In this work, we perform a numerical study on the flow induced by the motion of a rigid cantilever beam undergoing finite amplitude oscillations, in a viscous fluid, under a free surface. To this aim, we use a lattice Boltzmann volume of fluid (LB-VOF) integrated method, which includes the tracking of the fluid surface. The adopted approach couples the simplicity of the LB method with the possibility to track the free surface by means of a VOF strategy. Through a parametric analysis, we study the effects related to the depth of submergence, for several values of the oscillation frequency and amplitude. Results are provided in terms of a complex hydrodynamic function, whose real and imaginary parts are the added mass and the viscous damping, respectively, acting on the lamina. Validation of the results is carried out by comparing the solution, for the limit case of lamina submerged in an infinite fluid, with those from available literature studies. We find that the presence of the free surface strongly influences the flow physics around the lamina, especially at low values of the depth of submergence. In facts, when the lamina approaches to the free surface, the fluid waves, generated by the motion of the lamina, interact with the oscillating body itself, giving rise to additional effects, which we quantify in terms of added mass and viscous damping.

Many processes rely on wetting of liquids on surfaces. The way a liquid wets a solid depends on chemistry, geometry, and local energy inputs. Low-frequency surface vibrations can effect wetting changes prompted by droplet oscillations. High-frequency (ultrasonic) surface vibration can also cause a liquid to wet or spread out on a solid, but governing mechanisms are relatively uncharacterized. To investigate, droplets are imaged as they vibrate on a hydrophobic surface over different high frequencies (> 10 kHz). Wetting transitions occur abruptly over a range of parameters, but coincide with surface resonance modes. The wetting change is proportional to droplet volume and surface acceleration, and remains after cessation of vibration, however new droplets wet with the original contact angle. Wetting control has various industry applications, and understanding these basic phenomena will help develop a deeper understanding of how ultrasonic vibration can be utilized to tune the behavior of liquids on any surface.

Offshore petroleum production operations pose a unique set of challenges. A common undesirable phenomenon that occurs in these multiphase flow systems is known as slug flow. Slug flow is an oscillatory flow regime that creates large bullet shaped bubbles (also known as Taylor Bubbles) followed by large slugs of liquid. This high-rate alternation of liquid and gas production volumes in the surface facilities causes severe pressure oscillations. These oscillations adversely affect the structural health and individual components. A bench-scale closed flow loop was built with capabilities of measuring pressure and flow rates at different relevant sections. PID control strategy to mitigate the harmful effects of slug flow regime showed promise, although the tests were performed in the low pressure conditions of bench scale setup. The sensors and valve were programmed with MATLAB ® to provide real time analysis, and a PID controller was utilized to adjust the back pressure. Initial experimental data and visual observation provided better understanding of slug flow regime and some quantitative data was obtained through image processing. Theoretical estimates of Taylor bubble velocities were found to be in agreement with presented observations. Further experiments are being carried out to gather data and showcase this model to develop better multiphase flow control strategies.

Slug flow is a major problem to the structural integrity and production equipment in offshore production platforms. Pressure oscillations due to the alternation of liquid and gas phases in slug flow regime can cause fatigue on the structural components of the platform. Also, the intermittent high flow rates can cause adverse effects on the production equipment. A 28-foot pilot scale model was constructed to simulate the riser on offshore platforms. Three pressure sensors were attached to the model to monitor and record pressures in the riser during operations. A PID control strategy was utilized to regulate the pressure oscillations in the system by use of a linear actuated valve. Similarity between the pressure signals in the pilot scale model is qualitative when compared to actual pressures observed in an offshore riser system. A MATLAB ® GUI was designed to allow for manipulation of the valve and allow for instant graphing of data for real time visualization of the pressure signals. Pressure oscillations during slug flow with “no control” vary greatly and result in natural vibrations of the designed system. By pinching down on the choke valve to a designated opening, the back pressure in the riser increased, thereby slowing down the liquid slugs. However, an increase in the magnitude of the higher frequency oscillations can have adverse effects on the system. With the implementation of an active control, such as a linear actuated valve, a better control of back pressure on the riser and reduction in the magnitude of the higher frequency oscillations on the system is achieved.

