Rounded Step Research Articles

An investigation of a self-powered low-frequency nonlinear vibration isolation system

High-static-low-dynamic stiffness vibration isolation are of utmost significance in low-frequency vibration isolation. However, their intricate mechanisms are always challenging for environmental vibration changes. In this study, a self-powered nonlinear vibration isolation system with two stages is studied, with the aiming of obtaining the broadband vibration isolation. Magnetic springs of negative stiffness combined with the coil could transform mechanical vibration into electrical energy in lower stage. The feedback electrical energy could power the piezoelectric actuator in the upper stage. Based on the governing equations measured in stable equilibrium, the harmonic balance analysis is used to derive the frequency response functions of the transmissibility and the output power in the mechatronic resonance. The frequency band of vibration isolation extends to the lower frequencies and two resonance peaks reduce to the lower levels. The numerical simulations results validate the analytical solutions. Then the shock isolation performance is illustrated under the round step displacement and rounded pulse displacement. The parameter study demonstrates numerically that introduction of the high-static-low-dynamic stiffness improves the shock isolation performance. Moreover, the lower stage mechanical energy could drive the piezoelectric stack, resulting in high-efficiency shock isolation. Finally, an experiment is employed to prove the high-efficiency vibration isolation.

Calibration of a Near-Wall Differential Reynolds Stress Model Using the Updated Direct Numerical Simulation Data and Its Assessment

In the article, a differential Reynolds stress model is recalibrated using turbulent channel flow direct numerical simulation data in the range of friction Reynolds numbers 550–5200. The calibration aims to produce a RANS sublayer model for use within the hybrid RANS/LES framework. The model is designed to capture the average field of a thin near-wall part of a boundary layer as accurately as possible. An a posteriori procedure is employed in which one-dimensional channel flow calculations are performed for all variations of the model coefficients at each stage of the optimization procedure. The coefficients are initialized with their original values and then optimized by minimizing the appropriately chosen norm. An improved representation of the mean velocity profile and peak Reynolds stress values is demonstrated. Both models—baseline and recalibrated—are implemented in an in-house CFD code, and several simulations, including a channel flow, a flat plate boundary layer and a boundary layer separation from a rounded step, are performed. The latter benchmark flow is also simulated in hybrid RANS/LES mode. The updated model is compared to the original one, demonstrating improvements over the baseline model in the cases it was designed for.

A modified secure hash design to circumvent collision and length extension attacks

This paper introduces an improved version of the secure hash algorithms, SHA-1, and SHA-2. The proposed work produces a strengthened secure hash design using the fusion between the SHA-1 and SHA-2 hash standards. This design helps to protect the SHA-1 and SHA-2 against collision and length extension attacks. The proposed design is incorporated in the round steps of the hash functions using the function manipulators of the SHA-1 and SHA-2. Moreover, the proposed design employs a padding method that is different from the one used in the SHA-1 and SHA-2 construction. The proposed design is verified by the official test vectors that were confirmed by the National Institute of Standard and Technology. Moreover, the avalanche effect, hamming distance, and bit-hit properties were studied using different test cases. The proposed design gives over 52 percent of the avalanche effect and over 84 hamming distance. The proposed design was tested against collision attack and produced unique hash values for real collided examples and shows resistance against length extension attack.

An efficient MPC algorithm for switched systems with minimum dwell time constraints

This paper presents an efficient suboptimal model predictive control (MPC) algorithm for nonlinear switched systems subject to minimum dwell time constraints (MTC). While MTC are required for most physical systems due to stability, power and mechanical restrictions, MPC optimization problems with MTC are challenging to solve. To efficiently solve such problems, the on-line MPC optimization problem is decomposed into a sequence of simpler problems, which include two nonlinear programs (NLP) and a rounding step, as typically done in mixed-integer optimal control (MIOC). Unlike the classical approach that embeds MTC in a mixed-integer linear program (MILP) with combinatorial constraints in the rounding step, our proposal is to embed the MTC in one of the NLPs using move blocking. Such a formulation can speedup on-line computations by employing recent move blocking algorithms for NLP problems and by using a simple sum-up-rounding (SUR) method for the rounding step. An explicit upper bound of the integer approximation error for the rounding step is given. In addition, a combined shrinking and receding horizon strategy is developed to satisfy closed-loop MTC. Recursive feasibility is proven using a l-step control invariant (l-CI) set, where l is the minimum dwell time step length. An algorithm to compute l-CI sets for switched linear systems off-line is also presented. Numerical studies show significant speed-up and comparable control performance of the proposed MPC algorithm against the classical approach, though at the cost of significant solution quality degradation especially when the MTC are large.

