The simplest model possible for bouncing systems consists of a point mass bouncing passively on a mass-less spring without viscous losses. This type of spring-mass model has been used to describe the ...stance period of symmetric running gaits. In this study, we investigated the interaction between horse and rider at trot using three models of force-driven spring (-damper)-mass systems. The first system consisted of a spring and a mass representing the horse that interact with another spring and mass representing the rider. In the second spring-damper-mass model, dampers, a free-fall and a forcing function for the rider were incorporated. In the third spring-damper-mass model, an active spring system for the leg of the rider was introduced with a variable spring stiffness and resting length in addition to a saddle spring with fixed material properties. The output of the models was compared with experimental data of sitting and rising trot and with the modern riding technique used by jockeys in racing. The models show which combinations of rider mass, spring stiffness and damping coefficient will result in a particular riding technique or other behaviours. Minimization of the peak force of the rider and the work of the horse resulted in an 'extreme' modern jockey technique. The incorporation of an active spring system for the leg of the rider was needed to simulate rising trot. Thus, the models provide insight into the biomechanical requirements a rider has to comply with to respond effectively to the movements of a horse.
A literature review was performed for the years 1990-2007. It covered reports addressing the problems associated with the prevalence of low back pain and musculoskeletal disorders among farmers. In ...addition, the anticipated relationship between low back pain and whole body vibration in farmers was evaluated based on 12 reports for the years 1987-2009. The review confirmed that the prevalence of back pain is significantly higher in farmers exposed to whole body vibration than in the control group (not exposed to vibration). The frequency of back pain is related with whole body vibration, as well as with prolonged sitting position, wrong body posture and physical work load (especially lifting and carrying loads). The prevalence of these symptoms increases with the increased vibration dose and duration of exposure. Disorders in the lower section of the spine were associated with age, accidents (concerning the back), cumulative dose of whole body vibration, and overload due to wrong body posture. Long-term exposure affecting the whole body is harmful to the skeletal system (degeneration of the spine). The results of the study suggest that the repeated or constant exposure to mechanical shocks may increase the risk of low back pain. The investigations confirmed that there is a dose-response type of relationship between exposure to whole body vibration and pain in the lumbar section of the spine.
The role of occupational environment in the occurrence of low-back pain was analyzed for 1719 commercial travelers (1376 men and 343 women). At the beginning of the study (To) the group was ...interviewed to determine current lifestyle and occupational factors associated with low-back pain during the previous 12 months. Twelve months later (at T₁), a subsample of 1118 persons (893 men, 225 women) was reinterviewed to study the association between the incidence of low-back pain during the year of follow-up and the risk factors at T₀ . At T₀ low-back pain was significantly related with time spent driving a car at work, comfort of the car seat, carrying loads during work, standing for long periods at work, smoking, and psychosomatic factors. At T₁ driving 10 h/week or more, seat comfort, and psychosomatic factors were associated with first occurrence of low-back pain.
This chapter contains sections titled:
Introduction
Area Properties—Sign Conventions
Derivation and Solution of the Governing Equations
The Statically Determinate Case
Work and Energy—Castigliano's ...Second Theorem
The Statically Indeterminate Case
Solutions from the Theory of Elasticity
Variable Cross Sections
Shear Stress in Non Rectangular Cross Sections—Thin Walled Cross Sections
Design of Beams
Large Displacements
Summary and Conclusions
Vertical piezoelectric platform is the key equipment in precision engineering fields, however, the characteristics of carrying load capacity and the smoothness of cross-scale motion in the vertical ...direction restrict their applications. In this work, an alternate drive method for a vertical piezoelectric platform is proposed to solve these challenges, and the characteristics of cross-scale motion, large carrying load capacity and smooth displacement output are achieved simultaneously. The working principle of the vertical positioning platform and the theoretical analysis for the alternate drive mode are introduced in detail. A series of experiments are performed, and the results show that the motion of the vertical piezoelectric platform has good smoothness in the cross-scale motion and carrying load capacity based on the alternate drive mode. The maximum upward and downward velocities are 4.44 and 7.43 mm/s under the voltage of 600 Vp-p and the frequency of 850 and 925 Hz, respectively. Finally, the point positioning, oblique and sine trajectory tracking experiments are performed, which demonstrate that the vertical piezoelectric platform has the capacity of automated precision positioning and tracking target. Therefore, the alternate drive-based vertical positioning platform has huge potential in precise applications, such as micro/nano machining and complex biological manipulation.
