Transient Pressure Wave Research Articles

Pressure waves in the aorta during isolated abdominal belt loading: the magnitude, phasing, and attenuation

While rupture of the aorta is a leading cause of sudden death following motor vehicle crashes, the specific mechanism that causes this injury is not currently well understood. Aortic ruptures occurring in the field are likely due to a complex combination of contributing factors such as acceleration, compression of the chest, and increased pressure within the aorta. The objective of the current study was to investigate one of these factors in more detail than has been done previously; specifically, to investigate the in situ intra-aortic pressure generated during isolated belt loading to the abdomen. Ten juvenile swine were subjected to dynamic belt loads applied to the abdomen. Intraaortic pressure was measured at multiple locations to assess the magnitude and propagation of the resulting blood pressure wave. The greatest average peak pressure (113.6 +/- 43.5 kPa) was measured in the abdominal aorta. Pressures measured in the thoracic aorta and aortic arch were 70 per cent and 50 per cent, respectively, that measured in the abdominal aorta. No macroscopic aortic trauma was observed. To the authors' knowledge the present study is the first one to document the presence, propagation, and attenuation of a transient pressure wave in the aorta generated by abdominal belt loading. The superiorly moving wave is sufficient to generate hydrostatic and intimal shear stress in the aorta, possibly contributing to the hypothesized mechanisms of traumatic aortic rupture.

Scale Effects on Solid Rocket Combustion Instability Behaviour

The ability to understand and predict the expected internal behaviour of a given solid-propellant rocket motor under transient conditions is important. Research towards predicting and quantifying undesirable transient axial combustion instability symptoms necessitates a comprehensive numerical model for internal ballistic simulation under dynamic flow and combustion conditions. A numerical model incorporating pertinent elements, such as a representative transient, frequency-dependent combustion response to pressure wave activity above the burning propellant surface, is applied to the investigation of scale effects (motor size, i.e., grain length and internal port diameter) on influencing instability-related behaviour in a cylindrical-grain motor. The results of this investigation reveal that the motor’s size has a significant influence on transient pressure wave magnitude and structure, and on the appearance and magnitude of an associated base pressure rise.

Leak detection of hydrogen–natural gas mixtures in pipes using the characteristics method of specified time intervals

This paper presents a technique for detection and location of leaks in a single pipe, by means of transient analysis, of hydrogen–natural gas mixtures flows. The method uses transient pressure waves initiated by the sudden closure of a downstream shut-off valve. The presence of a leak in a pipe partially reflects these pressure waves and allows for the location of the leak. Pressure waves are governed by two coupled non-linear, hyperbolic partial differential equations with pressure dependent coefficients. The fluid pressure and velocity are considered as two principal dependent variables. To determine the leak location, the mathematical formulation has been solved by the characteristics method of specified time intervals. The computed results describe the influence of the leak on pressure time-history and the effect of hydrogen mass fraction in the mixture on the leak discharge behaviour. It was found that transient pressure is much important in the case of hydrogen than that in the case of natural gas.

Hydrodynamic Loading of Ceramic Components Due to Pulsed Discharge in Water

Pulsed discharge in water produces transient pressure waves. For one kind of high-current electron accelerators composed of a water pulse-forming line and a ceramic-insulated vacuum diode, the mechanical stability of the water-vacuum interface should be taken into account during operations. In this paper, by combining empirical formulas of a plasma-driven water-shock theory with a self-consistent underwater explosive approach, a finite element model was introduced to investigate the shock-wave behaviors. The pressure-time history and ceramic mechanical response to pressure waves were presented. In order to get the pressure profile and verify the calculation models, the arc pressure test, including ldquopoint-planerdquo electrode system, was carried out based on a ten-stage Marx generator. Peak pressures of shock waves were measured by the piezoelectric sensor, and related results have a close approximation to the predictions. The relationship between peak pressure and shock-wave energy under nanosecond time-scale pulsed-discharge condition was also obtained in the experiment. These results may be helpful for the estimation of a water shock when designing structural components of pulsed-power machines.