Outer layer turbulence dynamics in a high-Reynolds-number boundary layer up to recovering from mild separation

The outer layer dynamics of a high-Reynolds-number boundary layer recovering from non-equilibrium is studied utilising the multi-resolution approach of zonal detached eddy simulation mode 3. The non-equilibrium conditions are obtained from a boundary layer separation over a rounded step enhancing the turbulent production, and recovery happens during redevelopment after reattachment at high Reynolds numbers ( $Re_{\theta,max}\approx 24{,}000$ ). Most of the outer layer turbulence is resolved by the simulation, which reproduces accurately the experimental boundary layer relaxation. The spectral analysis of streamwise velocity fluctuations and turbulent kinetic energy (TKE) production evidences the different turbulent content distribution at separation and within the redevelopment region, at which very large-scale motions are identified with streamwise wavelengths up to $\lambda _x = 9\delta$ , where $\delta$ is the boundary layer thickness. The redevelopment of the boundary layer is analysed in terms of the persistence of a secondary peak in the TKE production and the evolution of the wall-shear stress statistics. The skewness and probability density function of the skin friction show a slower relaxation than the downstream flow fraction. This confirms the long-lasting impact of perturbations of the outer layer in high-Reynolds-number wall-bounded flows. This persistent non-equilibrium state is suggested to be the reason for the reported lack of accuracy of the considered Reynolds-averaged Navier–Stokes models in the relaxation region.

Development of the Prevent for Work questionnaire (P4Wq) for assessment of musculoskeletal risk in the workplace: part 1—literature review and domains selection

ObjectiveThis study aims to define appropriate domains and items for the development of a self-administered questionnaire to assess the risk of developing work-related musculoskeletal disorder (WMSD) and the risk of...

Ball bouncing down rounded edge stairs: chaotic but tricky

The aim of this study is to investigate the bouncing dynamics of a small elastic ball on a staircase consisting of rounded edge steps, as an example of a dissipative gravitational billiard, and to determine if its dynamics is chaotic. We derive a nonlinear recursion for the coordinates of the collisions, completed with numerical simulations, which indicate that the bouncing dynamics is chaotic, as also follows from elementary considerations regarding the Lyapunov exponent. It is, however, surprising that instead of permanent chaos, only the transient form is present. The main reason behind this is that a collision with the rounded edge of the step enhances the horizontal velocity leading to larger and larger jumps. Not even the introduction of a tangential coefficient of restitution (COR) on the curvature can hinder the flying away of some trajectories. There is also a chance for remaining trapped on a single step in the form of sliding, representing another possibility for escape. Therefore, chaoticity holds for long trajectories before any kind of escape takes place. We also show that an impact-velocity-dependent COR converts the dynamics to permanently chaotic with an underlying fractal attractor. Only elementary mathematics is required for the analytic calculations used, and we offer a set of problems to solve, as well as a user-friendly demo software on our website: https://theorphys.elte.hu/fiztan/stairs to facilitate experimentation and further understanding of this complex phenomenon.

