Zhiqu Lu

Acoustic method for measuring asphaltene flocculation in crude oils

Abstract With a view to evaluate the risk of asphaltene to flocculate in crude oils, an experimental device based on an acoustic technique of phase comparison has been developed. The operational method and the results concerning the influence of the precipitant concentration on crude–solvent mixtures at 323 K and atmospheric pressure thus obtained are presented. On the basis of the measurements carried out, it is shown that flocculation caused a sufficiently important change in the output phase signal which thus can be used as an indicator of the phenomenon.

Feasibility of Using a Seismic Surface Wave Method to Study Seasonal and Weather Effects on Shallow Surface Soils

ABSTRACT The objective of this paper is to study the feasibility of using a seismic surface wave method to investigate seasonal and weather effects on shallow surface soils. In the study, temporal variations of subsurface soil properties were measured and monitored by using a combination of a new seismic surface method and an existing acoustic probe system. A laser Doppler vibrometer (LDV)-based multi-channel analysis of surface wave (MASW) method is developed to measure the soil profile in terms of shear wave velocity at depths up to a few meters. While the conventional MASW uses geophones as surface vibration sensors, the present MASW uses a moving LDV as a non-contact sensor to detect Rayleigh wave propagation generated by an electromagnetic shaker operating in chirp mode. A long-term survey was conducted by measuring the S-wave velocity profile with the MASW along with measurements of soil temperature, water content, water potential, and P-wave velocity with the acoustic probe system. The results from...

A phase-comparison method for measurement of the acoustic nonlinearity parameter

This paper reports an improved thermodynamic method which uses a highly sensitive phase-comparison technique to measure the acoustic nonlinearity parameter . A phase-calibration procedure was introduced. The measurement can be achieved automatically by computer with a program written in HP VEE. Several measurements have been made for distilled water and organic liquids. The experimental results agree well with those in the literature. The inaccuracy of the method is 2.2%. parameter, phase-comparison technique, speed of sound, pressure, water, organic liquids

Phase comparison technique for measuring liquid–liquid phase equilibrium

In this article, a new method is demonstrated to measure the liquid–liquid phase equilibrium for binary systems. A phase comparison technique was employed to real-time display the phase–time curve in a “wave form (time) object” of Hewlett–Packard visual engineering environment. It was found that the phase–time curve showed a distorted wave form when liquid–liquid phase transition took place. The abnormal curve can therefore be used to detect liquid–liquid phase transitions. Measurements were performed in several binary systems such as nitromethane+1-hexanol, nitromethane+butanol, and nitroethane+n-hexane. The experimental results are in good agreement with those in the literature.

Acoustic Nonlinearity Parameter of Liquid Alkanes as a Function of Temperature, Chain Length and Isomerism

Abstract The acoustic nonlinearity parameter B/A along with intermediate quantities such as the pressure derivative of sound speed and the phase shift were measured in 8 linear alkanes and a series of four isomers of hexane. The influences of temperature and chain length on these quantities were revealed. It was found that the phase shift parameter is more sensitive to molecular structure and temperature than B/A and that the pressure derivative of sound speed.

Effect of ground variability on acoustic-to-seismic transfer function and false alarms in landmine detection

The spatial variability of ground properties leads to fluctuations in the acoustic-to-seismic transfer function (A/S TF), the ratio of the normal particle velocity on the ground to sound pressure. In some cases, these fluctuations may lead to false landmine detection alarms. This work shows that small variations in the ground properties may cause strong variations in the A/S TF. Experimental measurements of the A/S TF performed at a US Army eastern temperate site are presented and a correlation between high magnitudes of the A/S TF (false alarms) and moisture content on the surface is shown. A simple model of the ground explaining this correlation is suggested. This model was used to describe spatial distribution of high magnitudes in the TF and natural spatial variability of the TF. Results of calculations were compared with experimental data. Two frequency modulation scales in the A/S TF are observed at positions on the ground where land mines are not located. It was hypothesized that these are due to i...