Transient pressure characteristics in a pressure regulating system by using 1-D analytic valve modeling

Typically, a Pressure Control Valve (PCV) system is constructed with 3 to 4 PCV lines in order to prepare for both a future demand increase and a continuous supply of power after an emergency shutdown of the operating line. However, some operation failure cases that do not follow the original design concepts of a PCV system have been reported in the field. In this study, an accurate 1-D PCV system numerical model was built and a 1-D compressible flow theory was introduced for analytic valve modeling to find solutions for this problem. Several numerical analyses were successfully performed to examine the generation and propagation characteristics of the transient pressure and to clarify the relationships between the transient pressure or surge wave and each factor or parameter relating to fluid dynamics behavior in a PCV system. The relationship between the transient pressure and other factors, such as the size of pipe and header linked after a PCV, the pipe size of the added components linked after the header, and the generation time of the transient pressure and influence of the Slam Shut Valve were investigated in detail. Finally, in order to reduce the strength of the transient pressure and to delay its propagation, this study demonstrates the benefit both of enlargement of the pipe linked to the component added after the PCV system, and the installation of a dissipation component between the operation line and the other lines.

Pitfalls of water distribution model skeletonization for surge analysis

Skeletonization is the process of representing a water distribution system model by only selected pipes. Skeletonized models normally are adequate for master planning and energy studies, but the degree of skeletonization that is acceptable for surge analysis is an often‐raised question. Most of the guidelines used for skeletonizing hydraulic network models do not apply for surge modeling. Replacing two or more pipes in parallel or series into an equivalent pipe with the same carrying capacity and trimming dead‐end mains can be readily applied for steady‐state analysis with virtually no effect on the resulting flows and pressures, but their effect on the system transient response can be significant. Moreover, the ratio of the pipe diameters greatly affects the transient pressure wave attenuation. In addition, dead ends, which may be caused by closure of check valves, lock pressure waves into the system in a cumulative fashion, and wave reflections will double both positive and negative pressures. The rules of skeletonization ignore the transient interaction of transient pressure waves in the different components and pipe properties of a water distribution system. In this article, case studies highlight the pitfalls of skeletonization in pressure surge analysis and support the conclusion that surge analysis requires a detailed model to accurately estimate transient pressure extremes in a water distribution system. A highly skeletonized model may overlook critical locations that are vulnerable for intrusion of potentially contaminated water.

Photoacoustic spectroscopy of aromatic amino acids in proteins

This paper concerns the use of photoacoustic spectroscopy (PAS) to study the presence of aromatic amino acid in proteins. We examined the aromatic amino acids in six proteins with well-known structures using absorption spectra of near ultraviolet PAS over the wavelength range 240-320 nm. The fundamental understanding of the physical and chemical properties that govern the absorption of light and a subsequent release of heat to generate a transient pressure wave was used to test the concept of monitoring aromatic amino acids with this method. Second derivative spectroscopy in the ultraviolet region of proteins was also used to study the regions surrounding the aromatics and the percentage area in each band was related in order to determine the contribution in function of the respective molar extinction coefficients for each residue. Further investigation was conducted into the interaction between sodium dodecyl sulphate (SDS) and bothropstoxin-I (BthTx-I), with the purpose of identifying the aromatics that participate in the interaction. The clear changes in the second derivative and curve-fitting procedures suggest that initial SDS binding to the tryptophan located in the dimer interface and above 10 SDS an increased intensity between 260 and 320 nm, demonstrating that the more widespread tyrosine and phenylalanine residues contribute to the SDS/BthTx-I interactions. These results demonstrate the potential of near UV-PAS for the investigation of membrane proteins/detergent complexes in which light scattering is significant.

Underwater pressure amplification of laser-induced plasma shock waves for particle removal applications

Underwater amplification of laser-induced plasma (LIP)-generated transient pressure waves using shock tubes is introduced and demonstrated. Previously, it has been shown that LIP for noncontact particle removal is possible on the sub-100-nm level. This is now enhanced through shock tube utilization in a medium such as water by substantially increasing shock wave pressure for the same pulse energy. A shock tube constrains the volume and changes the propagation direction of the expanding plasma core by focusing a pulsed-laser beam inside a tube with a blind end, thus increasing the wave front pressure generated. Current amplification approach can reduce radiation exposure of the substrate from the shock wave because of the increased distance from the LIP core to the substrate provided by the increased pressure per unit pulse energy. For the same pulsed laser, with the aid of a shock tube, substantial levels of pressure amplitude amplification (8.95) and maximum pressure (6.48MPa) are observed and reported.

