bluuebunny/crossref_metadata_2025 huggingface dataset:
Alterations in Notch signalling in skeletal muscles from mdx and dko dystrophic mice and patients with Duchenne muscular dystrophy
Authors: Church Jarrod E. , Trieu Jennifer , Chee Annabel , Naim Timur , Gehrig Stefan M. , Lamon Séverine , Angelini Corrado , Russell Aaron P. , Lynch Gordon S.
Published: January 2014

New Findings

What is the central question of this study?

The Notch signalling pathway plays an important role in muscle regeneration, and activation of the pathway has been shown to enhance muscle regeneration in aged mice. It is unknown whether Notch activation will have a similarly beneficial effect on muscle regeneration in the context of Duchenne muscular dystrophy (DMD).

What is the main finding and its importance?

Although expression of Notch signalling components is altered in both mouse models of DMD and in human DMD patients, activation of the Notch signalling pathway does not confer any functional benefit on muscles from dystrophic mice, suggesting that other signalling pathways may be more fruitful targets for manipulation in treating DMD.

In Duchenne muscular dystrophy (DMD), muscle damage and impaired regeneration lead to progressive muscle wasting, weakness and premature death. The Notch signalling pathway represents a central regulator of gene expression and is critical for cellular proliferation, differentiation and apoptotic signalling during all stages of embryonic muscle development. Notch activation improves muscle regeneration in aged mice, but its potential to restore regeneration and function in muscular dystrophy is unknown. We performed a comprehensive examination of several genes involved in Notch signalling in muscles from dystrophin‐deficient mdx and dko (utrophin‐ and dystrophin‐null) mice and DMD patients. A reduction of Notch1 and Hes1 mRNA in tibialis anterior muscles of dko mice and quadriceps muscles of DMD patients and a reduction of Hes1 mRNA in the diaphragm of the mdx mice were observed, with other targets being inconsistent across species. Activation and inhibition of Notch signalling, followed by measures of muscle regeneration and function, were performed in the mouse models of DMD. Notch activation had no effect on functional regeneration in C57BL/10, mdx or dko mice. Notch inhibition significantly depressed the frequency–force relationship in regenerating muscles of C57BL/10 and mdx mice after injury, indicating reduced force at each stimulation frequency, but enhanced the frequency–force relationship in muscles from dko mice. We conclude that while Notch inhibition produces slight functional defects in dystrophic muscle, Notch activation does not significantly improve muscle regeneration in murine models of muscular dystrophy. Furthermore, the inconsistent expression of Notch targets between murine models and DMD patients suggests caution when making interspecies comparisons.
The role of brain natriuretic peptide in maintaining myometrial quiescence during pregnancy
Authors: Carvajal Jorge A.
Published: January 2014

New Findings

What is the topic of this review?

Myometrial quiescence is a highly regulated process, in which pregnant myometrium remains completely relaxed, overcoming its inherent tendency to contract. The maintenance of myometrial quiescence is a key step in controlling the duration of pregnancy. Currently, the mechanisms underlying myometrial quiescence of pregnancy are not fully known.

What advances does it highlight?

Brain natriuretic peptide is produced by the fetal membranes (chorion and amnion) and acts in a paracrine fashion. Brain natriuretic peptide plays a key role in maintaining myometrial quiescence. A premature decrease in production of brain natriuretic peptide may lead to preterm labour.

Myometrial quiescence is a physiological stage of the myometrium during pregnancy. It is a period of active relaxation of the myometrial smooth muscle cells; myometrial quiescence is responsible for maintaining pregnancy. The precise mechanisms underlying myometrial quiescence have not been completely elucidated, although many mediators and cellular pathways have been described as playing a role. Fetal membranes (chorion and amnion) produce and release one or more substances that inhibit myometrial contractions, playing a central role in the maintenance of myometrial quiescence. Brain natriuretic peptide (BNP) is more potent than any other natriuretic peptide in inhibiting myometrial contractions in vitro. Brain natriuretic peptide is produced by the chorion and amnion, mainly during myometrial quiescence, and decreasing towards the end of pregnancy. Production of BNP is reduced in fetal membranes obtained from women in preterm labour. It is postulated that BNP, acting in a paracrine fashion, plays a key role in the maintaining myometrial quiescence and, therefore, controlling the duration of pregnancy. Furthermore, it is postulated that a premature decrease of BNP production by the fetal membranes may cause preterm labour and preterm birth.
Design and Testing of a New Small Wind Turbine Blade
Authors: Song Qiyue , David Lubitz William
Published: January 2014

A small wind turbine blade was designed using blade element momentum (BEM) method for a three bladed, fixed pitch 1 kW horizontal axis wind turbine. The new blades were fabricated, fit to a Bergey XL 1.0 turbine, and tested using a vehicle-based platform at the original designed pitch angle, plus with 5 deg and 9 deg of additional pitch. The new blades had better aerodynamic performance than the original Bergey XL 1.0 blades at high speed, but in some cases at lower speeds the original blades performed better. The results demonstrated that selecting the blade pitch angle on a rotor is a tradeoff between starting performance and power output in high winds. The BEM simulations were evaluated against the test data and demonstrated that the BEM simulations predicted the rotor performance with reasonable accuracy.
Transient Three-Dimensional Heat Transfer Model of a Solar Thermochemical Reactor for H2O and CO2 Splitting Via Nonstoichiometric Ceria Redox Cycling
Authors: Lapp Justin , Lipiński Wojciech
Published: January 2014

