bluuebunny/crossref_metadata_2025 huggingface dataset:
Cost‐effectiveness considerations for home health V.A.C.® Therapy in the United States of America and its potential international application
Authors: Trueman Paul
Published: June 2008

Vacuum‐assisted closure (V.A.C.®) Therapy (KCI International, San Antonio, TX) has been widely used in hospital settings. However, use of V.A.C.® Therapy in home health settings outside of the United States of America (USA) is often limited because of financial considerations. This review paper considers the published evidence on V.A.C. Therapy in home health settings from the USA and beyond and explores the potential economic implications of V.A.C. Therapy in home health settings.
Vacuum‐assisted closure home care training: a process to link education to improved patient outcomes
Authors: Woo Kevin Y , Sibbald R Gary
Published: June 2008

Negative pressure wound therapy (NPWT) applies subatmospheric pressure across the wound bed inducing cellular and molecular changes that are beneficial to wound healing. This healing modality may facilitate tissue debridement, infection/inflammation control, and moisture balance; the key components of the wound bed preparation paradigm. To ensure that scientific evidence is diffused into daily clinical practice, we are proposing a knowledge transfer model that articulates an educational plan for the various levels of professional development. The discussion highlights the challenges and potential solutions to integrate NPWT into a seamless continuum of care including a community‐based patient care model.
Equal Sex Ratios of a Marine Green Alga, Bryopsis plumosa
Authors: Togashi Tatsuya , Cox Paul Alan
Published: June 2008

By finding some important culture conditions as below, we succeeded in experimentally controlling the whole life history of a dioecious marine green alga, Bryopsis plumosa (Hudson) C. Agardh. In this study, we focused on the primary and secondary sex ratios (i.e. at inception and maturity) using these culture techniques. Gametogenesis was induced by culturing haploid gametophytes with Provasoli's enriched seawater (PES) medium under a 14:10 h light : dark cycle at 14 °C. Formed zygotes grew into diploid sporophytes, which were cultured for 3 months with PES medium under a 14:10 h light : nbsp;dark cycle at 18 °C. Then they were transferred into Schreiber medium and cultured under a 10:14 h light : dark cycle at 22 °C. Within 1 week, zoosporogenesis was observed. Zoospores were released within a couple of days. Each zoospore soon germinated and grew into a unisexual gametophyte. The primary sex ratio was examined in gametophytes that originated from a single sporophyte. The secondary sex ratio was studied in the field. Both were estimated as 1:1. Synchronized meiotic cell divisions might occur during zoosporogenesis dividing each sex‐determining factor evenly among zoospores. Given the equal sex ratio at maturity, there seems to be no environmental factor that differentially affects the survival of male or female gametophytes in nature.
Accumulation of Zinc, Cadmium, and Lead in Four Populations ofSedum alfrediiGrowing on Lead/Zinc Mine Spoils
Authors: Deng Dong‐Mei , Deng Jin‐Chuan , Li Jin‐Tian , Zhang Jun , Hu Min , Lin Zhou , Liao Bin
Published: June 2008

Sedum alfrediiHance is a newly reported zinc (Zn) and cadmium (Cd) hyperaccumulator native to China. In this study, four populations ofS. alfrediiwere collected from Yejiwei (YJW), Jinchuantang (JCT) and Qiaokou (QK) lead (Pb)/Zn mines located in Hunan Province as well as Quzhou (QZ) Pb/Zn mine located in Zhejiang Province for exploring the intraspecies difference of this plant in metal accumulation. Although they grew in the Pb/Zn spoils with relatively similar levels of Zn, Cd and Pb, remarkable differences among the four populations in tissue heavy metal concentrations were observed. The shoot Zn concentration of QZ population (11 116 mg/kg) was highest and nearly five times higher than that of the JCT population (1 930 mg/kg). Furthermore, the shoot Cd concentration observed in the QZ population (1 090 mg/kg) was also highest and 144 times higher than that found in the JCT population (7.5 mg/kg). As for Pb concentrations in the shoot of different populations, a fourfold difference between the highest and the lowest was also found. Such difference on metal accumulation was population‐specific and may be significantly explained by differences in the soil properties such as pH, organic matter (OM), and electrical conductivity (EC). Taking biomass and metal concentration in plants into consideration, the QZ, YJW and QK populations may have high potential for Zn phytoremediation, the QZ population may have the highest potential in Cd phytoremediation, and the QK population may be the most useful in Pb phytoremediation.
Acid Phosphatase Activity May Affect the Tuber Swelling by Partially Regulating Sucrose‐mediated Sugar Resorption in Potato
Authors: Wang Da‐Yong , Lian Yong , Zhu De‐Wei
Published: June 2008

