Dynamic Coefficient Research Articles

A numerical study on performance efficiency of a low-temperature horizontal ground-source heat pump system

Exploitation of shallow ground and its low-grade heat potential is fundamental to designing 5th generation district heating and cooling (DHC) networks. Horizontal ground-source heat pump (HGSHP) systems are a common way to utilize shallow geothermal energy. Realistic estimation and prediction of performance of a HGSHP system and shallow ground thermal behaviour should consider the whole system including building heating and cooling load, heat pump and ground heat exchanger, and the ground. This should be accompanied by realistic atmospheric and ground conditions. In this paper, a three-dimensional coupled thermal–hydraulic model with realistic boundary conditions adopting a whole system approach is presented. Dynamic heat pump coefficient of performance (COP) that depends on seasonal variation of heating/cooling demand and ground conditions are also considered. Model validations are conducted against experimental and analytical results in literatures. The model is applied for evaluating a HGSHP system to support development of a 5th generation DHC network on a potential site in the UK. Several influencing factors, such as ground moisture transfer, building thermal load mode, buried depth of ground loops, and initial ground temperature profile are studied to assess performance efficiency of the HGSHP system and evolution of ground thermal behaviour in response to heat extraction or rejection into the ground. The results show that 5% of the monthly total heat demand of the site could be met by the designed HGSHP system, consisting of 200 U-shaped ground loops buried at the depth of 3 m and pure water as the heat carrier. Overlooking the ground moisture transfer or hyperbolizing the ground saturation would overestimate the load-carrying capacity of the HGSHP system. The HGSHP system is more efficient with a higher heat pump COP under the heating and cooling mode than under the heating-only mode. Predicted performance of the HGSHP system improves with buried depth of the ground loops. The results also show that a 1 ℃ increase in the undisturbed ground temperature could suffice up to 8% of the monthly total heat demand of the site.

Development of designs and research of the main tribotechnical parameters of friction pairs with plasma powder friction coatings and a steel counterbody when operating in oil for friction devices

Designs are developed and studies of the main tribotechnical parameters of friction pairs with plasma powder friction coatings and a steel counterbody when operating in oil for disc and cone friction devices are carried out. The threedimensional image shows the dependence of the dynamic coefficient of friction on the sliding speeds and specific loads for the considered friction devices. Keywords: friction in oil, tribological parameters, coefficient of friction, wear, sliding speed, specific load, temperature, friction machine, new friction material, steel counterbody. au@vstu.ru

Применение пьезокерамики для подавления вибраций полезной нагрузки многорежимного космического аппарата

Current trend in the spacecraft design lies in using large, complex and lightweight space structures to achieve increased functionality with the lower launch costs. Combination of large and lightweight designs results in these space structures becoming extremely flexible and acquiring the low frequency fundamental vibration modes. These modes could be used in various tasks, such as turning, guidance maneuvers and docking with the other spacecraft. Effective vibration suppression is a challenge for the spacecraft designers. One of the promising methods for solving this problem is introduction of the built-in piezoelectric elements as the actuators. The paper analyzes various control systems for the built-in piezoelectric elements to ensure the payload vibration protection. Experimental studies of these systems were carried out to determine the dynamics coefficient levels.

