Internal Pressure Response Research Articles

Numerical Study of the Performance of Existing Prestressed Cylindrical Concrete Pipes Strengthened with Reinforced Concrete or Carbon-Reinforced Fiber Polymer Jackets—Part B

A popular water pipe system, used in many countries, is one formed by prestressed cylindrical concrete pipes (PCCP). This study used the results of an experimental investigation on ten (10) PCCP samples taken from an existing water pipeline. The objective was to investigate their bearing capacity under three-edge bending or internal hydraulic pressure loads to check the capability of specific retrofitting/strengthening schemes to upgrade this bearing capacity and thus enhance the operational period (Part A). In this part B study, the measured response of the PCCP pipes was made to validate a numerical approach aimed at numerically simulating the behavior of the original and retrofitted PCCP pipes under hydraulic internal pressure. From the obtained numerical results, it was seen that the assumed nonlinear mechanisms for the concrete volume and steel membrane were verified by comparing numerical predictions with measurements in terms of strain response of the steel membrane, damage patterns of the concrete volume, and the overall internal pressure versus radial expansion response. The numerical predictions of the bearing capacity contribution of the fully active prestress as well as the three specific jacketing schemes, including carbon fiber reinforced polymer (CFRP) or reinforced concrete (RC) jackets, were also verified from comparisons with the corresponding measured response.

A CIP-based numerical simulation of wave interaction with a fluid-filled membrane submerged breakwater

This study proposes an CIP (Constraint Interpolation Profile) viscous flow model that couples the Finite Element Method for structural deformation, to investigate the wave interaction with a fluid-filled membrane submerged breakwater. A modified ghost-cell immersed boundary method is adopted to achieve an accurate simulation of the fluid-structure interaction. After validation by published experimental data, the model is used to study the interaction between regular waves and a fluid-filled membrane submerged breakwater. The excess internal pressure, vorticity field, elastic modulus and structural responses are analyzed. The results show that, in lower excess internal pressure, the wave reflection, vortex shedding and energy dissipation are more significant. Besides, through the analysis of displacement and velocity distribution, three different vibration modes of the membrane structure are identified at different wave frequencies.

Two-phase expanding mechanism and pressure response characteristic of boiling liquid expanding vapor explosion under rapid depressurization

The two-phase flow evolution, internal pressure, and thermodynamics responses during a BLEVE (boiling liquid expanding vapor explosion) process with water are assessed. Various initial pressures ranging from 1.7 to 5.7 barg, liquid fills load and different pressure relief ways were tested. Results show that after the pneumatic valve was opened, the rise velocity of the bubble increased first, and then decreased until the rupture or collision of the bubbles. The countercurrent flow reversed to the mainstream was experimentally observed and inhibited the expansion flow to reduce the boiling intensity. Thus, as the initial pressure increased, the average rate of pressure rose first increased, then slightly decreased due to the competitive effects of expansion flow and countercurrent flow. The interactions between the rarefaction wave driven by a sudden opening of a valve and the medium degree of superheat, control the pressure response, and the delay of boiling can be classified into the rarefaction wave control region (dp/dt < 0) and the superheat degree control regime (dp/dt> 0). And the effect of the liquid fill level on the rate of pressure rise was not affected by the countercurrent flow. The boiling explosion after the crack formed was intensified with pressure relief action caused by a separate piece of equipment, due to the enhanced heterogeneous boiling on the inner wall.

Influence of thermal stratification by fire on heat-mass coupling response mechanism of the liquefied tank

In order to study the explosion-inducing process and thermal response of fire-induced BLEVE(boiling liquid expanding vapor explosion), a small experimental device was established. The radiant heating source was used to simulate the external fire heat effect, and superheated water was used as the medium. The pneumatic ball valve was used to simulate the leakage action. The gas-liquid flow, internal pressure and temperature transient response of the tank during the heating and venting processes were measured, and the superheated process of the medium in the tank was analyzed. The temperature-pressure coupling response after the explosion was traced to investigate the thermal action of the fire on the tank. The experiment found that the heating of the storage tank was the generation and gradual disappearance of temperature stratification. The crack action would result in the breaking of phase equilibrium and pressure rebound. There was an overheat delay in the detonation, and the temperature stratification would prolong the overheat time of the medium. There was a lower limit for the occurrence of the BLEVE accident, the critical stratification degree was used to quantify the limit and the limit of this experimental condition was ξ≤2.33.