APase activity is involved in regulating many physiological and developmental events by affecting the resorption process. In this study, we investigate the role of APase activity in tuber development in potato. APase activities were mainly localized in cytoplasm, gaps among cells and stroma of amyloplasts of parenchyma cells at the stage of tuber swelling. AP1, encoding a putative APase, was also highly expressed in swelling tubers and a low level of expression was observed in elongated stolons and matured tubers. Inhibition of APase activity by applying Brefeldin A, an inhibitor of APase production and secretion, significantly suppressed the tuber swelling and moderately affected the stolon elongation and the tuberization frequency. During tuber development, sucrose serves as the main soluble sugar for long‐distance transportation and resorption. Moreover, inhibition of APase activity by Brefeldin A markedly reduced the sucrose content in tubers and further decreased the starch accumulation, suggesting that the function of APase in regulating the tuber swelling might be at least partially mediated by the sugar resorption. Exogenous sucrose treatments further indicate the important role of sucrose‐mediated sugar resorption in tuber swelling. These results suggest that the APase activity might affect the tuber swelling by partially regulating the sucrose‐mediated sugar resorption.
Is Mass‐based Metabolism Rate Proportional to Surface Area in Plant Leaves? A Data Re‐analysis
Authors: Jin Dongmei , Dai Yiqiang , Sun Li , Sun Shucun
Published: June 2008

We re‐analyzed two large published databases on leaf traits of plant species from seven different biomes, and determined the scaling relationship between leaf metabolism rate (mass‐based photosynthesis capacity, Amass, and mass‐based dark respiration, Rdmass) and specific leaf area (SLA) across biomes, using a standardized major axis (SMA) method. Overall pooled data produced a scaling exponent of 1.33 for the relationship between Amass and SLA, significantly larger than 1.0; and 1.04 between Rdmass and SLA. The scaling exponent of the relationship between Amass and SLA ranged between 1.23 (in tropical forest) and 1.66 (in alpine biome), and it was significantly larger in alpine (1.66) and grass/meadow (1.52) biomes than in tropical forest (1.23) and wetland (1.27). The exponent of the relationship between Rdmass and SLA, however, was much smaller in wetland (1.05) than in temperate forest (1.29) and tropical rainforest (1.65). In general, the predicated universal scaling relationship that the mass‐based metabolism rate should be proportional to surface area in organisms is not applicable at the leaf‐level in plants. Rather, the large slope difference of the relationship between leaf metabolism rate and SLA found among biomes indicates that the strength of the selective forces driving the scaling relationship is different among the biomes. The result basically suggests the importance of increasing SLA to plant carbon gain in stressful environments and to carbon loss in favorable habitats, and therefore has an important implication for survival strategies of plants in different biomes.
Modelling the RXTE light curve of η Carinae from a 3D SPH simulation of its binary wind collision
Authors: Okazaki A. T. , Owocki S. P. , Russell C. M. P. , Corcoran M. F.
Published: June 2008

The very massive star system η Carinae exhibits regular 5.54 yr (2024 d) period disruptive events in wavebands ranging from the radio to X-ray. There is a growing consensus that these events likely stem from periastron passage of an (as yet) unseen companion in a highly eccentric (e∼ 0.9) orbit. This Letter presents 3D smoothed particle hydrodynamics (SPH) simulations of the orbital variation of the binary wind–wind collision, and applies these to modelling the X-ray light curve observed by the Rossi X-ray Timing Explorer (RXTE). By providing a global 3D model of the phase variation of the density of the interacting winds, the simulations allow computation of the associated variation in X-ray absorption, presumed here to originate from near the apex of the wind–wind interaction cone. We find that the observed RXTE light curve can be readily fitted if the observer's line of sight is within this cone along the general direction of apastron. Specifically, the data are well fitted by an assumed inclination i= 45° for the orbit's polar axis, which is thus consistent with orbital angular momentum being along the inferred polar axis of the Homunculus nebula. The fits also constrain the position angle φ that an orbital-plane projection makes with the apastron side of the semimajor axis, strongly excluding positions φ < 9° along or to the retrograde side of the axis, with the best-fitting position given by φ= 27°. Overall the results demonstrate the utility of a fully 3D dynamical model for constraining the geometric and physical properties of this complex colliding wind binary system.
Stellar dynamical evidence against a cold disc origin for stars in the Galactic Centre
Authors: Cuadra Jorge , Armitage Philip J. , Alexander Richard D.
Published: June 2008

Observations of massive stars within the central parsec of the Galaxy show that, while most stars orbit within a well-defined disc, a significant fraction have large eccentricities and/or inclinations with respect to the disc plane. Here, we investigate whether this dynamically hot component could have arisen via scattering from an initially cold disc – the expected initial condition if the stars formed from the fragmentation of an accretion disc. Using N-body methods, we evolve a variety of flat, cold, stellar systems, and study the effects of initial disc eccentricity, primordial binaries, very massive stars and intermediate mass black holes. We find, consistent with previous results, that a circular disc does not become eccentric enough unless there is a significant population of undetected 100–1000 M⊙ objects. However, since fragmentation of an eccentric disc can readily yield eccentric stellar orbits, the strongest constraints come from inclinations. We show that none of our initial conditions yields the observed large inclinations, regardless of the initial disc eccentricity or the presence of massive objects. These results imply that the orbits of the young massive stars in the Galactic Centre are largely primordial, and that the stars are unlikely to have formed as a dynamically cold disc.
Extraction and Characterization of Chickpea (Cicer arietinum) Albumin and Globulin
Authors: Liu L.H. , Hung T.V. , Bennett L.
Published: June 2008