Studying the strength of a small-sized loader working equipment

Problem. The growth in the volume of construction work carried out in the improvement of adjacent territories, playgrounds, and pedestrian paths requires the use of a wide range of small-sized machines for earthwork and road construction, including loaders. The main requirements for small-sized loaders are small dimensions, which makes it possible to perform work in cramped conditions, good maneuverability, light weight, which allows for low pressure on the surfaces on which the equipment moves, ensuring the safety of loading operations, efficiency and economy. These conditions are fully met by a variety of construction equipment that is combined with self-propelled chassis, which have been manufactured for many years at Ukrainian enterprises and used by organizations for the improvement and beautification of urban space. The indisputable advantage of self-propelled chassis over a large number of short wheelbase loaders, which are also widely used in the public utilities sector, is greater stability due to the large wheelbase and the possibility of using additional outriggers installed on the machine, as well as the availability of a self-unloading platform for transporting goods. The operation of small-sized forklifts based on self-propelled chassis in cramped conditions, along with builders performing installation work, requires increased attention to ensuring the strength of the machine's metal structure, so the issue of studying the load of working equipment is an urgent task. Goal. The aim of the study is to develop scientifically based recommendations for reducing the load of small-sized forklift equipment based on the created design scheme, determining the acting forces and stresses, and rational modes of operation of the forklift. Methodology. The design position in which the handle of the working equipment is located horizontally and the maximum load acts on it is considered. The design load is the maximum weight of the cargo, taking into account the dynamic coefficient. The calculated position for the boom is the position of the greatest bending moment, i.e. the position at maximum reach. The center of gravity of the boom and handle, as well as the weight of the metal structure, were determined using a computer model. The loads acting in the boom joints are determined using a simplified, calculated, boom scheme, for which We will discard the handle, replacing its action with the corresponding reaction and consider the handle separately to determine this load. Given that the force of action from the boom on the handle will be equal in modulo to the force of action from the handle on the boom, and the reactions in the hydraulic cylinder joints will also be equal, we will depict the diagram of the forces acting on the boom. Results. Based on the developed design schemes of the boom and arm, we studied the loading of working equipment, which was carried out using the created program at variable values of the load weight from 4000N to 4500N, the coefficient of dynamism equal to 1, 1.1...1.5, and the height of the arm section from 0.14 to 0.16 m. The analysis of the research results showed that an increase in the coefficient of dynamism to a value of 1.5 at a load weight of 4500N leads to an increase in the acting force to 6840N, but the stresses are within the permissible limits. Increasing the load with which the forklift operates to 5000N requires an increase in the height of the handle section to 0.15m to ensure that the stresses are within the permissible limits. The analysis of the dependence of the acting stresses on the weight of the load and the coefficient of dynamism made it possible to propose recommendations for rational modes of operation of the forklift, which consist of limiting the load to 4500N and the coefficient of dynamism within 1.3-1.4 with a handle cross-sectional height of 0.14m and a wall thickness of 0.05m. It is also proposed to work without jerks, smoothly at low lifting speeds, within the range of the coefficient of dynamism up to 1.3-1.4. Practical meaning. The developed research methodology is proposed for use in the operation of a small-sized forklift in various modes, as well as in the design of working equipment for forklifts of a similar class and design.

Способы расчета несущих конструкций на устойчивость к прогрессирующему разрушению

Introduction. Calculation methods and current normative documents used in the calculation of buildings for resistance to progressive collapse are considered. The key methods of analysis are listed and fundamenta.rules of each of them are stated. The advantages and disadvantages of these methods are analyzed. Materials and methods. The calculations of stability to progressive collapse have been carried out for a multi-span flat frame at the failure of the middle post of the ground floor. The software complex LIRA-SAPR 2021 R1.2 was used to perform calculations. The task was solved by several methods: the static calculation, quasi-static calculation and dynamic calculation. The nonlinear functioning of construction and material was considered by step-methods with using the flow curve from SP 16.13330.2017. Quasistatic calculation was performed in two variants: pulldown and pushdown analysis. The dynamic calculation was carried out by direct integration of the equations of motion using the module “Dynamics in Time”. Two variants with different element elimination time were considered. Results. The results are analyzed and summarized in Table 2. The static calculation yields force and displacement values that are clearly underestimated as compared to other methods. Forces and displacements obtained by quasistatic analysis are greater than those obtained by dynamic analysis. The results obtained in the pulldown and pushdown analyses are close in value. Conclusions. Quasistatic calculations give higher forces and displacements than dynamic calculations. The results of pushdown analysis correlate better with the results of calculations in the dynamic formulation. In order to determine forces more accurately when using quasi-static calculation, a justification of the dynamical coefficient is necessary.

