a b s t r a c tA high fidelity approach for wind turbine aero-elastic simulations including explicit representation of the atmospheric wind turbulence is presented. The approach uses a dynamic overset computational fluid dynamics (CFD) code for the aerodynamics coupled with a multi-body dynamics (MBD) code for the motion responses to the aerodynamic loads. Mann's wind turbulence model was implemented into the CFD code as boundary and initial conditions. The wind turbulence model was validated by comparing the theoretical one-point spectrum for the three components of the velocity fluctuations, and by comparing the expected statistics from the CFD simulated wind turbulent field with the explicit wind turbulence inlet boundary from Mann model. Extensive simulations based on the proposed coupled approach were conducted with the conceptual NREL 5-MW offshore wind turbine in an increasing level of complexity, analyzing the turbine behavior as elasticity, wind shear and atmospheric wind turbulence are added to the simulations. Results are compared with the publicly available simulations results from OC3 participants, showing good agreement for the aerodynamic loads and blade tip deflections in time and frequency domains. Wind turbulence/turbine interaction was examined for the wake flow. It was found that explicit turbulence addition results in considerably increased wake diffusion. The coupled CFD/MBD approach can be extended to include multibody models of the shaft, bearings, gearbox and generator, resulting in a promising tool for wind turbine design under complex operational environments.
A high-fidelity simulation framework is presented to investigate wind turbine aero-servo-elastic behavior, coupling dynamic overset computational fluid dynamics (CFD) and multibody dynamics (MBD) approaches. The Gearbox Reliability Collaborative (GRC) project gearbox was up-scaled in size and installed in the NREL 5-MW offshore wind turbine to demonstrate drivetrain dynamics. Generator torque and blade pitch controllers were implemented to simulate operational conditions of commercial wind turbines. Interactions between wind turbulence, rotor aerodynamics, elastic blades, drivetrain dynamics at the gear-level and servo-control dynamics were studied. Results show that gear contact causes dynamic transmission error within the drivetrain, and results in a decreased turbine thrust and rotational speed. The generator torque controller optimizes efficiency below rated wind speed, while the blade pitch controller properly regulates the turbine near rated power and generator speed at higher than rated wind speed under both uniform and turbulent winds. The pitch controller effectively reduces turbine thrust, blade tip deflections, and velocity deficit of the wake, benefiting both standalone turbines and wind farms. The tool and methodology developed show promise to study complex aerodynamic/mechanic systems, being the first time a complete wind turbine simulation includes CFD of the rotor/tower aerodynamics, wind turbulence, elastic blades, gearbox dynamics and feedback control.
The solution of the constrained multibody system equations of motion using the generalized coordinate partitioning method requires the identification of the dependent and independent coordinates. Using this approach, only the independent accelerations are integrated forward in time in order to determine the independent coordinates and velocities. Dependent coordinates are determined by solving the nonlinear constraint equations at the position level. If the constraint equations are highly nonlinear, numerical difficulties can be encountered or more Newton-Raphson iterations may be required in order to achieve convergence for the dependent variables. In this paper, a velocity transformation method is proposed for railroad vehicle systems in order to deal with the nonlinearity of the constraint equations when the vehicles negotiate curved tracks. In this formulation, two different sets of coordinates are simultaneously used. The first set is the absolute Cartesian coordinates which are widely used in general multibody system computer formulations. These coordinates lead to a simple form of the equations of motion which has a sparse matrix structure. The second set is the trajectory coordinates which are widely used in specialized railroad vehicle system formulations. The trajectory coordinates can be used T. Sinokrot · M. Nakhaeinejad · A. A. Shabana ( ) to obtain simple formulations of the specified motion trajectory constraint equations in the case of railroad vehicle systems. While the equations of motion are formulated in terms of the absolute Cartesian coordinates, the trajectory accelerations are the ones which are integrated forward in time. The problems associated with the higher degree of differentiability required when the trajectory coordinates are used are discussed. Numerical examples are presented in order to examine the performance of the hybrid coordinate formulation proposed in this paper in the analysis of multibody railroad vehicle systems.
Human performance measures such as discomfort and joint displacement play an important role in product design. The virtual human Santos, a new generation of virtual humans developed at the University of Iowa, goes directly to the computer-aided design model to evaluate a design, saving time and money. This paper presents an optimization-based workspace zone differentiation and visualization. Around the workspace of virtual humans, a volume is discretized to small zones and the posture prediction on each central point of the zone will determine whether the points are outside the workspace as well as the values of different objective functions. Visualization of zone differentiation is accomplished by showing different colours based on values of human performance measures on points that are located inside the workspace. The proposed method can subsequently help ergonomic design. For example, in a vehicle's interior, the controls should not only lie inside the workspace, but also in the zone that encloses the most comfortable points. Using the palette of colours inside the workspace as a visual guide, a designer can obtain a reading of the discomfort level of product users.
