when the velocity between the model structure and the camcorder is high. The accuracy of dynamic characteristics estimation was determined by comparing the dynamic characteristics estimated using the LDSs and the accelerometers. The vision-based measurement system using the camcorder in both time domain and frequency domains showed very similar results to the existing LDS and accelerometer measurements.

Efficient implementation of a real-time estimation system for thalamocortical hidden Parkinsonian properties

Real-time estimation of dynamical characteristics of thalamocortical cells, such as dynamics of ion channels and membrane potentials, is useful and essential in the study of the thalamus in Parkinsonian state. However, measuring the dynamical properties of ion channels is extremely challenging experimentally and even impossible in clinical applications. This paper presents and evaluates a real-time estimation system for thalamocortical hidden properties. For the sake of efficiency, we use a field programmable gate array for strictly hardware-based computation and algorithm optimization. In the proposed system, the FPGA-based unscented Kalman filter is implemented into a conductance-based TC neuron model. Since the complexity of TC neuron model restrains its hardware implementation in parallel structure, a cost efficient model is proposed to reduce the resource cost while retaining the relevant ionic dynamics. Experimental results demonstrate the real-time capability to estimate thalamocortical hidden properties with high precision under both normal and Parkinsonian states. While it is applied to estimate the hidden properties of the thalamus and explore the mechanism of the Parkinsonian state, the proposed method can be useful in the dynamic clamp technique of the electrophysiological experiments, the neural control engineering and brain-machine interface studies.

Vibration-based system identification of wind turbine system

The goal of this study was to investigate the use of vibration-based system identification methods for detecting wind turbine blade delamination during operating conditions and when subjected to other excitations such as earthquake ground motion. In particular, multivariate singular spectrum analysis and two subspace identification techniques were tested for detecting the dynamic characteristics of the wind blade. A total of two series of experiments was conducted to verify the proposed algorithms. In both cases, accelerometers were installed on the blades for measuring their vibration response. The first test series were performed in the laboratory; a motor spun a small-scale customized wind turbine at controlled angular velocities, and the shaking table excited the entire structure. Artificial damage was introduced by loosening bolts at the blade-rotor connection. The second test was conducted in the field, and vibration data was collected from an operating small-scale wind turbine. The blade's vibration response was analyzed through time-frequency analyses and subspace identification. These tests confirmed that the estimation of dynamic characteristics of blade and rotating frequency of the turbine system was feasible, and the results will guide future monitoring studies planned for larger-scale systems. Copyright © 2016 John Wiley & Sons, Ltd.

Estimation of Dynamic Characteristics of a honeycomb Hybrid Composite Material

Estimation of Dynamic Characteristics of a honeycomb Hybrid Composite Material

VIBRATIONS RESONANCE ESTIMATION IN MARINE STRUCTURES

Dynamic analyses of marine structures are one of the most important during design process as well as during exploitation. Typically, two parts of vibrations calculations are performed. Firstly, natural vibrations frequencies and modes are determined. Forced vibrations analysis is the second step of calculations. Natural vibrations give us information about possibility (e.g. at which main engine speed) of dangerous vibrations amplitudes (resonances threat). Exact values of vibrations amplitudes are results of forced vibrations analysis. Confidence level (error value) of forced vibration calculations is much lower in comparison to uncertainty of natural vibration analysis. What is more, form engineering practice point of view, natural vibrations frequencies estimation (resonance avoidance) is the most important during dynamic analysis of marine structures with propulsion systems. In the paper some examples of dynamic characteristics estimation and their changing methods (possibility) was presented. Utility of relatively simple models, with low degree of freedom number, was discussed. Modelling methods depending on the analysis target of marine slow-speed crankshafts was presented. Advantages and disadvantages of subcritical and supercritical design of marine propulsion system were discussed. An example of propulsion system natural torsional vibrations simplified analysis was presented. Location of the main torsional resonance is one of the most important decisions during design process of the marine propulsion system. Methods of fast and easy estimation as well as changing possibility of natural vibrations frequencies of marine structures is the main objective of presented paper.

