bluuebunny/crossref_metadata_2025 huggingface dataset:
The Multi-Axial Failure Response of Porcine Trabecular Skull Bone Estimated Using Microstructural Simulations
Authors: Fang Ziwen , Ranslow Allison N. , De Tomas Patricia , Gunnarsson Allan , Weerasooriya Tusit , Satapathy Sikhanda , Thompson Kimberly A. , Kraft Reuben H.
Published: July 2018

The development of a multi-axial failure criterion for trabecular skull bone has many clinical and biological implications. This failure criterion would allow for modeling of bone under daily loading scenarios that typically are multi-axial in nature. Some yield criteria have been developed to evaluate the failure of trabecular bone, but there is a little consensus among them. To help gain deeper understanding of multi-axial failure response of trabecular skull bone, we developed 30 microstructural finite element models of porous porcine skull bone and subjected them to multi-axial displacement loading simulations that spanned three-dimensional (3D) stress and strain space. High-resolution microcomputed tomography (microCT) scans of porcine trabecular bone were obtained and used to develop the meshes used for finite element simulations. In total, 376 unique multi-axial loading cases were simulated for each of the 30 microstructure models. Then, results from the total of 11,280 simulations (approximately 135,360 central processing unit-hours) were used to develop a mathematical expression, which describes the average three-dimensional yield surface in strain space. Our results indicate that the yield strain of porcine trabecular bone under multi-axial loading is nearly isotropic and despite a spread of yielding points between the 30 different microstructures, no significant relationship between the yield strain and bone volume fraction is observed. The proposed yield equation has simple format and it can be implemented into a macroscopic model for the prediction of failure of whole bones.
Tribological Properties of Nitrile Rubber/UHMWPE/Nano-MoS2 Water-Lubricated Bearing Material Under Low Speed and Heavy Duty
Authors: Fuming Kuang , Xincong Zhou , Jian Huang , Xiaoran Zhou , Jun Wang
Published: July 2018

This study sought to investigate the tribological properties of nitrile rubber (NBR)/ultrahigh molecular weight polyethylene (UHMWPE)/nano-molybdenum disulfide (nano-MoS2) nanocomposites containing various quantities of nano-MoS2. The apparatus used for these tests was a marine stern tube bearing testing apparatus SSB-100V that was water-lubricated and was run at low speed under heavy duty conditions. The coefficient of friction coefficient (COF), wear rate, and surface abrasion of the composite were obtained to determine the effect of the addition nano-MoS2 and to obtain the optimum nano-MoS2 content. The mechanical and physical properties of the rubber-plastic material met the requirements of the Chinese Ship standard CB/T769-2008 and U.S. military standard MIL-DTL-17901C(SH). The experimental results showed that the nanocomposites that contained 9 phr nano-MoS2 (parts by weight per hundred parts of rubber materials) exhibited good comprehensive friction and wear properties. It is believed that the experience achieved from this study can form a theoretical foundation for the improving the properties of the subject rubber-plastic material.
Study on Lateral Jetting Range During an Arc-Curved Jet Impacting Nonplanar Solid Surfaces
Authors: Huang Fei , Li Shuqing , Zhao Yanlin , Liu Yong
Published: July 2018

This paper focuses on the lateral jetting commencing points associated with the peak pressure when an arc-curved jet impacts flat, concave, convex, and inclined solid surfaces, respectively. A theoretical method based on a shock wave background is used to establish models for these situations, which indicate that the critical radius for the initiation of lateral jetting is dependent on the combined actions of the jet velocity, surface shape, and surface angle. Arbitrary Lagrangian–Eulerian (ALE) formulations are then used to model the process of arc-curved jets impacting varied solid surfaces. The numeric simulation results are found to be in good agreement with the theoretical models.
A Wave-Based Analytical Solution to Free Vibrations in a Combined Euler–Bernoulli Beam/Frame and a Two-Degree-of-Freedom Spring–Mass System
Authors: Mei C.
Published: July 2018

In this paper, natural frequencies and modeshapes of a transversely vibrating Euler–Bernoulli beam carrying a discrete two-degree-of-freedom (2DOF) spring–mass system are obtained from a wave vibration point of view in which vibrations are described as waves that propagate along uniform structural elements and are reflected and transmitted at structural discontinuities. From the wave vibration standpoint, external forces applied to a structure have the effect of injecting vibration waves to the structure. In the combined beam and 2DOF spring–mass system, the vibrating discrete spring–mass system injects waves into the distributed beam through the spring forces at the two spring attached points. Assembling these wave relations in the beam provides an analytical solution to vibrations of the combined system. Accuracy of the proposed wave analysis approach is validated through comparisons to available results. This wave-based approach is further extended to analyze vibrations in a planar portal frame that carries a discrete 2DOF spring–mass system, where in addition to the transverse motion, the axial motion must be included due to the coupling effect at the angled joint of the frame. The wave vibration approach is seen to provide a systematic and concise technique for solving vibration problems in combined distributed and discrete systems.
Development of a Seismic Probabilistic Safety Assessment Quantification Tool
Authors: Gao Wei , Tang Guofeng , Zhang Jingyu , Zhang Qinfang
Published: July 2018

