Biodynamic Response Research Articles

Various vehicle speeds and road profiles effects on transmitted accelerations analysis to human body segments using vehicle and biomechanical models

In this paper, a biomechanical model of human body is proposed to evaluate the biodynamic responses to vertical vibration and transmitted accelerations for the seated position without backrest supp...

ANFIS modeling of vibration transmissibility of a power tiller to operator

This research was conducted to evaluate a 13-hp power tiller vibration transmitted to operator’s body experimentally at three-axis on transportation conditions. Also, to survey the usefulness of ANFIS in predicting vibration transmissibility (TR) from seat (WBV) and handle (HTV). Vibration acceleration signals were measured at the power tiller handle, trailer seat, and the operator’s wrist, arm, chest and head positions for four transmission gear ratios, five engine speeds, and three directions of measurement. The results indicated that the TR value was the greatest at the operator’s wrist, then at the operator’s arm, chest and head, respectively for all the gear ratios and engine speeds. The TR value at different body organs was dependent on measurement direction. The maximum TR was observed at the operator’s wrist and arm on the longitudinal direction and at the operator’s chest and head on the vertical direction. The frequency domain results showed that TR from the trailer seat to the operator’s chest was more than 100% in frequency range of 1–16 Hz. The TR was above 100% for the handle to the operator’s wrist in the frequency range of 3.15–6.3 Hz and for the operator’s wrist to the arm from 4 to 5 Hz. The TR more than 100% was observed at frequency range of 1.25–2 Hz for the operator’s chest to head. The TR from the operator’s wrist to the arm and the operator’s arm to the chest was not more than 100% in any frequency bands. The results also revealed that the TR from the seat to the operator’s chest was more than those of the handle to the arm and the handle to the wrist for all the three directions of vertical, lateral and longitudinal. The ANFIS methodology successfully learned the relationship between the input and output data sets. It can be concluded that the performance of subtractive clustering method was slightly better for HTV-TR(t) modeling (total TR) than grid partition method. In general, the performance of the ANFIS modeling for HTV-TR(t) is slightly better than for HTV-TR modeling, and this trend was also observed for WBV modeling. Because human response to multi-axis vibrations could not be easily understood using available laboratory equipment, investigation of human response to these vibrations in real conditions and modeling the results using machine learning and AI systems could increase our understanding of the biodynamic responses of the human body to multiple-axis excitations and assist the development of biodynamic models of the body.

The influence of variating passive user interactions on power tools in the context of product development

Comparing different development variants under same test conditions with the help of test rigs is one success factor within the power tool development process. One question in test rig design is about the necessity to model variating user’s biodynamic response within such test rigs. The objective of this contribution is to reveal the main influential factors on user’s biodynamic response which have to be included in test rig design for power tools. Therefore, this article presents a qualitative study to give indications for the relevance of user, posture, grip and push force on power tool’s behavior. It is shown that different user’s biodynamic response leading to different vibration levels at a hammer drill’s and impact driver’s handle. While assuming that any kind of vibration level influenced by the user’s biodynamic response will directly lead to different interactions of the technical subsystems inside the power tool, it is stated that variation of user’s biodynamic response has to be taken into account when designing test rigs for power tool development.

Exploring head and neck vibration exposure from quad bike use in agriculture

ObjectivesAlthough musculoskeletal disorders of the low back have been linked to excessive whole body vibration during vehicle use, there is a need to explore head/neck vibration in occupational environments. Resonant frequencies may amplify vibration transmitted to the head/neck and increase risk of musculoskeletal disorders. MethodsAn observational fieldwork study directly measuring vibration exposure at the seat and head of 10 rural workers operating quad bikes over farm terrain for ∼30 min. ResultsVertical axis root-mean-squared acceleration was higher at the head/neck compared to the seat. Mean spectral coherence was strong (>0.8) in the vertical axis from 1.3 to 4.9 Hz, indicating a strong relationship between vertical vibrations measured at the seat and the head. Power spectral densities demonstrated system amplification, with mean and peak seat-to-head transfer functions of 1.44 (95% CI ± 0.08) and 1.66 (±0.14), respectively, from 1.3 to 4.9 Hz. There was also a peak phase lag of −66.5° (±13.9°) at 4.9 Hz for head relative to seat measured vertical vibration, which may increase compressive loads of the cervical spine. ConclusionsWhile it is unknown whether these amplified and out-of-phase vibrations measured at the head/neck increase the risk of musculoskeletal disorder, the current biodynamic response to vibration exposure may help explain previously reported high prevalence of neck pain in farmers that use quad bikes. Our future laboratory based studies will aim to validate these fieldwork seat and head data and explore the effect of such vibration transmission on spinal biomechanical models as well as on proprioceptive and perceptual pathways that may also relate to injury.

