Magnitude Of Suction Research Articles

Influence of base suction on extraction of jack-up spudcans

Operators of mobile jack-up rigs often face difficulties when extracting spudcan foundations of jack-up rigs in the field. Centrifuge model tests were carried out to evaluate the uplift resistance of a jack-up spudcan in normally consolidated clay during extraction. The top and bottom faces of the model spudcan were instrumented with total pressure and pore pressure transducers. These pressure readings and pore pressure changes in the soil beneath the spudcan were monitored throughout the installation, operation and extraction of the spudcan. In the present study, the operation stage was simply simulated by maintaining a constant vertical load on the spudcan. Tests were conducted to examine the effects of duration of operation period and ratio of operational working load to installation load on the uplift resistance of the spudcan. The test results revealed that suction developed at the interface between the spudcan base and the underlying soil, and the magnitude of base suction increased with the operation period of the spudcan. It is noted that, during extraction, the resistance to overcome the soil resistance above the spudcan increases only slightly with spudcan operation period. Hence the increase in base suction is established to be the key contributor for the larger breakout force required to extract spudcans with longer operation periods.

Comparison of interface pressures with pin and suction suspension systems

A common mode of limb suspension for transtibial amputees is the pin liner/shuttle lock system. Despite its popularity, some clinicians question its use because of observed daily and chronic changes to the residual limb. For this study, we measured limb interface pressures during ambulation with pin and suction suspension systems. No pressure differences were seen between the modes of suspension during stance phase. However, during swing phase, pin suspension maintained an average occlusive compressive pressure of 6.7 kPa on the proximal tissues, as compared to the subocclusive pressure of 1.1 kPa with suction suspension. Simultaneously, pin suspension elevated the peak magnitude of suction to -39.5 kPa at the distal residual limb, compared to -26.1 kPa with suction suspension. During swing phase, the pin liner squeezes proximally while creating a large suction distally on the residual limb and is the likely cause of daily and chronic skin changes observed in pin users.

Suction in compacted states

Examines the possible magnitude of suction in compacted states of clayey soils. From the test results, it is concluded that suction is zero in monotonically loaded unsaturated states. This implies that suction in compacted states should be equal to the compaction stress itself. However, as data previously reported in literature have often shown - suction is strongly related to the water content and not much affected by the compaction stress.

Filter Paper Technique for Measuring Total Soil Suction

An experimental program was conducted to investigate the noncontact filter paper technique for total suction testing. Calibration curves for seven different batches of Whatman #42 filter paper were obtained to evaluate the variation in the calibration characteristics from one batch of paper to another. Additional tests using salt solutions for controlling suction were conducted to evaluate the measurement uncertainty as a function of suction magnitude. Calibration curves for the various papers varied significantly from batch to batch. This variation can be as much as 11% for filter paper water content, which results in a potential measurement error as high as 92% for suction. Scatter in the measurements appeared to increase with decreasing total suction. At relatively high values of suction (32 000 kPa), the standard deviation for five independent measurements was as much as 11.6% of the mean. At relatively low values (270 kPa), the deviation appeared to increase to 23.2% of the mean. One hundred measurements over a wide range of values for an expansive clayey soil confirmed the observation that the scatter in the measurements increases as total suction decreases.

Modulatory multiplicity in the feeding mechanism in cichlid fishes, as exemplified by the invertebrate pickers of Lake Tanganyika

Electromyography, motion analysis, osteology, myology and feeding behaviour of a morphologically specialized monophyletic lineage of cichlids in Lake Tanganyika have revealed that Eretmodus, Spathodus and Tanganicodus possess a feeding apparatus with a more extensive functional repertoire than that of any other teleost studied to date. When collecting a wide range of foods by inertial suction this trophic group can employ two strategies, a preprogrammed cyclical, energy saving pattern, or a modulated mode effected by extensive overlap of the firing patterns of multiple muscles resulting in a precise control of the magnitude and direction of suction. When dislodging sessile prey from the substrate the complexity of electromyographic and kinematic patterns increases. Because upper jaw protrusion can be effected and controlled independently from the complex couplings causing mouth opening and movements of the suspensory apparatus, a new decoupled model of upper jaw protrusion is proposed. The decoupled model predicts that upper jaw protrusion can be effected directly by contraction of epaxial muscles that raise the neurocranium, causing the premaxillae to slide anteroventrally. Upper jaw protrusion can be modulated continuously and directly by balanced cocontractions of antagonistic muscle sets giving the decoupled model an improved function over a very extensive range. The morphologically symmetrical muscular apparatus can function asymmetrically. Very pronounced asymmetrical firings of multiple muscles produce a continuously modulated jaw mechanism with an extensive repertoire.

Ecoulement turbulent en conduite annulaire avec aspiration aux parois

The effect of suction on a turbulent flow through a cylindrical conduit of annular section is investigated experimentally. The author presents the pattern of evolution of the mean longitudinal velocity profiles and of the coefficients of friction at the walls. The “pseudo-velocity” is correctly represented by an expression proposed by Simpson et al. The wall flows, relating to the small tube and the large tube, can be considered to be virtually independent of each other for the suction magnitudes used. The author also proposes an empirical relation which gives the position of the maximum mean velocity as a function of the ratio of the radii in the absence of suction.

An analytical solution for the laminar flow over a flat plate with similarity preserving suction

An exact analytical solution is presented for the laminar boundary-layer flow over a semi-infinite flat plate subjected to a type of similarity preserving suction. The solution is developed for the case of a plate immersed in either a uniform compressible stream with viscosity proportional to temperature or a uniform incompressible stream with constant viscosity. The problem is formulated in Crocco's variables. It is described by a second-order, non-linear, ordinary differential (and singular) boundary-value problem for the shear stress as a function of the velocity in the boundary layer. A unique solution is shown to exist and to possess a power series representation for all magnitudes of suction. The series is constructed explicitly and provides a transcendental equation for the shear stress at the plate (the important skin friction) which can be solved to any desired accuracy. Examples of upper and lower bounds for the wall shear are presented for several magnitudes of suction and confirm the reasonable accuracy of results obtained heretofore only by numerical solutions of the problem. In addition to the intrinsic value of the technique developed, it can be the basis of accurate checks for the numerical solution of more complex problems.

Plane Couette Flow with Suction or Injection over a Limited Portion of the Stationary Plane

AbstractThe paper discusses the upstream and downstream effects of a uniform suction or injection applied over a finite length of the stationary plate in a plane Couette flow using the full Navier‐Stokes equations. The variation of the tangential stress along the length of the stationary plane and the disposition of streamlines are exhibited by means of graphs for a number of values of the Reynolds number, suction or injection velocity and the impressed pressure gradient. The use of finite‐difference method has enabled us to avoid the restriction of smallness of the Reynolds number or of the magnitude of suction or injection velocity which is usually imposed in such investigations.

Laminar Flow Between Rotating Porous Disks

A perturbation solution of the equations of motion for steady, incompressible, laminar flow between a porous rotating disk and a stationary nonporous disk has been obtained. The solution obtained is valid for small wall Reynolds numbers and various values of the rotation coefficient, α=2h\U3\N ω\U2\N/v V, in which \Ih\N = the distance between disks, ω = the angular velocity, \IV\N = the magnitude of suction or injection velocity, and \Iv\N = the kinematic viscosity. Expressions for the velocity, pressure, viscous stress, and resisting moment are presented.