Principal Strain Rate Research Articles

Crust and Mantle Flow From Central Tibetan Plateau to the Indo‐Burma Subduction Zone

AbstractThe extremely oblique Indo‐Burma subduction zone exhibits dextral strike‐slip faulting along the Sagaing, Kabaw, and Churachandpur‐Mao Faults as well as east‐west shortening between the Sagaing Fault and Bengal Basin. Through regional stress analysis, considering areas from central Tibet, around the eastern Himalaya Syntaxis, to Burma, it has been determined that the principal compressive stress directions align with the principal strain rates. The northeast‐southwest oriented compressive stress direction from the western Shan Plateau continues into Burma. Notably, P axes align with the topographic gradients, and T axes are sub‐parallel to the topographic contours in the Shan Plateau region south of 27°N. These stress patterns are consistent with a gravitational potential energy induced crustal and mantle flow. The alignment of the fast shear wave with the maximum strain rate and the colinear NW‐SE to E‐W fast direction of the SKS wave and T axis determined from focal mechanisms in the Shan Plateau suggest that the mantle lithosphere deforms in concert with the crust. We suggest crust and mantle flow south of the Red River Fault has resulted in widening of the lithosphere in the Shan Plateau in an east‐west direction. Therefore, the Sagaing Fault has bowed approximately 50–100 km westward if we assume that the Sagaing Fault was originally straight. Our results of regional stress inversion are consistent with late Miocene to present E‐W shortening in the Indo‐Burma subduction zone resulting from the release of gravitational potential energy from the central Tibetan Plateau.

Contemporary crustal strain rates derived from GPS measurements in southwestern China

Surface strain rates in southwestern China can provide constraints on tectonic evolution of the Tibetan Plateau. Unfortunately, different strain rate fields were obtained from different authors although almost the same GPS data were exploited. Based on updated GPS data, in this paper, we calculate the strain rates in southwestern China using the method proposed by Zhu et al. (2005, 2006). The results confirm that the strain rates in the Sichuan Basin and the South China Block are very small, and the high values are largely concentrated along the Xianshuihe-Anninghe-Xiaojiang fault system and the Sagaing Fault. Furthermore, the highest principal strain rates are located around the eastern Himalayan syntaxis (EHS), with compressive orientations perpendicular to the strike of the Main Thrust Belt. The basic characteristic of the strain rate distribution is in accordance with the tectonic structures from the geological and geophysical investigations. In particular, the two calculated extensive deformation regions basically match the locations of normal-faulting earthquakes in the Sichuan-Yunnan Rhombic Block (SYRB), with one in N-S extension trending in the northern SYRB, and the other nearly E-W orientation in the southern SYRB. We suggest that the extensive deformation and the normal faulting earthquakes in southwestern China is mainly controlled by the lower crustal channel flow with a bend direction, rather than by gravitational spreading alone, as previous authors proposed.

A strain acceleration method to identify the onset of diffuse necking

This paper presents an innovative ‘strain acceleration method’ for determining the onset of diffuse necking in sheet forming tests using data obtained from digital image correlation (DIC). The method identifies the onset time of diffuse necking and provides the corresponding in-plane principal strain values by detecting a local extreme in the second derivative of the minor principal in-plane strain with respect to time at the edges of the sheet surface region where diffuse necking occurs. Results obtained from applying the method to tensile testing on two different materials and comparisons with available methods based on force-time or principal strain rate evolutions confirm its accuracy and validity. The new method was implemented in a computer software to be used for research and education that also enables determination of localized necking and fracture and plotting the strain loading paths in principal strain space.

Brain Deformation Estimation With Transfer Learning for Head Impact Datasets Across Impact Types.

