Browsing by Author "Goyder, Hugh"

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    Effect of wind turbulence on wind ballistic trajectory of a medium calibre weapon system
    (Cranfield University, 2023-10) Knight, Daniel; Simner, Dave; Goyder, Hugh; Helliker, Aimee
    Current ballistics and Fire Control Systems (FCS) use the assumption that crosswind located at the firing point will be constant between firing point and target location. The single constant crosswind value is then used to calculate the ballistic drift offset required to correctly engage a target at range and maintain an accurate firing solution. Variations in crosswind speed and direction are not considered by FCS but are known to cause drift errors in flight and offset the resulting impact point, the error is commonly known as gustiness. Applying a variable crosswind drift correction for both time of flight and projectile height could produce an improved result by considering variations in the crosswind dynamics. Using multiple crosswind sensors at difference heights, a wind gradient curve can be produced to model wind turbulence and speed variations in reference to the projectile trajectory height. Similarly, changes in the crosswind can be modelling against the engagement timeline to show gustiness in relation to the time of flight of the projectile. The accuracy and performance of the new ballistic model can be measured against the NATO standard coincidence window, which is used to evaluate FCS accuracy. The NATO error window of 0.3 mrads can be used to measure the probability of hit between the current constant crosswind and the new variable crosswind FCS model (US Army Aberdeen Test Center, 2009b). Using a reference tank target at a nominal distance of 2,000 meters, gives a coincidence window requirement of 60 cm square located on target centre mass. The thesis found for the reference projectile used, a 40CTAS 40 mm round (CTA International, 2018b), that the FCS accuracy could be improved by 10.95% when including variations in the crosswind. The probability of hit inside the NATO coincidence window is improved to 56.16% when using crosswind at the instant of firing, compared to holding a single constant value during the engagement timeline. It was also found that dynamic crosswind conditions can be included and modelled into a Point Mass Ballistic Model. Variations in the crosswind gradient curve can be used to assess turbulence and change in wind conditions. The wind gradient curve also demonstrates that wind conditions are not constant in relation to both time and height above ground, during an engagement sequence.
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    Experimental investigation of the nonlinear dynamic behaviour of bolted lap joints
    (2019-04) Lancereau, Damien Paul Thibaut; Goyder, Hugh; Purdy, David J.
    The physics behind the vibration of joints is currently unknown and therefore unpredictable. Consequently in sensitive structures, like aircraft or turbines, prototype testing is necessary to evaluate the dynamic behaviour and avoid catastrophic failures. The thesis objective is to reduce the unpredictability by identifying the dominant parameters linked to bolted lap joint nonlinear behaviour. This study has found that the size of the interface had the most impact. A large interface creates a receding contact which created an amplitude dependent damping and stiffness. In contrast, a small interface creates a complete contact, with limited nonlinear behaviour. In-between interface sizes involved a lock-up which was interpreted as amplitude dependent slip or bound regions in the lap joint interface. Accordingly, the bending moment dynamic loading at the joint location is correlated to the nonlinear behaviour, only if there is a receding contact. This correlation between bending and damping was interpreted as a rolling effect with a changing contact patch during a cycle of vibration, which creates a specific behaviour in different regions of the lap joint interface. An experimental approach was used to reach these conclusions. The use of shims allowed the comparison of seven sizes of interfaces on the same structure. Then, a novel method was developed to measure the effect of a receding contact at 18 joint locations, by placing or removing washer-size-shims in a beam with 18 identical lap joints. Hammer impact excitation allowed the 12 first bending modes to be measured with minimum interference. The decaying vibration time histories were filtered and fitted in the time domain, using novel signal processing methods, to extract the amplitude dependant damping ratio and natural frequencies. Also, a finite element simulation enabled the natural frequency to be predicted, using an approximated contact patch.
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    Models for the Dynamic Simulation of Tank Track Components
    (Cranfield University, 2006-01) Allen, P.; Hameed, Amer; Goyder, Hugh
    This project has been sponsored by QinetiQ Limited (QinetiQ); whose aim it is to model the dynamics of a prototype high-speed military tracked vehicle. Specifically their objective is to describe the mechanism by which force inputs are transmitted from the ground to the vehicle’s hull. Many track running gear components are steel and can be modelled as simple lumped masses or as linear springs without internal damping. These present no difficulty to the modeller. However tracked vehicle running gear also has nonlinear components that require more detailed descriptions. Models for two rubber components, the road wheel tyre and track link bush, and a model for the suspensions rotary damper, are developed here. These three components all have highly nonlinear dynamic responses. Rubber component nonlinearities are caused by the materials nonlinear elastic and viscoelastic characteristics. Stiffness is amplitude dependent and the material exhibits a significant amount of internal damping, which is predominantly Coulombic in nature but also relaxes overtime. In this work, a novel method for measuring the elastic and viscoelastic response of Carbon Black Filled Natural Rubber components has been devised and a ‘general purpose’ mathematical model developed that describes the materials response and is suited to use in multibody dynamic analysis software. The vehicle’s suspension rotary damper model describes three viscous flow regimes (laminar, turbulent and pressure relief), as a continuous curved response that relates angular velocity to damping torque. Hysteresis due to the compression of entrapped gas, compliance of the dampers structure and compression of damper oil is described by a single non-parametric equation. Friction is considered negligible and is omitted from the model. All components are modelled using MSC.ADAMS TM multibody dynamic analysis software. The models are shown to be easily implemented and computationally robust. QinetiQ’s requirement for ‘practical’ track running gear component models has been met.