A study of ground reaction forces due to human movement

<p>To predict floor vibration response using computer analysis, it is important to have reliable representations of the forcing function in the time and frequency domains. With the help of a number of volunteers, the ground reactions forces at different speeds from a slow walk to a run were measured using a force platform. The measurements included components of the force in the vertical, lateral, and longitudinal directions. The Fourier Series was used to compute the dynamic load factors for different harmonics as a function of the step frequency. The dynamic load factors of the actual forcing function were compared to the simplified case considering no differences between the right and left footfall forces. The distribution of the dynamic load factors as a function of step frequency were presented for both cases.</p>

Assessment of Internal Loads in the Joints of the Lower Extremities During the Snatch in Young Weightlifters

The aim of this paper is to present the results of an assessment of internal loads in the joints of the lower limbs during the snatch performed by young weightlifters. A planar model of a weightlifter composed of 7 rigid segments (the lower trunk, thighs, lower legs and feet) connected by six hinge joints was used in the computations. The dynamic equations of the motion of the model were obtained using a projective technique. Kinematic data were recorded by a Vicon system with a sampling frequency of 200 Hz. The ground reactions were measured independently for the left and right limbs on two force platforms. The inverse dynamics problem was solved to assess the internal loads (the muscle forces and joint reactions) in the lower limbs. Relatively high differences in the reactions in the joints and muscle forces in the left and right lower extremities were identified. The obtained results also reveal that the snatch, a lift which tends to be geometrically symmetrical in the sagittal plane, is not necessarily characterized by symmetry of internal loads. Thus, this study has shown that a kinematics analysis of the lifter’s movement, which is commonly used to assess the technique of the snatch, is insufficient and should be supplemented with a dynamics analysis.

Terrain Accessibility Prediction for a New Multi axle Armoured Wheeled Vehicle

Better terrain accessibility of military vehicle makes it possible to project force at desired points in a theatre of operation. The factors responsible for terrain accessibility are slope, obstacles and soil. Torque requirement for meeting vehicle speed and gradient requirement is understood and can be analytically arrived at. It can be met by appropriate choice of engine and transmission using. There is dearth of information as well as a common metric in quantification of terrain accessibility especially soft soil trafficability. Approach adopted in this study is that of characterisation of vehicle in terms of mobility characteristic and mobility limit parameters and comparing them with vehicle in-service worldwide. Simple empirical relation has been preferred over complex analytical approach for mobility prediction and gradient climbing capability in sand has been predicted and compared with other vehicles. parametric study for tyre sizes vis-a-vis mobility parameters have been obtained and results have been presented for chosen vehicle configuration. Second part of this study is obstacle crossing capability study for standard set of obstacles. Vehicle model has been built in multi-body environment and parameters of significance viz., wheel displacement to verify correctness of model and acceleration at CG for ride comfort and ground reactions for evaluation of dynamic loads on axles have been obtained. Vehicle drivetrain configuration to achieve desired terrain accessibility in terms of soft-soil trafficability and obstacle crossing has been demonstrated.

Optimal aircraft take-off with thrust vectoring

The short take-off capability is of paramount importance for a fighter airplane to enable its operation from short and damaged runways. This paper analyses the airplane take-off process from the viewpoint of reducing the ground roll/take-off distance with the use of thrust vectoring. The airplane take-off is modelled incorporating the ground reactions on the landing gear and the thrust vector forces and moments. The take-off problem is formulated as an optimal control problem with appropriate constraints. Though many researchers have applied optimal control techniques for designing airplane manoeuvres, its application to the airplane take-off problem is rarely available in the open literature. It is expedient to use such methodology to understand the use of thrust vectoring features of an aircraft to maximise the benefits in shortening the ground roll/take-off distance. An optimal control methodology has been applied in this paper with the objectives stated above to a twin-engine fighter nonlinear aircraft model popularly known as F-18/HARV. Computation of flight path and control schedules using optimal control has been carried out with and without the use of vector nozzles. A reduction of about 6% in take-off distance and about 29% in ground roll distance is obtained with the use of thrust vector for the configuration studied.

Development of an Advanced Model of Passive Dynamic Biped Walking

Passive dynamic walking is a manner of walking developed, partially or in whole, by the energy provided by gravity. Studying passive dynamic walking provides insight into human walking and is an invaluable tool for designing energy efficient biped robots. The objective of this research was to develop a continuous mathematical model of passive dynamic walking, in which the Hunt-Crossley contact model and the LuGre friction model were used to represent the normal and tangential ground reactions. A physical passive walker was built to validate the proposed mathematical model. A traditional impact-based passive walking model was also used as a reference to demonstrate the advancement of the proposed passive dynamic walking model. The simulated gait of the proposed model matched the gait of the physical passive walker exceptionally well, both in trend and magnitude.

Massively Parallel Discrete Element Modeling of Legged Mobility on Granular Terrain

Legged mobility of robotic systems is an active area of research. Quantitatively understanding mobility of these systems on natural terrain is critical for design and operations of these systems. In this paper, we present results of computational simulations of legged mobility on granular terrain using massively parallel Discrete Element Method. We model the interactions of a leg from a micro ground vehicle with sandy terrain made of polydispersed granular media. In these simulations, we model the interactions between millions of granules and the leg to quantify ground reactions and associated qualitative behaviors. The simulations are run on parallel computers to overcome the severe computational complexity of simulating these large problems in physically feasible time-frames. We are using high fidelity first-principles approaches to model emergent complex behavior that cannot otherwise be modeled. We present results from a parametric sweep where different leg speeds and penetrations are used to understand differences in ground reaction.

Impactless Biped Walking on Stairs

A motion/force control scheme was proposed to investigate biped impactless walking, which has proven to be used effectively to achieve stable walking on slopes. This paper aims to investigate the efficiency of walking stairs. Good trajectory generation and effective control method are important for operating and ensuring the stability of biped walking on stairs. Walking is illustrated by a seven-link biped with six control actuators, the number of which always equals to that of motion and force specifications. In order to avoid impacts, the specified motion of the biped and its ground reactions are controlled. Control torques, ground reaction forces and consumption energy of the biped lower limb joints are calculated for ascending stairs, walking on flat terrain and descending stairs. Three different locomotion velocities are studied in order to compare the energetic performance of the biped walking up-and-down stairs.