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Artykuły w czasopismach na temat "Linearized Driving Forces"
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Ye, Xiu Qian, Yi Bao Chen, Bih Sheng Hsu i Yuh Chung Hu. "On the Dynamics of the Micro-Ring Driven by Traveling Bias Voltages". Advanced Materials Research 311-313 (sierpień 2011): 1027–31. http://dx.doi.org/10.4028/www.scientific.net/amr.311-313.1027.
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There is no literature mentioned the modeling of the microstructures subjected to traveling electrostatic forces. This paper is the first time to present an analytical approach to investigate the dynamics of a micro-ring structure driven by the traveling bias voltage. The traveling electrostatic forces may come from the sequentially-actuated actuating electrodes arranged around the flexible ring. A linearized distributed model considering the electromechanical coupling effect is derived based on the small deflection assumption. According to the analytical results, the stiffness of the micro-ring will be softened periodically with the traveling speed of the driving voltage and the variation increases with the increasing of the voltage.
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Lee, Hyeongcheol, i Masayoshi Tomizuka. "Coordinated Longitudinal and Lateral Motion Control of Vehicles for IVHS". Journal of Dynamic Systems, Measurement, and Control 123, nr 3 (24.03.1998): 535–43. http://dx.doi.org/10.1115/1.1386395.
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This paper presents a systematic design of the combined control of vehicle longitudinal and lateral motions for the Intelligent Vehicle Highway Systems (IVHS). A fully coordinated control of the steering and the accelerating/braking actions is presented to maximize the ability of distributing the traction forces in a desired way. This control method covers a broad range of driving condition by removing several conventional simplification on vehicle dynamics, such as the linearized lateral traction force assumption, the bicycle model assumption, and the non-slip assumption. The nominal traction force concept is also introduced to handle the unknown traction forces. Robust Adaptive Control (RAC) by backstepping for MIMO nonlinear systems is utilized to control the unmatched nonlinear vehicle dynamics, in the presence of parametric uncertainties and uncertain nonlinearities.
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Candioti, Lorenzo G., Thibault Duretz, Evangelos Moulas i Stefan M. Schmalholz. "Buoyancy versus shear forces in building orogenic wedges". Solid Earth 12, nr 8 (10.08.2021): 1749–75. http://dx.doi.org/10.5194/se-12-1749-2021.
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Abstract. The dynamics of growing collisional orogens are mainly controlled by buoyancy and shear forces. However, the relative importance of these forces, their temporal evolution and their impact on the tectonic style of orogenic wedges remain elusive. Here, we quantify buoyancy and shear forces during collisional orogeny and investigate their impact on orogenic wedge formation and exhumation of crustal rocks. We leverage two-dimensional petrological–thermomechanical numerical simulations of a long-term (ca. 170 Myr) lithosphere deformation cycle involving subsequent hyperextension, cooling, convergence, subduction and collision. Hyperextension generates a basin with exhumed continental mantle bounded by asymmetric passive margins. Before convergence, we replace the top few kilometres of the exhumed mantle with serpentinite to investigate its role during subduction and collision. We study the impact of three parameters: (1) shear resistance, or strength, of serpentinites, controlling the strength of the evolving subduction interface; (2) strength of the continental upper crust; and (3) density structure of the subducted material. Densities are determined by linearized equations of state or by petrological-phase equilibria calculations. The three parameters control the evolution of the ratio of upward-directed buoyancy force to horizontal driving force, FB/FD=ArF, which controls the mode of orogenic wedge formation: ArF≈0.5 causes thrust-sheet-dominated wedges, ArF≈0.75 causes minor wedge formation due to relamination of subducted crust below the upper plate, and ArF≈1 causes buoyancy-flow- or diapir-dominated wedges involving exhumation of crustal material from great depth (>80 km). Furthermore, employing phase equilibria density models reduces the average topography of wedges by several kilometres. We suggest that during the formation of the Pyrenees ArF⪅0.5 due to the absence of high-grade metamorphic rocks, whereas for the Alps ArF≈1 during exhumation of high-grade rocks and ArF⪅0.5 during the post-collisional stage. In the models, FD increases during wedge growth and subduction and eventually reaches magnitudes (≈18 TN m−1) which are required to initiate subduction. Such an increase in the horizontal force, required to continue driving subduction, might have “choked” the subduction of the European plate below the Adriatic one between 35 and 25 Ma and could have caused the reorganization of plate motion and subduction initiation of the Adriatic plate.
