bluuebunny/crossref_metadata_2025 huggingface dataset:
The Reliability Calculation of Components Under Any Cyclic Fatigue Loading Spectrum
Authors: Le Xiaobin
Published: January 2018

The fatigue failure of metal components is due to cyclic fatigue loading. The typical cyclic fatigue loading spectrums described in the literature includes only a few simple cyclic loadings such as a constant amplitude of cyclic fatigue loading with a given cycle number, several constant amplitudes of cyclic fatigue loadings with given cycle numbers, and a distributed stress amplitude of a cyclic stress with a given cycle number or an infinite life. The systematic description of cyclic fatigue loading spectrums is necessary and wasn’t presented in the literature. This paper will present a systematic description of all possible types of cyclic fatigue loading spectrums, which includes 6 different cyclic fatigue loading spectrum models. The P-S-N curve fatigue theory is widely accepted not only for describing the fatigue test data, but also for estimating the reliability of components under cyclic fatigue loading spectrum. However, the reliability calculation of a component under several distributed stress levels with corresponding given cyclic numbers has not been solved according to the literature review. This paper presents a new approach to estimate the reliability of components under such cyclic fatigue loading spectrum. With the contribution of this paper, the P-S-N curve fatigue theory now becomes a complete fatigue reliability theory and can be used to estimate the reliability of components under any type of cyclic fatigue loading spectrum.
Global Research Engagement by Undergraduates and its Impact: Laser Metal Deposition Studies in US-South Africa Collaboration
Authors: Kumpaty Subha , Akinlabi Esther , Paoli Elizabeth , Ziemer Arianna , Pityana Sisa
Published: January 2018

This paper presents the follow-up work of research conducted by Milwaukee School of Engineering senior undergraduate students in South Africa under the second year of the Research Experiences for Undergraduates grant EEC-1460183 sponsored by the National Science Foundation (Principal Investigator Dr. Kumpaty). Elizabeth Paoli and Arianna Ziemer conducted research in summer of 2016 under advisement of Dr. Kumpaty and his South African collaborators, Dr. Esther Akinlabi and Dr. Sisa Pityana. Arianna extended the work of Mueller (reported in IMECE2016-65094), with 10% Mo in the combination of Ti64-Mo deposited on Ti64 substrate at a laser power of 1700 W for five scan speeds ranging from 0.5 to 1.5 m/min. It was observed that lower scan speeds produced elongated grains. Hardness and corrosion tests were also completed in her study. Elizabeth worked on varying the percent of Mo from layer to layer deposited (5%, 10%, 15%) and characterized these functionally graded samples for biomedical applications. Laser metal deposition was completed at the CSIR – National Laser Center, in Pretoria, South Africa and the material characterization was performed at the University of Johannesburg as in the previous year.

An alumnus of MSOE, Peter Spyres was an important liaison for our international REU participants as he engaged them during the weekends in a cultural immersion which otherwise would not have been possible. While the research collaborators have generously provided support, it is the care taken by Peter’s remarkable household, which enhanced the beneficial value of this global research enterprise. The paper addresses yet another successful completion of the international Research Experiences for Undergraduates.
Operational Aspects of Coatings Welds: Erosive Wear and Cavitation
Authors: da Silva Hebert Roberto , Ferraresi Valtair Antonio , Arencibia Rosenda Valdes
Published: January 2018

The GMAW process using two wires is an alternative to a coating process when high productivity is desired. The potential variants emerging from this process are GMAW cold wire and GMAW double wire. One of the greatest difficulties is the setting of its parameters, which duplication compared to conventional GMAW and also act in a dependent manner. A greater understanding of the technology applied to coatings on turbines in various positions is critical to master the process and its variables for enhancing industrial applications. This study involves an experimental evaluation to verify the influence of some variables on the profile of cord and wear resistance. This paper proposes making deposits with weld metal AWS 308LSi stainless steel and alloys of cobalt (Stellite 6 and 21) plates in carbon steel SAE 1020 in the flat positions. The wear characterization in the lining is used to determine the hardness and surface topography. It is concluded that cobalt alloys have superior resistance to erosive damage, with emphasis on Stellite 21 with respect to erosion and Stellite 6 with respect to cavitation. Mixtures of austenitic stainless steel and cobalt alloys have intermediate wear values. Therefore, it is essential to study welding processes with multiple wires, as proposed in this paper, to determine the optimal combination of alloys for resistance to cavitation-erosion phenomena.
Mechanisms Underlying Rapid Electronucleation and Freezing of Hydrates
Authors: Acharya Palash V. , Shahriari Arjang , Lin Denise , Bahadur Vaibhav
Published: January 2018

