bluuebunny/crossref_metadata_2025 huggingface dataset:
The reciprocal dynamics of organizing and sense‐making in the implementation of major public‐sector reforms
Authors: Denis Jean‐Louis , Lamothe Lise , Langley Ann , Breton Mylaine , Gervais Julie , Trottier Louise‐Hélène , Contandriopoulos Damien , Dubois Carl‐Ardy
Published: June 2009

Abstract: Drawing on a longitudinal study from the early years of implementation of health‐care networks in Quebec, this article describes how public‐sector managers deal with complex challenges when both organizational structures and organizational strategies are radically transformed simultaneously. The new organizations studied had to completely re‐shuffle roles and responsibilities of their management teams while making sense of their new mandate of developing a population‐focused approach to health problems – all the time maintaining day‐to‐day operations. The four health‐care networks studied proceeded somewhat differently to meet these reciprocal challenges. The study reveals the importance of balancing organizing initiatives (focused on structures) with “sense‐making” initiatives (focused on strategies), of developing capacities for sense‐making through the creation of key “sense‐maker/sense‐giver” positions whose occupants are able to ensure that conceptual activities engage people working at different levels, even as organizational structures are in flux, and of mobilizing external constraints and influences as opportunities and resources in sense‐making and organizing.

Sommaire : Se fondant sur une étude longitudinale des premières années de la mise en œuvre des réseaux de soins de santé au Québec, cet article décrit la manière dont les gestionnaires du secteur public font face à des défis complexes, alors que les structures et les stratégies organisationnelles sont radicalement transformées simultanément. Les nouveaux organismes étudiés ont dû complètement remanier les rôles et les responsabilités de leurs équipes de gestion et comprendre leur nouveau mandat d'élaborer une approche axée sur la population pour ce qui est des problèmes de santé, tout en maintenant leurs activités au jour le jour. Les quatre réseaux de soins de santéétudiés ont travailléà relever ces défis réciproques d'une manière assez différente. L'étude révèle l'importance de trouver un équilibre entre les initiatives consistant à organiser (axées sur les structures) et les initiatives consistant à interpréter les faits (axées sur les stratégies) ; de perfectionner les capacités à interpréter les faits grâce à la création de postes clés d'«interpréteurs de faits», dont les titulaires veilleraient à ce que des activités conceptuelles fassent intervenir les gens travaillant à différents niveaux même lorsque les structures organisationnelles fluctuent continuellement; et enfin de tirer parti des contraintes et influences externes comme autant d'occasions et de ressources pour interpréter et organiser les faits.
The evolution of federalism studies in Canada: From centre to periphery
Authors: Fafard Patrick , Rocher François
Published: June 2009

Abstract: Over the past decade, there have been a number of studies that seek to evaluate the state of federalism studies in Canada. The general conclusion seems to be that, while federalism continues to be an important part of the scholarly literature, there is a decline in the study of the traditional areas of federalism, a small number of federalism studies come from scholars in Quebec, and a relatively small number of studies are by female scholars. However, these analyses are based on a single, somewhat limited source of data, the reflections of a single scholar, or a review of a small number of Canadian scholarly journals. In this article, the authors combine a large quantitative assessment of relevant publications dealing with Canadian federalism with a brief qualitative assessment of the state of the federal studies from researchers active in the field. Their research supports some of the earlier conclusions but also suggests that, in recent years, federalism is, very often, a contextual or explanatory factor not the principal object of study. Moreover, there are potentially two Canadian scholarly traditions on federalism, one written in French and the other in English, with far too little engagement between them.

Sommaire: Au cours de la dernière décennie, un certain nombre d'études ont tenté d'évaluer l'état de la recherche sur le fédéralisme au Canada. La conclusion générale semble être que, même si le fédéralisme garde un place importante dans les publications savantes au Canada, on note une baisse dans la recherche portant sur les domaines traditionnels du fédéralisme, une faible proportion d'études sur le sujet étant réalisées par des universitaires au Québec, et un nombre relativement faible d'études étant entreprises par des femmes universitaires. Cependant, ces analyses reposent sur une seule source de données, quelque peu limitée, les réflexions d'un seul universitaire, ou sur un examen d'un petit nombre de revues savantes canadiennes. Dans le présent article, les auteurs combinent une importante évaluation quantitative de publications pertinentes portant sur le fédéralisme canadien avec une brève évaluation qualitative de la nature des études sur le fédéralisme entreprises par des chercheurs actifs dans le domaine. Leur recherche appuie certaines des conclusions antérieures mais laisse également entendre que, ces dernières années, le fédéralisme est très souvent un facteur contextuel ou explicatif plutôt que le principal sujet mis à l'étude. De plus, il pourrait fort y avoir deux traditions canadiennes de recherche sur le fédéralisme, une écrite en français et l'autre en anglais, et trop peu de relation entre elles.
Ecosystem management in Madagascar during global change
Authors: Virah‐Sawmy Malika
Published: June 2009

