Combinations Of System Parameters Research Articles

Pounding force assessment in performance‐based design of bridges

AbstractBridges with deck supported on either sliding or elastomeric bearings are very common in mid‐seismicity regions. Their main seismic vulnerabilities are related to the pounding of the deck against abutments or between the different deck elements. A simplified model of the longitudinal behavior of those bridges will allow to characterize the reaction forces developed during pounding using the Pacific Earthquake Engineering Research Center framework formula. In order to ensure the general applicability of the results obtained, a large number of system parameter combinations will be considered. The heart of the formula is the identification of suitable intermediate variables. First, the pseudo acceleration spectral value for the fundamental period of the system (Sa(Ts)) will be used as an intensity measure (IM). This IM will result in a very large non‐explained variability of the engineering demand parameter. A portion of this variability will be proved to be related to the relative content of high‐frequency energy in the input motion. Two vector‐valued IMs including a second parameter taking this energy content into account will then be considered. For both of them, a suitable form for the conditional intensity dependence of the response will be obtained. The question of which one to choose will also be analyzed. Finally, additional issues related to the IM will be studied: its applicability to pulse‐type records, the validity of scaling records and the sufficiency of the IM. Copyright © 2009 John Wiley & Sons, Ltd.

Theory of dissipative solitons in complex Ginzburg-Landau systems

Using soliton amplitude and phase ansatzes, a theory is proposed for searching for stationary soliton solutions to the cubic-quintic complex Ginzburg-Landau (CGL) equation. For arbitrary combinations of system parameters, our approach allows the existence of dissipative solitons together with their specific soliton characteristics to be determined, and we demonstrate this explicitly for the case of a pulsed fiber laser system. The regimes of existence of dissipative solitons and their rules of evolution in a complicated five-dimensional parameter space are also analyzed. This work may open other research opportunities in diverse areas of nonlinear dynamics governed by the CGL equation, and may impact significantly on experimental design.

Plus disease in retinopathy of prematurity: Pilot study of computer-based and expert diagnosis

To measure accuracy of plus disease diagnosis by recognized experts in retinopathy of prematurity (ROP), and to conduct a pilot study examining performance of a computer-based image analysis system, Retinal Image multiScale Analysis (RISA). Twenty-two ROP experts independently interpreted a set of 34 wide-angle retinal images for presence of plus disease. A reference standard diagnosis based on expert consensus was defined for each image. Images were analyzed by the computer-based system using individual and linear combinations of system parameters for arterioles and venules: integrated curvature (IC), diameter, and tortuosity index (TI). Sensitivity, specificity, and receiver operating characteristic areas under the curve (AUC) for plus disease diagnosis compared with the reference standard were determined for each expert, as well as for the computer-based system. Expert sensitivity ranged from 0.308 to 1.000, specificity ranged from 0.571 to 1.000, and AUC ranged from 0.784 to 1.000. Among individual computer system parameters, venular IC had highest AUC (0.853). Among all computer system parameters, the linear combination of arteriolar IC, arteriolar TI, venular IC, venular diameter, and venular TI had highest AUC (0.967), which was greater than that of 18 (81.8%) of 22 experts. Accuracy of ROP experts for plus disease diagnosis is imperfect. A computer-based image analysis system has potential to diagnose plus disease with high accuracy. Further research involving RISA system parameter cut-off values from this study are required to fully validate performance of this computer-based system compared with that of human experts.

Simulation of Kinetically Limited Nucleation and Growth at Monatomic Step Edges

A kinetic Monte Carlo (KMC) numerical approach was used to investigate initial stages of kinetically controlled nucleation and growth on electrodes. Deposition, surface diffusion, nucleation, and growth were simulated for a pristine system consisting of metal ions in solution adjacent to a face-centered-cubic (fcc) surface that is initially configured with a series of parallel, monatomic step edges. Simulations were carried out with an atomic-scale, solid-on-solid KMC algorithm, in which the deposited atoms occupied the sites of a fcc lattice. One series of simulations was carried out for metal deposition onto a substrate of the same metal. The results were characterized according to a dimensionless quantity, Λ, that represented the ratio of the rate of surface diffusion to the rate of deposition. It was found for large values of Λ that the deposit grew at the monatomic step edges, whereas for small values of Λ the step edges played no role in the nucleation of islands. A second series of simulations was carried out for deposition onto a foreign substrate. The growth modes associated with various combinations of system parameters was explored.