ABSTRACT:  Albumin and globulin fractions of 1 Desi and 2 Kabuli varieties of chickpeas (Cicer arietinum) were extracted with water and salt solutions (K2SO4 and NaCl). The extractable yields and particularly the albumin‐globulin ratio varied greatly with the extraction medium and chickpea variety. Depending on the procedure employed, albumin could be extracted as a major fraction of chickpea proteins. Higher levels of essential amino acids and sulfur containing amino acids were found in albumins than in globulins of all chickpeas investigated. The common structural characteristics of both Kabuli and Desi chickpea albumins and globulins were clearly identified by densitometric profiles of their sodium dodecyl sulfate polyacrylamide gel patterns. Albumins contained subunits with higher molecular weights than those of globulins. The in vitro digestibility of the chickpea proteins by papain, pepsin, chymotrypsin, and trypsin indicated that globulins were more susceptible to proteolytic hydrolysis.
Effect of Snow Cover Conditions on the Hydrologic Regime: Case Study in a Pluvial‐Nival Watershed, Japan1
Authors: Whitaker Andrew C. , Sugiyama Hironobu , Hayakawa Kaichi
Published: June 2008

Abstract:  Hydrologic monitoring in a small forested and mountainous headwater basin in Niigata Prefecture has been undertaken since 2000. An important characteristic of the basin is that the hydrologic regime contains pluvial elements year‐round, including rain‐on‐snow, in addition to spring snowmelt. We evaluated the effect of different snow cover conditions on the hydrologic regime by analyzing observed data in conjunction with model simulations of the snowpack. A degree‐day snow model is presented and applied to the study basin to enable estimation of the basin average snow water equivalent using air temperature at three representative elevations. Analysis of hydrological time series data and master recession curves showed that flow during the snowmelt season was generated by a combination of ground water flow having a recession constant of 0.018/day and diurnal melt water flow having a recession constant of 0.015/hour. Daily flows during the winter/snowmelt season showed greater persistence than daily flows during the warm season. The seasonal water balance indicated that the ratio of runoff to precipitation during the cold season (December to May) was about 90% every year. Seasonal snowpack plays an important role in defining the hydrologic regime, with winter precipitation and snowmelt runoff contributing about 65% of the annual runoff. The timing of the snowmelt season, indicated by the date of occurrence of the first significant snowmelt event, was correlated with the occurrence of low flow events. Model simulations showed that basin average snow water equivalent reached a peak around mid‐February to mid‐March, although further validation of the model is required at high elevation sites.
Institutional Investors and Shareholder Litigation
Authors: Barabanov Sergey S. , Ozocak Onem , Turtle H.J. , Walker Thomas J.
Published: June 2008

We examine whether institutional investors are able to avoid future litigation. Our results show that institutions provide a fiduciary role by decreasing or eliminating their positions in sued firms well before litigation begins. We also find that institutional groups with high monitoring ability (independent investment advisors and mutual funds) are more proactive in their trading behavior than are institutions with low monitoring ability (banks, insurance companies, and unclassified institutions such as endowments, foundations, and self‐managed pension funds). We find that percentage changes in institutional ownership are correlated with public information available more than two quarters before litigation.
Do Analysts Influence Corporate Financing and Investment?
Authors: Doukas John A. , Kim Chansog (Francis) , Pantzalis Christos
Published: June 2008

We examine whether abnormal analyst coverage influences the external financing and investment decisions of the firm. Controlling for self‐selection bias in analysts' excessive coverage, we find that firms with high (low) analyst coverage consistently engage in higher (lower) external financing than do their industry peers of similar size. Our evidence also demonstrates that firms with excessive analyst coverage overinvest and realize lower future returns than do firms with low analyst coverage. Our findings are consistent with the hypothesis that analysts favor the coverage of firms that have the potential to engage in profitable investment‐banking business.
Capital Structure Choice in a Nascent Market: Evidence from Listed Firms in China
Authors: Bhabra Harjeet S. , Liu Tong , Tirtiroglu Dogan
Published: June 2008

We study the capital structure decisions of listed firms in China between 1992 and 2001. The Chinese market exhibits high information asymmetry, phenomenal growth, highly concentrated ownership, and a lack of external market for corporate control. We find that Chinese firms use little long‐term debt, which is positively (negatively) related to firm size and tangibility (profitability and growth options). These results are robust to the degree of seasoning after the initial public offering and private versus State ownership. Although industry membership is important, the development and growth of the stock market did not affect the long‐term debt ratios over the years.
Computational Investigation of Torque on Coaxial Rotating Cones
Authors: Rapley Steve , Eastwick Carol , Simmons Kathy
Published: June 2008