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Bell, Michael J., Adam T. Blaker i Joël J. M. Hirschi. "Wind-Driven Oscillations in Meridional Overturning Circulations near the Equator. Part II: Idealized Simulations". Journal of Physical Oceanography 51, nr 3 (marzec 2021): 663–83. http://dx.doi.org/10.1175/jpo-d-19-0297.1.
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AbstractLarge-amplitude [±100 Sv (1 Sv ≡ 106 m3 s−1)], high-frequency oscillations in the Pacific Ocean’s meridional overturning circulation within 10° of the equator have been found in integrations of the NEMO ocean general circulation model. Part I of this paper showed that these oscillations are dominated by two bands of frequencies with periods close to 4 and 10 days and that they are driven by the winds within about 10° of the equator. This part shows that the oscillations can be well simulated by small-amplitude, wind-driven motions on a horizontally uniform, stably stratified state of rest. Its main novelty is that, by focusing on the zonally integrated linearized equations, it presents solutions for the motions in a basin with sloping side boundaries. The solutions are found using vertical normal modes and equatorial meridional modes representing Yanai and inertia–gravity waves. Simulations of 16-day-long segments of the time series for the Pacific of each of the first three meridional and vertical modes (nine modes in all) capture between 85% and 95% of the variance of matching time series segments diagnosed from the NEMO integrations. The best agreement is obtained by driving the solutions with the full wind forcing and the full pressure forces on the bathymetry. Similar results are obtained for the corresponding modes in the Atlantic and Indian Oceans. Slower variations in the same meridional and vertical modes of the MOC are also shown to be well simulated by a quasi-stationary solution driven by zonal wind and pressure forces.
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KACHURIN, Nikolai, Galina STAS i Alexander KACHURIN. "DYNAMICS OF GAS EMISSION FROM EXPOSED SURFACE OF GAS-BEARING COAL SEAMS HAVING MEDIUM THICKNESS". Sustainable Development of Mountain Territories 13, nr 3 (30.09.2021): 441–48. http://dx.doi.org/10.21177/1998-4502-2021-13-3-441-448.
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The goal of the research was to clarify the regularities of the dynamics of gas release from the surface of the outcrop of the developed coal seam. The main research methods were theoretical methods of mathematical physics and non-equilibrium thermodynamics. Gas-bearing coal seams are usually mined underground. When driving development workings, outcropping surfaces of gas-bearing coal seams appear and gases in the seams under excessive pressure are released into the atmosphere of the mine workings. Gas-bearing coal seams are usually mined underground. When driving preparatory workings, surfaces of outcropping of gas-bearing coal seams arise and gases that are in the seams under excessive pressure are released into the atmosphere of the mine workings. The most important gas-dynamic characteristic of this process is the rate of gas release, which represents the volume of gases released from a unit area of exposure of a coal seam per unit of time. A generalized law of resistance for gas filtration in a rock mass is recommended, and a fairly rigorous thermodynamic substantiation is given. It is shown that the densities of gas mass flows in accordance with the postulate of their linear relationship with the driving forces are determined by the Onsager relation. The results obtained and their discussion is presented. Mathematical models are proposed for engineering calculations of the dynamics of methane release from the outcropping surface of medium-thick coal seams. The error of the adopted approximations does not exceed 3%. The intensity of methane release is directly related to the planogram of work in the working face. Analysis of this dependence indicates that during the extraction cycle, methane release increases due to an increase in the area of the gas-release surface. The main conclusions are as follows: mathematical modeling of the processes of gas movement in a porous sorbing medium using approximate mathematical models representing linearized equations of mathematical physics; the regularities of the dynamics of the rate of gas release from the surface of the outcrop of a gas-bearing coal seam is the theoretical basis for the mathematical description of the process of gas release; the use of a linearized hyperbolic filtration equation most accurately describes the processes of methane release from the outcropping surface of mined coal seams.
