Experimental Parametric Study Research Articles

On the influence of head motion on the swimming kinematics of robotic fish.

Up to now bio-inspired fish-mimicking robots fail when competing with the swimming performance of real fish. While tail motion has been studied extensively, the influence of the head motion is still not fully understood and its active control is challenging. In this experimental study, we show that head yawing strongly impacts on the propulsion force and determines the optimal fin actuation amplitude and tail beat frequency when aiming for a maximal propulsion force. In a parametric experimental study on a tethered 367 mm long fish robot the pivot point location of the head yaw has been varied along with tail beat frequency and actuation amplitude. The experiments took place in a still water tank and the swimming force has been measured with a single axis load cell. The robot is actuated with non-conventional area actuators based on micro fiber composites. 105 parameter sets have been investigated while the highest pivot point distance of roughly 0.36 body length from the nose tip provided the highest propulsion force of 500 mN with the lowest actuation frequency of 2.5 Hz and the highest head motion amplitude of a magnitude of 0.18 body length. Even though the pivot point location on a free swimming robot is a consequence of the complex fluid-structure interactions of fish and fluid, the results provide valuable information for the design of fish mimicking robots and questions the paradigm that head yaw is a simple recoil effect from tail motion and has to be minimized for an effective propulsion.

High stiffness topology optimised lattice structures with increased toughness by porosity constraints

The stiffness and toughness of topology optimised structures containing lattices under three-point bending is studied. A porosity constraint is introduced to control the proportion of lattice generated while optimising the beams for minimum compliance. A novel tetrahedron element-based lattice with tapered trusses and a near-isotropic elastic response is developed to accurately map the relative densities from topology optimisation to a 3D printable structure. Topology optimised solid structures (0 % porosity), used for benchmarking, are found to have high stiffness but can be susceptible to buckling. At the other extreme, structures comprising entirely of lattice (100 % porosity) are shown to have low initial stiffness and low residual toughness. An experimental parametric study reveals that porosity can be tailored between these two bounds to achieve both high stiffness and high residual toughness.

A conceptual design of a thermal switch capacitor in a magnetocaloric device: experimental characterization of properties and simulations of operating characteristics

The quest for better performance from magnetocaloric devices has led to the development of thermal control devices, such as thermal switches, thermal diodes, and thermal capacitors. These devices are capable of controlling the intensity and direction of the heat flowing between the magnetocaloric material and the heat source or heat sink, and therefore have the potential to simultaneously improve the power density and energy efficiency of magnetocaloric systems. We have developed a new type of thermal control device, i.e., a silicon mechanical thermal switch capacitor (TSC). In this paper we first review recently developed thermal switches based on micro-electromechanical systems and present the operation and structure of our new TSC. Then, the results of the parametric experimental study on the thermal contact resistance, as one of the most important parameters affecting the thermal performance of the device, are presented. These experimental data were later used in a numerical model for a magnetocaloric device with a thermal switch-capacitor. The results of the study show that for a single embodiment, a maximum cooling power density of 970 W m−2 (510 W kgmcm −1) could be achieved for a zero-temperature span and an operating frequency of 5 Hz. However, a larger temperature span could be achieved by cascading multiple magnetocaloric elements with TSCs. We have shown that the compact TSC can be used in caloric devices, even with small temperature variations, and can be used in a variety of practical applications requiring thermal regulation.

Experimental parameter study and correlation development of microchannel membrane-based absorption process for efficient thermal cooling with high compactness

The microchannel membrane-based absorber occupies a crucial position in an efficient and compact absorption refrigeration system, as it directly influences the system's cooling capacity. However, existing numerical models for describing the absorption process of this absorber often exhibit large deviations, as they are adopted from other processes. To establish highly accurate correlations, extensive experiments are performed in this study to evaluate the absorption process using H2O/LiBr as the working fluids across a wide range of operating conditions. The experimental results demonstrate that enlarging the solution flow rate, vapor pressure, and solution concentration or lowering the cooling water temperature can improve the heat and mass transfer processes significantly. By analyzing the experimental results, new correlations of Nusselt number (Nu), Sherwood number (Sh), and friction factor (f) are developed for heat/mass transfer and solution pressure drop, respectively. It is verified that these newly developed correlations significantly enhance the prediction accuracy of the overall heat transfer coefficient (U), absorption rate (J), and pressure drop (DP) by 72.39%, 78.55%, and 64.56% when compared to existing literature correlations. The exceptional accuracy achieved by these correlations contributes significantly to the design, evaluation, and optimization of efficient and compact absorbers, enabling further advancements in this field.