This article looks at a modification of Taylor–Couette flow, presenting a numerical investigation of the flow around a shrouded rotating cone, with and without throughflow, using the commercial computational fluid dynamics code FLUENT 6.2 and FLUENT 6.3. The effects of varying the cone vertex angle and the gap width on the torque seen by the rotating cone are considered, as well as the effect of a forced throughflow. The performance of various turbulence models are considered, as well as the ability of common wall treatments/functions to capture the near-wall behavior. Close agreement is found between the numerical predictions and previous experimental work, carried out by Yamada and Ito (1979, “Frictional Resistance of Enclosed Rotating Cones With Superposed Throughflow,” ASME J. Fluids Eng., 101, pp. 259–264; 1975, “On the Frictional Resistance of Enclosed Rotating Cones (1st Report, Frictional Moment and Observation of Flow With a Smooth Surface),” Bull. JSME, 18, pp. 1026–1034; 1976, “On the Frictional Resistance of Enclosed Rotating Cones (2nd Report, Effects of Surface Roughness),” Bull. JSME, 19, pp. 943–950). Limitations in the models are considered, and comparisons between two-dimensional axisymmetric models and three-dimensional models are made, with the three-dimensional models showing greater accuracy. The work leads to a methodology for modeling similar flow conditions to Taylor–Couette.
An Energetic Control Methodology for Exploiting the Passive Dynamics of Pneumatically Actuated Hopping
Authors: Zhu Yong , Barth Eric J.
Published: June 2008

This paper presents an energetically derived control methodology to specify and regulate the oscillatory motion of a pneumatic hopping robot. An ideal lossless pneumatic actuation system with an inertia is shown to represent an oscillator with a stiffness, and hence frequency, related to the equilibrium pressures in the actuator. Following from an analysis of the conservative energy storage elements in the system, a control methodology is derived to sustain a specified frequency of oscillation in the presence of energy dissipation. The basic control strategy is to control the pressure in the upper chamber of the pneumatic cylinder to specify the contact time of the piston, while controlling the total conservative energy stored in the system to specify the flight time and corresponding flight height of the cylinder. The control strategy takes advantage of the natural passive dynamics of the upper chamber to provide much of the required actuation forces and natural stiffness, while the remaining forces needed to overcome the energy dissipation present in a nonideal system with losses are provided by a nonlinear control law for the charging and discharging of the lower chamber of the cylinder. Efficient hopping motion, relative to a traditional nonconservative actuator, is achieved by allowing the energy storing capability of a pneumatic actuator to store and return energy to the system at a controlled specifiable frequency. The control methodology is demonstrated through simulation and experimental results to provide accurate and repeatable hopping motion for pneumatically actuated robots in the presence of dissipative forces.
Multiharmonic Adaptive Vibration Control of Misaligned Driveline via Active Magnetic Bearings
Authors: DeSmidt Hans A. , Wang K. W. , Smith Edward C.
Published: June 2008

Active magnetic bearings (AMBs) have been proposed by many researchers and engineers as an alternative to replace traditional contact bearings in rotor and driveshaft systems. Such active, noncontact bearings do not have frictional wear and can be used to suppress vibration in sub- and supercritical rotor-dynamic applications. One important issue that has not yet been addressed by previous AMB-driveline control studies is the effect of driveline misalignment. Previous research has shown that misalignment causes periodic parametric and forcing actions, which greatly impact both driveline stability and vibration levels. Therefore, in order to ensure closed-loop stability and acceptable performance of any AMB controlled driveline subjected to misalignment, these effects must be accounted for in the control system design. In this paper, a hybrid proportional derivative (PD) feedback/multiharmonic adaptive vibration control (MHAVC) feedforward law is developed for an AMB/U-joint-driveline system, which is subjected to parallel-offset misalignments, imbalance, and load-torque operating conditions. Conceptually, the PD feedback ensures closed-loop stability while the MHAVC feedforward suppresses steady-state vibration. It is found that there is a range of P and D feedback gains that ensures both MHAVC convergence and closed-loop stability robustness with respect to shaft internal damping induced whirl and misalignment effects. Finally, it is analytically and experimentally demonstrated that the hybrid PD-MHAVC law effectively adapts to and suppresses multiharmonic vibration induced by imbalance, misalignment, and load-torque effects at multiple operating speeds without explicit knowledge of the disturbance conditions.
Dynamic Modeling and Experimental Testing of a Piano Action Mechanism With a Flexible Hammer Shank
Authors: Izadbakhsh Adel , McPhee John , Birkett Stephen
Published: June 2008

