Lentokoneen päälaskutelineen iskunvaimentimen mallinnus ja simulointi

Every traditional aircraft has a shock absorber in its main landing gear. A shock absorber takes the brunt of the shock imparted to the landing gear, absorbs it and dissipates the kinetic energy. This thesis is based on the construction of a realistic analytical model of an oleo-pneumatic shock absorber for a combat aircraft. The governing equations presented here include the effects of friction, gas spring and damping, among other things. The model was validated with a wide range of reference data, which revealed exceptionally high friction levels detected during the validation process. The reference data consists of measurements from a static test bench, a dynamic test system and an actual aircraft landing, and the corresponding simulations are presented in this thesis. The results of the simulations closely match the measured data. The effects of variations in the gas-liquid ratio and temperature on the pressure behaviour inside the shock absorber were simulated. If the gas-liquid ratio is distorted, the damping ability of the shock absorber is diminished, which may lead to faulty operation of the landing gear. Temperature variation was examined in two ways, firstly by varying the initial temperature and secondly, by heating and cooling the shock absorber. Filling the shock absorber in conditions which differ from the environment in which the aircraft will operate causes the pressure to decrease or increase, depending on whether the shock absorber is cooled or heated. The utilization of simulations as a tool in condition monitoring and fault detection is discussed, and as a result of that a new measuring instrument is proposed, whose design can be facilitated with this simulation model. Although the model presented in this thesis is not complete, it adequately mirrors the behaviour of the gas spring and the metering bin. However, the model does not include the deformations caused by high pressures. A number of possible improvements to the model are presented and discussed. In its present form, the load-stroke behaviour of the model is close to the real shock absorber, and the model can be used to analyse the forces and pressures generated by different shocks. Future work will involve improving the model and incorporation of the model into a larger main landing gear model so that a comprehensive investigation of the dynamics of an aircraft landing can be performed

Equations of State in Fighter Aircraft Oleo-pneumatic Shock Absorber Modelling

Most of all modern commercial and military aircraft have oleo-pneumatic shock absorbers in their landing gear. An oleo-pneumatic shock absorber consists of a gas charge and an oil fill. During the stroke oil is forced through orifices which provides damping, while the gas charge is compressed and acts as a spring by increasing the stiffness of the shock absorber. Typically, when the gas behaviour is modelled, the ideal gas law is used as the equation of state as this provides in most cases adequate fidelity with relatively light computational load. However, in a fighter aircraft, especially in naval service, the gas pressure inside a shock absorber raises too high during landing for the ideal gas assumption to be valid. Therefore, other well-established equations of state have been considered. These are Van der Waals, Redlich-Kwong-Soave, and Peng-Robinson equation of state. This paper presents a multi-physics simulation model of a two-chamber oleo-pneumatic shock absorber based on fundamental analytical equations. Using this model, the behaviour of the aforementioned equations of state are studied in two cases: quasi-static and dynamical compression. The simulation results are compared to laboratory measurements. This comparison verifies that the ideal gas law should not be used when modelling naval fighter aircraft shock absorbers.publishedVersionPeer reviewe

Lentokoneen päälaskutelineen iskunvaimentimen mallinnus ja simulointi

Every traditional aircraft has a shock absorber in its main landing gear. A shock absorber takes the brunt of the shock imparted to the landing gear, absorbs it and dissipates the kinetic energy. This thesis is based on the construction of a realistic analytical model of an oleo-pneumatic shock absorber for a combat aircraft. The governing equations presented here include the effects of friction, gas spring and damping, among other things. The model was validated with a wide range of reference data, which revealed exceptionally high friction levels detected during the validation process. The reference data consists of measurements from a static test bench, a dynamic test system and an actual aircraft landing, and the corresponding simulations are presented in this thesis. The results of the simulations closely match the measured data. The effects of variations in the gas-liquid ratio and temperature on the pressure behaviour inside the shock absorber were simulated. If the gas-liquid ratio is distorted, the damping ability of the shock absorber is diminished, which may lead to faulty operation of the landing gear. Temperature variation was examined in two ways, firstly by varying the initial temperature and secondly, by heating and cooling the shock absorber. Filling the shock absorber in conditions which differ from the environment in which the aircraft will operate causes the pressure to decrease or increase, depending on whether the shock absorber is cooled or heated. The utilization of simulations as a tool in condition monitoring and fault detection is discussed, and as a result of that a new measuring instrument is proposed, whose design can be facilitated with this simulation model. Although the model presented in this thesis is not complete, it adequately mirrors the behaviour of the gas spring and the metering bin. However, the model does not include the deformations caused by high pressures. A number of possible improvements to the model are presented and discussed. In its present form, the load-stroke behaviour of the model is close to the real shock absorber, and the model can be used to analyse the forces and pressures generated by different shocks. Future work will involve improving the model and incorporation of the model into a larger main landing gear model so that a comprehensive investigation of the dynamics of an aircraft landing can be performed