The relaxation response of viscoelastic fluids associated with the natural frequencies of oscillation that arise as a consequence of the structure of the constitutive equation is explored for the case of pulsating flow. The matching of the forcing frequency to the fluid’s natural frequencies induces a multiple resonance phenomenon. In this paper, the resonance phenomenon is investigated in pulsating flow in straight circular tubes when the fluid is characterized by the Johnson-Segalman constitutive model. An analytical solution is developed based on an asymptotic expansion in terms of a material parameter. The analysis reveals that the forcing frequency associated with the pressure gradient can generate a sequence of resonances of decaying intensity dependent on the material parameter and other fluid constitutive constants. The effects of resonance on the rate of flow and oscillating velocity field are explored for several values of the relevant parameters.

Reducing turbulent skin-friction drag is a subject of great interest due to the potential benefits. These benefits are reflected in applications such as aircraft and vehicles for which skin-friction drag constitutes a significant fraction of the total drag. For example, commercial airliners have up to 50% of their fuel consumption associated with turbulent drag. Thus, any drag reduction would result in substantial savings with regards to the operational cost of the airline industry. In this study, we investigated the effects of a spanwise body force on reducing skin-friction drag in turbulent channel flows. To this end, we performed direct numerical simulations (DNS) of turbulent channel flows with an applied spanwise body force. The body force consists of four control parameters: the amplitude of excitation, penetration depth, period of oscillation, and wavelength. A series of DNS were performed to investigate the effect of these parameters on drag reduction. We observed different levels of drag reduction and the magnitude of skin-friction varied considerably. The DNS results showed that the skin friction is reduced by as much as 20% with values for penetration lengths from 0.03 to 0.09 and periods between 10 and 20. An optimal combination of the four adjustable control parameters is yet to be concluded. In addition to skin-friction reduction, we found an intriguing observation from a time series of wall shear stress. When the wall shear stress is sufficiently lower than its mean value (i.e., low-drag intervals), the spanwise body force appears to significantly affect turbulent dynamics to make the wall shear stress not as chaotic as in other intervals. Specifically, the standard deviations of the peak-to-peak magnitudes of the wall shear stress during low-drag intervals are significantly lower than that of other intervals. This observation could be crucial in that it may lead to a further fundamental understanding of the drag reduction process. Moreover, it may aid in the development of more effective control schemes by way of anticipating that low-drag intervals are promising targets for drag reduction.

Solar trackers orient solar panels toward the Sun to increase solar energy harvesting. To enhance solar energy capture, solar trackers change solar panels’ orientation throughout the day to follow the Sun’s path and make solar panels normal to the solar ray. The current solar trackers make solar panels perpendicular to the solar ray because of the active motion control of the solar panels. However, they also consume considerable power since the motion of solar panels is usually generated by two motors simultaneously and continuously. The merits of the existing sensor-based dual-axis solar trackers are compromised by their motor power consumption. In this research, the Sun’s location relative to an arbitrary point on Earth is determined at any time on any day in any year. Because of the determined solar location and path, only one axis is needed for the proposed solar tracker since it does not rely on any sensor to determine the Sun’s location. The current single-axis solar trackers face challenges on the limited oscillation range of the solar panels and the potential interference between an oscillating solar panel and its corresponding ground. In this paper, a sensor-free single-axis solar tracking linkage is designed to surmount these challenges. The solar tracking motion of the designed linkage is simulated. The designed linkage is fabricated and tested. The motion of the fabricated linkage is controlled by a microcontroller to generate the desired intermittent solar tracking motion.

