Excessive Acceleration Research Articles

Numerical analysis of earth embankments in liquefiable soil and ground improvement mitigation

The security and stability of soil structures is seriously affected by earthquake-induced liquefaction, and many earth embankments located in seismically active areas failed to meet the new seismic design code criteria, introduced following the 2011 off the Pacific coast of Tohoku Earthquake. This paper proposes an appropriate in-situ countermeasure, and the seismic performance of the liquefaction mitigation method by grouting is numerically evaluated. The elastoplastic constitutive model of cyclic mobility (CM) model can present the cyclic shearing and liquefaction properties of cohesionless sand and cohesive clay in embankments, by considering stress-induced anisotropy, over-consolidation, and soil structure. A numerical investigation, based on the water-soil coupled finite element and finite difference (FE-FD) methods is conducted to explain the dynamic behavior of embankment in fully saturated sandy deposits, during an earthquake, and long-term post-consolidation in a consistent manner. Special emphasis is placed on the growth of excess pore water pressure (EPWP), acceleration response, and ground deformation (settlement and lateral spreading) in liquefiable soil during earthquake and post-earthquake consolidation (approximately 50 years). A comparative analysis demonstrates that the implemented countermeasure is effective in reducing co-seismic and post-seismic liquefaction-induced deformation, regardless of whether the top sandy layer on both sides of the embankment is completely liquified during the earthquake loading. However, there is local failure on the embankment slope instead of deep-seated failure in the embankment-soil system when grouting the saturated sandy layer, and appropriate countermeasures should be adopted to protect the slope. Furthermore, the ground strengthening effect is not apparent when the reinforcement thickness exceeds 6 m.

Probabilistic damage evaluation of base-isolated reinforced concrete structures under near-fault pulse-like bidirectional seismic excitations

In this article, seismic fragility of a base-isolated special Reinforced Concrete (RC) moment frame is investigated under near-fault pulse-type ground motion records. The vulnerability of the displacement-dominated performance of isolator devices to a likely vibration resonance caused by such records is the focus of the study. For this purpose, Lead-Rubber Bearings (LRBs) and Triple Friction Pendulum Bearings (TFPBs) are utilized to represent various isolator behaviorisms in different period ranges. The structures are modelled in three dimensions to account for the axial-bending-bending interaction in the isolator devices. The models are then subjected to IDAs under three sets of near-fault pulse-type ground motion records with different pulse periods. Four different damage states are considered and the IDA results are used for deriving fragilities that express probabilities of exceeding these states at various intensity levels. The study revealed that despite the amplifying effects of the employed records, using isolators is still feasible. That is, even for pulse periods near to the effective period of isolators, resonance has not led to higher failure probabilities in the isolated buildings compared to their fixed-base counterparts. Furthermore, at longer pulse periods, the gradual yielding behavior of TFPBs made them more effective than the LRBs. Results also disclosed that at lower intensities, damage of base-isolated structures is mainly caused due to excessive floor acceleration while at higher intensities the maximum inter-story drift plays the dominant role. This suggest these two response parameters to be alternatively used as the Engineering Demand Parameter (EDP) when defining damage states at the medium and high intensity levels.

Surface acceleration transmission during drop landings in humans

The purpose of this study was to quantify the magnitude and frequency content of surface-measured accelerations at each major human body segment from foot to head during impact landings. Twelve males performed two single leg drop landings from each of 0.15 m, 0.30 m, and 0.45 m. Triaxial accelerometers (2000 Hz) were positioned over the: first metatarsophalangeal joint; distal anteromedial tibia; superior to the medial femoral condyle; L5 vertebra; and C6 vertebra. Analysis of acceleration signal power spectral densities revealed two distinct components, 2–14 Hz and 14–58 Hz, which were assumed to correspond to time domain signal joint rotations and elastic wave tissue deformation, respectively. Between each accelerometer position from the metatarsophalangeal joint to the L5 vertebra, signals exhibited decreased peak acceleration, increased time to peak acceleration, and decreased power spectral density integral of both the 2–14 Hz and 14–58 Hz components, with no further attenuation beyond the L5 vertebra. This resulted in peak accelerations close to vital organs of less than 10% of those at the foot. Following landings from greater heights, peak accelerations measured distally were greater, as was attenuation prior to the L5 position. Active and passive mechanisms within the lower limb therefore contribute to progressive attenuation of accelerations, preventing excessive accelerations from reaching the torso and head, even when distal accelerations are large.