A comparative study on dynamic compression response of multi-cell thin-walled structures with filling foams and connecting ribs

In order to comparatively study effect of foam filling and connecting ribs on dynamic response of multi-cell thin-walled structure (MTS), high velocity (30–70 m/s) mass block impact tests were performed on empty MTS, polyurethane foam (PUR) filled MTS (FMTS) and 2nd order MTS (MTS-2nd) with connecting ribs between sub-cells. The dynamic enhancement mechanism of energy absorption of three kinds of thin-walled structures was discussed based on experimental and numerical results. The results indicate that the dynamic enhancement coefficient (DEC) of the mean crushing force (MCF) is 1.07–1.23 and 1.08–1.33 for empty MTS and FMTS, respectively. The dynamic enhancement of total energy absorption (EA) is 11.4–26.32% for MTS, 13.83–32.52% for FMTS and 4.3–9.68% for MTS-2nd, compared to the quasi-static compression. The multi-cellularization tends to degenerate the crushing force sensitivity of MTS to the loading rate, while the foam filling increases the sensitivity. The inertia effect is the main reason for the dynamic enhancement of crushing force of thin-walled structures. The coupling effect of FMTS is related to the dimensions of sub-cells, the impact velocity and the foam strength. The folding pattern and deformation stability of MTS can be improved by filling foams and increasing impact velocity. The multi-cellularization by using connecting ribs is still the most effective method to improve the specific energy absorption of thin-walled structures, although it causes a size effect and reduces the robustness of deformation modes.

Analysis of dynamic characteristics of liquid-lubricated mechanical face seals with inclined elliptical grooves

PurposeThe purpose of this paper is to study the dynamic characteristics of mechanical face seals with liquid-lubricated inclined elliptical grooves.Design/methodology/approachThe steady-state and perturbation Reynolds control equations of liquid films were established. The film pressure and the liquid film dynamic coefficients were obtained, impacts of groove structures on the liquid film dynamic characteristic coefficients were analyzed.FindingsThe analysis results indicate that the axial dynamic stiffness and damping coefficients of the liquid film seal with inclined elliptical grooves are far greater than those of the angular directions. Furthermore, the dynamic stiffness coefficient of the liquid film with the nonclosed inclined elliptical grooves is higher than those with the closed grooves, whereas the dynamic damping coefficient of the liquid film is lower.Originality/valueThe effects of inclined elliptical groove structures on the dynamic characteristics of the liquid film seal are investigated. The results presented are expected to enrich the theoretical basis of optimizing the dynamic performance of liquid film seals with textures.

Electrical output performance of PZT-5H under the superposition of temperature, temperature change rate and pulse stress

The static pyroelectric coefficient of PZT-5H thin slice was measured. The effects of temperatures, temperature change rates and pulse stress on the discharge characteristics of PZT under different electrical boundary conditions (open circuit and short circuit) were investigated by an improved split Hopkinson pressure bar system; The effects of temperature change rate and the pulse stress on dynamic piezoelectric coefficient and discharge characteristics of PZT were analyzed. The results show that the static pyroelectric coefficient of the piezoelectric ceramics is 4.16 × 10−8 C/cm2·°C. The piezoelectric voltage constant g33(σ, ∂ΔT), piezoelectric strain constant d33(σ, ∂ΔT), elastic compliance coefficient S and electromechanical coupling coefficient k were obtained by experiments at the given temperature and different temperature change rates.

CO2 Adsorption Properties of Amine-Modified Zeolites Synthesized Using Different Types of Solid Waste

In this study, organic amines were used to modify zeolite NaA and analcime synthesized using fly ash and iron tailing slag as raw materials, respectively, and the adsorption properties of the modified zeolites toward CO2 were determined. We found that when tetraethylenepentamine (TEPA) was used, the modified zeolite NaA and analcime had the highest nitrogen content. The adsorption capacity of the modified zeolite NaA for CO2 was 4.02 mmol/g and that of the modified analcime was 1.16 mmol/g when the adsorption temperature was 70 °C and the CO2 flow rate was 50 mL/min. According to the adsorption isotherm, kinetic, and thermodynamic model fitting, the adsorption surface of the modified zeolite was not uniform, and the CO2 adsorption of the modified zeolites was classified as chemical adsorption. In a mixed atmosphere of 15% CO2/85% N2, the dynamic selection coefficients of the modified zeolite NaA and analcime for CO2 were 3.8942 and 2.9509, respectively; thus, the two amine-modified zeolites had good selectivity for CO2. After five cycles, the adsorption efficiencies of the modified zeolite NaA and modified analcime for CO2 were 92.8% and 89%, respectively. Therefore, the two amine-modified zeolites showed good recycling performance.

