Mechanical Spring Research Articles

Multi wave absorber platform design, modelling and testing

The subject of this paper is the development of physical and numerical models and a tank test programme to investigate the performance of a multi wave energy absorber platform (MWAP). The platform is inspired by the proposed designs for large scale platforms to be used for floating offshore wind (FOW). The modular design of the physical model enables a variable number of absorbers to be mounted to the platform, with up to 9 absorbers tested simultaneously. The absorbers used are a simplified version of a submerged pressure differential device, with each absorber incorporating a set of mechanical springs to approximate the response of the real internal air spring. Physical model tank tests will be undertaken during 2023, utilizing a range of environmental conditions representative of those at an exposed site on the west coast of Scotland, leased through the ScotWind programme and which has an appropriate water depth and wave resource for large scale wave energy exploitation. Measurements taken during physical model testing will be used to validate numerical models of the MWAP and will allow subsequent investigation of key drivers of annual energy performance, exploring platform configuration options not tested in the wave tank. The motivation for this project, design considerations and balance between tank scale & full-scale design requirements will be given. Discussion will be provided on the implications of the limitations and assumptions made during the physical and numerical modelling work, as well as next steps for utilisation of the tools beyond the scope of this project.

Evaluation and Failure Analysis of Mechanical Springs Under Varying Stress Profiles: An Industrial and Nuclear Safety Perspective

Evaluation and Failure Analysis of Mechanical Springs Under Varying Stress Profiles: An Industrial and Nuclear Safety Perspective

Dielectric elastomer actuator biased by magnetorheological elastomer with permanent magnet

Dielectric elastomer actuators have become one of the most important smart material transducers in recent times. One of the crucial aspects in this field is the application of bias to find the best operating conditions. The basic task is to find the proper bias configuration to obtain a wide range of displacements in the actuator. In the literature, various biases, such as mechanical springs, permanent magnets (PMs), or pneumatic springs, are studied. In our work, the magnetorheological elastomer (MRE) is applied to build a novel bias that ensures a wide range of displacement. Because of the softness and the compliant chemical structure, the MRE can be easily integrated with the dielectric elastomer actuator. The MRE as a bias for a dielectric elastomer actuator is verified in the series of experiments. Finally, the discussion on the advantages and disadvantages of the new bias type is performed.

Design and analysis of a passive exoskeleton with its hip joint energy-storage.

A novel passive hip exoskeleton has been designed and built with the aim of reducing metabolic consumption during walking by a passive way of storing the negative mechanical energy in the deceleration phase and releasing it in the acceleration phase. A ratchet spiral spring mechanism with a set of double stable switches is designed inside the exoskeleton for the above purpose. An analysis is conducted on the mechanism and the switching timing for the energy management to automatically store or release the energy according to the biomechanics of walking. In addition, a gravity-balance mechanism embedded inside the exoskeleton is designed as well to minimize the influence of the lower limb weight on muscle work. Human-exoskeleton interaction has been studied using the Opensim software, and simulation results demonstrated the effectiveness of the exoskeleton in reducing metabolic consumption during walking. An exoskeleton prototype has been built and tested with experiments measuring assistive torque and surface electromyography signal, confirming the effectiveness of the gravity-balance mechanism and energy-storage method, as well as the exoskeleton's actual assistive effect.

Elastic pinch biomechanisms can yield consistent launch speeds regardless of projectile mass.

