Hard Springs Research Articles

Equivalent spring-like system for two nonlinear springs in series: application in metastructure units design

AbstractThe paper deals with the problem of design of unit in auxetic metastructure. The unit is modeled as a two-part spring-like system where each part is with individual stiffness. To overcome the problem of analyzing of each of parts separately, the equivalent spring is suggested to be introduced. In the paper, a method for obtaining the equivalent elastic force of the unit is developed. The method is the generalization of the procedure suggested for substitution of a hard and a soft spring in series with an equivalent one. The nonlinearity of original springs is of quadratic order. As a results, it is obtained that the equivalent elastic force for two equal springs remains of the same type as of the original springs (soft or hard). For two opposite type springs in series with equal coefficients, the equivalent force is soft. The method is applicable for any hard and soft nonlinear springs or spring-like systems. Thus the hexagonal auxetic unit which contains a soft and a hard part in series is analyzed. In the paper, a new analytic method for determination of the frequency of vibration for the unit under action of a constant compression force acting along the unit axis is introduced. The method is applied for units which contain two parts: hard–hard, soft–soft, hard–linear, soft–linear and opposite. The obtained approximate vibration results are compared with numerically obtained ones and show good agreement. The advantage of the method is its simplicity as it does not require the nonlinear equation of motion to be solved.

機構の特異姿勢を利用した受動的運動量交換型衝撃吸収ダンパの最適設計

When a mechanical system collides with the ground, the impact force may cause damage to its components. Generally, springs and elastic members are installed to prevent the impact. However, it is difficult to overcome this problem because hard springs have a large mass, a spring with a large mass cannot suppress the impact force, and the energy stored in the spring has to be dissipated. On the other hand, Momentum Exchange Impact Damper (MEID) aims to reduce the momentum of the main body by transferring momentum to the weight, and are effective for shock mitigation. From this point of view, we have proposed a passive MEID so far. This is a passive mechanism that achieves momentum exchange and prevents the propagation of the impulsive force by utilizing the singularity of the mechanism. The mechanism does not require any additional actuators or sensors, and is extremely effective in mitigating the impact force. However, there is a problem that the acceleration generated in the body during the motion of the mechanism is not small. In this paper, we propose a passive MEID that reduces the acceleration generated in the main body by changing the constraint of the mechanism, and design it by optimization. The effectiveness of the proposed mechanism is verified through experiments using a prototype.

Stiffening and dynamics of a two-dimensional active elastic solid.

This work deals with the mechanical properties and dynamics of an active elastic solid defined as a two-dimensional network of active stochastic particles interacting by nonlinear hard springs. By proposing a discrete model, it is numerically found that when activity in the system is turned on, the active solid stiffens as a function of propulsion forces, thus deviating from equilibrium mechanics. To understand this effect a minimal stochastic model is offered, and a physical explanation based on spatial symmetry-breaking is put forward. In addition, the dynamics of the active solid in the absence of an external stress is also studied. From this, three main features are observed to emerge, namely, a collective behavior within the active solid, a time-density fluctuation, and oscillating dynamics of the internal stresses towards a steady state.

Effect of thoracic stiffness on chest compression performance - A prospective randomized crossover observational manikin study

IntroductionHuman thoracic stiffness varies and may affect the performance during external chest compression (ECC). The Extra Compression Spring Resusci® QCPR Anne manikin is a high-fidelity training model developed for ECC training that can account for varying levels of thoracic stiffness. The aim of this study was to use this training model to investigate the effects of thoracic stiffness on ECC biomechanics and qualities. MethodsFifty-two participants performed standard ECC on the manikin with different thoracic springs to simulate varying levels of thoracic stiffness. The MatScan Pressure Measurement system was used to investigate the ECC pressure and force distribution. ResultsThe hard spring group’s performance had a better complete recoil ratio (90.06 ± 24.84% vs. 79.75 ± 32.17% vs. 56.42 ± 40.15%, p < 0.001 at second minute), but was more inferior than the standard and soft spring groups in overall quality, ECC depth (34.17 ± 11.45 mm vs. 41.25 ± 11.42 mm vs. 51.88 ± 7.56, p < 0.001 at second minutes), corrected depth ratio, and corrected rate ratio. The hard spring group had less radial-ulnar peak pressure difference (kgf/cm2) than the other two groups (−0.28 ± 0.38 vs. −0.30 ± 0.43 vs. −0.47 ± 0.34, p = 0.01), demonstrating that more symmetrical pressure was applied in the hard spring group. The soft spring group had better ECC depth, corrected depth ratio, corrected rate ratio, and overall quality, but its performance in complete recoil was inferior, and unbalanced pressure was more liable to cause injury. Hard springs caused operator fatigue easily. ConclusionThe thoracic stiffness greatly affected the performance of ECC. Our findings provided information for more effective ECC practices and training.