Nucleation of hydrates is constrained by very long induction (wait) times, which can range from hours to days. Electronucleation (application of an electrical potential across the precursor solution) can significantly reduce the induction time for nucleation. This study shows that porous aluminum foams (open-cell) enable near-instantaneous electronucleation at very low voltages. Experiments with tetrahydrofuran hydrates reveal that aluminum foam electrodes enable voltage-dependent nucleation with induction times of only tens of seconds at voltages as low as 20 V. Foam-based electrodes can reduce the induction time by up to 150X when compared to non-foam electrodes. Furthermore, this study reveals that electronucleation can be attributed to two distinct phenomena, namely bubble generation (due to electrolysis), and the formation of metal-ion coordination compounds. These mechanisms affect the induction time to different extents and depend on electrode material and polarity. Overall, this work uncovers the benefits of using foams for formation of hydrates, with foams aiding nucleation as well as propagation of the hydrate formation front.
Effect of Combining Buoyancy Driven and Winddriven Ventilation in a Two Dimensional Room Fitted With a Windcatcher
Authors: Abdo Peter , Huynh B. P.
Published: January 2018

Natural ventilation is the process of supplying and removing air through an indoor space by natural means. There are two types of natural ventilation occurring in buildings: winddriven ventilation and buoyancy driven ventilation, or stack ventilation. The most efficient design for natural ventilation in buildings should implement both types of natural ventilation. Stack ventilation which is temperature induced is driven by buoyancy making it less dependent on wind and its direction. Heat emitted causes a temperature difference between two adjoining volumes of air, the warmer air will have lower density and be more buoyant thus will rise above the cold air creating an upward air stream. Combining the winddriven and the buoyancy driven ventilation will be investigated in this study through the use of a windcatcher natural ventilation system. Stack driven air rises as it leaves the windcatcher and it is replaced with fresh air from outside as it enters through the positively pressured windward side. To achieve this, CFD (computational fluid dynamics) tool is used to simulate the air flow in a two dimensional room fitted with a windcatcher based on the winddriven ventilation alone and on the combined buoyancy and winddriven ventilation.
Bladelets-Winglets on Blades of Wind Turbines: A Multiobjective Design Optimization Study
Authors: Reddy Sohail R. , Dulikravich George S. , Sobieczky Helmut
Published: January 2018

The work presented in this paper used rigorous 3D flow-field analysis combined with multi-objective constrained shape design optimization for the design of bladelet (winglet) configurations for a three-blade propeller type wind turbine. The fluid flow analysis in this work was performed using 3D, steady, incompressible, turbulent flow Reynolds-averaged Navier-Stokes equations in the rotating frame of reference for each combination of a given wind turbine blade and a varying bladelet geometry. The free stream uniform wind speed in all cases was assumed to be 9 m s−1 and rotational speed was 12 rpm. These were off-design conditions for this rotor. The three simultaneous design optimization objectives were: a) maximize the coefficient of power, b) minimize the coefficient of thrust, and c) minimize twisting moment around the blade axis. The bladelet geometry was fully defined by using a small number of parameters. The optimization was carried out by creating a multi-dimensional response surface for each of the simultaneous objectives. The response surfaces were based on radial basis functions, where the support points were designs analyzed using the high fidelity CFD analysis of the full blade + bladelet geometry. The response surfaces were then coupled to a multi-objective optimization algorithm. The predicted values of the objective functions for the optimum designs were then again validated using the high fidelity computational fluid dynamics analysis code.

Results for a Pareto optimized bladelet on a given blade indicate that more than 4% increase in the coefficient of power at minimal thrust force penalty is possible compared to the same wind turbine rotor blade without a bladelet.
Assessment of a Modified Blade Element Momentum Methodology for Diffuser Augmented Wind Turbines
Authors: Leloudas Stavros N. , Lygidakis Georgios N. , Nikolos Ioannis K.
Published: January 2018

The Blade Element Momentum (BEM) theory is nowadays the cornerstone of the horizontal axis wind turbine design, as its application allows for the accurate aerodynamic simulation and power output prediction of wind turbine rotors in a remarkably short period of time. Therefore, efforts have been made for the extension of the classic BEM theory to the performance analysis of Diffuser Augmented Wind Turbines (DAWTs) as well. In this study, the development and assessment of such an in-house BEM code are presented. The proposed computational model is based on the modification of the momentum part of the classical BEM theory; thus, it is capable to account for the diffuser’s effect on the calculation of the axial and tangential induction factors, through the utilization of the velocity speed-up distribution over the rotor plane of the unloaded diffuser. Furthermore, a detailed Glauert’s correction model, which employs Buhl’s modification, specially tailored for the DAWT case is included, to deal with the high values of the axial induction factor. The accuracy of the model is assessed against numerical and experimental results available in the literature, while the impact of the Prandtl’s tip loss correction model on the rotor’s predicted power output is also examined.
Mechanical Stress Monitoring Sensor for 3-D Module During Manufacturing and Operation
Authors: Isobe Koki , Suzuki Ken , Miura Hideo
Published: January 2018

