The drilling industry has been suffering from huge monetary losses and non-productive time due to wear and fatigue of the drill string components. Vibration mitigation plays a pivotal role in extending the life of drill string components. The development of a comprehensive drill string vibration model will help in classifying the causes of drill string vibrations and helps in planning pro-active measures to suppress it. In the past, researchers have developed models based on factors like drill string length, axial compression load, lateral loads, shear deformation, rotary inertia and fluid damping. The four classical engineering vibration theories will be discussed in detail with the addition of fluid stiffness and fluid damping. This paper develops a drill string vibration model considering the effects of bending, translational inertia, rotary inertia, shear deformation, fluid stiffness and fluid damping. The drill string is considered as a cantilever beam of a circular cross-section immersed in water with equal pressure on both sides. The water is considered to be a spring and dash-pot model in parallel. It adopts a classical solution methodology based on D’Almbert’s principle. The eigen values, normalized mode shape, natural frequencies, orthogonality conditions and dynamic response equations are derived for all the theories. Natural Frequency and Dynamic response of the drill string are used to make informed decisions. Numerical simulation results show the influence of all the factors on vibration damping of the drill string. A critical understanding of the effects of all the above factors individually and in tandem will help in adopting a novel drilling strategy. To conclude, a complete step-by-step methodology for the proposed comprehensive drill string vibration model is put forth to determine the natural frequency and dynamic response of the drill string.

This paper presents a distributed current source (DCS) method for modeling the dynamic responses of eddy current density (ECD) induced in electrical conductors and its corresponding magnetic flux density (MFD); both nonmagnetic and weakly magnetized conductors are considered. Unlike conventional numerical methods such as finite element analysis (FEA), the DCS method, which accounts for the eddy-current and magnetization effects by means of equivalent volume and surface current-sources, derives closed-form solutions to the ECD and MFD fields in state-space representation. The model has been experimentally validated and verified by comparing results from FEA simulations with both harmonic and nonharmonic excitations. To gain physical insights to the measured MFD for simultaneous estimating the material/geometrical properties of a conductor, the static and dynamic responses to rectangular pulsed current excitations have been numerically investigated, confirming the feasibility and effectiveness of the measurement methods.

Curved beams are an essential structural form widely used in the engineering industry. When loaded past a critical point, they may buckle in a bifurcation or snap-through mode. Studies have shown that structural buckling problems are highly sensitive to slight changes in thermal properties. A shallow curved beam model subjected to a harmonic excitation is considered in this paper. A simplified, dimensionless one degree of freedom model is obtained following the works of [1]. Using this model, the transient dynamics of the system is analyzed for varying forcing parameters. The effect of the arch rise ( λ ) is also examined as the varying thermal properties effect the geometry of the beam system. Dynamic and transient dynamic responses of the system are obtained in the time domain for both constant and linearly varying λ . Wavelet analysis is utilized to analyze this data in the frequency domain and it provided an effective representation of the system responses that are localized in both time and frequency.

Super-coiled polymer (SCP), one of the newly-developed artificial muscles, has various advantages over traditional artificial muscles in terms of cost, flexibility and power-to-weight ratio. This paper investigates the performance of super-coiled polymer-based actuation in underwater robotics, and presents a novel design of robotic fish using antagonistic SCP actuators. Dynamic model of the robot is derived. An example robotic fish prototype is developed and used in experiments to study SCP actuation for underwater robots. Furthermore, experimental results show that using SCP actuators in robotic fish solves the challenging heat-dissipation problem at ease, thus improving the dynamic response of SCP actuation significantly. A PID controller is designed to regulate the tail flap angle of the designed robotic fish. Simulation results of the closed-loop system are presented to validate the proposed robot design and actuation approach.

This paper studies the use of an electric turbogenerator (ETG) for waste energy recovery from the exhaust gas of a 13 L Heavy Duty Diesel (HDD) engine. Up to 1% brake specific fuel consumption (BSFC) reduction is predicted for this system at high engine loads using a validated mean value engine model. However, the addition of the ETG reduces the air-fuel equivalence ratio (λ) and increases exhaust gas recirculation (EGR) rate by 10%, deteriorating the engine-out smoke emissions. This challenge is addressed by decreasing the EGR valve position and the asymmetry in the twin scroll turbine. With these modifications, the predicted high load BSFC reduction is 2% and the EGR and λ approach their original values. The HDD engine is then tested experimentally with the ETG emulated by a valve downstream of the main turbocharger. The experimental results confirm the simulation predictions with the stock engine calibration and geometry, where EGR valve sweeps show the potential of this actuator for remedying the detrimental ETG backpressure effects, which ultimately improves the combined engine and ETG BSFC by 0.6% at high loads. Combining the simulated turbo sizing and the experimental EGR valve results indicates that up to 1.6% BSFC reductions are possible for the HDD engine with an integrated ETG, without deteriorating emission levels. Finally, simulations show that during a torque step the ETG should be bypassed to avoid deterioration in the dynamic response of the engine.