Approximation algorithm for the multicovering problem

Let \(\mathcal {H}=(V,\mathcal {E})\) be a hypergraph with maximum edge size \(\ell \) and maximum degree \(\varDelta \). For a given positive integers \(b_v\), \(v\in V\), a set multicover in \(\mathcal {H}\) is a set of edges \(C \subseteq \mathcal {E}\) such that every vertex v in V belongs to at least \(b_v\) edges in C. Set multicover is the problem of finding a minimum-cardinality set multicover. Peleg, Schechtman and Wool conjectured that for any fixed \(\varDelta \) and \(b:=\min _{v\in V}b_{v}\), the problem of set multicover is not approximable within a ratio less than \(\delta :=\varDelta -b+1\), unless \(\mathcal {P}=\mathcal {NP}\). Hence it’s a challenge to explore for which classes of hypergraph the conjecture doesn’t hold. We present a polynomial time algorithm for the set multicover problem which combines a deterministic threshold algorithm with conditioned randomized rounding steps. Our algorithm yields an approximation ratio of \(\max \left\{ \frac{148}{149}\delta , \left( 1- \frac{ (b-1)e^{\frac{\delta }{4}}}{94\ell } \right) \delta \right\} \) for \(b\ge 2\) and \(\delta \ge 3\). Our result not only improves over the approximation ratio presented by El Ouali et al. (Algorithmica 74:574, 2016) but it’s more general since we set no restriction on the parameter \(\ell \). Moreover we present a further polynomial time algorithm with an approximation ratio of \(\frac{5}{6}\delta \) for hypergraphs with \(\ell \le (1+\epsilon )\bar{\ell }\) for any fixed \(\epsilon \in [0,\frac{1}{2}]\), where \(\bar{\ell }\) is the average edge size. The analysis of this algorithm relies on matching/covering duality due to Ray-Chaudhuri (1960), which we convert into an approximative form. The second performance disprove the conjecture of Peleg et al. for a large subclass of hypergraphs.

A Performance Guarantee for Spectral Clustering

The two-step spectral clustering method, which consists of the Laplacian eigenmap and a rounding step, is a widely used method for graph partitioning. It can be seen as a natural relaxation to the NP-hard minimum ratio cut problem. In this paper, we study the following central question: When is spectral clustering able to find the global solution to the minimum ratio cut problem? First, we provide a condition that naturally depends on the intra- and intercluster connectivities of a given partition under which we may certify that this partition is the solution to the minimum ratio cut problem. Then, we develop a deterministic two-to-infinity norm perturbation bound for the invariant subspace of the graph Laplacian that corresponds to the $k$ smallest eigenvalues. Finally, by combining these two results we give a condition under which spectral clustering is guaranteed to output the global solution to the minimum ratio cut problem, which serves as a performance guarantee for spectral clustering.

A new floating-point adder FPGA-based implementation using RN-coding of numbers

A well-known problem in the computer science area is related to numerical data representation, which directly affects adder circuits’ design and a reason to have different formats: IEEE Std. 754, Half-Unit-Biased (HUB), and Round-to-Nearest (RN). RN has an advantage that rounding to nearest is equivalent to a word truncation. It avoids double rounding errors and intermediate rounding steps with an exact conversion between formats, making it applicable to general problems. However, there is a lack of research on the hardware implementation of the RN representation. In this work, we propose hardware architectures for binary and floating-point adders, analyzing for the latter its performance in terms of error and resource consumption in FPGAs. To accomplish this, we have developed a one-bit RN-based adder that allows modular designs, considering an efficient signal propagation to obtain new architectures for both binary and floating-point single-precision adders. The results open new perspectives for further applications.

A new intelligent hybrid encryption algorithm for IoT data based on modified PRESENT-Speck and novel 5D chaotic system

Modern application based on IoT sensors/devices are growth in several fields. In several cases, the sensing data needs to be secure in transmission to control / administrator side. In this paper, the proposed secure Internet of Things data sensing and proposed algorithms will be explained, based on the main overarching novel 5-D Hyper chaotic system and new encryption mechanisms (contains hybrid encryption and two modified encryption algorithms) controlled by Fuzzy rules. The encryption mechanism combined by using the structure of PRESENT and SPECK algorithm with novel 5-D chaotic system. Also, for encryption will use the modified mechanisms of Round steps in PRESENT algorithm by SPEECK which were adopted on an IoT sensing data transferring. This proposed system provides a high level of security for any sensitive information that may be generated from sensors that may be installed in an important location to protect buildings and offices from theft by making certain modifications to the algorithms necessary to maintain the safety and security of the information, etc., which must be protected from Attacks. This system is designed to be effective in providing security features for data contents that include confidentiality, authentication and non-repudiation, and is compatible with all types of remote sensing data and sensors to send the final notification to the final administrator view. The proposed system is designed to provide users with high flexibility and ease in managing change operations, speeding up encryption operations and intruding the contents of message packets (types and forms of different sensor data) at the point of origin and decrypting and checking packet integrity messages upon receipt. These features make users of this system more confident with each other. The proposed encryption mechanism and novel chaotic system passed different testes. The generated chaos key space at least 22560probable different combinations of the secret keys to break the system used brute force attack.

