| 51. |
- Yarmohamadi, Hoda, 1980, et al.
(författare)
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Modeling of elastomeric engine mounts for commercial vehicles
- 2007
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Ingår i: Proceedings of the 20th Nordic Seminar on Computational Mechanics, NSCM 20, R.Larsson and K. Runesson (eds.), 23-24 November, 2007, Göteborg, Sweden. - 1652-8549.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, a model of the conventional engine mount is developed and the nonlinear behavior of dynamic stiffness and damping of the engine mounts of commercial vehicles are investigated. The model comprises elastic, viscous and friction functional components and expresses the stiffness and damping of the mount as a function of frequency and amplitude of harmonic excitation. Optimization is done to identify model parameters using measurements for real elastomeric engine mounts.
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| 52. |
- Asadi, Saeed, 1987, et al.
(författare)
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Global Sensitivity Analysis of High Speed Shaft Subsystem of a Wind Turbine Drive Train
- 2018
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Ingår i: International Journal of Rotating Machinery. - : Hindawi Limited. - 1542-3034 .- 1023-621X. ; 2018
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Tidskriftsartikel (refereegranskat)abstract
- The wind turbine dynamics are complex and critical area of study for the wind industry. Quantification of the effective factors to wind turbine performance is valuable for making improvements to both power performance and turbine health. In this paper, the global sensitivity analysis of validated mathematical model for high speed shaft drive train test rig has been developed in order to evaluate the contribution of systems input parameters to the specified objective functions.Thedrive train in this study consists of a 3- phase induction motor, flexible shafts, shafts’ coupling, bearing housing, and disk with an eccentric mass.The governing equations were derived by using the Lagrangian formalism and were solved numerically by Newmark method. The variance based global sensitivity indices are introduced to evaluate the contribution of input structural parameters correlated to the objective functions. The conclusion from the current research provides informative beneficial data in terms of design and optimization of a drive train setup and also can provide better understanding of wind turbine drive train system dynamics with respect to different structural parameters, ultimately designing more efficient drive trains. Finally, the proposed global sensitivity analysis (GSA) methodology demonstrates the detectability of faults in different components.
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| 53. |
- Berbyuk, Viktor, 1953
(författare)
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Controlled Multibody Systems with Magnetostrictive Electric Generators
- 2005
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Ingår i: Proc. The ECCOMAS Thematic Conference Multibody Dynamics 2005 on Advances in Computational Multibody Dynamics, Madrid, June 21-24, 2005, Eds. J.M. Goicolea, J. Cuardrado and J.C. Garcia Orden.. - 8474933536 ; , s. 1-14
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Konferensbidrag (refereegranskat)abstract
- The proposed paper addresses the problem of modeling and analysis of controlled multibody systems with embedded magnetostrictive transducers. Main emphasis is put on the modeling of the considered mechatronic systems for applications in the field of power harvesting from vibrations, namely vibration-to-electric energy conversion, using novel giant magnetostrictive materials. Mathematical model of the considered mechatronic system has been developed. It comprises the constitutive equations of magnetoelastic behavior of magnetostrictive rod (active element of transducers), standard formulae of electromagnetism for induced voltage and current in the pick-up coil due to variation of magnetic field intensity, and finally the equations of motion of multibody system itself. The last one can be derived using one of the well-known multibody dynamics formalism. Assuming that massinertia parameters of magnetostrictive transducers are negligible small the inverse dynamics based algorithm has been proposed for modeling the controlled motion of multibody systems with embedded transducers. This algorithm is also suitable to evaluate electrical power output of magnetostrictive electric generators for different controlled motions of the system and to optimize the generators design. The inverse dynamics based algorithm was implemented in Matlab/Simulink with user friendly interface. Its efficiency has been confirmed by simulation of performance of different magnetostrictive electric generators under the periodic excitations exerted by the hosting multibody system.