Investigation of dynamic characteristics of tall industrial chimney based on GPS measurements using Random Decrement Method

The paper is concerned with the investigation of dynamic characteristics, i.e. the natural frequencies and structural damping ratios, of a tall industrial chimney, located in the power station of Belchatow in Poland, excited by the wind, based on GPS measurements using Random Decrement Method (RDM). The GPS receiver was able to measure only the first natural frequency of the chimney. The basic characteristics of a background noise of GPS technology based on the result of a static test were examined thoroughly. In order to increase the accuracy of GPS measurements as well as the dynamic characteristics estimation the filtering procedure using Type 1 Chebyshev band-pass digital filter was adopted. Then, the principles of RDM taking into account the influence of GPS measurement random noise were considered. The influence of filter parameters on the stability of the RD signature was also examined. Based on the filtered record of chimney dynamic response, the dynamic characteristics of the chimney were investigated using RDM for response considered in ten various directions in the horizontal plane. The results delivered some important practical information about two symmetry axes of the chimney. The effective investigation of a damping ratio should be made based on the analysis of the chimney response considered only in the directions of symmetry axes of the chimney. The number of time segments of the chimney response taken into account in averaging of the RD signature as well as the time interval of the RD signature was also recommended. The obtained results proved that the dynamic characteristics of tall slender structures under wind excitations can be effectively determined based on GPS measurements using RDM.

Dynamics of scanning converters with sampling of instantaneous values of the control signal and various modulation patterns

Design principles and timing waveform diagrams of scanning converters (SCs) with sampling of instantaneous values of control signals and various patterns of pulse-width modulation used in analog and digital systems for control of valve converters (VCs) are considered. SCs with pulse-width modulation of the first, second and third kinds are considered. Their block diagrams and timing waveforms are provided. The method of analysis of the dynamic characteristics of SCs is given. On the basis of obtained transcendental equations and their solutions, the dynamic characteristics analysis of different classes of SCs by a method of the space of the dynamic state of the object under the impact of the harmonic signal of interference in a wide frequency range is given., The concept of an average statistical deviation of the duty factor of pulses and frequency of carrier waves in the space of the dynamic state of the object is introduced as a criterion of comparative estimation of dynamic characteristics of SCs. It is shown that, for an SC with sampling of instantaneous control signal values, only pulse-width modulation of the second kind provides the lowest level of errors in the frequency field of slow discretization; therefore, it is advisable to use this modulation pattern in systems for control of VC. When operating a dynamic signal “in the small,” pulse-width modulation of the second and third kinds appears to be a variety of frequency-pulse-width modulation, since it is characterized by deviation of the frequency of carrier waves from a set value.

Recording duration of ambient vibration monitoring for system identification of tall telecommunication towers

SUMMARYIt is necessary to have reliable field measurement records for estimation of dynamic characteristics. Increasing duration of the record is one of the common methods for reduction of such errors in the results. Dynamic characteristics of telecommunication towers in higher modes are important for designers, but these parameters could be obtained from ambient vibration monitoring during typhoons in which duration of vibration is not long enough for reducing measurement errors.This paper suggests a procedure for obtaining the duration of recording time for more reliable determination of structural characteristics of telecommunication towers. It is suggested to record the vibration of towers in the form of a set of long‐term and short‐term duration recordings for lower and higher modes, respectively. This procedure was verified with field measurement of Milad telecommunication tower. The results show that natural frequencies determined by this procedure are in good agreement with finite element model analysis. Copyright © 2013 John Wiley & Sons, Ltd.

Structural identification of concrete arch dams by ambient vibration tests

Modal testing, widely accepted and applied method for determining the dynamic characteristics of structures for operational conditions, uses known or unknown vibrations in structures. The method's common applications includes estimation of dynamic characteristics and also damage detection and monitoring of structural performance. In this study, the structural identification of concrete arch dams is determined using ambient vibration tests which is one of the modal testing methods. For the purpose, several ambient vibration tests are conducted to an arch dam. Sensitive accelerometers were placed on the different points of the crest and a gallery of the dam, and signals are collected for the process. Enhanced Frequency Domain Decomposition technique is used for the extraction of natural frequencies, mode shapes and damping ratios. A total of eight natural frequencies are attained by experimentally for each test setup, which ranges between 0-12 Hz. The results obtained from each ambient vibration tests are presented and compared with each other in detail. There is a good agreement between the results for all measurements. However, the theoretical fundamental frequency of Berke Arch Dam is a little different from the experimental.