The piano action is the mechanism that transforms the finger force applied to a key into a motion of a hammer that strikes a piano string. This paper presents a state-of-the-art model of a grand piano action, which is based on the five main components of the action mechanism (key, whippen, jack, repetition lever, and hammer). Even though some piano action researchers (e.g., Askenfelt and Jansson) detected some flexibility for the hammer shank in their experiments, all previous piano models have assumed the hammers to be rigid bodies. In this paper, we have accounted for the hammer shank flexibility using a Rayleigh beam model. It turns out that the flexibility of the hammer shank does not significantly affect the rotation of the other parts of the piano mechanism and the impact velocity of the hammer head, compared to the case that the hammer shank has been modeled as a rigid part. However, the flexibility of the hammer shank causes a greater scuffing motion for the hammer head during the contact with the string. To validate the theoretical results, experimental measurements were taken by two strain gauges mounted on the hammer shank, and by optical encoders at three of the joints.
A Direct Approach to Order Reduction of Nonlinear Systems Subjected to External Periodic Excitations
Authors: Redkar Sangram , Sinha S. C.
Published: June 2008

In this work, the basic problem of order reduction of nonlinear systems subjected to an external periodic excitation is considered. This problem deserves special attention because modes that interact (linearly or nonlinearly) with external excitation dominate the response. These dominant modes are identified and chosen as the “master” modes to be retained in the reduction process. The simplest idea could be to use a linear approach such as the Guyan reduction and choose those modes whose natural frequencies are close to that of external excitation as the master modes. However, this technique does not guarantee accurate results when nonlinear interactions are strong and a nonlinear approach must be adopted. Recently, the invariant manifold technique has been extended to forced problems by “augmenting” the state space, i.e., forcing is treated as an additional state and an invariant manifold is constructed. However, this process does not provide a clear picture of possible resonances and conditions under which an order reduction is possible. In a direct innovative approach suggested here, a nonlinear time-dependent relationship between the dominant and nondominant states is assumed and the dimension of the state space remains the same. This methodology not only yields accurate reduced order models but also explains the consequences of various primary and secondary resonances present in the system. One obtains various reducibility conditions in a closed form, which show interactions among eigenvalues, nonlinearities and the external excitation. One can also recover all “resonance conditions” obtained via perturbation or averaging techniques. The “linear” as well as the “extended invariant manifold” techniques are applied to some typical problems and results for large-scale and reduced order models are compared. It is anticipated that these techniques will provide a useful tool in the analysis and control of large-scale externally excited nonlinear systems.
Leveraging the Equivalence of Hysteresis Models From Different Fields for Analysis and Numerical Simulation of Jointed Structures
Authors: Royston T. J.
Published: June 2008

An important problem that spans across many types of systems (e.g., mechanical and biological) is how to model the dynamics of joints or interfaces in built-up structures in such a way that the complex dynamic and energy-dissipative behavior that depends on microscale phenomena at the joint/interface is accurately captured, yet in a framework that is amenable to efficient computational analyses of the larger macroscale system of which the joint or interface is a (spatially) small part. Simulating joint behavior in finite element analysis by meshing the joint regions finely enough to capture relevant micromechanics is impractical for large-scale structural systems. A more practical approach is to devise constitutive models for the overall behavior of individual joints that accurately capture their nonlinear and energy-dissipative behavior and to locally incorporate the constitutive response into the otherwise often-linear structural model. Recent studies have successfully captured and simulated mechanical joint dynamics using computationally simple phenomenological models of combined elasticity and slip with associated friction and energy dissipation, known as Iwan models. In the present article, the author reviews the relationship, and in some cases equivalence, of one type of Iwan model to several other models of hysteretic behavior that have been used to simulate a wide range of physical phenomena. Specifically, it is shown that the “parallel-series” Iwan model has been referred to in other fields by different names, including “Maxwell resistive capacitor,” “Ishlinskii,” and “ordinary stop hysteron.” Given this, the author establishes the relationship of this Iwan model to several other hysteresis models, most significantly the classical Preisach model. Having established these relationships, it is then possible to extend analytical tools developed for a specific hysteresis model to all of the models with which it is related. Such analytical tools include experimental identification, inversion, and analysis of vibratory energy flow and dissipation. Numerical case studies of simple systems that include an Iwan-modeled joint illustrate these points.
Investigation of Mechanical Couplings of Rigid Serial Manipulators
Authors: Herman Przemysław
Published: June 2008

In this paper, an approach that enables one to investigate and to reduce the mechanical couplings between the manipulator links is proposed. The presented method is based on equations of motion expressed in terms of the normalized quasivelocities (NQV) introduced originally by Jain and Rodriguez (1995, “Diagonalized Lagrangian Robot Dynamics,” IEEE Trans. Rob. Autom., 11, pp. 571–584). As a result, some observations and an algorithm which can be used at the design step of manipulators are done. Moreover, it is shown that for a rigid manipulator a class of integrable desired trajectories of the NQV can be given. The presented strategy was tested by simulation on a 3 DOF spatial manipulator.
Dynamics of Propagating Buckles in Deep-Water Pipelines
Authors: Song H.-W. , Tassoulas J. L.
Published: June 2008