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| 54. |
- Berbyuk, Viktor, 1953
(författare)
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Inverse dynamics and Fourier-based approach to solve optimal control problems for multi-link mechanisms
- 1997
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Ingår i: The NATO Advanced Study Institute on Computational Methods in Mechanisms. ; 2, s. 431-440
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Konferensbidrag (refereegranskat)abstract
- This paper is concerned with the investigation of multi-link mechanism controlled motion between fixed boundary conditions and given constraints on the phase coordinates. The moduli of the controlling moments at the hinges between the links are bounded. A computational method to the mathematical modeling of the optimal control laws which govern multi-link mechanism reaching motion is presented. This method is based on Fourier and spline approximations of the independently variable functions and inverse-dynamics approach. The method proposed makes it possible to satisfy the boundary conditions and some constraints on the phase coordinates automatically and accurately. The efficiency of the proposed method is illustrated by the solution of the energy-optimal control problem of a plane mobile three-link manipulator with a load on the grip.
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| 55. |
- Cheung, Hon Lam, et al.
(författare)
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A multi-fidelity data-driven model for highly accurate and computationally efficient modeling of short fiber composites
- 2024
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Ingår i: Composites Science and Technology. - 0266-3538. ; 246
-
Tidskriftsartikel (refereegranskat)abstract
- To develop physics-based models and establish a structure–property relationship for short fiber composites, there are a wide range of micro-structural properties to be considered. To achieve a high accuracy, high-fidelity full-field simulations are required. These simulations are computationally very expensive, and any single analysis could potentially take days to finish. A solution for this issue is to develop surrogate models using artificial neural networks. However, generating a high-fidelity data set requires a huge amount of time. To solve this problem, we used transfer learning technique, a limited amount of high-fidelity full-field simulations, together with a previously developed recurrent neural network model trained on low-fidelity mean-field data. The new RNN model has a very high accuracy (in comparison with full-field simulations) and is remarkably efficient. This model can be used not only for highly efficient modeling purposes, but also for designing new short fiber composites.
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| 56. |
- Okhovat, Reza, 1984
(författare)
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Dynamic Equations foe Spherical and Cylindrical Shells Using Power Series Method
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Shells are commonly used in many branches of engineeringand have therefore beeninvestigated for a number of different types of shells.A shell can be considered as a curved plate having small thickness compared to the other geometrical dimensions as well as to the wavelengths of importance. The most important superiority of shells in comparison to plates is that shell structures can provide high strength and low weight because of their membrane stiffness.Spherical and cylindrical shells appear in manyapplicationsand some dynamic shell theories have thus been developed for these cases.All these theories seem to depend on more or less ad hoc kinematical assumptions and/orother approximations.In this thesis, dynamic equations for an isotropic spherical and an anisotropic cylindrical shell are derived by using a method developed during the last decade for bars, plates, and beams.The main advantage with the method is that it is very systematic and can be developed to any order. It also seems that the resulting structural equations are asymptotically correct to any order.First, dynamic equations are derived for a spherical shell made of a homogeneous, isotropic material.The starting point is a power series expansion of the displacement components in the thickness coordinate relative to the mid-surface of the shell. By using these expansions, the three-dimensional elastodynamic equations yield a set of recursion relations among the expansion functions.Applying the boundary conditions on the surfaces of the spherical shell and eliminating all but the six lowest order expansion functions give the shell equations as a power series in the shell thickness.In principle, the equations can be truncated to any order in the shell thickness, leading to very complicated expressions. Surface differential operators are introduced to decrease the length of the shell equations and tackle this complexity.the displacement field is split into a scalar (radial) part and a vector (tangential) part, and the shell equations are given in terms of the surface operators. After some manipulations, the final four shell equations are obtained in a more compact form which can be presented explicitly.Dynamic equations for an anisotropic cylindrical shell are also derived using the same technique. As a special case a 2D circular ring is considered and the eigenfrequencies are computed and are compared with the exact solution which is obtained by expressing the displacements in terms of Bessel and Neumann functions. Graphite epoxy is considered as an anisotropic material.For all cases, results are compared to exact three-dimensional theory. The computations for eigenfrequencies from the power series approximation are in good correspondence with results from the exact solution.
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| 57. |
- Bayani, Mohsen, 1981, et al.
(författare)
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Squeak and rattle prevention by geometric variation management using a two-stage evolutionary optimisation approach
- 2020
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Ingår i: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE).