Stability analysis and μ-synthesis control of brake systems

The concept of friction-induced brake vibrations, commonly known as judder, is investigated. Judder vibration is based on the class of geometrically induced or kinematic constraint instability. After presenting the modal coupling mechanism and the associated dynamic model, a stability analysis as well as a sensitivity analysis have been conducted in order to identify physical parameters for a brake design avoiding friction-induced judder instability. Next, in order to reduce the size of the instability regions in relation to possible system parameter combinations, robust stability via μ-synthesis is applied. By comparing the unstable regions between the initial and controlled brake system, some general indications emerge and it appears that robust stability via μ-synthesis has some effect on the instability of the brake system.

Communication power optimization in a sensor network with a path-constrained mobile observer

We present a procedure for communication power optimization in a network of randomly distributed sensors with an observer (data collector) moving on a fixed path. The key challenge in using a mobile observer is that it remains within communication range of any sensor for a brief duration, and inability to transfer data in this duration leads to data loss. We establish that the process of data collection can be modeled by a queue with deadlines, where arrivals correspond to the observer entering the range of a sensor and a missed deadline means data loss. The queuing model is then used to identify the combination of system parameters that ensures adequate data collection with minimum power. The results obtained from the queuing analogy take a simple form in the asymptotic regime of dense sensor networks. Additionally, for sensor networks that cannot tolerate data loss, we derive a tight bound on minimum sensor separation that ensures that no data will be lost on account of mobility. We present two examples to illustrate our results, from which it is seen that power reduction by two orders of magnitude or more is typical relative to a static sensor network. The scenarios chosen for power comparisons also provide guidelines on the choice of path, if such a choice is available.

Selection of diversity and modulation parameters for Nakagami fading channels to jointly satisfy outage and bit error requirements

Outage events occur when the instantaneous signal-to-noise ratio or bit error rate fall into an unacceptable operational regime. Outage performance analysis is traditionally carried out for diverse channel behaviors and transmission techniques, leaving the identification of unacceptable operational regime to user specified performance requirements. An alternative approach is taken in this work and an acceptable combination of system parameters are identified such that the user specified quality of service (QoS) constraints are satisfied. The QoS constraints are specified jointly in terms of outage probability, outage duration and probability of occurrence of errors during the outage event. This work presents inter-dependencies between the QoS constraints and modulation, diversity and signal parameters in closed form. The analysis assumes identically, independently distributed Nakagami interferers using maximal ratio diversity combining (MRC)

Natural Frequncies of Coupled Blade‐Bending and Shaft‐Torsional Vibrations

In this study, the coupled shaft‐torsional and blade‐bending natural frequencies are investigated using a reduced order mathematical model. The system‐coupled model is developed using the Lagrangian approach in conjunction with the assumed modes method to discretize the blade bending deflection. The model accounts for the blade stagger (setting) angle, the system rotating speed and its induced stiffening effect. The coupled equations of motion are linearized based on the small deformation theory for the blade bending and shaft torsional deformation to enable calculation of the system natural frequencies for various combinations of system parameters. The obtained coupled eignvalue system is ready for use as a reference for comparison for larger size finite element simulations and for the use as a fast check on natural frequencies for the coupled blade bending and shaft torsional vibrations in the design and diagnostics processes. Some results on the predicted natural frequencies are graphically presented and discussed pertinent to the coupling controlling factors and their effects. In addition, the predicted coupled natural frequencies are validated using the Finite Element Commercial Package (Pro‐Mechanica) where good agreements are found.

A dynamic resource allocation scheme for delay-constrained multimedia services in CDMA 1/spl times/EV-DV forward link

CDMA2000 1/spl times/EV-DV has been proposed as one of the global standards of third-generation (3G) networks, which adopts TDM/CDM and adaptive modulation and coding (AMC) techniques to enhance the data rate. The current CDMA2000 1/spl times/EV-DV standard specifies all possible combinations of system parameters, but there is no any further specification in the standard on how to dynamically change the system parameters to support the quality-of-service (QoS) requirements imposed by the upper-layer applications. In the meantime, one of the major deficiencies of previous research work done in this area is that they all are based on the channel models of physical layer such as Rayleigh model, which is unable to capture the link-layer QoS parameters such as queueing delay. Since the dynamic resource allocation usually resides in the data link layer, a wireless channel model at the link layer would be desirable to handle the QoS requirements. In this paper, we develop a dynamic resource allocation scheme using the effective capacity link model to support delay-bounded multimedia services in CDMA2000 1/spl times/EV-DV networks. Extensive simulations have been set up and the simulation results show that the proposed dynamic resource allocation scheme significantly improves the delay and throughput performance for all types of application traffic with various QoS requirements.

