Browse Topic: Biomechanics
Letter from the Editor-in-Chief
Researchers recently helped Skydio, the leading U.S. drone manufacturer, demonstrate compliance to the Federal Aviation Administration's rules for safe flights over people and vehicles. Virginia Polytechnic Institute and State University, Blacksburg, VA Operators using a drone from the leading manufacturer in the U.S. can now conduct missions over people and vehicles much easier and with even greater confidence in their safety. In January, the Federal Aviation Administration (FAA) accepted a declaration of compliance for such flights for the parachute-equipped Skydio X10 drone from Skydio, a San Mateo, California-based company that supplies its drones to customers in public safety, utilities, and national security. The acceptance came as the result of working with Virginia Tech's Mid-Atlantic Aviation Partnership (MAAP) and Center for Injury Biomechanics to complete their FAA-approved means of compliance testing.
Letter from the Focus Issue Editors
Thorax injuries are a significant cause of mortality in automotive crashes, with varying susceptibility across sex and age demographics. Finite element (FE) human body models (HBMs) offer the potential for injury outcome analysis by incorporating anthropometric variations. Recent advancements in material constitutive models, cortical bone fracture and continuum damage mechanics model (CFraC) and an orthotropic trabecular bone model (OrthoT), offer the opportunity to further improve rib models. In this study, the CFraC and OrthoT material modes, coupled with age-specific material properties, were progressively implemented to the Global Human Body Model Consortium small female 6th rib. Four distinct 6th rib models were developed and compared against sex and age-specific experimental data. The updated material models notably refined the predictions of force–displacement responses, aligning them more closely with the experimental averages. The CFraC model significantly improved the prediction of displacement at fracture, suggesting that incorporating stress triaxiality criteria can better account for the complex loading conditions ribs face in crashes, such as combined cortical tension and shear due to rib bending and torque. The study highlights the importance of using biofidelic material models and sex and age-specific data to simulate hard tissue fractures. The improved rib model demonstrates the effectiveness of integrating updated material properties and constitutive models to enhance injury prediction accuracy, which can inform better automotive safety designs and reduce mortality rates. Further research is recommended to extend these models across different demographic groups to fully capture population variability in rib fracture risk.
Rear-end vehicle collisions may lead to whiplash-associated disorders (WADs), comprising a variety of neck and head pain responses. Specifically, increased axial head rotation has been associated with the risk of injuries during rear impacts, while specific tissues, including the capsular ligaments, have been implicated in pain response. Given the limited experimental data for out-of-position rear impact scenarios, computational human body models (HBMs) can inform the potential for tissue-level injury. Previous studies have considered external boundary conditions to reposition the head axially but were limited in reproducing a biofidelic movement. The objectives of this study were to implement a novel head repositioning method to achieve targeted axial rotations and evaluate the tissue-level response for a rear impact condition. The repositioning method used reference geometries to rotate the head to three target positions, showing good correspondence to reported interverbal rotations. Under a 7 g rear impact scenario, the head-turned models were compared with the neutral position and demonstrated increases in the maximum capsular ligament distractions. Increased head rotation was associated with increased ligament distractions. The locations with critical ligament distractions shifted to the lower cervical spine (below C3) and lateral portion of the capsular ligaments for the head-turned position cases. The proposed repositioning method introduced in this study enabled the model to achieve steady head rotations with realistic cervical spine movements, increasing the biofidelity of out-of-position rear impact simulations.
Pelvic orientation in vehicles is crucial for preventing injuries and creating safer vehicles and restraint systems. A better understanding of pelvic orientation could provide more accurate anthropomorphic test device (ATD) models of underrepresented populations such as obese individuals, children, and small females. Sonomicrometry is the use of piezoelectric transducers that transmit ultrasound signals to each other to measure the distance between them. These signals may be aggregated using triangulation. In this experiment, ultrasound crystals were secured to the surface of a porcine surrogate to evaluate pelvic movement. This data was then processed using Sonometrics software to generate a 3D model of four static positions and three dynamic tests. The test was validated using a camera and a 3D measurement arm (CMM) to validate XYZ positions. This article discusses how this method could be helpful for developing more accurate ATD models, preventing fatalities in vehicle crashes.
