249 research outputs found
Effects of Tryptophan on the Polymorphic Transformation of Calcium Carbonate: Central Composite Design, Characterization, Kinetics, and Thermodynamics
No full textThe objectives of this study were to: (i) determine the effects of tryptophan on the polymorphic phase transformation of CaCO3, (ii) investigate the thermal degradation characteristics of CaCO3 in terms of kinetics and thermodynamics using the Coats-Redfern method, and (iii) assess the influence of the experimental conditions on the vaterite composition of CaCO3 using response surface methodology based on central composite design. First, the CaCO3 crystals were prepared and analyzed using XRD, FTIR, SEM, BET, AFM, and zeta potential analysis. Based on the characterization results, the shape of the CaCO3 crystals changed from smooth cubic calcite crystals to porous irregular spherical-like vaterite crystals with increasing tryptophan concentration. Meanwhile, the kinetic results showed that the thermal degradation of CaCO3 followed the shrinkage geometrical spherical mechanism, R-3 and the average activation energy was 224.6 kJ/mol. According to the results of the experimental design, the tryptophan concentration was the most influential variable affecting the relative fraction of vaterite in the produced crystals. It can be concluded that tryptophan is important for better understanding and controlling the polymorph, size, and morphology of CaCO3 crystals
Simplified transfer function approach for modeling frequency dependency of damping characteristics of rubber bushings
No full textPhysical systems that consist of parts and vibration isolators such as rubber bushings are usually modeled in multibody simulations, where parts are represented as rigid bodies with their mass and inertia properties and rubber bushings are modeled with Voigt models to represent their stiffness and damping characteristics. Employment of Voigt models in multi-degree-of-freedom systems, however, may result in lower accuracy due to limitations in representing frequency-dependent dynamic characteristics of vibration isolators. To overcome this challenge, in this study, we develop and present a simplified frequency-dependent transfer function model by generating their frequency-dependent complex stiffness and damping from vehicle-level measurements. The damping characteristics of rubber bushings as a function of frequency is represented by a second-order transfer function. Three parameters of the transfer function are determined by solving an optimization problem to minimize the integral of absolute error between the measurement and simplified model's predictions. Sequential Quadratic Programming, a gradient descent-based algorithm, is selected as the optimization algorithm for this purpose. The proposed methodology is demonstrated on a heavy commercial truck. Truck cabin is represented as a rigid body connected to four rubber bushings, which are modeled to show the frequency dependency of the damping as a simple transfer function. Simulation results are well correlated with the measurements obtained from prototype vehicle tests on various road profiles showing capability improvement over Voigt modeling approach due to a more representative damping characteristic of rubber bushings as a function of frequency. Integration of the proposed method into multibody simulation software is also demonstrated with cosimulation between MSC.ADAMS and MATLAB software
A methodology to design multi-axis test rigs for vibration and durability testing using frequency response functions
No full textDue to copyright restrictions, the access to the full text of this article is only available via subscription.The multi-axis simulators are designed for experimental verification of the safe functioning of large components and subsystems under real world customer usage in vibration and durability testing. Transformation of the full vehicle conditions to mast rig testing with correct system dynamics and vibration characteristics and boundary conditions is a key challenge in the development of the experimental set-up. In this paper, a systematic methodology is formalized how to design the experimental set-up on MAST rig to replicate the vehicle dynamics and vibration characteristics in vehicle conditions. System modes and frequency response functions are chosen as key performance metrics to compare the dynamics of the system to be tested for both full vehicle and rig design. Criteria on the metrics are defined to make decision if the test rig design is sufficiently replicating the in-vehicle conditions. The methodology is illustrated on a side skirt attached to a heavy duty truck chassis that demonstrates the application of the methodology in practice
An efficient design methodology for graded surface-based lattice structures using free-size optimization and enhanced mapping method
No full textIn this paper, a novel Free-size Optimization based Graded Lattice Generation (FOGLG) method, that generates the functionally graded lattice (FGL) structures using free-size optimization, is proposed. In addition, the reconstruction method suitable for the construction of 3D FGL structures using Additive Manufacturing (AM) is presented. The proposed method employs the thickness information of each shell element obtained from a free-size optimization algorithm to determine the relative element densities, which collectively represent the set of design parameters. An additive manufacturing compatible mapping method of generating FGLs from 2D free-size optimization results is also proposed. The efficiency of the FOGLG was compared to the existing homogenization-based optimization (HMTO) and size optimization algorithms. The objective function of the three optimization strategies targets to minimize the total acceleration spectrum in the frequency range of interest. The effectiveness and validity of this new design method was also demonstrated from laser vibrometer measurements. The results show that the FOGLG reduces the overall acceleration spectrum by 3.6% and 19.4% compared to the HMTO and size optimization algorithms, respectively. High correlation between the numerical and experimental results validates the effectiveness of the proposed algorithm
Metaporous acoustic metamaterials with Helmholtz resonators for enhanced NVH performance in battery electric vehicles
No full textMetamaterials have gained an increasing attention as a way of absorbing noise to achieve improved acoustic performance on vehicles, and thanks to their novel functionalities compared to traditional designs, these structures are employed by many automotive companies as noise-reduction solutions for engineering applications. One of the key challenges for automotive original equipment manufacturers (OEMs) in the noise, vibration, and harshness (NVH) development process is absorption performance in the frequency range of 400 Hz-800 Hz. Although sound engineers use porous polyurethane in these frequency ranges, the absorption performance of these designs is limited to meet increasing customer expectations. Managing airborne noise in vehicles is particularly challenging in the low frequency spectrum, where Helmholtz resonators are widely used. The main purpose of this study is to develop a metaporous sound barrier incorporating a Helmholtz resonator, effective in the low to mid-frequency range of the spectrum. For this purpose, a frequency domain simulation was carried out to obtain the absorption coefficient, analyze frequency-dependent effects, and identify critical frequencies in vehicle acoustics. Furthermore, local resonance effects to prevent acoustic waves were investigated and design parameters of metastructure were analyzed using a multi-physics based simulation model. These results were validated experimentally using an acoustic impedance tube. The methodology is demonstrated in a battery electric vehicle (BEV) to improve airborne compressor noise during engine idling. The optimum design parameters were determined using the Taguchi design method. Finally, the performance of developed metaporous material was validated through vehicle-level tests, with results showing an improvement of 3 dB(A)