Minimal model of an active solid deviates from equilibrium mechanics

In this work, the mechanical response oF an one-dimensional active solid -- defined as a network of active stochastic particles interacting by nonlinear hard springs -- subject to an external deformation force, is numerically studied and rationalized with a minimal model. It is found that an active solid made of linear springs and subject to an external stress, presents an average deformation which is independent of the system's activity. However, when the active solid is made of nonlinear hard springs, the solid's average deformation decreases with respect to a passive system under the same conditions, and as a function of activity and rotational noise in the system. The latter result may shed light on new ways to creating an active metamaterial, which could tune its stiffness by moving either its activity or rotational noise.

Three New Diatom Species from Spring Habitats in the Northern Apennines (Emilia-Romagna, Italy)

Using light (LM, including plastid characterization on fresh material) and scanning electron microscopy (SEM), as well as a thorough morphological, physical, chemical, and biological characterization of the habitats, the present study aims at describing three species new to science. They belong to the genera Eunotia Ehrenb., Planothidium Round and L. Bukht., and Delicatophycus M.J. Wynne, and were found in two contrasting spring types in the northern Apennines. The three new species described differ morphologically from the most similar species by: less dense striae and areolae, and the absence of a ridge at the valve face-mantle transition (SEM feature) [Eunotia crassiminor Lange-Bert. et Cantonati sp. nov.; closest established species: Eunotia minor (Kütz.) Grunow]; narrower and shorter cells [Planothidium angustilanceolatum Lange-Bert. et Cantonati sp. nov.; most similar species: Planothidium lanceolatum (Bréb. ex Kütz.) Lange-Bert.]; barely-dorsiventral symmetry, set off ends, and lower density of the central dorsal striae [Delicatophycus crassiminutus Lange-Bert. et Cantonati sp. nov.; most similar species: Delicatophycus minutus M.J.Wynne]. Two of the three species we described are separated from the closest species by dimensions. Their description improved knowledge on two taxa (Eunotia minor s.l. and Planothidium lanceolatum s.l.) likely to be only partially resolved species complexes. We could also refine knowledge on the ecological profiles of the three newly-described species. Eunotia crassiminor sp. nov., as compared to Eunotia minor, appears to occur in colder inland waters with a circumneutral pH and a strict oligotrophy as well with respect to nitrogen. The typical habitat of Planothidium angustilanceolatum sp. nov. appears to be oligotrophic mountain flowing springs with low conductivity. Delicatophycus crassiminutus sp. nov. was observed only in limestone-precipitating springs, and is therefore likely to be restricted to hard water springs and comparable habitats where CO2 degassing leads to carbonate precipitation. Springs are a unique but severely threatened wetland type. Therefore, the in-depth knowledge of the taxonomy and ecology of characteristic diatom species is important, because diatoms are excellent indicators of the quality and integrity of these peculiar ecosystems in the face of direct and indirect human impacts.

Characteristics, vulnerability and conservation value of active tufa-forming springs on coastal cliffs in the NW Iberian Peninsula

Tufa-forming hard water springs are classified as a priority natural habitat of community interest and described in Annex I of Community Directive 92/43/EEC as “ (Natura, 2000 habitat type 7220* Petrifying springs with tufa formation [Cratoneurion])”. This type of habitat is scarce along the European Atlantic coast. In this study, petrifying springs in 36 coastal locations in the NW Iberian Peninsula were described on the basis of their physiographical characteristics, geomorphologic context, water chemistry, floristic composition and the types of disturbance endangering their conservation. The springs under study differed from other coastal and inland examples of this type of habitat in relation to the abiotic factors controlling their distribution and also some botanical traits. They are the southernmost petrifying springs reported to date on the Atlantic coast of Europe. Unfortunately, one third of the study sites lie outside of the protected areas delimited in the European Natura 2000 Network. This suggests that the network should be extended in order to conserve biodiversity and natural heritage in Atlantic Europe.

