Changes In Dynamic Characteristics Research Articles

Temperature Control via Affine Nonlinear Systems for Intermediate Point of Supercritical Once-Through Boiler Units

For the operation of the supercritical once-through boiler generation units, the control of the temperature at intermediate point (IPT) is highly significant. IPT is the steam temperature at the outlet of the separator. Currently, PID control algorithms are widely adopted for the IPT control. However, PID cannot achieve the optimal performances as the units’ dynamic characteristic changes at different working points due to the severe nonlinearity. To address the problem, a new control algorithm using affine nonlinear system is adopted for a 600 MW unit in this paper. In order to establish the model of IPT via affine nonlinear system, the simplified mechanism equations on the evaporation zone and steam separator of the unit are established. Then, the feedback linearizing control law can be obtained. Full range simulations with the load varying from 100% to 30% are conducted. To verify the effectiveness of the proposed control algorithm, the performance of the new method is compared with the results of the PID control. The feed-water flow disturbances are considered in simulations of both of the two control methods. The comparison shows the new method has a better performance with a quicker response time and a smaller overshoot, which demonstrates the potential improvement for the supercritical once-through boiler generation unit control.

The effect of cavitation on the hydrofoil dynamic characteristics

Cavitation in hydraulic machinery usually causes a change of fluid dynamic characteristics. In order to predict the effect of cavitation on hydrofoil characteristics, the cavitation around a hydrofoil was studied numerically. The full cavitation model and a modified RNG k ε-turbulence model were used. The finite volume method with the SIMPLEC scheme was used to discretize the time-dependent equations. The second-order upwind scheme was used for the convection terms with the central difference scheme used for the diffusion terms. Fluid dynamic characteristics including cavity's length, shedding frequency, pressure coefficient and lift and drag force coefficients features in a range of cavitation number were analyzed. Computations were made on the three-dimensional flow field around a NACA66 hydrofoil at 8° angle of attack. The recording force signals exhibit periodic behaviours with the time. And the cavity shedding frequency increases with the cavitation number, however the length of cavity decreases with the cavitation number, which result in changing of lift-drag ratio. Especially for larger cavitation numbers, the lift drag ratio of cavitation field is getting closer and closer to that of non-cavitation field.

Study on Bioinformatics with Dynamic Characteristics Change of the Hippocampal Neuron Model Caused by the Alzheimer Disease

In the paper, based on the electrophysiological experimental dada, the neuron model under the pathology condition of Alzheimer Disease (AD) is built. The neuron models dynamic variation characteristics before and after the effect of AD are comparatively studied. Under the currents stimulation, compared with the normal neuron model, the AD neuron models dynamic characteristics have been obviously changed. Its changing range of the membranes interspike intervals (ISIs) obviously narrows, and the discharge patterns change rather single. In addition, its discharge threshold is much higher than the normal neuron models. So AD causes the neuron models excitability to depress markedly. The research reveals the neuron models dynamic characteristics changing under the effect of AD, which shows bioinformatics change of the neuron caused by AD. The research provides some theoretic basis for AD research by the neurodynamics theory.

Social and economic sustainability of urban systems: comparative analysis of metropolitan statistical areas in Ohio, USA

The development of a comprehensive sustainability analysis tool for evaluating regional urban systems would present researchers, planners, and policy makers with a powerful tool to study and manage systems, with the goal of encouraging optimum social and economic trends, while maintaining long-term environmental protection that leads to sustainability. This article intends to aid in this effort by presenting a versatile methodology for assessing sustainability as a function of dynamic changes in significant characteristics of urban systems. Using statistical methods, this work presents a strategy for comparatively assessing the impact of social and economic characteristics on system stability at geographic scales which are critical to policy and management. Specifically, it employs the Fisher Information index as a measure of sustainability, in order to distinguish periods of stability. As an application of the approach, six Metropolitan Statistical Areas (MSAs) in Ohio (Cincinnati, Dayton, Cleveland, Akron, Columbus, and Toledo) were evaluated for a regional sustainability assessment. Results from the multiyear analysis suggest two distinct periods in these MSAs: one characterized by 30 years of socio-economic growth (1970–1999) and another (2000–2009) denoting a change in the trajectory of each system found to be related to economic recession. Columbus was identified as the most stable and sustainable of the MSAs during the study period. In contrast, Toledo exhibited the largest changes in economic trends, as distinguished by excessive increases in the growth rate of vacant housing units, unemployed civilian labor force, and inhabitants below the poverty level (2000–2009). Since such conditions are not desirable for urban systems, they are indicative of movement towards an unsustainable future.