Energetic trade-offs are particularly pertinent to bio-ballistic systems which impart energy to projectiles exclusively during launch. We investigated such trade-offs in the spring-propelled seeds of Loropetalum chinense, Hamamelis virginiana and Fortunearia sinensis. Using similar seed-shooting mechanisms, fruits of these confamilial plants (Hamamelidaceae) span an order of magnitude in spring and seed mass. We expected that as seed mass increases, launch speed decreases. Instead, launch speed was relatively constant regardless of seed mass. We tested if fruits shoot larger seeds by storing more elastic potential energy (PE). Spring mass and PE increased as seed mass increased (in order of increasing seed mass: L. chinense, H. virginiana, F. sinensis). As seed mass to spring mass ratio increased (ratios: H. virginiana = 0.50, F. sinensis = 0.65, L. chinense = 0.84), mass-specific PE storage increased. The conversion efficiency of PE to seed kinetic energy (KE) decreased with increasing fruit mass. Therefore, similar launch speeds across scales occurred because (i) larger fruits stored more PE and (ii) smaller fruits had higher mass-specific PE storage and improved PE to KE conversion. By examining integrated spring and projectile mechanics in our focal species, we revealed diverse, energetic scaling strategies relevant to spring-propelled systems navigating energetic trade-offs.

Spring exchange mechanism and temperature dependent magnetic properties of BaFe12O19/CoFe2O4 nanocomposites

Bare BaFe12O19, CoFe2O4, and their nanocomposites with concentration percentage 30–70, 50–50 and 70–30 were synthesized by sol–gel approach. The average crystallite size < D > of bare BaFe12O19 nanoparticles (NPs) was 35 nm which gets reduced with the addition of CoFe2O4 phase and found minimum for bare CoFe2O4 nanoparticles, i.e. 12 nm. Transmission electron microscopy (TEM) image showed the agglomeration of nanocomposites and mean particle size was observed to be 44 nm as estimated from normal size distribution. The ZFC/FC curves exhibited that the blocking temperature TB of all samples lies above room temperature. However, a small broad peak at ∼ 75 K in pure BaFe12O19 NPs is attributed to the surface freezing peak (Tf). The flatness in FC curve at low temperature with the addition of CoFe2O4 phase revealed the strong inter-particle interactions. From M−H loops, the value of saturation magnetization (MS) for Ba70/Co30 was found to be maximum (100.82 emu/g) than their corresponding bare nanoparticles. The higher value of MS showed the presence of exchange spring mechanism in these samples. The coercivity of BaFe12O19 sample was observed to be 4262 Oe which get increased with the addition of CoFe2O4 phase and found maximum for CoFe2O4 (7349 Oe), which shows the hard magnetic nature of CoFe2O4 NPs. However, the smaller value of Bloch’s constant “B” for BaFe12O19 phase (4.8 x10−6K-3/2) showed the strong intra-particle interactions in the core of BaFe12O19 NPs. The dM/dH vs. H curves showed the well-established exchange coupling of both hard and soft magnetic phases for 50% concentration of both phases and may be beneficial for high density recording devices.

Nonlinear Dynamics and Energy Harvesting of a Two-Degrees-of-Freedom Electromagnetic Energy Harvester near the Primary and Secondary Resonances

Energy harvesting is a useful technique for various kinds of self-powered electronic devices and systems as well as Internet of Things technology. This study presents a two-degrees-of-freedom (2DOF) electromagnetic energy harvester that can use environment vibration and provide energy for small electronic devices. The proposed harvester consists of a cylindrical tube with two moving magnets suspended by a magnetic spring mechanism and a stationary coil. In order to verify the theoretical model, a prototype electromagnetic harvester was constructed and tested. The influence of key parameters, including excitation acceleration, response to a harmonic frequency sweep, and electromechanical coupling on the generated characteristics of the harvester, was investigated. The experimental and theoretical results showed that the proposed electromagnetic energy harvester was able to increase the resonance bandwidth (60–1200 rad/s) and output power (0.2 W). However, due to strong nonlinearity, an unstable region occurred near the main first resonance, which resulted from the Neimark–Sacker bifurcation.

Development of adjustable variable stiffness restrainer for bridge subjected to seismic excitation.