The machine-learning head model (MLHM) to accelerate the calculation of brain strain and strain rate, which are the predictors for traumatic brain injury (TBI), but the model accuracy was found to decrease sharply when the training/test datasets were from different head impacts types (i.e., car crash, college football), which limits the applicability of MLHMs to different types of head impacts and sports. Particularly, small sizes of target dataset for specific impact types with tens of impacts may not be enough to train an accurate impact-type-specific MLHM. To overcome this, we propose data fusion and transfer learning to develop a series of MLHMs to predict the maximum principal strain (MPS) and maximum principal strain rate (MPSR). The strategies were tested on American football (338), mixed martial arts (457), reconstructed car crash (48) and reconstructed American football (36) and we found that the MLHMs developed with transfer learning are significantly more accurate in estimating MPS and MPSR than other models, with a mean absolute error (MAE) smaller than 0.03 in predicting MPS and smaller than [Formula: see text] in predicting MPSR on all target impact datasets. High performance in concussion detection was observed based on the MPS and MPSR estimated by the transfer-learning-based models. The MLHMs can be applied to various head impact types for rapidly and accurately calculating brain strain and strain rate. This study enables developing MLHMs for the head impact type with limited availability of data, and will accelerate the applications of MLHMs.

Strain accumulation in the Mentawai Forearc Sliver, Indonesia, inferred from continuous GNSS-derived strain rate

The Mentawai Forearc Sliver (MFS) is characterized by oblique deformation formed as slip partitioned between normal and parallel trench plate convergence. The surge of great earthquakes from 2004 to 2012 along the adjacent Sunda trench left a large unbroken segment known as the Mentawai Seismic Gap. Here, we adopted continuous Global Navigation Satellite System (GNSS) observation data to identify the present regional crustal deformation using geodetic strain rates. The principal strain rate, dilatation rate, and maximum shear strain rate are about 0.13 microstrain/yr, 0.2 microstrain/yr, and 0.1 microstrain/yr, respectively, with the range of its uncertainties between 0.01 and 0.04 microstrain/yr. The dilatation and maximum shear strain rates reveal the spatial coverage of strike-slip duplex and backthrust tectonics along the Mentawai Forearc Sliver.

High Basal Melt Rates and High Strain Rates Lead to More Fractured Ice

AbstractIce shelves limit the flux of grounded ice into the ocean by buttressing the discharge of land‐based ice upstream. Ice shelf weakening and collapse can lead to decreased buttressing and observations increasingly show that some ice shelves have experienced increased melt and increased calving, with recent hypotheses suggesting that increased melt leads to increased fracturing. However, the specific processes that control this correlation are not yet understood, with mechanisms other than melt affecting fracturing. Here we use the topography of the ice shelf base from BedMachine to investigate how basal melting and ice deformation contribute to crevasse and melt channel formation and evolution on the Pine Island Ice Shelf in West Antarctica. We find that high basal melt rates and high first principal strain rates lead to substantial roughening of the ice shelf through a collection of features, including melt channels and crevasses. Critically, melt channels and crevasses are the deepest in all directions at locations where the highest rates of melting and straining occur simultaneously. This suggests that the combination of melt rates and strain rates work in tandem to excavate and seed the deepest melt channels and crevasses on ice shelves. These features then may form lines of weakness that transform into rifts and, ultimately, the detachment boundary for calving events. This implies that melt and fracture play an important role in controlling the dynamics of ice shelves.

The present strain rate of Quang Nam - Quang Ngai and the surrounding region

Studying the present strain rate is significant in determining the characteristics and origin of geological anomalies in the region. Tectonic strain occurs under the influence of various factors, especially tectonic forces, and only a few cases of deformation occur at speeds observable by humans. This research uses velocity data from GNSS measurements in Quang Nam - Quang Ngai and surrounding regions to assess present tectonic strain. The combination of methods used in this study includes calculating the ITRF Earth-fixed frame to minimize errors, the method of relative velocity calculation to compare the speed variations between station positions, and the deformation calculation method using the QOCA software developed by NASA's Jet Propulsion Laboratory (JPL). The calculated results show that the coastal areas of the study have relatively low strain rates with the principal strain rate <15 nano-strain/year, the magnitude of deformation is always less than 7.5 nano-strain/year, and the area is conducive to the development of dominant reverse faulting.