Shanghai Nuclear Engineering Research and Design Institute (SNERDI) has been studying seismic risk analysis for nuclear power plant for a long time, and completed seismic margin analysis for several plants. After Fukushima accident, seismic risk has drawn an increasing attention worldwide, and the regulatory body in China has also required the utilities to conduct a detailed analysis for seismic risk. So, we turned our focus on a more intensive study of seismic probabilistic safety assessment (PSA/PRA) for nuclear power plant in recent years. Since quantification of seismic risk is a key part in Seismic PSA, lots of efforts have been devoted to its research by SNERDI. The quantification tool is the main product of this research, and will be discussed in detail in this paper. First, a brief introduction to Seismic PSA quantification methodology is presented in this paper, including fragility analysis on system or plant level, convolution of seismic hazard curves and fragility curves, and uncertainty analysis as well. To derive more accurate quantification results, the binary decision diagram (BDD) algorithm was introduced into the quantification process, which effectively reduces the deficiency of the conventional method on coping with large probability events and negated logic. Finally, this paper introduced the development of the seismic PSA quantification tool based on the algorithms discussed in this paper. Tests and application have been made for this software based on a specific nuclear power plant seismic PSA model.
Neutronic Study of Burnable Poison Materials and Their Alternative Configurations in Fully Ceramic Microencapsulated Loaded Pressurized Water Reactor Fuel Assembly
Authors: Awan Muhammad Qasim , Cao Liangzhi , Wu Hongchun , Zhao Chuanqi
Published: July 2018

Use of FCM fuel in light water reactors is an attractive option for existing and future generations of these reactors to make them accident tolerant in nature. This work focuses on the neutronic study of the use of burnable material in various configurations to control the excess reactivity and to keep the moderator temperature coefficient of reactivity (MTC) feedback negative for entire cycle length. Erbia and gadolinia, two conventional materials are used in three different configurations including quadruple isotropic (QUADRISO), bi-isotropic (BISO), and Matrix Mix forms. The results obtained from the implicit random treatment of the double heterogeneity of tri-structural isotropic (TRISO), QUADRISO, and BISO particles show that the erbia is the best material to be used in QUADRISO and Matrix Mix configurations with lowest reactivity swing for the life cycle and residual poison well below 0.5%. Gadolinia is usable in FCM environment only in the BISO form where enhanced self-shielding controls the depletion performance of the material. The gadolinia has almost zero residual poison at end of cycle (EOC); however, it has relatively large reactivity swing, which will need more micromanagement of the control rods during the plant operations. At the beginning of cycle (BOC), erbia-loaded assemblies have shown an increase in negative value of MTC compared with reference due to presence of resonance peak in erbium near 1 eV. The finally recommended material-configuration combinations have shown the excess reactivity containment in desired manner with good depletion performance and negative feedback of the MTC for life cycle.
Spreading and Contact Resistance Formulae Capturing Boundary Curvature and Contact Distribution Effects
Authors: Hodes Marc , Kirk Toby , Crowdy Darren
Published: July 2018

There is a substantial and growing body of literature which solves Laplace's equation governing the velocity field for a linear-shear flow of liquid in the unwetted (Cassie) state over a superhydrophobic surface. Usually, no-slip and shear-free boundary conditions are applied at liquid–solid interfaces and liquid–gas ones (menisci), respectively. When the menisci are curved, the liquid is said to flow over a “bubble mattress.” We show that the dimensionless apparent hydrodynamic slip length available from studies of such surfaces is equivalent to (i) the dimensionless spreading resistance for a flat, isothermal heat source flanked by arc-shaped adiabatic boundaries and (ii) the dimensionless thermal contact resistance between symmetric mating surfaces with flat contacts flanked by arc-shaped adiabatic boundaries. This is important because real surfaces are rough rather than smooth. Furthermore, we demonstrate that this observation provides a significant source of new and explicit results on spreading and contact resistances. Significantly, the results presented accommodate arbitrary solid-to-solid contact fraction and arc geometry in the contact resistance problem for the first time. We also provide formulae for the case when each period window includes a finite number of no-slip (or isothermal) and shear free (or adiabatic) regions and extend them to the case when the latter are weakly curved. Finally, we discuss other areas of mathematical physics to which our results are directly relevant.
Studies on Dynamic Tribology Properties of Friction Materials by Using an Approximate In Situ Observation for Worn Surfaces
Authors: Sun Weitao , Zhou Wenlong , Liu Jianfa , Fu Xuesong , Chen Guoqing , Yao Shan
Published: July 2018

This paper primarily focused on the dynamic tribology properties of one certain nonasbestos organic (NAO) friction material by using an approximate in situ method. This study was performed through a pad-on-disk type friction tester under different temperature conditions. Results showed that temperature has a significant effect on the dynamic tribology performance. At 100 °C, friction coefficient and wear rate after the running-in stage varied little with time. At 250 °C, friction coefficient after the running-in stage increased gradually and then tended to be stable, while wear rate decreased gradually. From 100 to 350 °C, friction coefficient increased first as a function of temperature, but decreased sharply when the temperature was over 250 °C. Simultaneously, wear rate also increased sharply over 250 °C. Additionally, three dynamic evolution models of worn surfaces corresponding to different cases were established.
Enhanced Power Generation in SOFCs Using Artificial Limits on Actuator Control Signals
Authors: Reineh Maryam Sadeghi , Jabbari Faryar
Published: July 2018