Optimal intensity measures for the structural assessment of buried steel natural gas pipelines due to seismically-induced axial compression at geotechnical discontinuities

This paper investigates the efficiency and sufficiency of various seismic intensity measures for the structural assessment of buried steel natural gas (NG) pipelines subjected to axial compression caused by transient seismic ground deformations. The study focuses on buried NG pipelines crossing perpendicularly a vertical geotechnical discontinuity with an abrupt change on the soil properties, where the potential of high compression strain is expected to be increased under seismic wave propagation. A detailed analytical framework is developed for this purpose, which includes a 3D finite element model of the pipe-trench system, to evaluate rigorously the pipe-soil interaction phenomena, and 1D soil response analyses that are employed to determine critical ground deformation patterns at the geotechnical discontinuity, caused by seismic wave propagation. A comprehensive numerical parametric study is conducted by employing the analytical methodology in a number of soil-pipeline configurations, considering salient parameters that control the axial response of buried steel NG pipelines, i.e. diameter, wall thickness and internal pressure of the pipeline, wall imperfections of the pipeline, soil properties and backfill compaction level and friction characteristics of the backfill-pipe interface. Using the peak compression strain of the pipeline as engineering demand parameter and a number of regression analyses relative to the examined seismic intensity measures, it is shown that the peak ground velocity PGV at ground surface constitutes the optimum intensity measure for the structural assessment of the examined infrastructure.

Coupling Vibration between Wind-Induced Internal Pressure and a Flexible Roof for Buildings with a Dominant Opening and Background Leakage

After considering the combination of internal pressure and external pressure acting on the roof, the coupling dynamic equations to describe the relationship between wind-induced internal pressure and flexible roof are reviewed and further refined. The internal pressure responses and the first order modal response of a flexible roof can be evaluated by the coupling equations. Wind tunnel test was carried out on an aeroelastic roof model which was treated as a single-degree-of-freedom system. Three factors, approaching wind velocities at the center of the dominant opening, acceleration responses at dominant opening areas and background leakages, which have effects on roof acceleration responses were studied. On this basis, the effectiveness and calculation precision of the coupling equations were verified. Results show that the root-mean-square (RMS) value of roof acceleration increases with the increase of the approaching wind velocity and dominant opening area, and in background leakage decreases. Meanwhile, theoretical calculation values of RMS internal pressure and RMS acceleration response corresponding to the first order modal of flexible roof agree well with the wind tunnel experimental data.

Passive acoustic damage detection of structural cavities using flow-induced acoustic excitations

Cavities with different geometries represent the internal volumes of various engineering applications such as cabins of passenger cars, fuselages and wings of aircraft, and internal compartments of wind turbine blades. Transmissibility of acoustic excitation to and from these cavities is affected by material and cross-sectional properties of the structural cavity, as well as potential damage incurred. A new structural damage detection methodology that relies on the detectability of the changes in acoustic transmissibility across the boundaries of structural cavities is proposed. The methodology is described with a specific focus on the passive damage detection approach applied to cavity internal acoustic pressure responses under external flow-induced acoustic excitations. The approach is realized through a test plan that considers a wind turbine blade section subject to various damage types, severity levels, and locations, as well as wind speeds tested in a subsonic wind tunnel. A number of statistics-based metrics, including power spectral density estimates, band power differences from a known baseline, and the sum of absolute difference, were used to detect damage. The results obtained from the test campaign indicated that the passive acoustic damage detection approach was able to detect all considered hole-type damages as small as 0.32 cm in diameter and crack-type damages 1.27 cm in length. In general, the ability to distinguish damage from the baseline state improved as the damage increased in severity. Damage type, damage location, and flow speed influenced the ability to detect damage, but were not significant enough to prevent detection. This article serves as an overall proof of concept of the passive-based damage detection approach using flow-induced acoustic excitations on structural cavities of a wind turbine blade. The laboratory-scale results reveal that acoustic-based monitoring has great potential to be used as a new structural health monitoring technique for utility-scale wind turbine blades.