Global path planning with lifetime constraint model-based offline optimized loading strategy for vehicle fuel cell system

To promote the commercialization of fuel cell vehicles, simultaneously improving the dynamic response and durability of fuel cells under loading conditions are extremely important. Since it can seriously affect the system design and lifespan of the fuel cell system. Unfortunately, fast and reliable loading is a pair of contradictory relationships and it needs an optimal loading slope under variable loading conditions. Therefore, this paper proposes a global path planning (GPP) model by considering lifetime limitations to solve the problem. Firstly, the initial GPP model is established according to the initial power and target power, which is exploited to determine exploratory and calibration tests. Subsequently, the trade-off relationship between fast and reliable loading is addressed by the multi-objective cost function based on the dynamic weight coefficient adjustment method to construct a complete GPP model. Eventually, the optimal slopes solution is calculated by the Dijkstra algorithm. The superiority, robustness, and feasibility of the presented method are successfully verified under a 90 kW fuel cell system test bench. The verification test results show that compared with the reference solution, the utilization of optimal solution loading can significantly reduce the dynamic response time by 22.22% and improve the loading reliability by 40.93%. Moreover, the number of calibration tests determined based on the GPP model is 85.19% less than that of the traditional method. Thus, the proposed loading strategy can load quickly and reliably.

MATHEMATICAL MODELING OF THE DYNAMICS OF AN ELASTIC HALF-MEDIUM WITH A CYLINDRICAL CAVITY REINFORCED BY A SHELL UNDER AXISYMMETRIC LOADS

Purpose. The development of a mathematical model of an elastic semi-medium with a cylindrical cavity reinforced by a shell and a plate that reinforces the surface of the semi-medium based on the finite-element approach. The non-stationary dynamic stress-strain state of this mechanical system under axisymmetric surface loads, which depends on time as a unit Heaviside function was analyzed. The solution of the corresponding static problem was obtained. Based on the obtained results, the dynamic coefficient of the considered mechanical system was calculated.
 Research methods. The finite element method and the Wilson - method were used for solving static and the corresponding dynamic matrix equation correspondingly. The last one allows reducing the differential matrix equation to an iterative sequence of quasi-static problems. To obtain an approximate solution of systems of linear algebraic equations that take place in the process of solving static and a sequence of quasi-statistical problems, the conjugate gradients method was used.
 Results. A finite-element model of the mechanical system of an elastic semi-medium with a cylindrical cavity reinforced by a shell and a plate reinforces the surface of the semi-medium was developed. The non-stationary dynamic stress-deformed state of this mechanical system under action of the surface axisymmetric loads was analyzed. The solution of the corresponding static problem was obtained. Based of the results has been obtained, the dynamic coefficient of the considered mechanical system was determined.
 Scientific novelty. The developed approach allows to take into account the mutual influence of a cylindrical cavity reinforced by a shell and a plate that reinforces the surface of the semi-medium under the action of the non-stationary dynamic loads applied to the surface of the plate.
 Practical value. The developed mathematical models and obtained results can be used in the design of underground structures, in particular mine shafts.

Experimental investigation and analysis of proposed hybrid vertical axis wind turbine design