A transient three-dimensional heat transfer model is developed for a 3 kWth solar thermochemical reactor for H2O and CO2 splitting via two-step nonstoichiometric ceria cycling. The reactor consists of a windowed solar receiver cavity, counter-rotating reactive and inert cylinders, and insulated reactor walls. The counter-rotating cylinders allow for continuous fuel production and heat recovery. The model is developed to solve energy conservation equations accounting for conduction, convection, and radiation heat transfer modes, and chemical reactions. Radiative heat transfer is analyzed using a combination of the Monte Carlo ray-tracing method, the net radiation method, and the Rosseland diffusion approximation. Steady-state temperatures, heat fluxes, and nonstoichiometry are reported. A temperature swing of up to 401 K, heat recovery effectiveness of up to 95%, and solar-to-fuel efficiency of up to 5% are predicted in parametric studies.
Robust Tracking Control for Takagi–Sugeno Fuzzy Systems With Unmeasurable Premise Variables: Application to Tank System
Authors: Ghorbel H. , El Hajjaji A. , Souissi M. , Chaabane M.
Published: January 2014

In this paper, a robust fuzzy observer-based tracking controller for continuous-time nonlinear systems presented by Takagi–Sugeno (TS) models with unmeasurable premise variables, is synthesized. Using the H∞ norm and Lyapunov approach, the control design for TS fuzzy systems with both unmeasurable premises and system states is developed to guarantee tracking performance of closed loop systems. Sufficient relaxed conditions for synthesis of the fuzzy observer and the fuzzy control are driven in terms of linear matrix inequalities (LMIs) constraints. The proposed method allows simplifying the design procedure and gives the observer and controller gains in only one step. Numerical simulation on a two tank system is provided to illustrate the tracking control design procedure and to confirm the efficiency of the proposed method.
Finite Element Method and Sharp Features Enhanced Laplacian for Interactive Shape Design of Mechanical Parts
Authors: Yi Bing , Liu Zhenyu , Duan Guifang , Cheng Fengbei , Tan Jianrong
Published: January 2014

Laplacian based model editing is one of the most popular shape modification methods for product design. However, most existing Laplacian based methods suffer shape structure and saliency feature distortion, which limits its possible application in shape design of mechanical parts. In this paper, to improve the mesh rigidity and to make the shape deforms physically, finite element method is employed to enhance the Laplacian based model editing, and to keep the saliency features, a robust sharp feature detecting method is further proposed for guiding the modification of the mesh Laplacian in shape deformation. We show how to utilize the enhanced Laplacian for interactive shape design of mechanical parts. The empirical results illustrate that the proposed method yield improved performance compared with conventional methods.
Analysis of Entropy Generation During Mixed Convective Heat Transfer of Nanofluids Past a Rotating Circular Cylinder
Authors: Sarkar Sandip , Ganguly Suvankar , Dalal Amaresh
Published: January 2014

The entropy generation due to mixed convective heat transfer of nanofluids past a rotating circular cylinder placed in a uniform cross stream is investigated via streamline upwind Petrov–Galerkin based finite element method. Nanosized copper (Cu) particles suspended in water are used with Prandtl number (Pr) = 6.9. The computations are carried out at a representative Reynolds number (Re) of 100. The dimensionless cylinder rotation rate, α, is varied between 0 and 2. The range of nanoparticle volume fractions (ϕ) considered is 0 ≤ ϕ ≤ 5%. Effect of aiding buoyancy is brought about by considering two fixed values of the Richardson number (Ri) as 0.5 and 1.0. A new model for predicting the effective viscosity and thermal conductivity of dilute suspensions of nanoscale colloidal particles is presented. The model addresses the details of the agglomeration–deagglomeration in tune with the pertinent variations in the effective particulate dimensions, volume fractions, as well as the aggregate structure of the particulate system. The total entropy generation is found to decrease sharply with cylinder rotation rates and nanoparticle volume fractions. Increase in nanoparticle agglomeration shows decrease in heat transfer irreversibility. The Bejan number falls sharply with increase in α and ϕ.
Mechanical Interaction of Angiogenic Microvessels With the Extracellular Matrix
Authors: Edgar Lowell T. , Hoying James B. , Utzinger Urs , Underwood Clayton J. , Krishnan Laxminarayanan , Baggett Brenda K. , Maas Steve A. , Guilkey James E. , Weiss Jeffrey A.
Published: January 2014