Promoting eco-driving behavior through multisensory stimulation: a preliminary study on the use of visual and haptic feedback in a virtual reality driving simulator

This paper describes the design and preliminary test of a virtual reality driving simulator capable of conveying haptic and visual messages to promote eco-sustainable driving behavior. The driving simulator was implemented through the Unity game engine; a large street environment, including high-speed and urban sections, was created to examine different driving behaviors. The hardware setup included a gaming driving seat, equipped with a steering wheel and pedals; the virtual scenarios were displayed through an Oculus Rift headset to guarantee an immersive experience. Haptic stimulation (i.e., vibrations) was delivered to the driver through the accelerator pedal, while visual stimuli (i.e., icons and colors) were shown on a virtual head-up display. The sensory feedbacks were presented both alone and in combination, providing information about excessive acceleration and speed. Four different virtual scenarios, each one including a distracting element (i.e., navigator, rain, call, and traffic), were also created. Ten participants tested the simulator. Fuel consumption was evaluated by calculating a mean power index (MPI) in reference to the sensory feedback presentation; physiological reactions and responses to a usability survey were also collected. The results revealed that the haptic and visuo-haptic feedback were responsible for an MPI reduction, respectively, for 14% and 11% compared with a condition of no feedback presentation; while visual feedback alone resulted in an MPI increase of 11%. The efficacy of haptic feedback was also accompanied by a more relaxing physiological state of the users, compared with the visual stimulation. The system’s usability was adequate, although haptic stimuli were rated slightly more intrusive than the visual ones. Overall, these preliminary results highlight how promising the use of the haptic channel can be in communicating and guiding the driver toward a more eco-sustainable behavior.

Theoretical estimation of roll acceleration in beam seas using PDF line integral method

The prevention of excessive roll acceleration is one of the fundamental requirements of an oceangoing vessel at sea. In this paper, aiming at this requirement, we propose a new theoretical method for calculating roll angular acceleration, called “PDF line integral method.”. This paper presents the derivation of this method and a numerical comparison with Monte Carlo simulation (MCS) results; also, its validity is shown. Although the utilized GZ curve (restoring curve) exhibits strong asymmetricity, the proposed method can provide for such a condition. With only the information of roll and roll rate joint probability density function (PDF), this method can approximately calculate the roll angular acceleration, which is a high-order differential property. In addition, a relatively good agreement is achieved between the theory and MCS results.

Research on oxidizing leaching tellurium from copper telluride material in acid condition with hydrogen peroxide

In view of the composition of copper telluride material phase, a process for oxidizing leaching tellurium from copper telluride material in acid condition with hydrogen peroxide was proposed. The effects of the sulfuric acid excess coefficient, leaching time, leaching temperature, hydrogen peroxide excess coefficient and droplet acceleration on tellurium leaching rate were discussed in this paper. The results show that the sulfuric acid excess coefficient has an obvious effect on tellurium leaching rate and the tellurium leaching rate increases with the increase of sulfuric acid excess coefficient. The optimum technological parameters were obtained by experiments: the excess coefficient of sulfuric acid was 1.6, the excess coefficient of hydrogen peroxide was 1.2 times of the theoretical value, the leaching temperature was 75 °C, the leaching time was 3.0 h, the particle size was 74–104 μm, the stirring speed was 250 rpm, and the acceleration of hydrogen peroxide droplets was 5 mL.min−1. Under these conditions, the leaching rate of tellurium can reach 98.03%.

Transient waves generated by a vertical flexible wavemaker plate with a general ramp function