Effects of structural and dynamic family characteristics on the development of depressive and aggressive problems during adolescence. The TRAILS study

Both structural (i.e., SES, familial psychopathology, family composition) and dynamic (i.e., parental warmth and rejection) family characteristics have been associated with aggressive and depressive problem development. However, it is unclear to what extent (changes in) dynamic family characteristics have an independent effect on problem development while accounting for stable family characteristics and comorbid problem development. This issue was addressed by studying problem development in a large community sample (N = 2,230; age 10-20) of adolescents using Linear Mixed models. Paternal and maternal warmth and rejection were assessed via the Egna Minnen Beträffande Uppfostran for Children (EMBU-C). Aggressive and depressive problems were assessed via subscales of the Youth/Adult Self-Report. Results showed that dynamic family characteristics independently affected the development of aggressive problems. Moreover, maternal rejection in preadolescence and increases in paternal rejection were associated with aggressive problems, whereas decreases in maternal rejection were associated with decreases in depressive problems over time. Paternal and maternal warmth in preadolescence was associated with fewer depressive problems during adolescence. Moreover, increases in paternal warmth were associated with fewer depressive problems over time. Aggressive problems were a stable predictor of depressive problems over time. Finally, those who increased in depressive problems became more aggressive during adolescence, whereas those who decreased in depressive problems became also less aggressive. Besides the effect of comorbid problems, problem development is to a large extent due to dynamic family characteristics, and in particular to changes in parental rejection, which leaves much room for parenting-based interventions.

Dynamic changes in ultrasound characteristics of nodules in cirrhotic liver and their implications in surveillance for malignancy.

To investigate whether there are ultrasound characteristics that can suggest HCC in ultrasound surveillance of nodules in cirrhotic liver. Data from 277 patients with hepatitis B virus-related nodules in cirrhotic liver undergoing ultrasound surveillance of the nodules for malignancy were reviewed. Size of the nodules ranged 6-23mm. The nodules were followed by color Doppler ultrasound at 3- to 6-month intervals, with focus on size, shape, echogenicity, margin, halo sign, and vasculature. Suspicious malignant nodules underwent contrast-enhanced CT/MRI, and some indeterminate nodules underwent biopsy. Nodules in 189 patients were hypo/isoechoic/faint high echoic, 23 were hyperechoic, and 65 were both hypo/isoechoic/faint high echoic and hyperechoic. Forty-two patients developed hepatocellular carcinoma: 35 from nodules and 7 from background parenchyma. Fourteen nodules recessed (size >10mm), 11 new nodules emerged (size >10mm), and the total number of nodules increased over 5years. All hepatocellular carcinomas developed from hypo/isoechoic/faint high echoic nodules, and no typical hyperechoic nodules developed into hepatocellular carcinomas. The size increased significantly when the nodules developed into hepatocellular carcinomas. No nodule presented an overt halo, seven hepatocellular carcinomas developed from nodules with a halo, and ill-defined margins of 16 nodules became well defined when they developed into hepatocellular carcinomas. No vasculature was detectable in the nodules, while it was detectable in eight hepatocellular carcinomas. No significant change occurred in nodules without malignancy. The characteristics for dynamic surveillance of nodules in cirrhotic liver for malignancy should include nodule growth, margin, halo, and vasculature. Apart from evident growth, an ill-defined margin becoming a well-defined margin, a newly emerged halo, and newly detectable vasculature are strongly suggestive of nodule malignancy.