Angiogenesis is the process by which new blood vessels sprout from existing blood vessels, enabling new vascular elements to be added to an existing vasculature. This review discusses our investigations into the role of cell-matrix mechanics in the mechanical regulation of angiogenesis. The experimental aspects of the research are based on in vitro experiments using an organ culture model of sprouting angiogenesis with the goal of developing new treatments and techniques to either promote or inhibit angiogenic outgrowth, depending on the application. Computational simulations were performed to simulate angiogenic growth coupled to matrix deformation, and live two-photon microscopy was used to obtain insight into the dynamic mechanical interaction between angiogenic neovessels and the extracellular matrix. In these studies, we characterized how angiogenic neovessels remodel the extracellular matrix (ECM) and how properties of the matrix such as density and boundary conditions influence vascular growth and alignment. Angiogenic neovessels extensively deform and remodel the matrix through a combination of applied traction, proteolytic activity, and generation of new cell-matrix adhesions. The angiogenic phenotype within endothelial cells is promoted by ECM deformation and remodeling. Sensitivity analysis using our finite element model of angiogenesis suggests that cell-generated traction during growth is the most important parameter controlling the deformation of the matrix and, therefore, angiogenic growth and remodeling. Live two-photon imaging has also revealed numerous neovessel behaviors during angiogenesis that are poorly understood such as episodic growth/regression, neovessel colocation, and anastomosis. Our research demonstrates that the topology of a resulting vascular network can be manipulated directly by modifying the mechanical interaction between angiogenic neovessels and the matrix.
Nonlinear Viscoelastic Behavior of Active Fiber Composites
Authors: Tajeddini Vahid , Ben Atitallah Hassene , Muliana Anastasia , Ounaies Zoubeida
Published: January 2014

In the present study, viscoelastic response of an active fiber composite (AFC) is investigated by conducting stress relaxation and creep deformation tests, and the quasi-linear viscoelastic (QLV) constitutive model is used to describe the viscoelastic response of the AFC. The AFC under study consists of unidirectional long piezoelectric ceramic fibers embedded in an epoxy polymer, encapsulated between two Kapton layers with interdigitated surface electrodes. The relaxation and creep experiments are performed by loading the AFC samples along the longitudinal axis of the fibers, under several strain and stress levels at three temperatures, namely 25 °C, 50 °C, and 75 °C. The experimental results reveal the nonlinear viscoelastic behavior of the composite. Next, simulation and prediction of the viscoelastic response, including stress relaxation and creep deformation of the material, are done by using semi-analytical QLV model in which a relaxation time-dependent function is used, which also depends on strain and temperature. The results from the model are compared with those from the experiments. In general, the experimental and simulation results are in good agreement, except in the case of some of the creep responses, where considerable discrepancies are seen between the experimental and analytical approaches. Possible reasons for these differences are discussed in details.
Simulations of High Reynolds Number Air Flow Over the NACA-0012 Airfoil Using the Immersed Boundary Method
Authors: Johnson James P. , Iaccarino Gianluca , Chen Kuo-Huey , Khalighi Bahram
Published: January 2014

The immersed-boundary method is coupled to an incompressible-flow Reynolds-averaged Navier Stokes solver, based on a two-equation turbulence model, to perform unsteady numerical simulations of airflow past the NACA-0012 airfoil for several angles of attack and Reynolds numbers of 5.0×105 and 1.8×106. A preliminary study is performed to evaluate the sensitivity of the calculations to the computational mesh and to guide the creation of the computational cells for the unsteady calculations. Qualitative characterizations of the flow in the vicinity of the airfoil are obtained to assess the capability of locally refined grids to capture the thin boundary layers close to the airfoil leading edge as well as the wake flow emanating from the trailing edge. Quantitative analysis of aerodynamic force coefficients and wall pressure distributions are also reported and compared to experimental results and those from body-fitted grid simulations using the same solver to assess the accuracy and limitations of this approach. The immersed-boundary simulations compared well to the experimental and body-fitted results up to the occurrence of separation. After that point, neither computational approach provided satisfactory solutions.
An Introduction to Optimal Control
Authors: Cossu Carlo
Published: January 2014

The goal of these lecture notes is to provide an informal introduction to the use of variational techniques for solving constrained optimization problems with equality constraints and full state information. The use of the Lagrangian augmented cost function and variational techniques by which the adjoint equation and the optimality condition are found are introduced by the use of examples starting from steady finite-dimensional problems to end with unsteady initial-boundary value problems. Gradient methods based on sensitivity and adjoint equation solutions are also mentioned.
A Full Two-Dimensional Thermodynamic-Based Model for Magnetic Shape Memory Alloys
Authors: LaMaster Douglas H. , Feigenbaum Heidi P. , Nelson Isaac D. , Ciocanel Constantin
Published: January 2014

