Papers by Salam Rahmatalla
Air Medical Journal, May 1, 2018
The purpose of this study was to compare the relative efficacy of immobilization systems in limit... more The purpose of this study was to compare the relative efficacy of immobilization systems in limiting thoracic-lumbar movements. Methods: A dynamic simulation system was used to reproduce transport-related shocks and vibration, and involuntary movements of the thoracic-lumbar region were measured using 3 immobilization configurations. Results: The vacuum mattress and the long spine board were generally more effective than the cot alone in reducing thoracic-lumbar rotation and flexion/extension. However, the vacuum mattress reduced these thoracic-lumbar movements to a greater extent than the long spine board. In addition, the vacuum mattress significantly decreased thoracic-lumbar lateral movement relative to the cot alone under all simulated transport conditions. In contrast, the long spine board allowed greater lateral movement than the cot alone in a number of the simulated transport rides. Conclusion: Under the study conditions, the vacuum mattress was more effective for limiting involuntary movements of the thoracic-lumbar region than the long spine board. Moreover, the increased lateral bend observed with the long spine board under some conditions suggests it may be inadequate for immobilizing this anatomic region as presently designed. Should emergency medical service providers choose to immobilize patients with suspected injuries of the thoracic-lumbar spine, study results support the use of the vacuum mattress.
Proceedings of SPIE, May 5, 2006
In the analysis and design of military uniforms and body armor systems it is helpful to quantify ... more In the analysis and design of military uniforms and body armor systems it is helpful to quantify the effects of the clothing/armor system on a wearer's physical performance capabilities. Toward this end, a clothing modeling framework for quantifying the mechanical interactions between a given uniform or body armor system design and a specific wearer performing defined physical tasks is proposed. The modeling framework consists of three interacting modules: (1) a macroscale fabric mechanics/dynamics model; (2) a collision detection and contact correction module; and (3) a human motion module. In the proposed framework, the macroscopic fabric model is based on a rigorous large deformation continuum-degenerated shell theory representation. The collision and contact module enforces nonpenetration constraints between the fabric and human body and computes the associated contact forces between the two. The human body is represented in the current framework, as an assemblage of overlapping ellipsoids that undergo rigid body motions consistent with human motions while performing actions such as walking, running, or jumping. The transient rigid body motions of each ellipsoidal body segment in time are determined using motion capture technology. The integrated modeling framework is then exercised to quantify the resistance that the clothing exerts on the wearer during the specific activities under consideration. Current results from the framework are presented and its intended applications are discussed along with some of the key challenges remaining in clothing system modeling.
Journal of Sound and Vibration, Dec 1, 2011
Seat-to-head transmissibility is a biomechanical measure that has been widely used for many decad... more Seat-to-head transmissibility is a biomechanical measure that has been widely used for many decades to evaluate seat dynamics and human response to vibration. Traditionally, transmissibility has been used to correlate single-input or multiple-input with single-output motion; it has not been effectively used for multiple-input and multiple-output scenarios due to the complexity of dealing with the coupled motions caused by the
Journal of Civil Structural Health Monitoring, Aug 8, 2020
During flood events, the dynamic interaction between flowing water and bridges generates random l... more During flood events, the dynamic interaction between flowing water and bridges generates random loadings that force bridges to vibrate in all six degrees of freedom. It is difficult for a structural damage detection method to select a degree of freedom, or damage feature, to accurately describe and predict damage. The methodology presented here identifies damagesensitive features and uses them to monitor bridge health. A small-scale physical model of a multi-span highway bridge was constructed to satisfy geometrical, Cauchy, and Froude similarities, and six-dimensional hydrodynamic forces induced by simulated flood events were investigated as an input excitation in a tilting flume. It was determined that pitch, roll, and surge motions can be used as damage features during the inundated stage, while pitch, roll, surge, and heave can be used before the inundated stage. In addition, angular velocity signals exhibited more consistent damage indices than acceleration. Using the damage features, the proposed algorithm could successfully detect damage and damage severity during simulated flood stages. Identifying damage features can reduce the size of the collected data and inform emergency responders' decisions. This case study can be used to test methods at full scale on similar structures to develop automated health-monitoring systems.