Long heavy-haul trains are now a reality, especially for ore transportation. In some railways, compositions of up to 330 wagons are in service, requiring several locomotives. Trains like that travel long distances, sometimes through cities or in uninhabited regions. They are driven by just one driver which must keep the whole train working safely on the track. The wagons don’t have any source of electrical energy to power sensors and to transmit their signals to the locomotive; nor wireless communication. In fact, in some of these railways, there is no internet along with the track out of the cities. One important indicator of the safety of the train is the force between the wagons during the trip, through the shunting. Using strain gauges to measure these forces is a possible solution and ultrasonic stress sensors (UST) is a suitable alternative. UST with L cr waves requires a low amount of energy and can be employed in rusty and dirty places. However, they also need an energy source. Wind and solar solutions are not always adequate because, unfortunately, there are places where these components have economic value and they can be stolen. A possible source of energy to power the USTs could be the Vibration Energy Harvester (VEH). These simple and not expensive systems can be built in small packs, giving the energy to measure the forces and transmit the data to the locomotive or designated sites along the track. This work aims to evaluate the possibility of using VEH to power USTs to measure the forces between the wagons during the journey. Knowing that the oscillation in the shunting has a very low frequency, the work intent to optimize a multi-beam VEH to be able to capture the highest amount of energy possible, in a very small arrangement, using genetic algorithm. The result shows that VEH is an adequate alternative to power autonomous UST sensors.

Fuel supply system, the regulation system for fuel delivery to the combustor, is one of the most important auxiliary systems in a gas turbine engine. Commonly, the fuel supply system was always simplified as a linear system. In fact, gas turbine engines almost use a hydromechanical main fuel control system which consists of electro-hydraulic servo actuator and fuel metering unit. These components have several nonlinear characteristics such as hysteresis, dead zone, relay, and saturator. These nonlinear characteristics can directly affect the performance a gas turbine engine. In this paper, a three-shaft gas turbine engine was taken as a research object. Firstly, a mechanism model of the fuel control system considering the nonlinear links was developed based on the hydro-mechanical theory. Then, the effect of dead zone-relay characteristic of the servo amplifier in electro-hydraulic servo actuator was analyzed. The results show that the dead zone width has great effect on the dynamic performance of the gas turbine engine. The fuel flow rate will be oscillating with small dead zone width. The parameters of the gas turbine engine will be stable with the increase of dead zone width. However, the larger dead zone width causes the hysteresis and the increase of the dynamic response time. At the same time, an improvement method with a two-dimensional fuzzy compensation was proposed. The results show that the fuzzy compensation can effectively solve the oscillation problem caused by the dead zone-delay. Finally, a Hardware-In-the-Loop (HIL) system is developed which is based on an electro-hydraulic servo actuator facility and a real-time software component of the gas turbine engine. An experiment is conducted on the HIL test rig to validate simulation result. The results show that the experiment matches well with the simulation results.

Using data series obtained by experiments at the Marine Renewable Energy Laboratory of the University of Michigan, a Data-Driven Model is constructed for further investigation of the Process Dynamics and Control System Design and Configuration. This will enable advances in hydrokinetic energy harvesting using Vortex Induced Vibrations (VIV) and galloping, or more generally, Flow Induced Oscillations (FIO). Typically in such energy converters, one or more multiple bluff bodies, such as cylinders are suspended on springs in a water flow (currents, tides, rivers). In commonly encountered flows, oscillations are induced to the bluff rigid bodies due to vortex shedding in their wake, or due to lift instabilities in galloping, or both. These phenomena are dependent on stiffness, damping, mass ratio and the resulting vortex shedding frequency. The experiments in the cases investigated generated position signal recordings for one or two cylinders used as bluff bodies in FIO in a cross-flow. The position signals are used to set up a dynamic model. The model equation helps in gaining insight into the dynamics and underlying physics of the modeled FIO and can be used for Control System Tuning and Verification.

