Dynamic Analytical Model Research Articles

Detection of fatigue damage precursor using a nonlinear vibration approach

A nonlinear dynamic methodology is developed for detecting and estimating fatigue damage precursor in isotropic metal structures, prior to fatigue crack initiation, based on measurement of changes in the structure nonlinear response to harmonic base excitation. As an example, a damage precursor feature was extracted for cantilever beams by quantifying the reduction in the nonlinear stiffness because of localized microscopic material softening. The nonlinear dynamic analytical model parametrically tracks changes in the nonlinear structural stiffening as a function of the structural response and the loading cycles. Experimental results are obtained by exciting the base of cantilever beams at various amplitude levels. At high response amplitudes, the beams experience three competing simultaneous nonlinear dynamic mechanisms: (i) stiffening because of high response amplitude at the fundamental mode; (ii) softening because of inertial forces; and (iii) softening because of localized microscopic material damage caused by cyclic micro-plasticity. The third mechanism—a potential precursor to fatigue crack initiation in the structure—resulted in a cumulative softening because of early accumulation of cyclic fatigue damage and is the focus of this study. The loading intensity and the number of cycles influenced the relative contribution of these dynamic mechanisms. Nanoindentation studies near the beam clamped boundary were conducted to confirm the fatigue degradation in the local mechanical properties as a function of loading cycles. The proposed detection method is simple to implement and detects the presence of damage precursors but lacks the resolution to discern spatial distributions of the damage intensity. Based on prior knowledge of the structural dynamic characteristics of the beam and using the proposed methodology, damage level and stiffness reduction can be detected and estimated based on changes in the nonlinear structural response. The nonlinear stiffness term in the equation of motion is found to be very sensitive to the proposed fatigue damage precursor, making it an effective method for monitoring structural degradation prior to crack developments. The proposed methodology provides new insights and constitutes a significant step toward the development of new inspection techniques. Copyright © 2016 John Wiley & Sons, Ltd.

서비스업생산지수와 서비스업도소매지수와의 상호연관성에 관한 연구

We examine the information transmission between the Service Industrial Production Index and the Service Industrial Wholesale and Retail Index, based on the returns data offered by the Korea Bank. The data includes daily return data from January 2000 to September 2015. Utilizing a dynamic analytical tool-the VAR model, Granger Causality test, Impulse Response Function and Variance Decomposition have been implemented. The results of the analysis are as follows. Firstly, results of Granger Causality test suggests the existence of mutual causality the Service Industrial Production Index precede and have explanatory power the Service Industrial Wholesale and Retail Index However the results also identified a greater causality and explanatory power of the Service Industrial Wholesale and Retail Index over the Service Industrial Production Index. Secondly, the results of impulse response function suggest that the Service Industrial Production Index show immediate response to the Service Industrial Wholesale and Retail Index and are influenced by till time 5 From time 2, the impact gradually disappears. Also the Service Industrial Wholesale and Retail Index show immediate response to the Service Industrial Production Index and are influenced by till time 2.5, the impact gradually disappears. Lastly, the variance decomposition analysis shows that the changes of return of Service Industrial Production Index are dependent on those of the Service Industrial Wholesale and Retail Index. This implies that returns on the Service Industrial Production Index have a significant influence over returns on the Service Industrial Wholesale and Retail Index. It contributes to the understanding of market price formation function through analysis of detached the Service Industrial Production Index and Service Industrial Wholesale and Retail Index. Finally, our results can be used as a guide by the Korea Bank and Republic of Korea and as well as Statistics Korea.

Small-Signal Dynamic DQ Model of Modular Multilevel Converter for System Studies

This paper presents three dynamic linear state-space models of the modular multilevel converter (MMC) which are suitable for small-signal dynamic studies and controller design. The three models differ by the number of states (two, six, and ten) and, therefore, are suitable for different applications based on the required accuracy. The 2nd- and 6th-order models ignore dynamics of the second harmonics and circulating current suppression control (CCSC). The main challenges of dynamic analytical modelling of MMC are the nonlinear multiplication terms in ABC frame equations for modulating oscillating signals. The multiplication nonlinear terms are therefore considered directly in the rotating DQ frame. This requires simultaneous modeling in zero sequence, fundamental frequency DQ and double fundamental frequency DQ2 frames. The proposed linear analytical models are implemented in state space in MATLAB. The validity and accuracy of the models are verified against a detailed 401-level MMC model in PSCAD/EMTDC in both time and frequency domains. The results show very good accuracy for the 10th-order model and decreasing accuracy for the lower order models. The influence of phase-locked loop and CCSC gains on the MMC dynamic is also studied using the proposed 10th model, and the results verify the suitability of the model for this purpose.