This paper presents a numerical and experimental assessment of a developed adjustable variable stiffness restrainer (AVSR) utilized for short span bridges. This restrainer has the ability to demonstrate multi stiffness capacity in different stages of bridge's superstructure movement to mitigate the severe damage of bridge due to an earthquake. The multi-level stiffness behavior of developed AVSR is achieved by using multiple mechanical springs with different lengths and placed in parallel in proposed design. A small prototype of developed AVSR has been fabricated and tested under incremental and cyclic loading in order to assess the restrainer performance and the behavior has been validated using finite element analysis. Thereafter, the constitutive model of AVSR was derived for the proposed restrainer in order to implement it in numerical simulations. Furthermore, a parametric study has been conducted numerically to evaluate the effectiveness of different parameters on the restrainer capacity. Moreover, the efficiency of AVSR application in a single degree of freedom system has been assessed by performing seismic analysis on a frame equipped with AVSR subjected to different seismic excitations using Newmark's method. The experimental and finite element results proved the efficiency of developed variable stiffness device to exhibit adjustable action against imposed loads in three designed stages. Furthermore, the parametric study results revealed that increasing the section area of the spring wire leads to increase the restrainer capacity. In contrast, the restrainer resistance is declined by an increase in the mean spring diameter and number of coils for each spring of AVSR. The time history analysis results also indicated that the frame response in terms of displacement, velocity and acceleration is improved by implementing the AVSR in the considered system.

Nonlinear earthquake responses of unanchored cylindrical liquid storage tanks on flexible soil

A sophisticated and versatile finite-element model of the nonlinear behavior of unanchored cylindrical liquid storage tanks on flexible soil is proposed and applied for nonlinear earthquake response analysis of the system. The tank is modeled using shell finite elements with material and geometric nonlinearities. The hydrodynamic pressure is represented by acoustic finite elements. The effects of the base uplift are considered by nonlinear springs with negligible and large stiffness coefficients in tension and compression, respectively. The flexible soil is modeled using mechanical springs and dashpots. The effects of base uplift and soil flexibility are examined for typical unanchored tall and broad tanks on flexible soil with various shear-wave velocities. It is observed that the structural responses and hydrodynamic pressure, including the convective pressure of an unanchored tall tank on rigid/flexible soil, are significantly influenced by the base uplift. Although the base uplift in a broad tank is not as large as that in a tall tank, the structural responses and hydrodynamic pressure of an unanchored broad tank can be different from those of an anchored system. However, the convective pressure of the broad tank is not significantly affected by the base uplift. The earthquake responses of the system are principally influenced by the horizontal component of the earthquake ground motion rather than the vertical component.

Coiling an optical fiber for long-range dynamic displacement and force sensing

Optical fiber sensors have been applied on detecting various physical parameters. In this work, inspired by the mechanism of tendril coiling, we designed a spring-like sensor using optical fibers based on macro bending loss. The proposed optical-fiber spring has good elasticity like a mechanical spring and thus can be used to measure large displacement. As a contact-type sensor, the fabricated optical-fiber spring can measure dynamic displacement, whose range is 4 orders of magnitude higher than that of the point-wise fiber Bragg grating displacement sensor. In addition to the point-wise displacement sensing, we further integrated the optical-fiber spring with a Kresling origami to form a force sensor.

Bi-stable electromagnetic generator with asymmetrical potential wells for low frequency vibration energy harvesting

Efficient energy harvesting from low and broadband frequency has always been a challenging problem. This paper proposes a solution in the form of an electromagnetic bi-stable vibration energy harvester (BVEH) with asymmetric potential barriers, in which the vibrator is attracted to the top magnet and repelled from the bottom magnet. By combining a magnetic spring and a mechanical spring, the BVEH achieves bi-stability with asymmetric potential barriers, enabling large amplitude vibration as the vibrator travels between the two potential wells. The traditional magnetic force model is modified to establish an electromechanical coupling model that accurately predicts the output of the BVEH. Numerical simulation results solved by the Runge-Kutta method show good agreement with experimental results. In addition, a prototype is fabricated and the system parameters are adjusted to achieve high-energy oscillation at the lowest frequency of 4 Hz. Under a sinusoidal excitation with an amplitude of 4 mm, the BVEH's bandwidth is expanded to 6 Hz, and the maximum power can reach 72.76 mW. Finally, the feasibility of the BVEH is demonstrated by powering different electrical appliances. The study provides a new technical approach for energy harvesting under low and broadband frequency vibration excitation.