Chapter 1 Landmines and Landmine Injuries: An Overview

Antipersonnel landmines are generally of two types. Blast mines are usually buried and are detonated by foot pressure. Injuries are caused by the blast and by thermal effects. The explosion of a blast mine produces a transient pressure wave that can have an initial velocity greater than the speed of sound and an overpressure of hundreds of pounds per square inch. (In contrast, an overpressure of only 5–6 pounds per square inch can rupture the eardrum.) Fragmentation mines lie above ground and are detonated by trip wires or other sensors. The blast is designed to drive hundreds of small fragments into a target area. Some are designed to detonate at waist height and may cause death within 25 meters and injury within 200 meters. In addition to multiple hits, the fragments may also be designed to penetrate deep into the body, as is the case with mines loaded with fleschettes. Both blast …

Thermal Conductivity in Nanoscale Lennard-Jones Systems: Size Effects in the Fluid and Solid Phases

We simulate fluid and solid Lennard-Jones argon systems via non-equilibrium molecular dynamics and study how the system behaves under an imposed temperature gradient until it reaches the stationary state, from where the thermal conductivity is calculated. We show that transient pressure waves propagate in the system giving rise to a density oscillation pattern. Based on the damping of this pattern we estimate the time needed to reach the stationary state. We also show that thermal conductivity is size independent in the fluid phase, while it increases until the Casimir limit in the solid phase.

Gas-phase photoacoustic sensor at 8.41 μm using quartz tuning forks and amplitude-modulated quantum cascade lasers

We demonstrate the performance of a novel infrared photoacoustic laser absorbance sensor for gas-phase species using an amplitude-modulated quantum cascade (QC) laser and a quartz tuning fork microphone. The photoacoustic signal was generated by focusing 5.3 mW of a Fabry–Perot QC laser operating at 8.41 μm between the tines of a quartz tuning fork which served as a transducer for the transient acoustic pressure wave. The sensitivity of this sensor was calibrated using the infrared absorber Freon 134a by performing a simultaneous absorption measurement using a 31-cm absorption cell. The power and bandwidth normalized noise equivalent absorption sensitivity (NEAS) of this sensor was determined to be D=2.0×10-8 W cm-1/Hz1/2. A corresponding theoretical analysis of the instrument sensitivity is presented and is capable of quantitatively reproducing the experimental NEAS, indicating that the fundamental sensitivity of this technique is limited by the noise floor of the tuning fork itself.

Burst detection and location in water distribution networks

An algorithm for the detection and location of sudden bursts in water distribution networks combining both continuous monitoring of pressure and hydraulic transient computation is presented. The approach is designed for medium and large bursts that are the result of the sudden rupture of the pipe wall or other physical element in the network and are accompanied by the transient pressure wave that propagates throughout the network. The burst-induced transient wave arrival times and magnitudes measured at two or more points are used to find the location of a burst. The wave arrival times and magnitudes are detected using the modified cumulative sum (CUSUM) change detection test. Results of validation on a real network show the potential of the proposed burst detection and location technique to be used in water distribution systems.

Computational Fluid Dynamics Investigation of the Hydraulic Behaviour of the Roman Inverted Siphon System at Aspendos, Turkey

The hydraulic characteristics of the 3rd century ce Roman inverted siphon system at Aspendos is subject to analysis using modern computational fluid dynamics methods. The 1·67 km long siphon consists of a header basin, two separate elevated tower open basins and a receiving basin all interconnected by long piping segments. The receiving basin distributes water to the fountains, baths and housing structures of the ancient city of Aspendos. Based upon the Roman text of Vitruvius, transient pressure wave phenomena occurring during siphon start-up, if not counteracted by hydraulic and structural defensive design measures, can lead to pipeline breakage. The present study examines the hydraulic behaviour of the Aspendos siphon during start-up and steady state conditions for both impulsive and slow-filling water supply conditions. By revealing the underlying hydraulic behaviour of the siphon, the meaning of Vitruvius' text statements concerning siphon operation, albeit in prescientific terminology, can be interpreted in light of the computed physical behaviour of the system. Analysis results indicate that impulsive siphon start-up is characterized by fluid column oscillations in all siphon branches downstream of the header basin. Depending upon the internal wall roughness of the piping and the filling rate, oscillations can vary in periodicity and amplitude before being damped by fluid friction effects. Slowing the siphon infilling rate (as Vitruvius advises) is shown to reduce start-up oscillatory behaviour and reduce forces on the piping. The presence of the elevated tower open basins is shown to limit oscillations from propagating into the downstream branches of the siphon, i.e., the tower basins act as accumulators to dampen the transmission of fluid column oscillations and pressure waves past the first leg of the siphon. Several suggestions as to the enigmatic meaning of the term colliquiaria with respect to siphon operation are investigated to attempt to recover Vitruvius' original meaning.

