bluuebunny/crossref_metadata_2025 huggingface dataset:
Robust H∞ Hybrid Observer-Controller Design With Application to Attitude Control of 2-DOF Helicopter
Authors: Razavi Hamidreza , Merat Kaveh , Salarieh Hassan , Alasty Aria , Meghdari Ali
Published: March 2015

In this paper, a class of uncertain piecewise affine (PWA) systems, subject to system and measurement external disturbances are studied. The uncertainties are assumed to be norm bounded and the external disturbance signals belong to the L2 space. The problem of optimizing the system response in the H∞ sense, by means of a piecewise affine observer-controller, is formulated as an optimization problem subject to a number of constraints in the form of matrix inequalities. The derived constraints are obtained by considering a partially piecewise quadratic Lyapunov function in combination with the general conditions for H∞ stability. Then the uncertain PWA approximation of the nonlinear attitude dynamics of a simplified helicopter model, subject to system and measurement external disturbances, is presented. The uncertainties arise in the form of the difference between the actual nonlinear dynamics and the PWA approximation. Utilizing the introduced methods, a robust PWA observer-controller is designed and implemented on the simplified nonlinear helicopter model to demonstrate the effectiveness of the proposed observer-controller design method.
Observation of Thrombus Formation Process by High Shear Rate on Various Flows and CFD Based Prediction Method for Thrombus Formation Rate
Authors: Tamagawa Masaaki
Published: March 2015

This paper describes visualization of thrombus formation process on orifice flows and Couette flows by normal illumination. The aim is to investigate the effects of shear stress or shear rate on the thrombus formation or thrombus formation rate. It was found that (1) effect of flow types on the thrombus ratio was obtained and (2) quantitative evaluation of thrombus formation rate by our proposed CFD based prediction method was established for various flows.
Dynamic Interaction Between Rotor and Axially-Magnetized Passive Magnetic Bearing Considering Magnetic Eccentricity
Authors: Enemark Søren , Santos Ilmar F.
Published: March 2015

Passive magnetic bearings are known due to the excellent characteristics in terms of friction and no requirement of additional energy sources to work. However, passive magnetic bearings do not provide damping, are not stable and, depending on their design, may also introduce magnetic eccentricity. Such magnetic eccentricities are generated by discrepancies in magnet fabrication. In this framework the main focus of the work is the theoretical as well as experimental investigation of the non-linear dynamics of a rotor-bearing system with strong emphasis on the magnetic eccentricities and non-linear stiffness.

In this investigation passive magnetic bearings using axially-aligned neodymium cylinder magnets are investigated. The cylinder magnets are axially magnetised for rotor as well as bearings. Compared to bearings with radial magnetisation, the magnetic stiffness of axially-aligned bearings is considerably lower, nevertheless they allow for asymmetric stiffness mounting, and it could be beneficial for rotor stabilization.

A theoretical model is proposed to describe the non-linear rotor-bearing dynamics. It takes into account non-linear behaviour of the magnetic forces and their interaction with a multi-body system composed of rigid rotor and flexible foundation. The magnetic eccentricities of the shaft magnets are modelled using the distances (amplitudes) and directions (phase angles) between the shaft axis and the centre of the magnetic fields generated. A perturbation method, i.e. harmonic balancing, is used in order to evaluate the frequency response of the non-linear system.

The experimental validation of the model is carried out using a dedicated rotor-bearing system set-up. The test set-up consists of a vertical rigid shaft and disc supported by two passive magnetic bearings using axially-aligned neodymium cylinder magnets. The magnetic bearing housings are flexibly supported, allowing horizontal motions. The housings are connected to each other by means of elastic beams. The shaft is free in one end and coupled to a DC motor on the other by means of a flexible coupling. On the free end a disc is attached where imbalances and gyroscopic effect can be generated.

Comparison between theory and experiment shows high level of resemblance, which validates the theoretical model and the explanations for the quasi-static and dynamic responses. The magnetic eccentricities and mass imbalance effects are clearly detected and distinguished.
Sliding Mode Reconfigurable Control for Cosmic Rays Faults in Flight Systems
Authors: Ghodbane Azeddine , Saad Maarouf , Boland Jean-François , Thibeault Claude
Published: March 2015

In this paper, a FTFC system is designed to handle a cosmic rays fault affecting actuator control signal. The geometric approach is used to design the fault diagnosis module. This module determines the gravity of the fault and calculates its parameters. Based thereon, a new reconfigurable Sliding Mode Control law is designed and applied on the longitudinal linear model of the F-16 aircraft. Simulations are performed using Matlab®/Simulink® to show the effectiveness of the proposed approach.
An Enhanced Extraction Method Based on EEMD for Processing a Bearing Vibration Signal With Multiple Vibration Sources
Authors: Guo Wei
Published: March 2015

