Field measurement of the air flow characteristics of big mechanically ventilated spaces

Air speeds induced by mechanical ventilation systems in the occupied zone are studied experimentally in seven railway stations in Hong Kong. Values of air speed at different positions are measured. From these values, air speed contours and turbulence intensities are calculated. Macroscopic numbers describing airflow in a space including the Reynolds number and the jet momentum number are estimated and their potential uses are discussed.     

Relations of calculated and actual settlement of a thawing foundation bed

Conclusions 1. The dependence of relative compression of thawing soil on pressure is nonlinear, and it is in agreement with views on the nature of deformation of thawing soil. A dominance of natural pressure in the total load on a foundation bed permits one to use the method of unit summation in calculating settlement of nonlinearly deformable soil. Such calculations, as compared with the linear formulas employed in SNiP, give better agreement with actual settlement.2. In calculating settlement of thawing foundation beds, we need differential consideration of soil compressibility with depth, since the combination of genetic features of frozen ground and the increasing natural pressure with depth may create a different inhomogeneity in the foundation bed.Yakutniproalmaz, Mirnyi. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 18–21, January–February, 1975.     

Procedure for predicting settlements of thawing bases for engineering calculations

It was shown that in order to compute the settlement of thawing cohesive soil under a load in time it is necessary to experimentally determine the consolidation coefficient. A procedure is suggested for determining this coefficient, as well as use of the classical solution of a differential equation for seepage consolidation to describe the settlement of soil, thawing of which can occur according to any law.State All-Union Scientific Research Institute of Roads. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 5–7, July–August, 1993.     

A new approach for simulating aerodynamic vibrations of structures in a wind tunnel—development of an experimental system by means of hybrid vibration technique

The present paper describes a newly proposed technique for simulating aerodynamic vibration of structures, which is referred to as the hybrid vibration technique or HVT. This technique is a combination of step-by-step computer calculation and measurement of the aerodynamic force acting on a model structure in a wind tunnel test. Even though the HVT can be applied effectively, problems still exist with respect to obtaining accurate simulations. These problems include response delay in controlling the model behavior and the inertia force component present in the measured aerodynamic force. Techniques for compensating for response delay and for eliminating inertia force from measured aerodynamic force are applied to a developed system based on HVT simulations of aerodynamic vibration of elastic structures and structures exhibiting elasto-plastic behavior are performed by means of the newly developed system. The effectiveness of the techniques for compensating for the response delay and eliminating the inertia force can be confirmed from the results of the simulations. In addition, the possibility and applicability of HVT is indicated.     

Continuous monitoring of short term dissolved oxygen and algal dynamics

Dissolved oxygen (DO) in coastal bays with frequent algal blooms can undergo significant diurnal changes. Short-term DO and algal dynamics in a sub-tropical, nitrogen-limited, marine ecosystem are studied by means of a specially designed telemetry system. The high resolution data show clearly the importance of the vertical DO structure, and its relationship with environmental variables (solar radiation, water temperature, wind, tidal current) and phytoplankton dynamics. The design, instrumentation and calibration, and operational experience of the system are described. The simple and robust system has proved useful in (i) providing continuous data for full testing of water quality models, and (ii) the planning of field experiments to study algal dynamics.     

Concurrent denitrification and oxygen uptake in microbial films

Mixed microbial films were grown on the inner walls of a tubular reactor with recirculation of the reactor contents and continuous flow-through of nutrient solution. The loss of total oxidized nitrogen was correlated to the film population, the nitrite concentration and the dissolved oxygen concentration in the reactor. When film population was greater than 0.5 × 10⁹ cells cm⁻², reactor dissolved oxygen concentration greater than 1 mg l⁻¹ had little effect on the nitrate loss. Nitrate loss declined for film populations greater than 2 × 10⁹ cells cm⁻². Models based on Monod and zero-order microbial kinetics were calibrated using these data and a nonlinear least squares method. There was little difference in the residual errors with these methods.     

A pore crack model for the mechanical behaviour of porous granular rocks in the brittle deformation regime

A model is developed for predicting and simulating the mechanical behaviour and failure mode of brittle porous granular rocks loaded in compression. It is based on a fracture mechanics analysis applied to cracks emanating from the surface of cylindrical pores in two-dimensional, which is well suited to the microstructure of such rocks. It is also consistent with the usual experimental procedure used for biaxial compression tests since the numerical scheme is implemented under the assumption of imposed axial strain. The model takes into account interactions between neighbouring cracks, which grow when their stress intensity factor reaches the fracture toughness of the rock. The simulation of crack growth from cylindrical holes, associated with a failure criterion based on the coalescence of interacting cracks, allows one to calculate the critical stress at rupture and to derive theoretical stress–strain curves.The present model is then used to compare theoretical results with laboratory data obtained on four sandstones with porosity ranging between 13% and 25.5% which were deformed under conventional triaxial compression conditions at confining pressures between 0 and 35 MPa. The comparison shows that by using a small number of parameters (pore size, pore density, fracture toughness, and elastic moduli), the model is able to predict the rock behaviour during the compression tests and the stress level at rupture in a quite accurate way, when the microstructural parameters introduced are consistent with the observations.     

Assessment of nitrification in groundwater filters for drinking water production by qPCR and activity measurement

In groundwater treatment for drinking water production, the causes of nitrification problems and the effectiveness of process optimization in rapid sand filters are often not clear. To assess both issues, the performance of a full-scale groundwater filter with nitrification problems and another filter with complete nitrification and pretreatment by subsurface aeration was monitored over nine months. Quantitative real-time polymerase chain reaction (qPCR) targeting the amoA gene of bacteria and archaea and activity measurements of ammonia oxidation were used to regularly evaluate water and filter sand samples. Results demonstrated that subsurface aeration stimulated the growth of ammonia-oxidizing prokaryotes (AOP) in the aquifer. Cell balances, using qPCR counts of AOP for each filter, showed that the inoculated AOP numbers from the aquifer were marginal compared with AOP numbers detected in the filter. Excessive washout of AOP was not observed and did not cause the nitrification problems. Ammonia-oxidizing archaea grew in both filters, but only in low numbers compared to bacteria. The cell-specific nitrification rate in the sand and backwash water samples was high for the subsurface aerated filter, but systematically much lower for the filter with nitrification problems. From this, we conclude that incomplete nitrification was caused by nutrient limitation.