Validation of Dynamic Simulation of Slow-Moving Surface Deflection Measurements

Recent studies have concluded that measured surface deflections can be used as a low-cost pavement monitoring and condition assessment tool to determine remaining structural life and pavement performance. Moving load devices are being used more often to measure continuous surface deflections. They are considered a faster alternative to falling weight deflectometer–based structural condition evaluation applications. The objective of the study was to compare the analytical dynamic simulation of slow-moving deflection measurements with field data. The surface pavement deflections and the pavement structural responses generated by the Euroconsult Curviametro loading at the Minnesota Department of Transportation’s MnROAD facility near Maplewood, Minnesota, were used in the evaluations. Four geophones were embedded near the pavement surface to measure surface deflections during field trials at each of three tested MnROAD cells. In addition, numerous other sensors, such as strain gauges and thermocouple trees, were available at the MnROAD facility. The 3D-Move program was used in the simulations because it can accommodate moving loads and the viscoelastic properties of pavement layers and produce continuous deflection basins. The viscoelastic properties of pavement layers were estimated on the basis of the actual temperatures at the time of the field trials and the appropriate loading frequency of the Curviametro. The proposed dynamic analytical model provided a good match with a variety of independent pavement responses, which included surface deflection basins (measured by embedded geophone sensors) as well as horizontal strains at the bottom of the asphalt concrete layers (measured by MnROAD sensors).

Modeling and Vector Control of Marine Current Energy Conversion System Based on Doubly Salient Permanent Magnet Generator

This paper provides a model and a control of a marine current energy conversion system. The modeled marine current energy conversion system is a 10-kW generating system with a low-speed doubly salient permanent magnet generator of 50rpm. First, the resource, the turbine, and a dynamic analytical model of the generator are developed. Second, due to variations of marine current speed, which may lead to strong fluctuations in the power extracted by the marine current turbine, control strategies for the marine current energy conversion system at both low and high marine current speeds are analyzed, assessed, and compared. Finally, simulations of the proposed system are carried out, modeled, and simulated on MATLAB/Simulink software.

네트워크 기반 보행 예측 기법간의 특성에 관한 비교 연구 - 정적 분석과 동적 분석의 관점으로 -

Despite the difficulty of predicting complex pedestrian flow, recently there have been considerable researches about the quantitative prediction model based on network structure. However, each models have its own focus on one specific feature in network structure, it is hard to find out the difference among those models, especially in terms of the prediction results' closeness to the real pedestrian volume. Therefore, in this study, a comparison study was conducted among the 4 pedestrian prediction models that have been widely researched in our country. In detail, the simulation results of each model have been compared with the real counted pedestrian volume of the selected target area. The result of this study is that the each pedestrian prediction model - mainly divided into static and dynamic, shows lots of differences which might come from the each models' specific focus of the network structure. The dynamic analytical model shows much closer results to the real pedestrian volume, however it needs more time for the pre-survey for the simulation. On the contrary, the static model is simple. Consequently, there should be careful consideration in selecting pedestrian prediction model suits the purpose of the pedestrian prediction experiment.

Dynamic analyses of traffic speed deflection devices

Two traffic speed deflection devices (TSDDs) that measure surface deflections at posted traffic speeds (up to 80–96 kph) were evaluated through a recent Federal Highway Administration project that included field trials at the MnROAD facility. Four geophones were embedded near the pavement surface to measure surface deflections during field trials at each of three MnROAD cells. In addition, the MnROAD facility counted with numerous other sensors such as strain gauges to measure pavement responses and thermocouple trees to collect pavement temperature at various depths. For the implementation of TSDDs in any network-level pavement management system, it is important to utilise a proper analytical model that can accommodate moving load and viscoelastic properties of pavement layers in the simulation of TSDD measurements. The 3D-Move software was chosen for this purpose. The viscoelastic properties used for the asphalt concrete (AC) layer include dynamic modulus and damping coefficient as a function of frequency relevant to the temperature at the time of the MnROAD field trials. The field trials and available data represented realistic field case scenarios to validate once more 3D-Move specifically for TSDD measurements. The proposed dynamic analytical model provided a good match with a variety of independent pavement responses that included surface deflection bowls (measured using embedded geophone sensors) as well as horizontal strains at the bottom of the AC layers (measured using MnROAD sensors).