Condition monitoring and fault diagnosis for rolling element bearings is an imperative part for preventive maintenance procedures and reliability improvement of rotating machines. When a localized fault occurs at the early stage of real bearing failures, the impulses generated by the defect are relatively weak and usually overwhelmed by large noise and other higher-level macro-structural vibrations generated by adjacent machine components and machines. To indicate the bearing faulty state as early as possible, it is necessary to develop an effective signal processing method for extracting the weak bearing signal from a vibration signal containing multiple vibration sources. The ensemble empirical mode decomposition (EEMD) method inherits the advantage of the popular empirical mode decomposition (EMD) method and can adaptively decompose a multi-component signal into a number of different bands of simple signal components. However, the energy dispersion and many redundant components make the decomposition result obtained by the EEMD losing the physical significance. In this paper, to enhance the decomposition performance of the EEMD method, the similarity criterion and the corresponding combination technique are proposed to determine the similar signal components and then generate the real mono-component signals. To validate the effectiveness of the proposed method, it is applied to analyze raw vibration signals collected from two faulty bearings, each of which involves more than one vibration sources. The results demonstrate that the proposed method can accurately extract the bearing feature signal; meanwhile, it makes the physical meaning of each IMF clear.
Viscoelasticity Measurement of Softness by Indentation Devices for Evaluation of Human Skin
Authors: Sakuma Atsushi , Sango Yuma
Published: March 2015

In this paper, spherical indentation testing is studied to evaluate the viscoelasticity of soft materials like human skin. Here, the Hertzian contact theory is functionally extended to evaluate indentations for the thin tissues. In the expansions, the technique used for evaluating the thickness of finite specimens is first explained by analyzing the experimental results of indentations. Then, the viscoelasticity of soft materials with finite thickness is theoretically derived by defining an equivalent indentation strain for the analysis of the indentation process. The expansions are examined to evaluate its reliability by applying them to measure the viscoelasticity of some soft materials. Furthermore, this technology is applied to the elasticity investigation of the human skin. Especially, the measurement results of viscoelastic characteristics of the skin of human face are shown as the first report. The influences of sex and ultraviolet rays and so on are discussed to reveal the mechanics of human skin in this report. Moreover, it is discussed about the validity of the device which measures the elasticity of the skin of human face.
Joint Impact Forces of a Biped Walking on an Uneven Ground
Authors: Mojaddarasil Marzieh , Sadigh Mohammad Jafar
Published: March 2015

This paper looks into the impact forces applied to the joints of a biped walking on an uneven surface. In this vein, impact dynamics of the swing leg are studied by considering a simple two-link planar manipulator model which comes in contact with the ground. The effect of different parameters and factors on the magnitude of the joint impact forces is investigated. Specifically, it is observed how the elasticity of the shoe, the leg configuration, and the muscular flexibility of the joints affect the joint impact forces. The obtained results can be of practical importance in developing bipedal robots and in the diagnosis and treatment of human gait issues related to joint problems.
Human Identification for Human-Robot Interactions
Authors: Burns Brian , Samanta Biswanath
Published: March 2015

In co-robotics applications, the robots must identify human partners and recognize their status in dynamic interactions for enhanced acceptance and effectiveness as socially interactive agents. Using the data from depth cameras, people can be identified from a person’s skeletal information. This paper presents the implementation of a human identification algorithm using a depth camera (Carmine from PrimeSense), an open-source middleware (NITE from OpenNI) with the Java-based Processing language and an Arduino microcontroller. This implementation and communication sets a framework for future applications of human-robot interactions. Based on the movements of the individual in the depth sensor’s field of view, the program can be set to track a human skeleton or the closest pixel in the image. Joint locations in the tracked human can be isolated for specific usage by the program. Joints include the head, torso, shoulders, elbows, hands, knees and feet. Logic and calibration techniques were used to create systems such as a facial tracking pan and tilt servomotor mechanism. The control system presented here sets groundwork for future implementation into student built animatronic figures and mobile robot platforms such as Turtlebot.
Chaos in Inverted Flexible Pendulum With Tip Mass
Authors: Gandhi Prasanna , Meena Jaish
Published: March 2015

Flexible link systems are increasingly being used in the robotic and other applications. The dynamics of distributed parameter single flexible link system, especially in the vertical planes, is known to demonstrate chaotic behavior upon harmonic excitation. However, to the best of authors knowledge, chaotic dynamics of ultra-large deflection flexible systems with distributed and lumped parameters considered together has not been considered in the literature so far. Dynamics of a representative case, an inverted flexible pendulum with tip mass on cart system, is analysed in this paper. Experimental results on a custom built system consisting of link having 1. ultra large deformation (300 times thickness) as compared to thickness, 2. a tip mass, and 3. base fixed to a cart, under harmonic excitation under several frequencies were obtained. Poincaré maps with large set of data show successive progression with a small cluster of points to start with splitting into two clusters finally leading to butterfly figure of chaotic vibrations. Effect of variation of the excitation amplitude is also explored leading to interesting change in the patterns of Poincaré maps observed.
Reduction of GPS Noise for Precision Control of Robot Navigation in Confined Areas
Authors: Narvesen Andrew , Selekwa Majura
Published: March 2015