Shock Isolation Capability of an Electromagnetic Variable Stiffness Isolator With Bidirectional Stiffness Regulation

This article presents a novel electromagnetic variable stiffness isolator that achieves bidirectional stiffness regulation, which means that the isolator experiences a reduced stiffness when the applied current is positive and an increased stiffness when the opposite current is applied. In addition, the stiffness variations are equal for two currents with the same magnitude but opposite polarities. The proposed isolator can not only ensure the vibration isolation performance in working frequency zone that is relatively far from the natural frequency, but also can realize high-damping-like effect for shock response attenuation, without introducing any additional damping components that may complicate the system. The bidirectional stiffness regulation was realized by combining mechanical springs with hybrid magnets (permanent magnets and coil windings). Variation in the overall stiffness of the proposed isolator occurred when the current was continuously adjusted. A prototype of the isolator was designed, fabricated, and then tested with a round displacement step shock at the base. The theoretical analysis revealed that this device could be utilized as an active vibration isolator through certain control strategies. The experimental results proved the effectiveness of the proposed mechanism in shock isolation and revealed that it outperforms the conventional isolator in suppressing the residual vibration.

Sound radiated by turbulent flow over unrounded and rounded forward-facing steps

This study presents measurements of the far-field noise radiated by forward-facing steps with and without rounded corners. A noise prediction formula, obtained by combining theory and measurements, to predict noise radiated by an unrounded forward step is also presented. The prediction methodology has also been extended to include the effects of rounding the step corner. The height of the step in measurements ranged between 78% to 84% of the incoming, turbulent wall-jet boundary layer. The Reynolds number based on step height was between 8300 and 16,800. Six roundings of the step corner were considered with radii equal to 0%, 6.25%, 12.5%, 25%, 50%, and 100% of the step height. It was found that rounding the forward step corner reduces the noise without affecting its directivity and scaling significantly. A slight rounding of the corner only affects the noise at high frequencies, however, a further increase in rounding leads to a broadband noise reduction. The prediction formula for the unrounded forward step yields reasonably good agreement with both past and present measurements. The predictions also suggest that the noise generated by a forward step is independent of the incoming boundary-layer thickness and scales with the step height. The predictions for rounded forward steps show that the noise attenuation due to corner rounding can be reasonably approximated if it is assumed that the unsteady surface loading in the vicinity of rounded steps scales with the reattachment length associated with each rounding.

Numerical Modelling of Air-Water Flows over a Stepped Spillway with Chamfers and Cavity Blockages

Owing to effective aeration and energy dissipation, a stepped spillway is commonly used in a roller-compacted concrete (RCC) dam. However, its complex air-water flow features are far from being fully understood. Roughness density, step and cavity shapes are essential parameters. Numerical simulations are carried out to investigate their effects on hydraulic properties. In combination with the realizable k-ε turbulence model, the two-phase Mixture Model is used. The results indicate higher air concentrations for the spillway with rounded steps than the ones with trapezoidal steps; the roughness density and cavity shape show no observable effects on the aeration performance with cavity blockages. The characteristic air-water velocity for the trapezoidal steps layout is larger than that for the rounded steps. However, neither layout is sensitive to the roughness density; the velocity results for trapezoidal cavity and rounded cavity cases are almost independent of the roughness density. The velocity for all cases exclusive of trapezoidal steps increase with an increase in roughness density. The min. and max. pressures on the trapezoidal steps are slightly larger than those on the rounded steps; they increase with an increasing roughness density. The cavity shape and roughness density do not evidently influence the extreme pressures. Compared with the conventional step layout, chamfering the step edges slightly enhance the energy dissipation; partially blocking the cavities do not lead to any substantial change. In addition, the energy loss is not clearly related to the roughness density and step edge/cavity shape.

