Modeling of Before Closure Zero Slope Pressure Derivative in a Diagnostic Fracture Injection Test DFIT

Recent diagnostic fracture injection test (DFIT) data presented on a Bourdet log-log diagnostic plot showed derivative slope of 0 in the before closure (BC) portion of the DFIT response. Some works qualitatively describe it as radial flow. This behavior has not been quantitatively analyzed, modeled and matched. The present work disagrees with the hypothesis of radial flow and successfully matches the relatively flat trend in the Bourdet derivative with a model dominated by friction dissipation coupled with tip extension. The flat trend in Bourdet derivative occurs shortly after shut-in during the before closure period. Because a flat derivative trend suggests diffusive radial flow, our first approach was to consider the possibility that an open crack at a layer interface stopped the fracture propagation and caused the apparent radial flow behavior observed in falloff data. However, a model that coupled pressure falloff from diffusive flow into a layer interface crack with pressure falloff from closure of a fracture that propagated up to the layer interface failed to reproduce the observed response. Subsequently, we discovered that existing models could match the data without considering the layer interface crack. We found that data processing is very important to what is observed in derivative trends and can mislead the behavior diagnosis. We succeeded to match one field DFIT case showing an obvious early flat trend. The presence and dominance of geomechanics, coupled with diffusive flow, disqualify the description of the flat trend in Bourdet derivative as radial flow. Instead, flow friction coupled with tip extension can completely match the observed behavior. Based on our model, cases with a long flat trend have large magnitude near-wellbore tortuosity friction loss and relatively long tip extension distance. Further, we match the near wellbore tortuosity behavior with rate raised to a power lower than the usually assumed 0.5. The significance of these analyses relates to two key factors. First, large magnitude near wellbore tortuosity friction loss increases the pressure required for fracture propagation during pumping. Second, tip extension is a way to dissipate high pumping pressure when very low formation permeability impedes leakoff. Matching transient behavior subject to the presence of both of these factors requires lowering the near-wellbore tortuosity exponent.

Controlling subterranean forces enables a fast, steerable, burrowing soft robot

Robotic navigation on land, through air, and in water is well researched; numerous robots have successfully demonstrated motion in these environments. However, one frontier for robotic locomotion remains largely unexplored—below ground. Subterranean navigation is simply hard to do, in part because the interaction forces of underground motion are higher than in air or water by orders of magnitude and because we lack for these interactions a robust fundamental physics understanding. We present and test three hypotheses, derived from biological observation and the physics of granular intrusion, and use the results to inform the design of our burrowing robot. These results reveal that (i) tip extension reduces total drag by an amount equal to the skin drag of the body, (ii) granular aeration via tip-based airflow reduces drag with a nonlinear dependence on depth and flow angle, and (iii) variation of the angle of the tip-based flow has a nonmonotonic effect on lift in granular media. Informed by these results, we realize a steerable, root-like soft robot that controls subterranean lift and drag forces to burrow faster than previous approaches by over an order of magnitude and does so through real sand. We also demonstrate that the robot can modulate its pullout force by an order of magnitude and control its direction of motion in both the horizontal and vertical planes to navigate around subterranean obstacles. Our results advance the understanding and capabilities of robotic subterranean locomotion.

Protein phosphatase SppA regulates apical growth and dephosphorylates cell polarity determinant DivIVA in Streptomyces coelicolor