Smart home gateway system over Bluetooth low energy with wireless energy transfer capability

As billions of sensors and smart meters connect to the Internet of Things (IoT), current wireless technologies are taking decisive steps to ensure their sustainable operation. One popular IoT scenario features a smart home service gateway, which becomes the central point of user’s home environment facilitating a multitude of tasks. Given that most IoT devices connected to residential gateway are small-scale and battery-powered, the key challenge is to extend their lifetime without recharging/replacing batteries. To this end, a novel radio technology named Bluetooth low energy (BLE) has recently been completed to enable energy-efficient data transfer. Another inspiring innovation is the capability of sensors to harvest wireless energy in their local environment. In this work, we envision a scenario where many in-home sensors are communicating with a smart gateway over the BLE protocol, while at the same time harvesting RF energy transmitted from the gateway wirelessly via a dedicated radio interface. We thoroughly investigate performance limitations of such wireless energy transfer interface (WETI) with dynamic analytical model and with important practical considerations. Our methodology delivers the upper bound on WETI operation coupled with BLE-based communication, which characterizes ultimate system performance over the class of practical radio and energy resource management algorithms.

FIELD TESTING AND VALIDATION OF DIRECTIONAL DYNAMICS MODEL OF A TANK TRUCK

A two–axle vehicle, equipped with a semi–transparent cylindrical tank, is fabricated and instrumented to determine the dynamics of sloshing cargo and its effects on directional response of the vehicle. The directional dynamics of a partially filled tank truck is investigated via computer simulation of a three–dimensional vehicle model incorporating a quasi–dynamic roll plane model of the tank. Field tests are performed for typical lane change and turning manoeuvres, and the corresponding directional response data are compared to the computer simulation results to validate the analytical model. The study concludes that the results obtained from the analytical vehicle model, incorporating quasi–dynamic fluid analysis, correlate well with the field measured data for different fill levels, vehicle speeds, and directional manoeuvres. Motion of the fluid–free surface and the corresponding lateral load transfer, attained via computer simulation, are further compared to those established from the field measured data to conclude that a quasi–dynamic analytical model can accurately predict the fluid slosh loads.

Interfacial damage analysis of shallow spherical shell with FGM coating under low velocity impact

Interfacial damage would seriously reduce the structures' property, especially structures with coating when under dynamic loading. In this paper, the interfacial damage of shallow spherical shell with functionally graded material (FGM) coating subjected to low velocity impact is studied. An interfacial damage analytical model is established based on the continuum theory-based interfacial damage constitutive relations. The A.E. Giannakopoulos's 2-D functionally graded material (FGM) contact model is applied to predict contact force. Motion equations for shallow spherical shell substrate and FGM coating are obtained by Reissner variation, respectively, and the dynamic analytical model is established by using interfacial connection relations to relate the motion equations for FGM coating and those for elastic shallow spherical substrate. The orthogonal collocation point method, the Newmark method and iterative method are used synthetically to solve the whole question. In numerical examples, the dynamic response of shallow spherical shell with FGM coating and contact force are obtained, and the effects of material and geometrical parameters of FGM coating on interfacial damage and contact force have been discussed.

Analysis of Delaminated Composite Plates

A mathematical model for plates with partially delaminated layers is presented to investigate their behavior. In this formulation account is taken of lateral strains. The principal advantage of the element is that it allows the modeling of delamination anywhere in the structure. The region without delamination is modeled to carry constant peel and shear stresses; while the region with delamination is modeled by assuming that there is no peel and shear stress transfer between the top and bottom layers. Numerical results of the present model are presented and its performance is evaluated for static problems. Laminated beams and plates are often used as primary load-carrying structures. However, the mechanical properties of composite materials may degrade severely in the presence of damage. One of the common types of damage modes in laminated composites is delamination. The presence of delamination is one of the most prevalent life-limiting failure modes in laminated composite structures. Many researchers had been studying the effect of delamination. Wee and Boay [1] developed an analytical model to predict the critical load of a delaminated composite laminated beam. Lee et al. [2] investigated the buckling behavior of the beam plate with multiple delaminations under compression. Kapania and Wolfe [3] examined the buckling behavior of a beam plate with two delaminations of equal length. Wang et al. [4] improved the analytical solution by including the coupling between the flexural and axial vibrations of the delaminated sub-laminates. Lee et al. [5] studied a composite beam with arbitrary lateral and longitudinal multiple delamination. Finite-element methods have been developed using the layerwise theory by Kim et al. [6]. Tan and Tong [7] developed a dynamic analytical model for the identification of delamination embedded in a laminated composite beam. To investigate the effects of delamination of a plate layers, a finite-element model is developed. Both displacement continuity and force equilibrium conditions are imposed between the regions with and without delamination. The accuracy of the approach is verified by comparing results with previously published data.