Wavemaker problem is a fundamental and important issue in the study of marine and coastal engineering.An accurate incident wave field provided by a wavemaker is crucial to explore the problems of wave and wave-structure interaction. Generally, wavemakers start working from a rest state both in physical and numerical tanks. Excessive acceleration induced by sudden motions of wavemaker will result in generating wave instability even wave breaking unexpectedly and has potential harm to wavemaker facilities in physical tanks. It might cause numerical instability in numerical tanks as well. Although different ramp functions can be constructed and introduced to mitigate this issue, theoretical analysis on the performance of different ramp functions is still lacking. In this study, based on the new elementary solution on transient waves given by Chen and Li (Journal of Engineering Mathematics, 2019, 115(1): 121-140), a time-domain analytical model on transient waves with a general ramp function is developed for a vertical flexible wavemaker plate. Two special ramp functions, namely Eatock Taylor's and Lighthill's ramp function, are used to investigate their effects on the spatial-temporal evolution of transient waves. Moreover, based on the open source two-phase flow model Basilisk, nonlinear effect on ramp functions’ performance is investigated by increasing wave steepness of incident waves. Under weakly nonlinear conditions, the numerical solution is consistent with the present analytical solution, which further confirms the validity of the present analytical solution. And it is found that computational cost for the Lighthill's ramp function is less than that of the Eatock Taylor's ramp function in numerical simulations. Finally, it should be pointed out that the present theoretical solution provides an effective way to obtain new insights on the performance of those potential ramp functions which might be useful and applied in future studies.

The 2016 Vela glitch: a key to neutron star internal structure and dynamics

ABSTRACT High-resolution, pulse-to-pulse observation of the 2016 Vela glitch and its relaxation provided an opportunity to probe the neutron star internal structure and dynamics with unprecedented detail. We use the observations of this glitch to infer superfluid characteristics in the framework of the vortex creep model. The glitch rise time constraint of 12.6 s put stringent limits on the angular momentum exchange between the crustal superfluid and the observed crust. Together with the observed excess acceleration in the rotation rate as compared to the post-glitch equilibrium value, this discriminates crustal superfluid-crust lattice and core superfluid-crustal normal matter coupling time-scales. An evident decrease in the crustal rotation rate immediately before the glitch is consistent with the formation of a new vortex trap zone that initiates the large-scale vortex unpinning avalanche. Formation of vortex trap by a crust breaking quake induces short-lived magnetospheric changes. The long-term post-glitch spin-down rate evolution reveals the moments of inertia and recoupling time-scales of the superfluid layers participating in the glitch and leads to an estimation of the time to the next glitch that agrees with the time interval between the 2016 and 2019 glitches. Our results are consistent with theoretical estimates of effective neutron and proton masses in the superfluid. We also constrain the vortex line-flux tube pinning energy per intersection as 2 MeV.

Strength‐reduction factors for the design of light nonstructural elements in buildings

SummaryStrength‐reduction factors that reduce ordinates of floor spectra acceleration due to nonlinearity in the secondary system are investigated. In exchange for permitting some inelastic deformation to occur in the secondary system or its supports, these strength reduction factors allow to design the nonstructural elements or their supports for lateral forces that are smaller than those that would be required to maintain them elastically during earthquakes. This paper presents the results of a statistical analysis on component strength‐reduction factors that were computed considering floor motions recorded on instrumented buildings in California during various earthquakes. The effect of yielding in the component or its anchorage/bracing in offering protection against excessive component acceleration demands is investigated. It is shown that strength‐reduction factors computed from floor motions are significantly different from those computed from ground motions recorded on rock or on firm soils. In particular, they exhibit much larger reductions for periods tuned or nearly tuned to the dominant modal periods of the building response. This is due to the large differences in frequency content of ground motions and floor motions, with the former typically characterized by wide‐band spectra whereas the latter are characterized by narrow‐band spectra near periods of dominant modes in the response of the building. Finally, the study provides approximate equations to estimate component strength‐reduction factors computed through nonlinear regression analyses.

The use of visco-elastic materials for the design of helmets and packaging

The design of packaging to protect delicate objects, such as a head and brain, against impact requires consideration of the duration of the impact compared to a characteristic time associated with the dynamic response of the object. Relatively short impacts cause damage as a result of an excessive change in velocity. Relatively long impacts cause damage as a result of an excessive acceleration. The design strategy of packaging must either mitigate the transmitted force (and increase the duration of the impact) through a compliant cushion, or dissipate energy. In this paper we show that both of these strategies can be implemented using visco-elastic materials. In particular, very efficient energy dissipation, with complete structural recovery, can be achieved by using a visco-elastic cushion with properties matched to the requirements of the design. Specifically, energy dissipation can be maximized by ensuring that the time-scale of the accumulation of stress within the system matches the optimal time-scale for dissipation within the cushion. A procedure is described by which an optimal design for the minimum thickness of packaging can be achieved by considering both strategies of velocity and acceleration control.

Cold-Inducible RNA-Binding Protein Prevents an Excessive Heart Rate Response to Stress by Targeting Phosphodiesterase.