The alarmingly degrading state of transportation infrastructures combined with their key societal and economic importance calls for automatic condition assessment methods to facilitate smart management of maintenance and repairs. In particular, scalable data-driven approaches is of great interest, because it can deal with large volume of streaming data without requiring models that can be inaccurate and computationally expensive to run. Properly designed, a data-driven methodology could enable fast and automatic evaluation of infrastructures, discovery of causal dependencies among various sub-system dynamic responses, and inference and decision making with uncertainties and lack of labeled data. In this work, a spatiotemporal pattern network (STPN) strategy built on symbolic dynamic filtering (SDF) is applied to explore spatiotemporal behaviors in bridge network. Data from strain gauges installed on two bridges are simulated by finite element method, and the causality among strain data in spatial and temporal resolutions is analyzed. Case studies are conducted for truck identification and damage detection from simulation data. Results show significant capabilities of the proposed approach in: (i) capturing spatiotemporal features to discover causality between bridges (geographically close), (ii) robustness to noise in data for feature extraction, and (iii) detecting and localizing damage via the comparison of behaviors within the bridge network.

Given the side effects and possible complications of current clinical treatments for severe pathological tremor, many researchers pursue the less invasive alternative of suppression at the musculo-skeletal level. In wearable robotics applications, the high strength-to-weight ratio, the low power consumption, and their adaptability allow magnetorheological (MR) fluid dampers and actuators to be personalized to the individual needs of a patient. Moreover, their rapid dynamic response makes them suitable for use in real time active devices. This paper presents the theoretical development and experimental validation of a tremor suppression control algorithm based on a dynamic lump parameter model of the MR damper and a real time adaptive tremor frequency estimator. The control strategy was experimentally evaluated using a one-DOF joint simulator. Experiments with ten datasets from patients with severe Parkinsonian and Essential Tremor show suppressions for the first and second harmonics of 28.7±2.2 dB and 11.8±4.8 dB, respectively. These results compare favorably with the suppression levels obtained by other researchers using constant current approach. In addition, the resistance that the orthotic device imposes to the voluntary motion was reduced by 33% under the active control strategy, while the power usage was dramatically reduced by nearly an order of magnitude.

The design and development of the rotating machinery require a precise identification of its dynamic response for efficient operation and failure prevention. Determination of critical speeds and mode shapes is crucial in this regard. In this paper, a finite element model (FEM) based on the Euler beam theory is developed for investigating the dynamic behavior of flexible rotors. In-house code in Scilab environment, an open source platform, is developed to solve the matrix equation of motion of the rotor-bearing system. The finite element model is validated by the impact hammer test and the dynamic testing performed on the rotors supported on a purpose-built experimental setup. Bearing stiffness is approximated by using the Hertzian contact theory. Obtaining the critical speeds and mode shapes further improves the understanding of dynamic response of rotors. This study paves way towards advanced research in rotordynamics in Faculty of Mechanical Engineering, GIK Institute.

A new method for road profile estimation in time domain with the application of vehicle system response was presented in this paper, and the problem was transformed as a system identification issue for an inverse nonlinear quarter vehicle model. Firstly, the inverse vehicle dynamic model was trained with specifically chosen white noise signal, and then eight different types of membership functions (MF) for Adaptive Neuro Fuzzy Inference System (ANFIS) were compared. Finally, the comparison of three different methods: ANFIS, Recursive Least Square (RLS) and Group Method of Data Handling (GMDH) were researched with different vehicle speeds and different road levels in the simulation part. The results showed that ANFIS is better in comparison with RLS and GMDH and this method can be further applied for vehicle system analysis.

Certain heavy-lifting applications require the coordinated movement of multiple cranes. Such tasks dramatically increase the complexity of crane operation, especially when the payload has a non-uniform shape. This paper studies the dynamic behavior of a dual-hoist bridge crane moving triangular payloads. Simulations and experiments are used to develop an understanding of the dynamic response of the system. Various inputs and system configurations are analyzed, and important response characteristics are highlighted.

