Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Semiactive control devices have received significant attention in recent years because they offer the adaptability of active control devices without requiring the associated large power sources. Magnetorheological (MR) dampers are semiactive control devices that use MR fluids to produce controllable dampers. They potentially offer highly reliable operation and can be viewed as fail-safe in that they become passive dampers should the control hardware malfunction. To develop control algorithms that take full advantage of the unique features of the MR damper, models must be developed that can adequately characterize the damper's intrinsic nonlinear behavior. Following a review of several idealized mechanical models for controllable fluid dampers, a new model is proposed that can effectively portray the behavior of a typical MR damper. Comparison with experimental results for a prototype damper indicates that the model is accurate over a wide range of operating conditions and is adequate for control design an...

Phenomenological model for magnetorheological dampers

Magnetorheological (MR) materials are a kind of smart materials whose mechanical properties can be altered in a controlled fashion by an external magnetic field. They traditionally include fluids, elastomers and foams. In this review paper we revisit the most outstanding advances on the rheological performance of MR fluids. Special emphasis is paid to the understanding of their yielding, flow and viscoelastic behaviour under shearing flows.

Magnetorheological fluids: a review

Populations of millions of colloidal rolling particles are shown to self-organize to achieve coherent motion; comparison between experiment and theory based on the microscopic interactions between these ‘rollers’ suggests that hydrodynamic interactions promote the emergence of the collective motion. Collective motion can be observed in the natural world at all scales, from flocking birds to schooling fish and swarming bacteria, but it is difficult to capture such behaviour in simple physical models. Artificial 'active matter' systems that show collective behaviour usually rely on collisions, making the description of interactions complex. Denis Bartolo and colleagues have now developed a unique experimental system consisting of self-propelled rolling spheres that self-organize and move in one direction in a crowd of millions. The spheres 'sense' each other via straightforward hydrodynamic interactions so that all parameters can be easily calculated and tuned. This work demonstrates that genuine physical interactions at the individual level are sufficient to set homogeneous active populations into stable directed motion. The system could be used to model natural collective motion and to design new self-organized materials and swarming microrobots. From the formation of animal flocks to the emergence of coordinated motion in bacterial swarms, populations of motile organisms at all scales display coherent collective motion. This consistent behaviour strongly contrasts with the difference in communication abilities between the individuals. On the basis of this universal feature, it has been proposed that alignment rules at the individual level could solely account for the emergence of unidirectional motion at the group level1,2,3,4. This hypothesis has been supported by agent-based simulations1,5,6. However, more complex collective behaviours have been systematically found in experiments, including the formation of vortices7,8,9, fluctuating swarms7,10, clustering11,12 and swirling13,14,15,16. All these (living and man-made) model systems (bacteria9,10,16, biofilaments and molecular motors7,8,13, shaken grains14,15 and reactive colloids11,12) predominantly rely on actual collisions to generate collective motion. As a result, the potential local alignment rules are entangled with more complex, and often unknown, interactions. The large-scale behaviour of the populations therefore strongly depends on these uncontrolled microscopic couplings, which are extremely challenging to measure and describe theoretically. Here we report that dilute populations of millions of colloidal rolling particles self-organize to achieve coherent motion in a unique direction, with very few density and velocity fluctuations. Quantitatively identifying the microscopic interactions between the rollers allows a theoretical description of this polar-liquid state. Comparison of the theory with experiment suggests that hydrodynamic interactions promote the emergence of collective motion either in the form of a single macroscopic ‘flock’, at low densities, or in that of a homogenous polar phase, at higher densities. Furthermore, hydrodynamics protects the polar-liquid state from the giant density fluctuations that were hitherto considered the hallmark of populations of self-propelled particles2,3,17. Our experiments demonstrate that genuine physical interactions at the individual level are sufficient to set homogeneous active populations into stable directed motion.

Emergence of macroscopic directed motion in populations of motile colloids

流体力学杂志“Journal of Fluid Mechanics”由剑桥大学教授George Batchelor在1956年5月创办，在国际流体力学界享有很高的学术声望，被公认为是流体力学最著名的学术刊物之一，2005年的影响因子为2．061，雄居同类期刊之首．在它创刊50周年之际，2006年5月JFM出版了第554卷的纪念特刊，其中刊登了现任主编（美国西北大学S．H．Davis教授和英国剑桥大学T．J．Pedley教授）合写的述评：“Editorial：JFM at50”，以JFM为背景，从独特的视角对近50年来流体力学的发展进行了简明的回顾和展望，并归纳了一系列非常有启发性的有趣统计数字．2006年7月21日在剑桥大学应用数学和理论物理研究所（DAMTP）举行了创刊50周年的庆祝会．下午2点，JFM的新老编辑和来宾会聚一堂，Pedley教授致开幕词，其后是5个精彩的报告：The mysterious rattleback and its fluid counterpart（Keith Moffatt），Developments in shear instabilities（Patrick Huerre），Falling clouds（Elisabeth Guazzelli），Ecotectural fluid mechanics（Paul Linden），The success of JFM（Herbert Huppert），最后由Davis教授致闭幕词．