The stress response of heart rate, which is determined by the plasticity of the sinoatrial node (SAN), is essential for cardiac function and survival in mammals. As an RNA-binding protein, CIRP (cold-inducible RNA-binding protein) can act as a stress regulator. Previously, we have documented that CIRP regulates cardiac electrophysiology at posttranscriptional level, suggesting its role in SAN plasticity, especially upon stress conditions. Our aim was to clarify the role of CIRP in SAN plasticity and heart rate regulation under stress conditions. Telemetric ECG monitoring demonstrated an excessive acceleration of heart rate under isoprenaline stimulation in conscious CIRP-KO (knockout) rats. Patch-clamp analysis and confocal microscopic Ca2+ imaging of isolated SAN cells demonstrated that isoprenaline stimulation induced a faster spontaneous firing rate in CIRP-KO SAN cells than that in WT (wild type) SAN cells. A higher concentration of cAMP-the key mediator of pacemaker activity-was detected in CIRP-KO SAN tissues than in WT SAN tissues. RNA sequencing and quantitative real-time polymerase chain reaction analyses of single cells revealed that the 4B and 4D subtypes of PDE (phosphodiesterase), which controls cAMP degradation, were significantly decreased in CIRP-KO SAN cells. A PDE4 inhibitor (rolipram) abolished the difference in beating rate resulting from CIRP deficiency. The mechanistic study showed that CIRP stabilized the mRNA of Pde4b and Pde4d by direct mRNA binding, thereby regulating the protein expression of PDE4B and PDE4D at posttranscriptional level. CIRP acts as an mRNA stabilizer of specific PDEs to control the cAMP concentration in SAN, maintaining the appropriate heart rate stress response.

Influence of the characteristics of isolation and mitigation devices on the response of single‐degree‐of‐freedom vibro‐impact systems with two‐sided bumpers and gaps via shaking table tests

During strong earthquakes, structural pounding may occur between structures (buildings, bridges, strategic facilities, critical equipment, etc.) and the surrounding moat wall because of the limited separation distance and the deformations of the isolator. An arrangement that favors the solution of this problem is the interposition of shock absorbers. Thus, the influence of geometrical and mechanical characteristics of isolation and mitigation devices on nonlinear, nonsmooth response of vibro-impact systems is experimentally investigated in this paper on the basis of a laboratory campaign of experimental tests. Shaking table tests were carried out under a harmonic excitation in order to investigate two different configurations: the absence and the presence of bumpers. Three different values of the table acceleration peak were applied, four different amplitude values of the total gap between mass and bumpers were considered, and also four different types of bumpers were employed; moreover, two problems were addressed, namely, control of excessive displacements and control of excessive accelerations, and hence, two types of normalization were adopted in order to better interpret experimental results. Suitable choices of pairs of bumpers and gaps were suggested as a trade-off between conflicting objectives. Furthermore, a numerical model was proposed, and its governing parameters identified in order to simulate the experimental results.

Fluid Dynamics of Ballistic Strategies in Nematocyst Firing

Nematocysts are stinging organelles used by members of the phylum Cnidaria (e.g., jellyfish, anemones, hydrozoans) for a variety of important functions including capturing prey and defense. Nematocysts are the fastest-known accelerating structures in the animal world. The small scale (microns) coupled with rapid acceleration (in excess of 5 million g) present significant challenges in imaging that prevent detailed descriptions of their kinematics. The immersed boundary method was used to numerically simulate the dynamics of a barb-like structure accelerating a short distance across Reynolds numbers ranging from 0.9–900 towards a passive elastic target in two dimensions. Results indicate that acceleration followed by coasting at lower Reynolds numbers is not sufficient for a nematocyst to reach its target. The nematocyst’s barb-like projectile requires high accelerations in order to transition to the inertial regime and overcome the viscous damping effects normally encountered at small cellular scales. The longer the barb is in the inertial regime, the higher the final velocity of the projectile when it touches its target. We find the size of the target prey does not dramatically affect the barb’s approach for large enough values of the Reynolds number, however longer barbs are able to accelerate a larger amount of surrounding fluid, which in turn allows the barb to remain in the inertial regime for a longer period of time. Since the final velocity is proportional to the force available for piercing the membrane of the prey, high accelerations that allow the system to persist in the inertial regime have implications for the nematocyst’s ability to puncture surfaces such as cellular membranes or even crustacean cuticle.