In this paper, we study a solid oxide fuel cell (SOFC) controlled by a multi-input multi-output (MIMO) compensator, which uses the blower/fan power and cathode inlet temperature as actuators. The usable power of the fuel cell (FC) is maximized by limiting the air flow rate deliberately when an increase in power is demanded. Possible rate bounds on the cathode inlet temperature are also modeled. These bounds could represent the physical limitations (due to slow dynamics of heat exchangers) and/or a control concept for accommodating the power saving objective. Applying proper limits to the amplitude and rate of the actuator signals, and incorporating antiwindup (AW) techniques, can raise the net power of the FC by 16% with negligible effects on the spatial temperature profile.
Simulation Modeling of the Combined Damage Caused by Cavitation and Abrasion in Sediment-Laden Liquids
Authors: Gou Wenjuan , Wu Jianhua , Zhang Hui , Lian Jijian
Published: July 2018

Combined damage caused by cavitation and abrasion is a serious problem concerning hydraulic structures and machinery operating in hyper-concentrated sediment-laden rivers. Conceptualization of a model for simulation and assessment of the combined damage, therefore, becomes necessary. Experimental results demonstrate that sediments cast a strong influence on the combined damage caused by cavitation and abrasion. Sediments with size larger compared to a critical size tend to aggravate the combined damage, while sediments with size smaller compared to critical relieve the combined damage effect when compared against cavitation-only damage. Based on these results, a new model has been proposed and built in order to predict the combined damage and assess the range of sediments that relieve or aggravate the damage as sediments pass through the structure and machinery. The model represents an integral with damage as the integrand and sediments representing the domain of integration, and was built in three steps—the first step establishes a relationship between damage and sediments of a single size (SS model); the second step establishes a relationship between damage and sediments from an actual river (MS model); and the third step proposes a standard to assess the damaging effect on hydro machinery (CS model). Model parameters were verified using 74 cases of laboratory experiments. By comparing simulation results against experimental data, it has been inferred that the proposed model can be employed to study practical problems in a predictive manner and promote safe operation of reservoirs by predicting damage characteristics of river water.
Tribological Behavior of Polymer Seal Materials in Water-Based Hydraulic Fluids
Authors: Bernat S. , Brink A. , Lucas M. , Espallargas N.
Published: July 2018

In this work, two polymer materials have been tested in a lubricated reciprocating pin-on-plate contact geometry using water-based hydraulic fluids to simulate sliding conditions of seal materials used in offshore equipment. The effect of load, speed, water content of the lubricant, and soaking of the ultra-high molecular weight polyethylene (UHMWPE) and a polyketone (PK) sliding against a super-duplex stainless steel (SDSS) was studied. The results showed that for UHMWPE, an increase in normal force leads to a decrease in coefficient of friction for all velocities. While under the same sliding conditions, no relevant influence of load on friction coefficient was found for PK. On the other hand, an increase in sliding speed decreased the coefficient of friction for both materials. The effect of the water content of the hydraulic fluid on the tribological performance was also studied. In UHMWPE-SDSS system, increasing water content in the hydraulic fluid resulted in steady growth of the transfer film. One reason for this might be the decreasing lubricant viscosity, which moves the system toward the boundary lubrication regime. In addition, it was found that the incubation of both UHMWPE and PK in water-based lubricants showed a beneficial effect on friction and wear, which was explained by the change in polymer visco-elastic behavior.
Influence of Injection Parameters and Operating Conditions on Ignition and Combustion in Dual-Fuel Engines
Authors: Grochowina Marcus , Schiffner Michael , Tartsch Simon , Sattelmayer Thomas
Published: July 2018

Dual-fuel (DF) engines offer great fuel flexibility since they can either run on gaseous or liquid fuels. In the case of diesel pilot-ignited DF engines, the main source of energy is provided by gaseous fuel, whereas the diesel fuel acts only as an ignition source. Therefore, a proper auto-ignition of the pilot fuel is of utmost importance for combustion in DF engines. However, auto-ignition of the pilot fuel suffers from lower compression temperatures of Miller or Atkinson valve timings. These valve timings are applied to increase efficiency and lower nitrogen oxide (NOx) engine emissions. In order to improve the ignition, it is necessary to understand which parameters influence the ignition in DF engines. For this purpose, experiments were conducted and the influence of parameters, such as injection pressure, pilot fuel quantity, compression temperature, and air–fuel (A/F) equivalence ratio of the homogenous natural gas–air mixture were investigated. The experiments were performed on a periodically chargeable combustion cell using optical high-speed recordings and thermodynamic measurement techniques for pressure and temperature. The study reveals that the quality of the diesel pilot ignition in terms of short ignition delay and a high number of ignited sprays significantly depends on the injection parameters and operating conditions. In most cases, the pilot fuel suffers from too high dilution due to its small quantity and long ignition delays. This results in a small number of ignited sprays and consequently leads to longer combustion durations. Furthermore, the experiments confirm that the natural gas of the background mixture influences the auto-ignition of the diesel pilot oil.
The Effect of Nonequilibrium Boundary Layers on Compressor Performance
Authors: Wheeler Andrew P. S. , Dickens Anthony M. J. , Miller Robert J.
Published: July 2018