In this research, an experimental and computational analysis of a novel hybrid vertical axis wind turbine (VAWT) arrangement has been performed. We suggest an innovative VAWT design that has a high power coefficient and self-starting capability. The inner side of the proposed hybrid system has been integrated with the H-rotor turbine with cambered blades, which demonstrates strong self-starting capabilities at various azimuths. Three NACA0018 airfoil blades are mounted on the outside of the proposed hybrid wind turbine, while three DU 06-W-200 airfoil blades are installed on the inside. Based on a similarity analysis, a scaled-down model was developed, and performance characteristics such as the output power, power coefficient ([Formula: see text]), dynamic torque coefficient ([Formula: see text]), and static torque coefficient ([Formula: see text]) were determined. An existing hybrid VAWT and a typical H-rotor Darrieus design were also examined for comparison. The highest [Formula: see text] for the proposed hybrid design was found to be 0.486 at a tip speed ratio (TSR) of 3, while the H-rotor Darrieus’ maximum value was 0.42 at a TSR of 2.62 and the existing hybrid VAWT’s value was 0.41 at a TSR of 2.5. Positive [Formula: see text] values at all azimuths demonstrate that the proposed hybrid wind turbine can start entirely on its own. In comparison to the existing H-rotor and hybrid VAWT, this novel hybrid system has shown enhanced performance parameters ([Formula: see text], [Formula: see text], [Formula: see text], output power) by around 11%–13% over a wide range of wind speeds.

Predicting frictional aging from bulk relaxation measurements

The coefficient of static friction between solids normally increases with the time they have remained in static contact before the measurement. This phenomenon, known as frictional aging, is at the origin of the difference between static and dynamic friction coefficients but has remained difficult to understand. It is usually attributed to a slow expansion of the area of atomic contact as the interface changes under pressure. This is however challenging to quantify as surfaces have roughness at all length scales. In addition, friction is not always proportional to the contact area. Here we show that the normalized stress relaxation of the surface asperities during frictional contact with a hard substrate is the same as that of the bulk material, regardless of the asperities’ size or degree of compression. This result enables us to predict the frictional aging of rough interfaces based on the bulk material properties of two typical polymers: polypropylene and polytetrafluoroethylene.

Preparation of a Ni-P-nanoPTFE Composite Coating on the Surface of GCr15 Steel for Spinning Rings via a Defoamer and Transition Layer and Its Wear and Corrosion Resistance.

In this study, a method of preparing a Ni-P-nanoPTFE composite coating on the surface of GCr15 steel for spinning rings is proposed. The method incorporates a defoamer into the plating solution to inhibit the agglomeration of nano-PTFE particles and pre-deposits a Ni-P transition layer to reduce the possibility of leakage coating. Meanwhile, the effect of varying the PTFE emulsion content in the bath on the micromorphology, hardness, deposition rate, crystal structure, and PTFE content of the composite coatings was investigated. The wear and corrosion resistances of the GCr15 substrate, Ni-P coating, and Ni-P-nanoPTFE composite coating are compared. The results show that the composite coating prepared at a PTFE emulsion concentration of 8 mL/L has the highest concentration of PTFE particles (up to 2.16 wt%). Additionally, its wear resistance and corrosion resistance are improved compared with Ni-P coating. The friction and wear study shows that the nano-PTFE particles with low dynamic friction coefficient are mixed in the grinding chip, which gives the composite coating self-lubricating characteristics, and the friction coefficient decreases to 0.3 compared with 0.4 of Ni-P coating. The corrosion study shows that the corrosion potential of the composite coating has increased by 7.6% compared with that of the Ni-P coating, which shifts from -456 mV to a more positive value of -421 mV. The corrosion current reduces from 6.71 μA to 1.54 μA, which is a 77% reduction. Meanwhile, the impedance increased from 5504 Ω·cm2 to 36,440 Ω·cm2, which is an increase of 562%.