PID control of a zero stiffness magnetic suspension system

–As a result of the developments in today's technology, magnetic suspensions have started to beused instead of traditional suspensions (mass-spring-damper) in order to prevent vibrations in structures. Inconventional suspensions, there is an undesirable continuous force transfer from the ground to the useraccording to the action-reaction principle of the existing spring and damper used in the suspension system.Although the mass-spring-damper parameters are well adjusted in a conventional suspension, thistransmitted force transfer cannot be reduced to zero. The main purpose of this study will be a magneticsuspension design to eliminate this undesirable situation. In the designed magnetic suspension, the magneton the linear guide system will be tried to be kept in the zero transmitted force position with the help ofonly magnetic forces without any mechanical contact and lubrication. A total of 3 magnets will be used inthe proposed magnetic suspension system. The magnet on the linear guide will be capable of free slidingand this sliding magnet will be actuated by the rotary magnets standing in a fixed position at ends of thelinear guide system by using the repulsive or pulling forces. The position control of the sliding magnet isachieved by a PID control. Therefore, since no mechanical spring and damper connections will be used inthe proposed suspension system, zero spring force effect could be created.

Review on self-centering damper for seismic resilient building structures

In recent years, major earthquakes in China, Chile, New Zealand and Japan caused many building structures severely damaged, which must be overhauled or rebuilt. Therefore, how to improve the seismic resilience of building structures has been widely concerned. The energy dissipation dampers are proposted to install in some parts of the structure to produce large damping and dissipate much seismic energy input. While, the disadvantage of these traditional dampers is that they cannot automatically restored to the original position after the earthquake, and the residual deformation may result in huge economic losses. In recent years, researchers proposed to combine self-centering devices with traditional dampers to obtain self-centering capacity in addition to energy dissipation capacity, and the self-centering dampers can effectively avoid post-earthquake damage of the structure. This paper first reviews the mechanical characteristics and development of traditional dampers, including metal yield dampers, friction dampers, viscoelastic dampers, viscous fluid dampers, etc. Then, the research of self-centering dampers is summarized according to the types of self-centering devices, including shape memory alloy (SMA) type, steel tendon and strand type, and mechanical spring type. Further, the experimental research and seismic design methods of structures with self-centering dampers are reviewed, as well as the classic engineering applications of different dampers. Finally, the future directions need to be concerned in the further research are mentioned, which is benefical to the future engineering popularization and applicaition of self-centering dampers.

Embodied latch mechanism of the mandible to power at ultra-high speed in the trap-jaw ant Odontomachus kuroiwae.

Rapid movements of limbs and appendages, faster than those produced by simple muscle contraction alone, are generated through mechanical networks consisting of springs and latches. The latch plays a central role in these spring-loaded mechanisms, but the structural details of the latch are not always known. The mandibles of the trap-jaw ant Odontomachus kuroiwae closes the mandible extremely quickly to capture prey or to perform mandible-powered defensive jumps to avoid potential threats. The jump is mediated by a mechanical spring and latch system embodied in the mandible. An ant can strike the tip of the mandible onto the surface of an obstacle (prey, predator or ground) in order to bounce its body away from potential threats. The angular velocity of the closing mandible was 2.3×104rads-1 (1.3×106degs-1). Latching of the joint is a key mechanism to aid the storage of energy required to power the ballistic movements of the mandibles. We have identified the fine structure of two latch systems on the mandible forming a 'ball joint' using an X-ray micro-computational tomography system (X-ray micro-CT) and X-ray live imaging with a synchrotron. Here, we describe the surface of the inner section of the socket and a projection on the lip of the ball. The X-ray live imaging and movements of the 3D model show that the ball with a detent ridge slipped into a socket and over the socket ridge before snapping back at the groove edge. Our results give insight into the complex spring-latch systems that underpin ultra-fast movements in biological systems.