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Jang, Hyun M., i Nong M. Hwang. "Theory of the charged cluster formation in the low pressure synthesis of diamond: Part II. Free energy function and thermodynamic stability". Journal of Materials Research 13, nr 12 (grudzień 1998): 3536–49. http://dx.doi.org/10.1557/jmr.1998.0482.
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To account for the dominant formation of diamond over graphite in the gas-activated chemical vapor deposition (CVD) process we have theoretically examined the free energy function of a small carbon-atom cluster as a function of the cluster size. The scalar potential around a charged spherical cluster was derived using the linearized Poisson–Boltzmann equation. It was shown that the repulsive electrostatic energy associated with the growth of the charged diamond cluster was proportional to the fifth power of the cluster size. This suggests the existence of a deep potential-energy-well for the cluster size larger than the critical size corresponding to the free energy barrier for the nucleation. Thus, the growing diamond cluster will be trapped in this potential well before it transforms to the thermodynamically stable graphite. Considering all the relevant thermodynamic driving forces, we have constructed the free energy function in terms of the cluster size. The numerical computation also supports the existence of the potential-energy-well. Therefore, the present theoretical model clearly explains why the charged diamond cluster does not transform to the neutral graphite cluster when the thermodynamic stability is reversed above a certain critical size during the growth.
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Alifov, Alishir. "Mixed forced, parametric, and self-oscillations with nonideal energy source and lagging forces". Izvestiya VUZ. Applied Nonlinear Dynamics 29, nr 5 (30.09.2021): 739–50. http://dx.doi.org/10.18500/0869-6632-2021-29-5-739-750.
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The purpose of this study is to determine the effect of retarded forces in elasticity and damping on the dynamics of mixed forced, parametric, and self-oscillations in a system with limited excitation. A mechanical frictional self-oscillating system driven by a limited-power engine was used as a model. Methods. In this work, to solve the nonlinear differential equations of motion of the system under consideration, the method of direct linearization is used, which differs from the known methods of nonlinear mechanics in ease of use and very low labor and time costs. This is especially important from the point of view of calculations when designing real devices. Results. The characteristic of the friction force that causes self-oscillations, represented by a general polynomial function, is linearized using the method of direct linearization of nonlinearities. Using the same method, solutions of the differential equations of motion of the system are constructed, equations are obtained for determining the nonstationary values of the amplitude, phase of oscillations and the speed of the energy source. Stationary motions are considered, as well as their stability by means of the Routh–Hurwitz criteria. Performed calculations obtained information about the effect of delays on the dynamics of the system. Conclusion. Calculations have shown that delays shift the amplitude curves to the right and left, up and down on the amplitude–frequency plane, change their shape, and affect the stability of motion.
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VARDANYAN, A., i A. KTEYAN. "STOCHASTIC DYNAMICS OF DC AND AC DRIVEN DISLOCATION KINKS". International Journal of Modern Physics B 27, nr 04 (20.12.2012): 1250206. http://dx.doi.org/10.1142/s0217979212502062.
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Dynamics of a pinned dislocation kink controlled by the acting DC and AC forces is studied analytically. The motion of the kink, described by sine-Gordon (sG) equation, is explored within the framework of McLaughlin–Scott perturbation theory. Assuming weakness of the acting AC force, the equation of motion of the dislocation kink in the pinning potential is linearized. Based on the equations derived, we study stochastic behavior of the kink, and determine the probability of its depinning. The dependencies of the depinning probability on DC and AC forces are analyzed in detail.
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de la Cruz, H., J. C. Jimenez i J. P. Zubelli. "Locally Linearized methods for the simulation of stochastic oscillators driven by random forces". BIT Numerical Mathematics 57, nr 1 (30.05.2016): 123–51. http://dx.doi.org/10.1007/s10543-016-0620-2.