Experimental parametric study of perforated steel plate fuses for mass timber seismic force resisting systems

The lack of practical connections with reliable desired energy dissipation capacity as the main components of a seismic force resisting system (SFRS) is a major obstacle in using mass timber in tall buildings located in seismically active regions. A common method to dissipate seismic energy in timber structures is through the yielding of steel material found in the mechanical connections. Under the induced seismic motions, these dissipative connections are intended to yield while the rest of the structure remains intact with minimum damage. In this research, the focus is on the use of perforated steel plate as a dissipating energy device and a seismic fuse. Previous tests have demonstrated the potential use of perforated steel plates as seismic fuses in mass timber SFRS and confirmed their scalability and predictability. Despite promising results under monotonic loading, their behavior under cyclic loading can be improved. This paper presents an experimental parametric study investigating the effects of the number of rows, shape, and size of perforations, the steel plate thickness, and the steel link size on the mechanical performance of the perforated plates. The obtained hysteresis responses and envelope curves are compared. It is found that the ellipse and stagger patterns possess the largest ultimate displacement and stiffness, respectively. In addition, no significant enhancement in the ultimate deformation was observed in the cyclic response of the fuse, beyond three rows of perforations. Within the range of the configurations considered, the reduced ultimate deformation under cyclic loading remains a technical challenge that needs to be addressed if this type of seismic fuse is to be installed in SFRS. The results will assist with the design of future test programs on full-size mass timber connections consisting of such fuses.

Experimental study on the effect of liquid loading on n-heptane spray jet flame stability

Flame stability significantly influences the performance of a practical combustor. The mechanisms governing the stability limits of spray jet flames are examined here using an annular co-flow spray burner. This study focuses on investigating the impact of liquid loading on spray jet flame stability, represented by flame lift-off height (LOH) and lean blow-out (LBO) limit. This is achieved by utilizing a parametric experimental study in which co-flow temperatures (Tco-flow = 298 K, 350 K, 400 K, and 450 K), spray nozzle sizes (dorifice = 0.209 mm, 0.219 mm, 0.232 mm, and 0.237 mm), fuel/air flow rates, and velocities are independently varied. A single liquid fuel, n-heptane, is used so that the vapor/liquid fractions (droplet lifetime) can be easily predicted via simple vapor–liquid equilibrium calculations to assist in the explanation of the stability mechanisms involved. The results show that the spray flame LOH mechanisms are affected by both chemical flame speed and, to a lesser extent, vaporization. On the other hand, the LBO limit is found to be controlled by the amount of liquid fuel in the presence/entering the flame. When the co-flow temperature is increased, while keeping constant co-flow velocity, the flame stabilizes near the burner lip. However, an opposite trend is noticed for flame blow-out limits, with the flame being more difficult to blow out when lower co-flow temperatures are applied. The variation of nozzle sizes leads to similar conclusions, i.e., when larger nozzle sizes are used, leading to the formation of larger droplets, the flame stabilizes further downstream and becomes more difficult to reach blow-out. The interpretation of the results indicates that delaying the vaporization and generating local enrichment regions near the flame edge enhances the flame LBO performance. Such an approach may be used as an efficient passive control mean to enhance flame stabilization; however, secondary impacts on emissions must be considered.

