Dynamic impact of ageing dump truck suspension systems on whole-body vibrations in high-impact shovel loading operations

Surface mining operations typically deploy large shovels, with 100+ tons per pass capacity, to load dump trucks in a phenomenon described as high-impact shovel loading operations (HISLO). The HISLO phenomenon causes excessive shock and vibrations in the dump truck assembly resulting in whole body vibration (WBV) exposures to operators. The truck suspension system performance deteriorates with time; therefore their effectiveness in attenuating vibrations reduces. No research has been conducted to study the impact of ageing suspension mechanisms on the magnitudes of WBV in HISLO operations. This study is a pioneering effort to provide fundamental and applied knowledge for understanding the impact of ageing on the magnitudes of WBV exposures. The effects of underlying ageing processes on a suspension performance index are mathematically modeled. The effects of scheduled maintenance and corrective maintenance on improving the performance index (PI) are also modeled. Finally, the proposed mathematical ageing model is linked to the truck operator\u27s exposure to WBVs via a virtual prototype CAT 793D truck model in the MSC ADAMS environment. The effects of suspension system ageing in increasing the WBV levels are examined in the form of both the vertical and horizontal accelerations under HISLO conditions. This study shows that the hydro-pneumatic suspension strut ageing results in deteriorating stiffness-damping parameters. The deteriorating suspension performance (with time) introduces more severe and prolonged WBVs in HISLO operations. The RMS accelerations increase significantly with time (suspension ageing). The vertical RMS accelerations increase to severe magnitudes of over 3.45, 3.75, and 4.0 m/s2 after 3, 5, and 7 years, respectively. These acceleration magnitudes are well beyond the ISO limits for the human body\u27s exposure to WBVs. This pioneering research effort provides a frontier for further research to provide safe and healthy working environments for HISLO operations --Abstract, page iii

Modeling Predictors of Whole Body Vibration Exposure among Saskatchewan Farmers: a Key Step in Low Back Disorder Prevention

Background Farmers experience a high rate of low back pain (LBP), with a lifetime prevalence of up to 75%. Whole body vibration exposure has been recognized as a significant physical risk factor associated with LBP. The agriculture sector has high whole body vibration exposures related to various machine types; however, little research has assessed vibration exposure in farming due to the inconvenience and cost of direct data collection. Prediction modelling is potentially a cost-efficient way to estimate directly measured exposure. Objectives The objectives of this study are to 1) measure the physical exposure of whole body vibration in Saskatchewan farmers and understand its magnitude and variability between farm machinery; and 2) use farm, vehicle, and task characteristics to determine any predictive relationship with directly-measured whole body vibration exposures among Saskatchewan farmers. Methods A 1-year field study with 3 repeated farm visits was conducted for whole body vibration measurements on 21 farms within a 400 km distance of Saskatoon. Whole body vibration was assessed using a tri-axial accelerometer embedded in a standard rubber seat pad according to international standards (ISO 2631-1). Whole body vibration data were summarized by machinery type into standardized metrics of root-mean-squared accelerations (RMS), peak, crest factor, and vibration dose value (VDV). Vehicle characteristics were gathered by on-site observations supplemented by open access vehicle descriptions through manufacturers. Farm characteristics and farmer’s self-reported whole body vibration exposure were collected via questionnaires. A manually stepwise method was conducted to build mixed-effects models for both RMS and VDV outcomes. Results A total of 87 whole body vibration measurements were gathered from 8 machine types: tractor, combine, pickup truck, grain truck, sprayer, swather, all-terrain vehicle, and skid steer. The average measurement duration was 85 minutes. The mean vector sums were RMS 0.78 m/s², peak 19.34 m/s², crest factor 27.64, and VDV 10.02 m/s1.75. The fixed effects of ‘horsepower’, ‘vehicle transmission type’, ‘farm size’, and ‘farm commodity’ explained 44% of the variance in RMS; while ‘horsepower’, ‘seat suspension type’, ‘loading frequency’, ‘tire tread type’, ‘jerk/jolt frequency’, ‘seat bottom-out frequency’, ‘farm commodity’, and ‘farm size’ explained only 20% of VDV variance. Conclusion High mechanical vibration and shocks from a range vehicle types call for action to reduce agricultural whole body vibration. Although VDV is relatively difficult to predict through farm and vehicle features collected in the present study, RMS can be predicted to a moderately useful degree. Predictors identified via modeling can help explain the variances of whole body vibration exposures and may also serve as new surrogates for future whole body vibration exposure assessment