A long‐held assumption about Madagascar is that all its open vegetation and forest fragments represent anthropogenically degraded landscapes. Further, its forests are believed to lack regenerative capacity following extirpation. This article presents a different ecological framework for southeast Madagascar, a region with diverse forest habitats (humid, littoral, and transitional forests) and exceptional biodiversity. Recently published reconstructions of vegetation change at millennial scales indicate that the mosaic vegetation in southeastern Madagascar represents a natural distribution, with littoral forest spatially constrained by soil moisture, rather than principally fragmented by human activity. There is also evidence that the littoral forest is resilient to climatic change and has acted as refuges and centers of diversification for millennia. By contrast, Uapaca woodlands, which connected the littoral forest fragments, switched to a stable fire‐maintained Ericoid grassland in response to climatic changes. Evidence also suggests that local communities managed forest resources sustainably in the past, but human migration, insecure land tenure, and road expansion may have accelerated forest loss over the last decades. This novel perspective demonstrates the integrated nature of ecological, geomorphological, climatical, and social systems. Finally, combining long‐term with contemporary perspectives, some strategies for maintaining biodiversity under global change, including anthropogenic climate change and mining pressures (and associated biodiversity offset projects) are suggested.
Phylogenetics and biogeography of eastern Asian–North American disjunct genusPachysandra(Buxaceae) inferred from nucleotide sequences
Authors: JIAO Zhihua , LI Jianhua
Published: June 2009

Abstract Pachysandrais an eastern Asian–North American disjunct genus with three species, two in eastern Asia (Pachysandra axillarisandPachysandra terminalis) and one in eastern North America (Pachysandra procumbens). Although morphological and cytological studies suggest a close affinity ofP. procumbenswithP. axillaris, molecular data from nuclear and chloroplast DNA regions have provided conflicting signals. In this study, we tested previous phylogenetic hypotheses using sequences of nuclear ribosomal DNA internal transcribed spacers and chloroplastndhFgene from multiple individuals of each of the three species. We also estimated the time of divergence between eastern Asia and eastern North America. Our results support the morphological and cytological conclusion thatP. procumbensis more closely related toP. axillaristhan toP. terminalis. The estimated time of divergence ofP. axillarisandP. procumbenswas 14.6±5.5 mya, consistent with estimates from many other eastern Asian–North American disjunct genera. The migration ofPachysandrapopulations from eastern Asia to North America might have occurred by way of the North Atlantic land bridge.
Cytological study on the genus Syncalathium (Asteraceae‐Lactuceae), an endemic taxon to alpine scree of the Sino‐Himalayas
Authors: ZHANG Jian‐Wen , NIE Ze‐Long , SUN Hang
Published: June 2009

Abstract  Cytological characters of four species in Syncalathium (Asteraceae: Lactuceae), a small genus with six identified species endemic to alpine scree of the Sino‐Himalayan region, are surveyed in this report. Three species (Syncalathium pilosum, Syncalathium chrysocephalum, and Syncalathium disciforme) are examined for the first time. Combined with our previous counts, five species have been cytologically investigated from the genus and the results indicated that all species are diploid with the basic somatic chromosome number of x=8. The karyotype asymmetry of Syncalathium souliei is 2A, distinct from the other four species of 1A, and the remaining species are divided into two subgroups with different karyotypes, consistent with their morphological features. The significance of the cytological evolution of Syncalathium is briefly discussed.
Reappraisal of Microtropis macrocarpa C.Y. Cheng & T.C. Kao (Celastraceae), a critically endangered species endemic to Yunnan, China
Authors: LIN Qin‐Wen , ZHANG Zhi‐Xiang
Published: June 2009

Abstract  Microtropis macrocarpa C.Y. Cheng & T.C. Kao has been treated as a synonym of Microtropis macrophylla Merr. & Freeman in most taxonomic reports in China. According to our study, M. macrocarpa is an independent species endemic to Yunnan, China. Microtropis macrophylla and Microtropis pachyphylla Merr. & Freeman should be treated as synonyms of Microtropis longifolia Wall. ex Kurz. M. macrocarpa is also identified as a critically endangered species, CR B1ab (i,ii,iii,v), based on the IUCN Red List Categories and Criteria. The foliar surface, anther and pollen structures were also observed with a scanning electron microscope.
NAMIBIA'S REAL EXCHANGE RATE PERFORMANCE1
Authors: Miyajima Ken
Published: June 2009

To assess Namibia's external competitiveness, this study estimates the country's equilibrium real exchange rate using the autoregressive distributed lag modelling approach that has superior small‐sample properties. The nominal depreciation of the Namibia dollar in 2002 created historically one of the largest deviations in the real exchange rate from its equilibrium level, but deviations are small at present. The half‐life of deviations from equilibrium is found to be about 1 year.
Rude Accountability in the Unreformed State: Informal Pressures on Frontline Bureaucrats in Bangladesh
Authors: Hossain Naomi
Published: June 2009