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Perig, Alexander V., Alexander N. Stadnik, Alexander I. Deriglazov i Sergey V. Podlesny. "3 DOF Spherical Pendulum Oscillations with a Uniform Slewing Pivot Center and a Small Angle Assumption". Shock and Vibration 2014 (2014): 1–32. http://dx.doi.org/10.1155/2014/203709.
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The present paper addresses the derivation of a 3 DOF mathematical model of a spherical pendulum attached to a crane boom tip for uniform slewing motion of the crane. The governing nonlinear DAE-based system for crane boom uniform slewing has been proposed, numerically solved, and experimentally verified. The proposed nonlinear and linearized models have been derived with an introduction of Cartesian coordinates. The linearized model with small angle assumption has an analytical solution. The relative and absolute payload trajectories have been derived. The amplitudes of load oscillations, which depend on computed initial conditions, have been estimated. The dependence of natural frequencies on the transport inertia forces and gravity forces has been computed. The conservative system, which contains first time derivatives of coordinates without oscillation damping, has been derived. The dynamic analogy between crane boom-driven payload swaying motion and Foucault’s pendulum motion has been grounded and outlined. For a small swaying angle, good agreement between theoretical and averaged experimental results was obtained.
Rozprawy doktorskie na temat "Linearized Driving Forces"
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Lahiri, Arka. "Theoretical and Numerical Study of Microstructure Formation in Multi-component Alloys". Thesis, 2018. https://etd.iisc.ac.in/handle/2005/4088.
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The length scale, composition, orientation of the phases in a material constitutes its microstructure. In order to appreciate the whole gamut of microstructures observed in multi-component alloys, an identification of the functional dependencies of different micro structural parameters like the length scales, phase compositions, etc., on thermodynamic (like driving forces) and kinetic (like solute diffusivities) factors is critical. In this thesis, we seek to understand such dependencies theoretically (analytically and numerically) for solidification (diffusion-controlled transformations) involving two and more phases in multi-component alloys.
We begin with a problem where a single solid phase forms from the multi-component liquid melt with a stable solidification front. We develop an analytical theory as an extension to Zener's theory for binary alloys to predict the interfacial compositions in either phase, alongside the velocity of the interface and the composition pro le in the liquid.
The solidification interface is usually susceptible to perturbations leading to the most commonly observed structures of dendrites. We attempt to understand this phenomenon by first developing a multi-component extension to the Mullins-Sekerka type linear stability analysis of the solidification front. Here, we present analytical expressions which allow us to calculate the length scales selected due to the instability as functions of solute diffusivities and driving forces. A theoretical study of the product of such an instability is presented next, where we extend the LGK theory to multi-component systems to study the steady-state growth of dendrites into a uniformly undercooled melt. Our theory is able to predict the selection of the dominant length scale in the problem, which is the dendrite tip radius, in addition to the tip-growth velocity and the compositions of the solid and the liquid phases.
For multi-phase solidification we follow a similar route and begin by developing a generalized Jackson-Hunt type analysis to predict the undercoolings, solid-phase fractions and phase compositions as functions of lamellar widths, during eutectic solidification of any number of solid phases from a multi-component melt. The instability of the eutectic solidification front leads to structures known as eutectic colonies. In this thesis, we present a study of the colony dynamics and the constituent lamellar morphologies in the presence of anisotropic solid-liquid and solid-solid interfacial energies through phase- field simulations.
Streszczenia konferencji na temat "Linearized Driving Forces"
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Irmer, Marcus, Robert Rosenthal, Alexander Nüßgen, René Degen, Karin Thomas PhD i Margot Ruschitzka PhD. "Design of a Model-Based Optimal Multivariable Control for the Individual Wheel Slip of a Two-Track Vehicle". W 23rd Stuttgart International Symposium. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2023. http://dx.doi.org/10.4271/2023-01-1219.
