Saman Farhangdoust | Stanford University (original) (raw)

Papers by Saman Farhangdoust

Smart Materials and Structures, 2021

Kirigami and auxetic topologies are combined to design an innovative metamaterial-based substrate... more Kirigami and auxetic topologies are combined to design an innovative metamaterial-based substrate (MetaSub) for piezoelectric energy harvesters. The proposed MetaSub piezoelectric energy harvester (MPEH) contains both advantageous metamaterial properties of negative Poisson's ratio capability and enhanced planar stretchability. A computational parametric analysis is conducted to develop the optimum design for the MPEH to trap the maximum elastic energy. A finite element analysis (FEA) is employed to analytically and numerically validate the simulation model of the MPEH. Accordingly, two experimental results of conventional and auxetic strain energy harvesters are used to evaluate the power enhancement of the MPEH. The FEA results demonstrate the average power gained by the MPEH at a low level of frequency and strain excitation (10 Hz and 150 με peak-to-peak) is 165 μW which easily satisfies the minimum electric power amount required as a sensor node for self-powered wireless sensor networks (SWSNs). The harvested power output of the MPEH is 19.2 times more than power output produced by an equivalent conventional harvester with a plain substrate (8.6 μW). The performance of the MPEH is investigated at different combinations of both low and high excitation frequencies. The creative design of the MetaSub can significantly improve the productivity of strain-induced devices whose efficiency is dependent on their deformation performance such as vibration energy harvesters, wearable sensors, flexible actuators, and micro electromechanical applications.

the Accelerated Bridge Construction University Transportation Center (ABC-UTC), 2019

In Accelerated Bridge Construction (ABC), prefabricated bridge deck elements are connected using ... more In Accelerated Bridge Construction (ABC), prefabricated bridge deck elements are connected using “Closure Joints.” Because of cast-in-place nature of closure joints that are expected to go into service and field observations, there have been some concerns about their long-term durability. This has necessitated the need for health monitoring of ABC closure joints using Non-Destructive Testing (NDT) methods. Closure joints contain unique features that sets them apart from conventional deck panels. They require a special treatment when it comes to selecting the appropriate NDT technique. However, a clear guideline for selection of the most applicable NDT method for various types of closure joints has not been developed yet. To address this, a research project was carried out at ABC-UTC at FIU. This report describes this investigation that includes review of all relevant NDT methods and efforts for categorizing closure joints based on features affecting the use of NDT. Since the applicability of NDT methods heavily depend on the type of expected anomaly to be detected and its root causes, all potential defects and damages were identified and investigated using a Damage Sequence Tree (DST). Consequently, damage etiology for closure joints were established using Fault Tree Analysis (FTA). Finally, a quantitative statistical analysis was performed to substantiate the selection of the most applicable NDT methods. The guide and process presented in Section 8 of this report can be readily used by bridge owners and consultants as a practical guide for selection of NDT methods for health monitoring of ABC bridges with closure joints. The proposed guide will be validated in upcoming projects to further support their implementation.

Proceedings Volume 10970, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2019; , 2019

Composite is one of the most widely used industrial materials because of high strength, low weigh... more Composite is one of the most widely used industrial materials because of high strength, low weight, and high corrosion resistance properties. Different parts of composite structures are normally joined using adhesives or fasteners that are prone to defects and damages. A reliable method for prediction of the defect location is needed for an efficient structural health monitoring (SHM) process. Heterodyne effect is recently utilized for damage detection in the bonding zone of composite structures where debonding is expected to change the linear characteristics of the system into nonlinear characteristics. This paper briefly introduces this novel defect locating approach in composite plates using the heterodyne effect. For the first time, an Artificial Neural Network methodology is utilized with heterodyne effect method to find the defect location in composite plates. The main objective of this article is to develop a neural network based methodology for prediction of damage location, particularly for the bond inspection of composite plates.