‘Rude’ forms of accountability are central to how poor people negotiate their entitlements on the frontline of service delivery in Bangladesh. This paper documents the unorganised, informal pressures that poor citizens exert on officials in a context where effective formal systems for accountability are absent, and the state remains unreformed in key respects. The paper explores the impact of ‘rude accountability’ on services, as well as their limitations and the consequences for formal accountability systems. Based on extensive research into how poor people experience safety nets, schools and health services, the paper argues that strong social and local political pressures go some way towards supplying a rough responsiveness to demands for service. These work through shame and embarrassment, pressures to maintain reputation and status, and the threat of violence. Poor people have good reasons to use these methods in preference to formal accountability mechanisms. And poor women may have a particularly strong comparative advantage in doing so – not because they are so much better than men or rich people at complaining and shaming, but because it is comparatively less difficult for them to do so than to engage in more formally structured means of complaint or feedback. The idea of rude accountability is seductive: when formal governance systems fail, the idea that there are informal mechanisms that are better suited to context and culture is intrinsically attractive. Yet the paper concludes that the gains from rude accountability are often short‐lived and may backfire, as public officials fear and resist efforts to enable citizen participation in holding them to account. There are features of contemporary Bangladeshi state‐society relations that lend themselves to informal means of accountability, the analysis here of informal accountability mechanisms has wider implications for the move towards citizen involvement in performance‐based accountability in other contexts.
Participatory Governance and the Challenge of Assumed Representation in Brazil
Authors: Houtzager Peter P. , Gurza Lavalle Adrian
Published: June 2009

The growth of participatory governance has had the unintended consequence of spawning complex new forms of political representation. The participatory governance structures that have emerged alongside classic institutions of representative democracy encompass not only direct citizen participation but also political representation by civil society (collective) actors. Using original data from Brazil, we show that many of these collective actors engage in what we call ‘assumed representation’. In contrast to political parties and labour unions, these actors lack widely accepted and historically consolidated mechanisms through which their publics can authorise representation or ensure accountability and responsiveness. In particular, most do not rely on formal electoral or membership mechanisms. This layer of collective actors therefore faces a historic challenge – the construction of novel notions of democratic legitimacy that can support their forms of representation. The survival of the democratising current of which they are a part depends in some measure on how this challenge is met. We examine what new notions of representations are emerging in participatory governance structures and trace the historic roots of the most widespread and promising, that focus on remedying inequality in access to the state.
Activity of pyramidal tract neurons in the cat during standing and walking on an inclined plane
Authors: Karayannidou A. , Beloozerova I. N. , Zelenin P. V. , Stout E. E. , Sirota M. G. , Orlovsky G. N. , Deliagina T. G.
Published: June 2009

To keep balance when standing or walking on a surface inclined in the roll plane, the cat modifies its body configuration so that the functional length of its right and left limbs becomes different. The aim of the present study was to assess the motor cortex participation in the generation of this left/right asymmetry. We recorded the activity of fore‐ and hindlimb‐related pyramidal tract neurons (PTNs) during standing and walking on a treadmill. A difference in PTN activity at two tilted positions of the treadmill (± 15 deg) was considered a positional response to surface inclination. During standing, 47% of PTNs exhibited a positional response, increasing their activity with either the contra‐tilt (20%) or the ipsi‐tilt (27%). During walking, PTNs were modulated in the rhythm of stepping, and tilts of the supporting surface evoked positional responses in the form of changes to the magnitude of modulation in 58% of PTNs. The contra‐tilt increased activity in 28% of PTNs, and ipsi‐tilt increased activity in 30% of PTNs. We suggest that PTNs with positional responses contribute to the modifications of limb configuration that are necessary for adaptation to the inclined surface. By comparing the responses to tilts in individual PTNs during standing and walking, four groups of PTNs were revealed: responding in both tasks (30%); responding only during standing (16%); responding only during walking (30%); responding in none of the tasks (24%). This diversity suggests that common and separate cortical mechanisms are used for postural adaptation to tilts during standing and walking.
Local tetrahydrobiopterin administration augments cutaneous vasoconstriction in aged humans
Authors: Lang James A. , Holowatz Lacy A. , Kenney W. Larry
Published: June 2009