Design of a coreless electromagnetic projector for an A-size sonobuoy

An electromagnetic projector has been designed that uses a pair of closely spaced pancake coils to produce low-frequency, high-power, steady-state and transient underwater pressure waves. The design requires no magnetic core materials with their associated weight and saturation limits. The projector is inexpensive to build, robust in construction, and small enough to fit with a power source in an A-size sonobuoy. An electromechanical circuit analysis of the design shows that high efficiencies can be achieved at low frequencies because the large surface motions, required to generate useful acoustic flows, do not cause significant stressing of the projector. [Research supported by ONR.]

Understanding Chemical-Potential-Related Transient Pore-Pressure Response To Improve Real-Time Borehole (In)Stability Predictions

Chemical potential related borehole (in)stabilities in the field are predominantly time-dependent. With the intention of developing a real-time wellbore (in)stability modelling capability, experimental work was undertaken to investigate the role of the chemical potential of drilling fluids on transient pore pressure and time-dependent rock property alterations of shale formations. The current work presents the concept, and discusses the results of these undertakings.The experiments using a Pore Pressure Transmission Test (PPT) apparatus expose formation (shale) cores under simulated downhole conditions to various salt solutions and drilling fluids. The uniqueness of this study comes from the fact that timedependent alteration in the pore pressure, acoustic and rock properties of formations subjected to compressive tri-axial stress are recorded during the PPT experiments. This eliminates the anisotropy-associated differences obtained when different samples are used to determine the relationship between these characteristic parameters of shale formations.The main objective of this effort is to translate the results of the PPT tests to actual drilling conditions. At that point, the formation- drilling fluid chemical potential borehole instability model would be validated and updated in real-time to predict borehole (in)stabilities.Introduction. Borehole instability in shales is a continuing problem that results in a substantial annual expenditure by the petroleum industry ($700 million according to conservative estimates). In the past, oil-based muds (OBM) have been the system of choice for difficult drilling. As environmental concerns restrict the use of oil-based muds, the petroleum service industry must provide innovative means to obtain OBM performance without negatively impacting the environment. Water-based muds (WBM) are attractive replacements from a direct cost viewpoint. However, conventional WBM systems have failed to meet key performance measures met with OBMs, especially while drilling high-angle, extended-reach well trajectories going through water-sensitive shale formations.Historically, wellbore (in)stability problems have been approached on a trial-and-error basis, going through a costly multiwell learning curve before arriving at reasonable solutions for optimized operations and systems. Recent studies(1, 2) of fluidshale interactions have produced fresh insights into the underlying causes of borehole (in)stability, and these studies suggest new and innovative approaches to the design of water-based drilling fluids.Since the identification of chemical-potential related instabilities in shales, a chemical-potential borehole stability analytical model has been proposed to describe the physio-chemical interaction(1, 3).Advances in technology are providing new downhole sensors and tools that are increasingly able to collect and transmit information to the surface in real time, thus enabling field personnel to make faster and more informed decisions.There are increasing economic demands on reducing rig downtimes associated with borehole instability problems. Thus, the anticipation and resolution of instabilities in the field using MWD/LWD data in conjunction with prior geophysical and shale/fluid interaction knowledge is becoming more critical.In this study, transient pore pressure, compressional and shear wave velocities, and the deformation of shale cores under geostatic stress are measured.

