Can a nonlinear Quasi-Zero-Stiffness spring improve the ride quality of a vehicle?

The paper examines the possibility of using a nonlinear Quasi-Zero-Stiffness (QZS) spring in a vehicle suspension. The response of a Single Degree of Freedom (SDOF) model to harmonic base excitations is obtained which may be unstable and unbounded depending on the excitation level and the damping ratio. This is followed by obtaining the response of the SDOF model to harmonic base excitation with an amplitude that is varying according to a road profile spectrum. Such dependency of the excitation amplitude to the frequency changes the qualitative behaviour of the nonlinear system and the responses would be always bounded. The QZS spring also improves the isolation of the system. Transient responses of a quarter car model with a QZS suspension to a road hump and random road profile are investigated. The maximum acceleration of the vehicle with the QZS suspension passing over the speed hump is considerably lower than a vehicle with a conventional linear suspension. Wb weighted RMS of acceleration (BS 6841-1987) is also lower by as much as 14% for a vehicle with the QZS suspension travelling at 30 km/h on a class E road compared to its linear counterpart

Reducing Energy Use in Excavators with Biodiesel

In assessing the life-cycle cost of a building, the operation energy and construction energy are considered. The operation energy constitutes 90 to 95 percent of the lifetime energy use of a building. Concern over reducing operation energy has led to advancements where many buildings can now be considered net zero. While considerable advancements were made in achieving net zero in the operation, construction energy use has largely remained the same. To achieve net zero for the entire life-cycle of the building, construction energy consumption needs to be reduced. Excavators are one of the most popular pieces of construction equipment. They are primarily run off diesel fuel which is a nonrenewable resource. Biodiesel is currently offered on the market in different blends. These blends combine alcohol with vegetable or animal oils to create a renewable fuel source. This report will examine if biodiesel can be a viable replacement to traditional diesel used in excavators, and ultimately reduce construction energy

Exploiting nonlinearity in a flapping wing mechanism of a bio inspired micro air vehicle to enhance energy effiency

Flying insect have evolved over thousands of years and have become efficient flying machines. They served as a source of inspiration for mini and micro unmanned air vehicles. For example, the aerodynamics and kinematic of the flapping wings are well investigated and it is shown that the flapping wings can produce higher lifts than fixed wing alternatives of similar sizes. In most of the insects, the flight muscles are not directly connected to the wings but they cause a deformation of the thorax. The movement of the thorax transfers to the wings through a complex mechanism. Different models are suggested for the wing-muscle interface [1] but its exact function yet still to be explored. The common theme between different models is the nonlinearity in restoring force of the “flight mechanism”. The benefit of such a nonlinear mechanism is attributed to an increase in the kinetic energy of the wings [2,3], modulation of the flapping amplitude [1] and an increase in the flapping speed during half of the flapping cycle [4]. One of the issues that is overlooked in the previous studies is the reactive power requirement which can be attributed to the forces requires for acceleration of masses and deformation of elastic elements of the system from a mechanical point of view. In theory, the energy attributed to the reactive power will return to the source in a cycle. However, it will increase energy loss as most mechanical actuator do not have an energy recovery capability. A larger actuator is also required to compensate the reactive power requirement. A nonlinear flight mechanism is investigated in this study in order to establish the power requirement of a flapping wing micro aerial vehicle. A lumped parameter model in form of a Duffing oscillator is used in this study as a simplified model of a flapping wing aerial vehicle. The generated lift is modelled by a linear damping term for the simplicity. The performance of the system for a range of parameters is evaluated and it is compared with a linear counterpart. The effect of the damping ratio on the ratio between reactive and active power is demonstrated. The reactive power will disappear at the natural frequency of a linear oscillator but it increases rapidly by any deviation in frequency from the natural frequency. For a nonlinear mechanism, the reactive power is lower at a wider frequency range than a linear mechanism although it never disappears at any frequency

Development of an Instrumented and Powered Exoskeleton for the Rehabilitation of the Hand