Prediction of fractures by using the stress field in medium to deep shale gas reservoirs: A case study of Late Ordovician–early Silurian shale gas reservoirs in the Nanchuan region, South China

Containing representative shale gas reservoirs, the Wufeng–Longmaxi Formations in the Nanchuan region in South China have been modified by three compressional tectonic movements (in the Late Jurassic to Early Cretaceous, Late Cretaceous, and Cenozoic to present). These movements formed deeply buried reservoirs with complex in situ stresses and rapid directional changes, influencing the state of shale gas reservoirs fractures. Numerical modeling applied to model the stress field in the three periods showed that the maximum compressive horizontal principal stress (σHmax), strain rate, and fault slip rate regimes transformed from a thrust and strike-slip regime to a thrust and strike-slip regime to a thrust regime. The σHmax direction changed from NW–SE and WNW–ESE to WNW–ESE and nearly E–W and then to multiple directions. The magnitude of strain rate changed from -16 ∼ -15 to -17.7 ∼ -15.6 to -18.8 ∼ -15.8. The fault slip rate changed from 0 to 0.029 mm/a to 0–0.0026 mm/a to 0–0.0012 mm/a. These data strongly agree with data from drilled wells and outcrops and show that the present-day stress field is the superposed effect of multistage movements. Semiquantitative research was conducted on shale gas fracture openness and fracture development. Fracture openness is favorable when the angle between the σHmax direction and nearby faults is ≤45° and the distance from the fault is >2 km, and fracture development is favorable when the magnitude of the strain rate is <-17.6 and the fault slip rate is <0.00036 mm/a. Accordingly, we predicted fractured shale gas reservoirs.

Effects of dilatation and turbulence on tangential strain rates in premixed hydrogen and iso-octane flames

The tangential strain rate in premixed flames impacts significantly the flame surface area generation and thus the combustion process. Studies on incompressible isotropic turbulence have revealed that the mean tangential strain rate at material and iso-scalar surfaces is positive and exhibits a universal value when normalized by the Kolmogorov time. This is associated with the preferential alignment of the surface normal with the most compressive principal strain rate. The present study investigates such effects in premixed hydrogen and iso-octane flame kernels using direct numerical simulations. It is shown that the normalized mean tangential strain rate of the investigated flames has a very similar value compared with the incompressible flows. However, in the reaction zone, the flame surface normal aligns preferentially with the most extensive principal strain rate. Furthermore, this alignment depends on the reaction progress variable and the Lewis number, while the tangential strain rate remains independent of these parameters. Such counter-intuitive behaviour is systematically investigated by decomposing the effects of dilatation and residual solenoidal turbulence. It is found that the solenoidal turbulence influences significantly the tangential strain rate. A general effect of turbulence on the tangential strain rate is identified, which is consistent with incompressible flows and independent of the Lewis number and the reaction progress variable. This is a remarkable finding indicating that models of the tangential strain rate developed based on incompressible flows apply also to premixed flames with different Lewis numbers, and, for the modelling, only the solenoidal turbulence should be considered.

Discrete modelling of the mechanical response of Cuxhaven sand under shear and oedometric conditions using the rolling resistance contact model

The Distinct element method (DEM) is a promising approach to model the microscopic behaviour of granular materials, but the capability of the simulations to reproduce the mechanical response of real granular materials depends strongly on the contact model parameters utilized. The present study focuses on the calibration and validation of the rolling resistance linear model parameters for Cuxhaven sand based on the experimental results from triaxial and oedometer tests. A sensitivity analysis was conducted to explore the influence of contact model parameters on the sample preparation and the shear stage of triaxial tests. The influence of parameters like rolling resistance friction coefficient, inter-particle friction coefficient, effective modulus, and normal-to-shear stiffness ratio were investigated. For calibration of the DEM model, the input parameters were selected such that the simulations reproduce the macro mechanical characteristics like dilation angle, peak stress, and stiffness. The calibrated parameters were then validated by simulating a one-dimensional compression test. The results are in good agreement with the experiments, which proves the suitability of the calibrated parameters. In addition, the validated parameters were applied to investigate the mechanical behaviour including the evolution of contact force chains, non-coaxiality of principal stress and strain rate, and sample inhomogeneity during a simple shear test.