SUBSTANTIATION OF PRAXEO-DYNAMIC APPROACH TO THE IMPROVEMENT OF FUTURE TEACHER’S READINESS FOR THE PRIMARY SCHOOLCHILD’S SPIRITUAL-MORAL DEVELOPMENT

The article is devoted to the substantiation of praxeo-dynamic approach to the improvement of future teacher’s readiness for the primary schoolchild’s spiritual-moral development. The use of this approach allows educators to develop a research program that will open new horizons in cognition and transformation of personality. The research has been conducted using scientific empirical and theoretical methods, common scientific methods: analysis, synthesis, comparison, induction and deduction. The descriptions have been used to determine the praxeo-dynamic approach to the future primary school teachers’ professional training. The article represents an analysis of studies, which suggest that a praxeo-dynamic approach to the improvement of future teacher’s readiness for the primary schoolchild’s spiritual-moral development should take into account the strength and pace of the development of each personality’s abilities. These findings confirm the idea that while working with students we should pay attention to the fact that excessive acceleration in the formation of cognitive, emotional and behavioral spheres of personality can lead to negative results (e.g, ignorance in other areas of life and interests, which are limited to narrow specialization). Therefore, when these features emerge, we should be more cautious about organizing the educational process in higher education institutions. This study is characterized by the fact that the author provides a rational for the praxeo-dynamic approach from the point of view of achievements of modern humanitarian knowledge. It allows educators to plan the actions of future teachers, which are aimed at the formation of their readiness for spiritual-moral development of primary schoolchildren. It also gives the opportunity to develop the abilities, which taken in a system, can affects this readiness. The results of this study can be used in the educational process of institutions of higher education in terms of improving teachers’ pedagogical skills in the system of postgraduate pedagogical education, in the process of design of compulsory and optional pedagogical courses while training students of the specialty “Primary Education”. Using a praxeo-dynamic approach to the improvement of future teacher's readiness for the primary schoolchild’s spiritual-moral development the following aspects should be taken into account: moral attitudes (restraint, compassion) and four emotional types of intelligence (according to T. Bradberry and D. Greaves), which have a direct impact on the productivity, effectiveness and dynamism of this area of professional activity. It is also important to use hands-on exercises, which help to increase emotional intelligence.

Excessive Acceleration Criterion: Application to Naval Ships

In this paper, the application of the excessive acceleration (EA) criterion, one of five intact stability failure modes, within the second generation intact stability criteria (SGISC) framework, is shown for a set of naval vessels. First and second level vulnerability assessment of the criterion is applied to parent hulls D1 and D5 of D-Systematic Series, the US Office of Naval Research (ONR) Topside Series model, and the European multi-purpose frigate FREMM. All of which are semi-displacement, transom stern, and round bilge hull forms. Relatively low ship roll periods and great variations of hull geometry in vertical direction make this kind of ship potentially vulnerable to the EA phenomenon. Five displacements are considered for each vessel, and the minimum value of the KG height, which satisfies the Level 2 assessment, is computed for each of them. The curve of the minimum allowable KG is compared with the curve of the maximum KG complying with intact stability criteria specified in RINA (Registro Italiano Navale), classification rules for naval ships.

Maximum resonance and cancellation phenomena in orthotropic plates traversed by moving loads: Application to railway bridges

The vibrational response of railway bridges is an issue of main concern, especially since the advent of High-Speed traffic. In the case of short-to-medium lengths and simply-supported spans excessive transverse acceleration levels may be induced at the platform, with detrimental consequences for passengers and infrastructures. The orthotropic plate has proven to be an appropriate model for the prediction of the response of certain typologies in the aforementioned cases such as multiple girder decks, solid or voided slabs or filler-beam multiple-track decks. In this contribution, the vibrational response of orthotropic plates, simply and elastically supported, circulated by vertical moving loads is investigated. First, maximum free vibration and cancellation conditions are derived analytically. From these, bridge span length-characteristic distance ratios leading to maximum and minimum resonances under series of equidistant loads are depicted. Second, the applicability of these ratios in oblique decks is analysed for the most common first three mode shapes: first longitudinal bending, first torsion and first transverse bending modes, and the errors in relation to the straight reference case are bounded. To this end, an extensive bridge catalogue of girder bridges is designed in the range of lengths of interest, covering flexural stiffnesses typical from both conventional and High-Speed railway lines. Finally, the applicability of the previous theoretical results is exemplified with experimental measurements performed on a bridge from the Spanish railway network.