Reflex vasoconstriction (VC) is attenuated in aged skin resulting in greater skin blood flow and heat loss during cold exposure. We hypothesized that adrenergic function is compromised due to depletion of tetrahydrobiopterin (BH4), an essential cofactor required for catecholamine synthesis, and therefore local BH4 supplementation would functionally augment reflex and pharmacologically induced VC elicited by gradual whole‐body cooling (skin temperature (Tsk) = 30.5°C) and tyramine infusion, respectively. Four microdialysis (MD) fibres were placed in the forearm skin of 11 young (Y) and 11 older (O) human subjects for infusion of (1) Ringer solution (control), (2) 5 mm BH4, (3) 5 mm BH4+ 10 mm ascorbate, and (4) 5 mm BH4+ adrenoreceptor blockade (5 mm yohimbine + 1 mm propranolol). Laser Doppler flux (LDF) was measured over each MD site and cutaneous vascular conductance was calculated as CVC = LDF/MAP and expressed as per cent change from baseline (%ΔCVCbase). The VC response was lower at the control site in O during cooling (Y: −34 ± 2%ΔCVCbase, O: −17 ± 2%ΔCVCbase; P < 0.001) and tyramine infusion (Y: −33 ± 4%ΔCVCbase, O: −15 ± 3%ΔCVCbase; P < 0.001). BH4 infusion normalized O to Y values during both cooling (Y: −34 ± 4%ΔCVCbase, O: −34 ± 2%ΔCVCbase; P < 0.001) and tyramine (Y: −38 ± 4%ΔCVCbase, O: −35 ± 3%ΔCVCbase; P < 0.001), however, adding adrenoreceptor blockade abolished VC in aged skin indicating that BH4 acts through adrenergic, not cotransmitter, mechanisms. Local BH4 supplementation augments reflex and tyramine‐induced VC in aged skin, suggesting that reduced BH4 bioavailability may contribute to attenuated VC during whole‐body cooling.
Scaling of Solutions for the Lateral Buckling of Elastic-Plastic Pipelines
Authors: Peek Ralf , Yun Heedo
Published: June 2009

Analytical solutions for the lateral buckling of pipelines exist for the case when the pipe material remains in the linearly elastic range. However for truly high temperatures and/or heavier flowlines, plastic deformation cannot be excluded. One then has to resort to finite element analyses, as no analytical solutions are available. This paper does not provide such an analytical solution, but it does show that if the finite element solution has been calculated once, then that solution can be scaled so that it applies for any other values of the design parameters. Thus the finite element solution need only be calculated once and for all. Thereafter, other solutions can be calculated by scaling the finite element solution using simple analytical formulas. However, the shape of the moment-curvature relation must not change. That is, the moment-curvature relation must be a scaled version of the moment-curvature relation for the reference problem, where different scale factors may be applied to the moment and curvature. This paper goes beyond standard dimensional analysis (as justified by the Bucklingham Π theorem), to establish a stronger scalability result, and uses it to develop simple formulas for the lateral buckling of any pipeline made of elastic-plastic material. The paper includes the derivation of the scaling result, the application procedure, the reference solution for an elastic-perfectly plastic pipe, and an example to illustrate how this reference solution can be used to calculate the lateral buckling response for any elastic-perfectly plastic pipe.
The Behavior of Shallow Cracks in a Pipeline Steel Operating in a Sour Environment
Authors: Holtam C. M. , Baxter D. P. , Ashcroft I. A. , Thomson R. C.
Published: June 2009

Setting conditions for the avoidance of in-service crack growth in aggressive corroding environments has long been a major challenge due to the number of variables that have a significant effect on material behavior. One area where both experimental data and a validated assessment methodology are lacking is the behavior of shallow cracks. This paper describes the early results of an ongoing research program aimed at addressing the shortfall in experimental data to characterize material behavior in the shallow-crack regime, with the long-term aim of improving the understanding and assessment of the early stages of environment assisted cracking. There is an industry need for a better understanding of material behavior under these conditions and for the development of a more robust assessment methodology. API 5L X65 pipeline steel parent material was tested in a sour environment with initial flaw sizes in the range 1–2 mm. Fatigue crack growth rate tests have been performed to investigate the influence of crack depth on crack growth rate (da/dN). Initial results suggest that crack growth rates for deep flaws can increase by a factor of 5–100 compared with air depending on the applied stress intensity factor range (ΔK). Shallow cracks have been shown to grow up to 130 times faster in a sour environment than in air and up to an order of magnitude faster than deep cracks in a sour environment at the same value of ΔK. Constant load tests have also been performed to investigate the influence of crack depth on the threshold stress intensity factor for stress corrosion cracking (KISCC). Preliminary results suggest that in this case there is no crack depth dependence in the range of flaw sizes tested. While further experimental work is required, the results obtained to date highlight the potential nonconservatism associated with extrapolating deep-crack data. Guidance is therefore provided on how to generate appropriate experimental data to ensure that subsequent fitness for service assessments are conservative.
Dynamic Material Response of Aluminum Single Crystal Under Microscale Laser Shock Peening
Authors: Vukelic Sinisa , Wang Youneng , Kysar Jeffrey W. , Yao Y. Lawrence
Published: June 2009