Embracing Today's Interpretation Technologies

Abstract Chemical potential related borehole (in)stabilities in the field are predominantly time-dependent. With the intention of developing a real-time wellbore (in)stability modelling capability, experimental work was undertaken to investigate the role of the chemical potential of drilling fluids on transient pore pressure and time-dependent rock property alterations of shale formations. The current work presents the concept, and discusses the results of these undertakings. The experiments using a Pore Pressure Transmission Test (PPT) apparatus expose formation (shale) cores under simulated downhole conditions to various salt solutions and drilling fluids. The uniqueness of this study comes from the fact that timedependent alteration in the pore pressure, acoustic and rock properties of formations subjected to compressive tri-axial stress are recorded during the PPT experiments. This eliminates the anisotropy-associated differences obtained when different samples are used to determine the relationship between these characteristic parameters of shale formations. The main objective of this effort is to translate the results of the PPT tests to actual drilling conditions. At that point, the formation- drilling fluid chemical potential borehole instability model would be validated and updated in real-time to predict borehole (in)stabilities. Introduction Borehole instability in shales is a continuing problem that results in a substantial annual expenditure by the petroleum industry ($700 million according to conservative estimates). In the past, oil-based muds (OBM) have been the system of choice for difficult drilling. As environmental concerns restrict the use of oil-based muds, the petroleum service industry must provide innovative means to obtain OBM performance without negatively impacting the environment. Water-based muds (WBM) are attractive replacements from a direct cost viewpoint. However, conventional WBM systems have failed to meet key performance measures met with OBMs, especially while drilling high-angle, extended-reach well trajectories going through water-sensitive shale formations. Historically, wellbore (in)stability problems have been approached on a trial-and-error basis, going through a costly multiwell learning curve before arriving at reasonable solutions for optimized operations and systems. Recent studies(1, 2) of fluidshale interactions have produced fresh insights into the underlying causes of borehole (in)stability, and these studies suggest new and innovative approaches to the design of water-based drilling fluids. Since the identification of chemical-potential related instabilities in shales, a chemical-potential borehole stability analytical model has been proposed to describe the physio-chemical interaction(1, 3). Advances in technology are providing new downhole sensors and tools that are increasingly able to collect and transmit information to the surface in real time, thus enabling field personnel to make faster and more informed decisions. There are increasing economic demands on reducing rig downtimes associated with borehole instability problems. Thus, the anticipation and resolution of instabilities in the field using MWD/LWD data in conjunction with prior geophysical and shale/fluid interaction knowledge is becoming more critical. In this study, transient pore pressure, compressional and shear wave velocities, and the deformation of shale cores under geostatic stress are measured.

Understanding Chemical-Potential-Related Transient Pore-Pressure Response To Improve Real-Time Borehole (In)Stability Predictions

Abstract Chemical potential related borehole (in)stabilities in the field are predominantly time-dependent. With the intention of developing a real-time wellbore (in)stability modelling capability, experimental work was undertaken to investigate the role of the chemical potential of drilling fluids on transient pore pressure and time-dependent rock property alterations of shale formations. The current work presents the concept, and discusses the results of these undertakings. The experiments using a Pore Pressure Transmission Test (PPT) apparatus expose formation (shale) cores under simulated downhole conditions to various salt solutions and drilling fluids. The uniqueness of this study comes from the fact that timedependent alteration in the pore pressure, acoustic and rock properties of formations subjected to compressive tri-axial stress are recorded during the PPT experiments. This eliminates the anisotropy-associated differences obtained when different samples are used to determine the relationship between these characteristic parameters of shale formations. The main objective of this effort is to translate the results of the PPT tests to actual drilling conditions. At that point, the formation- drilling fluid chemical potential borehole instability model would be validated and updated in real-time to predict borehole (in)stabilities. Introduction Borehole instability in shales is a continuing problem that results in a substantial annual expenditure by the petroleum industry ($700 million according to conservative estimates). In the past, oil-based muds (OBM) have been the system of choice for difficult drilling. As environmental concerns restrict the use of oil-based muds, the petroleum service industry must provide innovative means to obtain OBM performance without negatively impacting the environment. Water-based muds (WBM) are attractive replacements from a direct cost viewpoint. However, conventional WBM systems have failed to meet key performance measures met with OBMs, especially while drilling high-angle, extended-reach well trajectories going through water-sensitive shale formations. Historically, wellbore (in)stability problems have been approached on a trial-and-error basis, going through a costly multiwell learning curve before arriving at reasonable solutions for optimized operations and systems. Recent studies(1, 2) of fluidshale interactions have produced fresh insights into the underlying causes of borehole (in)stability, and these studies suggest new and innovative approaches to the design of water-based drilling fluids. Since the identification of chemical-potential related instabilities in shales, a chemical-potential borehole stability analytical model has been proposed to describe the physio-chemical interaction(1, 3). Advances in technology are providing new downhole sensors and tools that are increasingly able to collect and transmit information to the surface in real time, thus enabling field personnel to make faster and more informed decisions. There are increasing economic demands on reducing rig downtimes associated with borehole instability problems. Thus, the anticipation and resolution of instabilities in the field using MWD/LWD data in conjunction with prior geophysical and shale/fluid interaction knowledge is becoming more critical. In this study, transient pore pressure, compressional and shear wave velocities, and the deformation of shale cores under geostatic stress are measured.