Smart Structures and Systems, Jan 25, 2012
It is not easy to experimentally obtain the FRF (Frequency Response Function) matrix correspondin... more It is not easy to experimentally obtain the FRF (Frequency Response Function) matrix corresponding to a full set of DOFs (degrees of freedom) for a dynamic system. Utilizing FRF data measured at specific positions, with DOFs less than that of the system, as constraints to describe a damaged system, this study identifies parameter matrices such as mass, stiffness and damping matrices of the system, and provides a damage identification method from their variations. The proposed parameter identification method is compared to Lee and Kim's method and Fritzen's method. The validity of the proposed damage identification method is illustrated in a simple dynamic system.
Journal of Civil Structural Health Monitoring, Apr 29, 2015
This work presents a vibration-based damagedetection methodology that effectively captures crack ... more This work presents a vibration-based damagedetection methodology that effectively captures crack reinitiation and growth of retrofitted connections simulating those existing on stop-hole retrofitted highway bridges. The proposed methodology calculates a damage indicator, based on limited frequency bands of the transmissibility function that have high coherence, as a metric for changes in the dynamic integrity of the structure. The methodology was tested using numerical simulation and laboratory experimentation of the connections before and after stop holes were implemented as stress relief measures. Throughout both the numerical and laboratory analyses, the results were used to successfully detect damage as a result of crack growth or formation of new cracks. Laboratory experimentation on retrofitted specimens showed the tendency for the crack to branch in different directions in lieu of re-initiating through the holes. It was observed that the damage indicator magnitude increased monotonically as damage increased in the specimen.
SAE Technical Paper Series, Jun 12, 2007
A new methodology is introduced in this work to simulate normal walking using a spatial digital h... more A new methodology is introduced in this work to simulate normal walking using a spatial digital human model. The proposed methodology is based on an optimization formulation that minimizes the dynamic effort of people during walking while considering associated physical and kinematical constraints. Normal walking is formulated as a symmetric and cyclic motion. Recursive Lagrangian dynamics with analytical gradients for all the constraints and objective function are incorporated in the optimization process. Dynamic balance of the model is enforced by direct use of the equations of motion. In addition, the ground reaction forces are calculated using a new algorithm that enforces overall equilibrium of the human skeletal model. External loads on the human body, such as backpacks, are also included in the formulation. Simulation results with the present methodology show good correlation with the experimental data obtained from human subjects and the existing literature.
Vibration, Jan 27, 2021
Previous studies of human response to whole-body vibration demonstrated nonlinear softening behav... more Previous studies of human response to whole-body vibration demonstrated nonlinear softening behaviors with increasing vibration magnitudes. Most of these studies were conducted at relatively low vibration magnitudes of less than 3 m/s 2 root mean square (RMS), and not much knowledge is available to show if this softening behavior exists when humans are exposed to higher vibration magnitudes. In this work, 26 participants were transported in a supine position inside an army medical vehicle on a road that simulated field scenarios and were exposed to input acceleration magnitudes at 0.60, 0.98, 1.32, 3.25, 5.58, and 5.90 m/s 2 RMS. Motion response data were collected at the head, torso, and pelvis of the participants using inertial sensors. Transmissibility and coherence graphs were used to investigate the type of nonlinearity induced under these transport conditions. Participant responses showed softening behavior when the vibration magnitude increased from 0.60 to 0.98 to 1.32 m/s 2 RMS. However, this response behavior changed to stiffening when the vibration magnitude increased to 3.25, 5.58, and 5.90 m/s 2 RMS. In the stiffening range, the transmissibility of the torso transformed from two dominant peaks to a single peak, which may indicate a tonic muscle behavior. The resulting stiffening behaviors may be considered in the design of transport systems subject to rough terrains.