Effect of backward facing step shape on 3D mixed convection of Bingham fluid

The present paper examines the viscous laminar mixed convection flow of a Bingham viscoplastic fluid in order to enhance the thermal performance and thus reduce the pressure drop. To achieve this, three-dimensional numerical simulations for vertical, inclined, and round backward facing step inside a horizontal rectangular duct are established.The effects of variation in buoyancy, viscous and inertia forces variations as well as the step shape, on thermal and hydrodynamic behaviours of the fluid are investigated. The structure of the flow is significantly influenced by the variation of Bingham and Richardson numbers and the backward facing steps shape. It is found that the recirculation zones, which are the main source of thermal and hydrodynamic losses, are intensified with the increase in buoyancy forces represented by the Richardson number. Moreover, the recirculation zones are attenuated as the viscous forces predominate. It is also noticed that the recirculation zones decrease or disappear as the geometry is modified by reducing the angle or the shape of the step. The change of the step shape reduces significantly the pressure drops of about 11.77% and 58.83% for the inclined and rounded backward facing steps; respectively, compared to the vertical backward facing step. However, the pressure coefficient decreases along the duct and increases in presence of a recirculation zone. Also, the highest value of the total Nusselt number is obtained for a round backward facing step in mixed convection. Otherwise, an increase in the Bingham number extends the plug structure in the three geometries.

Neurocognitive Disorders in Heart Failure: Novel Pathophysiological Mechanisms Underpinning Memory Loss and Learning Impairment.

Heart failure (HF) is a major public health issue affecting more than 26 million people worldwide. HF is the most common cardiovascular disease in elder population; and it is associated with neurocognitive function decline, which represent underlying brain pathology diminishing learning and memory faculties. Both HF and neurocognitive impairment are associated with recurrent hospitalization episodes and increased mortality rate in older people, but particularly when they occur simultaneously. Overall, the published studies seem to confirm that HF patients display functional impairments relating to attention, memory, concentration, learning, and executive functioning compared with age-matched controls. However, little is known about the molecular mechanisms underpinning neurocognitive decline in HF. The present review round step recent evidence related to the possible molecular mechanism involved in the establishment of neurocognitive disorders during HF. We will make a special focus on cerebral ischemia, neuroinflammation and oxidative stress, Wnt signaling, and mitochondrial DNA alterations as possible mechanisms associated with cognitive decline in HF. Also, we provide an integrative mechanism linking pathophysiological hallmarks of altered cardiorespiratory control and the development of cognitive dysfunction in HF patients. Graphical Abstract Main molecular mechanisms involved in the establishment of cognitive impairment during heart failure. Heart failure is characterized by chronic activation of brain areas responsible for increasing cardiac sympathetic load. In addition, HF patients also show neurocognitive impairment, suggesting that the overall mechanisms that underpin cardiac sympathoexcitation may be related to the development of cognitive disorders in HF. In low cardiac output, HF cerebral infarction due to cardiac mural emboli and cerebral ischemia due to chronic or intermittent cerebral hypoperfusion has been described as a major mechanism related to the development of CI. In addition, while acute norepinephrine (NE) release may be relevant to induce neural plasticity in the hippocampus, chronic or tonic release of NE may exert the opposite effects due to desensitization of the adrenergic signaling pathway due to receptor internalization. Enhanced chemoreflex drive is a major source of sympathoexcitation in HF, and this phenomenon elevates brain ROS levels and induces neuroinflammation through breathing instability. Importantly, both oxidative stress and neuroinflammation can induce mitochondrial dysfunction and vice versa. Then, this ROS inflammatory pathway may propagate within the brain and potentially contribute to the development of cognitive impairment in HF through the activation/inhibition of key molecular pathways involved in neurocognitive decline such as the Wnt signaling pathway.