New Methodology of On-Line Monitoring for High Voltage Overhead Transmission Line Icing

In recent years,transmission lines icing leads to failure and accidents,such as large area ice flashover, fittings damaged, line dancing, pole (tower) failure, lines breakage even large-scale power outage, causing serious threat to grid. Nowadays, icing monitoring system mainly relies on detecting the meteorological parameters and the changes of dynamic characteristics for early warning, but the methodologies need additional equipment for data collection. In order to ensure the security and reliability of the grid, a safe, effective and economical methodology of monitoring transmission lines icing has great significance. The project proposed a Transmission Line Icing monitoring principle and algorithm, the method based only on the voltage and current from both ends of transmission lines can be generated dynamically monitoring criterion line icing. According to the criterion maximum, line icing center area, extent and severity can be recognized. The criterion of the method is used as a mathematical scanner, swept from one end of the line to the other end, comprehensive judgments are made on the basis of comprehensive criteria for integrated maximum value, thus the method has a high diagnostic accuracy and reliability. The methodology proposed in this paper is different from the current monitoring methodology; additional hardware devices are not required, and the methodology is simple and practical, has strong operability and enormous economic benefits, adapting to the requirements of the development of the smart grid.

Changes in dynamic characteristics of Lorca RC buildings from pre- and post-earthquake ambient vibration data

This paper estimates fundamental translational period and damping ratio parameters and examines the changes in dynamic characteristics of a set of low-to-medium rise buildings in Lorca town (SE of Spain) affected by the May 11th, 2011 earthquake. These building parameters have been calculated analysing structural dynamic response from ambient vibration measurements recorded at top RC buildings pre- and post earthquake, using the Fast Fourier Transform and the Randomdec technique. The empirical expression relating period \((T)\) and number of floor \((N)\) here obtained analysing ambient noise recorded on 59 healthy buildings before the earthquake is \(T= (0.054\pm 0.002)\, N\), very similar to others empirical period–height relationships obtained for RC structures in the European built environment but quite different from code provisions. Measurements performed in 34 damaged buildings show a period elongation after the quake according to \(T^{*} =(0.075\pm 0.002)\,N\) expression. Moreover, we found a rise of the fundamental period with the EMS’s grade of damage of buildings. In contrast to natural frequency, damping ratio \((\xi )\) do not shows a significant variation with earthquake damage degree and the product \(\xi \, T\) remains near constant.

Stochastic structural control under earthquake excitations

SUMMARY Structural control is an alternative tool, which can be used for the reduction of the response caused by earthquake excitations. Research and implementation in practice have shown that seismic control of structures has not only a lot of potential but also many limitations. Many control strategies are based on the dynamic characteristics of buildings. During the life of the structures, these dynamic characteristics change. So there is a need of modifying the control algorithm. The question that arises is what would happen to the response of controlled structure if the parameters that influence the dynamic characteristics such as mass and stiffness would change while the control algorithm would remain the same. In this paper, this practical issue is discussed, using a stochastic control approach. The influence of the random character of the loads and the stiffness to the response of structures controlled by a modified pole placement algorithm are investigated. Loads and stiffness are considered as random variables, and the response of a structure subjected to dynamic loads is calculated using Monte Carlo methods (i) without control and (ii) controlled by the mentioned algorithm. The methodology is implemented for three characteristic buildings. The cumulative distribution function of acceleration, velocity, and displacement is obtained using the controlled and the uncontrolled analysis for the examined buildings. Deterministic results of the response are also calculated and compared with the random characteristics of the stochastic analyses. Conclusions regarding the influence of the variance of loads and stiffness to the response of structures are presented. Copyright © 2013 John Wiley & Sons, Ltd.