Use of mechanical braking energy in vehicles as electricity and hydrogen energy

The work is devoted to developing a mechanism for returning the mechanical energy expended during braking of the vehicle, lost during transmission to the body and proportional to the loss of volume of the combustible engine. The withdrawal of mechanical energy from the wheel braking system is carried out by a cable having a connection with an additional element between the body and the rotating wheels. This element is an additional weight, which increases the wheel system in insignificant volume and weight - only a few %. The other end of the cable is connected to a special mechanical energy storage spring. The mechanical pulling force of the cable compresses the spring system of the special design and accumulates mechanical energy in a volume of approximately 60–70% of the braking energy. The same end of the cable is also connected to the freewheel clutch and the return spring. After the mechanical energy has been transferred, the cable and the brake disc (additional element) are freely returned to their original position by a return spring. The mechanical energy accumulator is constructed of springs made of good quality steel. It is possible to create a design that stores the energy of all four wheels of the vehicle with a single spring. For the design investigated in the work, a carbon steel spring was selected using the characteristics of this steel. The electric generator installed in the structure, mechanically connected with the mechanical energy accumulator, converts mechanical energy into electrical energy by rotation of the rotor under the action of spring forces. Electricity from the electric generator is directed for collection in the battery banks.

On latches in biological systems: a comparative morphological and functional study of the retinaculum and the dens lock in Collembola

BackgroundSpringtails have the ability to jump using morphological structures consisting of a catapult, the furca, and a latching system constructed with interaction of the retinaculum and the dens lock. The retinaculum engages in the furca at the dens lock in order to form a spring mechanism. They exhibit diversified morphological traits that serve as adaptations to a variety of terrestrial strata and aquatic surface environments. This comparative morphofunctional study centered on the retinaculum and the furcular region of the dens lock aims to describe the morphological variation between taxa and provide insights into the functional dynamics of the latching mechanism at work in the jumping apparatus. Using SEM, µCT and cLSM, we compared representatives of Collembola taxa, Poduromorpha (Neanura muscorum and Podura aquatica), Symphypleona (Dicyrtomina ornata) and Neelipleona (Megalothorax minimus), and examined extracts of the environment in which they were collected.ResultsA retinaculum is absent in N. muscorum, although vestigial muscles were found. Abdominal musculature varies significantly, being more abundant in springtails with clear segmentation (N. muscorum and P. aquatica), and reduced in springtails with fused segmentation (D. ornata and M. minimus). The M.a-ret varies as regards architecture and point of connection with the ramus, which is lateral in P. aquatica and median in the other species studied. The number of teeth in the retinaculum ramus also varies between three in M. minimus and four in the other species. The dens lock of all species studied has two locks and two furrows.ConclusionsThe retinaculum and dens lock interact in a key-lock relationship. The latching and unlatching mechanism from the retinaculum and dens lock appear to be similar in all the taxa examined, occurring by muscle force. This leads us to question the hypothesis that hemolymph pressure may be a force generator in jumping. We offer a reconstruction of the ground pattern of the retinaculum and dens lock and, in addition, an explanation of their functioning and the interaction between them. Finally, we frame the interaction between the retinaculum and the dens lock as a latch in a biological system, a mechanism which functions by force of physical contact.

Novel Adaptive Magnetic Springs for Reliable Industrial Variable Stiffness Actuation

Parallel elastic actuation is a highly promising concept for assisting preplanned trajectories such as repetitive tasks in industrial machines and robots. Nevertheless, due to the persisting challenges on spring lifetime, its full potential has yet to be leveraged in the industry. We propose a novel adaptive magnetic spring as a fatigue-free spring mechanism to enable variable stiffness actuators in long lifetime applications. The spring is designed to flexibly deal with variations in operating conditions, i.e., mass customization. We propose a co-design methodology which simultaneously optimizes the sizing of the magnetic spring (for the given machine and its operating conditions), together with the controls and ideal dynamic response of the system. This mechanism and the methodology are applied to a design problem of a weaving machine drivetrain, where the benefits of the adaptive magnetic spring are highlighted with respect to a fixed stiffness magnetic spring, and the current industrial benchmark without springs. Experimentally validated findings show a consistent and considerable improvement with respect to energy consumption and peak torque reduction of up to 47% and 64%, respectively, when comparing to the current industrial benchmark.

