bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical and Experimental Simulations of the Wireless Energy Transmission and Harvesting by a Camera Pill
Authors: Shumbayawonda Elizabeth , Salifu Ali A. , Lekakou Constantina , Cosmas John P.
Published: March 2018

This paper investigates the energy transmitted to and harvested by a camera pill traveling along the gastrointestinal (GI) tract. It focuses on the transmitted electromagnetic (EM) energy in the frequency range of 0.18 to 2450 MHz and compares it to the mechanical energy due to the motion of the pill and the force exerted from the intestine in its peristalsis onto the pill, and the electrochemical energy due to the change of pH along the path of the pill. A comprehensive multilayer EM power transmission model is constructed and implemented in a numerical code, including power attenuation through each layer and multireflections at material interfaces. Computer simulations of EM power transmission through a multilayer abdomen to a pill traveling in the intestine are presented for the human abdominal cavity as well as phantom organs and phantom environments, coupled with corresponding experimental studies using these phantom components and environments. Two types of phantom abdomen are investigated: a ballistic gel and a multilayer duck breast. Phantom small intestine involves gelatin gel layers with embedded phantom chyme. Due to limitations related to the energy safety limit of skin exposure and energy losses in the transmission through the abdomen and intestines, inductive range frequencies are recommended which may yield energy harvesting of 10–50 mWh during 8 h of pill journey, complemented by about 10 mWh of mechanical energy and 10 mWh of electrochemical energy harvesting, in addition to about 330 mWh typically stored in the coin batteries of a camera pill.
Task-Constrained Optimal Motion Planning of Redundant Robots Via Sequential Expanded Lagrangian Homotopy
Authors: Dharmawan Audelia G. , Foong Shaohui , Soh Gim Song
Published: March 2018

Real-time motion planning of robots in a dynamic environment requires a continuous evaluation of the determined trajectory so as to avoid moving obstacles. This is even more challenging when the robot also needs to perform a task optimally while avoiding the obstacles due to the limited time available for generating a new collision-free path. In this paper, we propose the sequential expanded Lagrangian homotopy (SELH) approach, which is capable of determining the globally optimal robot's motion sequentially while satisfying the task constraints. Through numerical simulations, we demonstrate the capabilities of the approach by planning an optimal motion of a redundant mobile manipulator performing a complex trajectory. Comparison against existing optimal motion planning approaches, such as genetic algorithm (GA) and neural network (NN), shows that SELH is able to perform the planning at a faster rate. The considerably short computational time opens up an opportunity to apply this method in real time; and since the robot's motion is planned sequentially, it can also be adjusted to accommodate for dynamically changing constraints such as moving obstacles.
Convective Boiling of R-134a Near the Micro-Macroscale Transition Inside a Vertical Brazed Plate Heat Exchanger
Authors: Jin Kim Hyun , Liebenberg Leon , Jacobi Anthony M.
Published: March 2018

Heat transfer and pressure drop characteristics of R-134a boiling in a chevron-patterned brazed plate heat exchanger (BPHE) are studied experimentally. With corrugated BPHE channels having hydraulic diameter of 3.4 mm and low refrigerant mass flux, boiling near the micro-macroscale transition is speculated. Heat exchanger performance is characterized with varying mass flux (30–50 kgm−2s−1), saturation pressure (675 kPa and 833 kPa), heat flux (0.8 and 2.5 kWm−2), and vapor quality (0.1–0.9). The two-phase refrigerant heat transfer coefficient increases with heat flux as often observed during nucleate boiling. It also weakly increases with saturation pressure and the associated lower latent heat during convective boiling; heat transfer is improved by the decreased liquid film thickness surrounding confined bubbles inside the narrow BPHE channels, which is the main characteristic of microscale boiling. As often observed in macroscale boiling, the inertial forces of the liquid and vapor phases cause an unsteady annular film, leading to premature partial dryout. The onset of dryout is accelerated at the lower saturation pressure, due to increased surface tension, another microscale-like characteristic. Higher surface tension retains liquid in sharp corners of the corrugated channel, leaving lateral surface areas of the wall dry. Two-phase pressure drop increases with mass flux and vapor quality, but with decreasing saturation pressure. Dryout decreases the friction factor due to the much lower viscosity of the gas phase in contact with the wall. Several semi-empirical transition criteria and correlations buttress the current analyses that the thermal-fluidic characteristics peculiar to BPHEs might be due to macro-microscale transition in boiling.
Kinematics, Workspace, and Singularity Analysis of a Parallel Robot With Five Operation Modes
Authors: Chablat Damien , Kong Xianwen , Zhang Chengwei
Published: March 2018