Transition to Equilibrium and Coherent Structure in Ideal MHD Turbulence, Part 2

We continue our study of the transition of ideal, homogeneous, incompressible, magnetohydrodynamic (MHD) turbulence from non-equilibrium initial conditions to equilibrium using long-time numerical simulations on a 1283 periodic grid. A Fourier spectral transform method is used to numerically integrate the dynamical equations forward in time. The six runs that previously went to near equilibrium are here extended into equilibrium. As before, we neglect dissipation as we are primarily concerned with behavior at the largest scale where this behavior has been shown to be essentially the same for ideal and real (forced and dissipative) MHD turbulence. These six runs have various combinations of imposed rotation and mean magnetic field and represent the five cases of ideal, homogeneous, incompressible, and MHD turbulence: Case I (Run 1), with no rotation or mean field; Case II (Runs 2a and 2b), where only rotation is imposed; Case III (Run 3), which has only a mean magnetic field; Case IV (Run 4), where rotation vector and mean magnetic field direction are aligned; and Case V (Run 5), which has non-aligned rotation vector and mean field directions. Statistical mechanics predicts that dynamic Fourier coefficients are zero-mean random variables, but largest-scale coherent magnetic structures emerge and manifest themselves as Fourier coefficients with very large, quasi-steady, mean values compared to their standard deviations, i.e., there is ‘broken ergodicity.’ These magnetic coherent structures appeared in all cases during transition to near equilibrium. Here, we report that, as the runs were continued, these coherent structures remained quasi-steady and energetic only in Cases I and II, while Case IV maintained its coherent structure but at comparatively low energy. The coherent structures that appeared in transition in Cases III and V were seen to collapse as their associated runs extended into equilibrium. The creation of largest-scale, coherent magnetic structure appears to be a dynamo process inherent in ideal MHD turbulence, particularly in Cases I and II, i.e., those cases most pertinent to planets and stars. Furthermore, the statistical theory of ideal MHD turbulence has proven to apply at the largest scale, even when dissipation and forcing are included. This, along with the discovery and explanation of dynamically broken ergodicity, is essentially a solution to the ‘dynamo problem’.

Ultralight and sensitive ferroelectret films with a human skin-like texture

Biologically inspired by natural skin, polypropylene (PP) ferroelectret films with a human skin-like texture, featuring lightweight, light transmittance, small thickness, stretchability, as well as significant longitudinal and transverse piezoelectric activity, are prepared with a simple procedure, and their piezoelectric properties are characterized. The mechanical structure of the fabricated ferroelectret films is of a double-level cellular structure with distributed tight junctions and dipolar charges deposited on the opposite inner walls of cells. The preliminary results show that the area density, light transmittance, and thickness of the films are 3.5 g/m2, 80%, and 10–20 μm, respectively. A quasi-static piezoelectric d33 coefficient of a few thousand pC/N at 3.4 kPa and a dynamic piezoelectric d31 coefficient of −40 pC/N at a frequency of 80 Hz and a stress of 20 kPa are achieved. The improved piezoelectric performance seems mainly owing to the reduction of the elastic modulus for the double-level structure and the enhancement of charges in deep traps in very thin cell walls. The sound pressure level, generated by an ultrasonic emitter made of the PP ferroelectret film, is about 87 dB at 46 kHz as driven by a voltage of 20 V (peak to peak voltage). An ultra-thin tactile sensor based on the fabricated films can localize positions and detect the track and moving speed of applied force. These results indicate that the cost-efficient films may extend the applications of ferroelectrets in flexible electronics.

Numerical simulation study on the spontaneous rupture process and its influencing factors of the 2001 MS 8.1 Kunlun earthquake in China

On November 14, 2001, the MS 8.1 Kunlun earthquake occurred in the west of Kunlun Mountain pass in the East Kunlun fault zone of the Qinghai-Tibet Plateau, China. The field investigation and the results of kinematic inversion indicate that it is a strike-slip earthquake with a complex rupture process. The study of the spontaneous rupture process of this earthquake and its influencing factors is of great significance for understanding the occurrence mechanism of continental large earthquakes. First, based on the results of geological survey and kinematic inversion, a three-dimensional non-planar fault model is established. Then, using the curved-grid finite difference method (CG-FDM), the dynamic rupture process of the 2001 MS 8.1 Kunlun earthquake is numerically reproduced by adjusting the parameters for numerical simulation experiments. On this basis, the influence of background stress field, fault geometry and friction coefficient on the surface slip distribution, seismic moment rate function and rupture velocity are discussed respectively. The results show that the important reasons for the super-long rupture scale and super-shear rupture velocity of this earthquake may be the clockwise rotation of the maximum horizontal principal compressive stress along the NNE ∼ NE direction and the low friction coefficient distribution on the whole fault surface. The difference between the dynamic and static friction coefficients along the fault strike may be non-uniform, and it may be larger on the main fault than that on the secondary fault. This will result in a higher level of stress drop on the main fault, leading to the occurrence of super-shear rupture and the slip distribution with the Kusai Lake as the macroseismic epicenter. The large local geometric variation along the strike of the main fault may also have some influence on the distribution of co-seismic slip and the location of the super-shear rupture. In addition, the numerical simulation results in this paper confirm the conclusion that the East Kunlun fault zone has low friction coefficient.