The global power potential of the waves that hit all the coasts worldwide has been estimated to be in the order of 1 TW. On an average, each wave crest transmits 10–50 kW/m of energy and this corresponds to 15 to 20 times more energy per meter than wind or solar energies. Wave energy is environmentally friendly and is the most consistent of all the intermittent sources. While wind, solar and wave are all intermittent, wave is the most consistent. Availability of waves is 90% compared to 30% for wind and solar energy. The oscillating water column (OWC) is the most investigated wave energy converter (WEC). OWC is a partially submerged hollow structure positioned, either vertically or at an angle. The bidirectional flow of air above the water column is used to drive a turbine. Majority of the OWC devices have chambers which are perpendicular to the incident waves. These conventional OWCs suffer severely from flow separation that occurs at the sharp corners of the chamber. In order to address this issue, researchers have proposed inclining the chamber at an angle with respect to the incident waves. This improves the flow characteristics. In addition to this, the flow in the chamber which ultimately decides the turbine performance, also increases. In the present study, the effect of OWC inclination on rotor performance was numerically studied using commercial computational fluid dynamics (CFD) code ANSYS CFX. The results highlight that the 55° inclined OWC showed improved performance when compared to the conventional OWC and current OWC. The maximum power for the inclined OWC was 13% higher than that recorded for the rotor in the current OWC and 28% than that recorded in the conventional OWC at mean wave condition. The 55° inclined OWC recorded peak rotor power of 23.2 kW which corresponded to an efficiency of 27.6% at the mean sea state. The peak power and efficiency at maximum sea state was 26.5 kW and 21.5% respectively. Higher oscillation was observed in the 55° inclined OWC. The combination of increased flow rate and energy in the flow lead to better performance of the 55° inclined OWC.

The stabilization of the inverted pendulum-cart system (IPCS) is a classical problem in the control engineering. The study of IPCS is motivated by its applications to the balancing of rocket boosters and bipedal robots. IPCS represents a class of nonlinear, under-actuated, and unstable system hard to be controlled in real-time. In this paper, a novel nonlinear time-frequency control (NTFC) strategy is applied to stabilize an inverted pendulum mounted on a cart. The proposed controller design is adaptive and employs discrete the wavelet transform and filtered-x least-mean-square (Fx-LMS) algorithm to realize the control in real-time. Using the wavelet transform, the adaptive controller is demonstrated to inhibit the deteriorations of the time and frequency responses simultaneously before the residual oscillation is too broadband to be controlled. The presented controller consists of two adaptive finite impulse response filers that operate on the wavelet coefficients: the first one realizes the online identification and provides a priori information in real-time while the second one realizes a feedforward control and rejects the uncontrollable input signal based on the first FIR filter. The equation of motion is derived based on the Newton’s Second law of motion and the model id simulated in MATLAB for verification. A number of commonly used control methods for the stabilization of the IPCS are investigated and evaluated against the proposed NTFC strategy. The simulation results show that the proposed control strategy is feasible for balancing the IPCS for a large, tilted initial angle within a short time interval and strongly robust to external impact and perturbation in real-time.

During the past few decades, significant interest in applying linear and nonlinear dynamical vibration absorbers for energy transfer and dissipation has significantly arisen. The existing studies of employing dynamical absorbers with small and large-scale dynamical structures have been mostly focusing on suppressing the oscillations for structures that move in one direction only. However, most of these structures are vulnerable to different sources and types of excitations that could induce two-dimensional oscillations into these structures. Consequently, this paper presents an application of a vibration absorber to suppress the two-dimensional vibration induced into the structure caused by a two-dimensional impulsive loading. The system description and the governing equations are firstly introduced and then followed by an optimization process to maximize vibration suppression. The response of the system under various combinations of longitudinal and lateral impulsive loadings is presented and the capability of the proposed absorber to suppress the induced vibration is evaluated.

