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Ahmed M.,Assiut University | Eslamian M.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Applied Thermal Engineering | Year: 2015

The multi-phase Lattice Boltzmann Method (LBM) is used to explore some unprecedented aspects of laminar forced convection in a bottom heated rectangular microchannel. Important physical parameters, such as forces exerted on fluid parcels as well as on the dispersed nanoparticle phase are studied, in an attempt to elucidate the mechanism that results in establishment of a relative velocity between nanoparticles and the continuous fluid phase (slip velocity). The significance of the external forces, such as the gravitational, thermophoresis and Brownian forces is investigated. A recently established expression for the estimation of thermophoresis force in nanofluids is employed to study the true effect of thermophoresis, as other studies either neglect this effect, or are parametric or employ expressions that overestimate this effect. The results indicate that in laminar forced convection, the Brownian force has a significant effect on flow and heat transfer characteristics for low Re number flows (Re∼1-10), but thermophoresis may be safely neglected for all flow conditions. At low Re number flows, the nanofluid flow is heterogeneous, and heat transfer characteristics of nanofluid compared to the base fluid, such as Nu and convection heat transfer coefficient, significantly increase, while at higher Re numbers, such as Re = 100, flow behaves homogeneously and therefore the application of a nanofluid may not be justified. © 2015 Elsevier Ltd. All rights reserved.

Parker R.G.,The University of Michigan - Shanghai Jiao Tong University Joint Institute | Wu X.,Ohio State University
Journal of Vibration and Acoustics, Transactions of the ASME | Year: 2012

The parametric instability of planetary gears having elastic continuum ring gears is analytically investigated based on a hybrid continuous-discrete model. Mesh stiffness variations of the sun-planet and ring-planet meshes caused by the changing number of teeth in contact are the source of parametric instability. The natural frequencies of the time invariant system are either distinct or degenerate with multiplicity two, which indicates three types of combination instabilities: distinct-distinct, distinct-degenerate, and degenerate-degenerate instabilities. By using the structured modal properties of planetary gears and the method of multiple scales, the instability boundaries are obtained as simple expressions in terms of mesh parameters. Instability existence rules for in-phase and sequentially phased planet meshes are also discovered. For in-phase planet meshes, instability existence depends only on the type of gear mesh deformation. For sequentially phased planet meshes, the number of teeth on the sun (or the ring) and the type of gear mesh deformation govern the instability existence. The instability boundaries are validated numerically. © 2012 American Society of Mechanical Engineers.

Qi H.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Cailiao Gongcheng/Journal of Materials Engineering | Year: 2012

Since its invention and initial application in gas turbine components in the early 60's of 20th century at INCO Huntington Alloys (now called Special Metals Co.), INCONEL 718 alloy (IN718) has become the most widely used nickel based superalloy in the aircraft engine industry. It was used in many critical aircraft engine components, accounting for over 30% of the total finished component mass of a modern aircraft engine. This article reviews IN718 alloy development history, its mechanical properties, long-term thermal stabilities, industrial processing methods, and current developing substitute alloys for enhanced thermal stability.

Muller A.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2014

This paper addresses the sensitivity of dexterity measures w.r.t. The posture of a manipulator, with given design parameters, as well as w.r.t. The manipulator's geometric parameters. These are required for placing a manipulator so to maximize dexterity and for the optimal layout of the link geometry, respectively. Explicit expressions are derived for first and second partial derivatives of dexterity measures w.r.t. to joint angles and w.r.t. geometric link parameters. The latter is obtained using a virtual joint method extending the product of exponentials formula for the forward kinematics. The approach applies to serial and parallel manipulators. © 2014 IEEE.