Analytical Solution of Horizontal Dynamic Response of a Floating Pile Embedded in an Elastic–Poroelasitc-Layered Soil

The horizontal dynamic interaction problems of a floating pile with soil have received little attention from scholars in recent years. This paper first proposed an analytical solution for the dynamic characteristics of the floating pile subjected to horizontal steady-state excitation embedded in soil containing the groundwater table level. Based on Biot’s elastodynamic theory, the governing equations of the soil around the pile are obtained. By virtue of the Hankel transform technique and variable separation method, the shaft reactions and base resistances transferred from the soil are calculated and substituted into the dynamic equation of the floating pile derived by the Euler beam model. The dynamic impedance coefficient of the pile head in the frequency domain is obtained by using the transfer matrix method. Comparisons with the previous studies are performed to validate the accuracy of the presented approach. The effects of the thickness of the pile end soil, the slenderness ratio of the pile, the groundwater table level and the relative modulus of pile material on the pile dynamic response are investigated through several numerical analyses. The results show that there is an “active soil thickness” for the horizontal dynamic forced floating piles due to the reflection and refraction of the stand waves. Meanwhile, the effect of the groundwater table level should not be neglected to ensure the safety of pile foundation under service life.

Friction between human skin and incontinence pads in the presence of barrier protection products.

This novel experimental work aims to bring further knowledge of frictional performance of common barrier products used in the treatment of incontinence-associated dermatitis and determine how the skin-pad interface changes when a treatment is applied to the skin. Key data is reported and there is an in-depth analysis into friction profiles which reveals great differences between how different skin-pad tribosystems operate when exposed to commercially available barrier treatments. In a wet-pad state Barrier cream A (3M™ Cavilon™ Barrier cream) reduced friction and had much lower dynamic and static coefficients of friction than the other barrier treatments (Barrier cream B (Sorbaderm Barrier cream) and the Barrier spray C (Sorbaderm Barrier spray)). Barrier cream A provided stable friction coefficients in reciprocating sliding, whereas the other treatments, and untreated skin, did not display this unique characteristic. The barrier spray gave rise to high static friction coefficients and exhibited the most stick-slip. All three candidate barrier protection products were found to reduce directional differences in the static coefficient of friction: indicative of reduced shear loading. Knowledge of the desirable frictional properties would drive innovation in product development, and benefit companies, clinicians and users.

Transfer matrix Method-based dynamic model to compensate the pulsating pressure in Strain-based nonintrusive pressure measurement for the L-shaped pipe

Currently, the strain-based nonintrusive pressure measurement does not consider the dynamic case, errors could be introduced. However, the calibration of the dynamic strain-pressure sensitivity coefficient (DSSC) is complicated due to the need to design a special standard dynamic pressure source for different pipes. To address this issue, the present study introduces a model-based and easy-to-implement approach to calibrate it indirectly. Firstly, the baseline dynamic model developed by transfer matrix method is calibrated with the tested static strain-pressure sensitivity coefficient and natural frequencies utilizing model updating. Secondly, the DSSC is generated by the calibrated dynamic model to compensate the dynamic pressure. The closed-form sensitivities of the DSSC and natural frequency are derived to conduct the parametric sensitivity analysis to select the reasonable parameters to calibrate the analytical model. The uniqueness of the field transfer matrix is also proven strictly to make sure the output from the model is unique. The case studies showed that the maximum relative errors of the natural frequencies and closed-form sensitivities predicted by the presented method to the tested results in the existing literature and those predicted by finite difference method are −10% and 1.20% respectively. The experimental results indicated that the proposed method can reduce the maximum relative error of the dynamic pressure to the one measured by commercial pressure sensor from 13.04% to 4.35%.