Most multimode parallel robots can change operation modes by passing through constraint singularities. This paper deals with a comprehensive kinematic study of a three degrees-of-freedom (DOF) multimode three-PRPiR parallel robot developed at Heriot-watt University. This robot is able to reach several operation modes without crossing any constraint singularity by using lockable Pi and R joints. Here, a Pi joint may act as a 1DOF planar parallelogram if its lockable P (prismatic) joint is locked or a 2DOF RR serial chain if its lockable P joint is released. The operation modes of the robot include a 3T operation mode and four 2T1R operation modes with two different directions of the rotation axis of the moving platform. The inverse kinematics and forward kinematics of the robot in each operation mode are dealt with in detail. The joint space and workspace analysis of the robot allow us to know the regions of the workspace that the robot can reach in each operation mode. It is shown that the robot is able to change assembly mode in one operation mode by passing through another operation mode.
Tribological Properties of Al 7075 Alloy and 7075/Al2O3 Composite Under Two-Body Abrasion: A Statistical Approach
Authors: Sardar Santanu , Kumar Karmakar Santanu , Das Debdulal
Published: March 2018

Tribological properties, i.e., wear rate, coefficient of friction (COF), and roughness of worn surfaces of an Al-Mg-Zn-Cu alloy and its composite reinforced with 20 wt % Al2O3 particles developed by stir-casting method have been studied and compared under two-body abrasion considering four independent control factors, i.e., load, abrasive grit size, sliding distance, and velocity each at three different levels. Design of test conditions and analyses of output responses have been performed employing standard Taguchi L27 orthogonal array, signal-to-noise ratio, analysis of variance technique, and regression method. Irrespective of wear conditions, composite exhibits lower wear rate and reduced COF with reference to base alloy owing to the load bearing ability and better wear resistance capability of Al2O3 particles. Roughness of worn surfaces of composite is, however, found to be higher over base alloy due to nonuniform abrasion in case of composite that generates the protruded Al2O3 particles on contact surfaces as the surrounding soft matrix is easily removed. For all three tribo-responses of both materials, the most influential factor is identified as grit size followed by load and then, grit size-load interaction except for the roughness of worn surfaces where the influence of sliding distance is also considerable. Linear regression models with excellent predictability have been developed for all tribo-characteristics separately for base alloy and composite. The predominant mechanisms of abrasion are identified as plowing and microcutting for base alloy, but delamination for composite.
Effect of Molybdenum on the Wear Properties of (Ti,Mo)C-TiB2-Mo2B Particles Reinforced Fe-Based Laser Cladding Composite Coatings
Authors: Zhang M. , Luo S. X. , Liu S. S. , Wang X. H.
Published: March 2018

(Ti,Mo)C, TiB2, and Mo2B particles reinforced Fe-based composite coatings were fabricated by laser cladding process. The effects of Molybdenum (Mo) on the microstructure and wear properties of the coatings were investigated. The results show that block-like or cuboidal TiB2, Mo2B and flower-like (Ti, Mo)C ceramics reinforcements were formed in the coatings. The size of reinforcements reduced with the increasing of FeMo70. However, cracks were found in the coating, while the addition of FeMo70 exceeded 9 wt %. The laser cladding coating presented a good wear resistance with a 9 wt % addition of FeMo70. With the increasing of FeMo70, the coatings enhanced the capability of resisting microcutting, microplowing, and surface plastic deformation.
System Dependence of Running-In Attractor Derived From Lubricated Sliding Contact of Steel Alloys 52100 and 1045
Authors: Zhou Yuankai , Zuo Xue , Zhu Hua , Fan Yujie
Published: March 2018

The steady-state described by running-in attractor in the perspective of nonlinearity, is closely dependent on the running-in parameters. To study the dependence of running-in attractor on system parameters, pin-on-disk friction tests were performed. A suitable contact between pin and disk was ensured by a self-adaptive pin holder, standard block, and self-adapting amendment with sandpaper. Range analysis of correlation dimension, predictability, and entropy shows that running-in attractor is system dependent, which is manifested by the dependence of nonlinear parameters of the attractor on the running-in parameters. Further results indicate that the correlation dimension and entropy increase with load and velocity, but decrease along with initial roughness of a harder counterface, and predictability shows an inverse variation tendency with correlation dimension and entropy.
The Efficiency of Dodecafluoro-2-Methylpentan-3-One on Suppressing the Lithium Ion Battery Fire
Authors: Wang Qingsong , Li Ke , Wang Yu , Chen Haodong , Duan Qiangling , Sun Jinhua
Published: March 2018

To investigate the efficiency of dodecafluoro-2-methylpentan-3-one (C6F-ketone) extinguishing agent on suppressing the lithium titanate battery fire, an experimental system was devised to implement suppression test. One 5 kW electric heater was placed at the bottom of the battery to cause the thermal runaway. The extinguishing agents of CO2 and C6F-ketone with different pressures were performed to suppress lithium ion battery (LIB) fire. The temperatures of the battery and the flame, the ignition time, the release time of the agent, the release pressure of the agent, the time to extinguish the fire, the battery mass loss, and the mass of used agent were obtained and compared in different aspects. The experimental results reveal that the lithium titanate battery fire can be suppressed by C6F-ketone within 30 s; the results further show that CO2 is incapable of fully extinguishing the flame over the full duration of the test carried out. Therefore, C6F-ketone extinguishing agent is a good candidate to put down the LIB fire.
Thermal Simulation of the Symmetric and Asymmetric Arrangement of Barriers on Heat Transfer Enhancement in a Porous Gas Heat Exchanger
Authors: Mehdi Keshtkar Mohammad , Dadkhodazadeh Mohammad
Published: March 2018