Ongoing research in simulated vehicle crash environments utilizes postmortem human subjects (PMHS) as the closest approximation to live human response. Lumbar spine injuries are common in vehicle crashes, necessitating accurate assessment methods of lumbar loads. This study evaluates the effectiveness of lumbar intervertebral disc (IVD) pressure sensors in detecting various loading conditions on component PMHS lumbar spines, aiming to develop a reliable insertion method and assess sensor performance under different loading scenarios. The pressure sensor insertion method development involved selecting a suitable sensor, using a customized needle-insertion technique, and precisely placing sensors into the center of lumbar IVDs. Computed tomography (CT) scans were utilized to determine insertion depth and location, ensuring minimal tissue disruption during sensor insertion. Tests were conducted on PMHS lumbar spines using a robotic test system for controlled loading in flexion, compression, and a combination, while monitoring pressure changes. The compression force, flexion angle, and sensor-recorded IVD fluid pressure were recorded during tests. CT images were analyzed to assess sensor placement and its impact on sensing ability. Pressure readings during various loading conditions were examined for different specimens, with data reported from the beginning of tests through relevant loading phases. The study successfully established a methodology for inserting pressure sensors into the IVD and assessed their ability to detect changes in flexion angle, compression, and combined loading. Sensors accurately tracked compression force and detected changes in flexion angle, although with some differences in response. Sensors placed optimally showed expected responses, while those placed suboptimally exhibited variability, particularly in detecting changes during flexion. This variability underscores the importance of sensor placement for accurate detection of loading states. Overall, the study provides a foundation for utilizing pressure sensors to monitor loading states in sled tests, with future work focusing on refining differentiation between loading types.
Scientists at Osaka University, in cooperation with Joanneum Research (Weiz, Austria), have introduced wireless health monitoring patches that use embedded piezoelectric nanogenerators to power themselves with harvested biomechanical energy. This work may lead to new autonomous health sensors as well as battery-less wearable electronic devices.
In the context of Rotorcraft Pilot Couplings, the biomechanics of the pilot body play a fundamental role in determining the stability of the pilot-vehicle closed loop system. The response of the pilot body is, in turn, inherently stochastic, being a function of pilot biometrics and muscular activation. Coupling the statistical distribution of pilot biomechanical behavior determined in specialized experimental campaign with linear models of the helicopter heave dynamics, an uncertainty propagation procedure is developed, with the aim of estimating the statistical distribution of the stability margins of the closed loop pilot-vehicle system. Results obtained varying the collective lever characteristics, as well as the helicopter model parameters, align well with results obtained previously in deterministic settings. However, the new scheme allows to define quantitative robustness indices.
Letter from the Special Issue Editors
Understanding Rotorcraft-Pilot Couplings phenomena is important for improving Human-Machine Interface design in rotorcraft. Although substantial progress has been made in the past decades, further effort is needed in enabling RPCfree or RPC-insensitive pilot-vehicle interface design. The design of an experimental testbed dedicated to investigating RPC interactions is presented, with a special focus on numerical simulation activities. The first results obtained in test campaigns involving non-skilled individuals are encouraging, showing that the testbed can enable more in-depth experimental analysis in the near future.
Exoskeletons, many of which are powered by springs or motors, can cause pain or injury if their joints are not aligned with the user’s. To mitigate these risks, a new measurement method was developed to test whether an exoskeleton and the person wearing it are moving smoothly and in harmony.