Most modern navigation systems solve the localization problem by extensively using global positioning system (GPS) data. Unfortunately the GPS data quality depends on several factors, which can lead to large positioning errors. Known GPS errors fall in two groups: either atmospheric errors, or multipath errors. Because of these errors, differential GPS systems have been developed using both ground based and satellite based reference systems. The cost of a differential GPS unit such as a Novatel range from a little over $2000 to over $9000, which can be prohibitive for use on certain home service robotic vehicles such as autonomous snow plows or autonomous lawn mowers. This paper discusses ways of mitigating GPS errors on low cost single frequency GPS units such as Copernicus II, Skytraq and U-Blox, which cost far less than $100 each, and hence are attractive for use in many robotic applications such as those mentioned above. The paper will present a model of GPS noise and use that model to process GPS data for use in navigation of an autonomous snow plow designed for use in residential driveways and side-walks; it will be supported by experimental results only.
Dynamics and Control of Four Wheeled Differentially Steered UGVs
Authors: Narvesen Andrew , Selekwa Majura F.
Published: March 2015

Autonomous navigation of ground vehicles is a growing research area. Skid steered wheeled ground vehicles are of interest because of the system’s relatively easy control parameters. Steered wheels require actuation and control for the steering and speed of the steered wheels while skid steering just requires actuation and control of the wheel speeds, usually just a left and right wheel speed. Four Wheeled differentially steered vehicles are built primarily for straight line motion since the instantaneous centers of zero velocities for the four wheels are always at infinity when there is no sliding in the wheels. When the vehicle has to negotiate a corner, it uses the differential velocities between sides to force the wheels to slide and perform the cornering maneuver. Maneuvering is difficult when the ground friction is very high because of undue stresses in the axle structure. This paper analyses the dynamics of such vehicles that relates the traction and skid friction forces and proposes a suitable control system. At this time, the paper is supported by simulation results while experimental work is still going on.
Visual-Servo Autonomous Robotic Manipulators for Capturing Non-Cooperative Target
Authors: Dong Gangqi , Zhu Z. H.
Published: March 2015

This paper presents a methodology of vision-based pose and motion estimation of non-cooperative targets as well as a control scheme for robotic manipulators to perform autonomous capture of non-cooperative targets. A combination of photogrammetry and extended Kalman filter is proposed for real time state estimation of the non-cooperative target. Once the vision-based estimation is obtained, a real state of the target regarding to the global frame is calculated based on the transformation matrices of coordinate frames. So as to make a capture, a desired state of the end effector is defined in accordance with the real state of the target aforementioned, and further a corresponding desired state of the robotic manipulator is derived by inverse kinematics. Then a close-loop control scheme is adopted to drive the robot to the desired state previously obtained. Experiments have been designed and implemented on a custom built six degrees of freedom robotic manipulator with an eye-in-hand configuration. The experimental results demonstrated the feasibility and effectiveness of the proposed methodology and control scheme.
Evaluation of Decalcification Induced Changes in Bone Strength Using Electrical Conductivity Measurements
Authors: Sevostianov Vladislav
Published: March 2015

The paper focuses on the effect of decalcification on microstructure and the mechanical and electrical properties of cortical bone. Decalcification is produced by placing the specimens into 5% vinegar acid for 72 hours. This acid treatment leads to a decrease in mass of the specimens 7.78 % (averaged over ten acid treated specimens). Microstructure of natural bone and acid treated bone is then compared using confocal microscopy. To estimate effect of acid treatment on electrical resistivity of bone, the specimens are rinsed and saturated with 0.9% NaCl solution for ten minutes. Then electrical resistance is measured by the four-point method and electrical resistivity is calculated. Averaging over ten acid treated specimens and ten control specimens show that decalcification lead to increase of electrical resistivity 5.85 times. Comparison of mechanical properties of natural and acid treated bones is done by three point bending using Instron 5882 testing machine. It is observed that 7.78 % mass loss in cortical bone yields reduction of the Young’s modulus about 2.7 times and bending strength of the specimens by 35%. A positive correlation between change in strength and Young’s modulus and electrical resistivity of the individual specimens is observed. The obtained results allows one to estimate changes in mechanical and electrical properties of bone from known losses in bone mass and, thus, non-destructively evaluate the decrease in bone strength through changes in electrical resistivity.
Design and Modeling of Hydraulic Pressure Energy Harvesters for Low Dynamic Pressure Environments
Authors: Skow Ellen , Cunefare Kenneth , Erturk Alper
Published: March 2015