Dual form of discontinuous deformation analysis

Discontinuous deformation analysis (DDA) is a numerical method for analyzing dynamic behaviors of an assemblage of distinct blocks, with the block displacements as the basic variables. The contact conditions are approximately satisfied by the open–close iteration, which needs to fix or remove repeatedly the virtual springs between blocks in contact. The results from DDA are strongly dependent upon stiffness of these virtual springs. Excessively hard or soft springs all incur numerical problems. This is believed to be the biggest obstacle to more extensive application of DDA. To avoid the introduction of virtual springs, huge efforts have been made with little progress related to low efficiency in solution. In this study, the contact forces, instead of the block displacements, are taken as the basic variables. Stemming from the equations of momentum conservation of each block, the block displacements can be expressed in terms of the contact forces acting on the block. From the contact conditions a finite-dimensional quasi-variational inequality is derived with the contact forces as the independent variables. On the basis of the projection–contraction algorithm for the standard finite-dimensional variational inequalities, an iteration algorithm, called the compatibility iteration, is designed for the quasi-variational inequality. The main processes can be highly parallelized with no need to assemble the global stiffness matrix. A number of numerical tests, including those very challenging, suggest that the proposed procedure has reached practical level in accuracy, robustness and efficiency, and the goal to abandon completely virtual springs has been reached.

An Acceleration-Based Robust Motion Controller Design for a Novel Series Elastic Actuator

This paper proposes an acceleration-based robust controller for the motion control problem, i.e., position and force control problems, of a novel series elastic actuator (SEA). A variable stiffness SEA is designed by using soft and hard springs in series so as to relax the fundamental performance limitation of conventional SEAs. Although the proposed SEA intrinsically has several superiorities in force control, its motion control problem, especially position control problem, is harder than conventional stiff and SEAs due to its special mechanical structure. It is shown that the performance of the novel SEA is limited when conventional motion control methods are used. The performance of the steady-state response is significantly improved by using disturbance observer (DOb), i.e., improving the robustness; however, it degrades the transient response by increasing the vibration at tip point. The vibration of the novel SEA and external disturbances are suppressed by using resonance ratio control (RRC) and arm DOb, respectively. The proposed method can be used in the motion control problem of conventional SEAs as well. The intrinsically safe mechanical structure and high-performance motion control system provide several benefits in industrial applications, e.g., robots can perform dexterous and versatile industrial tasks alongside people in a factory setting. The experimental results show viability of the proposals.

ŹRÓDLISKA Z MARTWICĄ WAPIENNĄ W DOLINIE POTOKU JAMNE W GORCACH

The study gives a detail characteristic of a hard water springs habitat with the communities of Cratoneurion commutati (habitat code of Nature 2000: 7220), localized within Nature 2000 protected area Ostoja Gorczanska PLH120018, in an upper part of the valley of Jamne creek. The vegetation is described along with the main habitat parameters, namely: altitude, exposition, slope gradient, insolation, type of bedrock, water flow regime and the spring outflow efficiency. The temperature, pH, electrical conductivity were measured in the field, the concentra tions of Ca and Mg in spring water were measured by Atomic Absorption Spectroscopy (AAS). The investigated headwater areas are small (0.7–80 m 2 ) and highly differentiated by the intensity of calcareous tufa precipitation and the degree of plant cover development.