In this paper, affecting parameters of porous medium to improve the rate of convective heat transfer in a two-dimensional porous gas heat exchanger (PGHE) for two arrangements (symmetric and asymmetric) of barriers are numerically investigated. Two barriers have been located on the top and bottom walls and one obstacle was placed in the central zone of the PGHE. In the present study, solving the momentum and energy equations has been done by Lattice–Boltzmann method with multiple-relaxation-time (LBM-MRT). The boundary conditions in both arrangements include the left and right walls which are kept at the cold constant temperature and both top and bottom walls are insulated. There is a volumetric heat source within the PGHE. The temperature of barriers and fixed obstacle are kept at hot temperature. In this study, impact of effective parameters in porous medium and heat transfer including dimensionless number of Darcy, porosity, and Rayleigh number on the flow and temperature fields has been investigated. According to the numerical results, it has been shown that the porous medium and barriers cause increase and improvement in the heat transfer within PGHE in both symmetrical and asymmetrical arrangements. The results also demonstrate that as dimensionless Darcy number increases, more convection occurs within the chamber. Examining arrangement of barriers shows that in asymmetrical arrangement, more space appears in chamber and convective heat transfer is done better.
Compressible Large Eddy Simulation of a Francis Turbine During Speed-No-Load: Rotor Stator Interaction and Inception of a Vortical Flow
Authors: Trivedi Chirag
Published: March 2018

This work investigates the unsteady pressure fluctuations and inception of vortical flow in a hydraulic turbine during speed-no-load conditions. At speed-no-load (SNL), the available hydraulic energy dissipates to the blades without producing an effective torque. This results in high-amplitude pressure loading and fatigue development, which take a toll on a machine's operating life. The focus of the present study is to experimentally measure and numerically characterize time-dependent pressure amplitudes in the vaneless space, runner and draft tube of a model Francis turbine. To this end, ten pressure sensors, including four miniature sensors mounted in the runner, were integrated into a turbine. The numerical model consists of the entire turbine including Labyrinth seals. Compressible flow was considered for the numerical study to account for the effect of flow compressibility and the reflection of pressure waves. The results clearly showed that the vortical flow in the blade passages induces high-amplitude stochastic fluctuations. A distinct flow pattern in the turbine runner was found. The flow near the blade suction side close to the crown was more chaotic and reversible (pumping), whereas the flow on the blade pressure side close to the band was accelerating (turbine) and directed toward the outlet. Flow separation from the blade leading edge created a vortical flow, which broke up into four parts as it traveled further downstream and created high-energy turbulent eddies. The source of reversible flow was found at the draft tube elbow, where the flow in the center core region moves toward the runner cone. The vortical region located at the inner radius of the elbow gives momentum to the wall-attached flow and is pushed toward the outlet, whereas the flow at the outer radius is pushed toward the runner. The cycle repeats at a frequency of 22.3 Hz, which is four times the runner rotational speed.
Performance Analysis of Solar-Assisted Desiccant Cooling System Cycles in World Climate Zones
Authors: Ali Muzaffar , Vukovic Vladimir , Muhammad Ali Hafiz , Ahmed Sheikh Nadeem
Published: March 2018

The demand for affordable, environment-friendly, and reliable water conditioning systems has led to the introduction of several standalone and/or hybrid alternatives. The technology of desiccant evaporative cooling (DEC) has proven to be dependable and has gained success at places where initially it was deemed unfeasible. Today, a number of related technologies and configurations are available. Among them, solar-assisted desiccant cooling system (SADCS) offers a cheap eco-friendly alternative, especially in hybrid configurations. Most studies have investigated the performance of numerous SADCS configurations in specific climatic conditions; however, at the global- and system-level scale, no such study is available. The current study investigates five different SADCS configurations using equation-based object-oriented modeling and simulation approach in five different climatic conditions. The selected climatic conditions cover a wide range of global weather data including arid/semiarid (Karachi), dry summer tropical (Adelaide), and mesothermal (Sao Paulo, Shanghai) to continental conditions (Vienna). The performance of all selected SADCS configurations (ventilation cycle, recirculation and ventilated-recirculation cycles, dunkle and ventilated-dunkle cycle) is analyzed for specified cooling design day of the selected cities. A uniform system control strategy based on the idea of displacement distribution (ventilation) system is used for each configuration and climatic zone. By monitoring their performances based on the values of cooling capacity (CC) and coefficient of performance (COP), the best SADCS configuration is proposed for each considered climatic condition in the world. The results revealed that the climates of Vienna, Sao Paulo, and Adelaide favor the use of ventilated-dunkle cycle configuration with average COP of 0.36, 0.84, and 0.93, respectively, while ventilation cycle based on DEC configuration suits the climate of Karachi and Shanghai with an average COP of 2.32 and 2.90, respectively.
Correlation of Interfacial Friction Coefficients for Predicting Countercurrent Flow Limitation at a Sharp-Edged Lower End of Vertical Pipes
Authors: Murase Michio , Kusunoki Takayoshi , Nishida Koji , Goda Raito , Tomiyama Akio
Published: March 2018