-
Konferensbidrag (refereegranskat)abstract
- Squeak and rattle are annoying sounds that often are regarded as the indicators for defects and quality issues by the automotive customers. Among the major causes for the generation of squeak and rattle sounds, geometric variation or tolerance stack-up is a key contributor. In the assembly process, the dimensional variation in critical interfaces for generating squeak and rattle events can be magnified due to tolerance stackup. One provision to manage the tolerance stack-up in these critical interfaces is to optimise the location of connectors between parts in an assembly. Hence, the focus of this work is to prevent squeak and rattle by introducing a geometric variation management approach to be used in the design phase in the automotive industry. The objective is to identify connection configurations that result in minimum variation and deviation in selected measure points from the critical interfaces for squeak and rattle. In this study, a two-stage evolutionary optimisation scheme, based on the genetic algorithm employing the elitism pool, is introduced to fine-tune the connectors’ configuration in an assembly. The objective function was defined as the variation and the deviation in the normal direction and the squeak plane. In the first stage, the location of one-dimensional connectors was found by minimising the objective function in the rattle direction. In the second stage, the best combination of some of the connectors from the first stage was found to define planar fasteners to optimise the objective function both in the rattle direction and the squeak plane. It was shown that by using the proposed two-stage optimisation scheme, the variation and deviation results in critical interfaces for squeak and rattle improved compared to the baseline results.
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| 58. |
- Heshmati, Mohsen, 1987, et al.
(författare)
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Dependency of cohesive laws of a structural adhesive in Mode-I and Mode-II loading on moisture, freeze-thaw cycling, and their synergy
- 2017
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Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 122, s. 433-447
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, adhesive bonding has found its way to construction applications such as bridges. Given the harsh conditions that such structures are usually exposed to, it is necessary to account for environmental factors, particularly moisture and temperature, in the design phase. Cohesive zone modelling has attracted much attention in the last decade as a promising method to design adhesive joints. Despite this interest, the effects of moisture and thermal cycles on cohesive laws have not been investigated to the knowledge of the authors. In this paper, we present a method to directly measure the environmental-dependent cohesive laws of a structural adhesive loaded in pure Mode-I and Mode-II. Special consideration is given to overcome issues such as the time-consuming nature of moisture ingression and specimen dimensions, which could be problematic due to the size-limitations of conditioning equipment. The accuracy of this method was verified through simulation of the experiments using the finite element analysis. The effects of exposure to 95% relative humidity, immersion in saltwater and distilled water, and freeze-thaw cycles in the presence or absence of moisture were investigated. The results indicate the damaging effects of combined saltwater and freeze-thaw cycles which were clearly reflected on the shape of the cohesive laws.
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| 59. |
- Chernoray, Valery, 1975
(författare)
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Prediction of Laminar-Turbulent Transition on an Airfoil at High Level of Free-Stream Turbulence
- 2015
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Ingår i: Progress in Flight Physics Vol. 7. - 9785945881655 ; , s. 704-
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Prediction of laminar-turbulent transition at high level of free-stream turbulence in boundary layers of airfoil geometries with external pressure gradient changeover is in focus. The aim is a validation of a transition model for transition prediction in turbomachinery applications. Numerical simulations have been performed by using a transition model by Langtry and Menter for a number of different cases of pressure gradient, at Reynolds number-range, based on the airfoil chord, 50 000 ≤ Re ≤ 500 000 and free-stream turbulence intensities 2 % and 4 %. The validation of the computational results against the experimental data showed good performance of used turbulence model for all test cases.
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| 60. |
- Chernoray, Valery, 1975
(författare)
-
Prediction of Laminar-Turbulent Transition on an Airfoil at High Level of Free-Stream Turbulence
- 2013
-
Ingår i: Proc of EUCASS Conf..
-
Konferensbidrag (refereegranskat)abstract
- Prediction of laminar-turbulent transition at high level of free-stream turbulence in boundary layers of airfoil geometries with external pressure gradient changeover is in focus. The aim is a validation of a transition model for transition prediction in turbomachinery applications. Numerical simulations have been performed by using a transition model by Langtry and Menter for a number of different cases of pressure gradient, at Reynolds number-range, based on the airfoil chord, 50 000 ≤ Re ≤ 500 000 and free-stream turbulence intensities 2 % and 4 %. The validation of the computational results against the experimental data showed good performance of used turbulence model for all test cases.
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