Shaking table testing method is one of the main sources of experimental means to evaluate the dynamic response of structural systems under earthquake loads. The experimental technique produces nearly realistic prototype conditions, giving important insight into critical issues such as collapse mechanisms, component failures, acceleration amplifications, residual displacements and post-earthquake capacities. Traditional tuning of shaking table relies on the use of linear controllers, which are designed to regulate linear systems. With most of the specimens being tested to highly nonlinear states (to understand the structural response under extreme loads), traditional linear controllers can no longer control the shaking table effectively. This results in experimental errors between commanded and measured shaking table movements which may produce an unintended response of the tested structure. Ultimately, it may result in a pre-mature failure of the specimen. To address this issue, a Lyapunov–based nonlinear control algorithm is utilized to develop an enhanced shaking table control system, which is based on nonlinear models accounting for the nonlinear response of the hydraulic actuator and specimens. A one-sixth-scaled model has been developed and constructed in the laboratory at the University of British Columbia, Vancouver. Advanced nonlinear system identification techniques have been developed to create the numerical model capable of recreating the nonlinearity experienced by the laboratory setup. Simulation results indicate that the developed nonlinear control algorithm can be used to achieve excellent tracking, even when the tested structure behaves nonlinearly. The example also demonstrates the ability of the nonlinear controller to compensate for disturbances in the actuating force applied to the shaking table. Thus, the proposed nonlinear shaking table control algorithm is not only a viable alternative, but also a way to significantly improve the quality of shaking table tests.

Cranes are used in manufacturing facilities, throughout nuclear sites, and in many other applications for various heavy-lifting purposes. Unfortunately, the flexible nature of cranes makes fast and precise motion of the payload challenging and dangerous. Certain applications require the coordinated movement of multiple cranes. Such tasks dramatically increase the complexity of the crane operation. This paper studies the dynamic behavior of a dual-hoist bridge crane. Simulations and experiments are used to develop an understanding of the dynamic response of the system. Various inputs and system configurations are analyzed and important response characteristics are highlighted.

In many engineering applications, diagnostic techniques are needed to characterize the mechanical properties of internal components that are not readily visible at the surface of an object, as in the use of nondestructive testing to detect sub-surface damage in composite materials. Understanding the role of structural interfaces between two bodies is a key factor in developing these diagnostic techniques because the mechanical and geometric properties of the interface determine the degree to which measurements on the surface can be used to interrogate sub-surface components. In this paper, vibration measurements on a polycarbonate material, henceforth referred to as the buffer, are used to characterize the mechanical properties of a polymer particulate composite, henceforth referred to as the target, which is located beneath the buffer. To this end, a three-dimensional laser Doppler vibrometer and piezoelectric inertial actuator are used to measure the broadband response of the two-body structural dynamic system. Because of the importance of the actuator dynamics to the diagnostic measurements, a descriptive model is developed to better understand these dynamics and interpret the results. The longitudinal dynamics of the two-body system are shown to involve stronger coupling between the target and buffer materials as compared to the transverse dynamics. A Complex Mode Indicator Function is then used to extract the modal deflection shapes, and it is shown that the interface between the bodies introduces complexity in the dynamic response. Changes in the surface velocity of the buffer material are also studied as a function of a key mechanical property — the volume fraction of crystals in the target composite material. It is demonstrated that both the linear and nonlinear vibration characteristics of the buffer material change as a function of the composition of the target material, suggesting that a compositional diagnostic procedure is possible using surface vibration measurements.

Periodic structures generally consist of spatially repetitive substructures, which are very common in industrial applications such as turbo-machinery bladed disks. The dynamic responses of these structures are very sensitive to variations in geometry and material properties. Previous studies have shown that, when the substructure-to-substructure coupling is weak, even small variations (referred to as mistuning) among the substructures can cause drastic different in the vibratory response of a periodic structure. The goal of this research is to analyze the variation propagation from substructural properties to the dynamic response of the integral structure, and then inversely identify the design perturbation needed to reduce the response anomaly when such anomaly exceeds the allowable threshold. An order-reduced modeling approach is formulated to facilitate the efficient analysis of vibratory response of the integral structure, and several design perturbations are evaluated in order to reduce the response variations in an example periodic structure.

Passive joint compliance is a key feature of the human hand that plays an important role in realizing dexterous, precise and graceful movements. Our goal is to study the role of passive compliance in the human hand joints and develop ways for implementing human-like passive compliance in a robotic form. While a variety of factors influence joint stiffness in a tendon-driven system the focus of this paper is on investigating the effects of variation in moment arms, defined by the joint shape, on the joint stiffness characteristics. We present a method for analyzing the effects of variable moment arms on the joint stiffness variations and a mathematical technique to synthesize joint shapes based on the stiffness requirements. We study the role of variable passive stiffness by analyzing energy consumption and dynamic response with system models. We validate our theoretical results in shape synthesis with an experimental platform involving a single degree of freedom tendon driven joint. The analysis and results of our work have implications in the design of various robotic systems, including robotic hands, that seek to incorporate human-like joint stiffness characteristics.