Magnetic shape memory alloys (MSMAs) are interesting materials because they exhibit considerable recoverable strain (up to 10%) and fast response time (higher than 1 kHz). MSMAs are comprised of martensitic variants with tetragonal unit cells and a magnetization vector that is innately aligned approximately to the short side of the unit cell. These variants reorient either to align the magnetization vector with an applied magnetic field or to align the short side of the unit cell with an applied compressive stress. This reorientation leads to a mechanical strain and an overall change in the material's magnetization, allowing MSMAs to be used as actuators, sensors, and power harvesters. This paper presents a phenomenological thermodynamic-based model able to predict the response of an MSMA to any two-dimensional (2D) magneto-mechanical loading. The model presented here is more physical and less empirical than other models in the literature, requiring only three model parameters to be calibrated from experimental results. In addition, this model includes evolution rules for the magnetic domain volume fractions and the angle of rotation of the magnetization vectors based on thermodynamic requirements. The resulting model is calibrated using a single, relatively simple experiment. Model predictions are compared with experimental data from a wide variety of 2D magneto-mechanical load cases. Overall, model predictions correlate well with experimental results. Additionally, methods for calibrating demagnetization factors from empirical data are discussed, and results indicate that using calibrated demagnetization factors can improve model predictions compared with the same model using closed-form demagnetization factors.
Distinct Element Method Modeling of Carbon Nanotube Bundles With Intertube Sliding and Dissipation
Authors: Ostanin Igor , Ballarini Roberto , Dumitrică Traian
Published: January 2014

The recently developed distinct element method for mesoscale modeling of carbon nanotubes is extended to account for energy dissipation and then applied to characterize the constitutive behavior of crystalline carbon nanotube bundles subjected to simple tension and to simple shear loadings. It is shown that if these structures are sufficiently long and thick, then they become representative volume elements. The predicted initial stiffness and strength of the representative volumes are in agreement with reported experimental data. The simulations demonstrate that energy dissipation plays a central role in the mechanical response and deformation kinematics of carbon nanotube bundles.
Direct and Adjoint Sensitivity Analysis of Ordinary Differential Equation Multibody Formulations
Authors: Dopico Daniel , Zhu Yitao , Sandu Adrian , Sandu Corina
Published: January 2014

Sensitivity analysis of multibody systems is essential for several applications, such as dynamics-based design optimization. Dynamic sensitivities, when needed, are often calculated by means of finite differences. This procedure is computationally expensive when the number of parameters is large, and numerical errors can severely limit its accuracy. This paper explores several analytical approaches to perform sensitivity analysis of multibody systems. Direct and adjoint sensitivity equations are developed in the context of Maggi's formulation of multibody dynamics equations. The approach can be generalized to other formulations of multibody dynamics as systems of ordinary differential equations (ODEs). The sensitivity equations are validated numerically against the third party code fatode and against finite difference solutions with real and complex perturbations.
Variable Distance Adjustment for Conformal Cooling Channel Design in Rapid Tool
Authors: Au K. M. , Yu K. M.
Published: January 2014

During thermoplastic injection moulding process, the gradual increase of the coolant temperature along the conformal cooling channel (CCC) inside the rapid tool reduces the rate of heat transfer from the polymeric melt to the cooling channel surface at the outlet portion. Injection moulded defects such as irregular warpage of the part between the coolant inlet and outlet cannot be avoided. Rapid tooling (RT) technology offers a speedy and automatic method for rapid tool design and fabrication integrated with complex internal structure such as CCC. This paper presents a novel adjustment method for cooling distance modification between the CCC and its mould cavity (or core) surface along the cooling channel. The proposed method can compensate the gradual increase of the coolant temperature from the coolant inlet to the coolant outlet. More heat can be transferred from the mould surface near the coolant outlet to the proposed variable distance conformal cooling channel (VDCCC). In this study, the cooling channel distance modification relies on two adjustment attributes: (1) the adjustment direction and (2) the adjustment amount, between the mould cavity (or core) surface (terrain) and the cooling channel axis (polyline) after the linearized approximation. A computer-aided melt flow analysis tool of moldflow plastics insight is employed in the case study in order to demonstrate the feasibility of the proposed method. The cooling performance of the proposed VDCCC design can be verified.
Inherent-Strain-Based Theory of Measurement of Three-Dimensional Residual Stress Distribution and Its Application to a Welded Joint in a Reactor Vessel
Authors: Nakacho Keiji , Ogawa Naoki , Ohta Takahiro , Nayama Michisuke
Published: January 2014

The stress that exists in a body under no external force is called the inherent stress. The strain that is the cause (source) of this stress is called the inherent strain. This study proposes a general theory of an inherent-strain-based measurement method for the residual stress distributions in arbitrary three-dimensional bodies and applies the method to measure the welding residual stress distribution of a welded joint in a reactor vessel. The inherent-strain-based method is based on the inherent strain and the finite element method. It uses part of the released strains and solves an inverse problem by a least squares method. Thus, the method gives the most probable value and deviation of the residual stress. First, the basic theory is explained in detail, and then a concrete measurement method for a welded joint in a reactor vessel is developed. In the method, the inherent strains are unknowns. In this study, the inherent strain distribution was expressed with an appropriate function, significantly decreasing the number of unknowns. Five types of inherent strain distribution functions were applied to estimate the residual stress distribution of the joint. The applicability of each function was evaluated. The accuracy and reliability of the analyzed results were assessed in terms of the residuals, the unbiased estimate of the error variance, and the welding mechanics. The most suitable function, which yields the most reliable result, was identified. The most reliable residual stress distributions of the joint are shown, indicating the characteristics of distributions with especially large tensile stress that may produce a crack.
Mathematical Modeling of Patient-Specific Ventricular Assist Device Implantation to Reduce Particulate Embolization Rate to Cerebral Vessels
Authors: Ricardo Argueta-Morales I. , Tran Reginald , Ceballos Andres , Clark William , Osorio Ruben , Divo Eduardo A. , Kassab Alain J. , DeCampli William M.
Published: January 2014