Surface and subsurface water quality assessment in semi-arid region: a case study from Quetta and Sorange Intermontane Valleys, Pakistan

&lt;div&gt; &lt;p&gt;Present investigation is an exertion to explore safe means of water for the community in the water scare region. In order to accomplish such goal origin of springs as well as chemical analyses of groundwater samples from different locations were carried out. Four zones are discovered on the basis of nature of water points, rock types and water chemistry. These zones are Hard Rocks Springs (HRS), Valley Springs (VS), Recharge Areas Aquifers (RAA) and Central Valley Aquifers (CVA). HRS are originated from thick successions of limestone (Kirthar Limestone) and thick packages of channelized sandstone and conglomerates of the Siwalik Group. It is recommended that Chiltan, Parh, Kirthar, Dhok Pathan and Soan formations may be focused for future needs of safe water supply in the Quetta valley. This study includes the analysis of different physico-chemical parameters such as Total dissolved solids (TDS), pH, turbidity, Electrical conductivity (EC), hydrochemical facies, Sodium Adsorption Ration (SAR), Sodium Percent (Na%), Kelleys Index (KI), Permeability Index (PI), major cation and anions to assess the quality of groundwater sources. The outcomes of groundwater analyses were equated with various drinking water standards e.g., NSDWQ-Pak, USEPA, and EU. The results are plotted for determination of lateral variations and to empathize the reasons of these variations. The affects of rock types, geological structures as well as anthropogenic causes on origin and results are discussed systematically. The hydrochemical facies identified show that the alkaline earth exceeds alkalies, strong acids exceeds weak acids, mixed type (no cation, anion exceeds 50%), no dominant cation and anion types but water of VS is calcium chloride and sulfate type. The water is classified as C2-S1 (HRS), C3-S1 (CVA &amp;amp; RAA) and C3-S2 (VS) based on SAR and EC values, which intend that most water samples can be used for irrigation safely except water samples collected from VS. Based on the Na% the water samples are categorized as excellent to good and good to permissible limits. The water is suitable for irrigation as all samples bear KI less than 1. The PI values in the water samples studied (less than 40) also contemplate that the water is desirable for irrigation use, although caution is needed of VS water.&lt;/p&gt; &lt;/div&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;

Functional helicoidal model of DNA molecule with elastic nonlinearity

We constructed a functional DNA molecule model on the basis of a flexible helicoidal sensor, specifically, a pretwisted hollow nano-strip. We study in this article the helicoidal nano- sensor model with a pretwisted strip axial extension corresponding to the overstretching transition of DNA from dsDNA to ssDNA. Our model and the DNA molecule have similar geometrical and nonlinear mechanical features unlike models based on an elastic rod, accordion bellows, or an imaginary combination of “multiple soft and hard linear springs”, presented in some recent publications.

DNA molecule elastic nonlinearity: A functional helicoidal model

AbstractWe constructed a functional DNA molecule model on the basis of a flexible helicoidal sensor, specifically, a pretwisted hollow nano‐strip. We study in this note the helicoidal nano‐sensor model with a pretwisted strip axial extension corresponding to the overstretching transition of DNA from dsDNA to ssDNA. Our model and the DNA molecule have similar geometrical and nonlinear mechanical features unlike models based on an elastic rod, accordion bellows, or a combination of “multiple soft and hard linear springs”, presented in some recent publications.

DNA elastic nonlinearities as multiple smooth combinations of soft and hard linear springs

AbstractDNA molecules perform biological functions via large elastic deformations and conformational changes in courses of their interactions with the cellular machinery. Adequate characterization of DNA elasticity is accordingly essential to an in‐depth understanding of DNA functions. Because of profound complexity, however, nonlinear features inherent in DNA elasticity remains to be uncovered in a direct, full sense and a unified, explicit characterization over the entire stretch range has been unavailable. Here it is suggested that DNA elastic nonlinearities may be understood by combining linear springs with high compliance and high rigidity. This finding uncovers the inherent geometrical feature in profound nonlinearities of DNA elasticity and leads to a unified, explicit force‐extension formula up to breaking. This formula reveals for the first time a complete set of characteristic constants for DNA elasticity and is shown to provide a unified characterization for both double‐ and single‐stranded DNA molecules. Results are presented in a straightforward, broad sense independent of any substructural details.

Limit cycles of a double pendulum with nonlinear springs

The limit cycles of a double pendulum with hard, soft, or linear springs subject to a follower force are drawn using computer simulation

Fracture toughness and maximum stress in a disordered lattice system

We model the disorder-induced increase in fracture strength by applying a two-dimensional elastic network with an initial crack. The model has all the nearest neighbors, except those on the initial crack, connected by springs, which are randomly chosen as either hard or soft. All the springs are cut at the same force threshold. Our calculations show that the maximum stress in the disordered system is increased if the initial crack length is sufficiently large, and we discuss the relationship between the crack length and the force distribution or the work done on the system. We also derive the enhancement of the stress intensity factor and fracture toughness by analyzing the generation of the fracture process zone.