AI-based denoising of head impact kinematics measurements with convolutional neural network for traumatic brain injury prediction.

Wearable devices are developed to measure head impact kinematics but are intrinsically noisy because of the imperfect interface with human bodies. This study aimed to improve the head impact kinematics measurements obtained from instrumented mouthguards using deep learning to enhance traumatic brain injury (TBI) risk monitoring. We developed one-dimensional convolutional neural network (1D-CNN) models to denoise mouthguard kinematics measurements for tri-axial linear acceleration and tri-axial angular velocity from 163 laboratory dummy head impacts. The performance of the denoising models was evaluated on three levels: kinematics, brain injury criteria, and tissue-level strain and strain rate. Additionally, we performed a blind test on an on-field dataset of 118 college football impacts and a test on 413 post-mortem human subject (PMHS) impacts. On the dummy head impacts, the denoised kinematics showed better correlation with reference kinematics, with relative reductions of 36% for pointwise root mean squared error and 56% for peak absolute error. Absolute errors in six brain injury criteria were reduced by a mean of 82%. For maximum principal strain and maximum principal strain rate, the mean error reduction was 35% and 69%, respectively. On the PMHS impacts, similar denoising effects were observed and the peak kinematics after denoising were more accurate (relative error reduction for 10% noisiest impacts was 75.6%). The 1D-CNN denoising models effectively reduced errors in mouthguard-derived kinematics measurements on dummy and PMHS impacts. This study provides a novel approach for denoising head kinematics measurements in dummy and PMHS impacts, which can be further validated on more real-human kinematics data before real-world applications.

Present-day crustal movement and seismic moment balance on major active faults around the easternmost segment of the Kunlun fault, Tibetan Plateau, China

After the 2021 Ms 7.4 Madoi, China earthquake located south of the eastern Kunlun fault, the coseismic Coulomb stress changes show that the earthquake potential is enhanced towards the easternmost segment of the Kunlun fault. Before the 2008 Mw 7.9 Wenchuan, China earthquake, the easternmost segment of the Kunlun fault is considered to being a region with the highest frequency occurrence of moderate-to-strong earthquakes in mainland China, where there are still at least three seismic gaps at present, indicating an urgent earthquake hazard. The tectonic deformation pattern is closely related to the development and occurrence of earthquakes. In this study, we collect all the available GPS data to obtain a crustal movement velocity field with high precision and high resolution by removing nontectonic effects within the study area. The GPS velocity profile and two-dimensional strain rates are then derived from the updated GPS velocities to analysis the characteristics of crustal deformation. Our results demonstrate that the Longriba fault zone slips predominantly right-laterally with the rate of 5.2 ± 0.5 mm/yr and the crustal shortening rate is ∼0.5 mm/yr across the Longriba and Longmenshan faults. Along with notable crustal extension and contraction, the principal strain rate field is distributed in a wide area on the northwest part of the Longmenshan fault, and decreases southwestward along the Longmenshan fault zone. In addition, we provide the time series of 8 campaign GPS stations which have never been published before. Moreover, the moment deficit estimate is a well-established way of assessing the earthquake hazard at a specific fault. Accompanying with the inverted slip rates and locking depth, we estimate the rates of moment accumulation on major faults and compare them with the seismic moment released on each fault derived from the Chinese historical earthquake catalog which extends for more than 2000 years in many regions. We find that the moment deficit is mainly concentrated on the Longriba fault with a value of 4.18 × 1017 Nm/yr. The Longriba fault have accumulated enough seismic energy to generate one Mw > 7.7 earthquake on it, or two Mw > 7.5 earthquakes on its two branches in the future. This study is an essential indicator for understanding the present-day tectonic deformation pattern in the Tibetan Plateau and is also helpful for seismic hazard assessment.