One-region (1-R) sensitivity computations with the annular-flow model were carried out for countercurrent flow limitation (CCFL) at a sharp-edged lower end in vertical pipes to generalize the prediction method for CCFL there (i.e., predicting effects of diameters and fluid properties on CCFL characteristics). In our previous study, we selected a correlation of interfacial friction coefficients, fi, with a function of average void fraction which gave a good prediction of the trend for air–water CCFL data, and we modified it to get good agreement with steam–water CCFL data under atmospheric pressure conditions, but it failed to predict CCFL reasonably at high pressure conditions. We recently found a Russian report on CCFL data at high pressure conditions, by which we improved the fi correlation using the dimensionless diameter and the viscosity ratio or density ratio of gas and liquid phases to get good agreement with CCFL data at high pressures. The improved fi correlation with the viscosity ratio and the improved fi correlation with the density ratio gave similar computed results, but the number of adjustment functions was one for the density ratio and two for the viscosity ratio (i.e., minimum value of two functions).
Analysis of an Approach for Detecting Arc Positions During Vacuum Arc Remelting Based on Magnetic Flux Density Measurements
Authors: Soler Miguel F. , Niemeyer Kyle E.
Published: March 2018

Vacuum arc remelting (VAR) is a melting process for the production of homogeneous ingots, achieved by applying a direct current to create electrical arcs between the input electrode and the resultant ingot. Arc behavior drives quality of the end product, but no methodology is currently used in VAR furnaces at large scale to track arcs in real time. An arc position sensing (APS) technology was recently developed as a methodology to predict arc locations using magnetic field values measured by sensors. This system couples finite element analysis of VAR furnace magnetostatics with direct magnetic field measurements to predict arc locations. However, the published APS approach did not consider the effect of various practical issues that could affect the magnetic field distribution and thus arc location predictions. In this paper, we studied how altering assumptions made in the finite element model affect arc location predictions. These include the vertical position of the sensor relative to the electrode–ingot gap, a varying electrode–ingot gap size, ingot shrinkage, and the use of multiple sensors rather than a single sensor. Among the parameters studied, only vertical distance between arc and sensor locations causes large sources of error and should be considered further when applying an APS system. However, averaging the predicted locations from four evenly spaced sensors helps reduce this error to no more than 16% for a sensor position varying from 0.508 m below and above the electrode–ingot gap height.
Bore Cylindricity in Finish Cylinder Boring
Authors: Chen Lei , Yang Juhchin A. , Shih Albert J.
Published: March 2018

Finish boring is a machining process to achieve the cylinder bore dimensional and geometrical accuracy. The bore cylindricity error sources, including the workpiece thermal expansion and deformation due to cutting and clamping forces, and spindle radial error motion, in finish boring were identified using combined experimental and finite element method (FEM) analysis. Experiments were conducted to measure the workpiece temperature, cutting and clamping forces, spindle error, and bore shape. FEM analysis of the workpiece temperature, thermal expansion, and deformation due to cutting and clamping forces was performed. The coordinate measurement machine (CMM) measurements of the bore after finish boring showed the 5.6 μm cylindricity and a broad spectrum from the second to tenth harmonics. The FEM revealed the effects of workpiece thermal expansion (1.7 μm cylindricity), deformation due to cutting force (0.8 μm cylindricity), and clamping force (1.9 μm cylindricity) on the finished bore and the dominance by the first to third harmonics using the three-jaw fixture. The spindle synchronous radial error motion (3.2 μm cylindricity) was dominated by the fourth and higher order harmonics and matched well with the high (above the fourth) harmonics in CMM measurements (2.9 μm cylindricity). The spindle error was the dominant error source for bore cylindricity in this finish boring study, contributing to about half of the total cylindricity error.
Technology Evolution Prediction Using Lotka–Volterra Equations
Authors: Zhang Guanglu , McAdams Daniel A. , Shankar Venkatesh , Mohammadi Darani Milad
Published: March 2018

During the development planning of a new product, designers and entrepreneurs rely on the prediction of product performance to make business investment and design strategy decisions. Moore's law and the logistic S-curve model help make such predictions but suffer several drawbacks. In this paper, Lotka–Volterra equations are used to describe the interaction between a product (system technology) and the components and elements (component technologies) that are combined to form the product. The equations are simplified by a relationship table and maturation evaluation in a two-step process. The performance data of the system and its components over time are modeled by simplified Lotka–Volterra equations. The methods developed here allow designers, entrepreneurs, and policy makers to predict the performances of a product and its components quantitatively using the simplified Lotka–Volterra equations. The methods also shed light on the extent of performance impact from a specific module (component technology) on a product (system technology), which is valuable for identifying the key features of a product and for making outsourcing decisions. Smartphones are used as an example to demonstrate the two-step simplification process. The Lotka–Volterra model of technology evolution is validated by a case study of passenger airplanes and turbofan aero-engines. The case study shows that the data fitting and predictive performances of Lotka–Volterra equations exceed those of extant models.
Overconstrained Mechanisms Derived From RPRP Loops
Authors: Hsu Kuan-Lun , Ting Kwun-Lon
Published: March 2018