Fluid flow and heat transfer characteristics of three-dimensional slot film cooling in an annular combustor

Film cooling methodologies in air-breathing gas turbines have been evolving for many decades. In the present work, a combined experimental and numerical parametric study is conducted to investigate the three-dimensional slot film cooling of an annular combustor. The experimental investigation is conducted to understand the fluid flow and heat transfer phenomenon of the film cooling and to validate the numerical study under laboratory conditions (low temperature and pressure). Transient infrared thermography is used to estimate both adiabatic film-cooling effectiveness (ηad) and heat transfer coefficient (h) simultaneously using a semi-infinite approximation method. The blowing ratios considered in the study are in the range of 0.5 to 5. The experimental results showed that film-cooling effectiveness (ηad) enhanced with an increase in the blowing ratio from 0.5 to 2 and deteriorated beyond BR = 2 due to the adverse effects of turbulence. A parametric study is conducted numerically to understand the effect of flow and geometrical parameters under actual engine conditions (high temperature and pressure). The parameters considered are slot Reynolds number (Res), slot jet diameter (d), slot jet pitch (p), lip taper angle (α), lip length (L), and slot jet injection angle (β). For the considered parameters, numerical results showed that the slot jet diameter (d) = 2 mm, dimensionless slot jet pitch (p/d) = 2, slot jet injection angle (β)=20o and dimensionless lip length (L/d) = 5.9 outperformed the other configurations due to the low turbulence and entrainment. Finally, an Artificial Neural Network-based mathematical model is developed that correlates the ηlat as a function of flow and geometrical parameters.

Metallization system as a part of thermal memory

This study aims to substantiate the potential of using “classical” metallization systems as microelectronic thermal memory cells. An experimental simulation is used to demonstrate that thermal information can be stored in memory for a certain time and then read without distortion. The possibility of using thin metal films on single-crystal silicon wafers as thermal memory cells is discussed. An experimental parametric study of “recording” thermal pulses and the temperature dynamics after their interruption is performed. This study uses rectangular current pulses with an amplitude of (1 … 6) × 1010 A/m2 and a duration of up to 1 ms. The temperature dynamics of a “thermal cell” are oscillographically studied up to the critical conditions when the contact area and metal film start degrading. The conditions of interconnections overheating up to the circuit break are considered.

Effect of dosage of superplasticizer on earth concrete

The environmental load put forth by the construction industry is tremendous. Being a major contributor to the present-day environmental situation, the construction industry must embrace the necessary changes. Sustainable development, effective utilization of resources and responsible engineering are of utmost priority. There are several alternative construction materials on the rise, adhering to such new requirements, in addition to the benefits of the materials that are already being employed. Earth concrete is one such emerging construction material. In earth concrete soil along with other constituents are made into a flowable form that can be cast into various shapes using forms and cured to attain certain desired strength characteristics. Binders, coarse aggregates and admixtures for earth concrete are selected on the basis of the characteristic requirements of the resulting matrix. In the present study, laterite soil is used to produce earth concrete, cement acts as binder, crushed stone as coarse aggregate and a naphthalene-based admixture helps in achieving the required workability characteristics. By the incorporation of Ceraplast 300, a naphthalene-based super plasticizer, the density, workability and the compressive strength of earth concrete have been enhanced. The paper considers the effect of dosage of super plasticizer on the workability, density and strength characteristics of earth concrete. Through parametric experimental study of earth concrete specimens, the optimum dosage of the naphthalene based super plasticizer has been determined. 1 % dosage of the super plasticizer with earth concrete exhibited the best results for the selected matrix. In the experimental program, earth concrete capable of sustaining 47.7 MPa stress at failure was achieved, which accentuates the possibilities and need for further studies on earth concrete.

Experimental and numerical study on behaviour of fibre reinforced lightweight hollow core slabs under different flexure to shear ratios