This paper develops an auxetic cantilever beam energy harvester (ACBEH) to enhance the harvesting... more This paper develops an auxetic cantilever beam energy harvester (ACBEH) to enhance the harvesting power from ambient vibration sources. A finite element analysis was performed to verify the power increase mechanism of the ACBEH. The simulation model of the ACBEH comprises of three main components: support, tip mass, and cantilever beam with a re-entrant hexagonal auxetic structure in which a piezoelectric element bonded to top of the auxetic region by using a thin elastic layer of epoxy. The performance of the ACBEH was computationally investigated and compared with an equivalent conventional energy harvester with a plain cantilever beam where they are attached to a bridge stay cable. The simulation result shows that the ACBEH excited by a harmonic acceleration of 1 m/s 2 at 3 Hz is able to produce electric power of 427.22 μW, which is 2.51 times that of the power produced by the equivalent plain cantilever beam energy harvester (170.17 μW). This paper opens up a great potential of using auxetic cantilever beam applications for different energy harvesting systems in Metamaterials, Acoustics, Civil, Electrical, Aerospace, Biomedical, and Mechanical Engineering.

The International Mechanical Engineering Congress and Exposition (ASME – IMECE), 2020

This paper presents a creative energy harvesting system using a bimorph piezoelectric cantilever-... more This paper presents a creative energy harvesting system using a bimorph piezoelectric cantilever-beam to power wireless sensors in an IoT network for the Sunshine Skyway Bridge. The bimorph piezoelectric energy harvester (BPEH) comprises a cantilever beam as a substrate sandwiched between two piezoelectric layers to remarkably harness ambient vibrations of an inclined stay cable and convert them into electrical energy when the cable is subjected to a harmonic acceleration. To investigate and design the bridge energy harvesting system, a field measurement was required for collecting cable vibration data. The results of a non-contact laser vibrometer is used to remotely measure the dynamic characteristics of the inclined cables. A finite element study is employed to simulate a 3-D model of the proposed BPEH by COMSOL Multiphasics. The FE modelling results showed that the average power generated by the BPEH excited by a harmonic acceleration of 1 m/s2 at 1 Hz is up to 614 μW which satisfies the minimum electric power required for the sensor node in the proposed IoT network. In this research a LoRaWAN architecture is also developed to utilize the BPEH as a sustainable and sufficient power resource for an IoT platform which uses wireless sensor networks installed on the bridge stay cables to collect and remotely transfer bridge health monitoring data over the bridge in a low-power manner.

Applied Energy, 2020

A new concept to enhance efficiency of the acoustic energy harvesting is presented and experiment... more A new concept to enhance efficiency of the acoustic energy harvesting is presented and experimentally tested in this paper. An auxetic latticed resonator backed by an acoustic rectangular tube is proposed for this purpose. The concept is tested and proved by comparing the extracted power against performance of a conventional cantilever resonator at resonant-resonant condition. The problem is modeled by the Finite Element Method. The models are validated using experimental tests. The energy harvesting performance is numerically evaluated in different sound powers, geometrical aspects and electrical properties. In a parametric study, performance of the proposed auxetic resonator is compared with a plain one. It is shown that employing the concept can remarkably enhance performance of the acoustic energy harvesting system. At low frequencies, 138 Hz in this study, at an optimum situation we could arrive at a large magnification factor around 10.5 for 100 dB sound pressure level.

Structural Engineering and Mechanics, 2020

The life of conventional steel plastic injection molds is long but manufacturing cost and time ar... more The life of conventional steel plastic injection molds is long but manufacturing cost and time are prohibitive for using these molds for producing prototypes of products in limited numbers. Commonly used 3D printers and rapid prototyping methods are capable of directly converting the digital models of three-dimensional solid objects into solid physical parts. Depending on the 3D printer, the final product can be made from different material, such as polymer or metal. Rapid prototyping of parts with the polymeric material is typically cheaper, faster and convenient. However, the life of a polymer mold can be less than a hundred parts. Failure of a polymeric mold during the injection molding process can result in serious safety issues considering very large forces and temperatures are involved. In this study, the feasibility of the inspection of 3D printed molds with the surface response to excitation (SuRE) method was investigated. The SuRE method was originally developed for structural health monitoring and load monitoring in thin-walled plate-like structures. In this study, first, the SuRE method was used to evaluate if the variation of the strain could be monitored when loads were applied to the center of the 3D printed molds. After the successful results were obtained, the SuRE method was used to monitor the artifact (artificial damage) created at the 3D printed mold. The results showed that the SuRE method is a cost effective and robust approach for monitoring the condition of the 3D printed molds.