Stability, bifurcation and chaos of a high-speed rub-impact rotor system in MEMS

A general model of a Jeffcott micro-rotor system with rub-impact is established based on the classic impact theory and is analyzed by the modern nonlinear dynamics and bifurcation theories. An investigation is carried out on the stability of the rub solutions of the rotor system and the results provide a better understanding of the dynamical characteristics, such as the transition among periodic, quasi-periodic and chaotic responses, of the rotor system with rub-impact under different system parameter combinations. Nonlinear behaviors of rub-related vibrations are studied with a large number of numerical simulations. The effects of rotating speed, imbalance, damping coefficient, impact stiffness, and friction coefficient on the micro-rotor responses are investigated in detail. It is demonstrated that the system goes through an extraordinary route to chaos and alternates among the periodic, quasi-periodic and chaotic motions as the system parameters change. These forms of dynamical characteristics can be effectively used to diagnose the rub-impact fault. The results help engineers to optimize the design of micro-rotating machinery in MEMS, as well as to develop sensitive monitoring/diagnosis systems assessing machinery conditions.

Simulation of soil erosion and nutrient impact using an integrated system dynamics model in a watershed in Taiwan

In recent years, erosion, sediment, and nutrient pollution have become issues of major concern in Taiwan. Keelung River, as it flows across the Taipei metropolitan area, is one of the most important rivers with regard to these issues. This research aims to compute and simulate erosion, sediment yield, and resulting nutrient pollution, together with related economic factors. Related physical models were programmed using a system dynamics software package Vensim ®, for convenience in scenario designs and simulations. GIS software ArcView ® was employed to integrate digitized themes that contain data necessary for further computation and applications. EXCEL ® was also used to link ArcView and Vensim and made an interactive computational model. Five submodels, i.e., the soil erosion model, the sediment transportation model, the runoff model, the nutrient model, and the economic model, were included in this integrated model. Through this model, it was estimated that, according to the hydrological and geographical data from last five years, the total annual amounts of soil erosion, sediment yield, and nutrient load are 292,327 tons, 101,661 tons, and 1428 tons, respectively. These results can be compared with those derived from models in other researches. As the model in this research was driven by a system dynamics core, scenario simulations can be carried out based on various combinations of system parameters. This offers the model additional flexibility and applicability.

Influence of atmospheric and system parameters on multiple scattering in spaceborne backscatter lidar measurements

We have simulated backscatter signals of spaceborne lidar systems with the help of a Monte Carlo model. Calculations were performed for various combinations of system parameters. As typical examples of atmospheric observation targets, two kinds of cirrus cloud and two kinds of aerosol were considered. Both total multiple scattering and the significance of individual higher scattering orders are discussed. For all cases, an approximate multiple scattering factor F was calculated that can be used to correct the single-scattering lidar equation to account also for multiple scattering.

Vibration and Stability of Uniform Euler–Bernoulli Beams with Step Change in Axial Force

Beams which carry a constant axial force in one portion of the beam and a different axial force in the rest of the beam occur in engineering applications. The system parameters are the position where the axial force change occurs and the two axial force parameters. Transverse vibration of such systems (based on the Euler—Bernoulli theory of bending) is considered in this paper. Tables of the first three frequency parameters are given for various combinations of classical boundary conditions and system parameters. High-precision computing is necessary to handle large axial forces. It is possible for a natural frequency to be zero for certain combinations of the system parameters. This is Euler buckling and a table of combinations of critical system parameters is given. Transverse vibration of tie-bars (a special case of the title problem) is covered in textbooks but benchmark frequencies are not documented. In the paper, a table of frequency parameters of beams carrying tensile or compressive axial forces is given for all the combinations of classical boundary conditions.

Optimisation of a hybrid diesel-hydraulic automotive powertrain using ADVISOR, Matlab and Simulink

The Hydraulic Hybrid Vehicle obtains energy for propulsion from two different sources, the Internal Combustion Engine (ICE) and a hydraulic pump/motor. Braking torque is supplied by operating the unit as a pump, and thus storing the otherwise lost kinetic energy of the slowing vehicle. During acceleration the unit is operated as a motor, using the stored energy to assist propulsion. A model of the systems was developed in the Matlab/Simulink environment then implemented into the automotive simulator ADVISOR. This paper outlines the procedures used for optimisation studies within ADVISOR, to find the ideal combination of system parameters, e.g., pump/motor displacement, accumulator size and pressures, that yield the best results for fuel consumption for a standard urban drive cycle.

A flow metamodel for delivery agents over a spatial area

This article studies fuzzy rules that were used to model autonomous entities and discusses the development of a metamodel to describe the traffic flow of autonomous agents over a spatial area. The agents deliver goods (and themselves) to prespecified locations on the given spatial area. The metamodel is defined as a set of equations, obtained through regression analysis, that are functions of several variables that affect the agent system. The performance measures are effective speed and collision probability. The fuzziest rule set consistently gave the best results in terms of collision avoidance for this study. The improved collision avoidance is gained at the cost of a lower effective speed. A “traffic control” policy may be desirable when congestion reaches a limit. The flow metamodel equations describe the emergent behavior of the system, or system-level behavior resulting from interactions at the level of the parts of the system. The equations can be used to determine whether congestion will be a problem before designing a system containing entities that navigate among themselves. The flow metamodel curves suggest combinations of system parameters that will alleviate congestion. The results have implications for several practical applications.