Ambulance Vibration Suppression via Force Field Domain Control

This PhD dissertation experimentally characterized the vibration amplitude, frequency, and energy associated with ambulance travel and defined the relationship of the vibration to safety, comfort and care of ambulance patients. Average vertical vibration amplitudes of .46 to 2.55 m/sec2 were recorded in the patient compartment of four ambulances over four road surfaces at three speed settings. Power spectrum analysis of the data revealed that the vibration energy and resulting vertical acceleration forces were concentrated in the .1 to 6 Hz range. Relationships between the measured ambulance vibration and the impact of whole body vibration on human physiology and performance were quantified. It was found that the accelerations measured in the ambulances were in excess of what is considered to be a normal human comfort level. Furthermore, the vibration measured was in a spectrum which could present physical impediments to optimum task performance for the on-board medical team. Phase portrait analysis combined with the power spectrum data revealed the presence of nonlinearities, stochastic fluctuations and time delays inherent in the data. The ambulance vibration data was then used to create a unique analytical model and library of forcing functions corresponding to the vehicles, road surfaces and vehicle speeds that were tested. Using the example of a vibration absorbing force plate fit over an existing ambulance floor, it was demonstrated how the model and forcing functions could be used to develop a control law equation to select parameters for active control of vibration to produce sustainable regions of patient safety, comfort and care

Magneto-rheological (MR) damper for landing gear system

Depending on the different sink speeds, angles of attack and masses; aircraft landing gears could face a wide range of impact conditions which may possibly cause structural damage or failure. Thus, in hard landing scenarios, the landing gear must absorb sufficient energy in order to minimize dynamic stress on the aircraft airframe. Semi-active control systems are the recent potential solutions to overcome these limitations. Among semi-active control strategies, those based on smart fluids such as magneto-rheological (MR) fluids have received recent attraction as their rheological properties can be continuously controlled using magnetic or electric field and they are not sensitive to the contaminants and the temperature variation and also require lower powers. This thesis focuses on modeling of a MR damper for landing gear system and analysis of semi-active controller to attenuate dynamic load and landing impact. First, passive landing gear of a Navy aircraft is modeled and the forces associated with the shock strut are formulated. The passive shock strut is then integrated with a MR valve to design MR shock strut. Here, MR shock strut is integrated with the landing gear system modeled as the 2DOF system and governing equations of motion are derived in order to simulate the dynamics of the system under different impact conditions. Subsequently the inverse model of the MR shock strut relating MR yield stress to the MR shock strut force and strut velocity is formulated. Using the developed governing equations and inverse model, a PID controller is formulated to reduce the acceleration of the system. Controlled performance of the simulated MR landing gear system is demonstrated and compared with that of passive syste

Transportation noise pollution - Control and abatement

Control and abatement of transportation noise pollutio

On the application of finite element analysis to wave motion in one-dimensional waveguides

This thesis considers issues concerning the application of the wave finite element (WFE) method to the free and forced vibrations of one-dimensional waveguides. A short section of the waveguide is modelled using conventional finite element (FE) methods. A periodicity condition is applied and the resulting mass and stiffness matrices are post-processed to yield the dispersion relations and so on. First, numerical issues are discussed and methods to reduce the errors are proposed. FE discretisation errors and errors due to round-off of inertia terms are described. A method using concatenated elements is proposed to reduce those round-off errors. Conditioning of the eigenvalue problem is discussed. An application of singular value decomposition is proposed to reduce errors in numerically determining eigenvectors together with Zhong’s formulation of the eigenvalue problem. Effects of the modelling of the cross-section on conditioning are shown. Three methods for numerically determining the group velocity are compared and the power and energy relationship is seen to be reliable. The WFE method is then applied to complicated structures and its accuracy evaluated. Dispersion curves are shown including purely real, purely imaginary and complex wavenumbers. Free wave propagation in a plate strip with free edges, a ring and a cylindrical strip is predicted and the results compared with analytical or numerical solutions to the analytical dispersion equations. In particular, dispersion curves for freely propagating flexural waves, including attenuating waves, are presented. Complicated phenomena such as curve veering, non-zero cut-on phenomena and bifurcations are observed as results of wave coupling in the wave domain. A method of decomposition of the power is proposed to reduce the size of the system matrices and to investigate the wave characteristics of each wave mode. The wave approach is then used to predict the forced response. A well-conditioned formulation for determining the amplitudes of directly excited waves is proposed. The forced response is determined by considering wave propagation and subsequent reflection at boundaries. Numerical examples of a beam, a plate and a cylinder are shown. Inclusion of rapidly decaying waves is discussed. As a practical application, free and forced vibrations of a tyre are analysed. The complicated cross-section of a tyre is modelled using a commercial FE package. Frequency dependent material properties of rubber are included. Free wave propagation is shown including attenuating waves and predicted responses are compared with experiment. Effects of the size of the excited region are discussed