Experimental investigation of wind-induced internal pressures in nominally sealed building structures

The action of internal pressure cannot be neglected in wind-resistant design of large-span structures, high-rise buildings, and low-rise residential buildings. In this study, the internal pressure characteristics were first measured in still air in a completely closed building structure without any leakage. Then a series of wind tunnel tests were conducted to study the probability density distribution characteristics of the internal pressure responses in a nominally sealed building with background leakage. The mean and peak internal pressure responses associated with different background leakage distributions and wind directions were further investigated, and the experimental results were compared with those suggested by the Chinese wind load code GB50009-2012. The results indicated that the internal pressure in the completely closed building was non-stationary, and varied significantly when collected at different time points. Furthermore, a period of about 24 h was observed from the measured time history of internal pressure over 9 d. The internal pressure in a nominally sealed building structure nearly fitted a normal Gaussian distribution. When background leakage was uniformly arranged on the surface of the building, the mean internal pressure coefficient remained unchanged with increasing background leakage, varying within the range from −0.15 to −0.14, indicating lower magnitudes than the value of −0.2 suggested by the Chinese wind load code. The minimum negative peak internal pressure coefficient was −0.255 when the peak factor was 3.5, indicating a lower magnitude than the value of −0.326 calculated in the Chinese wind load code.

Estimation Method of Loss Coefficient for Wind-Induced Internal Pressure Fluctuations

AbstractAs the importance of wind-induced internal pressure for building safety has continually been highlighted, increasing attentions have been paid to numerical methods for estimating fluctuating internal pressures, leading to the emergence of numerous second order nonlinear governing equations with two ill-defined parameters, namely inertial coefficient (CI) and loss coefficient (CL). Because resonance frequency and damping ratio of fluctuating internal pressures are susceptible to the values of inertial and loss coefficients, respectively, a correct understanding, and reasonable estimates, of these two parameters are required before using the governing equations to predict internal pressure responses. Compared with the inertial coefficient, which can be easily obtained from the Helmholtz frequency, a wider range of values of loss coefficient is in use, therefore this study focuses on the more uncertain parameter CL and presents an alternative method to identify loss coefficients of measured internal ...

The inertial coefficient for fluctuating flow through a dominant opening in a building

For a building with a dominant windward wall opening, the wind-induced internal pressure response can be described by a second-order non-linear differential equation. However, there are two ill-defined parameters in the governing equation: the inertial coefficient <TEX>$C_I$</TEX> and the loss coefficient <TEX>$C_L$</TEX>. Lack of knowledge of these two parameters restricts the practical use of the governing equation. This study was primarily focused on finding an accurate reference value for <TEX>$C_I$</TEX>, and the paper presents a systematic investigation of the factors influencing the inertial coefficient for a wind-tunnel model building including: opening configuration and location, wind speed and direction, approaching flow turbulence, the model material, and the installation method. A numerical model was used to simulate the volume deformation under internal pressure, and to predict the bulk modulus of an experimental model. In considering the structural flexibility, an alternative approach was proposed to ensure accurate internal volume distortions, so that similarity of internal pressure responses between model-scale and full-scale building was maintained. The research showed 0.8 to be a reasonable standard value for the inertial coefficient.

Time domain responses of hydraulic bushing with two flow passages

Abstract Hydraulic bushings are commonly employed in vehicle suspension and body sub-frame systems to control motion, vibration, and structure-borne noise. Since literature on this topic is sparse, a controlled bushing prototype which accommodates a combination of long and short flow passages and flow restriction elements is first designed, constructed and instrumented. Step-up and step-down responses of several typical fluid-filled bushing configurations are measured along with steady harmonic time histories of transmitted force and internal pressures. To analyze the experimental results and gain physical insights into the hydraulic bushing system, lumped system models of bushings with different design features are developed, and analytical expressions of transmitted force and internal pressure responses are derived by using the convolution method. Parametric studies are also conducted to examine the effect of hydraulic element parameters. System parameters are successfully estimated for both harmonic and step responses using theory and measurements, and the dynamic force measurements are analyzed using analytical predictions. Finally, some nonlinearities of the system are also observed, and the fluid resistance of flow passage is found to be the most nonlinear element.