The current work explores the behaviour of fibre-reinforced lightweight hollow core slabs (FR-LWHCS) intending to develop sustainable construction solutions. The FR-LWHCS investigated in this work contains sintered fly ash aggregate (SFA) as coarse aggregate. Due to the use of SFA, the behaviour of LWHCS is expected to be different from the hollow core slabs (HCS) constructed using normal density concrete. FR-LWHCS are tested at different shear span to depth (a/d) ratios of 3.5, 7 and 10 to understand the shear and flexure behaviour. Twelve full-scale hollow core slab (HCS) specimens of 3400 mm length, 600 mm width, and 150 mm thickness are tested. FR-LWHCS consists of monofilament macro synthetic fibre dosages of 0.4 %, and 0.6 %, along with fibrillated micro fibre of 0.02 % dosage. The digital image correlation (DIC) technique is adopted to understand the strain profile on the HCS at different levels of loading. The numerical analysis is performed using a commercially available finite element software and is corroborated with experimental findings and parametric studies have been performed. Both LWHCS and normal HCS specimens failed in shear, flexural-shear and flexure modes at a/d ratios of 3.5, 7 and 10, respectively. The addition of fibres increased the peak load by 65 % compared to control LWHCS specimens tested at an a/d ratio of 3.5. The use of fibres increased strain energy absorption and changed the failure to less brittle mode at all a/d ratios. The fibre reinforced specimens have nearly 3.5 times, 2.5 times and 1.3 times the strain energy absorption of the control LWHCS when tested at a/d ratio 3.5, 7 and 10 respectively.

Experimental Investigation of Pounding Responses in Base-Isolated Frame Structures at Expansion Gap

Experimental simulation and parametric studies have been conducted to investigate the effect of pounding in base-isolated (BI) frame structures with expansion gaps. Earthquakes often result in extensive damage at expansion joints, which encouraged this experimental evaluation of pounding between BI frames. In the present research, the pounding effect in a series of combinations, such as adjacent flexible and stiffer BI frames of similar frequency and different frequency to adjacent frames, were experimentally analysed to find better combinations of adjacent structures with an expansion gap. In the experiments, the surfaces at the isolation and frame slab levels were free to impact in order to investigate direct pounding (DP) and mitigated pounding (MP) by inserting a neoprene rubber pad into the gap. The investigation was conducted by comparing BI structures with and without pounding responses as a result of the El Centro earthquake excitation. To demonstrate the extent of the pounding effect in adjacent structures, the horizontal and pounding force variations in each combination during DP and MP were evaluated. The experimental responses analysis results help in justifying a better variety of adjacent BI structures with an expansion gap. This experimental study shows that mitigating material in the gap is more efficient for nearer frequency combinations than for different frequency frame combinations.

Исследование особенностей зажигания и горения высокоплотных зарядов в условиях постоянного объема

The study of combustion and ignition of charges with promising propellants or powder compositions in terms of initial conditions is an urgent problem of modern ballistics. Generally, combustion and ignition of charges are tested in a manometric closed vessel. The charge ignition conditions may affect the subsequent reactions. When designing a shot with a new charge, it is necessary to know what determines the moment of ignition (gas pressure, time, pressure rise rate, type of igniter, etc.) and which factor has a greater effect on the ignition. This paper presents a study of some features of high-density charge ignition under constant volume conditions. A brief description of the manometric setup is given. The effect of mass and type of igniter and combustion surface area on the high-density charge ignition and subsequent combustion is studied. The pressure-time dependences corresponding to high-density charge combustion in a textolite container with different diameters are presented and analyzed. The ignition of the paste high-density charge is revealed to be affected by the geometric dimensions of the container. The parametric experimental study results show that the ignition conditions of a model high-density propellant (MHDP) strongly depend on the method of initiation, namely the number of burning particles and ambient pressure; however, these factors do not affect the dependence of the MHDP combustion rate on pressure. The ignition momentum is obtained as a function of the ratio of the container burning surface circumference to the burning surface area.

Numerical and Experimental Parametric Study on the Mechanism of Web-Warping in Chain-Die Forming with Variable Cross-Section

Numerical and Experimental Parametric Study on the Mechanism of Web-Warping in Chain-Die Forming with Variable Cross-Section

Fabrication of oxide-free dimple structure on germanium via electrochemical jet machining enhanced by opposing laser irradiation