In three-dimensional packaging module which have been used in electronic equipment, the size of partial interconnections and total structure have been continuously miniaturized for improving the performance of the products. Due to the fluctuation of the mechanical properties of the component materials and the drop impact towards the fragile modules during manufacturing and operation, the final residual stress varies easily in a chip of the 3-D structure. Both the static and dynamic changes of the stress distribution induce the variation of the performance of electronic devices and the degradation of their long-term reliability. It is, therefore, important to control and optimize the residual stress quantitatively. In this study, a stress sensor which can monitor the change of the local residual stress in 3-D module was developed by applying the piezoresistance effect of single-crystalline silicon. The sensor was embedded in a silicon chip, and it can measure the periodic stress in a silicon chip assembled by area-arrayed bump structure. The impact stress during the manufacturing process was successfully monitored by using this sensor. It was also confirmed that the effective amplitude of the impact stress varies drastically depending on the mechanical properties of the stacked thin films.
An Infinite Model Predictive Controller for Multi Input Nonlinear Processes
Authors: Abu-Ayyad Ma’moun , Abdessameud Abdelkader , Abu-Mahfouz Issam
Published: January 2018

This paper presents a novel algorithm of an infinite model predictive controller for controlling nonlinear multi-input multi-output (MIMO) processes. The new strategy uses a set of continuous nonlinear functions that captures the nonlinear characteristics of the MIMO plant over a wide operating range resulting in a more accurate prediction of the controlled variables. The method formulates a nonlinear dynamic matrix that is manipulated variable dependent during closed-loop control. The proposed algorithm was implemented on a nonlinear MIMO thermal system comprising of three temperature zones to be controlled with interacting effects. The experimental closed-loop responses of the proposed algorithm were compared to a multi-model dynamic matrix controller (DMC) with improved results for various setpoint trajectories. The MIMO process has nonlinear parameters such as process gain and time constant that are dependent on the size of the control actions. Good disturbance rejection was attained resulting in improved tracking of multi-setpoint profiles in comparison to multi-model DMC.
An Experimental Study of the Structural Dynamic Response of a Biomimetic Insect-Sized Wing
Authors: Rubio Jose E. , Chakravarty Uttam K.
Published: January 2018

This investigation describes a method for both manufacturing a biomimetic insect-sized wing using the photolithography technique and experimentally analyzing its structural dynamic response. The wing geometry of a crane fly forewing is captured using a micro-computed tomography scanner for its replication. A photomask of the membrane and venation pattern is designed from a computer-aided design model developed from the reconstructed scanned model of the wing. The photolithography process is conducted using the negative photoresist SU-8 and the Kapton film to biomimic the veins and the membrane of the crane fly forewing, respectively. A digital image correlation (DIC) system is used in conjunction to a shaker vibrational setup to determine the natural frequencies of the artificial wing from the fast Fourier transform of the time-varying out-of-plane displacement data. Wind-tunnel experiments are conducted using the DIC system to determine the structural response of the artificial wing under different freestream velocities and angles of attack within the regime of insect flight. The vibration modes are dominated by a bending and torsional deformation response. The deformation along the span of the wing increases nonlinearly from the root to the tip of the wing with Reynolds number.
Designing Roof Structures for Real-World Rollovers
Authors: Herbst Brian , Meyer Steven , Bell Lauren , Bish Jack , Clarke Christopher , Rogers Chuck
Published: January 2018

This paper presents a real world rollover accident involving a common make and model sport utility vehicle, or SUV, analyzed using a well-validated, publicly available finite element analysis, or FEA, model of the same vehicle. The FEA model was utilized to evaluate the loading conditions of a real-world rollover accident that had previously been reconstructed using standard engineering techniques. Iteration of the conditions of the finite element, or FE, simulation to match the damage observed in the subject vehicle provided a quantification of the rollover crash loading.

Once the damage pattern of the real world accident was achieved in the FE simulation, reinforcement techniques utilizing changes to the material properties and thicknesses of selected roof structure components were used to represent a re-designed roof. The re-designed roof improved intrusion resistance by more than 80% with a minimal weight penalty.
A Generalization of the Heuristic Gradient Projection for 2D and 3D Frame Optimization
Authors: Abd El-Rahman Mahmoud S. , Abd El-Aziz Khalid M. , Metwalli Sayed M.
Published: January 2018