With improvements in actuation technology and sensory systems, it is becoming increasingly feasible to create powered exoskeletal garments that can assist with the movement of human limbs. This class of robotics referred to as human-machine interfaces will one day be used for the rehabilitation of paralysed, damaged or weak upper and lower extremities. The focus of this project was the development of an exoskeletal interface for the rehabilitation of the hands. A novel sensor was designed for use in such a device. The sensor uses simple optical mechanisms centred on a spring to measure force and position simultaneously. In addition, the sensor introduces an elastic element between the actuator and its corresponding hand joint. This will allow series elastic actuation (SEA) to improve control and safely of the system. The Hand Rehabilitation Device requires multiple actuators. To stay within volume and weight constraints, it is therefore imperative to reduce the size, mass and efficiency of each actuator without losing power. A method was devised that allows small efficient actuating subunits to work together and produce a combined collective output. This work summation method was successfully implemented with Shape Memory Alloy (SMA) based actuators. The actuation, sensory, control system and human-machine interface concepts proposed were evaluated together using a single-joint electromechanical harness. This experimental setup was used with volunteer subjects to assess the potentials of a full-hand device to be used for therapy, assessment and function of the hand. The Rehabilitation Glove aims to bring significant new benefits for improving hand function, an important aspect of human independence. Furthermore, the developments in this project may one day be used for other parts of the body helping bring human-machine interface technology into the fields of rehabilitation and therapy

Application of Smoothed Particle Hydrodynamics (SPH) in Nearshore Mixing: A Comparison to Laboratory Data

A weakly compressible smoothed particle hydrodynamics (WCSPH) method is used to simulate the nearshore flow hydrodynamics. The wave induced dispersion and diffusion are determined for monochromatic waves with significant wave height of 0.12 m and the wave period of 1.2 sec (Sop=5%) based on WCSPH wave dynamics. The hydrodynamics of WCSPH model are compared to the laboratory results obtained from series of LDA measurements. The overall mixing coefficients across the nearshore are determined from WCSPH hydrodynamics. The mixing coefficients obtained are compared with the values determined from a series of fluorometric studies performed in a large-scale facility in DHI, Denmark. The results show that the wave profiles are in good agreement with the experimental data. The WCSPH model is proven to be well capable of estimating the dispersion across the nearshore

SOLUTE DISPERSION IN THE NEARSHORE DUE TO OBLIQUE WAVES

An experimental study has been conducted in a large scale basin at Danish Hydraulic Institute (DHI). Simultaneous measurements of hydrodynamics using Laser Doppler Anemometry (LDA) and fluorescent tracer studies were undertaken within the surfzone under a regular wave condition with waves approaching the shore at 20. Through a series of hydrodynamic and tracer measurements and their comparison with the existing theoretical values, this study quantifies the physical processes and their integrated effects on a solute tracer in the nearshore zone subject to combined waves and the induced longshore currents. A theoretical dispersion model has been developed, adopting both experimental and theoretical velocimetry approaches. The results of theoretical model have been compared to the tracer data. Using the results from this study together with all known previous studies of dispersion measurements within the surfzone, good agreement exists

Approximate 2-dimensional Pexider Quadratic Functional Equations In Fuzzy Normed Spaces and Topological Vector Space

In this paper, we prove the Hyers-Ulam stability of the 2-dimensional Pexider quadratic functional equation in fuzzy normed spaces. Moreover, we prove the Hyers-Ulam stability of this functional equation, where f, g are functions defined on an abelian group with values in a topological vector space

Effect of asymmetry in the restoring force of the "click" mechanism in insect flight

The aim of this paper is to examine the effect of asymmetry in the force-deflection characteristics of an insect flight mechanism on its nonlinear dynamics. An improved simplified model for insect flight mechanism is suggested and numerical methods are used to study its dynamics. The range at which the mechanism may operate is identified. The asymmetry can lead to differences in the velocity in the upward and downward movements which can be beneficial for the insect flight