Stroke is the most devastating complication after ventricular assist device (VAD) implantation, with an incidence of 14%–47% despite improvements in device design and anticoagulation. This complication continues to limit the widespread implementation of VAD therapy. Patient-specific computational fluid dynamics (CFD) analysis may elucidate ways to reduce this risk. A patient-specific three-dimensional model of the aortic arch was generated from computed tomography. A 12 mm VAD outflow-graft (VAD-OG) “anastomosed” to the aorta was rendered. CFD was applied to study blood flow patterns. Particle tracks, originating from the VAD, were computed with a Lagrangian phase model and percentage of particles entering the cerebral vessels was calculated. Twelve implantation configurations of the VAD-OG and three particle sizes (2, 4, and 5 mm) were considered. Percentage of particles entering the cerebral vessels ranged from 6% for the descending aorta VAD-OG anastomosis, to 14% for the ascending aorta at 90 deg VAD-OG anastomosis. Values were significantly different among all configurations (X2 = 3925, p < 0.0001). Shallower and more cephalad anastomoses prevented formation of zones of recirculation in the ascending aorta. In this computational model and within the range of anatomic parameters considered, the percentage of particles entering the cerebral vessels from a VAD-OG is reduced by nearly 60% by optimizing outflow-graft configuration. Ascending aorta recirculation zones, which may be thrombogenic, can also be eliminated. CFD methods coupled with patient-specific anatomy may aid in identifying the optimal location and angle for VAD-OG anastomosis to minimize stroke risk.
Nanoparticles-Laden Gas Film in Aerostatic Thrust Bearing
Authors: Yang Zhiru , Diao Dongfeng , Fan Xue , Fan Hongyan
Published: January 2014

Nanoparticles-laden gas film (NLGF) was formed by adding SiO2 nanoparticles with volume fraction in the range of 0.014–0.330% and size of 30 nm into the air gas film in a thrust bearing. An effective viscosity of the gas-solid two phase lubrication media was introduced. The pressure distribution in NLGF and the load capacity of the thrust bearing were calculated by using the gas-solid two phase flow model with the effective viscosity under the film thicknesses range of 15–60 μm condition. The results showed that the NLGF can increase the load capacity when the film thickness is larger than 30 μm. The mechanism of the enhancement effect of load capacity was attributed to the increase of the effective viscosity of the NLGF from the pure air film, and the novel lubrication media of the NLGF can be expected for the bearing industry application.
Galloping of a Wind-Excited Tower Under Internal Parametric Damping
Authors: Mokni Lahcen , Kirrou Ilham , Belhaq Mohamed
Published: January 2014

The effect of harmonic internal parametric damping (IPD) on the amplitude and the onset of the periodic galloping of a tower is investigated in the presence of steady and unsteady wind. The structure is modeled by a lumped single degree of freedom (sdof) equation and attention is focused on the cases where the unsteady (turbulent) wind activates the external excitation, the parametric one, or both. A perturbation analysis is performed to approximate periodic solutions and the effect of the IPD on the amplitude and the onset of periodic galloping is examined in different cases of loading. It is shown that the IPD substantially improves the reduction in the galloping amplitude for all cases of loading and it has no influence on the galloping onset.
A Novel Method to Design and Optimize Flat-Foldable Origami Structures Through a Genetic Algorithm
Authors: McAdams Daniel A. , Li Wei
Published: January 2014

As advantages of foldable or deployable structures have been established, origami artists and engineers have started to study the engineering applications of origami structures. Methods of computational origami design that serve different types of origami have already been developed. However, most of the existing design methods focus on automatically deriving the crease pattern to realize a given folded finished shape, without actually designing the finished shape itself. To include final shape design into the computational origami design and optimization process, this paper presents a genetic algorithm that aims to develop origami structures featuring optimal geometric, functional, and foldability properties. In accordance with origami, the genetic algorithm is adapted both in the aspects the individual encoding method and the evolutionary operators. To compliment the Genetic algorithms (GA), a new origami crease pattern representation scheme is created. The crease pattern is analogous to the ice-cracks on a frozen lake surface, where each crack is equivalent to a crease and each forking point to a vertex. Thus to form the creases and vertices in an “ice-cracking”-like origami crease pattern, we pick one vertex as the starting location, and let the rest of the creases and vertices grow in the same manner that cracks extend and fork form in ice. In this research, the GA encodes the geometric information of forming the creases and vertices according to the development sequence through the ice-cracking process. Meanwhile, we adapt the evolutionary operators and introduce auxiliary mechanisms for the GA, so as to balance the preservation of both elitism and diversity and accelerate the emergence of optimal design outcomes through the evolutionary design process.
Ejecta Production and Transport From a Shocked Sn Coupon
Authors: Liu Y. , Grieves B.
Published: January 2014