Internal pressure dynamics of a leaky and quasi-statically flexible building with a dominant opening

An analytical model of internal pressure response of a leaky and quasi-statically flexible building with a dominant opening is provided by including the effect of the envelope external pressure fluctuations on the roof, in addition to the fluctuating external pressure at the dominant opening. Wind tunnel experiments involving a flexible roof and different building porosities were carried out to validate the analytical predictions. While the effect of envelope flexibility is shown to lower the Helmholtz frequency of the building volume-opening combination, the lowering of the resonant peak in the internal and net roof pressure coefficient spectra is attributed to the increased damping in the system due to inherent background leakage and envelope flexibility. The extent of the damping effects of "skin" flexibility and background leakage in moderating the internal and net pressure response under high wind conditions is quantified using the linearized admittance functions developed. Analytical examples provided for different combinations of background leakage and envelope flexibility show that alleviation of internal and net pressure fluctuations due to these factors by as much as 40 and 15% respectively is possible compared to that for a nominally sealed rigid building of the same internal volume and opening size.

Internal and net roof pressures for a dynamically flexible building with a dominant wall opening

This paper describes a study of the influence of a dynamically flexible building structure on pressures inside and net pressures on the roof of low-rise buildings with a dominant opening. It is shown that dynamic interaction between the flexible roof and the internal pressure results in a coupled system that is similar to a two-degree-of-freedom mechanical system consisting of two mass-spring-damper systems with excitation forces acting on both the masses. Two resonant modes are present, the natural frequencies of which can readily be obtained from the model. As observed with quasi-static building flexibility, the effect of increased dynamic flexibility is to reduce the first natural frequency as well as the corresponding peak value of the admittance, the latter being the result of increased damping effects. Consequently, it is found that the internal and net roof pressure fluctuations (RMS coefficients) are also reduced with dynamic flexibility. This model has been validated from experiments conducted using a cylindrical model with a leeward end flexible diaphragm, whereby good match between predicted and measured natural frequencies, and trends in peak admittances and RMS responses with flexibility, were obtained. Furthermore, since significant differences exist between internal and net roof pressure responses obtained from the dynamic flexibility model and those obtained from the quasi-static flexibility model, it is concluded that the quasi-static flexibility assumption may not be applicable to dynamically flexible buildings. Additionally, since sensitivity analyses reveal that the responses are sensitive to both the opening loss coefficient and the roof damping ratio, careful estimates should therefore be made to these parameters first, if predictions from such models are to have significance to real buildings.

Wind induced internal pressure overshoot in buildings with opening

The wind-induced transient response of internal pressure following the creation of a sudden dominant opening during the occurrence of high external pressure, in low-rise residential and industrial buildings was numerically investigated. The values of the ill-defined parameters namely the flow contraction coefficient, loss coefficient and the effective slug length were calibrated by matching the analytical response with the computational fluid dynamics predictions. The effect of a sudden i.e., "instantaneously created" windward opening in the Texas Technical University (TTU) test building envelope was studied for two different envelope flexibility-leakage combinations namely: (1) a quasi-statically flexible and non-porous envelope and (2) a quasi-statically flexible and porous envelope. The responses forced by creating the openings at different time leads/lags with respect to the occurrence of the peak external pressure showed that for cases where the openings are created in close temporal proximity to the peak pressure, the transient overshoot values of internal pressure could be higher than the peak values of internal pressure in the pre-sequent or subsequent resonant response. In addition, the influence of time taken for opening creation on the level of overshoot was also investigated for the TTU building for the two different envelope characteristics. Non-dimensional overshoot factors are presented for a variety of cavity volume-opening area combinations for (1) buildings with rigid/quasi-statically flexible non-porous envelope, and (2) buildings with rigid/quasi-statically flexible and porous envelope (representing most low rise residential and industrial buildings). While the factors appear slightly on the high side due to conservative assumptions made in the analysis, a careful consideration regarding the implication of the timing and magnitude of such overshoots during strong gusts, in relation to the steady state internal pressure response in cyclonic regions, is warranted.