Bauchau O.A.,The University of Michigan - Shanghai Jiao Tong University Joint Institute | Han S.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Journal of Computational and Nonlinear Dynamics | Year: 2014

In multibody systems, it is common practice to approximate flexible components as beams or shells. More often than not, classical beam theories, such as the Euler-Bernoulli beam theory, form the basis of the analytical development for beam dynamics. The advantage of this approach is that it leads to simple kinematic representations of the problem: the beam's section is assumed to remain plane and its displacement field is fully defined by three displacement and three rotation components. While such an approach is capable of accurately capturing the kinetic energy of the system, it cannot adequately represent the strain energy. For instance, it is well known from Saint-Venant's theory for torsion that the cross-section will warp under torque, leading to a three-dimensional deformation state that generates a complex stress state. To overcome this problem, sectional stiffnesses are computed based on sophisticated mechanics of material theories that evaluate the complete state of deformation. These sectional stiffnesses are then used within the framework of a Euler-Bernoulli beam theory based on far simpler kinematic assumptions. While this approach works well for simple cross-sections made of homogeneous material, inaccurate predictions may result for realistic configurations, such as thin-walled sections, or sections comprising anisotropic materials. This paper presents a different approach to the problem. Based on a finite element discretization of the cross-section, an exact solution of the theory of three-dimensional elasticity is developed. The only approximation is that inherent to the finite element discretization. The proposed approach is based on the Hamiltonian formalism and leads to an expansion of the solution in terms of extremity and central solutions, as expected from Saint-Venant's principle. Copyright © 2014 by ASME.

Dugnani R.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Key Engineering Materials | Year: 2013

Piezoelectric materials such as lead-zirconate-titanate (PZT), lead-metaniobate, and piezo-composites are the materials of choice for acoustic imaging in medical diagnosis as well as underwater ultrasonic microphones and underwater sonar. PZT materials have the advantage of having high electro-mechanical coupling, low internal losses and excellent environmental durability. Nonetheless, in order to improve energy transmission the high acoustic impedance of piezoelectric ceramics needs to be matched to the lower acoustic impedance of biological tissues and water. For actuators resonated in their thickness mode, energy transmission can be improved by means of intermediate layers of material of carefully selected thicknesses and acoustic properties. Sometimes a backing layer is also added to the back of the actuator to damp the acoustic backwave. The process of making these types of transducers is generally costly due to the nature of the manufacturing process and the required level of accuracy. This paper describes an inexpensive method of manufacture low-cost, low-impedance, piezoelectric transducers. The fundamental physical principles behind this new type of sensor-actuator, as well as various examples of imaging low-impedance targets using a prototype of this newly developed sensor-actuator system will be presented. © (2013) Trans Tech Publications, Switzerland.

Liu Z.,The University of Michigan - Shanghai Jiao Tong University Joint Institute | Qi H.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2014

A turbine blade made of single-crystal superalloys has been commonly used in gas turbine and aero engines. As an effective repair technology, laser powder deposition has been implemented to restore the worn turbine blade tips with a near-net shape capability and highly controllable solidified microstructure. Successful blade repair technology for single-crystal alloys requires a continuous epitaxial grain growth in the same direction of the crystalline orientation of the substrate material to the newly deposited layers. This work presents a three-dimensional numerical model to simulate the transport phenomena for a multilayer coaxial laser powder deposition process. Nickel-based single-crystal superalloy Rene N5 powder is deposited on a directional solidified substrate made of nickel-based directional-solidified alloy GTD 111 to verify the simulation results. The effects of processing parameters including laser power, scanning speed, and powder feeding rate on the resultant temperature field, fluid velocity field, molten pool geometric sizes, and the successive layer remelting ratios are studied. Numerical simulation results show that the maximum temperature of molten pool increases over layers due to the reduced heat dissipation capacity of the deposited geometry, which results in an increased molten pool size and fluid flow velocity at the successive deposited layer. The deposited bead geometry agrees well between the simulation and the experimental results. A large part of the first deposition layer, up to 85 pct of bead height, can be remelted during the deposition of the second layer. The increase of scanning speed decreases the ratio of G/V (temperature gradient/solidification velocity), leading to an increased height ratio of the misoriented grain near the top surface of the previous deposited layer. It is shown that the processing parameters used in the simulation and experiment can produce a remelting ratio R larger than the misoriented grain height ratio S, which enables remelting of all the misoriented grains and guarantees a continuous growth of the substrate directional-solidified crystalline orientation during the multilayer deposition of single-crystal alloys. © 2014 The Minerals, Metals & Materials Society and ASM International.