Practical Techniques for Enhancing the High-Frequency MASW Method

ABSTRACT For soil exploration in the vadose zone, a high-frequency multi-channel analysis of surface waves (HF-MASW) method has been developed. In the study, several practical techniques were applied to enhance the overtone image of the HF-MASW method. They included (1) the self-adaptive MASW method using a variable sensor spacing configuration, (2) the phase-only MASW method, and (3) a nonlinear acoustic technique. To demonstrate the capability of these techniques, a HF-MASW test was conducted, which consisted of a small shaker operated in chirp mode with three gapped frequency bands and a geophone array with a variable spacing configuration. The overtone images obtained from (1) full spreadlength, (2) self-adaptive spreadlength, (3) full-spectra analysis including magnitude and phase spectra, and (4) phase-only spectrum analysis MASWs, respectively, were compared in each frequency bands. The results revealed the enhanced dispersive images by the HF-MASW using the self-adaptive and phase-only with the va...

The measurement of the hysteretic nonlinearity parameter of a field soil by the phase shift method: A long‐term survey

Soil properties significantly affect the performance of the acoustic landmine detection. The climate and seasonal changes cause the variations of soil properties and smear landmine signature over time. On the other hand, soil is a complicated granular material that exhibits strong nonlinear acoustic behaviors. To understand the weather and seasonal effects on nonlinear acoustic behaviors of soils, a phase shift method is used to measure the hysteretic nonlinearity parameter of a field soil. The technique is based on measuring the variation of phase difference between two transducers, i.e., the phase shift, induced by changing sound level. The hysteretic nonlinear parameter can be extracted from the measured phase shift as a function of sound level or dynamic strain. In a long‐term survey, the nonlinearity parameter, sound speed, and environmental conditions such as temperature, moisture, soil water potential, and rainfall precipitation are measured. It is found that the nonlinearity parameter is much more...

A Study of Soil‐Pipe Flow and Internal Erosion by Acoustic Techniques

Internal erosion of soil pipes can lead to embankment failures, landslides, and gully erosion. This talk presents a lab study using both active and passive acoustic techniques to monitor and assess a soil pipe flow and internal erosion event. In active test, the phase slope method was employed to measure the P-wave velocity of soils under noisy and ever-changing conditions. The study showed that the variation of the P-wave velocity reflected the ongoing internal erosion processes such as the onset of soil pipe flow, the buildup of hydraulic pressure, the evolution of saturation, the variation of hydraulic pressure due to the change in flow rate, as well as aftermath events such as drainage, and relaxation. These observations can be analyzed and understood by using the concept of the effective stress and its relationship with the P-wave velocity. In passive measurement, water flow sound was recorded by a sensor buried inside the soil and close to the pipe. Three signal processing algorithms were applied for the water flow sound analysis, which revealed the common temporal characteristic of the water flow sounds. The passive study suggested that the soil pipe flow can be identified and assessed from the noise levels in terms of TD-RMS and FD-RMS and from the contrasts of the power spectrum image. No full paper available.

Noncontact MASW methods for near surface soil/infrastructure assessment

In near surface geophysics, a multi-channel analysis of surface wave (MASW) method has been increasingly applied for underground infrastructure assessments, in which conventional contact sensors like geophones and accelerometers were mostly employed to detect surface vibrations. In this study, noncontact sensors technology such as a laser Doppler vibrometer (LDV) and a microphone were used to measure Rayleigh wave and leaky Rayleigh waves respectively. These noncontact sensors were installed in a scanning platform that was driven by a stepper motor. The scanning MASW system consisted of two excitation sources: an electromechanical shaker and steel-balls to generate frequency sweeping (chirp) signals with frequency from 30 Hz to 500 Hz and high frequency (up to 40 kHz) impulsive signals respectively. The LDV-shaker-MASW was developed for near surface soil profile exploration and the microphone-steel ball-MASW was built for pavement assessment. The details of the system and several case studies will be addr...