When a shock interacts with a Sn coupon, micrometer-scale particulate fragments, called ejecta, are usually formed and emitted from its free surface. Understanding the characteristics of such ejecta is of great importance in many fields. The velocity distribution and amount of particulate mass are directly dependent on several physical properties of the shock wave and shocked material states. In this paper, we numerically interrogate ejecta production and its dynamics for a wide range of shock loading conditions in a supported wave form and quantify the correlation of ejecta source with shock strength as well as surface roughness, which is represented by randomly perturbed surfaces and the one with a macrofeature superimposed. Furthermore, an unsteadiness-aware drag coefficient is discussed and implemented to accomplish ejecta transport studies.
Fault Diagnosis for Satellite Attitude Control Systems With Four Flywheels
Authors: Wang Zhenhua , Shen Yi , Zhang Xiaolei , Wang Danwei
Published: January 2014

This paper proposes a novel fault diagnosis approach for the satellite attitude control system with flywheel faults. The key contributions include fault estimation by sparse approximation algorithm and diagnosis of multiple faults. In this paper, a Taylor series expansion is used to derive a fault estimation representation. Based on the sparse property of the faults, fault estimation is formulated as a sparse approximation problem and solved using the orthogonal matching pursuit (OMP) algorithm. Simulation results demonstrate the effectiveness of the proposed method.
Identification of Non-Gaussian Stochastic System
Authors: Park Sung-man , Kwon O-shin , Kim Jin-sung , Lee Jong-bok , Heo Hoon
Published: January 2014

This paper proposes a method to identify non-Gaussian random noise in an unknown system through the use of a modified system identification (ID) technique in the stochastic domain, which is based on a recently developed Gaussian system ID. The non-Gaussian random process is approximated via an equivalent Gaussian approach. A modified Fokker–Planck–Kolmogorov equation based on a non-Gaussian analysis technique is adopted to utilize an effective Gaussian random process that represents an implied non-Gaussian random process. When a system under non-Gaussian random noise reveals stationary moment output, the system parameters can be extracted via symbolic computation. Monte Carlo stochastic simulations are conducted to reveal some approximate results, which are close to the actual values of the system parameters.
Predicting Hydrodynamic and Heat Transfer Effects of Sparger Geometry and Placement Within a Column Photobioreactor Using Computational Fluid Dynamics
Authors: Bari Ghazi S. , Suess Taylor N. , Anderson Gary A. , Gent Stephen P.
Published: January 2014

This research investigates the effects of the sparger on flow patterns and heat transfer within a column photobioreactor (PBR) using computational fluid dynamics (CFD). This study compares two types of spargers: a porous membrane, which occupies the entire floor of the reactor, and a single sparger, which is located along the centerline of the PBR floor. The PBR is modeled using the Lagrangian–Eulerian approach. The objective of this research is to predict the performance of PBRs using CFD models, which can be used to improve the design of PBRs used to grow microalgae that are used to produce biofuels and bioproducts.
Machining of Carbon Fiber Reinforced Plastics/Polymers: A Literature Review
Authors: Che Demeng , Saxena Ishan , Han Peidong , Guo Ping , Ehmann Kornel F.
Published: January 2014

Carbon fiber reinforced plastics/polymers (CFRPs) offer excellent mechanical properties that lead to enhanced functional performance and, in turn, wide applications in numerous industrial fields. Post machining of CFRPs is an essential procedure that assures that the manufactured components meet their dimensional tolerances, surface quality and other functional requirements, which is currently considered an extremely difficult process due to the highly nonlinear, inhomogeneous, and abrasive nature of CFRPs. In this paper, a comprehensive literature review on machining of CFRPs is given with a focus on five main issues including conventional and unconventional hybrid processes for CFRP machining, cutting theories and thermal/mechanical response studies, numerical simulations, tool performance and tooling techniques, and economic impacts of CFRP machining. Given the similarities in the experimental and theoretical studies related to the machining of glass fiber reinforced polymers (GFRPs) and other FRPs parallel insights are drawn to CFRP machining to offer additional understanding of on-going and promising attempts in CFRP machining.
Effects of Temperature Changes on Creep Crack Growth for a Low Alloy Butt Weld
Authors: Shi Jinhua
Published: January 2014

R5 is an assessment procedure for the high temperature response of structures and R5 Volume 7 specifies the creep crack growth assessment for low alloy welds.

For high temperature low alloy butt welds, the effects of the welding residual stresses on the creep crack growth for a circumferential defect has been investigated by Shi under a constant temperature of 532.7°C.

In addition to the welding residual stresses, it is well known that temperatures also affect significantly creep deformation, creep rupture and accordingly creep crack growth. Hence, in this paper an investigation for the effects of temperature changes on the creep crack growth and also on component remnant lives has been carried out.

In this paper, for a typical low alloy butt weld in ½Cr½Mo¼V (‘½CMV’) pipework with 2¼Cr weld metal under a given internal pressure and a bending welding residual stress of 60MPa, a series of creep crack growth analyses have been conducted using the R5 Volume 7 assessment procedure, assuming different operating temperatures during different operating periods. A postulated internal circumferential defect (semi-elliptical surface-breaking surface defect) of 2.3 mm deep by 15 mm long has been used.

