G.Q. Chen

Sustainability of a typical biogas system in China: Emergy-based ecological footprint assessment

Abstract Integrated biogas utilization has experienced a rapid development in recent years in rural China, for both renewable energy production and waste treatment. On the basis of a modified Ecological Footprint (EF) indicator, this paper provides a comprehensive assessment of a “pig–biogas–fish” system, a typical household integrated biogas-utilization system in southern China, by focusing on the resources consumed and produced within the system. The method of Emergy Environmental Footprint as a combination of EF and emergy accounting is introduced to quantify the sustainability of the overall biogas system and its three subsystems. Results reveal that the resource use intensity of the “pig–biogas–fish” system, defined as the ratio of footprint investment to footprint delivered, is 0.48. Compared with the conventional animal husbandry system, the “pig–biogas–fish” system proves to be of higher sustainability. And the findings have essential policy making implications supportive to a further spread of integrated biogas-utilization modes in rural areas.

Some issues in constitutive modeling

Abstract Some basic issues in constitutive modeling are examined. The first concerns the requirement of material frame indifference, the commonly used version is analyzed under the restriction that the effect of relativity is negligible. The second deals with the entropy production inequality in the modeling of large scale motions and the uncertainty involved in formulating such an inequality as a constraint in developing constitutive relations is discussed. Finally, the use of Lagrangian frames and reference configurations and related questions concerning the development of a constitutive model for turbulent flows of a fluid, on the basis of laminar flows of that fluid, is discussed.

Remarks on large eddy simulation

Abstract For large eddy simulation of turbulent flows, some analysis and general remarks on the filtering operation and modeling under small filtering length scales are presented.

Retrospect and prospect of watershed hydrological model

A brief review is presented of the development of watershed hydrological models. Conventional Hydrological Model, Grey Hydrological Model, Digital Hydrological Model and Intelligent Hydrological Model are analyzed. The frameworks of Fuzzy Cognitive Hydrological Model and Integrated Digital Watershed Hydrological Model are presented.

Discrete large eddy simulation

Abstract Despite the intense effort expended towards obtaining a model for describing the turbulent flows of fluid, there is no model at hand that can do an adequate job. This leads us to look for a non-traditional approach to turbulence modeling. In this work we conjoin the notion of large eddy simulation with those of fuzzy sets and neural networks to describe a class of turbulent flows. In previous works we had discussed several issues concerning large eddy simulation such as filtering and averaging. Here, we discuss tile use of fuzzy sets to improve the filtering procedure.