Case Studies in Mechanical Systems and Signal Processing最新文献

The study deals with an experimental campaign to analyze the effects on an automatic machine for plastic cap assembly of the increased vibrations occurring when speeding up its operation. The new velocity specifications are required by the machine manufacturer for raising the production capacity. The analysis successfully identified the functional units critically affected by elastodynamic issues related to the speed increment. Hence it permitted to focus the redesign process on the critical groups in order to implement the desired machine upgrade by means of limited modifications to the current machine version. The most relevant experimental results are presented and discussed. The paper also reports data provided by further tests carried out on a machine variant (obtained after the implementation of the first design modifications), which prove the effectiveness of the proposed solutions to improve the machine performance.

The diagnosis of bearing faults at the earliest stage is critical in avoiding future catastrophic failures. Many diagnostic techniques have been developed and applied in for such purposes, however, these traditional diagnostic techniques are not always successful when the bearing fault occurs within a gearbox where the vibration response is complex; under such circumstances it may be necessary to separate the bearing vibration signature.

This paper presents a comparative study of four different techniques for bearing signature separation within a gearbox. The effectiveness of these individual techniques were compared in diagnosing a bearing defect within a gearbox employed for endurance tests of an aircraft control system. The techniques investigated include the least mean square (LMS), self-adaptive noise cancellation (SANC) and the fast block LMS (FBLMS). All three techniques were applied to measured vibration signals taken throughout the endurance test. In conclusion it is shown that the LMS technique detected the bearing fault earliest.

The deformation of parts of a tire is the direct result of tire–road interactions, and therefore is of great interest in tire sensor development. This case study focuses on the analysis of the deformation of the tire carcass and investigates its potential for the estimation of the in-plane tire force. The deformation of the tire carcass due to applied steady-state in-plane forces is first analyzed with the flexible ring model and then validated through optical tire sensor measurements. Coupled deformations of the tire carcass in the radial and tangential directions are observed. This reveals a promising method for tire sensing applications in the estimation of the in-plane tire force, which relies only on direct measurements of the radial deformation of the tire carcass. Moreover, indicators are proposed to correlate the radial deformation of the tire carcass with in-plane tire forces.

Gearbox failure is one of the highest risk events in wind turbines. In most of the wind turbines, planetary gearboxes are preferred over conventional gearboxes due to their significant advantages. But condition monitoring of planetary gearboxes present a huge challenge to the vibration analysts due to complex design and construction of its unit, vibration transducer type and locations, wide frequency range of the vibrations, resolution required to separate frequencies and dynamic range required to observe both low frequency and high frequency components in the spectrum.

Due to strong Gear Mesh Frequency (GMF) signals, gear defect vibration characteristics can often be suppressed in the overall vibration signal. So there is a need to develop or utilize various special signal processing techniques in order to identify and monitor the progression of defects in gears more effectively.

This paper focuses on one such technique namely Sideband Energy Ratio (SER) for monitoring of gear defect progression in wind turbine gearboxes. Theory behind SER is and its significance in gear defect monitoring is presented in this paper through three case studies. In all the three case studies, SER of 2XGMF were found to be more sensitive than 1XGMF towards gear defect progression.

In this paper, concepts are investigated for tuning material properties and component configurations in order to design structures with unique dynamic characteristics for mitigating blast loads while maintaining or reducing weight. The dynamic response index (DRI) is employed as an occupant injury metric for determining the effectiveness of each blast mitigation configuration that is considered. A finite element model of a notional V-hull structure is used as a numerical example in this study. The material properties and the configuration of the inner bulkheads that connect the V-shaped outer surface with the inner floor are used as design parameters for reducing the DRI at a typical occupant location. In this particular example, it is demonstrated that both the weight of the structure and the DRI can be reduced simultaneously. This is achieved by creating a new structural design that features energy absorbing and decoupling mechanisms among the bulkheads, floor, seat, and the occupant.

This paper proposes a low-cost, high precision and efficient throttle-less hydraulic circuit that utilizes off-the-shelf industrial elements to control single rod hydraulic cylinders. The circuit uses an on/off solenoid valve to redirect the differential flow of a single rod hydraulic cylinder, and two counterbalance valves to manage switching (resistive–assistive) loads. Conducted experiments on a prototype system indicated a maximum steady state positional error of 0.2 mm. The circuit consumes only 20% of energy that is required by a valve controlled circuit to follow the same tracking signal. A simple proportional controller, that uses readings of a linear position transducer, is employed for all experiments, which makes the designed circuit easy to be implemented.

The increasing importance of human joints study as complex mechanical systems involves medical data processing, system fluid dynamic modelling and the establishing of reliable boundary conditions. Understanding the dynamical behaviour of joints is crucial to face prosthesis design and the associated research. This process is presented in a case study of the human ankle joint. From a proper medical image segmentation, bone surfaces are 2D-modelled as constant curvature surfaces (circles) under different criteria. The fluid dynamic problem is solved under different boundary conditions. Finally, the pressure field is obtained inside the joint and the sensitivity of the system with respect to the fitting methodology is consequently analyzed. Concluding remarks outline the findings for practical use in system study.

In the automotive field, size optimization procedures can be combined with concept modelling approaches, in order to design a vehicle Body-In-White (BIW) model with optimal static and dynamic performances already in the early design stages. However, this specific optimization problem, with hundreds of design variables, limited design space and often conflicting objectives, makes the choice of the appropriate optimization method really difficult. The aim of this paper is to show an industrial case study, where two different implementations of the classical gradient-based (GB) method are used in combination with a technique for vehicle body concept modelling to achieve a multi-objective BIW optimization of a passenger car.

Small experimental test-rigs are often used to investigate active vibration control concepts in the laboratory because of ease of construction and implementation. However, in marine applications, there is a large gap between this type of experiment and full-scale implementation onboard a ship. In this article a large-scale laboratory based active vibration control system is demonstrated. It involves a floating raft system attached to a hull-like structure by way of four hydraulic actuators, which are placed in parallel with eighteen passive resilient isolators. The flexible hull-like structure is supported on twenty six pneumatic springs to simulate a floating ship. A decentralized feedforward control strategy was implemented resulting in the reduction of vibration levels on the flexible hull-like receiving structure of up to 36 dB at some tonal excitation frequencies. The passive isolation results in broadband control and is most effective at higher frequencies.