The paper investigates the effect of nonequilibrium behavior of boundary layers on the profile loss of a compressor. The investigation is undertaken using both high fidelity simulations of a midheight section of a compressor blade and a reduced order model, MISES. The solutions are validated using experimental measurements made in the embedded stage of a multistage low speed compressor. The paper shows that up to 35% of the suction surface boundary layer of the compressor blade exhibits nonequilibrium behavior. The size of this region reduces as the Reynolds number is increased. The nonequilibrium behavior was found to reduce profile loss in cases of attached transition and raise loss where transition occurs through separation.
Modeling and Design Method for an Adaptive Wind Turbine Blade With Out-of-Plane Twist
Authors: Nejadkhaki Hamid Khakpour , Hall John F.
Published: July 2018

A modeling framework to analyze a wind turbine blade subjected to an out-of-plane transformation is presented. The framework combines aerodynamic and mechanical models to support an automated design process. The former combines the National Renewable Energy Lab (NREL) aerodyn software with a genetic algorithm solver. It defines the theoretical twist angle distribution (TAD) as a function of wind speed. The procedure is repeated for a series of points that form a discrete range of wind speeds. This step establishes the full range of blade transformations. The associated theoretical TAD geometry is subsequently passed to the mechanical model. It creates the TAD geometry in the context of a novel wind turbine blade concept. The blade sections are assumed to be made by additive manufacturing, which enables tunable stiffness. An optimization problem minimizes the difference between the practical and theoretical TAD over the full range of transformations. It does so by selecting the actuator locations and the torsional stiffness ratios of consecutive segments. In the final step, the blade free shape (undeformed position) is found. The model and design support out-of-plane twisting, which can increase energy production and mitigate fatigue loads. The proposed framework is demonstrated through a case study based on energy production. It employs data acquired from the NREL Unsteady Aerodynamics Experiment. A set of blade transformations required to improve the efficiency of a fixed-speed system is examined. The results show up to 3.7% and 2.9% increases in the efficiency at cut-in and rated speeds, respectively.
On the Importance of Engine-Representative Models for Fan Flutter Predictions
Authors: Stapelfeldt Sina , Vahdati Mehdi
Published: July 2018

Discrepancies between rig tests and numerical predictions of the flutter boundary for fan blades are usually attributed to the deficiency of computational fluid dynamics (CFD) models for resolving flow at off-design conditions. However, as will be demonstrated in this paper, there are a number of other factors, which can influence the flutter stability of fan blades and lead to differences between measurements and numerical predictions. This research was initiated as a result of inconsistencies between the flutter predictions of two rig fan blades. The numerical results agreed well with rig test data in terms of flutter speed and nodal diameter (ND) for both fans. However, they predicted a significantly higher flutter margin for one of the fans, while measured flutter margins were similar for both blades. A new set of flutter computations including the whole low-pressure system was therefore performed. The new set of computations considered the effects of the acoustic liner and mistuning for both blades. The results of this work indicate that the previous discrepancies between CFD and tests were caused by, first, differences in the effectiveness of the acoustic liner in attenuating the pressure wave created by the blade vibration and second, differences in the level of unintentional mistuning of the two fan blades. In the second part of this research, the effects of blade mis-staggering and inlet temperature on aerodynamic damping were investigated. The data presented in this paper clearly show that manufacturing and environmental uncertainties can play an important role in the flutter stability of a fan blade. They demonstrate that aeroelastic similarity is not necessarily achieved if only aerodynamic properties and the traditional aeroelastic parameters, reduced frequency and mass ratio, are maintained. This emphasizes the importance of engine-representative models, in addition to accurate and validated CFD codes, for the reliable prediction of the flutter boundary.
Coupled Model of Rotary-Tilting Spindle Head for Pose-Dependent Prediction of Dynamics
Authors: Du Chao , Zhang Jun , Lu Dun , Zhang Huijie , Zhao Wanhua
Published: July 2018

Five-axis machine with rotary-tilting spindle head (RTSH) is always used for sculptured surface machining, and the tool-tip dynamics in various machining postures along the tool path directly affect the machining accuracy and stability. To rapidly evaluate the tool-tip dynamics at different postures during the structural design of tool-spindle-spindle head (TSSH) assembly, this paper proposes a coupled dynamic model of tool-spindle-bearing system (TSBS) and RTSH. The model is a rigid-flexible multibody dynamic model with 36 degrees-of-freedom (DOFs), where in the rotary shaft, swivel shaft and housing are treated as rigid bodies; the tool, tool holder, and spindle shaft are modeled by reduced beams; the bearings and flexible joints are modeled as spring-damping elements. The fully Cartesian coordinates and Lagrangian method are employed to deduce a general parametric dynamic equation. The analytical method for calculating the contact stiffness of bearings and flexible joints is systematically presented, including tool-holder joint, holder-spindle joint, spindle bearings, hirth coupling, and the bearings and locking joints of rotary and swivel shafts. The model is verified by the frequency response functions (FRFs) testing and modal testing at different postures. The experimental results show that the proposed model can be used for accurate and efficient evaluation of the tool-tip FRFs, natural frequencies and mode shapes of TSSH at an arbitrary posture.
Experimental Studies and Comparison of Centrifugally Cast Cu/SiC and Cu/Si3N4 Functionally Graded Composites on Mechanical and Wear Behavior
Authors: Radhika N. , Andrew Jefferson J.
Published: July 2018

