The formation and geometry characteristics of boulder bars due to outburst floods triggered by overtopped landslide dam failure

Boulder bars are a common form of riverbed morphology that could be affected by landslide dams. However, few studies have focused on the formation and geometry characteristics of boulder bars due to outburst floods triggered by landslide dam failure. In such a way, eight group landslide dam failure experiments with a movable bed length of 4 to 7 times the dam length with 25 boulder bars were carried out. In addition, 38 boulder bars formed in the field triggered by four landslide dam failures were investigated. The aim of this paper is to study the formation and geometry characteristics of boulder bars along the riverbeds. The results show that boulder bars are formed after peak discharge of outburst flow. The number of boulder bars is 0.4 to 1.0 times the ratio of riverbed length to dam bottom length. Besides, boulder bars have the characteristic of lengthening upstream during the failure process. A boulder bar's upstream edge has a more extensive development than a boulder bar's downstream edge. The length of a boulder bar along the channel changes faster than the boulder bar's width and height. After the dam failure, the boulder bar's length is about 8 to 14 times its width. The relationship between the ratio of boulder bar length to width and the boulder bar's dimensionless length could be described with a hyperbolic equation. The dimensionless area of the boulder bar increases linearly with the dimensionless area of the river section, and the linear ratio is about 0.5. With the field data, this demonstrates that the formation and geometry characteristics of boulder bars in tests are consistent with the field boulder bars. Therefore, the results in this paper are credible and can be applied to the riverbed's geomorphological characteristics analysis triggered by overtopped landslide dam failure. The plentiful experimental and field data could contribute to the community boulder bar research.

COMPARATIVE STUDY ON HEAT TRANSFER CALCULATION IN TRANSITION AND TURBULENT FLOW REGIME INSIDE TUBES

In this paper is compared a proposal model for heat transfer calculations during fluid flow in single-phase inside tubes with others existing in the literature. This comparison used 3096 available experimental data of 36 different fluids. The proposal model is valid for a range from to and 0.65 to for Reynolds and Prandtl number respectively, dimensionless length values and viscosity correction in the interval . The comparison proves that the suggested model presents the better index of correlation, being found an average error of 13.8% in the 80.6% of the experimental data and a maximum error of 24.6%.

Pressure behaviour of a horizontal well sandwiched between two parallel sealing faults

Generally, reservoir fluid flow is governed by diffusivity equation and solution to this equation helps to investigate pressure behaviour under certain reservoir and wellbore boundary conditions. In this paper however, the analytical solution method of Green and Source function is deployed to determine the performance of a horizontal well located between two parallel sealing faults, assuming simple rectangular reservoir geometry. Also, the dimensionless pressure and derivative approach is applied for all computations as it prevents the problem of unit conversions, reduces longer expressions and it helps to handle numerical values. The pressure expression derived from this work reveals that a maximum of two flow periods occur for the stated reservoir model. It was found out that an inverse relationship exists between dimensionless pressure and dimensionless length while pressure increased with thickness. Also high vertical permeability shortens the effect of the early radial flow period experienced by the horizontal well, thereby increasing productivity index. Finally, it was discovered that increased perforation length reduces the production potential of the horizontal well. Keywords: Dimensionless pressure, pressure derivatives, heterogeneity, pressure performance, reservoir and wellbore characterization.

Dynamic stability analysis of microcomposite annular sandwich plate with carbon nanotube reinforced composite facesheets based on modified strain gradient theory

In this article, dynamic stability of annular sandwich plate with carbon nanotubes reinforced composite facesheets and an isotropic homogeneous core are presented based on first-order shear deformation theory and modified strain gradient theory. The generalized rule of mixture is employed to predict mechanical properties of microcomposite sandwich plate. The equations of motion are derived from Hamilton’s principle and solved by differential quadrature method. The fast rate of convergence of the method is shown and the results are compared against existing results in the literature. The results indicate that volume fraction of carbon nanotubes in facesheets and dimensionless length scale parameter has significant effects on the dynamic stability region and the parametric resonance. Dynamic stability region increases with considering of dimensionless length scale parameter, increasing of volume fraction of carbon nanotubes, and static load factor. Also, the influence of inner-to-outer radius ratios, radius-to-thickness ratios, and core-to-facesheets ratios are considered. The results can be employed for design of materials science, in junction high pressure micropipe connections, solid-state physics, micro-electro-mechanical systems, and nano electromechanical systems such as microactuators and microsensor.