Development of a plant dynamics analytical model using flow network for the MONJU ex-vessel fuel storage system

If a station blackout (SBO) occurs in a fast breeder reactor, heat removal by natural circulation is expected, because the height between the heat source and the sink was considered in the plant design to provide the potential for natural circulation. Therefore, many studies about heat removal by natural convection have been reported to date. In these studies, it was determined that the thermal hydraulics for natural circulation depend on the plant structure, cooling system, and component positions, unlike in the case of forced circulation. Thus, the heat removal ability by natural circulation differs in each system and each plant.For the fast breeder reactor (FBR) “MONJU” during normal operation, the ex-vessel fuel storage system (EVSS), which uses a natural circulation flow inside the ex-vessel fuel storage tank (EVST), and the EVST sodium cooling system rely on forced convection with an electromagnetic pump. The decay heat can be removed by air coolers and blowers. If an SBO occurs in this EVSS, all pumps and blowers would be stopped. However, the plant dynamics of the EVSS in the time after all the pumps and the blowers were tripped has not yet been evaluated.Therefore, in this study, a plant dynamics analysis model was developed using a flow network to calculate the entire dynamics of the EVSS in the event of an SBO. The Super-COPD program, which has been validated for models of the reactor and the main cooling system using several tests including the plant trip test and the natural circulation test, was used. A model of the EVSS was developed by considering the design information, and the modeling technique was based on specific analytical models for the reactor and the main cooling system, because there was no sufficient data to confirm the behavior of the sodium temperature and flow in this EVSS. For the model to simulate natural circulation, the heat capacity of the coolant plenum of the EVST, geometrical information such as the height of the components, and the heat transfer characteristics of the cooling coils were considered.Based on a comparison to experimental data, it was confirmed that the calculated the behavior of the sodium temperature and flow of the EVST sodium cooling system in an SBO is accurate. The thermal center of the heat transfer area of only the helical coils decreased to approximately 21% in comparison with that under normal operation, and the flow rate in the EVST decreased by approximately 20%. The natural convection force depends on the differences in the densities and the thermal centers of the heat transfer areas between each component. The calculation results based on the theory were almost equivalent to the analysis results. It is estimated that the developed model correctly considered the heat transfer characteristics of each component and can accurately calculate the natural convection force.From these results, it is concluded that the developed model for the EVSS is effective for calculating the temperature and flow behavior of the entire system under natural circulation conditions like those expected during an SBO. In the future, these models will be validated using a 3D fluid dynamics analysis and additional test results.

Dynamic analytical model for charge transport in octithiophene thin film transistors

In this paper, we develop a device model of an organic thin film transistor (OTFTs) in which the active layers are made of octithiophene. This model is based on variable range hopping theory, i.e., a carrier may either hop over a small distance with a high activation energy or hop over a long distance with a low activation energy. The model takes into account all the operating regimes in direct current and transient mode; the transistor symmetry is also considered. The model has been developed using a physical basis where the model parameters can easily be extracted. The current–voltage characteristics of short-channel organic TFTs have been calculated starting from the solution of the drain current equation for an enhancement mode p-channel MOSFET. A good agreement between theory model and experimental results is obtained. Different transport parameters are extracted by using a fitting method. We have extracted the mobility of charge in saturation regime using differential method. Based on first and second derivative of transfer characteristic we extracted a serial resistance, intrinsic mobility and threshold voltage. The mobility in saturation regime is reproduced using the VRH model. Finally, we give a simple small-signal equivalent circuit.

Thermo Fluid Dynamics Tests on the Single Channel Prototypes for the SPIDER Grids

The ITER Neutral Beam Test Facility (PRIMA - Padova Research on ITER Megavolt Accelerator) is planned to be built at Consorzio RFX (Padova, Italy). PRIMA includes two experimental devices: a full-size plasma source with low voltage extraction called SPIDER (Source for Production of Ions of Deuterium Extracted from RF plasma) and a full-size neutral beam injector at full beam power called MITICA (Megavolt ITER Injector Concept Advancement).The beam source components are exposed to high and focused heat loads during beam production, and they are actively cooled, being at high voltage, by ultrapure water, which flows through cooling channels machined inside the components. The high power loads, the complexity of the cooling circuits, and their small, rectangular cross sections are design critical issues.The results of the tests carried out on the single cooling channel prototypes (SCPs) for the SPIDER accelerator grids and their performances in terms of pressure drop and heat exchange calculation are presented. The SCPs have been tested in environmental conditions similar to injector ones, i.e., they have been subjected to thermal loads up to the average heat power density of 1 MW/m2, in a vacuum environment (0.5 Pa). The experimental results have been cross-checked with computational fluid dynamics analyses and analytical models.