The objective of this research work is to synthesize functionally graded Cu-11Ni-4Si/10 wt % SiC, Cu-11Ni-4Si/10 wt % Si3N4 composite using horizontal centrifugal casting method and to analyze its mechanical and adhesive wear behavior. The cast samples with dimension of Øout100 × Øin70 × 100 mm were synthesized and variation in volume of SiC and Si3N4 particles on inner (1 mm), middle (8 mm), and outer surfaces (15 mm) along radial direction of the composites was analyzed. Microstructural images revealed that inner zone of the both composites had highest distribution of reinforcement particles. Tensile tests on inner (1–7 mm) and outer (8–15 mm) zones of composites revealed that the inner zones had highest tensile and yield strength. Fractography test was conducted for both composites at inner and outer zones to observe the mode of failure. Hardness tests taken along radial direction of the composites revealed that, the inner surface had better hardness and it reduced toward outer periphery. The outer and inner surfaces of Cu/SiC were compared with Cu/Si3N4 composites and results revealed that inner surface of Cu/SiC had highest wear resistance among all surfaces of composites. It was also observed that, while increasing load, wear rate increased with it for all composites. Wear rate of composites majorly decreased while increasing the sliding velocity due to formation of tribolayer. Scanning electron microscopy (SEM) analysis carried out on worn surfaces of Cu/SiC and Cu/Si3N4 composite revealed that, plastic deformation, and plowing were the dominant wear mechanism for varied parameters.
Measurements and Modeling of the Dynamic Response of a Pilot Stabilized Premixed Flame Under Dual-Input Perturbation
Authors: Li Chunyan , Li Suhui , Cheng Xu , Zhu Min
Published: July 2018

Pilot flames have been widely used for flame stabilization in low-emission gas turbine combustors. Effects of pilot flame on dynamic instabilities, however, are not well understood. In this work, the dynamic interactions between main and pilot flames are studied by perturbing both flames simultaneously, i.e., with a dual-input forcing. A burner is used to generate a premixed axisymmetric V-shaped methane flame stabilized by a central pilot flame. Servo valve and sirens are used to produce forcing in the pilot and main flames, respectively. A diagnostic system is applied to measure the flame structure and heat release rate. The effects of forcing frequency, forcing amplitude, phase difference between the two forcing signals as well as the Reynolds number are studied. Both the flame transfer function (FTF) and the flame dynamic position are measured and analyzed. It is found that the total flame response can be modified by the perturbation in the pilot flame. The mechanism can be attributed to the effect of pilot flame on the velocity field of the burnt side. Vortex is found to be able to amplify the pilot–main dynamic interactions under certain conditions. An analytical model is developed based on the linearized G-equation, to further understand the flame interactions through the velocity perturbations in the burnt side. Good agreements were found between the prediction and the experiment results.
A Coronally Clutching Ankle to Improve Amputee Balance on Coronally Uneven and Unpredictable Terrain
Authors: Yeates Kyle H. , Segal Ava D. , Neptune Richard R. , Klute Glenn K.
Published: July 2018

To improve the balance of individuals with lower limb amputation on coronally uneven terrain, a coronally clutching ankle (CCA) was developed to actively adapt through ±15 deg of free coronal foot rotation during the first ∼60 ms of initial contact. Three individuals with lower limb amputations were fit with the CCA and walked across an instrumented walkway with a middle step that was either flush, 15 deg inverted, or 15 deg everted. An opaque latex membrane was placed over the middle step, making the coronally uneven terrain unpredictable. Compared to participants' clinically prescribed prosthesis, the CCA exhibited significantly more coronal angular adaption during early stance. The CCA also improved participants' center of mass (COM) path regulation during the recovery step (reduced variation in mediolateral position) and reduced the use of the hip and stepping recovery strategies, suggesting it improved participants' balance and enabled a quicker recovery from the disturbance. However, use of the CCA did not significantly affect participants' ability to regulate their coronal angular momentum during the disturbance, suggesting that the CCA did not improve all elements of dynamic balance. Reducing the distance between the CCA's pivot axis and the base of the prosthetic foot might resolve this issue. These findings suggest that actively adapting the coronal plane angle of a prosthetic ankle can improve certain elements of balance for individuals with lower limb amputation who walk on coronally uneven and unpredictable terrain.
Evolving Hidden Genes in Genetic Algorithms for Systems Architecture Optimization
Authors: Abdelkhalik Ossama , Darani Shadi
Published: July 2018