Enhancing cervical spine health: A vibration-focused multibody dynamics model for neck support system design
No full textNeck injuries can range from mild discomfort to severe disability. Despite the abundance of biomechanical models of the cervical spine in the literature, their capabilities for modal and frequency response analysis are limited. A comprehensive head-cervical spine model was developed to address this gap, enabling frequency domain analysis. A multi-body dynamics (MBD) model with 20 degrees-of-freedom (DoFs) was created using ADAMS software's frequency response analysis capabilities. This model incorporates elements, including vertebrae, ligaments, and muscles. The validation was performed using OpenSim and existing experimental findings. The model was then employed to conduct a Design of Experiments (DoE) study, where key design factors of a conceptual neck support system were varied. Two vibration objective functions were selected to evaluate the parametric designs. The first function identifies the maximum value of the head's acceleration, while the second measures overall vibration within the frequency range of interest. In a case study, the model's capabilities were demonstrated, identifying key design parameters for the neck support system. The methodology has the potential to make significant contributions across multiple industries. Applications range from designing anti-vibration devices to reduce fatigue in the automotive and aerospace sectors to enhancing rehabilitation systems in healthcare, ultimately improving patient exercise effectiveness.TÜBİTA
Design and kinematics of 4- DoF multi-purpose wearable mechanical arm (MUWA) support for enhanced operation stability
No full textA low-cost motor-less simple wearable mechanical arm support unit is presented as a viable alternative to todays assistive exoskeleton support units. By limiting the functionality of the device to stabilization rather than actuation, the cost could significantly be reduced while still maintaining a wide range of applications. The basic idea is to let the device follow the wearers actions freely without obscuring the motion in normal mode, while fixating the arm at the desired angle and location when the user expect to receive support; namely in lock mode. The lock-unlock mechanism is simple Bluetooth activated palm gesture of the non-operating arm while the support unit Bluetooth receiver stabilizes the arm at any desired angle or position in response to sensed gesture command. The lock-unlock mechanism is achieved by solely two solenoids, one at each of the joints; shoulder and elbow, with 3 Degree of Freedom (DoF) and 1 DoF respectively, leaving the wrist free to perform the desired hand operation and increasing the precision of the locking mechanism
Impact of orifice location on the mechanical response of side and central orifice synthetic jets
No full textSynthetic jets have been at the focus of a number applications including flow control and thermal management of microelectronics due to their unique characteristics of transferring linear momentum through a flow structure without causing a change in net mass flux. Even though there has been extensive research on central orifice synthetic jets in recent years, side slotted synthetic jets have not yet been fully explored in terms of their mechanical and heat transfer properties. The objective of this paper is to gain more insight on the mechanical properties of the side slotted synthetic jets and to compare them with previously published data on central orifice jets. Three different types of rectangular orifice synthetic jets with 10°, 30° and 60° orifice have been designed and manufactured. The orifices represent the measure of the angular portion occupied by the orifice. Analytical and numerical analyses of those synthetic jets have been performed in terms of the modal characteristics of the diagram and the fluid cavity. Results have been compared with the actuator deflection tests using a laser Vibrometer. It was found out that side slotted synthetic jets lead to a higher actuator deflection and consequently may lead to higher heat transfer enhancement than central orifice jets. Results also demonstrate that 60° orifice has the highest actuator deflection, while 10° orifice results in the smallest actuator deflection and lower heat transfer due to high internal resistance in the cavity
Physical system modeling: Algorithms for assessing model quality based on design specifications.
No full textPhysical system models, with physically meaningful states and parameters, have become increasingly important, parts of the design, control and even procurement processes. However, while algorithms have been developed to help formulate and integrate physical system models, and while algorithms have been developed to generate minimum complexity physical system models subject to a modeling metric constraints, missing from the literature are the algorithms to assess the quality of dynamic system models. The objective of this research is to develop a methodology to quantify the accuracy of the predicted system variables and to determine the validity of a model of given complexity with respect to a set of criteria derived from engineering design specifications or measurement noise. Another objective of this thesis to integrate the methodology with an activity based MORA (Louca et al., 1998) to quantify the accuracy of the different models as a function of activity model complexity. A&barbelow;ccuracy & V&barbelow;alidation A&barbelow;lgorithm for Simulation (AVASIM), proposed in this dissertation, is a time-domain perspective comparing the model's time based output trajectories to targets at user-defined points. In addition, the model accuracy over the total simulation horizon is also used. The tolerances on specific time point and overall response are determined by the user's domain knowledge (design specifications) or the measurement noise associated with empirical validation studies. The performance of the models is formulated as a performance index that is determined from measures such as relative error, residuals sum, etc. to quantify the accuracy with respect to target points and overall response. The validity of model is then determined by comparing the performance indices to that of a threshold model derived from the design specifications or measurement noise on a data set. To illustrate the AVASIM, case studies based on automotive applications are presented. Results from the case studies show that accuracy and validity of the reduced models can be systematically assessed using the proposed AVASIM. Integration of AVASIM with MORA seems to be a very powerful design tool to generate the proper design model with desired accuracy.PhDApplied SciencesMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130522/2/3042166.pd
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