Effects of Inlet Flow Boundary Conditions on the Thermal Performance of a Plate-Fin Heat Sink With an Impinging Flow

This paper discusses the effect of inlet flow boundary conditions on the performance of a plate-fin heat sink with an impinging flow. The inlet flow boundary conditions of the plate-fin heat sink are decided by duct configurations and heat sink geometries. First, velocity distributions according to the inlet flow boundary conditions of the plate-fin heat sink are obtained using numerical simulations. These results clearly show that the inlet flow boundary condition is divided into two branches: one is uniformly impinging flow and the other is non-uniformly impinging flow. Also, the fluid characteristics of the plate-fin heat sink with an impinging flow according to the inlet flow boundary conditions are experimentally examined by measuring the stagnation pressure distributions on the bottom of the plate-fin heat sink. Based on Do et al., correlations for pressure drop and thermal resistance of the plate-fin heat sink with uniformly impinging flow are proposed. Also, pressure drop and thermal resistance correlations of the plate-fin heat sink with uniformly impinging flow are compared with those of the plate-fin heat sink with non-uniformly impinging flow using correlations suggested by Kim et al. Finally, it is shown that the plate-fin heat sink with uniformly impinging flow has a lower thermal resistance than the plate-fin heat sink the non-uniformly impinging flow when the dimensionless length of the plate-fin heat sink is small and the dimensionless pumping power is large.

Natural convection analysis for both protruding and flush-mounted heaters located in triangular enclosure

A numerical was performed analysis on laminar natural convection heat transfer and fluid flow in both protruding heaters (PHs) and flush-mounted heaters (FMHs) located in a triangular enclosure using finite-difference technique. The heaters were isothermal and the temperature of the inclined wall was lower than that of the heaters while the remaining walls of the triangular enclosure were adiabatic. Results are presented according to the location of the heaters in two cases. In the first case, the PH was located near the vertical wall and the FMH near the right corner. In the second case, the PH was located near the right corner of the enclosure, whereas the FMH was located close to the vertical wall. The governing parameters on natural convection were Rayleigh number (104≤Ra≤106), dimensionless length of the PH ( W1), dimensionless length of the FMH ( W2), dimensionless height of the PH (Hp), dimensionless distance between the heater and the vertical wall ( S1), dimensionless distance between the PH and the FMH ( S2), and aspect ratio of the triangular enclosure (0.25 ≤AR≤ 1.0). It was found that better heat transfer occured when the PH was located near the right corner of the triangular enclosure, while the other heater was mounted near the left vertical wall. Heaters behaved as a single heater when they were close to each other.

Nonequilibrium consolidation model for pressured shale layers

A simplified mathematical model is developed for fluid migration as a separate phase in the consolidation process due to sedimentation. The consolidation mechanism is presented and the sedimentation ratio is related to the consolidation of shales. The model is composed of simple differential equations which relate the mass balance equation to the linear fluid flow law and pressure increment. In the derivation of equations the fluid and shale compressibilities are taken into consideration. In addition, the shale porosity decrease with depth is included in the consolidation equations. These equations are converted into dimensionless standard forms, which are universally valid for any fluid migration or shale consolidation calculations. The equations are solved numerically by the finite difference method, and the results are presented as graphs referred to as type curves. These type curves are simple tools for those who do not want to be concerned with the mathematical aspects but are interested particularly in quantitative answers concerning the fluid-migration and consolidation processes.Key words: consolidation, dimensionless length, fluid migration, nonequilibrium, shale.

Expansion Factors for Two Variable Area Flow Meters

Data acquired in the years 1958 to 1960 at the Naval Ship Engineering Center under sponsorship of the American Society of Mechanical Engineers are used to derive semiempirical equations for the performance of two variable area meters with both liquid and gas flow. As the measurements are put to a useage for which they were not intended, the data treatment is considered illustrative of the application of a flow equation derived by an analysis based upon a force and momentum balance. The hydraulic flow coefficient is expressed in terms of a function of (a) pressure drop divided by float weight and of (b) a dimensionless length ratio β for float position. Density ratio is used to modify the function of β to derive the expansion factor Y for gas flow as suggested by the analysis. Reasonable agreement between measured and derived values of Y is demonstrated, and approximate measures of the velocity profiles in the meter are derived from the correlation equations. One set of air tests at one float position in which the viscous influence number N was changed from 500,000 to 783,000 indicated (within this range) a possible insensitivity of the derived function of β to change of N.