Hydraulic Pressure Energy Harvesters (HPEHs) use the direct piezoelectric effect to extract electrical power from the dynamic pressure ripple present in hydraulic systems. As with other energy harvesters, an HPEH is intended to be an enabling technology for powering sensor nodes. To date, HPEH devices have been developed for high-pressure, high-dynamic pressure ripple systems. High-pressure applications are common in industrial hydraulics, where static pressures may be up to 35 MPa. Other fluid systems, such as cross-country pipelines as well as water distribution networks operate at much lower pressures, e.g., from around 1 to 4 MPa, with proportionally lower dynamic pressures. Single-crystal piezoelectric materials are incorporated into the HPEH design, along with means to increase the load transfer into the piezoelectric material as well as increased output harvester circuits, so as to increase the power output of these devices. The load transfer from the pressurized fluid into the piezoelectric material is through an interface, where the interface area may be designed such that the area exposed to the fluid is greater than the cross-sectional area of the piezoelectric, yielding higher stress in the material than the pressure in the fluid. Furthermore, given the relatively large capacitance of the piezoelectric elements used in HPEH devices, inductive-tuned resonant harvester circuits implemented with passive elements are feasible. HPEH devices integrating these features are shown to produce viable power outputs from low dynamic pressure systems.
Data-Driven Model-Based Fault Diagnosis in a Wind Turbine With Actuator Faults
Authors: Badihi Hamed , Rad Javad Soltani , Zhang Youmin , Hong Henry
Published: March 2015

Wind turbines are renewable energy conversion devices that are being deployed in greater numbers. However, today’s wind turbines are still expensive to operate, and maintain. The reduction of operational and maintenance costs has become a key driver for applying low-cost, condition monitoring and diagnosis systems in wind turbines. Accurate and timely detection, isolation and diagnosis of faults in a wind turbine allow satisfactory accommodation of the faults and, in turn, enhancement of the reliability, availability and productivity of wind turbines. The so–called model-based Fault Detection and Diagnosis (FDD) approaches utilize system model to carry out FDD in real-time. However, wind turbine systems are driven by wind as a stochastic aerodynamic input, and essentially exhibit highly nonlinear dynamics. Accurate modeling of such systems to be suitable for use in FDD applications is a rather difficult task. Therefore, this paper presents a data-driven modeling approach based on artificial intelligence (AI) methods which have excellent capability in describing complex and uncertain systems. In particular, two data-driven dynamic models of wind turbine are developed based on Fuzzy Modeling and Identification (FMI) and Artificial Neural Network (ANN) methods. The developed models represent the normal operating performance of the wind turbine over a full range of operating conditions. Consequently, a model-based FDD scheme is developed and implemented based on each of the individual models. Finally, the FDD performance is evaluated and compared through a series of simulations on a well-known large offshore wind turbine benchmark in the presence of wind turbulences, measurement noises, and different realistic fault scenarios in the generator/converter torque actuator.
Towards the Development of an Ontology-Based Product Requirement Model
Authors: Yaman Omer , Zhu Bicheng , Roy Utpal
Published: March 2015

Determination of appropriate product design criteria depends on the requirement specifications as well as their interrelations with other life cycle process information. Although the representation of the design requirements for creating a desirable product/part is a necessity, most of the time it has been carried out by the designer based on his/her own experiences. Such requirement handling processes need deep understanding of the product design, materials, manufacturing, working environments, finance and regulations, and are normally cost ineffective and error prone. Furthermore, very little attentions have been paid to the development of a structured requirement modeling for future intelligent applications. After a systematic study on the categorization of product design related information and requirements, this paper proposes an ontological framework for representing information and knowledge about the engineering product requirements. To demonstrate the use of the proposed requirement model and its role in the requirement management process, a case study related to an automotive brake rotor has been discussed in detail.
Numerical Study of Nonlinear and Transient Behaviors of a Variable Electromotive-Force Generator With an Adjustable Overlap Between the Rotor and the Stator Using the Finite Element Method
Authors: Agbormbai J. , Goudarzi N. , Zhu W. D.
Published: March 2015

A modified generator, referred to as the variable electromotive-force generator, is developed to enhance fuel efficiency of hybrid vehicles and expand operational range of wind turbines. Obtaining a numerical model that provides accurate estimates on the generator output power at different overlap ratios and rotor speeds, comparable with those from experimental results, would expand the use of the proposed modified generator in different applications. The general behavior of the generated electromotive forces at different overlaps and rotor speeds is in good agreement with those from experimental and analytical results at steady-state conditions. Employing generator losses due to hysteresis and eddy currents in a three-dimensional model would generate more realistic and comparable results with those from experiment. In this work, electromagnetic analysis of a modified two-pole DC generator with an adjustable overlap between the rotor and the stator at transient conditions is performed using finite element simulation in the ANSYS 3D Low Frequency Electromagnetics package. The model is meshed with tetrahedral or hexahedral elements, and the magnetic field at each element is approximated using a quadratic polynomial. For a fixed number of coils, two cases are studied; one with constant magnetic properties and the other with nonlinear demagnetization curves are studied.
Experimental Assessment of Emitted Dose From Valved Holding Chamber Devices
Authors: Oliveira Ricardo F. , Silva Manuel V. , Machado Ana V. , Oliveira Manuel , Cabral-Marques Helena Maria , Teixeira Senhorinha F. , Teixeira José Carlos
Published: March 2015

Due to the increasing worldwide incidence of asthma, a growing usage of inhalation devices has been observed. Some of the pressurized Metered Dose Inhalers (pMDI) limitations have been overcome by the introduction of newly and improved Valved Holding Chambers (VHC), resulting in good patient acceptance.