A computational technique is described for the analysis of propagating buckles in deep-water piplines. The technique is applied to an aluminum-alloy pipe for which experimental results are available. Quasi-static as well as dynamic buckles are obtained. The analytical results are presented and discussed in comparison with the experimental data.
Foundation Safety of Gravity-Based Systems During Severe Storms
Authors: Ronold K. O. , Haver S.
Published: June 2008

The temporal evolutions of the most important sea state characteristics during storms are presented together with the corresponding uncertainties. Storm data from the Northern North Sea are used for this purpose. The influence of the uncertainties associated with an extreme storm on the foundation safety is demonstrated for a gravity-based structural system founded on a clay. The stability is analyzed with respect to failure in large cyclic displacements accumulated during the storm. The failure probability is estimated by a first-order reliability method and the most important variables concerning their contribution to the failure probability are indicated. In most practical foundation safety investigations, an idealized deterministic storm profile is adopted. The adequacy of this profile is considered by calibrating a “load factor” to be used in connection with the idealized profile.
Estimation of Ship Roll Parameters in Random Waves
Authors: Roberts J. B. , Dunne J. F. , Debonos A.
Published: June 2008

The problem of estimating the parameters in an equation of roll motion from roll measurements only, taken in an irregular sea, is discussed. A single degree of freedom equation of motion is assumed, with a wide-band stochastic input and with a linear-in-the-parameters representation of both the damping and restoration terms. A method based on the Markov property of the energy envelope process, associated with the roll motion, is developed which enables all the relevant parameters to be estimated. The method is validated by applying it to some simulated data, for which the true parameters are known.
Vortex Trajectories Around a Circular Cylinder in Oscillatory Plus Mean Flow
Authors: Sarpkaya T. , Putzig C. , Gordon D. , Wang X. , Dalton C.
Published: June 2008

The vorticity-stream function equations and a third-order in time, second-order in space, three-level predictor-corrector finite-difference scheme has been used to carry out numerical experiments on laminar pulsatile flow (with nonzero mean). The results have revealed, for the first time, the existence of a very interesting wake comprised of three rows of heterostrophic vortices at certain Keulegan-Carpenter numbers and relative current velocities. The existence of such a street has been vindicated by physical experiments. The calculations have also shown that the drag and inertia coefficients for K=4–6 are in reasonable agreement with those obtained experimentally at corresponding relative current velocities.
A Numerical Solution for Potential Flows Including the Effects of Vortex Shedding
Authors: Wong L. H. , Calisal S. M.
Published: June 2008

This paper reports on an attempt to include vortex shedding effects into potential flow calculations using the boundary element method. Significant computational advantages result because of the relatively simple approach to handling separation at the sharp edges while working only with the boundary values. A discrete vortex method was incorporated into a time domain boundary element algorithm for the numerical simulation of oscillating flow past a normal flat plate. Separation from a sharp edge results in the formation of a vortex sheet issuing from the edge. This vortex sheet is modeled by a series of discrete vortices introduced one at a time into the flow field at regular intervals. The motion of each vortex is traced over time using its convection velocity. As long as the Keulegan-Carpenter number is small enough, vortex shedding takes place close to the edge. The discrete vortex method can, in such cases, be looked upon as the inner region solution to the problem of normal oscillating flow past the flat plate. This inner region solution has to be matched with the outer potential flow solution. The combination of boundary element and discrete vortex methods provides this matching and at the same time does not require calculations inside the domain.
Buckle Propagation Pressure for Submarine Pipelines
Authors: Hahn G. D. , She M. , Carney J. F.
Published: June 2008

A new analytical expression is proposed for the prediction of the buckle propagation pressure for deepwater offshore pipelines. The expression accounts for the influences of the main factors involved, including the effects of material and geometrical nonlinearities. Predictions of the proposed expression are shown to be in good agreement with available experimental data, and valuable information is developed that can guide applications of the expression in design practice. In addition, a discussion is presented which outlines the derivation of the proposed expression.
Reliability of Complex Structures by Large Admissible Perturbations
Authors: Beyko E. , Bernitsas M. M.
Published: June 2008

The perturbation approach to reliability (PAR) is a powerful methodology for reliability analysis and design of large structures. Its main features are: F1) PAR provides the exact global failure equation for any failure criterion for which the corresponding structural analysis can be performed by finite elements. F2) Geometry, material, and loads appear explicitly in the global failure equations and are treated as random variables. No need arises for load path selection or load pattern specification. F3) PAR introduces an invariant and consistent redundancy definition as an injective mapping restricted on the failure surface. Thus, the redundancy/reliability of the structure is expressed in terms of the redundancy/reliability of its structural components. F4) The norm of the Rosenblatt transformed reliability injection is the reliability index. F5) For each global failure equation or combination of failure equations, PAR computes the individual or joint design points without enumerating paths to failure, trial and error, or repeated finite element analyses. F6) Serviceability or ultimate global structural failure is defined by specifying a threshold value of any quantity that can be computed by finite elements: natural frequencies, dynamic normal modes, static deflections, static stresses, buckling loads, and buckling modes are implemented in PAR. Stress failure equations are used along with linearized plasticity surfaces to identify element failure. Several applications are presented to assess PAR.
Effect of Thread Pitch and Frictional Coefficient on the Stress
Concentration in Metric Nut-Bolt Connections
Authors: Dragoni E.
Published: June 2008