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<div class="section abstract"><div class="htmlview paragraph">The concept of autonomous driving has gained increasing relevance, leading to a need for the development of innovative drive concepts for motor vehicles. Therefore, this paper presents a model-based optimal multivariable control for the wheel slip, which allows specifying the wheel slip and thus the tire force individually for each wheel. The plant model consists of a multibody two-track model of a vehicle, a tire model, an air resistance model and a motor model. In addition, the contact forces of the individual wheels are calculated dynamically. The resulting nonlinear model is linearized and used for the design of a linear optimal static state space controller with reference and disturbance feedforward. The contact point velocities at the wheels are defined as the controlled variables, since they are proportional to the wheel slip and thus to the driving forces within the operating range of the controller. In addition, the rates of change of the contact point velocities are also chosen as controlled variables to set damping of the closed-loop system. The four drive torques of the wheels represent the control variables. Therefore, a true multivariable control is developed. In the first step of the analysis, the linearized closed-loop system is investigated regarding stability, robustness and its dynamic behavior. The control system shows a high bandwidth, a well damped dynamic behavior and a large phase margin. In the second step of the analysis, various simulations of realistic experiments, such as an accelerated cornering maneuver or the Fishhook road test, are performed with the nonlinear closed-loop system. The results of these experiments confirm the high robustness and good dynamic behavior of the control system in most cases. Moreover, the results demonstrate how the control considers the dynamic contact forces of the wheels to achieve the requested wheel slip at any time. Lastly, dominant transfer paths are identified based on the gain matrix of the state space controller, showing which input and state variables have significant influence on the control variables. Based on this, single-input single-output controls for the individual wheels can be derived.</div></div>
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Ishimoto, Sagiri, i Hiromu Hashimoto. "Self-Excited Vibration Model of Dragonfly’s Wing Based on the Concept of Bionic Design for Small- or Micro-Sized Actuators". W ASME 1997 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/detc97/vib-4185.
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Abstract This paper describes a self-excited vibration model of dragonfly’s wing based on the concept of bionic design, which is expected as a technological hint to solve the scale effect problems in developing the small- or micro-sized actuators. From a morphological consideration of flight muscle of dragonfly, the nonlinear equation of motion for the wing considering the air drag force due to flapping of wing is formulated. In the model, the dry friction-type and Van der Pol-type driving forces are employed to power the flight muscles and to generate the stable self-excited wing vibration. Two typical Japanese dragonflies, “Anotogaster sieboldii Selys” and “Sympetrum frequens Selys”, are selected as examples, and the self-excited vibration analyses for these dragonfly’s wings are demonstrated. The linearized solutions for the nonlinear equation of motion are compared with the nonlinear solutions, and the vibration system parameters to generate the stable limit cycle of self-excited wing vibration are determined.
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Krieg, Michael, i Kamran Mohseni. "Dynamic Control of Biologically Inspired Pulsatile Jet Propulsion Thrusters". W ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/omae2009-80019.
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Inspired by the propulsion techniques employed by squid and other cephalopod, a new type of thruster was designed which utilized pulsatile jet propulsion to generate controlling forces. The thrust production from this jet actuator was characterized in a static environment and seen to be well approximated by a simple fluid slug model. A linear transfer function model was derived to describe the transient dynamics of this thruster being employed in a virtual vehicle simulation; which was developed to test the thruster with unsteady driving signals. It was predicted that an impulsive type of thrust (as is found in our jet actuator) is ideal in a non-linear damping environment, since all of the acceleration is being added to the system while its at its lowest velocity and therefore lowest drag. Due to the extremely nonlinear nature of underwater vehicle environments we developed a scaling system to classify regimes of maneuvers and characterize their dynamics independently. Assuming a simple proportional derivative control algorithm, the vehicle closed loop frequency response was predicted using the transfer function model; which was linearized according to the maneuvering regime. Within the hybrid simulation environment, the closed loop frequency response was tested empirically and seen to be well approximated by the model.
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Toso, Alessandro, Bruno Darnis, Bill Prescott i Joris De Cuyper. "Integration of Time Waveform Replication Process in a Multibody Software for Reverse Load Identification". W ASME 2011 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/detc2011-48539.