International Society for Optics and Photonics, 2020

This paper introduces a creative metamaterial-based substrate (MetaSub) for piezoelectric energy ... more This paper introduces a creative metamaterial-based substrate (MetaSub) for piezoelectric energy harvesters. The MetaSub is a platform with a high flexibility in both longitudinal and transverse directions. The novel design of the MetaSub remarkably improves the productivity of strain-induced devices in structural health monitoring (SHM) applications, internet of thing (IoT) networks, micro electromechanical (MEMS) systems, vibration energy harvesters, sensor and actuators, and hundreds applications that its performance is related to their deformation capability. In this paper, a piezoelectric type of energy harvester is selected to be studied numerically as the first application of the MetaSub. The finite element results predict the average power output gained by the MetaSub piezoelectric energy harvester to be up to 19.2 times more than power generated by an equivalent conventional piezoelectric energy harvester.

publication descriptionSensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2020, 2020

In this paper, an auxetic design is proposed for the flexible membrane of a piezoelectric pulse s... more In this paper, an auxetic design is proposed for the flexible membrane of a piezoelectric pulse sensor and computationally analyzed for a high-sensitivity vibration sensing in micro electro-mechanical system (MEMS). Auxetics are metamaterial structures with negative Poisson’s ratio which enables sensor’s flexible diaphragm to be expanded in both longitudinal and transverse directions easily. The sensitivity of a pulse sensor with an auxetic membrane was studied and compared to an equivalent plain membrane when the substrate was under harmonic bending. The sensing response was determined for the both models using detailed Finite Element Model (FEM) simulations. The sensor with the auxetic membrane demonstrated excellent sensitivity output over a harmonic pressure input which shows its strong potential for high-sensitive MEMS sensing applications. A detailed fabrication process is also discussed.

Earthquakes and Structures, 2020

The usage of conventional tuned mass damper (TMD) was proved as an effective method for passive m... more The usage of conventional tuned mass damper (TMD) was proved as an effective method for passive mitigating vortex-induced vibration (VIV) of a bridge deck. Although a variety of linear TMD systems have been so far utilized for vibration control of suspension bridges, a sensitive TMD mechanism to wind spectrum frequency is lacking. Here, we introduce a bistable tuned mass damper (BTMD) mechanism which has an exceptional sensitivity to a broadband input of vortex shedding velocity for suppressing VIV in suspension bridge deck. By use of the Monte Carlo simulation, performance of the nonlinear BTMD is shown to be more efficient than the conventional linear TMD under two different wind load excitations of harmonic (sinusoidal) and broadband input of vortex shedding. Consequently, an appropriate algorithm is proposed to optimize the design parameters of the nonlinear BTMD for Kap Shui Mun Bridge, and then the BTMD system is localized for the interior deck of the suspension bridge.

Nondestructive Characterization and Monitoring of Advanced Materials, Aerospace, Civil Infrastructure, and Transportation IX - SPIE, 2020

Vibration is an available source of energy to supply electrical power demand of the freight wagon... more Vibration is an available source of energy to supply electrical power demand of the freight wagons as it is one the most important challenges in railway engineering. Here we propose an efficient bistable mechanism with linear power take-off and nonlinear stiffness for energy harvesting of freight wagon vibrations. Design parameters of the bitable systems is optimized by genetic algorithm (GA) and simulated annealing (SA) to extract maximum power. It is shown that remarkable enhancement can be achieved in comparison with conventional linear energy harvesters. The reason for this enhancement is harmonic oscillation between stable equilibrium points of the system which is very well matched with the nature of random excitation exerted by the rail irregularities.