This paper addresses the assembly strategy capable of deriving a family of overconstrained mechanisms systematically. The modular approach is proposed. It treats the topological synthesis of overconstrained mechanisms as a systematical derivation rather than a random search. The result indicates that a family of overconstrained mechanisms can be constructed by combining legitimate modules. A spatial four-bar linkage containing two revolute joints (R) and two prismatic joints (P) is selected as the source-module for the purpose of demonstration. All mechanisms discovered in this paper were modeled and animated with computer-aided design (CAD) software and their mobility were validated with input–output equations as well as computer simulations. The assembly strategy can serve as a self-contained library of overconstrained mechanisms.
A Method for Matching Two-Stage Turbocharger System and Its Influence on Engine Performance
Authors: Wu Binyang , Han Zhiqiang , Yu Xiaoyang , Zhang Shunkai , Nie Xiaokun , Su Wanhua
Published: March 2018

Matching of a two-stage turbocharging system is important for high efficiency engines because the turbocharger is the most effective method of exhaust heat recovery. In this study, we propose a method to match a two-stage turbocharging system for high efficiency over the entire range of operational conditions. Air flow is an important parameter because it influences combustion efficiency and heat load performance. First, the thermodynamic parameters of the engine and the turbocharging system are calculated in eight steps for selecting and matching the turbochargers. Then, by designing the intercooler intensity, distribution of pressure ratio, and compressor operational efficiency, it is ensured that the turbochargers not only meet the air flow requirements but also operate with high efficiency. The concept of minimum total drive power of the compressors is introduced at a certain boost pressure. It is found that the distribution of pressure ratio of the high- and low-pressure (LP) turbocharger should be regulated according to the engine speed by varying the rack position of the variable geometry turbocharger (VGT) to obtain the minimum total drive work. It is verified that two-stage turbochargers have high efficiency over the entire range of operational conditions by experimental research. Compared with the original engine torque, low-speed torque is improved by more than 10%, and the engine low fuel consumption area is broadened.
Comparative Analysis on Traumatic Brain Injury Risk Due to Primary and Secondary Impacts in a Pedestrian Sideswipe Accident
Authors: Tamura Atsutaka , Hasegawa Junji , Koide Takao
Published: March 2018

A series of pedestrian sideswipe impacts were computationally reconstructed; a fast-walking pedestrian was collided laterally with the side of a moving vehicle at 25 km/h or 40 km/h, which resulted in rotating the pedestrian's body axially. Potential severity of traumatic brain injury (TBI) was assessed using linear and rotational acceleration pulses applied to the head and by measuring intracranial brain tissue deformation. We found that TBI risk due to secondary head strike with the ground can be much greater than that due to primary head strike with the vehicle. Further, an “effective” head mass, meff, was computed based upon the impulse and vertical velocity change involved in the secondary head strike, which mostly exceeded the mass of the adult head-form impactor (4.5 kg) commonly used for a current regulatory impact test for pedestrian safety assessment. Our results demonstrated that a sport utility vehicle (SUV) is more aggressive than a sedan due to the differences in frontal shape. Additionally, it was highlighted that a striking vehicle velocity should be lower than 25 km/h at the moment of impact to exclude the potential risk of sustaining TBI, which would be mitigated by actively controlling meff, because meff is closely associated with a rotational acceleration pulse applied to the head involved in the final event of ground contact.
An Approach to Uncertainty Identification in the Valuation of
Transactive Energy Systems
Authors: Veeramany Arun , Woodward James T. , Hammerstrom Donald J.
Published: March 2018

Valuation of transactive energy (TE) systems should be supported by a structured and systematic approach to uncertainty identification, assessment, and treatment in the interest of risk-informed decision making. The proposed approach, a variation of fault tree analysis, is anticipated to support valuation analysts in analyzing conventional and transactive system scenarios. This approach allows for expanding the entire tree up to the level of minute details or collapsing them to a level sufficient enough to get an overview of the problem. Quantification scheme for the described approach lends itself for valuation. The method complements value exchange analysis, simulation, and field demonstration studies. The practicality of the proposed approach is demonstrated through uncertainty assessment of the smart grid interoperability panel peak heat day scenario.
Some Kinds of the Controllable Problems for Fuzzy Control Dynamic Systems
Authors: Phu N. D. , Tri P. V. , Ahmadian A. , Salahshour S. , Baleanu D.
Published: March 2018