Bacteria that exhibit polar growth, i.e. build their peptidoglycan cell walls in restricted zones at cell poles, often show large morphological diversity and plasticity. However, their mechanisms for regulation of cell shape and cell wall assembly are poorly understood. The Gram-positive Streptomyces bacteria, like other Actinobacteria, depend on the essential coiled coil protein DivIVA for establishment of cell polarity and direction of polar growth. Streptomycetes grow as filamentous hyphae that exhibit tip extension. New hyphal tips are generated by lateral branching. Cell shape is largely determined by the control of cell wall growth at these hyphal tips. The Ser/Thr protein kinase AfsK is involved in controlling polar growth and directly phosphorylates DivIVA. Here, we identify a protein phosphatase in Streptomyces coelicolor , SppA, that dephosphorylates DivIVA in vivo and in vitro and affects growth and cell shape. An sppA mutant shows reduced rate of hyphal tip extension, altered hyphal branching patterns, and exhibits frequent spontaneous hyphal growth arrests, all contributing to the unusually dense mycelial structure and slow growth rate that characterize sppA mutants. These phenotypes are largely suppressed in an afsK sppA double mutant, showing that AfsK and SppA partially affect the same regulatory pathway and share target proteins that are involved control of polar growth in S. coelicolor . Strains with a non-phosphorylatable mutant DivIVA were constructed and confirm that the effect of afsK on hyphal branching during normal growth is mediated by DivIVA phosphorylation. However, the phenotypic effects of sppA deletion are independent of DivIVA phosphorylation and must be mediated via other substrates. Altogether, this study identifies a PPP-family protein phosphatase directly involved in the control of polar growth and cell shape determination in S. coelicolor and underscore the importance of eukaryotic-type Ser/Thr phosphorylation in regulation of growth and cell envelope biogenesis in Actinobacteria.

Global phenotypic profiling identifies a conserved actinobacterial cofactor for a bifunctional PBP-type cell wall synthase

Members of the Corynebacterineae suborder of Actinobacteria have a unique cell surface architecture and, unlike most well-studied bacteria, grow by tip-extension. To investigate the distinct morphogenic mechanisms shared by these organisms, we performed a genome-wide phenotypic profiling analysis using Corynebacterium glutamicum as a model. A high-density transposon mutagenized library was challenged with a panel of antibiotics and other stresses. The fitness of mutants in each gene under each condition was then assessed by transposon-sequencing. Clustering of the resulting phenotypic fingerprints revealed a role for several genes of previously unknown function in surface biogenesis. Further analysis identified CofA (Cgp_0016) as an interaction partner of the peptidoglycan synthase PBP1a that promotes its stable accumulation at sites of polar growth. The related Mycobacterium tuberculosis proteins were also found to interact, highlighting the utility of our dataset for uncovering conserved principles of morphogenesis for this clinically relevant bacterial suborder.

Numerical studies of active flow control on wing tip extension

Purpose In the European project AFLoNext, active flow control (AFC) measures were adopted in the wing tip extension leading edge to suppress flow separation. It is expected that the designed wing tip extension may improve aerodynamic efficiency by about 2 per cent in terms of fuel consumption and emissions. As the leading edge of the wing tip is not protected with high-lift device, flow separation occurs earlier than over the inboard wing in the take-off/landing configuration. The aim of this study is the adoption of AFC to delay wing tip stall and to improve lift-to-drag ratio. Design/methodology/approach Several actuator locations and AFC strategies were tested with computational fluid dynamics. The first approach was “standard” one with physical modeling of the actuators, and the second one was focused on the volume forcing method. The actuators location and the forcing plane close to separation line of the reference configuration were chose to enhance the flow with steady and pulsed jet blowing. Dependence of the lift-to-drag benefit with respect to injected mass flow is investigated. Findings The mechanism of flow separation onset is identified as the interaction of slat-end and wing tip vortices. These vortices moving toward each other with increasing angle of attack (AoA) interact and cause the flow separation. AFC is applied to control the slat-end vortex and the inboard movement of the wing tip vortex to suppress their interaction. The separation onset has been postponed by about 2° of AoA; the value of ift-to-drag (L/D) was improved up to 22 per cent for the most beneficial cases. Practical implications The AFC using the steady or pulsed blowing (PB) was proved to be an effective tool for delaying the flow separation. Although better values of L/D have been reached using steady blowing, it is also shown that PB case with a duty cycle of 0.5 needs only one half of the mass flow. Originality/value Two approaches of different levels of complexity are studied and compared. The first is based on physical modeling of actuator cavities, while the second relies on volume forcing method which does not require detailed actuator modeling. Both approaches give consistent results.