This paper introduces a generalization of the heuristic gradient projection (HGP) method for solving 2D and 3D frames. The main objective is to minimize the frame weight by means of size, topology and shape optimization considering stress constraint activation. HGP can give a specific iterative equation for each element cross section and loading type and consequently reach the optimum solution in a relatively smaller number of iterations compared to general heuristic recursive equations. However, the solution of frames with combined loads applied on the elements might converge slowly or oscillate around the constrained optimum value. Many approaches were investigated for the generalization of the HGP. However, the emphasis was always directed towards axial and bending loads. Although other types of loads may have an effect on the problem, like shear and torsion stresses in shafts or 3D frames. These types of loads are introduced into the optimization problem with more general algorithm. Weighting factors are utilized to give a weight to each stress type applied on each element. This factor is used to change the power of the HGP iterative formula for each element in the frame, which changes the power of the recursive formula according to the contribution of each loading type applied on the element. The proposed technique shows more accurate results in activating the stress constraints than previously developed HGP when dealing with combined loads, and keeps the advantage of the HGP in finding the optimum solution in a relatively small number of structural analyses. In the case studies several sample applications were solved to highlight the robustness of the proposed method.
Effect of Ratio Control Algorithm on Stability Characteristics of Half-Toroidal IVT Variator
Authors: Saito Toshihiro , Inoue Eiji , Tamoto Yoshitaka
Published: January 2018

Half-toroidal variators are core components in Infinitely variable transmissions (IVT). These variators realize smoother and more rapid ratio change than other shift mechanisms. However, the effect of ratio control methods on these characteristics is not necessarily clear. Research was therefore conducted to examine these effects. Using an existing half-toroidal variator analysis model, behavioral analyses were conducted by substituting only the ratio control method. Three control methods were studied: A mechanical control mass-produced by a competitor, direct ratio control that feeds back only input and output revolutions, and observer control that adds shift mechanism state estimation to direct control. With regard to responsiveness in relation to the desired ratio, the direct control provided the best performance from the perspective of accurately realizing the desired ratio. On the other hand, under conditions in which external disturbance cannot be ignored (full closure of the throttle from acceleration at wide-open throttle), the mechanical control displayed the greatest ratio stability. Because control gain in mechanical control can only take a fixed value due to the lead angle of the precise cam, it is not possible to obtain the optimum gain for each ratio. Observer control is based on direct ratio control, but supplements the function of the precise cam with state estimation, and makes it possible to optimize control gain. The research discussed in this paper investigated the ability of the internal behavior of the variator to track target values calculated based on state estimation using simulations, and verified the validity of the state estimation equations. The results obtained indicated that observer control is a control method that balances the ability to track the desired ratio with ratio stability.
Uncertainty Quantification for Laser Ablation of Aluminum
Authors: Wang Yeqing , Befekadu Getachew K. , Pasiliao Crystal L.
Published: January 2018

In recent years, a number of research efforts have been devoted to understand the mechanisms and develop accurate simulation models for laser ablation of solid materials. However, uncertainty quantification (UQ) for laser ablation of solid materials, when the sources of uncertainty are inherently stochastic (e.g., material and optical properties of target materials at elevated temperatures), is not sufficiently understood or addressed, despite having critical impact on guiding experimental efforts and advanced manufacturing. In this paper, we consider the problem of UQ for pulsed laser ablation of aluminum. In particular, a generalized polynomial chaos (PC) method is used to incorporate constitutive parameter uncertainties within the representation of laser heat conduction phenomena, where the parameter uncertainties are either presumed from the mathematical modeling approximation for the laser heat conduction model and/or from the laser source. Moreover, numerical simulation studies for laser ablation of aluminum, with nanosecond Nd:YAG 266nm pulsed laser, that demonstrate the proposed generalized PC predictions are also presented. Finally, a sensitivity study is used to identify those parameters that provide the most variance in the thermal and ablation response.
Development of an Analytical Model for Beams With Two Dimples in Opposing Direction
Authors: Ghazwani Mofareh , Myers Kyle , Naghshineh Koorosh
Published: January 2018

Structures such as beams and plates can produce unwanted noise and vibration. An emerging technique can reduce noise and vibration without any additional weight or cost. This method focuses on creating two dimples in the same and opposite direction on a beam’s surface where the effect of dimples on its natural frequencies is the problem of interest. The change in the natural frequency between both cases have a different trend. The strategic approach to calculate natural frequencies is as follows: first, a boundary value model (BVM) is developed for a beam with two dimples and subject to various boundary conditions using Hamilton’s Variational Principle. Differential equations describing the motion of each segment are presented. Beam natural frequencies and mode shapes are obtained using a numerical solution of the differential equations. A finite element method (FEM) is used to model the dimpled beam and verify the natural frequencies of the BVM. Both methods are also validated experimentally. The experimental results show a good agreement with the BVM and FEM results. A fixed-fixed beam with two dimples in the same and opposite direction is considered as an example in order to compute its natural frequencies and mode shapes. The effect of dimple locations and angles on the natural frequencies are investigated. The natural frequencies of each case represent a greater sensitivity to change in dimple angle for dimples placed at high modal strain energy regions of a uniform beam.
Joint Torque Control of a Collaborative Robot Based on Active Disturbance Rejection With the Consideration of Actuator Delay
Authors: Ren Tianyu , Dong Yunfei , Wu Dan , Wang Guolei , Chen Ken
Published: January 2018

The application of a robot manipulator to the task of parts assembling or collaboration with human workers requires compliant control and intrinsic safety. As a result, it is necessary to exert accurate torque on each joint of the robot through torque sensing and implementing closed-loop joint torque control. This torque servo system is required to track reference torque signals while operating under the influence of motor friction, flexibility of the harmonic drive, noise from the sensor, robot dynamics modelling error and other unknown certainties, resulting in large control efforts.