Effects of posture and vibration magnitude on seat to head transmissibility during exposure to fore-and-aft vibration

An experimental study has been conducted on the vibration simulator, developed as a mockup of a railway vehicle. In this paper, the effect of variations in the posture and vibration magnitude on head motions in three translational directions (fore-and-aft, lateral and vertical) are studied with seat vibration in fore-and-aft direction. Thirty healthy male subjects are exposed to random vibration with three vibration magnitudes of 0.4, 0.8 and 1.2 m/s2 r.m.s. over the frequency range 1–20 Hz. The data results are analyzed in terms of seat-to-head transmissibility (STHT) in two sitting postures; backrest and forward lean. Vibration measurements of the head motions are made with an apparatus (bite-bar). The study confirms that the measured responses to single fore-and-aft axis vibration have shown notable cross-axis responses. An increase in the excitation magnitude consistently revealed a decrease in the response peak magnitude and the corresponding resonant frequency, particularly in the presence of a back support. Such non-linear behavior has been interpreted as a non-linear softening effect in the muscle tension under increasing intensity of vibration. The use of a back support significantly alters the biodynamic responses of the seated body, which is attributable to the constraint due to the backrest support.

Development of a Five‐Degree‐of‐Freedom Seated Human Model and Parametric Studies for Its Vibrational Characteristics

This study focuses on the biodynamic responses of a seated human model to whole‐body vibrations in a vehicle. Five‐degree‐of‐freedom nonlinear equations of motion for a human model were derived, and human parameters such as spring constants and damping coefficients were extracted using a three‐step optimization processes that applied the experimental data to the mathematical human model. The natural frequencies and mode shapes of the linearized model were also calculated. In order to examine the effects of the human parameters, parametric studies involving initial segment angles and stiffness values were performed. Interestingly, mode veering was observed between the fourth and fifth human modes when combining two different spring stiffness values. Finally, through the frequency responses of the human model, nonlinear characteristics such as frequency shift and jump phenomena were clearly observed.

Multibody Biomechanical Modelling of Human Body Response to Direct and Cross Axis Vibration

Operators of the vehicles and heavy earth moving machinery are continuously exposed to low frequency whole-body vibration (WBV) of comprehensive magnitudes arising from tire/track-terrain interactions. Research studies shown a high presence of back disorders such as disc degeneration, muscular pain, among the occupational vehicle drivers subjected to whole-body vibration. The modelling and measurement of the biodynamic response of human body is major research topic, with applications to ergonomics, paasive or active suspension control system technologies, adverse effects on the human body that causes discomfort and some health issues. The risk of the vibration exposure depends on three different factors: the time span, the amplitude and the frequency of the transmitted vibration. In the field of automotive engineering, manufacturers and designers require to understand how the acceleration signals are amplified or damped by the human-seat interface in order to increase human comfort.Most of human body models reported in literature are lumped parameter. The limitation with lumped parameter model is that they can be analysed in one direction only. Human body is having complex motion so minimum two dimensional (2D) model need for analysing human body response. The models considered two objective functions with considering vertical or fore and aft vibrations. Multibody human body models of 20 degree of freedom (DOF) developed for seated human, and model parameters are optimized using genetic algorithm (GA) for published experimental data from literature. Model is able to match the published experimental data for Seat to Head Transmissibility (STHT) and Apparent Mass (AM).

A nonlinear model of the hand-arm system and parameters identification using vibration transmissibility

In the present paper a lumped single degree-of-freedom nonlinear model is used to study biodynamic responses of the hand arm system (HAS) under harmonic vibrations. Then, the harmonic balance method is implemented to derive the vibration transmissibility. Furthermore,Padé approximations are used in the identification process of biodynamic characteristics of the HAS model. This process is based on minimizing the distance between the theoretical and the experimentally measured transmissibilities. The proposed identification workflow is applied to vibrations at the wrist in two cases: 1) the transmissibility versus the grip force for fixed excitation frequencies, and 2) the transmissibility versus the excitation frequency for fixed grip force.