Spine, 2019
The purpose of this study was to compare the relative efficacy of immobilization systems in limit... more The purpose of this study was to compare the relative efficacy of immobilization systems in limiting thoracic-lumbar movements. Methods: A dynamic simulation system was used to reproduce transport-related shocks and vibration, and involuntary movements of the thoracic-lumbar region were measured using 3 immobilization configurations. Results: The vacuum mattress and the long spine board were generally more effective than the cot alone in reducing thoracic-lumbar rotation and flexion/extension. However, the vacuum mattress reduced these thoracic-lumbar movements to a greater extent than the long spine board. In addition, the vacuum mattress significantly decreased thoracic-lumbar lateral movement relative to the cot alone under all simulated transport conditions. In contrast, the long spine board allowed greater lateral movement than the cot alone in a number of the simulated transport rides. Conclusion: Under the study conditions, the vacuum mattress was more effective for limiting involuntary movements of the thoracic-lumbar region than the long spine board. Moreover, the increased lateral bend observed with the long spine board under some conditions suggests it may be inadequate for immobilizing this anatomic region as presently designed. Should emergency medical service providers choose to immobilize patients with suspected injuries of the thoracic-lumbar spine, study results support the use of the vacuum mattress.
Stroke, Feb 1, 2020
Background: Understanding the potential effects on stroke outcome of the unique physical factors ... more Background: Understanding the potential effects on stroke outcome of the unique physical factors present in a helicopter ambulance flight is critical in the era of thrombectomy. However, this factor in patient care has not been adequately investigated. Methods: This was a prospective randomized blinded end-point animal study. A murine model of middle cerebral artery autologous thromboembolic occlusion (eMCAO) with rtPA reperfusion was exposed to three different settings: 1) a standardized actual helicopter flight, 2) a motion platform simulator that delivered the exact LFV signature of the helicopter, and 3) a ground control. Outcome measures included infarct size and BBB permeability on MRI, and neurological scores. Results: A total of 106 mice were analyzed. Within the rtPA group, LFV simulator mice displayed lower infarction volumes on MRI (31.6 vs. 54.9 mm 3 , p=0.007) and improved neurological scores (87 vs. 28%, p=0.0001) compared to ground control mice. By contrast, mice receiving saline did not show change in either infarction volume (80.9 vs. 95.3, p=0.8) or neurological scores (37 vs. 28%, p=0.7). No differences were seen in the actual helicopter flight group as compared with ground control. No treatment group showed any difference in permeability of the blood brain barrier, assessed by MRI. Conclusion: We found a synergistic beneficial effect of combining helicopter-like LFV and rtPA, which could provide a novel, safe, and potentially more efficacious intervention for patients with stroke. These results also suggest that non-LFV helicopter physical factors, such, as hypobaric environment, accelerations and noise, may have a negating effect on the otherwise positive effect of helicopter vibration on stroke outcomes. If so, strategies to minimize these negating factors might be expected to improve patient outcome.
Noise Notes, Mar 1, 2013
Accurate measurements of human response to whole-body vibration are essential to any conclusions ... more Accurate measurements of human response to whole-body vibration are essential to any conclusions about the health risks, discomfort, and assessment of suspension systems in vibration environments. While accelerometers are traditionally considered the main measurement tools in whole-body vibration studies, their measurements become questionable when they are attached to inclined surfaces or when the motion has coupled components in multiple directions. Current measurement correction methodologies are subjective and limited to simple cases. A comprehensive correction methodology using inertial sensors was used in this work to quantify human response under single fore-aft, single-vertical, and multiple-axis whole-body vibration of twelve seated subjects with supported-backrest and unsupported-backrest upright posture. Vibration files of white noise random signals with frequency content of 0.5-12 Hz and vibration magnitude of 1.8 m/s 2 RMS were used in the testing. The results have shown considerable differences in the transmissibility measurements without proper correction. The work presented has the potential to standardize experimentation in whole-body vibration and make measurements more accurate and defined across labs.
Journal of Low Frequency Noise Vibration and Active Control, Mar 9, 2020
The effects of gender, stature, and body mass on the biodynamic response of supine humans during ... more The effects of gender, stature, and body mass on the biodynamic response of supine humans during transport are presented in this work. Twelve female and 14 male subjects were strapped to a litter and spine board and transported in a military ground ambulance that was driven on a track ranging from smooth to bumpy conditions. Female subjects showed more pelvis vertical motion, less pelvis roll, and more pelvis pitch (p < 0.05 for most conditions) than male subjects. Subjects with higher body mass showed less pelvis vertical motion, more torso roll, more pelvis roll, and more torso pitch than subjects with lower body mass (p < 0.05 for some conditions). Differences were also seen among subjects with different statures but were not as significant. The subjects showed softening and stiffening behavior across the different road-sections with different vibration magnitudes and the results will be investigated in detail in future work.