This paper focuses on providing better compliance control for collaborative robots and proposes a joint torque controller design under development with active disturbance rejection concept. The controller is designed through a novel extended state observer to estimate and compensate for the unmodelled dynamics of the system, nonlinearly variable motor friction, and other uncertainties. Then, a simple proportional differential controller is designed to produce control law. In spite of the remarkable performance in dealing with the mechanical dynamics of the joint actuator, the original controller does not work well with the electrical factor of the joint actuator due to the limited current loop bandwidth in the hardware of motor and driver. To eliminate the detrimental effect of the time delay in current servo, a predictive output method based on a nonlinear tracking differentiator (TD) is used to improve the controller within the framework of active disturbance rejection control. Both simulations and experiments are conducted on a prototype one degree of freedom manipulator with a joint torque sensor. The results demonstrate the enhancement of both the system stability and disturbance rejection performances. Based on the proper treatment of actuator delay, the dominant effect of the motor friction and the flexibility of the harmonic drive has been reduced to insignificance. Moreover, the proposed controller is easy to implement because the explicit dynamic model of the system is not required.
Wheelchair.q05 Final Design: An Innovative Stair-Climbing Wheelchair
Authors: Quaglia Giuseppe , Nisi Matteo , Franco Walter
Published: January 2018

The presence of architectural barriers in public or private buildings represents an important limit for the mobility of wheelchair users. Although norms promote barriers removal, often a complete accessibility cannot be guaranteed due to economic or technical reasons. In such cases, it is necessary to provide disable people with devices able to autonomously climb architectural barriers or obstacles.

Referring to user needs, some requirements for the wheelchair can be defined. Firstly, the user must use it autonomously. Secondly, it should be easy to use, simple in the mechanical and control systems and with limited weight, dimensions, and cost. Finally, also the appearance of the wheelchair must be adequate to guarantee the user acceptability.

In literature, several solutions of stair-climbing wheelchair are proposed. However, none of these completely satisfies the identified requirements.

In this paper, the Wheelchair.q05, an innovative concept for a stair-climbing wheelchair, is presented. This idea has been developed through several years of researches and functional designs. In detail, this work presents the final design for a constructive and real scale prototype.

The proposed wheelchair, thanks to a smart and hybrid locomotion system, is able to move on flat ground and to climb stairs and sidewalks. A triangular shaped frame with a wheel on each corner, connected through an internal epicyclical transmission system, constitutes the locomotion unit. This system provides the traction both for flat ground and stair motion. Moreover, the wheelchair has an idle track that represents the rear contact point during stair-climbing and guarantees only a stable and regular climbing motion. The wheelchair structure is thus constituted by the following functional elements: two locomotion units, the track, the seat and a couple of pivoting wheels connected to floating arms that represents the rear support during flat ground motion and during sidewalks overcoming.

Through a kinematic synthesis, the optimal layout has been defined and the mechanisms that connect the functional elements with the frame have been designed. These mechanisms allow controlling the wheelchair reconfiguration that is necessary to adapt the vehicle to different working conditions.

Moreover, attention has been paid to the user comfort. Thanks to the introduction of a mechanism that controls the seat orientation, the oscillations generated by the motion on stair are compensated and a regular trajectory is guaranteed for the user center of mass.
Study of Vibration of Electric Power Steering Systems Using a Continuous System Model
Authors: Freund Mary K. , Farzaneh Joubaneh Es’hagh , Barry Oumar R. , Tanbour Emad Y.
Published: January 2018

Electric power steering systems (EPS) offer better fuel efficiency than hydraulic power steering system. However, EPS systems are plagued with noise and vibrations, which can undermine the comfort of drivers. In previous works, steering systems have been analyzed using two degree of freedom system. In this paper, a mathematical model of an electric power steering system is presented using a continuous system to model the steering column. The equations of motion and boundary conditions are derived using Lagrangian method. Explicit expressions are presented for the characteristic equation and mode shapes. Parametric studies are conducted to study the effects of different parameters on natural frequency.
On the Application of Biomimicked Composites in 3D Printed Artifacts
Authors: Allameh Seyed M. , Miller Roger
Published: January 2018