Present-day crustal deformation based on GPS measurements in southeastern Tibetan Plateau: implications for geodynamics and earthquake hazard

GPS-derived strain rates can provide a tight constraint in understanding tectonic evolution of the Tibetan Plateau and are helpful in seismic hazard assessment. For this purpose, we at first verify the method, proposed by Zhu et al. in 2005 and 2006, for the computation of the strain rates, and found that the approach is reasonable and accurate. Then, based on the updated GPS data, we compute strain rates in southeastern Tibetan Plateau (SETP). The computed results showed that the strain rates in the Sichuan Basin and South China Block are very small, and the high values are largely concentrated along the Sagaing Fault and Xianshuihe-Anninghe-Xiaojiang fault system. In addition, the highest principal strain rates are located around the eastern Himalayan syntaxis (EHS), with the compressive orientations perpendicular to the Main Thrust Belt. In particular, the calculated extensive deformation basically matches the normal faulting earthquakes. In general, the characteristic of the strain rate distribution is in good agreement with the tectonic structures from the geological and geophysical investigations. At last, according to the strain rates, seismicity, and tectonic structures, we estimate five most likely zones for future major earthquakes in SETP. These areas include the Zemuhe Fault, northwestern segment of the Red River Fault, and at the intersection between the Ganzi-Yushu Fault and the Xianshuihe Fault, and at the one between the Zhongdian Fault and Jinshajiang Fault. Consequently, this study is significant in deep understanding of the geodynamics in the Tibetan Plateau and earthquake hazard assessment.

Time-Independent Grid-Based Forecast Model for M ≥6.0 Earthquakes in Southeastern Tibetan Plateau Using GNSS Strain Rates and Seismicity

ABSTRACT Earthquake forecasting models play a vital role in earthquake occurrence assessment. Despite improved availability of seismic and geodetic data and processing techniques to produce high-resolution catalogs and deformation history, the implementation of earthquake forecasting models with seismic and geodetic data remains a challenge. In this study, we utilize seismicity and Global Navigation Satellite Systems (GNSS) data to propose time-independent grid-based regional earthquake likelihood models for southeastern Tibetan plateau (RELM-TibetSE). First, we solve the GNSS velocity field and strain rates from 1999 to 2017, deriving geodetic moment rates and introducing empirical correction coefficients to balance them with historical seismic moment rate. Subsequently, we employ a truncated Gutenberg–Richter law and Poisson process to calculate time-independent probabilities for M ≥ 6 earthquakes in 0.2° × 0.2° cells. The grid-based forecasting models indicate that the 30-year probability for M ≥ 6 earthquakes exceeds 1% in more than one-third of the entire study area, highlighting prominently higher earthquake occurrence in these regions. Probability distribution exhibits significant spatial variations. Finally, the predictive performance of the forecasting models is validated based on historical seismicity. The validation indicates that all RELM-TibetSE exhibit good predictive capability relative to a spatially uniform model. The RELM-TibetSE incorporating principal strain rates outperforms those involving maximum shear strain rate in forecasting seismicity. And the differences in forecasting performance between the RELM-TibetSE accounting for spatially varied seismogenic thickness and rigidity and those with uniform thickness and rigidity are not significant. The forecasting models also exhibit better predictive performance for seismic source areas than for epicenters. Moreover, the optimal model highlights zones with higher earthquake occurrence, including the zones about 50 km wide across the Ninglang fault, the zones across the southwestern segment of the Lijiang–Xiaojinhe fault, the China–Myanmar borderland north of the Nantinghe fault, and so on. Therefore, it is justified to conduct multidisciplinary rigorous observations to capture the potential nucleation process of future large earthquakes in these zones.

Effects of Damköhler Number on Lean Premixed Jet Flames in Crossflow Using Direct Numerical Simulation

ABSTRACT In the present work, lean premixed jet flames in crossflow were studied using direct numerical simulation to explore the effects of Damköhler numbers () on turbulence and flame characteristics. The configuration is based on an experiment, where a jet of lean premixed ethylene-air mixtures ( = 0.6) was injected into a hot vitiated crossflow. The case with a higher and lower Da is denoted as case Da+ and case Da-, respectively. It was found that the turbulence is weakened around the reaction zone of case . In contrast, the turbulence of case is barely influenced by heat release. The vorticity dynamics are examined with the enstrophy transport equation budget terms, and the viscous dissipation term is the main sink for both cases. The windward and leeward flame branches of case are dominated by auto-ignition and premixed flame propagation respectively, while the auto-ignition and flame propagation modes coexist on the leeward flame branch of case . The scalar gradient magnitude in the leeward branch is generally lower compared with the windward branch so that the flame is overall thicker. The normal strain rate is negative, which tends to enhance the scalar gradient, but it becomes positive on the leeward side of case , which is influenced by the alignment between the scalar gradient and the principal strain rates.