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In the automotive industry, the need to meet the durability requirements in a very early stage of the development of a new vehicle model is becoming more and more crucial. This is a key factor that can reduce the time to market and avoids modifying substantially the design if a component fails earlier than expected. This is also a challenging task for several reasons; in the early phase the primary design suffers from a lack of knowledge about the loads that the new vehicle will experience in its life. In literature ([1][2][5][6][7]) several methods have been proposed; for instance the so-called digital test track approach ([1]) is a CAE-based tool in which the vehicle and the road are modeled in a multibody environment together with a detailed representation of the tire and the driver in order to perform a replication of a test drive. This predictive method is very valuable but still requires a lot of information about the vehicle’s components that is usually not available at this stage of the vehicle development. On the other hand a pure test-based procedure suffers from other problems such as the need of a mule vehicle and long and costly test campaigns that need to be repeated at each component’s modification. A hybrid approach has then been proposed and implemented successfully by LMS on industrial size cases. This approach known as Time Waveform Replication (TWR) ([2]) relies on a set of test data and multibody model available from test drives carried out on a predecessor or a vehicle similar to the one that is being currently designed. The data collected on a road test is used to back-calculate the equivalent spindle displacements that will cause the same forces on the multibody model that are experienced in the test sessions. This approach has several beneficial aspects with respect to the two mentioned before. The tire model does not need to be accurate since the displacement are applied directly to the spindles (but the application can be easily extended to “road profile identification” if a detailed tire model is available). Moreover it is well known that if the forces measured at the spindles are applied directly to the unconstrained multibody model, it will result in an undesired drift of the model due to a mismatch in the mass and inertial properties between the real vehicle and its model. This is even more important when measured forces are applied to a new vehicle model that is only similar to the tested one. The TWR approach relies on a linearized model of the vehicle that is derived directly from its multibody representation. Then the spindle displacements are back-calculated by pseudo-inversion of the Frequency Response Function of the system and the application of the desired target signals. This method gives a direct result only if the system is linear; this is typically not the case in the field of vehicle dynamics where the geometry of the suspension, the non-linear properties of the dampers and bushings together with the intrinsic non-linear nature of the constrained equation of motion implies that the linearized model used by TWR is valid only for small changes to the configuration at the instant of linearization. To cope with this problem, the TWR sets up an iterative process that uses the output error to update the input. In case of high non-linearities or large changes in the configuration the linearized model can be also updated. In this paper the integration of the TWR process in a multibody code such as LMS Virtual.Lab Motion is described. In particular a new tool named LMS Motion-TWR has been developed. The application guides the engineer in setting up the models inputs and outputs, allows to drive the multibody code to compute the linearized model and the association between the test data and the numerical responses of the model. The computation of the driving signals is performed by TWR core solver as a background process allowing the user to focus on the analysis of the results rather than spending time in dealing with file conversion and transfer from one software to another as was done in the past. Moreover several post-processing tools are available such as time and frequency domain plots, RMS error and X-Y plots. Finally this paper describes the application of the tool in an industrial case scenario using a model of a quad. A quad was equipped with several sensors and driven on a test track. The collected data is then used in the Motion TWR software to compute the equivalent spindle displacements. Since some of the front suspension parts are modeled as flexible bodies the reverse load identification analysis is completed by a durability calculation.
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Chen, Xi, Fengtian Han i Yunfeng Liu. "Modeling of an Electrostatic Micromotor Based on a Levitated Rotor". W 2007 First International Conference on Integration and Commercialization of Micro and Nanosystems. ASMEDC, 2007. http://dx.doi.org/10.1115/mnc2007-21078.