The process of laser shock peening induces compressive residual stresses in a material to improve material fatigue life. For micron sized laser beams, the size of the laser-target interaction zone is of the same order of magnitude as the target material grains, and thus the target material must be considered as being anisotropic and inhomogeneous. Single crystals are chosen to study the effects of the anisotropic mechanical properties. It is also of interest to investigate the response of symmetric and asymmetric slip systems with respect to the shocked surface. In the present study, numerical and experimental aspects of laser shock peening on two different crystal surfaces (110) and (11¯4) of aluminum single crystals are studied. Lattice rotations on the top surface and cross section are measured using electron backscatter diffraction, while residual stress is characterized using X-ray microdiffraction. A numerical model has been developed that takes into account anisotropy as well as inertial terms to predict the size and nature of the deformation and residual stresses. Obtained results were compared with the experimental finding for validation purpose.
Development of an Engineering Model for Predicting the Transverse Coefficients of Thermal Expansion of Unidirectional Fiber Reinforced Composites
Authors: Dong Chensong
Published: June 2009

The coefficients of thermal expansion (CTEs) of fiber reinforced composites play an important role in the design and analysis of composite structures. Since the thermal expansion coefficients of polymer matrix materials are typically much higher than those of fibers, and the fiber often exhibits anisotropic thermal and mechanical properties, the stress induced in the composite due to temperature change is very complex. Large discrepancies exist among the analytical models for the transverse CTE of unidirectional composites. Hence, it is problematic when choosing a suitable model. With the development of computer technologies, finite element analysis (FEA) proved its effectiveness in calculating the effective CTE of composites. In this study, the transverse CTEs of unidirectional carbon fiber composites were calculated by finite element analysis using a representative unit cell. The analytical micromechanical models from literature were compared against the FEA data. It shows that Hashin’s concentric cylinder model is the best. However, it is inconvenient for practical applications due to the amount of computation. In this study, based on the FEA data, an engineering model for predicting the transverse CTE of unidirectional composites was developed by regression analysis. This model was validated against the FEA and experimental data. It shows that the developed model provides a simple and accurate approach to calculate the transverse CTE of unidirectional composites.
Numerical Simulation of Random Packing of Spherical Particles for Powder-Based Additive Manufacturing
Authors: Zhou Jianhua , Zhang Yuwen , Chen J. K.
Published: June 2009

Powder-based additive manufacturing is an efficient and rapid manufacturing technique because it allows fabrication of complex parts that are often unobtainable by traditional manufacturing processes. A better understanding of the packing structure of the powder is urgently needed for the powder-based additive manufacturing. In this study, the sequential addition packing algorithm is employed to investigate the random packing of spherical particles with and without shaking effect. The 3D random packing structures are demonstrated by illustrative pictures and quantified in terms of pair distribution function, coordination number, and packing density. The results are presented and discussed aiming to produce the desirable packing structures for powder-based additive manufacturing.
Modeling and Control of Contouring Errors for Five-Axis Machine Tools—Part I: Modeling
Authors: Sencer Burak , Altintas Yusuf , Croft Elizabeth
Published: June 2009

Aerospace, die, and mold industries utilize parts with sculptured surfaces, which are machined on five-axis computer numerical controlled machine tools. Accurate path tracking for contouring is not always possible along the desired space curves due to the loss of joint coordination during the five-axis motion. This two-part paper presents modeling and robust control of contouring errors for five-axis machines. In Part I, two types of contouring errors are defined by considering the normal deviation of tool tip from the reference path, and by the normal deviation of the tool axis orientation from the reference orientation trajectory defined in the spherical coordinates. Overall contouring errors are modeled during five-axis motion that has simultaneous translation and rotary motions. The coupled kinematic configuration and the rigid body dynamics of all five drives are considered. The contouring error model is experimentally validated on a five-axis machine tool. The error model developed in this paper is then used for simultaneous, real-time robust control of all five drives in Part II.
Modeling and Control of Contouring Errors for Five-Axis Machine Tools—Part II: Precision Contour Controller Design
Authors: Sencer Burak , Altintas Yusuf
Published: June 2009

The accurate tracking of tool-paths on five-axis CNC machine tools is essential in achieving high speed machining of dies, molds, and aerospace parts with sculptured surfaces. Because traditional CNCs control the tracking errors of individual drives of the machine, this may not lead to desired contouring accuracy along tool-paths, which require coordinated action of all the five drives. This paper proposes a new control approach where the tool tip and tool orientation errors, i.e., the contouring errors, are minimized along the five-axis tool-paths. The contouring error and kinematic model of the machine, which are presented in Part I of the paper, are used in defining the plant. A multi-input–multi-output sliding mode controller, which tries to minimize path tracking and path following velocity errors, is introduced. The stability of the system is ensured, and the proposed model is experimentally demonstrated on a five-axis machine tool. The path errors originating from the dynamics of five simultaneously active drives are significantly reduced.
Effect of Carbon Nanotube (CNT) Loading on the Thermomechanical Properties and the Machinability of CNT-Reinforced Polymer Composites
Authors: Samuel J. , Dikshit A. , DeVor R. E. , Kapoor S. G. , Hsia K. J.
Published: June 2009