Use of non-destructive techniques in Chinese traditional timber structures

The study of structural damage detection in ancient Chinese timber buildings is very important in the protection and rehabilitation of the ancient architectural culture. The purpose of structural damage detection is to identify the location and grade of structural damage based on the variation in characteristics of the structure, which is dependent on positioning techniques and quantitative analysis of structural damage detection. These elements are studied thoroughly by introducing microtremor measurements and using the finite-element method. Multi-domain microtremor measurements are performed to detect the tilting and twisting of the structure. From the observational data, the natural frequencies and vibration modes of the structure are evaluated, and these are compared with numerical results. In the numerical analysis, the changes in dynamic characteristics of the structure, such as natural frequencies and natural modes, are obtained, with special attention paid to the characteristics of brackets. Comparing the natural frequencies and natural modes from microtremor measurements with those from three-dimensional numerical analysis, the location and form of the damage is qualitatively delimited. Through continued reduction of the stiffness of the damaged layer in different directions, until the natural frequencies and natural modes from the simulation are shown to be consistent with those of the microtremor measurements, the severity of damage to the structure is quantitatively evaluated.

Impact of increased penetration of photovoltaic generation on power systems

Present renewable portfolio standards are changing power systems by replacing conventional generation with alternate energy resources such as photovoltaic (PV) systems. With the increase in penetration of PV resources, power systems are expected to experience a change in dynamic and operational characteristics. This paper studies the impact of increased penetration of PV systems on static performance as well as transient stability of a large power system, in particular the transmission system. Utility scale and residential rooftop PVs are added to the aforementioned system to replace a portion of conventional generation resources. While steady state voltages are observed under various PV penetration levels, the impact of reduced inertia on transient stability performance is also examined. The studied system is a large test system representing a portion of the Western U.S. interconnection. The simulation results obtained effectively identify both detrimental and beneficial impacts of increased PV penetration both for steady state stability and transient stability performance.

Dynamic behavior of railway embankment slope subjected to seismic excitation

To reveal the dynamic behavior of a railway embankment slope subjected to seismic excitation, a shaking table model test was performed on a 1:8 scale embankment slope. Different types of seismic wave of differing amplitudes were applied to study the dynamic behavior of the embankment slope, and white noise excitations were interspersed among the seismic waves to observe the changes of dynamic characteristics of the embankment slope. Residual deformation behaviors of the embankment slope were also investigated. The results of the tests show that the natural frequency of the embankment slope exhibits a decreasing trend and that the damping ratio exhibits an increasing trend. The embankment slope exhibits a significant amplification effect on the input acceleration, and the acceleration response differs greatly when subjected to different seismic excitations of differing spectrum characteristics. The filler of the embankment slope affects the changes of the spectrum characteristics of the seismic wave. The filler performs a filtering effect on high-frequency seismic waves and amplifies the energy of low-frequency seismic waves, especially when the frequency is close to the natural frequency of the embankment slope. A bidirectional excitation creates a greater acceleration response than a unidirectional excitation does. The seismic residual deformation of the embankment slope occurs under the seismic subsidence mode.

Identification and agreement of first turn point by mathematical analysis applied to heart rate, carbon dioxide output and electromyography

BackgroundThe second heart rate (HR) turn point has been extensively studied, however there are few studies determining the first HR turn point. Also, the use of mathematical and statistical models for determining changes in dynamic characteristics of physiological variables during an incremental cardiopulmonary test has been suggested. ObjectivesTo determine the first turn point by analysis of HR, surface electromyography (sEMG), and carbon dioxide output () using two mathematical models and to compare the results to those of the visual method. MethodTen sedentary middle-aged men (53.9±3.2 years old) were submitted to cardiopulmonary exercise testing on an electromagnetic cycle ergometer until exhaustion. Ventilatory variables, HR, and sEMG of the vastus lateralis were obtained in real time. Three methods were used to determine the first turn point: 1) visual analysis based on loss of parallelism between and oxygen uptake (); 2) the linear-linear model, based on fitting the curves to the set of data (Lin-Lin ); 3) a bi-segmental linear regression of Hinkley' s algorithm applied to HR (HMM-HR), (HMM- ), and sEMG data (HMM-RMS). ResultsThere were no differences between workload, HR, and ventilatory variable values at the first ventilatory turn point as determined by the five studied parameters (p>0.05). The Bland-Altman plot showed an even distribution of the visual analysis method with Lin-Lin , HMM-HR, HMM-CO2, and HMM-RMS. ConclusionThe proposed mathematical models were effective in determining the first turn point since they detected the linear pattern change and the deflection point of , HR responses, and sEMG.