Optimal suspension settings for ride comfort of road vehicles

In this paper a numerical study is presented for the effect of the settings of the suspension parameters of a road vehicle for the ride comfort. The chassis of the IK GMC midibus model is investigated as an example. The suspension parameters are represented by hard springs and dampers. By the appropriate choice of the suspension parameters it can be achieved that the influence of the dynamical forces is minimal for the oscillation of the carbody and for the dynamically computed internal forces, respectively. The nonlinear constrained optimization models provide appropriate tools to investigate the effect of the suspension parameters for the average acceleration and displacement of the chassis, respectively.

Dynamical models of molecular chains and efficient integration algorithms

Chains of point masses and chains of rigid bodies are used to model biological polymers. To investigate their dynamics we propose a method which allows an efficient realization of the constraints jointly with a simple and accurate integration of the free rigid body motion. The method is quite effective to evolute the geodesic flow of a rigid body chain and the global performance depends on the computational complexity of the algorithms used to compute the interaction forces. Our approach is suitable to describe a chain of rigid bodies immersed in a thermal bath. In the method we propose, the constraints are realized by hard springs whose elastic constant is set to maximize the energy dissipation rate of a Runge–Kutta integrator scheme. Moreover the use of local Lagrangian coordinates is introduced using the possibility of a continuous change of chart, such that the distance from the coordinate singularities is the highest possible. For a chain of point masses the numerical results are checked with another method where the constraints are exactly realized by means of Lagrangian coordinates. When the chain is subject to regular interactions potentials plus a thermal bath the exact and approximate constraints realization provide comparable results.

Validation of the Soft Tissue Restraints in a Force-Controlled Knee Simulator

In vitro testing of total knee replacements (TKRs) is important both at the design stage and after the production of the final components. It can predict long-term in vivo wear of TKRs. The two philosophies for knee testing are to drive the motion by displacement or to drive the motion by force. Both methods have advantages and disadvantages. For force control an accurate simulation of soft tissue restraints is required. This study was devised to assess the accuracy of the soft tissue restraints of the force-controlled Stanmore knee simulator in simulating the restraining forces of the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). In order to do this, human cadaver knee joints were subjected to the ISO Standard Walking Cycle. The resulting kinematics were monitored when the soft tissue structures were intact, when the ACL and PCL were resected, and when they were simulated by springs positioned anteriorly and posteriorly. The stiffness of the springs was determined from the literature. Two different stiffnesses of springs were used which were 7.24 N/mm (designated as soft springs) and 33.8 N/mm (designated as hard springs). All the intact knees showed displacements that were within the range of the machine. Cutting the ACL and PCL resulted in anterior and posterior motion and internal external rotation that were significantly greater than the intact knee. Results showed that when the ACL and PCL were cut hard springs positioned anterior and posterior to the knee returned the knee to near normal anterior-posterior (AP) motion. Using hard springs in the posterior position in any condition reduced rotational displacements. Therefore using springs in a force-controlled simulator is a compromise. More accuracy may be obtained using springs that are of intermediate stiffness.

Ecología y conservación de &lt;i&gt;Centaurium somedanum&lt;/i&gt; M. Laínz (Gentianaceae), planta endémica de la Cordillera Cantábrica (España)

Centaurium somedanum is a cantabrian endemism, with less than twenty localities known in the western Cantabrian Mountains. In order to assess its conservation status, a short-term study has been developed, by applying a Basic Study and an Habitat Integrated Study, which have defined the habitat for the plant, number of populations and some demographic information. The results from the study have confirmed the extinction of the plant in some localities where it had been recorded. C. somedanum is a short-lived chamaephyte plant, limited to fourteen populations at present, and only four of them exceed five hundred adult individuals. They occur on very specific habitats, in the surroundings of calcareous hard water springs, between 500 and 1600 meters of altitude. The specific nature and scarcity of its habitat are the main reasons of the rareness and threat of this species. Some other rare species and plant communities from Cantabrian Mountains share with C. somedanum the need of this type of spring communities conservation, which are currently under different threats.