The efficiency is assessed by the VHC Emitted Dose (ED), i.e. the amount of drug available to the patient.

Using the pMDI salbutamol sulfate formulation (Ventolin® HFA-134a) as the test drug, several VHC devices were assessed. These latest were grouped by material characteristics: dissipative (OptiChamber Diamond®, AeroChamber Plus®, Vortex®, A2A Spacer®), non-dissipative (SpaceChamber Plus®, Compact SpaceChamber Plus®, Volumatic®) and stainless steel (Nebuchamber®).

The pMDI + VHC were assembled to a filter housing, which comprises an induction port with similar USP Throat dimensions, and connected to a vacuum pump (calibrated at 15, 26 and 40 L/min). Using UV-Vis Spectrophotometry equipment at 244 nm, it was possible to determine its concentration for later mass calculation. For all the VHC devices tested, the total mass recovery percentage was between 85% and 120%.

At 26 L/min, the Vortex® VHC has shown the highest ED (47.3 ± 1.8 %).

The ED may not be dependent on the volume of the VHC. Although, further analysis of the results suggests the existence of a linear correlation between the ED and the VHC body length.

SpaceChamber Plus® results show an increase of the ED and, subsequently, a decrease in VHC deposition fraction, with the increase of airflow.
Comparative Study of Evolutionary Algorithms for Parameter Identification of an Impact Oscillator
Authors: Banerjee Amit , Abu Mahfouz Issam
Published: March 2015

The use of non-classical evolutionary optimization techniques such as genetic algorithms, differential evolution, swarm optimization and genetic programming to solve the inverse problem of parameter identification of dynamical systems leading to chaotic states has been gaining popularity in recent years. In this paper, three popular evolutionary algorithms — differential evolution, particle swarm optimization and the firefly algorithm are used for parameter identification of a clearance-coupled-impact oscillator system. The behavior of impacting systems is highly nonlinear exhibiting a myriad of harmonic, low order and high order sub-harmonic resonances, as well as chaotic vibrations. The time-history simulations of the single-degree-of-freedom impact oscillator were obtained by the Neumark-β numerical integration algorithm. The results are illustrated by bifurcation graphs, state space portraits and Poincare’ maps which gives valuable insights on the dynamics of the impact system. The parameter identification problem relates to finding one set of system parameters given a chaotic or periodic system response as a set of Poincaré points and a different but known set of system parameters. The three evolutionary algorithms are compared over a set of parameter identification problems. The algorithms are compared based on solution quality to evaluate the efficacy of using one algorithm over another.
Anterior Spinal Cord Contusion on Porcine Model
Authors: Cliche Francis , Mac-Thiong Jean-Marc , Petit Yvan
Published: March 2015

Animal models are commonly used to study spinal cord injuries (SCI). These models aim to better understand the traumatic behaviour of the spinal cord in vivo. However, experimental SCI models usually simulate a posterior contusion of the spinal cord on small animals, which do not reproduce completely the SCI mechanisms in humans.

The objectives of the study are: 1) to develop an experimental anterior contusion of the spinal cord on porcine models, and 2) to compare biomechanical differences between ventral and dorsal approaches.

A total of 6 specimens were tested in vivo with a drop weight bench test. Impacts were produced at T10 with 5mm diameter impactor of 50g and dropped from a height of 100mm. Compression time was set to 5min for 4 specimens (2 ventral, 2 dorsal) and 60min for 1 ventral and 1 dorsal. The outcome measures were the compression displacement, blood pressure, heart rate and macroscopic inspection of the spinal cord.

This is the first study proposing an animal model of anterior SCI. Preliminary results suggest that there is a biomechanical difference between ventral and dorsal contusion approaches. A new bench test especially designed for ventral contusion will allow additional tests analyzing more variables, such as the motor evoked potentials and arterial blood flow.
High Rate Impact to the Human Calcaneus: A Micromechanical Analysis
Authors: Fielding Rebecca A. , Kraft Reuben H. , Tan X. G. , Przekwas Andrzej J. , Kozuch Christopher D.
Published: March 2015