Research of Moving Table with Aluminum Foam-Filled Structure

In order to explore the changes of static and dynamic characteristics of machine tool components in which aluminum foam material was used, the characteristics of the prototype table and filled structure one was analyzed by ANSYS.It is shown that static and dynamic characteristics of machine tool can be improved by using aluminum foam-filled structure.Compared with cast iron material,the inherent frequency of table with aluminum foam-filled structure significantly improved,resonant response amplitude has decreased.It was accord with the requirements in the lightweight and high dynamic performance under the condition of ultra-high speed processing.

Uncertainty quantification of the finite element model of existing bridges for dynamic analysis

With increasing number of aging civil structures including bridges, the finite element (FE) analysis assumes key roles in the use of the maintenance and repair design, and structural health monitoring. Despite the changes in dynamic characteristics of the aging structures from the nominal condition due to deteriorations or possible damages, limited attention has generally been paid to the verification and validation (V&V) of the numerical models used in the dynamic analysis. In this paper, we describe some practical considerations on the systematic V&V especially for the modeling of existing and aging bridges by applying a series of V&V procedure to the bridge FE model. The applied V&V procedure includes: (1) experimental data acquisition by impact tests, (2) model verification using grid convergence index, (3) sensitivity analysis to extract influential parameters to the comparative feature, namely the modal parameters, and (4) uncertainty quantification based on Bayesian inference. Posterior probability distributions of uncertain parameters in the FE model, especially material properties of the girders and slab, were then successfully derived in the uncertainty quantification procedure. The study also discusses some important considerations to improve implementation of V&V for the modeling of existing structures in terms of the verification procedure for complex FE models, the choice of comparative features, and the appropriate experimental data acquisition.

Change in Dynamic Characteristics of Spindle for Machining Centers Caused by Chucking Mechanism of Clamped Toolholders

In this study, the effects of clamping toolholders on the dynamic characteristics of spindle systems are evaluated experimentally. In the experiments, the transfer functions are obtained by the impulse response method, and then, the dynamic characteristic parameters are identified based on the vibration model of single-degree of freedom. Two types of machining center spindles and four types of toolholders are evaluated. From the experimental results, the following are revealed: (1) the clamping toolholder enhances the vibration amplitude markedly compared with that of the spindle not clamping toolholder. (2) The different chucking mechanisms clearly change the dynamic stiffness of the spindle systems. (3) The order of magnitude of the dynamic stiffness of the spindle systems agrees well with that of the isolated toolholders. It is confirmed experimentally that clamping of the appropriate toolholder improves the dynamics stiffness of the spindle systems for machining centers.

Influence of Radial Slots on the Vibration Characteristics of Circular Saw Blade

In order to improve thin circular saw blade’s cutting stability, it’s nonlinear dynamic incremental equilibrium equation was obtained according to nonlinear vibration theory and D’Alembert principle. It could be concluded from the above equation that cutting several radial slots on the circumference of the saw blade will cause significant change of dynamic characteristics of the saw blade. This thesis, employing the finite element method and matrix perturbation principle, calculated and studied respectively the effect of number, length and width of the radial slots on natural frequencies of the saw blade. Results show that number and length have distinct influence on natural frequencies but hardly does width have. So proper choice of number, length and width of the radial slots can improve effectively the dynamic characteristics of the saw blade.