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This paper presents a mathematical model developed for an electrostatically levitated micromotor in which the ring-shaped rotor is levitated by electrostatic force in five degrees of freedom (DOFs). A glass/silicon/glass sandwich structure is utilized in this electrostatic micromotor, which is based on the technology of micro-electro-mechanical systems (MEMS). In the center of ring-shaped cavity formed by ICP between the top and bottom glass plates, the rotor is levitated by the five DOFs position servo system and driven by speed control system. In this paper, the mathematical model for the motion control of the rotor in five DOFs is developed. This model describes the capacitances and electrostatic forces between the rotor and associated electrodes, and moments of two rotations about the x, y-axis. The rotational torque model governing the rotor’s rotational speed is also described. In order to obtain the analytical nonlinear models for error analysis, these integral equations are expanded using the Taylor’s series. Moreover the finite element model and its simulation results are obtained by using ANSYS. In terms of comparison between the simulated results and the nonlinear models, the modeling accuracy of the micromotor can be evaluated. Furthermore, the error characteristics of the linearized models via rotor displacement are analyzed. Thus, position sensing and control of both the rotor’s motion, and the rotational speed, can be achieved based on these linearized models of electrostatically levitated micromotors.
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"A linearized theory for unsteady surface tension driven flow along supercritical vane-formed fillets". W 27th Joint Propulsion Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1991. http://dx.doi.org/10.2514/6.1991-2175.
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Taheri, Peyman, i Majid Bahrami. "Thermal Transpiration Flow in Annular Microchannels". W ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/icnmm2012-73006.
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Thermal transpiration flows of rarefied gases in annular channels are considered, where the driving force for the flow is a temperature gradient applied in the channel walls. The influence of gas rarefaction, aspect ratio of the annulus, and surface accommodation coefficient on mass and heat transfer in the process are investigated. For this, the linearized Navier–Stokes–Fourier (NSF) and regularized 13-moment (R13) equations are solved analytically, and a closed-form expression for Knudsen boundary layers is obtained. The results are compared to available solutions of the Boltzmann equation to highlight the advantages of the R13 over the NSF equations in describing rarefaction effects in this particular thermally-driven flow. Through comparisons with kinetic data it is shown that R13 equations are valid for moderate Knudsen numbers, i.e., Kn < 0.5, where NSF equations fail to describe the flow fields properly.
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Untaroiu, Alexandrina, Patrick Migliorini, Houston G. Wood, Paul E. Allaire i John A. Kocur. "Hole-Pattern Seals: A Three Dimensional CFD Approach for Computing Rotordynamic Coefficient and Leakage Characteristics". W ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11558.
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Labyrinth and other annular seals are commonly used in the turbomachinery industry to limit the leakage between different pressure regions. The pressure driven flow these seals experience can produce significant forces on the rotor. These fluid-induced excitation forces can exert a strong influence on the dynamic characteristics of the machine. Such seal forces can cause the rotor to become unstable, or when properly designed, stabilize a troublesome machine. Thus, it is important to accurately quantify the fluid-induced forces exerted on the rotor to effectively predict the dynamic behavior. Traditional annular seal models are based on bulk flow theory. While these methods are computationally efficient, due to the assumptions made to simplify the flow equations, seal bulk flow models lack accuracy when dealing with more complex geometry seals, such as hole-pattern seals. Unlike the bulk flow model, computational fluid dynamics (CFD) makes no simplifying assumption on the seal geometry, shear stress at the wall, relationship between wall shear stress and mean fluid velocity, or characterization of interfaces between control volumes. This paper presents a method to calculate the linearized rotordynamic coefficients for a hole-pattern seal by means of a three dimensional CFD approach to estimate the fluid-induced forces acting on the rotor. The system is modeled as a rigid rotor, with rotational speed, ω, and whirl frequency, Ω, describing non-synchronous whirl orbits around a static operating point. The Reynolds-averaged Navier-Stokes equations for fluid flow are solved by dividing the volume of fluid into a discrete number of points at which unknown variables (velocity, pressure, etc.) are computed. As a result, all the details of the flow field, including the fluid forces with potential destabilizing effects, are calculated. A 2nd order regression method is then utilized to express the fluid induced forces in terms of equivalent linearized stiffness, damping, and fluid inertia coefficients.
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Bartashevich, M. V., V. V. Kuznetsov i O. A. Kabov. "Mathematical Modeling of Rivulet Flow Driven by Variable Gravity and Gas Flow in a Minichannel". W ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2008. http://dx.doi.org/10.1115/icnmm2008-62135.