Response of a supersonic turbulent boundary layer to different streamwise adverse pressure gradients

An adverse pressure gradient (APG) has an impact on the boundary layer, increasing the turbulent intensity of the layer. The mean and turbulent properties of the turbulent boundary layer on a flat plate with different APGs were investigated at Mach 2.7 in the present work utilizing the particle image velocimetry and nanoparticle-based planar laser scattering techniques. According to analysis, the changing trends of boundary layer parameters are different depending on whether the local mainstream velocity or freestream velocity of the wind tunnel is used to normalize. Using the former might make the enhanced effect of the rising APG more visible. With the rise in APG, the principal strain rate, turbulent fluctuation, Reynolds stress, and turbulence production in the boundary layer all increased, while the turbulent boundary layer's thickness dropped. Furthermore, the heightened upward ejection and downward sweep events caused the streamwise turbulence intensity to reach its outer peak under the influence of strong APG. The characteristics of the spanwise vortex in the boundary layer are investigated in conjunction with the probability density function analysis. The growing APG, which primarily promote negative vorticity, can strengthen the rotational strength of spanwise vortices, which are a component of hairpin vortices. As APG rises, the number of small-scale vortices in the boundary layer increases and the fractal dimension grows. The increase in small-scale vortices tends to induce strong transportation and promotes turbulence intensity. Further investigation reveals that the increased volume change caused by the enhanced compression effect with increasing APG exacerbated the vorticity.

Turbulence Effects on the Statistical Behaviour and Modelling of Flame Surface Density and the Terms of Its Transport Equation in Turbulent Premixed Flames

The influence of the ratio of integral length scale to flame thickness on the statistical behaviours of flame surface density (FSD) and its transport has been analysed using a Direct Numerical Simulation database of three-dimensional statistically planar turbulent premixed flames for different turbulence intensities. It has been found that turbulent burning velocity based on volume-integration of reaction rate and flame surface area increase but the peak magnitudes of the FSD and the terms of the FSD transport term decrease with an increase in length scale ratio for a given turbulence intensity. The flame brush thickness and flame wrinkling increase with an increase in length scale ratio for all turbulence intensities. However, the qualitative behaviours of the unclosed terms in the FSD transport equation remain unaltered by the length scale ratio and in all cases the tangential strain rate term and the curvature term act as leading order source and sink, respectively. A decrease in length scale ratio for a given turbulence intensity leads to a decrease in Damköhler number and an increase in Karlovitz number. This has an implication on the alignment of reactive scalar gradient with local strain rate eigenvectors, which in turn increases positive contribution of the tangential strain rate term with a decrease in length scale ratio. Moreover, an increase in Karlovitz number increases the likelihood of negative contribution of the curvature term. Thus, the magnitude of the negative contribution of the FSD curvature term increases with a decrease in length scale ratio for a given turbulence intensity. The model for the tangential strain rate term, which explicitly considers the scalar gradient alignment with local principal strain rate eigenvectors, has been shown to be more successful than the models that do not account for the scalar gradient alignment characteristics. Moreover, the existing model for the curvature and propagation term needed modification to account for greater likelihood of negative values for higher Karlovitz number. However, the models for the unclosed flux of FSD and the mean reaction rate closure are not significantly affected by the length scale ratio.