Direct Stability Assessment for excessive acceleration failure mode and validation by model test

Abstract The excessive acceleration is one of five stability failure modes for intact stability being discussed at IMO. The trial calculation for Direct Stability Assessment (DSA) and the model test have been carried out to verify two prediction methods of ship motions in the short-crested irregular waves for DSA. The ship motions in the short-crested irregular waves calculated by the linear superposition of frequency responses and the time domain simulation agree well with the results of the model test. Using experimentally validated prediction method and wave scatter table of North Atlantic, the long term probabilities have been calculated and the results obtained by two prediction methods become closer to each other. DSA evaluated by using the long-term failure probabilities obtained by two prediction methods are same.

Operational limitations of a river-sea container vessel in the framework of the Second Generation Intact Stability Criteria

The paper examines the possibilities for using the Second Generation Intact Stability Criteria (SGISC) framework in stability assessment and calculation of operational limitations of the river-sea ships. The level 2 vulnerability assessment procedures for dead ship condition (DSC) and excessive accelerations (EA) are used to derive the operational limitations of a typical European inland container vessel in the North Sea coastal zone. The results are in good agreement with the operational experience in the designated area, but provide additional insights into safety of river-sea ships that could not have been observed by the classic stability analysis. It is shown that the approach used by the SGISC could be successfully applied to river-sea ships, provided that appropriate modifications of the Criteria are introduced.

Shake‐table investigation of scoured RC pile‐group‐supported bridges in liquefiable and nonliquefiable soils

SummaryThis paper presents results of one‐g shake‐table tests on scoured pile‐group‐supported bridge models in saturated (liquefiable) and dry (nonliquefiable) sands. The primary objective is to reveal the influence of liquefaction on seismic demands and failure mechanism of scoured bridges. To this end, two identical models, each consisting of a 2 × 2 reinforced concrete pile‐group with a center‐to‐center spacing of 3 times pile diameter, a cap and a single pier with a lumped iron block, were constructed and embedded into saturated and dry sands, respectively, with the same scour depth of 4 times pile diameter. Typical test results, including excess pore pressure, acceleration and displacement demands are interpreted first, followed by the focus on curvature demands and associated seismic failure mechanism identification. Finally, inertial and kinematic effects on pile curvature demands are estimated using cross‐correlation analyses. Results show that near‐pile liquefied soils exhibit more remarkable dilation tendency as compared to far field. For bridges under the given scour depth, soil liquefaction tends to significantly affect the failure modes via transferring damage positions from pier bottom to pile head and meanwhile from underground pile to pile head. In addition, pile group effects appear to be significant in nonliquefiable soils while to be relatively inessential in liquefied soils. Moreover, the inertial effect is more prominent in nonliquefiable soils, while the kinematic effect itself generally appears to be more significant in liquefiable soils. The test results can be used to validate numerical models for future studies.

Effect of Obstacle Type on Methane–Air Flame Propagation in a Closed Duct: An Experimental Study

The combustion in a closed environment was the subject of many works in the past century due to its importance and complex nature compared with the combustion in an open environment. Most research works in this field have investigated different types of gas mixtures, the governing boundary conditions and their effect on the flame propagation structure. Additionally, several investigations have been performed on creating disturbance through obstacles in the flow path as well as the process of deflagration to detonation transition. This paper, for the first time, investigates the effect of porous and solid obstacles on the propagation and the structure of premixed methane–air flame in a closed duct with dimensions of 50 × 11 × 8 cm. The blockage created in the duct by obstacles is in such a way that the detonation process does not occur. The results for the unconstrained duct correctly represent the process of forming the classical tulip flame inside the closed duct. The location of the obstacles is changed in four different distance of 5, 10, 15, and 20 cm from the spark plug, and its effect on combustion characteristics has been evaluated. The results show that the obstacles create fundamental changes in the structure and flame propagation. A significant difference between solid and porous obstacles is that the porous obstacle, in proportion to the solid obstacle, creates less disturbance in the flow field and also does not cause excessive acceleration in the flame propagation. Porous obstacles also reduce the maximum pressure in the chamber during the process, more than the solid obstacles.