Ergonomics, Sep 29, 2015
This work presents a predictive model to evaluate discomfort associated with supine humans during... more This work presents a predictive model to evaluate discomfort associated with supine humans during transportation, where whole-body vibration and repeated shock are predominant. The proposed model consists of two parts: (i) static discomfort resulting from body posture, joint limits and ambient discomfort; and (ii) dynamic discomfort resulting from the relative motion between the body segments as a result of transmitted vibration. Twelve supine subjects were exposed to single and 3D random vibrations and 3D shocks mixed with vibrations. The subjects&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; reported discomfort and biodynamic response were analysed under different support conditions, including a rigid surface, a stretcher and a stretcher with a spinal backboard. The results demonstrated good correlations between the predictive discomfort and the reported discomfort for the different conditions under consideration, with R(2) = 0.69-0.94 for individual subjects and R(2) = 0.94 for the group mean. The results also indicated a strong relationship between the head-neck and trunk angular velocities and discomfort during supine transportation. Practitioner Summary: The quantification of discomfort of supine humans under vibration and shocks by using a predictive model is an important contribution to this field, whereby the efficacy of different transport systems can be compared. The predictive discomfort model can be used as design criteria for ergonomic enhancement in supine transportation of humans.
Ergonomics, Mar 1, 2011
It seems obvious that human head-neck posture in whole-body vibration (WBV) contributes to discom... more It seems obvious that human head-neck posture in whole-body vibration (WBV) contributes to discomfort and injury risk. While current mechanical measures such as transmissibility have shown good correlation with the subjective-reported discomfort, they showed difficulties in predicting discomfort for non-neutral postures. A new biomechanically based methodology is introduced in this work to predict discomfort due to non-neutral head-neck postures. Altogether, 10 seated subjects with four head-neck postures--neutral, head-up, head-down and head-to-side--were subjected to WBV in the fore-aft direction using discrete sinusoidal frequencies of 2, 3, 4, 5, 6, 7 and 8 Hz and their subjective responses were recorded using the Borg CR-10 scale. All vibrations were run at constant acceleration of 0.8 m/s² and 1.15 m/s². The results have shown that the subjective-reported discomfort increases with head-down and decreases with head-up and head-to-side postures. The proposed predictive discomfort has closely followed the reported discomfort measures for all postures and rides under investigation. STATEMENT OF RELEVANCE: Many occupational studies have shown strong relevance between non-neutral postures, discomfort and injury risk in WBV. With advances in computer human modelling, the proposed predictive discomfort may provide efficient ways for developing reliable biodynamic models. It may also be used to assess discomfort and modify designs inside moving vehicles.
Abstract : In this study, an optimization-based approach for simulating the walking motion of a d... more Abstract : In this study, an optimization-based approach for simulating the walking motion of a digital human model is presented. A spatial skeletal model having 55 degrees of freedom is used to demonstrate the approach. Design variables are the joint angle profiles. Walking motion is generated by minimizing the mechanical energy subjected to basic physical and kinematical constraints. A formulation for symmetric and periodic normal walking is developed and results are presented. Backpack and ground reaction forces are taken into account in the current formulation, and the effects of the backpack on normal walking are discussed.
Advances in transportation studies, 2020
International journal of vehicle performance, 2014
Effective seat-to-head transmissibility (ESTHT) is introduced in this work to objectively evaluat... more Effective seat-to-head transmissibility (ESTHT) is introduced in this work to objectively evaluate human biodynamical response in a six-degree-offreedom input/output vibration environment. In ESTHT the complex transmissibility matrix is transformed to simple forms that can be easily interpreted. In this study, human responses were compared using ESTHT under different seated postures, including an upright seated posture with no backrest, a backrest-supported sitting posture, a backrest-supported sitting posture with forearms resting on armrest supports, and a backrest-supported sitting posture in which participants used the armrest supports and rotated their heads to the side. Twelve healthy males participated in the study and were tested under random-vibration files of 0.5-12 Hz with different magnitudes. The results showed the capability of ESTHT to identify the frequency spectrum at which the motion is magnified. The study also revealed that ESTHT was able to detect differences in human response due to different postures and vibration directions.
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Papers by Salam Rahmatalla