We recently developed a three-direction (vertical, longitudinal, and lateral) coupled biodynamic model of seated posture under vibration. However, in that study we only tested one algorithm to identify the model parameters. This article investigates four different optimization solvers in Matlab®, i.e., particle swarm optimization (particleswarm), particle swarm and local optimization method (fmincon), genetic algorithm (ga) and local optimization method (fmincon), and local optimization method (fmincon) to identify coupled biodynamic model parameters. Based on the obtained parameters, it further compares experimental and simulation results to determine the best optimization solver in terms of the root mean square error (RMSE), linear regression (R 2), goodness of fit (ε), and Central Processing Unit (CPU) time. The results show that particle swarm optimization is the best one for identifying the biodynamic model’s parameters.
In the fields of forensic accident reconstruction and biomechanical engineering, it is often necessary to estimate the length of a specific body segment for an individual, about whom little is known besides overall stature. Since body proportions and body segment lengths vary throughout the population, there will be some error in these estimations. The current study provides estimates for the accuracy of human body segment length predictions based on stature. In this study, four different methods for predicting body segment lengths based on stature were evaluated. Using publicly available adult and child anthropometric datasets, a leave-one-out cross validation analysis was conducted to evaluate the accuracy of each of the four methods in predicting body segment lengths. The results of the leave-one-out analysis showed that different prediction methods produced the best estimates for different body segment length measurements. When using the best method for each body segment, body segment lengths for an individual on average can be predicted within 2.5% of the actual measurement. The 50th percentile best estimates for each body segment length studied are provided for males and females, over a range of child and adult statures. The data presented in this study can be used to provide estimates of error rates of human body segment length predictions.
This work presents the results of a piloted flight simulator campaign aimed at measuring biomechanical performance indicators -- upper limbs motion and electromiography of main muscle bundles -- of pilots performing complex, realistic tasks. Ship deck landings performed by a single pilot, flying several helicopter configurations with sea conditions of increasing intensity have been considered. The analysis of the results shows an increase in muscular activity in relation with the increase in task difficulty, in agreement with subjective ratings (Bedford workload scale). The study provided useful indications to improve the corresponding biomechanical simulations, as well as to characterize pilot performance during specific tasks.
The paper investigates structural coupling problems in tiltrotor aircraft. A detailed tiltrotor model, representative of the Bell XV-15, has been built. The airframe model has been modified with a thinner wing to better reveal structural coupling proneness. A linearized FCS has been introduced to analyze the overall stability on an extended frequency band, ranging from the flight mechanics up to the aeroelastic modes. In addition to the FCS, biomechanical models of the pilot, acting on the power-lever and on the center stick, are included in feedback loop. Overall stability analyses demonstrate that the FCS improves handling qualities although several structural coupling mechanisms arise, in combination with the involuntary pilot's response, reducing flutter clearance. A modified version of the XV-15, using differential collective pitch for yaw control in airplane mode, has been also investigated. This configuration reduces costs and weights although the FCS destabilizes the antisymmetric wing chord mode at low speed flight, severely limiting the flight envelope. Means of prevention, based on notch filters, are implemented and discussed.
This work investigates rotorcraft-pilot coupling phenomena in tiltrotors. A detailed tiltrotor model, representative of the Bell-Boeing XV-15, has been built. Biomechanical models of the pilot, acting on the power lever and on the centre stick, are included in feedback loop to define the Pilot-Vehicle System. Pilot-Assisted Oscillation phenomena are investigated on the overall conversion corridor using Nyquist's criterion. Pilot-in-the-loop analyses demonstrate that a critical parameter is detected in the vertical fins geometry. Due to an asymmetric flaperons deflection the wing's wake impacts on the vertical fins, producing a side force. The pulsating tail-side-force makes the fuselage to yaw and excites the asymmetric wing chord mode coupled with the lateral pilot's biomechanics, leading to a reduction, or even a loss, of stability. No unstable event is detected about the longitudinal direction. Conversely, a resonance between the pilot's biomechanics and the aircraft poorly damped symmetric wing bending mode is predicted about the vertical axis. The instability is found on the whole conversion corridor, although the source of excitation changes with reference to the nacelle angle. Means of prevention are implemented and discussed.
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