A one-dimensional model for the propagation of transient pressure waves through the lung

The propagation of pressure waves in the lung has been investigated by many authors concerned with respiratory physiology, ultrasound medical techniques or thoracic impact injuries. In most of the theoretical studies, the lung has been modeled as an isotropic and homogeneous medium, and by using Hooke's constitutive law (see e.g. Ganesan et al. Respir. Physiol. 110 (1997) 19; Jahed et al. J. Appl. Physiol. 66 (1989) 2675; Grimal et al. C.R. Acad. Sci., Paris 329 (IIb) (2001) 655–662), or more elaborated material laws (see, e.g. Bush and Challener (Proceedings of the International Research Council on Biokinetics Impacts (IRCOBI), Bergish-gladbach, 1988); Stuhmiller et al. J. Trauma 28 (1988) S132; Yang and Wang, Finite element modeling of the human thorax. Web page: http://wwwils.nlm.nih.gov/research/visible/vhpconf98/AUTHORS/YANG/YANG.HTM.). The hypothesis of homogeneous medium may be inappropriate for certain problems. Because of its foam-like structure, the behavior of the lung—even if the air and the soft tissue are assumed to behave like linearly elastic materials—is susceptible to be frequency dependent. In the present study, the lung is viewed as a one-dimensional stack of air and soft tissue layers; wave propagation in such a stack can be investigated in an equivalent mass–spring chain (El-Raheb (J. Acoust. Soc. Am. 94 (1993) 172; Int. J. Solids Struct. 34 (1997) 2969), where the masses and springs, respectively, represent the alveolar walls and alveolar gas. Results are presented in the time and frequency domains. The frequency dependence (cutoff frequency, variations in phase velocity) of the lung model is found to be highly dependent on the mean alveolar size. We found that short pulses induced by high velocity impacts (bullet stopped by a bulletproof jacket) can be highly distorted during the propagation. The pressure differential between two alveoli is discussed as a possible injury criterion.

Tunable ultraviolet visible photoacoustic detection: Analysis of the sensitivity and selectivity provided by a xenon flash lamp

A fundamental understanding of the physical and chemical properties that dictate the absorption of pulsed light and subsequent release of heat to generate a transient pressure wave was used to test the concept of a multi-wavelength photoacoustic detector. Analysis of the wave equation predicts that with long-pulse excitation, i.e. microseconds FWHM, absorption by the solvent, and not electrostriction determines the limit of detection. Calculation of the mechanical to electrical conversion efficiencies of piezoelectric transducers shows that absorbed pulse energies of microjoules, typical of pulsed flash lamps, are sufficient to provide measurable photoacoustic signals. A pulsed xenon flash lamp (2 μs FWHM) which emits a broad spectrum over the UV and visible region is used as an excitation source to detect trace quantities of metals in aqueous solution using pulsed photoacoustic detection. In this work, dielectric mirrors were used to detect two analytes, CrO 4 2− (monitored at 355 nm) and Co 2+ (monitored at 532 nm), simultaneously. This approach increases both the flexibility and selectivity of pulsed photoacoustic methods. We obtained a detection limit of 2.6×10 −4 absorbance units per centimeter in aqueous samples. This work shows that pulsed lasers are not a necessity for ultra-sensitive photoacoustic spectroscopy.

Numerical treatment of acoustic problems with the hybrid boundary element method

The symmetric hybrid boundary element method in the frequency and time domain is introduced for the computation of acoustic radiation and scattering in closed and infinite domains. The hybrid stress boundary element method in a frequency domain formulation is based on the dynamical Hellinger–Reissner potential and leads to a Hermitian, frequency-dependent stiffness equation. As compared to previous results published by the authors, new considerations concerning the interpretation of singular contributions in the stiffness matrix are communicated. On the other hand, the hybrid displacement boundary element method for time domain starts out from Hamilton's principle formulated with the velocity potential. The field variables in both formulations are separated into boundary variables, which are approximated by piecewise polynomial functions, and domain variables, which are approximated by a superposition of singular fundamental solutions, generated by Dirac distributions, and generalized loads, that are time dependent in the transient case. The domain is modified such that small spheres centered at the nodes are subtracted. Then the property of the Dirac distribution, now acting outside the domain, cancels the remaining domain integral in the hybrid principle and leads to a boundary integral formulation, incorporating singular integrals. In the time domain formulation, an analytical transformation is employed to transform the remaining domain integral into a boundary one. This approach results in a linear system of equations with a symmetric stiffness and mass matrix. Earlier 2D results are generalized in the present paper by a 3D implementation. Numerical results of transient pressure wave propagation in a closed domain are presented.