An “underbody blast” (UBB) is the detonation of a mine or improvised explosive device (IED) underneath a vehicle. In recent military conflicts, the incidence of UBBs has led to severe injuries, specifically in the lower extremities The foot and ankle complex, particularly the calcaneus bone, may sustain significant damage. Despite the prevalence of calcaneal injuries, this bone’s unique properties and the progression of fracture and failure have not been adequately studied under high strain rate loading. This research discusses early efforts at creating a high-resolution computational model of the human calcaneus, with primary focus on modeling the fracture network through the complex microstructure of the bone and creating micromechanically-based constitutive models that can be used within full human body models. The ultimate goal of this ongoing research effort is to develop a micromechanics-based simulation of calcaneus fracture and fragmentation due to impact loading. With the goal of determining the basic mechanisms of stress propagation through the internal structure of the calcaneus, a two-dimensional model was employed for preliminary simulations with a plane-strain approximation. In this effort, a cadaveric calcaneus was scanned to a resolution of 55 μm using an industrial micro-computed tomography (microCT) scanner. A mid-sagittal plane slice of the scan was selected and post-processed to generate a 2D finite element mesh of the calcaneus that included marrow, trabecular bone, and cortical bone elements. The calcaneus was modeled using two-dimensional quadratic plane strain elements. A fixed boundary condition was applied to the portion of the calcaneus that, in situ, would be restrained by the talus. A displacement of 1.25 mm was applied to the heel of the calcaneus over 5 ms. In a typical result, following impact, the strain and stress are propagated throughout the cortical shell and then began to radiate into the bone into the bone along the trabeculae. Local stress concentrations can be observed in the trabecular structure in the posterior region of the bone following impact. Upon impact, cortical and trabecular bone show different stresses of 13MPa and 1 MPa, respectively, and exhibit complex high frequency responses. Observed results may offer insight into the wave interactions between the different materials comprising the calcaneus, such as impedance mismatch and refraction. Pore pressure in the marrow may be another important factor to consider in understanding stress propagation in the calcaneus.
Application of Variational Iteration Method in Nonlinear Free Vibration Analysis of Multi-Layered Nano-Scale Graphene Sheets
Authors: Sadri Mehran , Younesian Davood , Esmailzadeh Ebrahim
Published: March 2015

The nonlinear free vibration of multi-layered nano-scale graphene sheets is studied. Using the von Kármán and nonlocal continuum theories, large amplitude of vibration is included in the analysis as well as the size effect of nano-structure. The SSSS boundary condition is considered for the multi-layered graphene sheet and coupled nonlinear differential equations of motion of layers are taken into account based on Galerkin method. Variational iteration method (VIM) is employed as the solution procedure and nonlinear natural frequencies of the system are analytically determined. Two different geometries are taken into account and the analytical results are compared with frequencies obtained by numerical method. Finally, influence of geometrical parameters and amplitude of vibration on nonlinear frequencies of the system is examined.
Nonlinear Normal Modes and the LuGre Friction Model Parameter Identification
Authors: Hadji Abdallah , Mureithi Njuki
Published: March 2015

A Hybrid friction model has recently been developed by Azizian and Mureithi [1] to simulate the general friction behavior between surfaces in contact. However, identification of the model parameters remains an unresolved problem.

To identify the parameters of the friction model, the following quantities are required: contact forces (friction and impact forces), the slip velocity and displacement in the contact region. Direct measurement of these quantities is difficult. In the present work, a beam clamped at one end and simply supported with the consideration of friction effect at the other is used as a mechanical amplifier of the friction effects at the microscopic level. Using this simplified approach, the contact forces, the sliding velocity and the displacement can be indirectly obtained by measuring the beam vibration response. A new method based on nonlinear modal analysis to calculate the contact forces is developed in the present work. The method is based on the modal superposition principle and Fourier series expansion.

For the harmonic balance method, two approaches were tested. The approach based on sub-harmonic forms gave the best results.

Signal reconstruction made it possible to accurately identify the parameters of the hybrid friction model with a multiple step approach.
A Two-Fiber Anisotropic Constitutive Model of Human Brain With Intravoxel Heterogeneity of Fiber Orientation Using Diffusion Spectrum Imaging (DSI)
Authors: Garimella Harsha T. , Yuan Hao , Johnson Brian D. , Slobounov Semyon L. , Kraft Reuben H.
Published: March 2015

Sports-related concussion is a major public health problem in the United States that is estimated to occur in 1.6–3.8 million individuals annually, and is particularly common in football. Despite the significance and growing concerns about the potential long-term consequences of concussion, its biomechanical mechanisms are not fully understood. Since 1970’s computational head modeling has proved to be an efficient tool for establishment of health injury criteria and studies on head injury mitigation.

One important step in the computational modeling of the human head is to develop the mathematical material models (constitutive models) for the tissue. There have been many attempts to develop an accurate constitutive model for brain tissue. Recent experimental studies have highlighted the significant influence of axonal fibers on the non-linear and anisotropic behavior of brain tissue. Tractography based on diffusion tensor imaging (DTI) has been used in various previous studies to develop a constitutive model for human brain by including the anisotropic properties. Though DTI provides a macro scale information about the axonal fibers in the brain, it cannot directly describe multiple fiber orientations within a single voxel. To address this limitation within the DTI tractography, Diffusion Spectrum imaging (DSI), a variant of Diffusion Weighted Imaging, is used. DSI is generally used in deriving connectome sets and is sensitive to intravoxel heterogeneities of fiber orientation in diffusion direction caused by crossing fiber tracts and thus allowing for more accurate mapping of axonal trajectories than other diffusion methods. Thus more accurate constitutive models can be developed from the structural information about the human brain using DSI.