The concept of hidden genes was recently introduced in genetic algorithms (GAs) to handle systems architecture optimization problems, where the number of design variables is variable. Selecting the hidden genes in a chromosome determines the architecture of the solution. This paper presents two categories of mechanisms for selecting (assigning) the hidden genes in the chromosomes of GAs. These mechanisms dictate how the chromosome evolves in the presence of hidden genes. In the proposed mechanisms, a tag is assigned for each gene; this tag determines whether the gene is hidden or not. In the first category of mechanisms, the tags evolve using stochastic operations. Eight different variations in this category are proposed and compared through numerical testing. The second category introduces logical operations for tags evolution. Both categories are tested on the problem of interplanetary trajectory optimization for a space mission to Jupiter, as well as on mathematical optimization problems. Several numerical experiments were designed and conducted to optimize the selection of the hidden genes algorithm parameters. The numerical results presented in this paper demonstrate that the proposed concept of tags and the assignment mechanisms enable the hidden genes genetic algorithms (HGGA) to find better solutions.
Development of a Computational Fluid Dynamics Model to Simulate Three-Dimensional Gap Resonance Driven by Surface Waves
Authors: Wang Hongchao , Draper Scott , Zhao Wenhua , Wolgamot Hugh , Cheng Liang
Published: July 2018

This paper expounds the process of successfully establishing a computational fluid dynamics (CFD) model to accurately reproduce experimental results of three-dimensional (3D) gap resonance between two fixed ship-shaped boxes. The ship-shaped boxes with round bilges were arranged in a side-by-side configuration to represent a floating liquefied natural gas offloading scenario and were subjected to NewWave-type transient wave groups. We employ the open-source CFD package openfoam to develop the numerical model. Three-dimensional gap resonance differs from its two-dimensional (2D) counterpart in allowing spatial structure along the gap and hence multiple modes can easily be excited in the gap by waves of moderate spectral bandwidth. In terms of numerical setup and computational cost, a 3D simulation is much more challenging than a 2D simulation and requires careful selection of relevant parameters. In this respect, the mesh topology and size, domain size and boundary conditions are systematically optimized. It is shown that to accurately reproduce the experimental results in this case, the cell size must be adequate to resolve both the undisturbed incident waves and near-wall boundary layer. By using a linear iterative method, the NewWave-type transient wave group used in the experiment is accurately recreated in the numerical wave tank (NWT). Numerical results including time series of gap responses, resonant amplitudes and frequencies, and mode shapes show excellent agreement with experimental data.
Heat Transfer in a Rotating Cooling Channel (AR = 2:1) With Rib Turbulators and a Tip Turning Vane
Authors: Chen Andrew F. , Wu Hao-Wei , Wang Nian , Han Je-Chin
Published: July 2018

Experimental investigation on rotation and turning vane effects on heat transfer was performed in a two-pass rectangular internal cooling channel. The channel has an aspect ratio of AR = 2:1 and a 180 deg tip-turn, which is a scaled up model of a typical internal cooling passage of gas turbine airfoils. The leading surface (LS) and trailing surface (TS) are roughened with 45 deg angled parallel ribs (staggered P/e = 8, e/Dh = 0.1). Tests were performed in a pressurized vessel (570 kPa) where higher rotation numbers (Ro) can be achieved with a maximum Ro = 0.42. Five Reynolds numbers (Re) were examined (Re = 10,000–40,000). At each Reynolds number, five rotational speeds (Ω = 0–400 rpm) were considered. Results showed that rotation effects are stronger in the tip regions as compared to other surfaces. Heat transfer enhancement up to four times was observed on the tip wall at the highest rotation number. However, heat transfer enhancement is reduced to about 1.5 times with the presence of a tip turning vane at the highest rotation number. Generally, the tip turning vane reduces the effects of rotation, especially in the turn portion.
Design of a Spatial Translation Mechanism by Optimizing Spatial Ground Structures and Its Kinematic Analysis
Authors: Yu Weidong , Wang Hao , Chen Genliang , Zhao Longhai
Published: July 2018

In our previous work, we designed a three-degrees-of-freedom (3DOF) translational parallel mechanism based on a proposed design strategy. In this paper, the design strategy is further improved, and a novel spatial translation mechanism (STM) is found. The novel STM consists of a platform, a base, and six modules between the platform and the base. Each module is a passive planar 6R single-loop closed chain, and it is connected with two other modules. Meanwhile, three modules are connected to the base, and the other three modules are connected to the platform. All the connections among the modules, platform, and base are realized by revolute joints. There are no obvious limbs in the mechanism due to the complex connections. The mobility of the STM is analyzed, and the forward kinematics is investigated. To validate the effectiveness and feasibility of the design, one prototype is fabricated. At the end of the paper, we draw some conclusions and discuss the future works.
Linear Solar Concentrator Structural Optimization Using Variable Beam Cross Sections
Authors: Yang Moucun , Zhu Yuezhao , Fu Wei , Pearce Garth , Taylor Robert A.
Published: July 2018