The machinability of carbon nanotube (CNT)-reinforced polymer composites is studied as a function of CNT loading, in light of the trends seen in their material properties. To this end, the thermomechanical properties of the CNT composites with different loadings of CNTs are characterized. Micro-endmilling experiments are also conducted on all the materials under investigation. Chip morphology, burr width, surface roughness, and cutting forces are used as the machinability measures to compare the composites. For composites with lower loadings of CNTs (1.75% by weight), the visco-elastic/plastic deformation of the polymer-phase plays a significant role during machining, whereas, at loadings ≥5% by weight, the CNT distribution and interface effects dictate the machining response of the composite. The ductile-to-brittle transition that occurs with an increase in CNT loading results in reduced minimum chip thickness values and burr dimensions in the CNT composite. The increase in thermal conductivity with the increase in CNT loading results in reduced number of adiabatic shear bands being observed on the chips and reduced thermal softening effects at high cutting velocities. Thus, overall, an increase in CNT loading appears to improve the machinability of the composite.
Effect of Wave Age on Wind Gust Spectra Over Wind Waves
Authors: Myrhaug Dag , Ong Muk Chen
Published: June 2009

This paper considers the effect of wave age on wind gust spectra over wind waves. Here, two wind gust spectra based on maritime data are used to serve the purpose of demonstrating the effect of wave age; the spectra according to Wills et al. (1986 “Offshore Mean Wind Profile,” Department of Energy, Offshore Technical Report No. OTH86226) and Ochi and Shin (1988, “Wind Turbulent Spectra for Design Considerations of Offshore Structures,” Proceedings of the 20th Offshore Technology Conference, Houston, TX, Paper No. 5736, pp. 461–467). The effect of wave age is taken into account by using the Volkov (2001, “The Dependence on Wave Age,” in Wind Stress Over the Ocean, Cambridge University Press, Cambridge, UK, pp. 206–217) sea surface roughness formula. The wave age independent Charnock (1955, “Wind Stress on a Water Surface,” Q. J. R. Meteorol. Soc., 81, pp. 639–640) sea surface roughness is used as a reference. The results are valid for wind waves in local equilibrium with steady wind in laterally homogeneous flow. An example of results demonstrates a clear effect of wave age on the wind gust spectra; also, distinct differences between the two spectra for a given wave age are demonstrated. Finally, an example of application is provided, demonstrating clear effects of the two spectra and the sea surface roughness on slowly varying surge motion of a marine structure due to wind gust.
A Three-Dimensional Coupled Fluid-Sediment Interaction Model With Bed-Load/Suspended-Load Transport for Scour Analysis Around a Fixed Structure
Authors: Nakamura Tomoaki , Mizutani Norimi , Yim Solomon C.
Published: June 2009

The predictive capability of a three-dimensional (3D) numerical model for sediment transport and resulting scour around a structure is investigated in this study. Starting with the bed-load and suspended-load sediment transport (reference) model developed by Takahashi et al. (2000, “Modeling Sediment Transport Due to Tsunamis With Exchange Rate Between Bed Load Layer and Suspended Load Layer,” Proceedings of the 27th International Conference on Coastal Engineering, ASCE, Sydney, Australia, pp. 1508–1519), we first introduce an extension to incorporate Nielsen’s modified Shields parameter to account for the effects of infiltration/exfiltration flow velocity across the fluid-sand interface on the sediment transport (the modified Shields-parameter model). We then propose a new model to include the influence of the effective stress to account for the stress fluctuations inside the surface layer of the sand bed (the effective-stress model). The three analytical models are incorporated into a 3D numerical solver developed by Nakamura et al. (2008, “Tsunami Scour Around a Square Structure,” Coast. Eng. Japan, 50(2), pp. 209–246) to analyze the dynamics of fluid-sediment interaction and scour. Their solver is composed of two modules, namely, a finite-difference numerical wave tank and a finite-element coupled sand-skeleton pore-water module. The predictive capability of the three alternative coupled models is calibrated against hydraulic experiments on sediment transport and resulting scour around a fixed rigid structure due to the run-up of a single large wave in terms of the sediment transport process and the final scour profile after the wave run-up. It is found that, among the three models considered, the proposed effective-stress model most accurately predicts the scouring process around the seaward corner of the structure. The results also reveal that the deposition and erosion patterns predicted using the effective-stress model are in good agreement with measured results, while a scour hole at the seaward corner of the structure cannot be always predicted by the other two models.
Life-Cycle Cost-Effective Optimum Design of Ice-Resistant Offshore Platforms
Authors: Li Gang , Zhang Dayong , Yue Qianjin
Published: June 2009