Early stage design of a spherical underwater robotic vehicle

This paper presents a high performance autonomous underwater robot under development for inspection of flooded mines up to 500 meters depth. Underwater robots have multiple advanced subsystems and mechanisms. Initial structure design of subsystems and their functions are demonstrated here briefly. In addition, Hydrodynamic coefficients that contribute to robot equation of motion are addressed. The advantage of utilizing spherical design is verified by applying simplification to determine the main coefficient of motion theoretically.acceptedVersionPeer reviewe

Digital twin:Multi-dimensional model reduction method for performance optimization of the virtual entity

Digital Twin (DT) is an emerging technology that allows manufacturers to simulate and predict states of complex machine systems during operation. This requires that the physical machine state is integrated in a virtual entity, instantaneously. However, if the virtual entity uses computationally demanding models like physics-based finite element models or data driven prediction models, the virtual entity may become asynchronous with its physical entity. This creates an increasing lag between the twins, reducing the effectiveness of the virtual entity. Therefore, in this article, a model reduction method is described for a graph-based representation of multi-dimensional DT model based on spectral clustering and graph centrality metric. This method identifies and optimizes high-importance variables from computationally demanding models to minimize the total number of variables required for improving the performance of the DT.publishedVersionPeer reviewe

Finite element modelling of temperature in cylindrical grinding for future integration in a digital twin

This paper focuses on finite element modelling of temperature field in cylindrical grinding. The developed model is validated against two established and validated thermal models in cylindrical grinding. The models' results are compared in terms of suitability for a digital twin application. The computation time requirement for a real-time temperature estimator in grinding digital twin is defined. The FEM model offers the most fidelity, but computational demands prevent its use in a digital twin. Therefore, the need for coupling the FEM model with an AI-based approaches for future work is highlighted to achieve temperature estimation within the wheel contact time.publishedVersionPeer reviewe

Evidential Reasoning based Digital Twins for Performance Optimization of Complex Systems

Digital twins (DTs) are fast becoming an important technology in manufacturing companies for predicting failures of critical assets. However, such a digital twins is a hybrid representation with multiple parameters which need to be monitored to predict complex phenomena occurring in the asset in real time. This high-fidelity model of the twin makes the computation of the output extensive. Therefore, it is necessary to develop model reduction methods that simplify the high-fidelity model for faster computation with an acceptable degree of error. Such a method was proposed in previous studies to identify important nodes in graph-based DT representation. This article provides an improvement of previous method, considering the uncertainty in important node selection with Dempster-Shafer Theory (DST). The method is demonstrated with a grinding case study.publishedVersionPeer reviewe

Mechatronic Architecture Development of UX-1

This paper presents novel design of underwater robot for exploring abandoned mines. The hazardous environment of such mines due to unknown hydrodynamic forces and faulty navigations, brings the need of developing a reliable system able to be controlled autonomously. This capability highly rely on the basis of low level control and mechatronic architecture of the robot which demonstrate robot potential for performing real-time operations. Following, describes rapid prototyping during development phase of the robot. Further, it investigates on mechatronic development of main controller unit, propulsion system and ballast.acceptedVersionPeer reviewe

Mechanical subsystems integration and structural analysis for the autonomous underwater explorer

The aim of this study is to analyse the modular mechanical design and integration of all three low-level modules in UX-1 (pendulum, ballast system and propulsion unit). The components of the perception and navigation systems have position and orientation requirements that dictate the shape of the hull. A structural strength analysis using Finite Element Method (FEM) was made to study the hull strength during deep dives. The results are presented here, which indicates that the hull endures pressures related to deep dives. Also for validation, strain gauge locations were defined.acceptedVersionPeer reviewe