In this work, we have discussed the fuzzy solutions for fuzzy controllable problem, fuzzy feedback problem, and fuzzy global controllable (GC) problems. We use the method of successive approximations under the generalized Lipschitz condition for the local existence and furthermore, we have described the contraction principle under suitable conditions for global existence and uniqueness of fuzzy solutions. We have too the GC results for fuzzy systems. Some examples and computer simulation illustrating our approach are also given for these controllable problems.
Automatic Toolpath Generation for Heterogeneous Objects Manufactured by Directed Energy Deposition Additive Manufacturing Process
Authors: Xiao Xinyi , Joshi Sanjay
Published: March 2018

A heterogeneous object (HO) refers to a solid component consisting of two or more material primitives distributed either continuously or discontinuously within the object. HOs are commonly divided into three categories. The first category has distinct material domains separating the different materials. The second, called functionally graded materials (FGMs), has continuous variation of material composition that produces gradient in material properties. The third category allows for any combinations of the first two categories within the same part. Modeling and manufacturing of HOs has recently generated more interest due to the advent of additive manufacturing (AM) technology that makes it possible to build such parts. Directed energy deposition (DED) processes have the potential for depositing multiple powdered materials in various compositions in the process of creating a single layer of material. To make this possible, tool paths that provide proper positioning of the deposition head and proper control over the material composition are required. This paper presents an approach for automatically generating the toolpath for any type of HO considering the material composition changes that are required on each layer. The toolpath generation takes into account the physical limitations of the machine associated with powder delivery and ability to continually grade the materials. Simulation results using the toolpath generation methodology are demonstrated by several example parts.
Gaming the System: An Agent-Based Model of Estimation Strategies and their Effects on System Performance
Authors: Meluso John , Austin-Breneman Jesse
Published: March 2018

Parameter estimates in large-scale complex engineered systems (LaCES) affect system evolution, yet can be difficult and expensive to test. Systems engineering uses analytical methods to reduce uncertainty, but a growing body of work from other disciplines indicates that cognitive heuristics also affect decision-making. Results from interviews with expert aerospace practitioners suggest that engineers bias estimation strategies. Practitioners reaffirmed known system features and posited that engineers may bias estimation methods as a negotiation and resource conservation strategy. Specifically, participants reported that some systems engineers “game the system” by biasing requirements to counteract subsystem estimation biases. An agent-based model (ABM) simulation which recreates these characteristics is presented. Model results suggest that system-level estimate accuracy and uncertainty depend on subsystem behavior and are not significantly affected by systems engineers' “gaming” strategy.
Energy-Optimal Hopping in Parallel and Series Elastic One-Dimensional Monopeds
Authors: Yesilevskiy Yevgeniy , Gan Zhenyu , David Remy C.
Published: March 2018

In this paper, we examine the question of whether parallel elastic actuation or series elastic actuation is better suited for hopping robots. To this end, we compare and contrast the two actuation concepts in energy optimal hopping motions. To enable a fair comparison, we employ optimal control to identify motion trajectories, actuator inputs, and system parameters that are optimally suited for each actuator concept. In other words, we compare the best possible hopper with parallel elastic actuation to the best possible hopper with series elastic actuation. The optimizations are conducted for three different cost functions: positive mechanical motor work, thermal electrical losses, and positive electrical work. Furthermore, we look at three representative cases for converting rotary motor motion to linear leg motion in a legged robot. Our model featured an electric DC-motor model, a gearbox with friction, damping in the leg spring, and contact collisions. We find that the optimal actuator choice depends both on the cost function and conversion of motor motion to leg motion. When considering only thermal electrical losses, parallel elastic actuation always performs better. In terms of positive mechanical motor work and positive electrical work, series elastic actuation is better when there is little friction in the gear-train. For higher gear-train friction parallel elastic actuation is more economical for these cost functions as well.
Dynamically Feasible Periodic Trajectories for Generic Spatial Three-Degree-of-Freedom Cable-Suspended Parallel Robots1
Authors: Mottola Giovanni , Gosselin Clément , Carricato Marco
Published: March 2018

Cable-suspended robots may move beyond their static workspace by keeping all cables under tension, thanks to end-effector inertia forces. This may be used to extend the robot capabilities, by choosing suitable dynamical trajectories. In this paper, we consider three-dimensional (3D) elliptical trajectories of a point-mass end effector suspended by three cables from a base of generic geometry. Elliptical trajectories are the most general type of spatial sinusoidal motions. We find a range of admissible frequencies for which said trajectories are feasible; we also show that there is a special frequency, which allows the robot to have arbitrarily large oscillations. The feasibility of these trajectories is verified via algebraic conditions that can be quickly verified, thus being compatible with real-time applications. By generalizing previous studies, we also study the possibility to change the frequency of oscillation: this allows the velocity at which a given ellipse is tracked to be varied, thus providing more latitude in the trajectory definition. We finally study transition trajectories to move the robot from an initial state of rest (within the static workspace) to the elliptical trajectory (and vice versa) or to connect two identical ellipses having different centers.
Shakedown Limits for Hillside Nozzles in Cylindrical Vessels
Authors: Bakry Ahmed K. , Saleh Chahinaz A. , Megahed Mohammad M.
Published: March 2018