In China, the oil and natural gas resources in Bohai Bay are mainly marginal oil fields, which freeze in the winter. It is necessary to build both ice-resistant and economical offshore platforms. However, risk is involved in the design, construction, utilization, and maintenance of offshore platforms as uncertain events may occur within the life-cycle of a platform. In this paper, the optimum design model of the expected life-cycle cost for ice-resistant platforms based on the cost-effectiveness criterion is proposed. Multiple performance demands of the structure, facilities and crew members, associated with the failure assessment criteria and evaluation functions of costs of construction, consequences of structural failure modes including damage, revenue loss, death, and injury, as well as discounting cost over time are considered. Different reliability analysis approaches involved in life-cycle cost evaluation, such as the global reliability under the extreme ice load, the dynamic reliability, and fatigue life induced by ice vibration, are studied. The proposed life-cycle optimum design formulas are applied to a typical ice-resistant platform in Bohai Bay, and the results demonstrate that the life-cycle cost-effective optimum design model is more rational compared with the conventional static design and the optimum dynamic design.
A Direct Design Procedure for FPSO Side Structures Against Large Impact Loads
Authors: Hong Lin , Amdahl Jørgen , Wang Ge
Published: June 2009

The performance and consequence of FPSOs subjected to large impact loads such as collisions from supply vessels or merchant vessels are of great concern in the offshore industry, notably when they are located close to heavy traffic lanes. Due to the lack of operation experience for ship-shaped FPSOs, direct design procedures are needed to rationalize the structural design of FPSOs, which can mitigate the consequence of collision accident and avoid possible contaminated compartment flooding. In this paper, three collision scenarios between a FPSO and a bulbous supply vessel are analyzed through explicit nonlinear finite element analysis code LS-DYNA. Thereafter, a direct design procedure is proposed for ship-shaped FPSO side structure against accidental collision forces, which follows the principle of accidental limit state. The procedure comprises the determination of the impact forces, shell plating, and stiffener framing design, and the consideration of the acceptance criterion. The proposed method is especially useful in the preliminary design phase because the design procedure for plating and stiffener is based on analytical formulas derived from plastic method and appropriate collapse mechanism. The side structure decided by the proposed design procedure also complies with the strength design principle that has been adopted in NORSOK standard. The proposed approach is demonstrated by the design of the FPSO side structure against impact loads from a 7500 tons supply vessel and verified by means of integrated collision analysis. The procedure could also be served to estimate the damage due to accidental loads.
A Dual Environment for 3D Modeling With User-Defined Freeform Features
Authors: Langerak Thomas R. , Vergeest Joris S. M.
Published: June 2009

Modeling with freeform features has become the standard in computer-aided design. Features offer a high-level approach to modeling shapes. However, in most commercial modeling packages, only a static set of freeform features is available. A new method for user-driven feature definition is presented, as well as a method to instantiate these user-defined features on a target surface. We propose the concept of a dual environment, in which the definition of a feature is maintained parallel to its instance on a target surface. This dual environment enables dynamic feature modeling, in which the user is able to change the definition of instantiated features on-the-fly.
An Analytical Model to Predict Residual Stress Field Induced by Laser Shock Peening
Authors: Hu Yongxiang , Yao Zhenqiang , Hu Jun
Published: June 2009

Laser shock peening (LSP) is an innovative surface treatment technique similar to shot peening. An analytical model to predict the residual stress field can obtain the impact effect much quickly, and will be invaluable in enabling a close-loop process control in production, saving time and cost of processing. A complete analytical model of LSP with some reasonable simplification is proposed to predict residual stresses in depth by a sequential application of a confined plasma development model and a residual stress model. The spatial distribution of the shock pressure and the high strain rate effect are considered in the model. Good agreements have been shown with several experimental measured results for various laser conditions and target materials, thus proving the validity of the proposed model.
Structural Dynamics with Parameter Uncertainties
Authors: Ibrahim R. A.
Published: June 2009

The treatment of structural parameters as random variables has been the subject of structural dynamicists and designers for many years. Several problems have been involved during the last few decades and resulted in new theorems and interesting phenomena. This paper reviews a number of topics pertaining to structural dynamics with parameter uncertainties. These include direct problems such as random eigenvalues and random responses of discrete and continuous systems. The impact of these problems on related areas of interest such as sensitivity of structural performance to parameter variations, design optimization, and reliability analysis is also addressed. The paper includes the results of experimental investigations, the phenomenon of normal modes localization, and the effect of mistuning of turbomachinery blades on their flutter and forced response characteristics.
Instability of Dynamically-Loaded Structures
Authors: Simitses George J.
Published: June 2009

The article presents a review of the field of dynamic stability of structures. By structure, one means a flexible solid and therefore applications to rigid solids are excluded. Since many phenomena and many classes of problems have been included under the heading of dynamic stability, an effort is made to classify the various phenomena, and discuss similarities and differences. Furthermore, whenever applicable, criteria and estimates of critical conditions are presented. Moreover, an attempt is made to identify important effects and influences of various parameters, through proper referencing. Finally, in the case of fluid–structure type of instabilities the review is rather sketchy. For these types of problems the reader is referred to recent reviews of substantially greater depth and detail.
Nonlinear Vibration Analysis of Plates: A Review and Survey of Current Developments
Authors: Sathyamoorthy M.
Published: June 2009