This paper extends, the anisotropic constitutive models developed previously, for two family of fibers which will be useful in the computational modeling of the human brain using DSI.
Towards a Micromechanical Model of Intervertebral Disc Degeneration Under Cyclic Loading
Authors: Makwana Anand R. , Krishna A. R. , Yuan Hao , Kraft Reuben H. , Zhou Xianlian , Przekwas Andrzei J. , Whitley Phillip
Published: March 2015

A number of activities subject the spinal cord [1] to various loading conditions that lead to disc degeneration. In this paper a brief overview on the understanding of the micromechanics and mechanisms of intervertebral disc degeneration is presented and extended to include water loss and disc height change. The focus is on a computational model of the intervertebral disc degeneration that attempts to capture the initiation and the progression of the damage mechanism under fatigue. This model can be used to study the effects on disc under short or long period biomechanical loading in work or combat environments.
Formability Characterization of Aluminum Lithium Alloys Used in Spacecraft Industry
Authors: Saxena Krishna Kumar , Mukhopadhyay Jyoti , Ramesh K. V.
Published: March 2015

Aluminum-Lithium (Al-Li) alloys launched in 1982 have gained a widespread focus in aerospace industry due to their unique combination of high elastic modulus and decreased density. As these alloys are under intensive development stage; various research agencies particularly those of defense, space and aviation, etc are still pursuing research regarding the behavior of these alloys. Since Al-Li alloys are used in aviation, their formability characterization is essential. Hence it is important to study the Forming Limit Diagram (FLD) which predicts the limit strains that can be imposed safely during forming. This paper focuses on the experimental strategies used in constructing the FLD of Al-Li alloys and to study the effect of punch velocity, strain hardening exponent and temperature on the level of FLD.
Parameter Optimization of a Linear-Quadratic-Gaussian Controller for a Proton Exchange Membrane Fuel Cell Using Genetic Algorithms
Authors: Rodríguez-Barrera Jairo A. , Parra-Raad Jaime A. , Roa-Prada Sebastián
Published: March 2015

Fuel cells are sources of clean energy which have become a key enabling technology in a wide spectrum of applications, ranging from automotive and aerospace applications to power supply for off-grid communities. The adequate functioning of a fuel cell requires permanent electrical power delivery to its load, operating at its maximum possible efficiency, even under load variations. Controlling the operating point of the fuel cell to manage changes in load conditions allows extending its service life. Several variables must be monitored and/or controlled to achieve optimal operating conditions of the fuel cell. This work deals with the design of a linear-quadratic-Gaussian, LQG, state-space controller for a proton exchange membrane fuel cell. The LQG controller is commonly used in fuel cell applications because it features an observer which can reconstruct states that are needed for the control strategy and that many times are difficult or too expensive to measure. The tuning of the parameters of the controller is performed by means of genetic algorithms procedures. The goal of the optimization is to prevent low levels of reactant gases due to sudden increases in the load. This will avoid damages to the membrane and other components of the stack while improving the overall performance of the system. The open loop and closed loop system response are presented using the lineal and non-lineal model of the plant. The response of the compensated system using the LQG controller is compared to the response using a basic state space controller, designed by the pole placing method, to assess the robustness of the LQG controller under disturbances. The results demonstrate the ability of the genetic algorithm technique to design a controller that can help preserving the integrity of the fuel cell while optimizing its performance.
Virtual Training of Assembly Tasks Using Virtual Reality Techniques and Haptic Systems
Authors: Gallegos-Nieto Enrique , Medellín-Castillo Hugo I. , González-Badillo Germánico , Lim Theodore
Published: March 2015

Traditional computer aided design (CAD) and computer aided assembly planning (CAAP) systems are still limited because they do not consider human experience and knowledge capture to support intuitively the assembly planning. Moreover, some aspects such as quality testing, shop floor layout, human ergonomics and physical constraints are not considered during the assembly evaluation. Virtual reality (VR) systems can be used to simulate, analyze and optimize manufacturing processes including assembly. The use of (VR) and haptic systems can improve the efficiency of assembly process planning, evaluation and training.

This paper describes an experiment conducted to investigate the benefits of a haptic aided virtual reality system for assembly training of real assembly tasks. Three groups of individuals with different level of training were considered in the evaluation. The first group received training by the virtual reality system including haptic feedback. The second group also received the same virtual training but without haptic feedback. The third group received no training in the virtual environment. Upon completion of the training, the assembly performance of the three different groups was evaluated by the construction of a real assembly task. The results have shown a significant improvement in the assembly performance of individuals who undertook a virtual training with force feedback, compared with those who did not take training.
Effects of Rod Shapes on the Drag Force of Particles in a Shear Flow
Authors: Musong Samuel , Feng Zhi-Gang , Chen Kai , Xu Quan-Wei
Published: March 2015