Application of 3D printing to works of art is not new. However, with the advent of larger and more affordable 3D printers, it is possible to fabricate works of art including statues, sculptures, and architectural structures from biomimicked composites. Made of hard ceramic and soft polymer with or without reinforcement, these composites have shown to be much tougher than their monolithic counterparts. The use of biomimicking will increase the durability and strength of such artifacts. In this study, a newly developed architectural 3D printer is used to create works of art using concrete, with and without reinforcement fibers. The challenge that face creating tough artistic display structures include durability, hardness and resistance to impact. To determine the right combination of hard ceramic and soft polymer, a series of experiments were conducted. These included the fabrication of biomimicked composites with different materials and testing them for fracture energy as well as maximum strength. Earlier published works demonstrate the effect of various parameters such as type of ceramic layer, layering, fiber reinforcement type, fiber length, and fiber loading. In this paper, the effect of hard layer thickness and the type of polymer on the mechanical properties of the biomimicked composites was investigated. Preliminary results show the highest fracture energy for composites made with concrete bonding adhesive (CBA) and Quikrete™ concrete, with a spacing of 5mm. The application of 3D printing to the educational activities of a museum in Newport KY will be explained and its implication in relation with civic engagement activities of Northern Kentucky University will be elucidated.
Period-1 Motions to Chaos in a Parametrically Excited Pendulum
Authors: Guo Yu , Luo Albert C. J.
Published: January 2018

In this paper, bifurcation trees of period-1 motions to chaos are investigated in a parametrically excited pendulum. To construct discrete mapping structures of periodic motions, implicit discrete maps are developed for such a pendulum system. The bifurcation trees from period-1 motions to chaos are predicted semi-analytically through period-1 to period-4 motions. The corresponding stability and bifurcation analysis are carried out through eigenvalue analysis. Finally, numerical simulations of periodic motions can be completed through numerical methods. Such simulation results are illustrated for verification of the analytical predictions.
General Integral Equations and Bounds of the Effective Moduli of Random Structure Composites
Authors: Buryachenko Valeriy A.
Published: January 2018

One considers a linear elastic random structure composite material (CM) with a homogeneous matrix. The idea of the effective field hypothesis (EFH, H1) dates back to Faraday, Poisson, Mossotti, Clausius, and Maxwell (1830–1870, see for references and details [1], [2]) who pioneered the introduction of the effective field concept as a local homogeneous field acting on the inclusions and differing from the applied macroscopic one. It is proved that a concept of the EFH (even if this term is not mentioned) is a (first) background of all four groups of analytical methods in physics and mechanics of heterogeneous media (model methods, perturbation methods, self-consistent methods, and variational ones, see for refs. [1]). New GIEs essentially define the new (second) background (which does not use the EFH) of multiscale analysis offering the opportunities for a fundamental jump in multiscale research of random heterogeneous media with drastically improved accuracy of local field estimations (with possible change of sign of predicted local fields).

Estimates of the Hashin-Shtrikman (H-S) type are developed by extremizing of the classical variational functional involving either a classical GIE [1] or a new one. In the classical approach by Willis (1977), the H-S functional is extremized in the class of trial functions with a piece-wise constant polarisation tensors while in the current work we consider more general class of trial functions with a piece-wise constant effective fields. One demonstrates a better quality of proposed bounds, that is assessed from the difference between the upper and lower bounds for the concrete numerical examples.
CFD Study of Effects of Boundary Layer Suction on Transonic SC(2)-0714 Airfoil Performance
Authors: Khamedov Ruslan , Baitlessov Ruslan , Rojas-Solórzano Luis
Published: January 2018

The complete understanding of the aerodynamics of wings and blades under transonic conditions represents a substantial challenge in the design of modern airplanes and turbomachinery. Transonic flow over airfoils may result in appearance of shock waves, which lead to increase in drag if not properly considered during the design stage. Therefore, it is a major challenge to design transonic airfoils such that potential appearance of shock waves is foreseen and negative drag effects are minimized. This paper presents the computational study of the SC(2)-0714 airfoil, focusing on its aerodynamics characteristics at Reynolds number of 35 × 106 and angle of attack of 2 and 10 degrees which are the most common operational conditions of transonic wings using this airfoil. The study was undertaken at free-stream Mach 0.72. The numerical simulation was conducted using the finite volume method on platform ANSYS CFX™ and solving the Reynolds-Averaged Navier-Stokes, mass conservation and energy equations. Mesh verification and model validation are presented. The latter is developed by using two different isotropic turbulence models: k-ω and Shear Stress Transport (SST) and the comparison of results with NASA experimental data to determine the best among the treated models. Thereafter, effects of local boundary-layer suction on shock wave strength and characteristics during transonic speed are analyzed for the two aforementioned angles of attack. Two suction slots were placed along the airfoil contour to determine their control effectiveness when compared to standard closed-contour airfoil. Suction slots were placed at the leading edge and in the middle of the upper camber of the airfoil with inflow in the normal direction to the surface. The slot length was 2.5 % of the chord with inflow velocity of 30%, 40% and 50% of free-stream velocity. Effects of suction slots were assessed on the wake region and by computing the resulting lift-to-drag ratio. Concluding remarks on the turbulence model and global aerodynamics performance of the airfoil are presented.
Contact Variation Optimization for Surface-to-Surface Contacts
Authors: Camuz Soner , Bengtsson Magnus , Söderberg Rikard , Wärmefjord Kristina
Published: January 2018