In accelerated bridge construction (ABC), prefabricated bridge deck elements are merged using "cl... more In accelerated bridge construction (ABC), prefabricated bridge deck elements are merged using "closure joints." Because of the cast-in-place nature of closure joints that are expected to go into service rapidly and problems observed for some types of closure joints, there have been some concerns about their long-term durability. This has necessitated the need for monitoring the condition of ABC closure joints using non-destructive testing (NDT) methods. Closure joints contain unique features and details that sets them apart from conventional deck panels. This requires a special treatment of closure joints when it comes to selecting the appropriate NDT technique for their health monitoring. A clear guideline for selecting an applicable NDT method for various types of closure joints has not been developed yet. For this purpose, an investigation was carried out in the Accelerated Bridge Construction University Transportation Center (ABC-UTC) at Florida International University. This paper summarizes the result of this investigation. It includes reviews of all relevant NDT methods for applicability to ABC closure joints and efforts for categorizing closure joints according to joint features that affect the use of NDT. Since the applicability of NDT methods heavily depend on the type of expected anomaly to be detected and its root causes, all potential defects and types of damage were identified and investigated using a damage sequence tree (DST). Consequently, damage etiology for ABC closure joints were established using fault tree analysis (FTA). Finally, a quantitative statistical survey was used to substantiate the selection of the NDT methods that were most applicable to the health monitoring of ABC bridges containing closure joints. The results presented in this paper can be used by bridge owners and consultants as an effective and practical guide for the selection of NDT methods for monitoring the health of ABC closure joints.

International Journal of Energy Research, 2019

This paper proposes a new concept to enhance the efficiency of the vibration energy harvesting vi... more This paper proposes a new concept to enhance the efficiency of the vibration energy harvesting via an intermediate booster. The boosters have auxetic structures and exert extra stretching strain in two perpendicular directions. The concept is tested on a conventional cantilever beam under the base excitation. The problem consists of a cantilever beam subjected to a body load at low frequencies. An auxetic substrate is bonded to the beam with a thin epoxy layer, and the piezoelectric (PZT) element is attached on top of it. Two different auxetic structures are investigated in this study. It is shown that employing these kinds of boosters can remarkably enhance the performance of the energy harvesting system. The harvesting efficiency is numerically evaluated in different load amplitudes and frequencies. A parametric study is then carried out, and effects of different geometrical design parameters of the auxetic boosters on the performance of the energy harvesting system are investigated. Comparing with the case in which the PZT is straightly attached to the cantilever, it is shown that adding such intermediate boosters at low‐frequency range can increase the extracted power by factors of 3.9 and 7.0 for the two proposed geometries.

$Research paper thumbnail of Vibro-acoustic response analysis of fractional railpads in frequency domain$

Mechanics Based Design of Structures and Machines, 2019

Frequency response of a railway track including fractional railpad is studied in this paper. Frac... more Frequency response of a railway track including fractional railpad is studied in this paper. Fractional finite ele1ment formulation is derived for a compound model including the rail, sleepers, and ballast. The fractional equations of motion are solved by fractional interpretation of the Newmark method. Based on the Rayleigh integral approach, acoustic pressure distribution around the beam is obtained. A parametric study is carried out and effects of different parameters on the frequency spectrum of displacement, stress and sound pressure level are investigated. It is found that the frequency responses are remarkably influenced by the fractional parameters in mid frequency range.

Journal of Advanced Concrete Technology, 2019

Accelerated Bridge Construction (ABC) uses prefabricated elements that are made continuous using ... more Accelerated Bridge Construction (ABC) uses prefabricated elements that are made continuous using cast-in-place joints. Deck joints are normally referred to as “Closure Joints.” There have been concerns about long-term durability of these joints that are expected to become rapidly serviceable. Normally, they contain reinforcing bars and enclosures of various shapes that in some cases create congestion within the joint. The specific nature of the joint application, in-situ casting, curing, material incompatibility, cold joints, cavities and steel congestion contribute to creating the potential for leaving defects and anomalies in the closure joints. This, in turn, results in a higher potential for exposure and other detrimental effects with possible degradation in time, and therefore reducing the strength and serviceability of the joint, hence creating a weak link for the structure. The long-term deflections and environmental loading will only exacerbate the situation. Hence, evaluation and health monitoring of the closure joints becomes inevitable. Despite the wide use of non-destructive testing (NDT) methods for bridge structures in general, a concerted attempt for categorization of these methods, comparison of capabilities, and selection of methods most applicable to closure joints is lacking. To address this, a research project was carried out as part of activities in the Accelerated Bridge Construction University Transportation Center (ABC-UTC) of Florida International University. This study included a comprehensive literature review with a focus on NDT methods applicable to health monitoring of ABC closure joints. The study focused on joint types relevant to precast concrete decks commonly used for ABC bridges, therefore, FRP (fiber reinforced plastic), timber (wood), and steel of any shape were excluded for the time being. The study resulted in categorizing the most common closure joints in five general groups based on their features affecting the application of the NDT methods. Accordingly, the most promising NDT methods were identified taking into account the distinctive defects and anomalies associated with closure joints. These methods were evaluated for their efficacy, ease of use and other characteristic influencing their use as preferred methods for each type of joint. A flowchart was introduced to assist in selection of the most applicable NDT method to each type of defect in closure joints. This paper summarizes the results of this study.