Contact area affects frequency-dependent responses to vibration in the peripheral vascular and sensorineural systems

ABSTRACTRepetitive exposure to hand-transmitted vibration is associated with development of peripheral vascular and sensorineural dysfunctions. These disorders and symptoms associated with it are referred to as hand-arm vibration syndrome (HAVS). Although the symptoms of the disorder have been well characterized, the etiology and contribution of various exposure factors to development of the dysfunctions are not well understood. Previous studies performed using a rat-tail model of vibration demonstrated that vascular and peripheral nervous system adverse effects of vibration are frequency-dependent, with vibration frequencies at or near the resonant frequency producing the most severe injury. However, in these investigations, the amplitude of the exposed tissue was greater than amplitude typically noted in human fingers. To determine how contact with vibrating source and amplitude of the biodynamic response of the tissue affects the risk of injury occurring, this study compared the influence of frequency using different levels of restraint to assess how maintaining contact of the tail with vibrating source affects the transmission of vibration. Data demonstrated that for the most part, increasing the contact of the tail with the platform by restraining it with additional straps resulted in an enhancement in transmission of vibration signal and elevation in factors associated with vascular and peripheral nerve injury. In addition, there were also frequency-dependent effects, with exposure at 250 Hz generating greater effects than vibration at 62.5 Hz. These observations are consistent with studies in humans demonstrating that greater contact and exposure to frequencies near the resonant frequency pose the highest risk for generating peripheral vascular and sensorineural dysfunction.

The relationships between hand coupling force and vibration biodynamic responses of the hand-arm system

This study conducted two series of experiments to investigate the relationships between hand coupling force and biodynamic responses of the hand–arm system. In the first experiment, the vibration transmissibility on the system was measured as a continuous function of grip force while the hand was subjected to discrete sinusoidal excitations. In the second experiment, the biodynamic responses of the system subjected to a broadband random vibration were measured under five levels of grip forces and a combination of grip and push forces. This study found that the transmissibility at each given frequency increased with the increase in the grip force before reaching a maximum level. The transmissibility then tended to plateau or decrease when the grip force was further increased. This threshold force increased with an increase in the vibration frequency. These relationships remained the same for both types of vibrations. The implications of the experimental results are discussed.Practitioner Summary: Shocks and vibrations transmitted to the hand–arm system may cause injuries and disorders of the system. How to take hand coupling force into account in the risk assessment of vibration exposure remains an important issue for further studies. This study is designed and conducted to help resolve this issue.

Dynamic forces over the interface between a seated human body and a rigid seat during vertical whole-body vibration

Biodynamic responses of the seated human body are usually measured and modelled assuming a single point of vibration excitation. With vertical vibration excitation, this study investigated how forces are distributed over the body-seat interface. Vertical and fore-and-aft forces were measured beneath the ischial tuberosities, middle thighs, and front thighs of 14 subjects sitting on a rigid flat seat in three postures with different thigh contact while exposed to random vertical vibration at three magnitudes. Measures of apparent mass were calculated from transfer functions between the vertical acceleration of the seat and the vertical or fore-and-aft forces measured at the three locations, and the sum of these forces. When sitting normally or sitting with a high footrest, vertical forces at the ischial tuberosities dominated the vertical apparent mass. With feet unsupported to give increased thigh contact, vertical forces at the front thighs were dominant around 8Hz. Around 3–7Hz, fore-and-aft forces at the middle thighs dominated the fore-and-aft cross-axis apparent mass. Around 8–10Hz, fore-and-aft forces were dominant at the ischial tuberosities with feet supported but at the front thighs with feet unsupported. All apparent masses were nonlinear: as the vibration magnitude increased the resonance frequencies decreased. With feet unsupported, the nonlinearity in the apparent mass was greater at the front thighs than at the ischial tuberosities. It is concluded that when the thighs are supported on a seat it is not appropriate to assume the body has a single point of vibration excitation.

Human body modeling method to simulate the biodynamic characteristics of spine in vivo with different sitting postures.

The aim of this study is to model the computational model of seated whole human body including skeleton, muscle, viscera, ligament, intervertebral disc, and skin to predict effect of the factors (sitting postures, muscle and skin, buttocks, viscera, arms, gravity, and boundary conditions) on the biodynamic characteristics of spine. Two finite element models of seated whole body and a large number of finite element models of different ligamentous motion segments were developed and validated. Static, modal, and transient dynamic analyses were performed. The predicted vertical resonant frequency of seated body model was in the range of vertical natural frequency of 4 to 7Hz. Muscle, buttocks, viscera, and the boundary conditions of buttocks have influence on the vertical resonant frequency of spine. Muscle played a very important role in biodynamic response of spine. Compared with the vertical posture, the posture of lean forward or backward led to an increase in stress on anterior or lateral posterior of lumbar intervertebral discs. This indicated that keeping correct posture could reduce the injury of vibration on lumbar intervertebral disc under whole-body vibration. The driving posture not only reduced the load of spine but also increased the resonant frequency of spine.