This research paper is concerned with the mechanical behavior of the cylindrical vessels with hillside nozzles when subjected to both pressure and nozzle bending loads in cyclic forms. The influence of hillside angle on shakedown (SD) limits of the connection under cyclic pressure and combined steady pressure with cyclic nozzle bending is investigated. A shell finite element analysis model is built for the assembly using five different hillside angles ranging from 0 deg to 40 deg. Shakedown limits are determined by a direct technique known as the nonlinear superposition method (NSM). Bree diagrams for cyclic out of plane opening (OPO)/in plane (IP) nozzle moments combined with steady internal pressure are determined. The results show an increase in both OPO and IP shakedown moments as the hillside angle is increased. In addition, the OPO shakedown limit moments for all hillside angles were found to be insensitive to the level of internal pressure; this differs from the IP shakedown moment which starts to decrease with pressure for the high pressures.
Coefficient of Performance of Battery Running and Charging by Magnet Generator Bedini
Authors: Sriphan Uthai , Kerdchang Pongsakorn , Prommas Ratthasak , Bunnang Tika
Published: March 2018

In this research study, the performance in battery running and charging of an original circuit design is compared with the performance between the developed DC–DC boost converter running and charging replication circuit design. Bedini generators are a kind of magnetic generator designed by John Bedini on the basis of zero point technology. The generator serves as a self-battery charger. In this study, the two types of circuit design, namely, the original and the replication, are examined in terms of performance in battery running and charging. The DC–DC boost converter offers greater voltage boost capabilities and hence has the potential to enhance step-up power conversions. The novel design was a prototype of the six-pole eight-neodymium magnet generator, which potentially offers free energy and could therefore serve as an alternative means of addressing energy needs when the current nonrenewable fuel sources have been wholly depleted in the future. The coefficient of performance (COP) for the battery performance of both designs is calculated in this study in order to allow comparisons to be drawn. Upon analysis, it is discovered that the DC–DC boost converter circuit is both practical and efficient, offering a high level of step-up power conversion capacity for battery running and charging. The COP of the new system provides a significant increase in COP when compared to the original design.
Three-Objective Optimization of a Centrifugal Pump to Reduce Flow Recirculation and Cavitation
Authors: Shim Hyeon-Seok , Kim Kwang-Yong , Choi Young-Seok
Published: March 2018

This work presents a three-objective design optimization of a centrifugal pump impeller to reduce flow recirculation and cavitation using three-dimensional (3D) Reynolds-averaged Navier–Stokes equations. A cavitation model was used to simulate the multiphase cavitating flow inside the centrifugal pump. The numerical results were validated by comparing them with experimental data for the total head coefficient and critical cavitation number. To achieve the optimization goals, blockage at 50% of the design flow rate, hydraulic efficiency at the design flow rate, and critical cavitation number for a head-drop of 3% at 125% of the design flow rate were selected as the objective functions. Based on the results of the elementary effect (EE) method, the design variables selected were the axial length of the blade, the control point for the meridional profile of the shroud, the inlet radius of the blade hub, and the incidence angle of tip of the blade. Kriging models were constructed to approximate the objective functions in the design space using the objective function values calculated at the design points selected by Latin hypercube sampling (LHS). Pareto-optimal solutions were obtained using a multi-objective genetic algorithm (MOGA). Six representative Pareto-optimal designs (POD) were analyzed to evaluate the optimization results. The PODs showed large improvements in the objective functions compared to the baseline design. Thus, both the hydraulic performance and the reliability of the centrifugal pump were improved by the optimization.
Drag and Side Force Analysis on Bicycle Wheel–Tire Combinations
Authors: Crane Robert , Morton Chris
Published: March 2018

Aerodynamic forces on bicycle racing wheels were investigated experimentally in a wind tunnel facility at the University of Calgary. The main geometric parameters investigated were the tire sidewall width, (21.40 mm≤T≤26.15 mm), rim depth, (55 mm≤D≤90 mm), rim width, (19.28 mm≤W≤25.75 mm), and angle of attack, (0deg≤ψ≤12.6deg). A total of six wheels and five tires were tested. Coefficient of drag area (CdA) and coefficient of side force area (CsA) versus angle of attack (ψ) were measured using a multi-axis force transducer. Wind tunnel conditions were set to simulate 2.94 m/s (6.6 mph) wind speeds and 13.4 m/s (30 mph) cyclist speeds. The performance of the wheel tire combinations was assessed using a wind-averaged drag method. The results show that the CdA of aerodynamic wheels is highly dependent on the wheel-tire combination. There is a strong linear correlation between wind averaged drag (CdA¯) and the ratio of the tire and rim width (T/W). The CsA of wheels is primarily controlled by the rim depth (D) and only weakly correlated with tire width (T).
Effect of Gas Diffusion Layer Surface Wettability Gradient on Water Behavior in a Serpentine Gas Flow Channel of Proton Exchange Membrane Fuel Cell
Authors: Malhotra Sneha , Ghosh Sumana
Published: March 2018