Effect of Height and Geometry of Stepped Spillway on Inception Point Location

Air entrainment in a stepped spillway is very important to protect the spillway from cavitation damage. The inception point is the location where air starts entering the non-aerated flow zone. The inception point location depends on different parameters, such as the discharge, step height, and step shape. In this paper, various stepped spillways, including flat steps, pooled steps, and round steps with different step heights were numerically simulated using the volume of fluid and realizable k-ε models. The results indicate that the inception point location moves downwards with the increase of the discharge of the stepped spillways. The length of the non-aerated flow zone increases with the discharge. The inception point location moves downwards as the step height decreases and the step number increases at the same discharge. The inception point location of the round stepped spillway model is much closer to the spillway crest than that of the flat stepped spillway with the same number of steps. The inception point location of the pooled stepped spillway is closer to the spillway crest than that of the flat stepped spillway, but more downstream than that of the round stepped spillway.

Aeroacoustics of Rounded Forward-Facing Steps: Far-Field Behavior

Measurements and predictions of far-field sound radiated by rounded forward-facing steps immersed in an incompressible turbulent boundary were performed. Four different corner rounding radii equal to 0%, 6.25%, 12.5%, and 25% of the step height were considered. The step height was 26.2% of the incoming boundary-layer thickness and the Reynolds number based on step height ranged between 35,000 and 104,000. Measurements of the spanwise averaged unsteady pressure show that the pressure on the downstream surface is a function of rounding due to change in the size and strength of the separation bubble, whereas on vertical face it remains independent of corner rounding. The pressure on either surface scales on the step height and free-stream velocity. Rounding the step corner leads to a consistent reduction in noise without changing the overall shape of the sound spectrum significantly. The sound from each rounded step exhibits the effects of step noncompactness, which prevents spectral scaling. The predictions of sound from an unrounded forward-facing step were made by combining a theoretical formulation with surface pressure measurements. The predictions describe the overall shape of the sound spectrum including the effects of step noncompactness accurately.

Time since death nomographs implementing the nomogram, body weight adjusted correction factors, metric and imperial measurements.

The concept of nomography was developed around 1880 as a means to compute formulas graphically. Regular use has decreased over time in most fields, mainly owing to progress in electronic computation devices. In forensic pathology, nomography is still used in the so-called "nomogram method" for the estimation of time since death. It is the graphical representation of the formula by Marshall and Hoare with the parameters of Henssge. Here, two nomograms exist (for ambient temperatures below and above 23 °C, no imperial measurements). Rounding for body weight input and result reading introduces errors. In addition, correction factors, applied to body weight, allow to adapt for certain conditions on the crime scene and are essential to the method. They are not directly integrated into the nomograms but must be applied in advance. A formula, scaling correction factors for different body weights, was later added by Henssge, along with a simplified table for case work. In this publication, we present newly designed time since death nomographs as representations of Henssge's parameters with the addition of both metric and imperial measurements, integration of weight adjusted scaling of correction factors, and a geometrically consistent framework for body weight and result reading, which eliminates some rounding steps and reduces the overall rounding-related estimation errors.

Improving the Randomization Step in Feasibility Pump

Feasibility pump is a successful primal heuristic for mixed-integer linear programs. The algorithm consists of three main components: rounding fractional solution to a mixed-integer one, projection of infeasible solutions to the linear programming relaxation, and a randomization step used when the algorithm stalls. While many generalizations and improvements to the original Feasibility Pump have been proposed, they mainly focus on the rounding and projection steps. We start a more in-depth study of the randomization step in Feasibility Pump. For that, we propose a new randomization step based on the WalkSAT algorithm for solving instances of the Boolean satisfiability problem. First, we provide theoretical analyses for instances with disjoint equality constraints that show the potential of this randomization step; to the best of our knowledge, this is the first time any theoretical analysis of the running-time of Feasibility Pump or its variants has been conducted, even for a special class of instances. Moreover, we propose a practical version of a new randomization step, and incorporate it into a state-of-the-art Feasibility Pump code. Our experiments suggests that this simple-to-implement modification consistently dominates the standard randomization previously used.