Journal of Fluid Mechanics创刊50周年

This paper presents three-dimensional numerical simulations of non-Brownian concentrated suspensions in a Couette flow at zero Reynolds number using a fictitious domain method. Contacts between particles are modelled using a discrete element method (DEM)-like approach, which allows for a more physical description, including roughness and friction. This work emphasizes the effect of friction between particles and its role on rheological properties, especially on normal stress differences. Friction is shown to notably increase viscosity and second normal stress difference and decrease , in better agreement with experiments. The hydrodynamic and contact contributions to the overall particle stress are particularly investigated. This shows that the effect of friction is mostly due to the additional contact stress since the hydrodynamic stress remains unaffected by friction. Simulation results are also compared with experiments, such as normal stresses or effective friction coefficient , and the agreement is improved when friction is accounted for. This suggests that friction is operative in actual suspensions.

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Rheology of sheared suspensions of rough frictional particles

The yield stress of a magnetorheological suspension is calculated from two different approaches. The first one is based on a mesoscopic description of the structure taking only into account the shape anisotropy of the strained aggregates. The second one is based on a microscopic approach where the interparticle forces, due to the application of the field, are calculated numerically by taking into account the magnetostatics between the particles inside the aggregates. We show that the macroscopic description well applies to suspensions of nonmagnetic particles in a ferrofluid and that a layered structure, consisting of parallel slabs of magnetizable materials should have a yield stress much higher than a structure made of cylindrical aggregates. On the other hand the microscopic approach is appropriated for the description of suspensions of particles of high permeability. In this case, the yield stress is mainly determined by the rupture between pairs of particles and, consequently, it strongly increases with the angle between the line of centers of the pair undergoing the rupture and the field.

/pdf/yield-stress-in-magnetorheological-and-electrorheological-4sakvc2j29.pdf

Yield stress in magnetorheological and electrorheological fluids: A comparison between microscopic and macroscopic structural models

The rheogram, shear stress versus shear rate of magnetic suspensions composed either of monodisperse or polydisperse spherical particles, has been measured for different particle sizes. For small particles, where the ratio λ of magnetostatic energy to thermal energy is already much larger than unity (λ≊102–103), we find that the apparent yield stress is still strongly increasing with the size of the particles. It is only for very high values of λ (λ≊109) that we find experimental results which show no dependence on the size of the particles. These results are discussed with the help of a structural model based on the deformation of simple chains of particles, with an interparticle distance which depends on λ. It is shown that the experimental results can be explained by taking into account the fluctuations of the positions of the particles in a chain.

Influence of the particle size on the rheology of magnetorheological fluids

We present an experimental approach used to measure both normal stress differences and the particle phase contribution to the normal stresses in suspensions of non-Brownian hard spheres. The methodology consists of measuring the radial profile of the normal stress along the velocity gradient direction in a torsional flow between two parallel discs. The values of the first and the second normal stress differences, is obtained. Most of our results compare well with the different experimental and numerical data present in the literature. In particular, our results show that the magnitude of the particle stress tensor component and their dependence on the particle volume fraction used in the suspension model balance proposed by Morris & Boulay (J. Rheol., vol. 43, 1999, p. 1213) are suitable.

Normal stresses in concentrated non-Brownian suspensions

Static yield stresses are measured on magnetic suspensions as a function of the applied magnetic field. Two differents systems are used: One is an aqueous suspension of polystyrene spheres containing iron oxide inclusions and the second one is of ordinary polystyrene spheres dispersed in a ferrofluid. The experimental results are analyzed with the help of a model based on the calculation of forces between two particles in an effective medium. This model is discussed and tested against experimental measurements of forces on centimetric iron spheres placed in a magnetic field.

Elisabeth Lemaire

Papers

Rheology of sheared suspensions of rough frictional particles

Yield stress in magnetorheological and electrorheological fluids: A comparison between microscopic and macroscopic structural models

Influence of the particle size on the rheology of magnetorheological fluids

Normal stresses in concentrated non-Brownian suspensions

Yield stresses in magnetic suspensions