Ashkan Haji Hosseinloo

Non-resonant energy harvesting via an adaptive bistable potential

Narrow bandwidth and easy detuning, inefficiency in broadband and non-stationary excitations, and difficulties in matching linear harvesters resonance frequency to low-frequency excitations at small scales, have convinced the researchers to investigate the nonlinear, in particular the bistable energy harvesters in the recent years. However, the bistable harvesters suffer from co-existing low and high energy orbits, and sensitivity to initial conditions, and have been recently proven inefficient when subjected to many real-world random and non-stationary excitations. Here, we propose a novel buy-low-sell-high strategy that can significantly improve the harvesters efficiency at low-frequencies in a much more robust fashion. This strategy could be realized by a passive adaptive bistable system. Simulation results confirm high efficiency of the adaptive bistable system following a buy-low-sell-high logic when subjected to harmonic and random non-stationary walking excitations compared to its conventional bistable and linear counterparts.

Design and analysis of shock and random vibration isolation system for a discrete model of submerged jet impingement cooling system

High-powered embedded computing equipment using air transport rack (ATR) form-factors are playing an ever-increasing role in critical military applications in air, land and sea environments. High power and wattage of the electronics and processors require large heat dissipation, and thus more sophisticated and efficient thermal cooling systems such as loop heat pipes or jet impingement systems are demanded. However, these thermal solutions are more susceptible to harsh military environments and thus, for proper performance of thermal and electronic equipment, they need to be protected against shock and vibration inherent in harsh environments like those in military applications. In this paper, an isolated ATR chassis including two jet impingement chambers is modeled as a three-degrees-of-freedom system and its response to random vibration and shock has been studied. Both finite element and experimental modal analysis is utilized to characterize dynamics of the components of the jet impingement system. The response of the model is compared to that of the traditional single-degree-of-freedom model, and the isolation system is optimized in terms of its damping.

Design of vibratory energy harvesters under stochastic parametric uncertainty: a new optimization philosophy

Vibratory energy harvesters as potential replacements for conventional batteries are not as robust as batteries. Their performance can drastically deteriorate in the presence of uncertainty in their parameters. Parametric uncertainty is inevitable with any physical device mainly due to manufacturing tolerances, defects, and environmental effects such as temperature and humidity. Hence, uncertainty propagation analysis and optimization under uncertainty seem indispensable with any energy harvester design. Here we propose a new modeling philosophy for optimization under uncertainty; optimization for the worst-case scenario (minimum power) rather than for the ensemble expectation of the power. The proposed optimization philosophy is practically very useful when there is a minimum requirement on the harvested power. We formulate the problems of uncertainty propagation and optimization under uncertainty in a generic and architecture-independent fashion, and then apply them to a single-degree-of-freedom linear piezoelectric energy harvester with uncertainty in its different parameters. The simulation results show that there is a significant improvement in the worst-case power of the designed harvester compared to that of a naively optimized (deterministically optimized) harvester. For instance, for a 10% uncertainty in the natural frequency of the harvester (in terms of its standard deviation) this improvement is about 570%.

Performance of spade-less wheeled military vehicles with passive and semi-active suspensions during mortar firing

Many armies are replacing heavy slow tracked vehicles with their lighter wheeled counterparts for their high mobility and better shoot and scoot capabilities. These features make the vehicle hard to track and target in counter-battery fire. However, when firing high calibre guns, spades are needed to connect the vehicle chassis to the ground, so as to transmit parts of the large firing force directly to the ground. Use of spades hinders the vehicle mobility, while elimination of them paves the way for having quicker and more mobile wheeled vehicles. In this article, vibration response of a spade-less High Mobility Multi-purpose Wheeled Vehicle with a mounted mortar is studied and controlled using stock passive, optimised passive, and optimised semi-active dampers as primary suspensions. The spade-less vehicle with optimised passive and semi-active dampers has a better response in heave, pitch, and fore-aft motions and can fire with better accuracy compared to a spade-less vehicle with stock passive dampers. Simulation results indicate that the spades can be removed from wheeled military vehicles if the precautions are taken for the tyres.

Robust and adaptive control of coexisting attractors in nonlinear vibratory energy harvesters

An immense body of research has focused on nonlinear vibration energy harvesting systems mainly because of the inherent narrow bandwidth of their linear counterparts. However, nonlinear systems driven by harmonic excitation often exhibit coexisting periodic or chaotic attractors. For effective energy harvesting, it is always desired to operate on the high-energy periodic orbits; therefore, it is crucial for the harvester to move to the desired attractor once the system is trapped in any other coexisting attractor. Here we propose a robust and adaptive sliding mode controller to move the nonlinear harvester to any desired attractor by a short entrainment on the desired attractor. The proposed controller is robust to disturbances and unmodeled dynamics and adaptive to the system parameters. The results show that the controller can successfully move the harvester to the desired attractor, even when the parameters are unknown, in a reasonable period of time, in less than 30 cycles of the excitation force.

