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The thixotropy properties and the motion law of a sphere in the Bingham fluid have been studied. Through observation of the settling motion of a single sphere in the Bingham fluid on the X- ray screen, it has been discovered that the mud in estuaries and along sea bay. and the hyperconcentrated flow all behave as the Bingham fluid with thixotropy properties as the large sediment concentration. Through derivation, the theoretical relationship between the yield stress and non-settling maximum sphere supported by the stress for the Bingham fluid has been developed, the equations for calculating the increasing yield stress and the non-settling maximum sphere diameter with the duration at rest of the slurry have been obtained. In consideration of the effect of thixotropy on fluid motion, the Navier-Stokes equation group for the Bingham thixotropy fluid has been developed. Through further study of the flow boundary condition of settling motion of a single sphere in the Bingham thixotropy fluid, and the solving of the Navier-Stokes equation group under the small Reynolds number, the theoretical equation of the drag force of the Bingham thixotropy fluid flowing around a sphere has been deduced. The theoretical relationship between drag coefficient and Reynolds number has been derived. By use of the experimental data of Theological test of various slurries measured with viscometer and those of single sphere motion observed on the X-ray screeen, the above equations have been verified. The equations are in good agreement with the experimental data for various slurries.
This paper presents the optimal design procedure of Tuned Mass Damper (TMD) for reducing vibration of an actual steel jacket offshore platform excited by random wave loading. In this study, a frequency domain is taken. The force on the structure is determined by use of the linearized Morison equation for an input Power Spectral Density (PSD) of wave elevation. The sensitivity of optimum values of TMD to characteristic parameters of random wave spectrum is analyzed. An optimized TMD design for the modeled platform is given based on design conditions and the findings of the study.
The hydrodynamic coefficients Cd and Cm are not only dependent on the size of slender cylinder, its location in water, KC number and Re number, but also vary with environmental conditions, i. e., in regular waves or in irregular waves, in pure waves or in wave-current coexisting field. In this paper, the normalization of hydrodynamic coefficients for various environmental conditions is discussed. When a proper definition of KC number and proper characteristic values of irregular waves are used, a unified relationship between Cd, Cm and KC number for regular waves, irregular waves, pure waves and wave-current coexisting field can be obtained.
For higher accuracy in simulating the transformation of three dimensional waves, in consideration of the advantages of constant panels and linear elements, a combined boundary elements is applied in this research. The method can be used to remove the transverse vibration due to the accumulation of computational errors. A combined boundary condition of sponge layer and Sommerfeld radiation condition is used to remove the reflected waves from the computing domain. By following the water particle on the water surface, the third order Stokes wave transform is simulated by the numerical wave flume technique. The computed results are in good agreement with theoretical ones.
The rate of change of wave surface elevation is of much importance in ocean engineering, especially for the determination of the limitation of wave breaking. This paper gives a kind of joint distribution of wave periods and the rate of change of wave surface elevation by means of calculation of the two-order to four-order moment of the frequency spectrum based on the linear wave theory. For the first time, the distribution density function of wave periods determined by peaks is provided, and the conclusion is drawn that the rate of change of wave surface elevation obeys the Rayleigh distribution.
Test studies on the wave pressure on a breakwater pier show that the influence of transmissive wave pressure on the outside wall of the breakwater pier is considerable, when the width of the pier is not very large. The variations of transmissive wave pressure on the breakwater pier with different widths are compared and the relationship is obtained between relative transmitting distance b / L and wave pressure reduction factor K, which may be used in the design of similar breakwater piers.
Fine grids with small spacing in boundary-fitted coordinates are normally used to treat the computation of fluid dynamics for estuarine areas and tidal flats. However, the adoption of Cartesian components of velocity vectors in this kind of non-orthogonal coordinates will definitely result in a difficulty in solving implicitly the transformed momentum equations, and also complicate the wet-dry point judgement used for flood areas. To solve this problem, equations in terms of generalized contravariant velocity vectors in curvilinear coordinates are derived in the present study, by virtue of which, an Alternative-Direction-Implicit numerical scheme in non-orthogonal grids would then be easily obtained, and wet-dry point judgement would as well be largely simplified. A comparison is made between the explicit scheme and implicit scheme, showing that the present model is accurate and numerically stable for computations of fluid dynamics for estuarine areas and tidal flats.
Based on historic topographic maps and field surveys, this paper mainly deals with the formation and evolution of the Jiuduansha Shoal and the North Passage and South Passage in the Changjiang Estuary. Jiuduansha Shoal originated from the partition of the south part of the Tongsha Shoal as the result of connection of a flood channel and an ebb channel. The embryo of the North Passage was a flood channel, and that of the South Passage was the lower reaches of the former South Channel. There were two basic kinds of change in erosion and accumulation since the formation of Jiuduansha Shoal: continuous change and periodic change. The former includes the broadening of the island area, accretion on the tidal marsh and tidal flat and downstream migration of the island. The latter includes cyclic erosion and accumulation on the two river channel banks of the island and the North and South Passages. The island and the two bifurcated river passages interacted on each other in erosion and accumulation changes. At present, the courses of the North Passage and the South Passage are relatively stable.
By use of the parabolic equation of numerical simulation of wave which is suitable for large-angle propagation and Crank-Nicolson differential method, the wave field at the Kemema River mouth has been studied for analysis of sediment movement in the area. In order to reflect wave energy loss accurately, the Bretchneider-Reid formula is quoted and the friction coefficient in the formula is discussed in this paper. The calculation results indicate that the wave becomes a little damped at the mouth of Kemena River influenced by the topography and bottom friction, and the wave at the east beach is higher than that at the west beach, because the east beach extends out.
A nonlinear model of mean free surface of waves or wave set-up is presented. The model is based on that of Roelvink (1993), but the numerical techniques used in the solution are based on the Weighted-Average Flux (WAF) method (Watson et al., 1992), with Time-Operator-Splitting (TOS) used for the treatment of the source terms. This method allows a small number of computational points to be used, and is particularly efficient in modeling wave set-up. The short wave (or primary wave) energy equation is solved by use of a more traditional Lax- Wendroff technique. A nonlinear wave theory (James, 1974) is introduced. The model described in this paper is found to be satisfactory in most respects when compared with the measurements conducted by Stive (1983) except in modeling the mean free surface very close to the mean shoreline.
According to the Mohr-Coulomb yield criterion, the stress field of the infinite slope is derived under a vertical uniform load q on the top of the slope. It is indicated that elastic and elasto-plastic states would occur in the slope. When q is smaller than the critical load, qp, the slope is in the elastic state. If q equals qp, the slope is in the critical state, and the plastic deformation would occur along the critical angle. With the increase of q, the plastic zone would extend, and the slope is in the elasto-plastic state. If q equals limit load, the slope is in the limit equilibrium state. The slope may be divided into three zones. Some charts of the critical angle, the critical and limit load coefficients are presented in this paper.
ScholarOne Manuscripts Log In
- Volume 33
- Issue 6
- December 2019
- Superintended by:
CHINA ASSOCIATION FOR SCIENCE AND TECHNOLOGY
- Sponsored by:
Chinese Ocean Engineering Society （COES）
- Edited by:
Nanjing Hydraulic Research Institute
Adaptive Predictive Inverse Control of Offshore Jacket Platform Based on Rough Neural Network
Numerical Simulation of Water Exchange Characteristics of the Jiaozhou Bay Based on A Three-Dimensional Lagrangian Model
A Global Reliability Assessment Method on Aging Offshore Platforms with Corrosion and Cracks