A study on wrinkling characteristics and dynamic mechanical behavior of membrane

An eigenvalue method considering the mem- brane vibration of wrinkling out-of-plane deformation is in- troduced, and the stress distributing rule in membrane wrin- kled area is analyzed. A dynamic analytical model of rect- angular shear wrinkled membrane and its numerical analysis approach are also developed. Results indicate that the stress in wrinkled area is not uniform, i.e. it is larger in wrinkling wave peaks along wrinkles and two ends of wrinkle in ver- tical direction. Vibration modes of wrinkled membrane are strongly correlated with the wrinkling configurations. The rigidity is larger due to the heavier stress in the part of wrin- kling wave peaks. Therefore, wave peaks are always located at the node lines of vibration mode. The vibration frequency obviously increases with the vibration of wave peaks.

Nonlinear Dynamic Response and Active Control of Piezoelastic Laminated Shallow Spherical Shells with Damage

Based on Talreja’s damage model with tensor valued internal state variables and geometric nonlinear theory, the constitutive relations for a moderately thick shallow spherical shell with damage are derived. The distribution of electric potential along the thickness direction in the piezoelectric layer is simulated by a sinusoidal function, and accordingly the dynamic analytical model for the cross-ply laminated moderately thick piezoelectric shallow spherical shell is established. Using the negative velocity feedback control algorithm, an analytical model for active vibration control of the piezoelectric laminated moderately thick piezoelectric shallow spherical shell is built when the damage effect is considered. And the solutions to the whole problem are obtained with synthetical utilization of the orthogonal collocation point method and the Newark method. In numerical examples, the effects of damage, piezoelectric effect, and the structure’s geometrical parameters on the dynamic response and vibration control of the piezoelastic laminated shallow spherical shells with damage are investigated.

Dynamics Analytical Model of Cutting Force in Metal Cutting Processing

Cutting force is an important parameter in machining. The static balance method and experience formulas had been adopted to find its value, but the theoretical calculated value is not good agreement with the experimental value for the same set of cutting conditions. In practical machining, the cutting tool has obvious impact effect on workpiece, so a dynamics analytical model for cutting process is established in this paper. Based on the proposed solution, a new formula for cutting force has been obtained. The suggested formula has shown to correspond well with the experimental data.

Seismic Reliability Analysis of Hydraulic Aqueduct with Maximum Entropy Method

With the thin-wall dynamic analytical model of aqueduct for fluid-structure coupling, the seismic reliability of aqueduct is studied. In this model the influence of the bend-torsion coupling, water-structure coupling and nonlinear rubber bearing isolation are all taken into consideration. Based on the type of site soil, the artificial seismic waves are created. In accordance with the maximum entropy principle and the measured data of structural internal force under earthquake, the reliability distribution function and the aqueduct reliability are calculated.

Vibration Simulation of Air Slide Table in Ultra Precision Machines

The compressed air vibration in air slide table of ultra precision machines is an obstacle for gaining Nano-metric level of accuracies in the products created by these machines. In this article, the vibration behavior of air slide table due to compressed air layer is analyzed. The air slide table fluid and dynamic analytical model has been derived. In order to have air exit velocity from clearance gap, the finite element software FLUENT was applied. Finally, in order to calculate the displacements of table due to vibration and drawing its curves via time at the presence of varieties of air pressure, the second order differential equation was solved by MATLAB. In solving differential equation the Rang-Kutta method was used.

Numerical simulation for designing tuned liquid dampers to damp out double-pendulum oscillations

This paper presents a simplified dynamic analytical model based on the Lagrangian formalism to describe the annular sloshing damper behavior used to damp out free oscillations of a double-pendulum system. A simulation program using this model has been developed with the mathematical software MATLAB®. This simulation method is applied to design dampers for the mass and coil suspensions of the French watt balance experiment. The motion of each suspension is equivalent to a double-pendulum motion having two main natural frequencies for each configuration considered. The shape of the damper used is a ring composed of one or two concentric annular channels partially filled with a liquid (water for instance). The depth of the liquid must be adjusted in each channel in order to tune the resonance frequency of the liquid to a natural frequency of the suspension. Two corrective parameters determined experimentally have been added to our model in order to yield results in fair agreement with experiment. The numerical simulation based on our analytical model has provided useful information for designing annular sloshing dampers as efficient as possible for the experiment concerned. Furthermore, this method can be used to study any pendulous load system behavior and to design appropriate sloshing dampers.