Seismic response of linked column steel braced frame with mechanical springs

Linked column frame (LCF) is a new resilient structure. However, previous studies have shown that both the plastic rotation and plastic hinge distribution of link beams in LCF system are unsatisfactory, which significantly affect the seismic performance. To expand the plastic deformation and optimize the plastic hinge distribution, an uplifted column foot with springs is introduced. A 1:3 scale pseudo-static test and numerical analysis were conducted to evaluate the hysteresis performance of LCF system with springs, specifically the frame lateral deformation, the shear deformation of link beams and yielding mechanism. Moreover, the virtual work principle was applied to analyze the lateral bearing capacity theoretically. The result shows that when the frame was subjected to lateral forces, axial deformation was observed in the springs, thus releasing the vertical restraint of columns, eventually the link beams are motivated to develop inelastic deformation and the frame rotated, similar to a rocking structure. Additionally, compared to the numerical simulation and experiment results, the relative errors were analyzed and the theoretical bearing capacity was modified. In conclusion, the proposed foot configuration can significantly improve the energy dissipation capacity of LCF system. The shear deformations of link beams in different storeys are relatively uniform along the frame height.

Electromagnetic vibration energy harvester using magnetic fluid as lubricant and liquid spring

Using vibration energy harvester (VEH) to achieve self-power supply is an effectively way to ensure long-term use of electronic devices. In this paper, an electromagnetic VEH using magnetic fluid (MF) as lubricant and liquid spring is proposed, the VEH uses a hollow shell with variable internal diameter together with MF to form a liquid spring with variable stiffness coefficient to replace the traditional mechanical or magnetic spring, and planar coils and helical coils are used together to harvest the vibration energy, thereby broadening response frequency, improving energy harvest efficiency, and reducing VEH volume and damping. The influence of MF on the lubrication, liquid spring, and vibration state is studied theoretically, and the induced voltage is simulated. A crank-slider linkage has been built to test the performance of VEH, and the influence of vibration frequency, mass of MF, and coil type on the output performance has been studied during a 7.5 mm reciprocating linear motion of VEH. Results show that an appropriate amount MF can improve the output voltage by 173 % at 3.25 Hz, but too much MF will cause a rapid drop in output voltage. Helical coils generate higher voltage than planar coils, and the output power density of the helical coil is 0.92 mW/cm3 at 8.5 Hz. The energy management module can manage electric energy well, and half wave rectifier with low forward voltage drop may be more suitable for VEH with low output voltage. Besides, the VEH delivers a 1.36 mW/cm3 power density with a 10 Ω load when it is swung by human at 6.4 Hz.

Dynamic analysis of a tunable electromagnetic bistable system

Bistable structures exhibit a unique snap-through behaviour, which is widely used in different engineering disciplines. Some bistable systems have the ability to change dynamic characteristics such as the depth of the potential wells, distribution of the stable equilibrium points, and symmetry of the potential function, but only for the initial assembly. Therefore, this study presents a novel tunable electromagnetic bistable system (EBS), which can be adjusted online. An EBS is composed of a mechanical spring and an electromagnetic negative-stiffness unit in parallel. To characterise such a system, a static model was developed using the filament method, and the dynamic response was calculated using the harmonic balance method to better understand the EBS tunability. We conducted a series of studies aimed at revealing the effects of the geometric parameters, initial conditions, and excitation level on the dynamic characteristics. Finally, a switch between the interwell and intrawell oscillations of the actively tunable EBS was experimentally demonstrated, improving applications such as adaptive energy harvesting and active vibration control.