The investigation results are presented by a series of graphs which show the effects of the temperature changes on the creep crack growth and plant remnant lives for the weld studied. After a detailed discussion, conclusions can be drawn.
Effect of Sound on the Wake of Side-by-Side Cylinders in a Duct
Authors: Arthurs David , Bolduc Michael , Ritcey Adam , Ziada Samir
Published: January 2014

The phenomenon of flow-excited acoustic resonance, where periodic flow oscillations are enhanced by a resonant sound field, is a design concern in many engineering applications such as in heat exchangers, piping systems, and cavity flows. This study experimentally examines the phenomenon of flow-excited acoustic resonance for two side-by-side cylinders in a duct with cross-flow. This geometry has been investigated for three cylinder spacing ratios, defined as the center-to-center distance, normalized by the diameter, of T/D = 1.25, 1.46 and 2.5, and for a range of acoustic pressure amplitudes. Intermediate and small spacing ratios have been given special attention, as these cases have been found to exhibit bistable flow in the wake in the absence of acoustic resonance. Phase-locked PIV measurements reveal that the self-excited sound field produces a strong oscillatory flow pattern in the cylinder wakes, which is symmetric for large spacing ratios and high acoustic amplitudes, but remains bistable for small spacing ratios, even during very intense acoustic resonances. The aeroacoustic sources and sinks within the flow have been computed using Howe’s theory of vortex sound, and the distribution of these sources will be compared for the range of spacing ratios examined in this study.
Aeroacoustics of Opposing Planar Air Jets
Authors: Hassaballa Moustafa , Ziada Samir , Arthurs David
Published: January 2014

The self-excited response of two opposing planar air jets is experimentally examined as a function of both flow velocity of the jets, as well as the impingement distance, i.e. the distance z between them. This initial study is performed for a single jet thickness of h = 2 mm and a spanwise aspect ratio of 50. Two sets of experiments have been performed, with the first set of measurements having been obtained over a range of impingement ratios from z/h = 7 to z/h = 130 for several moderate Mach numbers (M = 0.44, 0.58 & 0.73), whereas the second set of measurements has been performed by varying the jet Mach number at fixed impingement ratios.

The opposing planar jets are found to produce intense acoustic tones over the entire range of impingement ratio and flow velocity examined in this study, showing robust oscillation behavior even for very large distances between the jets. Acoustic tone frequency has been found to increase linearly with the jet exit velocity at constant impingement ratio and to decrease with the impingement distance at constant jet velocity. The flow field over the oscillation cycle has been investigated by means of phase-averaged PIV measurements technique, which has shown that the high noise levels and acoustic tones are produced by a pronounced flapping oscillation of the opposing jet columns.
Comparison of Radiation Embrittlement Prediction Models to High Fluence U.S. Power Reactor Surveillance Data
Authors: Hall Brian , Server William , Rosier Ben , Hardin Tim
Published: January 2014

Uncertainty regarding radiation embrittlement at high fluence, indicative of extended operating life beyond 60 years for current operating pressurized water reactor (PWR) vessels, has been identified as a potential limiting degradation mechanism. There are limited U.S. power reactor surveillance data at fluences greater than about 4E19 n/cm2 (E > 1 MeV) currently available for comparison with existing embrittlement prediction models. Extended operating life to 80 years is projected to have vessel peak fluence approaching 1E20 n/cm2, for a small number of plants. The two current U.S. embrittlement models are contained in Nuclear Regulatory Commission (NRC) Regulatory Guide 1.99, Revision 2, and the Code of Federal Regulations, 10 CFR 50.61a. This paper compares the latest available high fluence power reactor surveillance data to the predictions of these two models, and to another model that has been proposed as better for high fluence data based on combined test reactor and power reactor data from sources extending beyond the U.S. These comparisons indicate the fluence ranges and material groups where the different models deviate from the measured data. The results from these comparisons have been used to select materials for a proposed new PWR supplemental surveillance program (PSSP) that utilizes previously tested irradiated surveillance specimens reconstituted and subsequently re-irradiated to higher fluences.
A New Constitutively Accurate Lower Bound Direct Shakedown Method
Authors: Jappy Alan , Mackenzie Donald , Chen Haofeng
Published: January 2014

Ensuring sufficient safety against shakedown or ratchet is a fundamental requirement of pressure vessel design. Determining the shakedown or ratchet boundary can however prove difficult when using a full elastic plastic finite element analysis and a number of direct methods have been proposed that overcome the difficulties associated with shakedown or ratchet boundary evaluation. Here a new direct lower bound shakedown method, which can be extended to a ratchet method, is proposed. The method maintains a constitutively accurate description of the assumed material response through the use of non-smooth multi yield surface plasticity models. The proposed shakedown method can consider arbitrary load cases and may be solved in a single analysis step in a standard finite element analysis with a user-programed non-smooth multi yield surface plasticity model. It is demonstrated that by maintaining a constitutively accurate description of the plastic strains the method is able to calculate strict lower bound shakedown boundaries. The resulting boundary is shown to give excellent agreement with the upper and lower bound linear matching method.
Assessment of the Influence of Bulging and the Thermal Gradients in the Stress Level in the Cylindrical Section of a Coke Drum
Authors: Araque Egler D. , Vivas Gabriel A.
Published: January 2014

Several studies recognized that cracks in delayed coke drums resulted from low cycle fatigue induced by cyclic thermal stress [1], [2], [3]. According to a coke drum survey coordinated by API in 1996 [1], there are two different areas where cracks are produced. The first zone is located at the shell to skirt weld, and the second at the bulging areas found in the cylindrical section. In the second case, from 145 coke drums 57% reported that had shell bulging problems. Of the drums that bulged, 87% also showed cracks.