Measuring dynamic stiffnesses of preloaded distal phalanges in vibration - Test bench validation and parameter study

An experimental vibration test bench was built for measuring the dynamic stiffnesses and dissipated power densities of preloaded distal phalanges undergoing vibration. The aim of this test bench was to analyse the effects of vibration frequency, static preloading, and vibration excitation amplitude on local biodynamic response. Prior to implementation, the test bench was validated by comparison with a tension–compression testing machine and a reference dynamic mechanical analyser. A measurement study was then conducted on a group of 20 subjects. The mean dynamic stiffness showed that the mechanical behaviour of the index finger distal phalanx is similar to that of a complex amorphous polymer: it exhibits frequency-related stiffening with a rubbery plateau, a glassy transition zone, and a glassy state. The static preloading condition considerably modifies the dynamic response of the phalanx, as well as the dissipated power, which is significantly greater when the preloading is high. An amplitude-related softening phenomenon, similar to the Payne effect for rubber, was also revealed. This can be explained by the thixotropic character of the extracellular matrix of the distal phalanx soft tissues. Relevance for industryExtensive exposure of the hand–arm system to regular vibration may lead to various disorders and injuries, due in part to changes in mechanical quantities, such as dynamic stress, strain, or dissipated power density, arising from the propagation of such vibration. Nowadays, the direct measurement of this biodynamic response inside soft tissues is still extremely challenging. A way to assess the overall mechanical effects of these local quantities on the human finger is to measure and analyse both the macroscopic stiffness and the dissipated power of fingers.

Finite Element Analysis of Humerus Bone for Cup Radious Variations

Humerus bone is the longest bone of human hand that connects the shoulder to elbow. The 3D modelling of humerus bone consists of cylindrical shaft and two cups varying in size. Upper portion of cylindrical shaft fits into a socket in shoulder and lower portion connected to elbow. The size of shoulder cup and elbow cup varies in radious as variation of human geographical conditions. The main objective of this research work is to study the variation of human humerus bone cup size and find the biodynamic response in terms of modal frequency (Hz) and mode shapes. Four cases of cup radious variation were simulated using FEA. Modal frequency was used for evaluation of resonance condition and mode shapes were used to locate the fracture in bone. FEA (Finite Element Analysis) were used to simulate the boundary conditions and evaluate the results. For case I (R1= 29.32 mm, R2= 28.99 mm), first ten natural frequency varies (660.24-5932.3) Hz. For all four cases the natural frequency varies (660.24-5969.5) Hz. The fundamental frequencies varies (660.24, 670.65, 664.65 and 676.92) Hz. The results of FEA simulation were compared with experimental results available in literature. For the design of humerus bone model Solid Edge was used.

Biodynamic modelling of seated human body under whole body vibration exposure using ANN

Vehicle developers and design engineers require understanding of human response to vibration for optimising the seat in order to meet the objective of passenger ride comfort. This paper attempts to develop an artificial neural networks (ANN) based model to measure biodynamic response seat to head transmissibility (STHT), incorporating factors like vibration frequency, vibration magnitude and posture for seated subjects exposed to random whole body vibration (WBV) in three different directions (vertical, fore-aft, lateral). After training the model is able to predict STHT with high accuracy when compared with the experimental values. Cross-axis coupling, i.e., excitation in one axis producing a response in the other axis, is also validated through ANN modelling in this paper.

A Sequential Approach to the Biodynamic Modeling of a Human Finger

In an effort to understand the vibration-induced injuries incurred by manual workers, mechanical models are developed and used to predict the biodynamic responses of human body parts that are exposed to vibration. Researchers have traditionally focused on the arms and hands, but there has been only limited research on finger modeling. To simulate the accurate response of a single finger, a detailed mechanical model based on biodynamic finger measurements is necessary. However, the development of such models may prove difficult using the traditional one-point coupling method; therefore, this study proposes a new approach. A novel device for single-finger measurements is presented and used to expose the finger to a single-axial broadband excitation. The sequentially measured responses of the different finger parts are then used to identify the parameters of a multibody mechanical model of the index finger. Very good agreement between the measured and the simulated data was achieved, and the study also confirmed that the obtained index-finger model is acceptable for further biodynamic studies.