This paper deals with a dynamic analysis of a racing kart considering an elastic deformation of the kart frame. As the first step of this research, an FEM kart frame model was validated by means of static and dynamic tests. In the static test, the strain on the kart frame caused by a steering operation was measured by strain gauges, and compared to the simulation result. The dynamic response of the frame was evaluated by hammering test, and the test result was compared to that of the modal analysis. Next, a flexible multibody vehicle model was developed with this FEM frame model. In this process, model reduction based on the modal analysis was applied to reduce the degree of freedom of the flexible body. Some running tests with actual racing kart were carried out to evaluate the handling characteristic, and the comparison between simulation and experiment are discussed.

Motivated by the interest to increase production throughputs of immersion lithography machines, wafers are scanned at increasingly high velocities and accelerations, which may result in liquid loss at the receding contact line. The dynamic characteristics of the immersion fluid with free boundary play an important role for fluid management system, and are concerned in various potential immersion unit designs. To offer intuitive insights into the dynamic effects of the immersion fluid due to scan speeds, a lumped-parameter model is developed to characterize the hydrodynamics of the immersion flow process. To validate the model, meniscus behavior information under dynamic conditions is extracted experimentally and analyzed using image processing techniques. The reduced model agrees qualitatively well with the experimental data revealing that parts of the surface tension have an effect on the dynamic response of the menisci similar to that due to a pure time delay in the system.

The subject of this paper is a VPVC (variable pressure valve-controlled) hydraulic actuation system, which is a hydraulic plant with variable supply pressure. The concept is similar to a load sensing system but it is implemented using an electronic controller, instead of a hydraulic one, and the flow is provided using a servo pump, instead of a variable displacement pump. The intention is to maintain a high dynamic response but substantially improve efficiency compared to a conventional system with fixed supply pressure. FPVC (fixed pressure valve-controlled) systems are unable to completely modulate the input energy due to the constant supply pressure. However, since the ability to control the energy flow is usually needed, a proportional valve for each actuator is used to dissipate the extra input energy. This leads to a simple but inefficient way to control, for example, the velocity of a piston. The idea of a VPVC system is that, instead of dissipating energy by throttling flow, it is better to generate less fluid power in the first place: this is achieved by adjusting the speed of the servo pump as well as the spool positions. In this paper, a controller for a VPVC system is presented along with numerical simulations showing a comparison with a fixed pressure system. Up to 70% energy saving is predicted.

One of the primary challenges in diagnostic health monitoring and control of wind turbines is compensating for the variable nature of wind loads. Given the sometimes large variations in wind speed, direction, and other operational variables (like wind shear), this paper proposes a data-driven, online rotor model identification approach. A 2 m diameter horizontal axis wind turbine rotor is first tested using experimental modal analysis techniques. Through the use of the Complex Mode Indication Function, the dominant natural frequencies and mode shapes of dynamic response of the rotor are estimated (including repeated and pseudo-repeated roots). The free dynamic response properties of the stationary rotor are compared to the forced response of the operational rotor while it is being subjected to wind and rotordynamic loads. It is demonstrated that both narrowband (rotordynamic) and broadband (wind driven) responses are amplified near resonant frequencies of the rotor. Blade loads in the flap direction of the rotor are also estimated through matrix inversion for a simulated set of rotor blade input forces and for the operational loading state of the wind turbine in a steady state condition. The analytical estimates are shown to be accurate at frequencies for which the ordinary coherence functions are near unity. The loads in operation are shown to be largest at points mid-way along the span of the blade and on one of the three blades suggesting this method could be used for usage monitoring. Based on these results, it is proposed that a measurement of upstream wind velocity will provide enhanced models for diagnostics and control by providing a leading indicator of disturbances in the loads.

This paper presents a computer-simulation based feasibility study of a passive Reduced Gravity Simulator (RGS), which uses spring-based static gravity-balancing technology to simulate a reduced-gravity environment. The concept of the simulator was developed for providing a potentially low-cost and easy-to-use simulation method for assisting astronauts training. The proposed RGS is capable of compensating full or partial gravitational effect of the trainee, providing a similar experience or feeling as if he/she is in a real reduced-gravity environment. Due to the safety requirements, the proposed technology has to be fully studied by means of simulation and nonhuman experiments before it can be safely tested with a human subject. The work presented here is the result of such a simulation study. In the study, a physical human is modeled as a multibody dynamical system with 54 degrees of freedom. The dynamic responses of a human jumping and walking with the RGS are simulated and analyzed. The simulation results are compared to those of the same human body on free jumping and walking in the same reduced-gravity environment.