Publications

High-viscosity modified asphalt is mainly used as a binder for porous asphalt in China and Japan. In order to meet the demand for using porous asphalt under high temperature condition in Africa, high-viscosity asphalt made from low-grade matrix asphalt, which is commonly used in Africa is investigated. Based on simulation of local climate in Africa, the suitable range of high viscosity additive content for different matrix asphalt was obtained by analyzing dynamic viscosity of the asphalt. Through PG high temperature grading, multi-stress repeated creep, accelerated fatigue, temperature sweep and other tests, changes of high temperature, anti-fatigue and anti-shear indicators before and after modification were compared and analyzed and effects of different matrix asphalt were also studied. Finally, considering engineering requirements, mixing and compaction temperatures of various high-viscosity modified asphalt were determined through study of viscosity-temperature characteristics. This research provides a support for preparation of high-viscosity modified asphalt and porous asphalt mixture by using low grade asphalt. The research achievements can help to guide the material design and application of porous asphalt in Africa and other high temperature areas.

Based on the extensive studies of conventional and unconventional hydrocarbon accumulations, the concept, classification and formation as well as distribution of petroleum reservoirs are discussed. The revised concept defined the petroleum reservoir as a continuous hydrocarbon accumulation in a single or a set of reservoirs with an independent or uniform pressure system. In terms of the pattern of hydrocarbon accumulation and distribution, the hydrocarbon accumulations are classified into three basic types, i.e., the continuous accumulation, the quasi-continuous accumulation and the discontinuous accumulation. The hydrocarbon accumulation was demonstrated as a process from continuous accumulation to discontinuous accumulation, and therefore these three basic types of hydrocarbon accumulations were identified. The continuous hydrocarbon accumulation is principally formed in source rocks, and typical examples are shale hydrocarbon reservoirs and coal-bed methane reservoirs; it is mainly characterized by tight-ultra tight reservoirs with permeability of nanodarcy to millidarcy; the hydrocarbons occurred in free, adsorbed or dissolved state; a continuous accumulation comprises actually only a single reservoir, and hydrocarbons are extensively and continuously distributed within the scope of effective source rocks; the accumulation has neither defined boundaries nor bottom or edge water; oil and gas mainly accumulate in situ or near the generation of hydrocarbons with no prominent migration; this hydrocarbon accumulation process is basically not controlled by traps. The quasi-continuous hydrocarbon accumulation mostly occurs in the tight reservoirs adjacent to source rocks, and typical examples are most of tight hydrocarbon reservoirs; the hydrocarbons are distributed quasi-continuously in large areas, and each quasi-continuous hydrocarbon accumulation includes numerous adjacent small- to medium-size reservoirs; reservoirs of this kind of hydrocarbon accumulation have no defined boundaries, no or only local edge and bottom water distribution, and no regional oil-gas-water inversion; hydrocarbons are pervasively charged in large areas, and oil and gas accumulation is caused by primary migration and short-distance secondary migration; the hydrocarbon migration and accumulation is principally driven by non-buoyant forces in non-Darcy flow; and the hydrocarbon accumulation is basically not controlled by anticline traps, but largely by non-anticline traps, especially lithological traps. The discontinuous hydrocarbon accumulation is also named as the hydrocarbon accumulation of the conventional-trap type, and typically occurs in conventional reservoirs, but some tight hydrocarbon reservoirs, coalbed methane reservoirs and even possible shale hydrocarbon reservoirs also belong to this kind of hydrocarbon accumulation; the hydrocarbon reservoirs are distributed discontinuously, and have clear boundaries and complete edge water or bottom water; the hydrocarbon migration and accumulation is mainly driven by buoyancy and secondary migration is usually indispensable; the hydrocarbon accumulation is strictly controlled by various traps, especially structural traps. In a petroliferous basin, above three types of hydrocarbon accumulation may coexist, andhydrocarbons are often derived from a common source kitchen(s). Therefore, these three types of hydrocarbon accumulation should be considered and studied as a whole to maximize hydrocarbon exploration efficiencvy.

Direct numerical simulations are performed to investigate the wake transitions of the flow normal to a circular rotating disk. The diameter-thickness aspect ratio of the disk is $\chi =50$ . The Reynolds number of the free stream is defined as $Re_s=U_\infty D/\nu$ , with incoming flow velocity $U_\infty$ , disk diameter $D$ , and kinematic viscosity of the fluid $\nu$ . The rotational motion of the disk is described by the Reynolds number of rotation $Re_r=\varOmega Re_s$ , with non-dimensional rotation rate $\varOmega =\frac {1}{2}\omega D/U_\infty$ , where $\omega$ is the angular rotation speed of the disk. Extensive numerical simulations are performed in the parameter space $50 \leqslant Re_s \leqslant 250$ and $0 \leqslant Re_r \leqslant 250$ , in which six flow regimes are identified as follows: the axisymmetric state, the low-speed steady rotation (LSR) state, the high-speed steady rotation (HSR) state, the low-speed unsteady rotation (LUR) state, the rotational vortex shedding state, and the chaotic state. Although plane symmetry exists in the wake when the disk is stationary, a small rotation will immediately destroy its symmetry. However, the vortex shedding frequencies and wake patterns of the stationary disk are inherited by the unsteady rotating cases at low $Re_r$ . A flow rotation rate jump is observed at $Re_s\approx 125$ . The LUR state is intermediate between the LSR and HSR states. Due to the rotational motion, the wake of the disk enters the steady rotation state earlier at large $Re_r$ , and is delayed into the vortex shedding state in the whole range of $Re_r$ . In the steady rotation states (LSR and HSR), the steady flow rotation rate is linearly correlated with the disk rotation rate. It is found that the rotation of the disk can restrain the vortex shedding. The chaotic state can be regularized by the medium rotation speed of the disk.

Abstract Polynomial chaos (PC) expansion meta-model has been wildly employed and investigated in the field of uncertainty quantification (UQ) and sensitivity analysis (SA). However, the majority of the multi-fidelity polynomial chaos expansion (MF-PC) models in the literature are still focused on using high-fidelity (HF) PC model to correct low fidelity (LH) model directly, without cross-correlation between PC models of different fidelities. To address this shortcoming, a multi-fidelity sparse polynomial chaos expansion (MF-sPC) model is proposed based on least angle regression (LAR) and recursive Gaussian process regression (GPR) in this paper. From low to high degree of fidelity, the autoregressive scheme in MF GPR is employed to construct MF-sPC model, in which the sparse polynomial chaos (sPC) model of each fidelity is built iteratively coupling with GPR, LAR and cross validation (CV), as gradually expanding the design of experiment (DoE) to reach a given CV error. This recursive scheme finally yields a MF-sPC model with highest fidelity which takes advantage of all sPC models of the lower fidelities. And the proposed MF-sPC model is validated by a test example in detail, and the results reveal that this MF meta-model performs outstanding both in convergence speed and model accuracy.