Analysis of the dynamic behavior of the car user in the irregular terrain

Many people experience vibration effects on whole-body throughout their lives frequently. Vibrating energy absorbed is exposed all-body caused with vibration hazard in the vertically on body and biodynamic responses from body in speed 2.37 to 5.14 m/s could captivate with car seat on user body, so the vibration energy transferred to a seated people body. In this paper, the human body is modeled as a series/parallel 4 DOF dynamic models of system and use Lagrange equation for calculate head and neck equation and investigation the effect of vibration energy absorbed in whole body. The hybrid model is analyzed with Matlab software for vertical vibration responses and vibration energy absorption. It is shown improvement seat vehicle cause, drastically ameliorate the tolerance to high-intensity vibrations in the 0.8 Hz range with reducing the maximum amplitude ratios and relative displacements of the body.

Hand-arm and whole-body vibrations induced in cross motorcycle and bicycle drivers

Generally, and particularly at sports, the human body is constantly exposed to physical requests and to tests in many different situations. Although the practice of sports is considered a healthy act, there are limits and, when these limits are reached, the benefits of sport can turn into problems. Thus, the biodynamic response method is increasingly being used to study the human injuries induced by external vibrations. Moreover, the European Directive 2002/44/EC on the minimum health and safety requirements, regarding worker exposure to risks from physical agents (e.g. vibration), limit the exposure to vibrations. The aim of this study is to analyze the exposure level of cross motorcycle and of cycling drivers to hand-arm vibration (HAV) and to whole-body vibration (WBV). For this research, vibration levels of a common 200 cc cross motorcycle were experimentally measured and the maximum driving time that could be safely used in a stone road was established. Moreover, bicycle vibration measurements were performed using two different bicycles: a road cycling bike; a bike for track cycling. The road bike was evaluated at three road scenarios: asphalt; paved; and stone road pavement. The track bike was evaluated in track cycling and rollers. In the case of cycling the results indicate that impacts and transient vibrations lead to a higher musculoskeletal request particularly in what concerns shoulders, arms, wrists, knees and spine.

Vibrations transmitted from human hands to upper arm, shoulder, back, neck, and head

Some powered hand tools can generate significant vibration at frequencies below 25 Hz. It is not clear whether such vibration can be effectively transmitted to the upper arm, shoulder, neck, and head and cause adverse effects in these substructures. The objective of this study is to investigate the vibration transmission from the human hands to these substructures. Eight human subjects participated in the experiment, which was conducted on a 1-D vibration test system. Unlike many vibration transmission studies, both the right and left hand-arm systems were simultaneously exposed to the vibration to simulate a working posture in the experiment. A laser vibrometer and three accelerometers were used to measure the vibration transmitted to the substructures. The apparent mass at the palm of each hand was also measured to help in understanding the transmitted vibration and biodynamic response. This study found that the upper arm resonance frequency was 7–12 Hz, the shoulder resonance was 7–9 Hz, and the back and neck resonances were 6–7 Hz. The responses were affected by the hand-arm posture, applied hand force, and vibration magnitude. The transmissibility measured on the upper arm had a trend similar to that of the apparent mass measured at the palm in their major resonant frequency ranges. The implications of the results are discussed. Relevance to industryMusculoskeletal disorders (MSDs) of the shoulder and neck are important issues among many workers. Many of these workers use heavy-duty powered hand tools. The combined mechanical loads and vibration exposures are among the major factors contributing to the development of MSDs. The vibration characteristics of the body segments examined in this study can be used to help understand MSDs and to help develop more effective intervention methods.

Tremor Reduction at the Palm of a Parkinson's Patient Using Dynamic Vibration Absorber.

Parkinson’s patients suffer from severe tremor due to an abnormality in their central oscillator. Medications used to decrease involuntary antagonistic muscles contraction can threaten their life. However, mechanical vibration absorbers can be used as an alternative treatment. The objective of this study is to provide a dynamic modeling of the human hand that describes the biodynamic response of Parkinson’s patients and to design an effective tuned vibration absorber able to suppress their pathological tremor. The hand is modeled as a three degrees-of-freedom (DOF) system describing the flexion motion at the proximal joints on the horizontal plane. Resting tremor is modeled as dual harmonic excitation due to shoulder and elbow muscle activation operating at resonance frequencies. The performance of the single dynamic vibration absorber (DVA) is studied when attached to the forearm and compared with the dual DVA tuned at both excitation frequencies. Equations of motion are derived and solved using the complex transfer function of the non-Lagrangian system. The absorber’s systems are designed as a stainless steel alloy cantilevered beam with an attached copper mass. The dual DVA was the most efficient absorber which reduces 98.3%–99.5%, 97.0%–97.3% and 97.4%–97.5% of the Parkinson’s tremor amplitude at the shoulder, elbow and wrist joint.