The design and construction of solar concentrators heavily affects their optical efficiency, heat utilization, and cost. Current trough concentrators use an equivalent uniform beam with a metal grid substructure. In this conventional design, there is surplus stiffness and strength, which unnecessarily increases the overall weight and cost of the structure. This paper describes a variable cross section structural optimization approach (with the EuroTrough design, including safety factors, taken as an example) to overcome this issue. The main improvement of this design comes from keeping the beams rigid and strong near the two ends (at the torque box structure) while allowing the middle of the structure to be relatively weak. Reducing the cross-sectional area of the middle beams not only reduces the amount of material needed for the structure but also reduces the deflection of the reflector. In addition, a new connection structure between two neighboring concentrator elements was designed to reinforce the structure. The simulated results show that the concentrator's structural weight (including the torque box, endplates, and cantilever arms) is reduced by 13.5% (i.e., about 133 kg per 12 m long element). This represents a meaningful capital and installation cost savings while at the same time improving the optical efficiency.
Impact of Flow Unsteadiness on Steady-State Gas-Path Stagnation Temperature Measurements
Authors: Bonham Clare , Brend Mark , Spencer Adrian , Tanimizu Katsu , Wise Dylan
Published: July 2018

Steady-state stagnation temperature probes are used during gas turbine engine testing as a means of characterizing turbomachinery component performance. The probes are located in the high-velocity gas-path, where temperature recovery and heat transfer effects cause a shortfall between the measured temperature and the flow stagnation temperature. To improve accuracy, the measurement shortfall is corrected post-test using data acquired at representative Mach numbers in a steady aerodynamic calibration facility. However, probes installed in engines are typically subject to unsteady flows, which are characterized by periodic variations in Mach number and temperature caused by the wakes shed from upstream blades. The present work examines the impact of this periodic unsteadiness on stagnation temperature measurements by translating probes between jets with dissimilar Mach numbers. For conventional Kiel probes in unsteady flows, a greater temperature measurement shortfall is recorded compared to equivalent steady flows, which is related to greater conductive heat loss from the temperature sensor. This result is important for the application of post-test corrections, since an incorrect value will be applied using steady calibration data. A new probe design with low susceptibility to conductive heat losses is therefore developed, which is shown to deliver the same performance in both steady and unsteady flows. Measurements from this device can successfully be corrected using steady aerodynamic calibration data, resulting in improved stagnation temperature accuracy compared to conventional probe designs. This is essential for resolving in-engine component performance to better than ±0.5% across all component pressure ratios.
Effects of Purge Flow Configuration on Sealing Effectiveness in a Rotor–Stator Cavity
Authors: Clark Kenneth , Barringer Michael , Johnson David , Thole Karen , Grover Eric , Robak Christopher
Published: July 2018

Secondary air is bled from the compressor in a gas turbine engine to cool turbine components and seal the cavities between stages. Unsealed cavities can lead to hot gas ingestion, which can degrade critical components or, in extreme cases, can be catastrophic to engines. For this study, a 1.5 stage turbine with an engine-realistic rim seal was operated at an engine-relevant axial Reynolds number, rotational Reynolds number, and Mach number. Purge flow was introduced into the interstage cavity through distinct purge holes for two different configurations. This paper compares the two configurations over a range of purge flow rates. Sealing effectiveness measurements, deduced from the use of CO2 as a flow tracer, indicated that the sealing characteristics were improved by increasing the number of uniformly distributed purge holes and improved by increasing levels of purge flow. For the larger number of purge holes, a fully sealed cavity was possible, while for the smaller number of purge holes, a fully sealed cavity was not possible. For this representative cavity model, sealing effectiveness measurements were compared with a well-accepted orifice model derived from simplified cavity models. Sealing effectiveness levels at some locations within the cavity were well-predicted by the orifice model, but due to the complexity of the realistic rim seal and the purge flow delivery, the effectiveness levels at other locations were not well-predicted.
Laboratory Validation of a Wearable Sensor for the Measurement of Head Acceleration in Men's and Women's Lacrosse
Authors: Buice Jessica M. , Esquivel Amanda O. , Andrecovich Christopher J.
Published: July 2018

Mild traumatic brain injuries, or concussions, can result from head acceleration during sports. Wearable sensors like the GForceTrackerTM (GFT) can monitor an athlete's head acceleration during play. The purpose of this study was to evaluate the accuracy of the GFT for use in boys' and girls' lacrosse. The GFT was mounted to either a strap connected to lacrosse goggles (helmetless) or a helmet. The assembly was fit to a Hybrid III (HIII) headform instrumented with sensors and impacted multiple times at different velocities and locations. Measurements of peak linear acceleration and angular velocity were obtained from both systems and compared. It was found that a large percent error between the GFT and headform system existed for linear acceleration (29% for helmetless and 123% for helmet) and angular velocity (48% for helmetless and 17% for helmet). Linear acceleration data transformed to the center of gravity (CG) of the head still produced errors (47% for helmetless and 76% for helmet). This error was substantially reduced when correction equations were applied based on impact location (3–22% for helmetless and 3–12% for helmet impacts at the GFT location and transformed to the CG of the head). Our study has shown that the GFT does not accurately calculate linear acceleration or angular velocity at the CG of the head; however, reasonable error can be achieved by correcting data based on impact location.
Novel Moving Mass Flight Vehicle and Its Equivalent Experiment
Authors: Li Jianqing , Gao Changsheng , Feng Tianming , Jing Wuxing
Published: July 2018