Dynamic simulation techniques that are based on Multibody system approaches have become an important topic in studying the performance of various mechanical components that comprise an automotive system. One of the challenging issues in such studies is the ability to properly account for the flexibility of certain parts in the system. One example where this is important is the design of twist beam axles in car suspension systems where twisting deformations are present. These deformations are geometrically nonlinear and require a special handling. In this paper two multibody system approaches that are commonly used in overcoming such problem are examined. The first method is a sub-structuring technique that is based on the popular method of component mode synthesis. This method is based on dividing the flexible component into sub-structures, in which, the linear elastic structural theory is sufficient to describe the deformation of each sub-structure. Using this method the deformation of the beam is described using the mode shapes of vibration of each sub-structure. The equations of motion, in this case, are written in terms of the system’s generalized coordinates and modal participation factors. In the second method a Multibody System (MBS) solver and an external nonlinear Finite Element Analysis (FEA) solver are coupled together in a co-simulation manner. The nonlinear FEA solver, in this case, is used in modeling the deformation of the twist beam. The forces due to the nonlinear deformations of the flexible beam are communicated to the MBS solver at certain attachment points where the flexible body is attached to the rest of the multibody system. The displacements and velocities of these attachment points are calculated by the MBS solver and are communicated back to the nonlinear FEA solver to advance the simulation. The two methods described above will be reviewed in this paper and an example of a twist beam axle in a car suspension system model will be examined twice, once using the sub-structuring method, and once using the co-simulation method. The numerical results obtained using both methods will be analyzed and compared.
The current trend in railroad industry is the development of reliable non-linear computational dynamic algorithms that can be used in the simulations of vehicle behaviour under different operating conditions. Of similar importance, is the development of experimental models that can be used in the validation of the proposed numerical algorithms. The objective of this investigation is to examine the accuracy of the results obtained using different multi-body contact formulations by comparing these results with experimental results. The numerical results are obtained using two different multi-body contact formulations: the embedded constraint contact formulation and the quasi-elastic contact formulation; both are implemented in general purpose multi-body computer programs. The numerical results obtained using these two different methods are analysed and compared. These results are also compared with the test results of a bogie prototype that can be used with a roller rig built at Turin Polytechnic. The roller rig, which is designed to be used with full scale or reduced scale models, provides an efficient and economic way to validate the results of the computer algorithms. This roller rig, which can also be used to perform tests on bogies with different rail gauge and wheel base, has been designed using Jaschinski's scaling method. A bogie computer model based on the same dimensions and material properties of the Turin roller rig was developed using two different general purpose multi-body computer programs that employ the two different non-linear wheel/rail contact formulations and two different numerical algorithms for the automatic generation and solution of the system equations of motion. The results of the two different multi-body formulations used in this study show a good agreement. Furthermore, the results show that the bogie critical speed predicted using the computer simulations is very close to the one obtained using the roller rig.two decades with the aim of providing realistic and accurate measures for the analysis of rail road vehicle systems. One of the many challenges in railroad dynamic simulations is the ability of such new algorithms and codes in correctly evaluating the stability, curving behaviour, and passenger comfort of the railway vehicles. In general, the main differences between different dynamic simulation codes lie in the formulation of the dynamic equations of motion, the definition of the kinematic constraints, and the numerical procedures used in such codes to solve the non-linear dynamic equations. It is necessary, however, to validate the results of the new algorithms using experimental models. One effective, efficient, JMBD107
The objective of this study is to examine the geometric description of the spiral sections of railway track systems, in order to correctly define the relationship between the geometry of the right and left rails. The geometry of the space curves that define the rails are expressed in terms of the geometry of the space curve that defines the track center curve. Industry inputs such as the horizontal curvature, grade, and superelevation are used to define the track centerline space curve in terms of Euler angles. The analysis presented in this study shows that, in the general case of a spiral, the profile frames of the right and left rails that have zero yaw angles with respect to the track frame have different orientations. As a consequence, the longitudinal tangential creep forces acting on the right and left wheels, in the case of zero yaw angle, are not in the same direction. Nonetheless, the orientation difference between the profile frames of the right and left rails can be defined in terms of a single pitch angle. In the case of small bank angle that defines the superelevation of the track, one can show that this angle directly contributes to the track elevation. The results obtained in this study also show that the right and left rail longitudinal tangents can be parallel only in the case of a constant horizontal curvature. Since the spiral is used to connect track segments with different curvatures, the horizontal curvature cannot be assumed constant, and as a consequence, the right and left rail longitudinal tangents cannot be considered parallel in the spiral region. Numerical examples that demonstrate the effect of the errors that result from the assumption that the right and left rails in the spiral sections have the same geometry are presented. The numerical results obtained show that these errors can have a significant effect on the quality of the predicted creep contact forces.
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