The understanding of its shape on the movement of microparticles and nanoparticles is crucial to the development of technologies of using these particles in drug delivery systems. The effect of shape on nanoparticles used in drug delivery, in particular, is a very active area of experimental investigation. Also, the determination of the drag force on nanoparticles of different shapes is very important in designing effective nanoparticle-mediated therapies. One of the common shapes of nanoparticles is rod. In this study we present a resolved discrete particle method (RDPM), which is also called the Direct Numerical Simulation (DNS), to investigate the effect of rod shapes on the drag force in a vicious fluid as compared to other particle shapes such as a sphere and a cone. These particles are assigned the same volume and placed in contact with the bottom wall in a simple shear flow. Their drag forces are computed numerically; it is found that the particle shape has a significant effect on the drag forces. In the case of a spherical particle, our results agree very well with the analytical results found in the literature. The drag force on a rod at different orientations and the motion of two rod-shaped particles of identical volume are in a shear flow are also examined. The motion of a rod-shaped particle and a cone-shaped particle in a shear flow at low Reynolds number is also compared.
Model of Drug Delivery to the Eye
Authors: Shafahi Maryam , Piroozan Parham
Published: March 2015

Ocular diseases cause vision deficiency and blindness in a substantial number of people in the world every day. Therefore, a controlled and sustained system of drug delivery to a specific spot within the eye is of interest for the ophthalmology community. The unique and complicated anatomy, physiology, and biochemistry of the eye make this organ highly resistant to drug delivery systems. The major challenge is to improve the efficiency of each treatment method along with avoiding the invasive techniques which damage the eye’s protective barrier tissues. In this work we make a computer model for the drug delivery to the anterior sections of the eye and provide a summary of transport characteristics of the eye, pharmacokinetics and efficacy of the utilized drugs. A two dimensional finite element model is utilized to solve the conservation of mass and momentum equations within different eye sub-domains such as cornea, anterior chamber, iris and sclera. The commercial software Comsol Multiphysics was utilized to obtain the profile of concentration in the eye and the grid independency of the numerical results has been checked. The results are being shown in terms of transient drug concentration profile in the eye subdomains. The influence of the modeling parameters on the efficiency of the drug delivery system is studied. The effect of physical variables such as drug molecular size and its bioavailability are investigated. The results are compared with the available literature data which are based on the drug diffusion within the domain.
Aquaponics: A Sustainable Food Production System
Authors: Shafahi Maryam , Woolston Daniel
Published: March 2015

Aquaponics is an eco-friendly system for food production utilizing aquaculture and hydroponics to cultivate fish and crop without soil. It is an inexpensive symbiotic cycle between the fish and plant. In an aquaponic system, fish waste (ammonia) is fed into the plant bed which acts as a bio-filter and takes the nitrate which is essential to grow vegetation. The fresh new water is then returned to the fish enclosure to restart the cycle. A unique advantage of an aquaponic system is conserving water more effectively compared to traditional irrigation systems. Conservation of water is accomplished by recirculating water between the plant bed and the fish habitat continuously. Organic fertilization of plants using dissolved fish waste is the other benefit of aquaponics. Utilizing plants as a natural alternative to other filters, requires less monitoring of water quality. In our project, an aquaponics system was designed and built in Lyle Center for Regenerative Studies at California State Polytechnic University of Pomona. The future purpose of our project is finding an optimized situation for the aquaponics system to produce food and save water more efficiently and eco-friendly.
Vibration Analysis of Machine Tool Spindle Systems: A Calibrated Finite Element Model
Authors: Hashemi Seyed M. , Sambandamurthy Hemachandran , Ghaemi Hamid
Published: March 2015

The effects of spindles vibrational behavior on the stability lobes and the chatter behavior of machine tools have been established, and the service life has been observed to reduce the system natural frequencies. In this paper, a ‘calibrated’ FEM model of the spindle system, where the bearings are modeled as linear spring elements, is introduced. The numerical models of a sample spindle system are developed in ANSYS® software using BEAM188 and SOLID187 elements. COMBIN14 elements are used to model the bearings; by varying the spring constant value of these elements the spindle’s fundamental frequency is tuned to match the nominal value, also verified experimentally. The beam element-based model is observed to converge faster than the one based on solid elements. The uncalibrated frequencies resulting from latter model are also found to be lower than those obtained from the former one, which could be associated with the shear/rotary inertia effects present in the SOLID187 element.
Enhancement of Ultrasonic Cavitation Yield by Dual-Frequency Sonication
Authors: Guo Sijia , Jiang Xiaoning
Published: March 2015

This paper reports the experimental study on the enhanced cavitation yield via dual-frequency ultrasonic sonication and the multi-frequency single-bubble cavitation bubble modeling. The cavitation yield was characterized using the PCD (passive cavitation detection) method. A dual-frequency (1.5 MHz/3 MHz) pulse ultrasound was used in the tests. It was found that the sonication of dual-frequency ultrasound can produce a significant increase in cavitation yield compared with single-frequency irradiation. The possible mechanisms of the enhanced effect were explained by the single-bubble cavitation model, where the calculated radiated pressure generated by acoustic bubble cavitation was found greater in dual-frequency cases. The findings from this paper are promising for the design of multi-frequency ultrasound system with enhanced cavitation for a number of biomedical, biological and chemical processing applications.