By means of the finite element method, this paper establishes how much the stress state within standard metric nut-bolt connections is affected by variations of the thread pitch and of the frictional coefficient. Following a validated simplified approach, the actual three-dimensional geometry of each connection is replaced by an axisymmetric model which recreates the outline of the joint on an appropriate meridional section. The numerical data prove that, for prescribed nominal thread diameter and bolt load, the peak stress in the screw monotonically increases as the pitch decreases. Further, as far as complete sticking between nut and bolt is not achieved, the stress level linearly increases with the coefficient of friction, the rate of variations being higher at the lowest pitches.
Propagation of Continuum Damage in a Viscoelastic Ice Bar
Authors: Shin J. G. , Karr D. G.
Published: June 2008

An initial value problem of a semi-infinite nonlinear viscoelastic bar is solved with continuum damage evolution. The evolution law of the continuum damage for a viscoelastic material is used in order to explore the propagation of two crushing mechanisms: grain boundary cracking and transgranular cracking. Using the method of characteristics, the speed of propagation is found to be dependent on the continuum damage. On the wave front, the delayed elastic strain is zero, and only the continuum damage due to the transgranular cracking evolves. A finite difference method is developed to solve the governing equations on the obtained characteristic lines, and gives a stable solution of the propagation of the stress, strain, and damage. Numerical results are obtained and discussed using the material properties of polycrystalline ice.
Wave Force Coefficient Correlation Based on Wake Volume Scaling
Authors: Horton T. E. , Feifarek M. J. , Golestanian H.
Published: June 2008

A correlation of the hydrodynamic drag force on a cylinder for a periodic motion is demonstrated. The correlation indicates the dependance of the unsteady flow drag coefficient on the wake volume parameter. This parameter is a measure of the volume of flow through the boundary layer and into the wake in a half-cycle. For a laminar boundary layer, this dimensionless parameter is proportional to the Keulegan-Carpenter number and inversely proportional to the square root of the Reynolds number. Using wake volume scaling, drag coefficients were effectively collapsed into a single curve.
Statistics of Combined Linear and Quadratic Springing Response of a
TLP in Random Waves
Authors: Naess A.
Published: June 2008

The paper presents the results of statistical analyses of combined first-order and second-order, sum-frequency response in heave, pitch, and roll of a TLP structure subjected to random, long-crested seas. The results are based on available numerically calculated data for the linear and quadratic transfer functions from the waves to the hydrodynamic loads on the TLP. It has also been assumed that the equations of motion in heave, pitch, and roll can be reasonably well approximated by a set of uncoupled, linear, and time-invariant equations.
Hydrodynamic Force Corrections for Model Tests in a Narrow Wave Tank
Authors: McIver P.
Published: June 2008

During physical model tests of offshore structures in narrow wave tanks, wave reflections from the tank walls may substantially affect the hydrodynamic pressures and forces on the structure when compared with the values that would be experienced in the open sea. A number of recent papers have given theoretical models for the scattering and radiation of waves by specific bodies in a narrow wave tank, and this body of work gives valuable insight into tank confinement effects. The question arises: “Can the open sea characteristics be deduced solely from measurements of the wave field made in the tank, and without resort to detailed numerical calculations for the particular structure concerned?” This question is addressed in the present work in which a method is presented for constructing the open-sea scattered wave field solely from knowledge of the wave field in a narrow tank. Here the method is used to correct the mean drift force on a vertical, circular cylinder.
Effect of Rib-Angle Orientation on Local Mass Transfer Distribution in a Three-Pass Rib-Roughened Channel
Authors: Han J. C. , Zhang P.
Published: June 2008

In this experimental investigation of the heat transfer characteristics of turbulent air flow in a three-pass square channel, the test section consisted of three straight square channels jointed by two 180 deg turns, modeling the internal cooling passages of gas turbine airfoils. Naphthalene-coated ribs were attached to the top and bottom walls of the naphthalene-coated, three-pass channel. The rib height-to-hydraulic diameter ratio was 0.063; the rib pitch-to-height ratio was 10; the rib angles were 90 and 60 deg. For α = 60 deg, both the crossed ribs (on two opposite walls of the cooling channel) and the parallel ribs (on two opposite walls of the cooling channel) were investigated. The combined effects of the two sharp 180 deg turns and the rib orientations on the distributions of the local mass transfer coefficient in the entire three-pass channel were determined. The rib angle, the rib orientation, and the sharp 180 deg turn significantly affect the local mass transfer distributions. The combined effects of these parameters can increase or decrease the mass transfer coefficients after the sharp 180 deg turns. The angled ribs, in general, provide higher mass transfer coefficients than the transverse ribs; the parallel ribs give higher mass transfer than the crossed ribs.
Assessment of Laminar-Turbulent Transition in Closed Disk Geometries
Authors: Morse A. P.
Published: June 2008