The electrochemical machining (ECM) of germanium (Ge) wafer can be significantly improved in terms of efficiency and localization by introducing laser irradiation. However, residual oxide particles usually exist when using neutral electrolyte. In this study, the NaNO3 electrolyte jet is formed via a cathodic nozzle and impacts perpendicularly on the bottom of the Ge wafer, at which position the nanosecond (ns) laser irradiates from opposing side to locally and precisely enhance the electrical conductivity. In this way, the dimple structure without any detectable oxidation products can be efficiently fabricated. Characterization of surface morphology is then amply conducted. The radial lines consisting of regular micro-waving structure are usually noticeable, especially near the dimple edge, which may be attributed to the rapid and radial electrolyte flow along the concave sidewall. In contrast, irregular corrugated pattern can be observed near the dimple center, which may be caused by the electrolyte turbulence after impingement. In addition, parametric experimental study has been carried out, and the effects of the applied voltage, laser power and electrolyte concentration on the dimple profile and surface characteristics have been respectively detailed discussed. Finally, simulation study of the electrolyte flow field is conducted to reveal the distribution regularities of velocity and pressure, to deepen the understanding of formation mechanism of the complex surface morphology.

A parametric study on the subharmonic isolas in a bistable dielectric elastomer actuator

Resonant actuation of dielectric elastomer actuators (DEAs) greatly improves their output power densities and energy efficiencies. However, their outstanding performance usually accompanies complex dynamics which hinder the robust applications of DEAs. Isolated frequency responses, or isolas, are branches of resonant curves that are isolated from the main frequency response curve, hence can be easily overlooked during the dynamic analyses of DEAs. Once triggered, however, isolas can lead to dramatic changes in frequency responses, which pose great threats to system stability. As a critical step towards controlling the isolas within DEAs, this work adopts a bistable cone DEA (BCDEA) configuration and conducts dedicated numerical and experimental parametric studies on its isolas to uncover the physical mechanisms that create them. The effects of potential barriers, equilibrium positions and excitation level on the evolutions of isolas are studied with the aim of finding the critical parameters that determine their evolutions. The outcomes of this paper help to gain more insights into the complex isola phenomena in BCDEAs, which may offer guidelines for eliminating undesired isolas within BCDEAs or for exploiting isolas for applications in, e.g. energy harvesting, soft robotic locomotion and vibro-tactile feedbacks.

A detailed experimental parametric analysis of bolted and hybrid bolted/bonded composite joints

AbstractHybrid bolted/bonded joints may have the advantages of both mechanical and adhesively bonded joints or disadvantages, which depends entirely on reasonable design. The design of the hybrid bolted/bonded joint is a complex issue, which is related to the material properties of the connected parts and adhesive layer, the number and size of the bolt, and the geometrical characteristics of the joint. Furthermore, the secondary bending in the single‐lap joint and the bypass load in the multirow bolted joint to increase the complexity of the problems. Therefore, detailed tests and adequate data are essential to do further research on the mechanical behaviors of bolted and hybrid bolted/bonded composite joints, especially for the joints of bismaleimide resin composite. An experimental parametric study was carried out to reveal the effect mechanisms of different configurations on the mechanical properties of bismaleimide resin composite joints in this study. Single‐lap bolted and hybrid bolted/bonded composite joints were focused on and their mechanical behaviors were discussed. According to the investigation of experimental analysis, some useful conclusions have been deduced, which are helpful for the design of bolted and hybrid bolted/bonded composite joints.

Towards a digital twin approach – Experimental analysis and energy optimization of a multi-bed adsorption system

An adsorption chiller system is one of the most promising technologies that utilize waste thermal energy to simultaneously produce cooling and potable water. However, the energy utilization optimization and detection of desiccant’s sorption capacity degradation are two unresolved issues that have severely impeded the development and commercial applications of adsorption chiller technologies. This study is pioneered to develop a digital twin platform specifically designed for an experimental four-bed two-evaporator adsorption chiller system prototype. Leveraging this platform, system monitoring, performance prediction, and optimization functions are achieved. Relying on the monitoring function, the digital twin can detect the capacity degradation of desiccant-coated heat exchangers. By employing the prediction and optimization functions, the application performance of the adsorption chiller system under varying ambient and load conditions can be simulated and optimized under real-time operating conditions. Additionally, this work projects a first-time experimental parametric study analysis for a four-bed two-evaporator adsorption chiller system prototype under a heat recovery scheme that considers fourteen operating parameters. Key results revealed that COPth reaches 0.68 when the cycle time is 2240 s. Case studies also showed that the adsorption chiller system can yield significant energy-saving performance for climatic conditions in Malaysia and Saudi Arabia. The proposed digital twin optimization method demonstrates that COPth is enhanced by 8.5 %, 9.5 %, and 8.5 %, respectively. In contrast to the conventional method, optimizing the adsorption chiller’s performance through the digital twin platform enables a reduction of the annual electricity consumption by up to 10.3 %.