Water removal and behavior, in proton exchange membrane fuel cell (PEMFC) gas flow channel has been investigated in this work. Single serpentine gas flow channel has been simulated. Hydrodynamics of water drops in a serpentine channel are studied as a function of nature of gas diffusion layer (GDL) surface wettability. In one case, the surface becomes gradually hydrophobic starting from 90 deg to 170 deg. In this second case, the value of contact angle reduces to 10 deg. A three-dimensional model has been developed by using cfd software. Two different drop of diameter 0.2 mm and 0.4 mm are simulated for all the cases. It is observed that, water coverage is always lesser for a gradual hydrophobic surface. Also at low air velocity and gradual hydrophobic GDL surface results in lesser pressure drop as well as water coverage.
Effective Placement of a Cantilever Resonator on Flexible Primary Structure for Vibration Control Applications—Part 1: Mathematical Modeling and Analysis
Authors: Lundstrom Troy , Jalili Nader
Published: March 2018

In this Part 1 of a two-part series, the theoretical modeling and optimization are presented. More specifically, the effect of attachment location on the dynamics of a flexible beam system is studied using a theoretical model. Typically, passive/active resonators for vibration suppression of flexible systems are uniaxial and can only affect structure response in the direction of the applied force. The application of piezoelectric bender actuators as active resonators may prove to be advantageous over typical, uniaxial actuators as they can dynamically apply both a localized moment and translational force to the base structure attachment point. Assuming unit impulse force disturbance, potential actuator/sensor performance for the secondary beam can be quantified by looking at fractional root-mean-square (RMS) strain energy in the actuator relative to the total system, and normalized RMS strain energy in the actuator over a frequency band of interest with respect to both disturbance force and actuator beam mount locations. Similarly, by energizing the actuator beam piezoelectric surface with a unit impulse, one can observe RMS base beam tip velocity as a function of actuator beam position. Through such analyses, one can balance both sensor/actuator performance and make conclusions about optimally mounting the actuator beam sensor/actuator. Accounting for both sensing and actuation requirements, the actuator beam should be mounted in the following nondimensionalized region: 0.4≤e≤0.5.
Computational Study to Identify Feasible Operating Space for a Mixed Mode Combustion Strategy—A Pathway for Premixed Compression Ignition High Load Operation
Authors: Kavuri Chaitanya , Kokjohn Sage L.
Published: March 2018

A mixed mode combustion strategy with a premixed compression ignition (PCI) combustion event and a mixing controlled load extension injection was investigated in the current study. Computational fluid dynamics (CFD) modeling was used to perform a full factorial design of experiments (DOE) to study the effects of premixed fuel fraction, load extension injection timing, and exhaust gas recirculation (EGR). The goal of the study was to identify a feasible operating space and demonstrate a pathway to enable high-load operation with the mixed mode combustion strategy. The gross-indicated efficiency (GIE) increased with premix fraction, but the maximum premix fraction was constrained by pressure rise rate which confined the feasible operating space to a premix fuel mass range of 70–80%. Injecting part of the premixed fuel as a stratified injection relieved the pressure rise rate constraint considerably through in-cylinder equivalence ratio stratification. This allowed operation with premix fuel mass of 70% and higher and EGR rates less than 40% which resulted in improved GIE of the late cycle injection cases. It was also identified that by targeting the fuel from the stratified injection into the squish region, there is improved oxygen availability in the bowl for the load extension injection, which resulted in reduced soot emissions. This allowed the load extension injection to be brought closer to top dead center while meeting the soot constraint, which further improved the GIE. Finally, the results from the study were used to demonstrate high-load operation at 20 bar and 1300 rev/min.
A Feasibility Study of the Use of Solar Photovoltaic Energy in Saudi Arabia: A Case Study Assessment in a Factory in Zulfi City
Authors: Azzam Yosry A. , Ibrahim Nagwa
Published: March 2018

Few studies have been implemented to evaluate whether the renewable energy generation could fit into industrial locations in Saudi Arabia. We completed this feasibility study to investigate whether using photovoltaic (PV) solar arrays to power industrial cities at Saudi Arabia is economically feasible. The case study is a factory in Zulfi city, Riyadh Region. We used National Renewable Energy Laboratory's modeling tool, system advisor model (SAM) to evaluate the economic benefits of using a 150 kW DC PV system to cover 100% of the factory monthly power demand. Over 25 years, the system is estimated to generate about 6,000,000 kWh of electricity whose net savings are $398,000 (1 US$ is equal to about 3.75 Saudi Riyals) represented by a discounted cash flow. The proposed system will save the factory around $304,000 that would have to be paid in electric bills and will eliminate considerable amount of CO2 emissions. Sensitivity analysis has been conducted to determine the effects of underlying parameters on the economic feasibility of the proposed system. Levelized cost of electricity (LCOE) generated and net present value (NPV) are used as indicators of proposed system feasibility. The results indicate that these projects can be profitable under some certain assumptions and can potentially be generalized for all industrial locations in Saudi Arabia.