Hybrid Electromagnetic Vibration Isolation Systems

Traditionally, dynamic systems are equipped with passive technologies like viscous shock absorbers and rubber vibration isolators to attenuate disturbances. Passive elements are cost effective, simple to manufacture, and have a long life span. However, the dynamic characteristics of passive devices are fixed and tuned for a set of inputs or system conditions. Thus in many applications when variation of input or system conditions is present, sub-optimal performance is realized. The other fundamental flaw associated with passive devices is that they expel the undesired kinetic energy as heat. Recently, the introduction of electromagnetic technologies to the vibration isolation systems has provided researchers with new opportunities for realizing active/semi-active vibration isolation systems with the additional benefit of energy regeneration (in semi-active mode). Electromagnetic vibration isolators are often suffer from a couple of shortcomings that precludes their implementations in many applications. Examples of these short comings include bulky designs, low force density, high energy consumption (in active mode), and fail-safe operation problem. This PhD research aims at developing optimal hybrid-electromagnetic vibration isolation systems to provide active/semi-active and regenerative vibration isolation for various applications. The idea is to overcome the aforementioned shortcomings by integrating electromagnetic actuators, conventional damping technologies, and stiffness elements into single hybrid packages. In this research, for both semi-active and active cases, hybrid electromagnetic solutions are proposed. In the first step of this study, the concept of semi-active hybrid damper is proposed and experimentally tested that is composed of a passive hydraulic and a semi-active electromagnetic components. The hydraulic medium provides a bias and fail-safe damping force while the electromagnetic component adds adaptability and energy regeneration to the hybrid design. Based on the modeling and optimization studies, presented in this work, an extended analysis of the electromagnetic damping component of the hybrid damper is presented which can serve as potent tool for the designers who seek maximizing the adaptability (and regeneration capacity) of the hybrid damper. The experimental results (from the optimized design) show that the damper is able to produce damping coefficients of 1300 and 0-238 Ns/m through the viscous and electromagnetic components, respectively. In particular, the concept of hybrid damping for the application of vehicle suspension system is studied. It is shown that the whole suspension system can be adjusted such that the implementation of the hybrid damper, not only would not add any adverse effects to the main functionally of the suspension, but it would also provide a better dynamics, and enhance the vehicle fuel consumption (by regenerating a portion of wasted vibration energy). In the second step, the hybrid damper concept is extended to an active hybrid electromagnetic vibration isolation systems. To achieve this target, a passive pneumatic spring is fused together with an active electromagnetic actuator in a single hybrid package. The active electromagnetic component maintains a base line stiffness and support for the system, and also provides active vibration for a wide frequency range. The passive pneumatic spring makes the system fail-safe, increases the stiffness and support of the system for larger masses and dead loads, and further guarantees a very low transmissibility at high frequencies. The FEM and experimental results confirmed the high force density of the proposed electromagnetic component, comparing to a voice coil of similar size. In the proposed design, with a diameter of ~125 mm and a height of ~60 mm, a force variation of ~318 N is obtained for the currents of I=±2 A. Furthermore, it is demonstrated that the proposed actuator has a small time constant (ratio of inductance to resistance for the coils) of less than 5.2 ms, with negligible eddy current effect, making the vibration isolator suitable for wide bandwidth applications. According to the results, the active controllers are able to enhance the performance of the passive elements by up to 80% and 95% in terms of acceleration and force transmissibilities, respectively

An analysis of the prevalence of musculoskeletal disorders in heavy, civil construction operations and the impact of job, age, and experience

Includes bibliographical references

Structures and Dynamics Division research and technology plans for FY 1894 and accomplishments for FY 1982

The Objectives, Expected Results, Approach, and Fiscal Year FY 1984 Milestones for the Structures and Dynamics Division's research programs are examined. The FY 1983 Accomplishments are presented where applicable