Preformed-Particle-Gel Placement and Plugging Performance in Fractures With Tips

Summary Preformed-particle gels (PPGs) have been applied for reducing excessive water production caused by fractures in reservoirs. A portion of the fractures existing in reservoirs is composed of a void part and a fracture tip. The PPG placement behavior and plugging performance could be mainly affected by the fracture tips. A fracture with a tip, called a “partially open fracture” in this paper, was designed to investigate the placement and water-plugging performance of PPG. Cylindrical sandstone cores were used to manufacture partially open fractures. Pressure data of PPG injection, post-gel water breakthrough, and stable injection were analyzed to investigate the PPG propagation and plugging performance with respect to water. Experiments with different PPG placing pressures were conducted to explore the effects of pressure on PPG water-plugging performance and dehydration. In the fractures with tips, the PPG injection pressure increased rapidly, and could reach any designed pressure with continued injection after gel filled the fracture. By setting the PPG placing pressure at 500, 1,000, and 2,000 psi, the blocking efficiency to water showed a growth with the increase of placing pressure. The reswelling experiments show that PPG samples dehydrated when exposed to a high pressure difference between fracture and porous rock. Moreover, the placed PPG dehydrated relatively evenly along the fracture. Some gel particles were found whitening and reducing the capability of reswelling at the placing pressure of 2,000 psi. Scanning-electron-microscope (SEM) images indicated that the distinct 3D network of the PPG was compressed or damaged in the whitish sample. In addition, a discussion about PPG dehydration and fracture-tip extension is provided. In general, this study experimentally characterized PPG placement and plugging performance with respect to water in the fracture with tips. The PPG dehydration and fracture extension in PPG treatment, which have not drawn much attention in the literature, are investigated in this paper.

Realistic Stacking Sequence Optimisation of an Aero-Engine Fan Blade-Like Structure Subjected to Frequency, Deformation and Manufacturing Constraints

Aims:A procedure to optimise the stacking sequence of a composite fan blade-like structure is proposed in this article. The aim of the optimisation is to minimise weight when respecting deformation, frequency and strain constraints. The literature often deals with stacking sequence optimisation of airplane wings or wind turbine blades whilst less attention has been dedicated to aero-engines fan blades, the objective of the present paper. The manufacturing constraints are also implemented in the optimisation process in order to obtain a manufacturable structure.Background:Stacking sequence of composite laminates can be tailored to drive the deformation towards the desired shape (potentially exploiting unbalanced laminates and their anisotropy). When optimising the stacking sequence (including blending/tapering) of an aero-engine fan blade-like structure, manufacturing constraints must be included in order to apply the results of the optimisation procedure into a “Real World” design.Objectives:To define an engineering procedure able to provide a good design point to minimise the weight of a fan blade-like structure subjected to deformation (tip extension and untwist), frequency and strain constraints.Methods:A two-level optimisation procedure is proposed. At the first level, the stacking sequence is optimised in such a way to maximise stiffness (and therefore to minimise deformation). Less stringent limits are applied to the constraints of such a level 1 optimisation. In the second step of the optimisation, the blending/tapering of each ply of the stacking sequence is searched.Results:The fan blade-like structure is loaded only with a centrifugal load (the main load acting on this kind of components). The stacking sequence obtained to minimise the weight contains 42.3% of 0 degrees fibres, 19.25% of 45 degrees fibres, 19.25% of -45 degrees fibres and 19.2% of 90 degrees fibres. Blending in terms of width and length of each layer is given in the numerical results section.Conclusions:When the fan blade-like structure is loaded with a centrifugal force only, in order to minimise weight by respecting untwist, tip extension, frequency and integrity constraints, no unbalance in the laminate has been found necessary. An “Optimum” point has been found after a two steps optimisation. This design point is claimed as a good industrial design point rather than as “optimum” in the mathematical sense. Such a “Best Solution” design point has been verified by exploring the design space near it. All the performance of the neighbour points has been found worse. A comparison between a quasi-isotropic laminate and a zero degreed dominated laminate has been also performed.