Damage assessment of GFRP pultruded structural elements

This study shows a procedure for the identification of the mechanical characteristics and dynamic parameters of glass fiber-reinforced polymer (FRP) pultruded elements. The matching between analytical model and experimentally acquired modal and natural frequency data is used to investigate the homogeneity of materials (resin and fibers) and the mechanical characteristics variation for pultruded profile with different cross sections, also in presence of induced damage. The experimental results are given primacy, and then the model must be modified by trial and error methodologies of model updating approach. This work depicts the sensitivity analysis based FE model updating procedure and its application to mechanical characteristics and damage assessment of different GFRP members from modal parameters. The accuracy analysis, that relies upon the relative confidence between the results (exp. and analytical) features a FE model of pultruded composite profiles with orthotropic behavior. The same structures were subjected to damage and their identification is based on dynamic response through the curvature mode shapes. This approach allows to know the location and size of damage, the change in dynamic characteristics and thus the decrease in strength and stiffness. The damage identification was carried out also with FE analysis by updating the undamaged beam model.

발전기 변류기 건전성 확보를 위한 연구

This thesis is the result of conducting an analysis to find the solution to the phenomenon of power stoppage due to the disconnection of a CT (Current Transformer) because of vibration. The CT which measures the most essential current is used in power industries as part of a generator protection relay. When it comes to the bottom plate of a CT, nonconductor; such as bakelite and laminates; these material elements should be used because it is impossible to utilize the conductor when measuring the current of a generator which carries a high current if you use other materials. These nonconductor`s material properties are irregular and interpretation errors often occur because the weight is light. In addition, since the change of dynamic characteristics which are related to the temperature often occur, it is important to match the real situation by considering an error of interpretation rather than selecting the quality of the material. Lastly, the conclusion that the study drew is that it is possible to avoid the resonance by utilizing three changes to the components to solve the problem concerning the high vibration which is caused by non-conductive objects. These changes are the most crucial points in this thesis: First, material changes to the Plate. Second, weight changes to the Coil. Third, thickness changes to the Plate.

Variation of Small Amplitude Vibration Dynamic Properties with Displacement in Reinforced Concrete Structures

Correlating damage level and changes in dynamic characteristics of a structure forms the basis for damage detection techniques in structural health monitoring. In reinforced concrete building structures such correlation is not well established. A damage detection technique capable of identifying the structural condition of the system based on its small amplitude vibration response is desirable because such response is easier to obtain. It is a common practice in engineering applications to estimate dynamic parameters from small-amplitude vibrations assuming a linear behavior of the structure. This simplification causes inaccurate estimation of the dynamic properties in reinforced concrete structures due to the presence of nonlinear elastic behavior. In this study no such assumption is made and a linear model is only used for sets of data corresponding to the same displacement amplitude of a nonlinear elastic system. The trends found between small-amplitude vibration dynamic properties and past levels of maximum displacement in various reinforced concrete structures are reported. In addition to analytical and numerical studies, results from a series of laboratory tests are reported to demonstrate the use of the approach. One full-scale three-story reinforced concrete flat-plate building and six small-scale reinforced concrete beams were examined. In this study, small displacements are defined as displacements below an overall drift ratio of 0.03%. The displacement dependence of the dynamic properties is considered explicitly. It was found that while fundamental frequencies of the examined reinforced concrete specimens were found to decrease uniformly as past peak displacement level increased, the equivalent viscous damping ratio was found to increase until the past peak displacement reached the neighborhood of nominal yield displacement and then observed to decrease when the specimens are pushed beyond the nominal yield displacement level, which has not been reported in literature before. Recommendations are provided as to how small amplitude vibration tests should be set up to avoid misleading observations due to nonlinear response at small amplitude response, observations that could lead to erroneous conclusions regarding the damage state of a structure.