In order to estimate the level of stress, finite element analysis of a bulged cylinder was performed. The study was carried out running a sequentially-coupled thermo-mechanical analysis. In the first step, a thermal analysis is used to estimate the variation of temperature with time. These temperatures serve as input to a mechanical stress analysis that was made in a second step.

The assessment shows the influence of thermal gradients obtained for a period of 26 months for several bulging patterns that were identified from the analysis of 28 laser mappings of coke drums. The results indicated that the level of stress could reach the plastic deformation considering that the material has yield strength equal to the minimum specified in ASME Section II, part D. The zones where maximum axial stresses were found are consistent with areas where cracking has been reported in many coke drums.
Deep Well Drilling Applications
Authors: McKie Nigel R. , Peters Daniel T. , Tooley Keegan A.
Published: January 2014

The majority of oilfield Wellhead and Tree equipment has been designed with guidance from codes API 6A and 17D. However, their design methods are not the most appropriate for the new High Pressure High Temperature (HPHT) applications; equipment rated above 15 ksi (103 MPa) Working Pressure and/or above 350 °F (177 °C). This paper discusses the limitations of established design methods and presents more suitable methods for HPHT applications.

FEA is well established as a stress analysis method for use in conventional Pressure Vessel design; however it is not so well established for load bearing interfaces. This leaves a gap in our Design Methods, since load bearing interfaces are intrinsic to Wellhead Equipment Pressure Vessel design. Intrinsic because many of our Pressure Vessels are “capped” by hangers and connectors instead of flanges; if a hanger Load Shoulder fails then the Pressure Vessel above it has failed.

Unique to the oilfield are infrequent but extremely high loads. These loads are much higher than the Working Condition and in most cases they stem from field testing and emergency situations. If the established ASME methods are used for these cases certain projects may not be viable.
A Simplified Method to Determine Initial Estimates of Peak Strains in Composite Explosive Containment Vessels
Authors: Clayton Alan M.
Published: January 2014

Explosive containment vessels made of a fiber-matrix composite require specialized finite element programs to estimate their strains. However for centrally loaded cylindrical vessels the stresses for any general lay up of the fibers in the vessel at the shortest offset of the explosive to the vessel can be assessed by simple analytical methods and these can be used to make initial assessments of the required material and thickness. The results of this simplified method are compared with experimental data on open ended composite tubes carried out by RFNC-VNIIF for Sandia National Laboratories and calculations on these performed by O’Toole et al at the University of Nevada [1].
A Comparison of Finite Element Cohesive-Zone Modelling With the Process-Zone Approach for the Prediction of Delayed Hydride Cracking
Authors: Martin Michael
Published: January 2014

Zirconium alloys, as used in water-cooled nuclear reactors, are susceptible to a time-dependent damage mechanism known as Delayed Hydride Cracking, or DHC. Corrosion of the zirconium alloy in the presence of water generates hydrogen that subsequently diffuses through the metallic structure towards stress concentrating features such as notches or cracks.

Canadian standard CSA N285.8–10 uses a process-zone modelling approach to define a threshold stress level beyond which DHC is predicted to occur. The process-zone analysis to calculate the threshold stress level generally proceeds by representing the process-zone as a crack, the length of which is determined by the superposition of stress intensity factors obtained from handbook solutions or cracked-body finite element models. Process-zone models are a subset of the more general class of cohesive-zone models and cohesive elements are available in a number of standard finite element codes. Cohesive elements can be used to simulate the process-zone response, or indeed more complex cohesive behaviour.

In this paper, the stress and displacement results from finite element based cohesive-zone modelling of a sharp crack and blunt notches of various root radii are compared with analytical process-zone solutions. The cohesive-zone results are also compared with the process-zone formulation used in CSA N285.8–10. The results show that finite element based cohesive-zone analysis can be used to replicate the process-zone results. The key benefit of finite element based cohesive-zone modelling is that it provides a framework for investigating the DHC characteristics of arbitrary hydride distributions, using readily available techniques.
The IN Vessel Retention Strategy to Mitigate the Severe Accidents for the VVER 1000/320 Type NPPs
Authors: Zdarek Jiri
Published: January 2014

After the Fukushima Accident there is a worldwide strategy to develop the Defense in Depth strategy to mitigate the Severe Accidents. This effort has long tradition for new designs of NPPs. However the existing NPPs are lacking such a systematic approach. For the VVER 440 type NPP family the concept of the IN Vessel Strategy was adopted many years ago for the Loviisa NPP in Finland. However the VVER 1000/320 Units are lacking final treatment with the Severe Accidents. Effort of our research is to prepare the analytical and experimental proof to justify this concept for higher power VVER type NPPs.