Magnetic levitation (maglev) concepts are applied to a variety of industries such as the automotive, aerospace, or energy in order to accomplish different tasks: suspension and propulsion in maglev trains, rocket propulsion and spacecraft attitude control, centrifuge of nuclear reactors. In this paper, maglev is implemented in environmentally friendly hydrokinetic energy harvesting to achieve contactless bearing, thus, minimizing friction and improving efficiency. Generally, maglev systems exhibit higher efficiency and reduced maintenance while providing longer lifetime and higher durability when appropriate engineering design and control are applied. A Flow Induced Oscillation (FIO) energy-harvesting converter is considered in this work. To minimize friction in the support of the cylinder in FIO (vortex induced vibrations and galloping) due to high hydrodynamic drag, a maglev system is proposed. In the proposed configuration, a ferromagnetic core (element 1), of known dimensions, is considered under the effects of an externally imposed magnetic field. A second ferromagnetic element, of smaller dimensions, is then placed adjacent to the previous considered core. This particular configuration results in a non-homogenous magnetic field for element 1, caused by dimensional disparity. Specifically, the magnetic flux does not follow a linear path from the ferromagnetic core to element 2. A general electromagnetic analysis is conducted to derive an analytical form for the magnetic field of element 1. Subsequent numerical simulation validates the obtained formula. This distinct expression for the magnetic field is valuable towards calculating the magnetic energy of this specific configuration, which is essential to the design of the FIO energy harvesting converter considered in this work.

In this paper, negative stiffness in static state is made stable by constraining it in positive matrix. The stability of the system is tested using energy function. The motion of the two mass model system is described with a system of two coupled nonlinear differential equations. The numerical results are validated by comparing the predictions with calculations from analytical method. For small oscillations about the static equilibrium position the numerical model agree with analytical model. The developed model can be served as an efficient means of eliciting negative stiffness.

Vibration suppression has been implemented for many years as a way for a building’s occupants to feel more comfortable in structures prone to horizontal swaying or vertical oscillation. Suppression of a structure’s natural vibrations becomes even more important when delicate work, like surgeries, will be performed within. The purpose of this experiment was to confirm the validity of a passive vibration suppression unit to reduce the vibration in a portable shelter floor where surgeries would take place. Impact tests were done to determine the natural frequency of the floor, and along with the weight of the floor, were used to calculate operating parameters for a tuned mass damper, or TMD. A TMD was then assembled and vibration suppression effects were tested at 4% of total floor mass, to confirm the viability of the design. Additionally, TMDs of 2%, 3%, 4%, and 5% of the mass of the floor and shaker combined were made so frequency sweep tests could be done. Finally, a cantilever beam TMD was made, to test effectiveness of an easily adjustable TMD variant. The produced TMDs are expected to reduce the time the floor is vibrating and reduce vibration of the floor by up to 60%, bringing oscillations within comfortable levels even at the floor’s natural frequency.

An experimental investigation was conducted to correlate thermal characteristics with primary reference fuel (PRF) using an “isothermal” flow reactor. Objective of the investigation was to assess whether or not thermal characteristics measured in a radiant-heated flow reactor could serve as an indicator of fuel octane number. The experimental set-up consisted of a radiant furnace and a pyrex-tube test section inside. The pyrex tube was fitted with thermocouples alongside the tube wall. Four PRF compositions of iso-octane and n-heptane were considered: 0, 65, 85 and 100% of iso-octane by volume; noted as PRF0, 65, 85 and 100, respectively. The test conditions reported in the paper set the fuel-air mixture temperature to 180 °C at the inlet of the test section and the radian furnace temperature to 345 °C. The equivalence ratio was set in the range 0.93 to 2.0. For a pre-set PRF and equivalence-ratio condition, the experiments were run with fixed mixture velocities over the range 0.019 m/s to 0.400 m/s. Over the conditions tested, the thermocouples recorded two temperature oscillations along the flow reactor for each of PRF0, 65 and 85 mixtures. Both oscillation locations moved downstream when PRF number was increased and the two oscillation locations merged when PRF was set to 85. No temperature oscillations were recorded for experiments with PRF100 mixture. The results suggest that the temperature oscillation locations from the experiments using isothermal flow-reactors can be used to correlate fuel octane number.