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Rivulet flows are a special type of thin film flows with a bounded width. The use of rivulet flows is very perspective in various types of process equipment such as evaporators. The flow dynamics in rivulets has some peculiarities, the investigation of which allows understanding the gist of possible mechanism of enhancement of heat transfer. In the present work a mathematical model for the rivulet flow in conditions of a variable gravity has been elaborated. The liquid flow takes place in a slot between two plates and is caused by a co-current gas flow. The numerical calculations of the flow parameters depending from the gravity forces have been made. The analytical formula for connection of the main rivulet parameters (width, contact angle, liquid flow rate ...) in a linearized approach has been derived. The comparison of numerical results with experimental data obtained during 44 Parabolic Flights campaign of the European Space Agency has been carried out. Liquid film of FC-72 driven by the Nitrogen gas has been studied in experiments. Force balance is changed during a parabolic flight and due to surface tension effect the liquid film in a horizontal minichannel 40 mm width became a flattened rivulet 9 mm width at microgravity.
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Ren, Huilong, Jian Zhang, Guoqing Feng, Hui Li i Chenfeng Li. "Influence of Nonlinear Mooring Stiffness on Hydrodynamic Performance of Floating Bodies". W ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/omae2009-79697.
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Coupled dynamic analysis between floating marine structures and flexible members such as mooring lines and risers, is a challenging work in the ocean engineering field. Coupled analysis on mooring-buoy interactions has been paid more and more concern for recent years. For floating offshore structures at sea, the motions driven by environmental loads are inevitable. The movement of mooring lines occurs due to the excitation on the top by floating structures. Meanwhile the lines restrict the buoy’s motion by forces acting on the fareleads. Positioning is the main function of mooring system, its orientation effects can’t be ignored for floating structures such as semi-submersible, FPS, and TLP, especially when the buoy’s equilibrium position shifting to another place. Similar as hydrostatic restoring forces, mooring force related with the buoy’s displacement can be transformed into mooring stiffness and can be added in the differential equations of motion, which is calculated at its equilibrium point. For linear hydrodynamic analysis in frequency domain, any physical quantity should be linear or be linearized, however mooring stiffness is nonlinear in essence, so the tangent or differential stiffness is used. Steel chains are widely used in catenary mooring system. An explicit formulation of catenary mooring stiffness is derived in this article, which consists of coupled relations between horizontal and vertical mooring forces. The effects of changing stiffness due to the shift of equilibrium position on the buoy’s hydrodynamic performance are investigated.
Raporty organizacyjne na temat "Linearized Driving Forces"
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An Input Linearized Powertrain Model for the Optimal Control of Hybrid Electric Vehicles. SAE International, marzec 2022. http://dx.doi.org/10.4271/2022-01-0741.
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Models of hybrid powertrains are used to establish the best combination of conventional engine power and electric motor power for the current driving situation. The model is characteristic for having two control inputs and one output constraint: the total torque should be equal to the torque requested by the driver. To eliminate the constraint, several alternative formulations are used, considering engine power or motor power or even the ratio between them as a single control input. From this input and the constraint, both power levels can be deduced. There are different popular choices for this one control input. This paper presents a novel model based on an input linearizing transformation. It is demonstrably superior to alternative model forms, in that the core dynamics of the model (battery state of energy) are linear, and the non-linearities of the model are pushed into the inputs and outputs in a Wiener/Hammerstein form. The output non-linearities can be approximated using a quadratic model, which creates a problem in the linear-quadratic framework. This facilitates the direct application of linear control approaches such as LQR control, predictive control, or Model Predictive Control (MPC). The paper demonstrates the approach using the ELectrified Vehicle library for sImulation and Optimization (ELVIO). It is an open-source MATLAB/Simulink library designed for the quick and easy simulation and optimization of different powertrain and drivetrain architectures. It follows a modelling methodology that combines backward-facing and forward-facing signal path, which means that no driver model is required. The results show that the approximated solution provides a performance that is very close to the solution of the original problem except for extreme parts of the operating range (in which case the solution tends to be driven by constraints anyway).