Locating schemes, used to position parts during manufacturing, are usually designed in such a way that the response from the system is minimized. This implies that the position of the fasteners and/or welds are known in an assembly. Today there exist numerous of methods aiming to find an optimal set of locating points to increase the stability of an assembly, for both rigid and compliant parts. However, various industrial applications use surface-to-surface contacts to constrain certain degrees of freedom. This can lead to designs sensitive to geometric and load variations. As the complexity of the surfaces increases, difficulties of allocating geometric tolerances arise. An approach to control this is to keep the contact locations statistically stable. In this paper a methodology is presented where the First-Order Reliability Method (FORM) is applied for numerical data, retrieved through Finite Element Analysis (FEA), to ensure that statistically stable contact location are achieved for two bodies with surface-to-suface contact. The FEA data represents how much of the total stress that lies within a given area, σΩ. The data is continuous and therefore it is assumed that the gradient can be calculated numerically with small steps. The objective function is to maximize σΩ for n variables. The data set is simulated through Finite Element Analysis using the commercial software Ansys and the results is illustrated on a case study from the machining industry.
Experimental Study of Impact Force of a Low-Speed Droplet Colliding on the Solid Surface at Different Impact Angles
Authors: Zhang Bin , Lv Qian , Guo Penghua , Li Jingyin
Published: January 2018

Erosion problems due to droplet impacts are widely encountered in many fields. This may result in deterioration or even failure of the elements, and should be taken into consideration in the design of machines. The impact force is thought of as an essential factor in material erosion. In this paper, a highly sensitive piezoelectric force transducer was employed to record the impact force of the low-speed droplet colliding on an aluminum plate at different impact angles, in combination with a high-speed camera used to capture the impact process of the droplet. The results showed that the experimental setup can measure the impact force evolution precisely and reliably. The peak of the normal impact force increases with the normal velocity quadratically, while the impulse increases with the normal velocity linearly. In addition, a smaller impact angle would lead to longer time duration of the impact force. The high-speed images show that the initial impact patterns of the droplet have similar behavior in the initial impact process, with regardless of vertical or oblique impacts.
Computational Fluid Dynamics Simulations in Flow Past Arrays of Finite Plate: Marine Current Energy Harvesting Applications
Authors: Attiya Bashar , Liu I-Han , Daskiran Cosan , Riglin Jacob , Oztekin Alparslan
Published: January 2018

Computational fluid dynamics simulations have been conducted for flows past two finite tandem plates at Reynolds number of 50,000. Large Eddy Simulations (LES) were employed in two and three-dimensional geometries to study the interference between tandem plate pair. In order to study the effects of plate corner angle on the flow field and drag forces, two different plate end corners, 90° and a sharp 45° corner angle, were also investigated. The switching from 90° to 45° corners complicate the flow pattern, increase the mean value of drag force and the fluctuations of the drag on the plate. As vortices shed from the upstream plate and reached close proximity to the face of the downstream plate, the vortex cores deformed highly. This behavior reduces the drag coefficient in the downstream plate. Drag coefficient was higher in the 45° case, for both the up and downstream plates by 5% and 10% respectively. Drag coefficient of downstream is recovered almost fully in the 45° case with just 3% difference from the upstream compared to 7% difference in 90° case. Lagrangian Coherent structures were identified and presented in a two-dimensional geometry. This gave a better understanding of the wake flow structure and their influence on the hydrodynamic loading on plates. Contours of vorticity fields and iso-surfaces of Q-criterion, and pressure distribution around the plates were also presented and discussed.
Numerical Analysis of Hydrodynamic Performance of FX-83-W Hydrofoil Current Turbine
Authors: Shang Yuchen , Xiros Nikolaos I.
Published: January 2018

Ocean current flow characteristics are relatively stable and predictable, current turbine absorbs the energy of the ocean currents by the blades with a relative stable and lower angular velocity which indicates the capacity of current turbine greater than the onshore wind turbine. In this paper, the CFD method is utilized to calculate and analyze the working principle of FX-83-W current turbine. The three-dimensional coordinate of FX-83-W Hydrofoil blade surface have been calculated by MATLAB code, and 3D model has been established in Gambit. The basic control equations of CFD and its numerical solution are described, Reynolds Averaged N-S equations is used, and the realizable k-e turbulence model is introduced to solve the Reynolds stress in the RANS equation. The numerical algorithm is the finite volume method (FVM), and the numerical simulation of CFD is used to study the open water performance, leading to thrust coefficient KT and torque coefficient KQ of FX-83-W Hydrofoil. The hydrodynamic thrust and hydrodynamic power of the ocean current turbine under different sea conditions have been obtained by numerical simulation.
Polymer-Nanoparticle Composite Foams for Energy Harvesting Applications
Authors: Nalbach Joseph R. , Schwenger Matthew S. , Koleszar Zachary M. , Greiser Kelly , Ozalas David , Michel Taissa , Bovenzi Craig , Xue Wei
Published: January 2018