Appraisal of Takagi–Sugeno type neuro-fuzzy network system with a modified differential evolution method to predict nonlinear wheel dynamics caused by road irregularities

Wheel dynamics play a substantial role in traversing and controlling the vehicle, braking, ride comfort, steering, and maneuvering. The transient wheel dynamics are difficult to be ascertained in tire–obstacle contact condition. To this end, a single-wheel testing rig was utilized in a soil bin facility for provision of a controlled experimental medium. Differently manufactured obstacles (triangular and Gaussian shaped geometries) were employed at different obstacle heights, wheel loads, tire slippages and forward speeds to measure the forces induced at vertical and horizontal directions at tire–obstacle contact interface. A new Takagi–Sugeno type neuro-fuzzy network system with a modified Differential Evolution (DE) method was used to model wheel dynamics caused by road irregularities. DE is a robust optimization technique for complex and stochastic algorithms with ever expanding applications in real-world problems. It was revealed that the new proposed model can be served as a functional alternative to classical modeling tools for the prediction of nonlinear wheel dynamics.

Optimal control strategies for efficient energy harvesting from ambient vibration

Ease of miniaturization and minimal maintenance are among the advantages for replacing conventional batteries with vibratory energy harvesters in a wide of range of disciplines and applications, from wireless communication sensors to medical implants. However, the current harvesters do not extract energy from the ambient vibrations in a very efficient and robust fashion, and hence, there need to be more optimal harvesting approaches. In this paper, we introduce a generic architecture for vibration energy harvesting and delineate the key challenges in the field. Then, we formulate an optimal control problem to maximize the harvested energy. Though possessing similar structure to that of the standard LQG problem, this optimal control problem is inherently different from the LQG problem and poses theoretical challenges to control community. As the first step, we simplify it to a tractable problem of optimizing control gains for a linear system subjected to Gaussian white noise excitation, and show that this optimal problem has non-trivial optimal solutions in both time and frequency domains.

A new passive vibration isolator design for random base excitations in zero and non-zero G-loading situations

The frequency range and isolation quality of linear isolation systems are usually affected and deteriorated due to the requirements to support a static load. This is usually the case in the aerospace applications where the airplane and the avionics are subjected to high G-loadings. Moreover, G-loading usually does not exist throughout the whole flight mission, meaning that, the avionics should be protected against vibrations in presence and absence of G-loading during a full flight mission. However, linear or simple softening or hardening isolation systems cannot fulfil the requirements to isolate the avionics from base vibrations in both presence and absence of G-loading, while opposing the G-loading if it exists, to reduce the total vibration travel. In this paper, a new passive isolation design is proposed that caters for the requirements mentioned where the vibration excitation is random and undeterministic. The new design integrates a linear isolation subsystem with a bilinear softening one to isolate the system in both absence and presence of the G-loading. The linear subsystem caters for the situation when there is no G-loading on the system while the bilinear softening subsystem together with the linear one, cater for vibration isolation of the payload when subjected to the G-loading. Design optimization problem of the isolation system is defined, and it is shown that the optimized new isolator has better performance than a linear or a simple hardening or softening isolator.

Vibration protection of laptop hard disk drives in harsh environmental conditions

Ultra-portability and compact design of laptop computers have made them more vulnerable to harsh environments. Hard disk drives (HDDs) in particular, are critical components in laptop computers whose read/write performance is severely affected by excessive vibrations. Here we take a system-level approach to design an optimal vibration isolator so as to minimize the transmitted vibration to the HDD while the laptop chassis is confined within an allowable vibration travel. The laptop is modeled as a 3-dof lumped-parameter system and the base excitation is assumed Gaussian random vibration with zero mean and uniform power spectral density over the frequency range [0–2000] Hz. The problem is cast as a constrained optimization problem with two decision variables, namely isolation frequency and damping. A combination of analytical and numerical approaches is utilized to solve the constrained optimization problem. It is shown that the optimized isolation system could reduce the transmitted root-mean-square acceleration to the HDD by a factor of over four compared to a rigidly-mounted laptop. Furthermore, the methodology presented here is not case-specific and could be applied to the isolation system design of a wide range of systems.

Energy harvesting via wrinkling instabilities

Conventional vibratory energy harvesters, working based on linear resonance, suffer from narrow bandwidth and are very inefficient at small scale for low frequency harvesting. Here, to improve the harvesting effectiveness, we propose to exploit surface instability or in general instability in layered composites where intriguing morphological patterns with large strain are formed under compressive loads. The induced large strains, which are independent of the excitation frequency, could be exploited to give rise to large strains in an attached piezoelectric layer to generate charge and, hence, energy. In this study, we particularly focus on wrinkling of a stiff interfacial layer embedded within a soft matrix. We derive the governing dynamical equation of thin piezoelectric patches attached at the peaks and troughs of the wrinkles. Results show that wrinkling could help to increase the harvested power by more than an order of magnitude.