High-resolution three-dimensional azimuthal velocity anisotropy of S-waves in southern-central Japan, based on ambient noise tomography

To investigate the dominant deformational patterns and stress conditions in the upper crustal structure of the Kinki region, southern-central Japan, we constructed a high-resolution 3D azimuthal anisotropy model to a depth of ~ 11 km. We used 6-month-long ambient noise data recorded by the densely distributed permanent and temporary stations. From this dataset, cross-correlations were retrieved. We then obtained a 3D isotropic velocity model by inverting Rayleigh wave dispersion data, followed by a direct joint inversion for both 3D azimuthal anisotropy and additional isotropic velocity perturbation. The resolved 3D azimuthal anisotropy reveals significant contrasts of anisotropy across the Kinki region. The predominant fast axes observed in the northwestern Kinki region align with the direction of the maximum horizontal compressional stress and the principal strain rate axes, suggesting that the observed anisotropy is mainly stress-induced. In the southern part of the study area, furthermore, the predominant fast axes trend NE–SW and near E–W, also indicating the presence of stress-induced anisotropy. On the depth profile of the anisotropy, we found depth-dependent variation of azimuthal anisotropy. There exists a significant consistency between the anisotropy observed beneath 3 km depth and the dense distribution of earthquake hypocenters. This interrelationship between anisotropy and seismicity demonstrates that the observed anisotropy could be linked to local crustal stress or fractures relevant to earthquake ruptures. Our 3D anisotropy model therefore contributes towards understanding the locations and features of the seismicity region.Graphical

An experimental investigation on the isoenergetic supersonic cooling films subjected to different ratios of static pressure

Ratio of static pressure (RSP) is a critical factor affecting the development of supersonic cooling film flow field. To give a good account of flow characteristics and physical mechanisms on the influences of RSPs, experiments are conducted employing the nanoparticle planar laser scattering (NPLS) and particle-image velocimetry (PIV) techniques. A supersonic cooling film is tangentially injected at a Mach number of Maj=2 into a laminar boundary layer at a mainstream Mach number of Ma∞=3 with different RSP cases. The flow field is divided into four sections: the wake region, the potential core region, the wall-jet region, and the fully developed turbulent boundary layer region. The velocity profile extracted at the fully developed turbulent boundary layer region is proved to be consistent with the theoretical composite profile. Moreover, a new criterion that distinguishes the specific position of the impingement point where the mixing layer approaches the bottom boundary layer is proposed based on the distribution of principal strain rate of the mean velocity field. The analysis of turbulent structures finds that the K–H vortex structures are sensitive to RSPs, and more broken vortices generated when the two fluids mix. The intensity of wave structures is depicted in the synthetic schlieren images when subjected to different RSPs. In addition, the turbulent characteristics show a weaker mixing process with increased RSP, indicating a prolonging in the effective cooling length. Furthermore, the disturbance at the slot and variations of velocity gradient downstream are addressed and analyzed to reveal the physical mechanisms for the mixing process on RSP differences.

A Method for Evaluating Brain Deformation Under Sagittal Blunt Impacts Using a Half-Skull Human-Scale Surrogate.

Physical head models consisting of a half, sagittal plane skull, brain, and neck were constructed and subjected to crown and frontal impacts at two impact speeds. All tests were recorded with a high-speed camera at 1000 frames per second. Motion of visual markers within brain surrogates were used to track deformations and calculate spatial strain histories in 6 brain regions of interest. Principal strains, strain rates and strain impulses were calculated and reported. Higher impact velocities corresponded to higher strain values across all impact scenarios. Crown impacts were characterized by high, long duration strains distributed across the parietal, frontal and hippocampal regions whereas frontal impacts were characterized by sharply rising and falling strains primarily found in the parietal, frontal, hippocampal and occipital regions. High strain rates were associated with short durations and impulses indicating fast but short-lived strains. 2.23 m/s (5 mph) crown impacts resulted in 53% of the brain with shear strains higher than 0.15 verses 32% for frontal impacts. The results reveal large differences in the spatial and temporal strain responses between crown and forehead impacts. Overall, the results suggest that for the same speed, crown impact leads to higher magnitude strain patterns than a frontal impact. The data provided by this model provides unique insight into the spatial and temporal deformation patterns that have not been provided by alternate surrogate models. The model can be used to investigate how anatomical, material and loading features and parameters can affect deformation patterns in specific regions of interest in the brain.