Estimation of Long Period Ground Motion Earthquake Effects to High-rise Buildings at Hanoi and HoChiMinh Cities, Vietnam

Estimation of dynamic characteristics of subsurface such as predominant period, amplification factor, shear wave velocity play an important role in researchs of the effects of long-period ground motion earthquakes on high-rise buildings in big cities. However, in Vietnam, due to the lack of observation devices, there is a shortage of dynamic ground information. Consequently, in this paper, at first, the results of applying the Nakamura Method to data processing of microtremor observations in Hanoi and HoChiMinh City of Vietnam are presented. By using this method, the predominant period of the ground at the sites could be estimated from the horizontal to vertical (H/V) spectral ratios of microtremors. The obtained results show that the grounds of the mentioned two cities have considerable possibility of resonating with long-period ground motions. Then, the spectral accelerations in bedrock of Hanoi and HoChiMinh city were estimated by attenuation relationship of Uchiyama and Midorikawa 2006 with the far-source rupture faults that were Sumatra earthquake 2004 and Tha-Khaek fault line in Thailand. Next, the accelerations on ground surface of the above two Vietnamese cities were calculated by using spectral ratio of microtremor and inverse Fourier transform. Finally, those obtained accelerations were used to do the time history analysis applied for 8 high-rise buildings in Hanoi and HoChiMinh city. The results of this final step show that far-source rupture faults have considerable possibility to generate long-period ground motions that cause certain affects to the behaviors of high-rise buildings in Vietnamese cities.

The application of interval calculus in estimation of dynamic characteristics of structures

The paper analyzed application of interval calculus in estimation of dynamic characteristics of linear systems. The eigen periods of oscillation of structures are affected by several parameters: geometrical characteristics of cross sections of members, magnitude of the mass concentrated in the floors and modulus of elasticity of materials. As a numerical example, the frame reinforced concrete structure was taken, for which the mentioned parameters are given in the form interval. The result is also obtained in the form of interval so it is possible to observe the direct effects on the value of the structural oscillation periods by changing one or several parameters.

Ambient vibration data re-sampling by cubic spline interpolation for accuracy improvement of bridge dynamic characteristics estimation using realization theory

Ambient vibration data re-sampling by cubic spline interpolation for accuracy improvement of bridge dynamic characteristics estimation using realization theory

Dynamic characteristics estimation from the ambient vibration of existing bridge by realization theories

An automatic estimation system for bridge dynamic characteristics (frequency, damping ratio, and vibration mode) under ambient vibration by ERA, ERA/DC and PHCA method is presented in this paper. The Hankel matrix was derived from block covariance of ambient vibration data. The experiments were conducted under (a) strong wind, (b) weak wind and (c) under traffic condition to estimate the dynamiccharacteristics of existing steel langer girder bridge. As a result of this study, the better result is realized from the strong wind data. In contrast, the inducement of high frequency by the data under traffic condition leads to frequent estimation of higher mode with inconsistent level of accuracy. In the various method of analysis, ERA/DC method has the advantages for its simple algorithm and ability to provide accurate estimation with fast calculation speed.

Estimation of dynamic characteristics of the International Space Station from measurements of microaccelerations

We describe the results of determining the mass of the International Space Station using the data of MAMS accelerometer taken during correction of the station orbit on August 20, 2004. The correction was made by approach and attitude control engines (ACE) of the Progress transporting spacecraft. The engines were preliminary calibrated in an autonomous flight using the onboard device for measuring apparent velocity increment. The method of calibration is described and its results are presented. The error in station mass determination is about 1%. The same data of MAMS and similar data obtained during the orbit correction on August 26, 2004 were used for the analysis of high-frequency vibrations of the station mainframe caused by operation of the ACE of Progress. Natural frequencies of the ACE are determined. They lie in the frequency band 0.024–0.11 Hz. ACE operation is demonstrated to result in a substantial increase of microaccelerations onboard the station in the frequency range 0–1 Hz. The frequencies are indicated at which disturbances increase by more than an order of magnitude. The study described was carried out as a part of the Tensor technological experiment.

Automated dynamic characteristics estimation of highway bridge under ambient vibration by block companion form realization

In this research, vibration characteristics are estimated from the ambient vibration of highway bridge by the block companion form realization theory. Two methods are stated herein such as formulation of block companion system matrix; (i) directly from block Hankel matrix, (ii) from ARMA model parameter G through Yule-Walker equation. These methods have applied to a 152m long Langer bridge and its dynamic characteristics were estimated automatically from multipoint measurement of ambient vibration. As the ambient vibration characteristics affect the estimation accuracy, two different cases were taken into consideration and the estimation accuracy was evaluated.