In this study, we perform uncertainty quantification of a nonlinear dynamical system consisting of a circular cylinder undergoing free vibrations with two degrees-of-freedom in the presence of a fluctuating flow-field. Most of the studies in Vortex Induced Vibrations till now are conducted in a deterministic environment. Real life situations involving VIV are subjected to high amount of uncertainties, with the main culprit being the randomness in the incoming flow. Studies involving modelling of the flow with a prescribed set of parameters, represents only an idealistic situation and hence is not sufficient for a complete understanding of the associated dynamics. In this context, we make an attempt to characterise the flow by doing a stochastic modelling on the same. In the current study, we have mathematically modelled the noise through a uniform distribution. These fluctuations are superimposed on a mean flow at every time step. We use a Duffing Van der Pol combined system to model the structure and flow oscillators. It is observed that stochastic modelling brings noticeable changes in the structural responses both quantitatively and qualitatively. The influence of the fluctuations on both the transverse and inline oscillations have been studied. One of the most important changes in the response of the structure is in its amplitude. Noise amplifies the maximum amplitude attained both for transverse and inline oscillations. Further, additional qualitative types of responses are visible in the presence of noise which were absent in the deterministic environment. One such behaviour the ‘intermittent’ response which occurs during the transition from higher to lower amplitudes in the lock-in region. Intermittency is observed both for transverse and inline oscillations. It has been seen that the system undergoes stochastic Phenomenological bifurcations, which have been characterised by the probability density functions of both the transverse and inline responses.

A prototype of a hovering multi-terrain mobile robot platform that makes use of a flywheel for stabilization and heading control for rapid maneuverability was developed and presented in a prior paper. It was shown that flywheel stored energy could be transferred to the overall body to generate rapid angular motion once wheel is instantaneously stopped. Solution improved localization accuracy and reduced the overall sensitivity with respect to external disturbances such as non-flat terrain. In this paper, we present a feedback control system to measure dynamic parameters before and after the wheel is stopped. System is designed to follow a predefined path plan and instantaneous torque change causes oscillation after a waypoint is reached. To address this issue, we updated system with an inertial measurement unit (IMU) as a feedback sensor. Then, we investigate the feedback control of individual forward thrust vectors as well as wheel braking timing to minimize amplitude of transient response oscillation and to reduce the steady-state error to an acceptable level that differential drive fans could compensate this error and correct the heading after the rotation around a waypoint occurs. In addition to that, previous mechanical system could transfer all energy stored at once and was not adjustable. In this research, we also investigate varying amount of angular inertia generated by fans and wheel individually and together. To do so, system is modified with stronger forward thrusters. Prior to running the system with a full dynamic model with real mechanism, we implemented a simulation to empirically extract system parameters and adjust controller gains to follow a predefined path with open and closed loop control schemas with objective of minimizing localization error. Finally system is tested with real mechanism. Governing equations, simulation and empirical results comparison are presented and generated trajectories of various simulation and real world settings are listed. Test results verify that, with a closed loop control system, overshoot and total error about a waypoint can be minimized to an acceptable level at and after transient response phase.

This paper presents a novel and improved technique in manual control of flexible systems. Flexible systems, when subject to a rapid movement commanded by a human operator, exhibit severe oscillation, causing low positioning accuracy, high fatigue to the human operator, and unsafe accidents. Input shaping filter was proposed to reduce this oscillation by using the destructive interference principle where impulse responses cancel one another resulting in zero residual vibration. Recently, the input shaping filter was placed inside the feedback loop, so-called closed-loop signal shaping, to assist with the manual control of the flexible systems. The vibration was successfully suppressed. However, the input shaping filter also introduced time delays in the feedback loop, which limit the performance of the human operator. This paper offers a breakthrough idea by introducing an anti-delay algorithm called Smith predictor inside the feedback loop. When the plant model is perfect, it can be shown that the Smith predictor can entirely remove the effect of time delay from the feedback loop; therefore, improving the performance of the human operator. Experiments on manual control of a two-link pendulum on a gantry crane show the effectiveness of the proposed algorithm. The human operator was able to move the two-link pendulum with minimum residual vibration. Comparing to the currently world-best technique, the proposed technique could achieve faster maneuvering time, higher accuracy, and with less subjective difficulty.