Wang L.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Physics of Fluids | Year: 2012

To address the geometrical properties of the turbulent velocity vector field, a new concept named streamtube segment has been developed recently [L. Wang, "On properties of fluid turbulence along streamlines," J. Fluid Mech.648, 183-203 (2010)10.1017/S0022112009993041]. According to the vectorial topology, the entire velocity field can be partitioned into the so-called streamtube segments, which are organized in a non-overlapping and space-filling manner. In principle, properties of turbulent fields can be reproduced from those of the decomposed geometrical units with relatively simple structures. A similar idea is implemented to study the turbulent vorticity vector field using the vorticity tube segment structure. Differently from the conventional vortex tubes, vorticity tube segments are space-filling and can be characterized by non-arbitrary parameters, which enables a more quantitative description rather than just an illustrative explanation of turbulence behaviors. From analyzing the direct numerical simulation data, the topological and dynamical properties of vorticity tube segments are explored. The characteristic parameters have strong influence on some conditional statistics, such as the enstrophy production and the probability density function of vorticity stretching. Consequently the common knowledge in turbulence dynamics that vorticity are more stretched than compressed need to be rectified in the vorticity tube segment context. © 2012 American Institute of Physics.

Dugnani R.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Journal of Intelligent Material Systems and Structures | Year: 2013

Structural health monitoring refers to the interdisciplinary engineering field whose objective is to monitor and evaluate the integrity of mechanical structures. Often times, structural health monitoring diagnostics utilize piezoelectric (lead zirconate titanate) transducers bonded to the surface of the structure monitored. Nonetheless, unexpected variations in the mechanical properties of the adhesive film could affect the dynamic behavior of the system and potentially mischaracterize the fitness for service of a structure. In this article, we presented an analytical model to describe the dynamic coupling between the structure and the lead zirconate titanate transducer that includes the adhesive layer. An electromechanical impedance-based method capable of assessing the integrity of the adhesive bondline was developed based on the proposed analytical model. Our study found that the phase angle of the transducer's electrical admittance was correlated to the mechanical impedance of the adhesive film following a power law behavior. Validation of the proposed model was carried out both by testing transducers bonded to aluminum plates and through a numerical parametric study. In the future, the method proposed could be used to detect preexisting defects in the adhesive bondline, to estimate the adhesive's thickness at manufacturing, and to monitor the degradation of the adhesive material during the life of the system. © 2013 The Author(s).

Fu M.,The University of Michigan - Shanghai Jiao Tong University Joint Institute | Ma C.,The University of Michigan - Shanghai Jiao Tong University Joint Institute | Zhu X.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
IEEE Transactions on Industrial Informatics | Year: 2014

Wireless power transfer (WPT) has attracted an ever increasing interest from both industry and academics over the past few years. Its applications vary from small power devices such as mobile phones and tablets to high power electric vehicles and from small transfer distance of centimeters to large distance of tens of centimeters. In order to achieve a high-efficiency WPT system, each circuit should function at a high efficiency along with the proper impedance matching techniques to minimize the power reflection due to the impedance mismatch. This paper proposes an analysis on the system efficiency to determine the optimal impedance requirement for coils, rectifier, and dc-dc converter. A novel cascaded boost-buck dc-dc converter is designed to provide the optimal impedance matching in WPT system for various loads including resistive load, ultracapacitors, and batteries. The proposed 13.56-MHz WPT system can achieve a total system efficiency over 70% in experiment. © 2005-2012 IEEE.

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