This paper is concerned with the recent developments in the nonlinear vibrational analysis of plates of various geometries. Although most of the material presented here deals with geometric type nonlinearities, attention is also given to other types of nonlinearities such as nonlinear material behavior. Particular attention is given to the recent developments in the analytical methods of solution. Recent research leading to advances in numerical techniques is also included. Complicating effects such as the effects transverse shear deformation, rotatory inertia, anisotropy, initial imperfections, and variable rigidity on the vibration behavior of plates are reviewed and discussed. Finally, some general conclusions are presented along with the author’s views regarding the future research trends in this area.
Advances in Ice Mechanics in the United Kingdom
Authors: Hallam S. D. , Sanderson T. J. O.
Published: June 2009

The United Kingdom has made substantial contributions during the last few years to the field of ice mechanics and ice forces on offshore structures. Experimental studies have been carried out in the field and in the laboratory, and significant advances have been made in theoretical understanding. This paper summarizes the most recent contributions.
Recent Advances in Ice Mechanics in Canada
Authors: Sinha N. K. , Timco G. W. , Frederking R.
Published: June 2009

Work on the mechanics of ice, which has been carried forward on a broad front in Canada, has resulted in a number of significant advances in the last 10 years. The factors influencing the growth of various types of sea ice have been quantified fundamentally and methods for examining the resulting material structure have been developed. Extensive work has been done on strength and deformation characteristics of ice. A significant effort has been the development of analytical expressions to describe the rheological behavior of ice. Elastic modulus, Poisson’s ratio, and creep were also treated. A great deal has been done on measuring the compressive strength of various types of naturally occurring ice and subsequently these data were combined into a suitable description of a failure envelope. Work has also been done on measuring the flexural strength, shear strength, adhesion and fracture toughness. Methods for laboratory testing and in situ measurements of mechanical properties have been developed. The problem of defining ice forces on structures has been the primary motivation for research on ice. Analytical modelling, physical modelling, laboratory studies and very extensive field studies have been used. Work done in this area has included development of methods and their application to actual problems and has benefitted greatly from the integration of all four approaches. Very significant progress has been made. Ice and ice covers have been successfully used to support various offshore activities: drilling off floating ice platforms, stabilizing grounded rubble fields to protect structures and transporting large loads over ice.
Advances in Sea Ice Mechanics in the USA
Authors: Sodhi Devinder S. , Cox Gordon F. N.
Published: June 2009

A brief review of significant advances in the field of sea ice mechanics in the United States is presented in this paper. Emphasis is on ice forces on structures, as the subject relates to development of oil and gas resources in the southern Beaufort Sea. The main topics discussed here are mechanical properties, ice–structure interaction, modeling of sea ice drift, and oil industry research activities. Significant advances in the determination of ice properties are the development of testing procedures to obtain consistent results. Using stiff testing machines, researchers have been able to identify the dependence of tensile and compressive strengths on different parameters, eg, strain rate, temperature, grain size, c-axis orientation, porosity, and state of stress (uniaxial or multiaxial). Now reliable data exist on the tensile and compressive strengths of first-year and multi-year sea ice. Compressive strengths obtained from field testing of large specimens (6 × 3 × 2 m thick) were found to be within 30% of the strengths obtained from small samples tested in laboratory at the same temperature and strain rate as found in the field. Recent advances in the development of constitutive relations and yield criteria have incorporated the concept of damage mechanics to include the effect of microfracturing during the ice failure process. Ice forces generated during an ice–structure interaction are related to ice thickness and properties by conducting analytical or small-scale experimental studies, or both. Field measurements of ice forces have been made to assess the validity of theoretical and small-scale experimental results. There is good agreement between theoretical and small-scale experimental results for ice forces on conical structures. Theoretical elastic buckling loads also agree with the results of small-scale experiments. Though considerable insight has been achieved for ice crushing failure, estimation of ice forces for this mode is based on empirical relations developed from small-scale experiments. A good understanding of the ice failure process has been achieved when ice fails in a single failure mode, but our understanding of multi-modal ice failure still remains poor. Field measurements of effective pressure indicate that it decreases with increasing contact area. Research in fracture mechanics and nonsimultaneous failure is underway to explain this observed trend. Ice ridge formation and pile-up have been modeled, and the forces associated with these processes are estimated to be low. The modeling of sea ice drift has progressed to a point where it is able to determine the extent, thickness distribution, and drift velocity field of sea ice over the entire arctic basin. Components of this model relate to momentum balance, thermodynamic processes, ice thickness distribution, ice strength, and ice rheology.
Initial Value Problems in Viscoelasticity
Authors: Hrusa W. J. , Nohel J. A. , Renardy M.
Published: June 2009

We review some recent mathematical results concerning integrodiff erential equations that model the motion of one-dimensional nonlinear viscoelastic materials. In particular, we discuss global (in time) existence and long-time behavior of classical solutions, as well as the formation of singularities in finite time from smooth initial data. Although the mathematical theory is comparatively incomplete, we make some remarks concerning the existence of weak solutions (i e, solutions with shocks). Some relevant results from linear wave propagation will also be discussed.