Toward the flexible production of large-format lithium-ion batteries using laser-based cell-internal contacting

Lithium-ion battery cells are used for energy storage in many industrial sectors, such as consumer electronics or electromobility. Due to the diversity of these applications, the demand for tailored battery cells is increasing. Consequently, the technical development of the cells leads to numerous coexisting cell variants. Examples of such variants are altering cell materials, formats, and capacities. Different target capacities can be realized by changing the geometrical dimensions of the individual electrodes or the number of electrodes in the cell cores. The increasing quantity of variants poses challenges within battery cell manufacturing, such as the need to adapt the process parameters for the cell-internal contacting of a higher number of electrode sheets in the cell stack. Each new cell variant currently requires elaborate experimental parameter studies for its manufacture. An approach for selecting suitable process parameters for laser-based cell-internal contacting in terms of a modification of the cell properties is presented in this paper. A model was built to determine the weld depth in copper sheets using a millisecond pulsed laser welding strategy. The process parameters for welding stacks of electrode sheets to an arrester tab were calculated on the basis of this model. The necessary weld depth in the arrester tab for achieving suitable mechanical properties of the cell-internal joint was considered. The presented approach was validated by welding different numbers of foils to an arrester tab and varying the thickness of the foils. It was shown that the experimental effort for the selection of the process parameters for laser-based contacting can be reduced significantly.

Modeling of submicron particle transport based on VOF-LPT method

The submicron particle transport inside a single bubble rising in water is investigated by the VOF-LPT method. As an improvement of the previous particle transport assumption in numerical studies, a new interfacial penetration model is developed according to the observed particle behavior in experimental works. The new criterion, namely particle Weber number is derived based on the dimensional analysis of the kinetic energy equation. The developed model is calibrated and evaluated based on the experimental data and parametric studies including particle size, density and gas–liquid surface tension are performed. The results indicated that the consideration of the interfacial penetration model is reasonable due to the presence of particle interfacial behavior dominant by surface tension force. The application of particle Weber number as the criterion is found to agree well with the experimental observations from both quantitative and qualitative aspects. In the presence of large particle inertia, the particle may deviate from the gas streamline and impact the bubble surface on one side, while the particle presents enhanced penetration capacity through the gas–liquid interface on the other side. With the decreasing gas–liquid surface tension, a competitive mechanism between the weakened internal flow and the enhanced penetration capacity is found, which complexes the effect of surface tension on particle transport in a non-monotonic way. In general, the interfacial penetration model developed in this study is proven to be feasible to describe submicron particle transport inside the rising bubble.

A 3D numerical and experimental parametric study of wave-induced scour around large bluff body structures

This is the first study to undertake a comprehensive parametric study of wave-induced scour around a large bluff body structure, and also presents experimental data to validate a CFD model for wave-induced scour around the structure. A parametric study is undertaken using the REEF3D CFD model for varying incident wave condition (depth, wave amplitude, frequency, and direction), structure geometry (width, length, and corner curvature), and sediment size. The numerical model is validated against experimental datasets, demonstrating that the model can accurately replicate scour around large bluff body structures.Two new equations are proposed for prediction of non-dimensional equilibrium scour depths at the front and back corners of a large bluff body structure using the Keulegan-Carpenter (KC) number based on 18 and 24 datapoints respectively. The equations are valid within the following limits: 0.37 ≤ KC ≤ 1.75, 0.10 ≤ B/λp and 0.14 ≤ L/λp, where B and L are the structure width and streamwise length, and λp is the peak wave length. It is further demonstrated that the non-dimensional scour depth does not vary significantly with the sediment size (for 0.075 ≤ θ ≤ 0.117 where θ is the Shields parameter), or the structure width/length for the limits stated above.