This paper presents a novel configuration of flight vehicle with moving mass control. We focus on the development of the proposed control mechanism and investigate the feasibility of an equivalent experimental setup. First, the effect of the moving mass parameters on the control authority is investigated. Then, a control law based on immersion and invariance (I&I) theory is presented for the moving mass control system. In the design process, we select a first-order target system to reduce the difficulty of controller design. To deal with the coupling caused by the additional inertia moment, which is generated by the motion of the moving mass, the extended state observer (ESO) is designed. The proposed adaptive controller is simulated and tested on the experimental setup. Finally, the simulation results validate the quality of the proposed adaptive controller, which ensures a good performance in the novel configuration with internal moving mass.
Swelling-Driven Crack Propagation in Large Deformation in Ionized Hydrogel
Authors: Ding Jingqian , Remij Ernst W. , Remmers Joris J. C. , Huyghe Jacques M.
Published: July 2018

Stepwise crack propagation is evidently observed in experiments both in geomaterials and in hydrogels. Pizzocolo et al. (2012, “Mode I Crack Propagation in Hydrogels is Step Wise,” Eng. Fract. Mech., 97(1), pp. 72–79) show experimental evidence that mode I crack propagation in hydrogel is stepwise. The pattern of the intermittent crack growth is influenced by many factors, such as porosity of the material, the permeability of the fluid, the stiffness of the material, etc. The pause duration time is negatively correlated with the stiffness of the material, while the average propagation length per step is positively correlated. In this paper, we integrate extended finite element method (XFEM) and enhanced local pressure (ELP) method, and incorporate cohesive relation to reproduce the experiments of Pizzocolo et al. in the finite deformation regime. We investigate the stepwise phenomenon in air and in water, respectively, under mode I fracture. Our simulations show that despite the homogeneous material properties, the crack growth under mode I fracture is stepwise, and this pattern is influenced by the hydraulic permeability and the porosity of the material. Simulated pause duration is negatively correlated with stiffness, and the average propagating length is positively correlated with stiffness. In order to eliminate the numerical artifacts, we also take different time increments into consideration. The staccato propagation does not disappear with smaller time increments, and the pattern is approximately insensitive to the time increment. However, we do not observe stepwise crack growth scheme when we simulate fracture in homogeneous rocks.
Quantitative Prediction of the Whole Peeling Process of an Elastic Film on a Rigid Substrate
Authors: Yin H. B. , Chen S. H. , Liang L. H. , Peng Z. L. , Wei Y. G.
Published: July 2018

The whole peeling behavior of thin films on substrates attract lots of research interests due to the wide application of film-substrate systems, which was well modeled theoretically by introducing Lennard–Jones (L-J) potential to describe the interface in Peng and Chen (2015, Effect of Bending Stiffness on the Peeling Behavior of an Elastic Thin Film on a Rigid Substrate,” Phys. Rev. E, 91(4), p. 042401). However, it is difficult for real applications because the parameters in the L-J potential are difficult to determine experimentally. In this paper, with the help of the peeling test and combining the constitutive relation of a cohesive zone model (CZM) with the L-J potential, we establish a new method to find the parameters in the L-J potential. The whole peeling process can then be analyzed quantitatively. Both the theoretical prediction and the experimental result agree well with each other. Finite element simulations of the whole peeling process are carried out subsequently. Quantitative agreements among the theoretical prediction, numerical calculation, and the experiment measurement further demonstrate the feasibility of the method. Effects of not only the interface strength but also the interface toughness on the whole peeling behavior are analyzed. It is found that the peeling force at a peeling angle of 90 deg during the steady-state stage is affected only by the interface toughness, while the peeling force before the steady-state stage would be influenced significantly by the interface toughness, interface strength, and bending stiffness of the film. All the present results should be helpful for deep understanding and theoretical prediction of the interface behavior of film-substrate systems in real applications.
Measurement and Modeling of Forces in Extrusion-Based Additive Manufacturing of Flexible Silicone Elastomer With Thin Wall Structures
Authors: Plott Jeffrey , Tian Xiaoqing , Shih Albert
Published: July 2018

Flexible thin wall silicone parts fabricated via extrusion-based additive manufacturing (AM) tend to deform due to the AM forces, limiting the maximum build height. The tangential and normal forces in AM were measured to investigate effects of three key process parameters (volumetric flow rate Q, nozzle tip inner diameter di, and layer height t) on the build height. The interaction between the nozzle tip and the extruded silicone bead is controlled to prevent interaction, flatten the top surface of the extruded silicone, or immerse the nozzle in the extruded silicone. Results show that tangential and normal forces in AM strongly depend on this interaction. Specifically, the AM forces remained low (less than 0.2 mN) if the nozzle tip did not contact the extruded silicone bead. Once the nozzle interaction with extruded silicone came into effect, the AM forces quickly grew to over 1 mN. The single wall tower configuration was developed to determine a predictive deflection resistance approach based on the measured AM forces and the resultant bending moment of inertia. This approach shows that a smaller di can produce taller towers, while a larger di is better at bridging and overhangs. These results are applied to the AM of a hollow thin wall silicone prosthetic hand.