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This paper proposes an optimization study for both structure and materials to obtain an affordable, long-span, light-weight, and fast-constructing T-shape lightweight concrete-filled steel tubular ...(LWCFST) girder in order to be used in bridge construction. This research was performed on a hollow steel tube of Steel-52 (yield limit 360 MPa), which was filled with LWC. A set of parameters had been investigated to illustrate its effect on T-shape LWCFST girder stiffness, toughness, resilience, and ultimate carrying load capacity in order to obtain an equivalent stiffness to that of the typically used precast concrete girder. Based on design codes (EN 1994-1-1/Euro code 4 and ANSI/AISC 360-10) that permit the use of LWC as a filler material, the parameters considered were: the thickness of the steel tube, compressive strength of the filler concrete, and the bond condition between the steel tube and filler lightweight concrete. The yielding and ultimate bending capacity were determined based on the interpreted failure criteria of T-shape LWCFST girder, considering non-linear analysis for both material and loads using ANSYSWORKBENCH software. The results showed that T-shape LWCFST girder can be employed as a significant relative economic alternative to a typical precast girder in the bridge construction field, thanks to its high stiffness/weight ratio. The lightweight concrete inside was effectively employed to delay the local web buckling of the steel tube to increase its bending capacity. In addition, it reduced the total self-weight of the bridge’s superstructure by 20% compared with a typical precast concrete girder. The dominant failure of T-shape LWCFST girders was found in the upper concrete slab due to the compression stress, even though the tensile cracks in the filler concrete occurred after reaching tensile yield stress in the steel tube. Additionally, increasing the value of friction coefficient between steel tube and lightweight concrete up to 0.8 was found to significantly affect the girder stiffness and has a slight effect after, no matter how high it is.
Melamine-impregnated paper decorated medium-density fiberboard (MIP-MDF) is the main board used for wooden furniture materials in China, and the formaldehyde released from the board and furniture ...products is harmful to human beings and is a wide concern. This paper aimed to pay attention to the formaldehyde emission of MIP-MDF and its furniture products. This study utilized a 1 m³climatic chamber to measure the formaldehyde emission of MIP-MDF and nightstand made of MIP-MDF in relation to the time and load factors. According to the results, in the 2 to 24 h stage, the emission of formaldehyde in the nightstand made of MIP-MDF materials changed significantly, and the overall trend showed a changing trend of first increasing and then declining. The formaldehyde emission of MIP-MDF stabilized after 40 h, while the formaldehyde emission of the nightstand stabilized after 60 h. As time passed, the formaldehyde emission changes of MIP-MDF and nightstand were almost the same. The formaldehyde emission of MIP-MDF and nightstand has a specific positive correlation with the carrying load. With increased carrying loads, the formaldehyde emission tends to increase, but the degree of influence gradually decreases with the addition of the carrying loads.
This study investigates the safe carrying load limit in relation to gender of workers in the sugar industry. A total of 632 workers (male and female) were interviewed following a physiological and ...psycho-physiological methodology. All of these workers were in the age groups of 21-30, 31-40 and ≥41 years. In this study, for the physiological methodology, both field and laboratory data were collected, which included heart rate, heart rate variability, energy expenditure and maximum rate of oxygen consumption. Information regarding hemoglobin content, weight, age, lean body weight, etc., was recorded to know the physical health of the workers. In the psycho-physiological evaluation, load-carrying limits were determined by the psychophysical rating of the load by workers from the selected age groups. By considering the physiological stresses and psycho-physiological evaluation, the safe carrying load limit was determined in head and back mode for male and female workers as per their age groups.
Improper posture of carrying loads can cause low back disorders. This study investigates the impact of using a footstool in spinal force and muscle activity when: (1) pushing/pulling load ...farther/nearer from the body and (2) twisting the trunk while carrying load. A whole body musculoskeletal model carrying a light load of 5, 7.5 and 10 kg is developed and inverse dynamics analyzes are conducted. Electromyography activities are also recorded to compare to the results from analyzes. Analyzes demonstrated that using a footstool when carrying a light load can reduce the intradiscal compression force. The results from the analysis are found to be consistent with the electromyogram measurement. This study suggests that load should be positioned closer to the body and footstool of 5 cm height should be used to reduce spinal forces and muscle activity on the lumbar region.
Exoskeletons are used in rehabilitation, military, industrial applications and rescuing, heavy-weight lifting and civil defense applications as well. This paper presents to design of a ...lower-extremity exoskeleton assisting walking of a load carrying human. Proposed exoskeleton system is designed to be appropriate mechanism with human lower extremity and it operates synchronously with the human realizes. The aim of exoskeleton actuator system is to provide forces against to external load carried by user during walking, sitting, and standing motions. Thus, it supports human walking and significant portion of external load carrying by the user. Also it makes possible to user spend less energy, less stress and fatigue. Proposed work involves the following design steps: kinematic synthesis of the exoskeleton, mechanical and electro-hydraulic system design.
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