Finite-difference solutions are presented for rotationally induced flows in the closed space between two coaxial disks and an outer cylindrical shroud, in which there is no superimposed flow. The solutions are obtained with an elliptic-flow calculation procedure and an anisotropic low turbulence Reynolds number k-ε model for the estimation of turbulent fluxes. The transition from laminar to turbulent flow is effected by including in the energy production term a small fraction (0.002) of the “turbulent viscosity” as calculated from a simple mixing length model. This level for the artificial energy input was chosen as that appropriate for transition at a local rotational Reynolds number of 3 × 105 for the flow over a free, rotating disk. The main focus of the paper is the rotor-stator system, for which the influence of rotational Reynolds number (over the range 105–107) is investigated. Predicted velocity profiles and disk moment coefficients show reasonably good agreement with available experimental data. The computational procedure is then extended to cover the cases of corotating and counterrotating systems, with variable relative disk speed.
Simulating Boundary Layer Transition With Low-Reynolds-Number k–ε Turbulence Models: Part 2—An Approach to Improving the Predictions
Authors: Schmidt R. C. , Patankar S. V.
Published: June 2008

An approach for improving the prediction of boundary layer transition with k–ε type low-Reynolds-number turbulence models is developed and tested. A modification is proposed that limits the production term in the turbulent kinetic energy equation and is based on a simple stability criterion and correlated to the free-stream turbulence level. The modification becomes inactive in the fully turbulent regime, but is shown to improve both the qualitative and quantitative characteristics of the transition predictions. Although the approach is not limited to a particular low-Reynolds-number model, it is implemented herein using the model of Lam and Bremhorst (1981).
The Mass Transfer Analogy to Heat Transfer in Fluids With Temperature-Dependent Properties
Authors: Shadid J. N. , Eckert E. R. G.
Published: June 2008

The analogy between heat transfer in a single-component fluid and isothermal mass transfer of a two-component fluid without chemical reaction is presented. The analogy is well established and frequently used for fluids with constant properties. However, in various applications such as in the cooling of hot components in gas turbines, the temperature varies widely, causing significant fluid property variations. The present paper reviews the constant-property situation and considers in detail the conditions necessary to ensure similarity of the two transport processes with temperature and concentration-dependent fluid properties. An application of the variable property analogy to mass transfer in binary mixtures is presented along with specific recommendations for the CO2–air and Freon-air systems. It is demonstrated that the essential similarity conditions of the analogy are very well fulfilled for film cooling, total coverage film cooling, and impingement cooling when the heat (mass) flux into the wall in the transport process is zero. The heat/mass transfer analogy can, therefore, be used with confidence for these processes.
Aerodynamic and Torque Characteristics of Enclosed Co/Counterrotating Disks
Authors: Daniels W. A. , Johnson B. V. , Graber D. J.
Published: June 2008

Experiments were conducted to determine the aerodynamic and torque characteristics of adjacent rotating disks enclosed in a shroud. These experiments were performed to obtain an extended data base for advanced turbine designs such as the counterrotating turbine. Torque measurements were obtained on both disks in the rotating frame of reference for corotating, counterrotating, and one-rotating/one-static disk conditions. The disk models used in the experiments included disks with typical smooth turbine geometry, disks with bolts, disks with bolts and partial bolt covers, and flat disks. A windage diaphragm was installed at midcavity for some experiments. The experiments were conducted with various amounts of coolant throughflow injected into the disk cavity from the disk hub or from the disk o.d. with swirl. The experiments were conducted at disk tangential Reynolds number up to 1.6 × 107 with air as the working fluid. The results of this investigation indicated that the static shroud contributes a significant amount to the total friction within the disk system, the torque on counterrotating disks is essentially independent of coolant flow total rate, flow direction, and tangential Reynolds number over the range of conditions tested, and a static windage diaphragm reduces disk friction in counterrotating disk systems.
Heat Transfer in Rotating Serpentine Passages With Smooth Walls
Authors: Wagner J. H. , Johnson B. V. , Kopper F. C.
Published: June 2008

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large-scale, multipass, smooth-wall heat transfer model with both radially inward and outward flow. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. These four parameters were varied over ranges that are typical of advanced gas turbine engine operating conditions. It was found that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs and that the effect of rotation on the heat transfer coefficients was markedly different depending on the flow direction. Local heat transfer coefficients were found to decrease by as much as 60 percent and increase by 250 percent from no-rotation levels. Comparisons with a pioneering stationary vertical tube buoyancy experiment showed reasonably good agreement. Correlation of the data is achieved employing dimensionless parameters derived from the governing flow equations.