Throughout the course of one day, the human body goes through numerous mechanical activities. These activities, while usually not very powerful individually, produce an ample amount of energy collectively. This mechanical energy can be harvested into electrical energy via piezoelectricity. Recent research into piezoelectric nanocomposites has yielded techniques to foam the materials into softer, porous structures more suitable for human comfort. This study focuses on using a host polymer polydimethylsiloxane (PDMS) and citric acid to create foams. Citric acid, a common industrial chemical blowing agent (CBA), is used in this project due to its capabilities to produce foams with consistent pore sizes and distribution. These foams, coupled with piezoelectric nanoparticles, are fabricated, analyze, and tested. They are mechanically characterized using tensile testing. Electrical characterization is carried out using an integrated mechanical-electrical testing setup. These foams are lighter, softer, and can produce higher electrical output than non-porous counterparts. We believe that these foams have great potential in upcoming piezoelectric technology.
Feasibility Study of Different Pseudopotential Multiphase Lattice Boltzmann Methods for Dendritic Solidification
Authors: Nabavizadeh Seyed Amin , Eshraghi Mohsen , Felicelli Sergio D.
Published: January 2018

The formation of porosity and bubbles during solidification in manufacturing processes like casting or welding of metals has a negative effect on the mechanical properties of the manufactured components. Numerical simulation of this problem is important since the direct observation of the interaction of bubbles with dendrites is limited by the opacity of metals. Therefore, developing a reliable numerical model is essential to predict the mechanical properties of materials after solidification.

The pseudopotential multiphase model is a popular method for simulating multiphase flow using the lattice Boltzmann method. This model and its variations have been used to simulate a variety of problems successfully. However, the original pseudopotential model has some deficiencies, including large spurious current and restriction to model low density and viscosity ratios. Several schemes have been proposed to improve the pseudopotential multiphase model and overcome the limitations, including using a realistic equation of state, introducing a force with higher order of isotropy, introducing a middle-range repulsion force, and implementing the force similarly to the Exact Difference Method (EDM).

The aim of this article is to investigate these various enhancements available for the pseudopotential multiphase model in order to come up with a reliable scheme to simulate motion and interaction of bubbles during dendritic solidification in binary alloys. The proposed model is validated against published literature.
Adaptive Backstepping Control of the Gripping Process of Heavy Manipulators
Authors: Yang Lixin , Zhang Xianmin
Published: January 2018

A valve-controlled asymmetrical cylinder model was established to study the gripping hydraulic drive system of the grip device of heavy manipulator. Due to the strong nonlinear characteristics and uncertain parameters of the model, the Lyapunov stability principle was used to design a multistage inversion adaptive controller based on backstepping method and by introducing the virtual control parameter. The simulation results reveal that the tracking control and adaptive of uncertain parameters are very effective, which confirm that the designed controller can guarantee the stability of the closed-loop clamping hydraulic drive system.
Model-Based Optimal Control of a Small Remotely Operated Vehicle
Authors: Aldana Afanador Andrés Felipe , Esteban Villegas Helio Sneyder , Roa Prada Sebastián
Published: January 2018

Remotely Operated Vehicles, ROVs, are useful devices that can greatly assist humans in the development deep-sea exploration and underwater tasks. These unmanned vehicles require human intervention for the realization of its underwater jobs and have the ability to carry multiple instruments, sensors and actuators according to the application. There are numerous commercial ROV platforms, ranging from inexpensive to very advanced and costly systems.

Being an underactuated system, one of the most important factors in the development of a ROV is the design of its control system. Depending on the quality of the implemented control strategy, the functioning of the vehicle may or may not fail, or the accuracy with which its assignments are done may be seriously compromised. Different control strategies can be utilized for the stabilization and maneuvering of a ROV. The design of these strategies often require system parameter identification. Appropriate modeling and knowledge about the dynamic behavior of the system is essential for a successful parameter identification. One of the main parameters that must be identified is the drag coefficient of the ROV as it moves in the fluid. This parameter can be either experimentally measured, or estimated using the finite element method, to quantify the forces due to fluid-structure interaction.

This work seeks the design and comparison of different advanced control techniques as applied to a small ROV. A commercial small ROV system has been chosen as the object of study and finite element simulations were carried out to estimate some of its mechanic parameters, using the commercial software COMSOL Multiphysics®. The nonlinear model of the system is developed and linearized to obtain its state space representation. The state space representation of the system is then used in the design of a LQR control system. The comparisons of the responses of the compensated systems allows assessing the suitability of the optimal control strategy for stabilization of ROVs.