ACECR of Sharif University of Technology, 2019

American Society of Civil Engineers, 2019

Accelerated bridge construction (ABC) employs prefabricated bridge elements moved to the bridge l... more Accelerated bridge construction (ABC) employs prefabricated bridge elements moved to the bridge location and installed in place. Accordingly, ABC reduces many uncertainties associated with construction processes and performance during service life. It also improves the life cycle cost by reducing construction time and traffic interruptions, better control over schedule, and normally by the higher quality of elements resulting in better life-cycle performance. Nevertheless, prefabricated elements need to be made continuous using cast-in-place joints. ABC “closure joints” connecting deck elements to each other and to the bridge girders have greater exposure to degrading environmental effects, and often there is more focus on their evaluation. These joints, expected to become serviceable quickly can therefore be viewed as critical elements of the ABC bridges. Instances of defective (leaky) joints have been reported, and concerns have been raised about the long-term durability of the joints. The long-term deflections and environmental loading will only exacerbate this situation. These may overshadow the many advantages of ABC specifically as life-cycle performance and costs are concerned. Hence, health monitoring of ABC critical details, i.e., joints, becomes a priority for first assuring a life-cycle performance compatible with the prefabricated elements, and more importantly to address potential problems before damages become excessive. A variety of non-destructive testing (NDT) methods has been utilized in the past for structural health monitoring of bridges in general. However, a concerted attempt for evaluation of NDT techniques, comparison of capabilities, and selection of methods most applicable to ABC closure joints is lacking. As a part of the ABC-UTC program at the Florida International University, a research study is being undertaken to identify the defects associated with closure joints, to evaluate NDT methods for applicability to ABC closure joints, and finally to determine the most promising methods. This paper summarizes the results of this research study.

International Society for Optics and Photonics

The Surface Response to Excitation (SuRE) method is a guided-wave based Structural Health Monitor... more The Surface Response to Excitation (SuRE) method is a guided-wave based Structural Health Monitoring (SHM) technique. Up to date, no analytical model has been developed and validated for the SuRE method. This paper experimentally and analytically investigates the delamination between two plates using the SuRE method in conjunction with the COMSOL Multiphysics software. Simulation results are validated by experimental results. The results showed that the findings from the analytical approach correspond with the experimental results and can be effectively used for studying delamination. This approach can be utilized for different types of structures with similar conditions.

SPIE, 2019

Low reliability and high maintenance cost of using power and data cables are two main reasons mot... more Low reliability and high maintenance cost of using power and data cables are two main reasons motivating the application of the self-powered wireless sensors for structural health monitoring (SHM) systems in bridge structures. On the other hand, energy harvesting systems have been introduced as a solution for the current limitations of the batterypowered wireless sensors associated with the finite life-span of batteries and their replacements. The objective in this paper is to propose a new optimized nonlinear energy harvesting concept, namely Bistable Energy Harvesting (BEH) system, for smart SHM of bridge structures. In this study, a dynamic analysis of the energy harvesting system for cablesupported bridges subject to wind-induced vibration is carried out and the feasibility of the energy harvesting device is investigated. This paper presents efficient linear and nonlinear energy harvesting systems for wireless monitoring of long-span cable-supported bridges. It is shown that level of the extracted energy from such energy harvesting system is quite sufficient to supply energy for self-powered sensors of a bridge health monitoring system. This study is to promote the recent line of research on self-powered sensor networks for smart bridge monitoring being performed at the Florida International University.

Japan Concrete Institute, 2019