Responses of wind-induced internal pressure in a two-compartment building with a dominant opening and background porosity Part 1: Theoretical formulation and experimental verification

The equations governing wind-induced internal pressure responses for a two-compartment building with a dominant opening and background porosity were derived. The unsteady form of the Bernoulli equation, the law of mass conservation, and adiabatic equation were used for the derivation. The precision of the governing equations was verified by a wind tunnel test on a rigid model of a low-rise building. The results show that the governing equations can effectively analyze the wind-induced internal pressure responses. The internal pressure responses in both compartments are suppressed due to the additional damping provided by background porosity. The responses of internal pressure in both compartments, especially in the compartment without an external opening, decrease with increased lumped leakage area.

Study on the Compensated Flow Control Valve Based on AMESim Code

The working characteristics which included static characteristics and dynamic characteristics were analyzed. On the basis of establishing the characteristic mathematical equations of compensated flow control valve, the feature of static characteristics of the valve was obtained. By mathematical analysis, the relationship of static differential pressures of interior and exterior with original flow pressure P0, main chamber pressure P1 and throttling chamber pressure P2 was ascertained. For main chamber pressure P1, its static value is the linear combination of P0 and P2; for throttling chamber pressure P2, the mathematical expression consists of flow coefficient Cq1 and Cq2, spool throttling diameter d1 and d2, cone half angle of spools α1 and α2, valve opening xpc and xv, velocity coefficient Cv1, leakage matching surface diameter dt and aperture mean width Δdt. The equivalent dynamic simulation model of compensated flow control valve was established by AMESim. Based on the simulation results, dynamic characteristics curves of load, dynamic response of internal and external differential pressure under different parameters were obtained.

Internal Pressure in Real Flexible Porous Buildings with a Dominant Opening: Design Perspective

AbstractAnalytical and associated numerical investigations of the fluctuating internal pressures induced through a dominant opening in real buildings with leaky and flexible envelopes are undertaken. The damping effect of these factors both separately and in combination are quantified using RMS internal pressure coefficients and equivalent damping ratios for a range of envelope flexibilities and background porosities for the case of the Texas Technical University test building and a large-span industrial building. Simulated ratios of the RMS internal pressures and the peak spectral response of internal pressure for leaky and flexible buildings to that of rigid nonporous envelopes are presented in nondimensional format for a range of building volumes, opening areas, and porosity ratios. Additionally, nondimensional curves of the RMS internal to external pressure ratios for real flexible and leaky envelopes are presented along with experimental data reported in the literature in a form suitable for design p...

Internal pressure dynamics of a leaky building with a dominant opening

A simplified and computationally efficient model of internal pressure response of a building with a dominant opening and background leakage is presented based on certain simplifications shown to be adequate for all practical purposes. The presented model adequately linearized is used to develop closed form non-dimensional design solutions that can be used to estimate the ratio of internal to external pressure fluctuations and gust factors for a range of building volumes, opening sizes and porosity ratios. Experiments carried out with different combination of leakages in the presence of dominant openings of various sizes are used to justify the simplifications adopted in the derivation of the model and validate the model predictions. A performance analysis of the model carried out in conjunction with some approaches found in the literature on benchmarking data exhibits the relative advantage of the model in terms of accuracy, practical usage and computational expense.

Dendritic structures for fluid flow: Laminar, turbulent and constructal design

Fluid flow in dendritic structures is approached based on hydrodynamics and a geometric description of the network. The hydrodynamic performance of the network, composed of series of rough ducts, is studied for both laminar and turbulent flow regimes. Transient response of internal fluid pressure is also modelled and analyzed. The oscillatory character of the internal pressure is linked with characteristics of the fluid and characteristics of the network.

Wind-induced internal pressure response for structure with single windward opening and background leakage

Theoretical analysis and wind tunnel tests were carried out to study wind-induced internal pressure response for the structure with single windward opening and background leakage. Its governing differential equation was derived by the Bernoulli equation in an unsteady-isentropic form. Numerical examples were provided to study the additive damping caused by background leakage in laminar and turbulent flow, and the influence of background leakage on fluctuating internal pressure response was quantized. A series of models for low-rise building with various opening ratios and background leakage were designed and wind tunnel tests were conducted. It is shown that the fluctuating internal pressure reduces when the background leakage are considered and that the effect of background leakage can be predicted accurately by the governing differential equation deduced in this paper.