A Re-Configurable Test Apparatus for Complex Nonlinear Dynamic Systems

This paper reports the results of an analytical and experimental study to design, analyze, construct, test, and evaluate a re-configurable test-bed to allow the convenient performance of sophisticated experiments in a laboratory setting for investigating a broad category of important nonlinear, time-varying phenomena that are widely encountered in the applied mechanics field. The essential elements of the test apparatus include an electro-dynamic exciter that drives an oscillating mass whose restoring force is easily adjustable from one resembling a linear SDOF mass-spring-damper system with constant coefficients, to one that can represent systems with nonlinear elastic forces, to one that models systems possessing hysteretic properties with precisely-controlled time-varying characteristics. The apparatus design is economical to fabricate, convenient to manipulate, and it provides results that can be accurately replicated under repeated test combinations of system parameters and dynamic loads. The utility of the apparatus to provide an investigational tool for studying the dynamic response of systems with time-varying dry-friction forces that give rise to hysteretic phenomena is demonstrated. Sophisticated on-line system-identification techniques are used to estimate the parameters of reduced-order models that capture the dominant features of the physical model. It is shown that the apparatus under discussion is a useful research tool for investigators conducting studies in physics-based models of generic nonlinear dynamic systems.

Behaviour of impact oscillator with soft and preloaded stop

New phenomena of the dynamics of oscillators with impacts, when the stiffness of the stop changes from zero to infinity, are described. Dynamics of one example of the system with soft impacts, as the model of the piercing machine, is explained in more detail by bifurcation diagrams, time series, phase trajectories and Poincarè maps of periodic and chaotic impact motions. Optimal combinations of system parameters are found for the obtaining of maximum before-impact velocities.

Simulation of Digital Control Systems

A computer technique for simulating digital control systems is presented. It is conceived with recursion formulas to describe the interconnected elements of the system, those of the digital and the continuous elements, in a unified fashion. The technique permitted experimentation with different combinations of system parameters and system configurations. The efficiency of the techniques suggest its suitability for a rational engineering design of a control system before implementation.

Hybrid algorithms for complete exchange in 2D meshes

Parallel algorithms for several common problems such as sorting and the FFT involve a personalized exchange of data among all the processors. Past approaches to doing complete exchange have taken one of two broad approaches: direct exchange or the indirect message-combining approaches. While combining approaches reduce the number of message startups, direct exchange minimizes the volume of data transmitted. This paper presents a family of hybrid algorithms for wormhole-routed 2D meshes that can effectively utilize the complementary strengths of these two approaches to complete exchange. The performance of hybrid algorithms using Cyclic Exchange and Scott's Direct Exchange are studied using analytical models, simulation, and implementation on a Cray T3D system. The results show that hybrids achieve lower completion times than either pure algorithm for a range of mesh sizes, data block sizes, and message startup costs. It is also demonstrated that barriers may be used to enhance performance by reducing message contention, whether or not the target system provides hardware support for barrier synchronization. The analytical models are shown useful in selecting the optimum hybrid for any given combination of system parameters (mesh size, message startup time, flit transfer time, and barrier cost) and the problem parameter (data block size).

Dynamics of flexible-link and flexible-joint manipulator carrying a payload with rotary inertia

A dynamic model of a flexible-arm and flexible-joint manipulator carrying a payload with rotary inertia is presented. The Lagrangian approach in conjunction with the finite element method is employed in deriving the equations of motion, within the assumption of a small deformation theory. All the dynamic coupling terms between the system reference rotational motion, joint torsional deformations and arm bending deformations are accounted for. The dynamics of a payload with rotary inertia are incorporated in the model in a consistent manner. Furthermore, the effects of axial shortening due to beam and bending deformations and motions induced inertial forces as well as the effects of gravity are included in the model. The resulting model and simulation results have shown that the joint flexibility has a pronounced effect on the dynamic behavior of rotating flexible arms that should not be simply neglected. The effect is shown to be due to the nonlinear dynamic interaction between the joint torsional deformations, the arm bending deformations and the system reference rotational motion. Simulation results of the nonlinear and the linearized models are compared and the results are discussed. The effects of the payload are shown to be increasing the elastic deformations’ amplitudes and reducing the frequency of oscillations. Due to the model nonlinearity, different combinations of system parameters are expected to develop different effects. This makes the proposed model valid in the design process as well as in the performance evaluation.