Unit Length Increase Research Articles

Cell Design in Crash Box to Increase the Energy Absorption Efficiency

Researchers have completed many methods to increase the ability of thin tubes to absorb impact energy. Various methods are proposed covering the use of different materials, including new designs, which are expected to improve their performance. This study aims to obtain an Impact Energy Absorber (IEA), which has a low peak impact force and has better crash force efficiency (CFE), energy absorption (EA), and specific energy absorption (SEA). This study made a design change from an empty square tube to a square tube with a cell structure inside. A thin-walled box in the form of a box with a base size of 50 mm x 50 mm without a lid and a height of 150 mm with a thickness of 2 mm was used in this study. A load strikes the tube from the axial direction with a speed of 100 m/s while the other end is supported by fixed support. Deformation, impact force, and absorbed energy were recorded in all types of specimens. The results showed an increase in the reaction force between boxes that were given cells compared to empty ones. While the addition of cell variations from 1 to 2 did not experience a significant change in the impact force. The maximum deformation decreases with the number of cells, while the energy absorbed per unit length increases. The deformation pattern changes due to cells in the box because there is an obstacle when it is deformed towards the outside of the tube. The results of this study are considered in manufacturing high-speed crash boxes.

Heat Transfer Enhancement Analysis of Collector Tube in LFR-CSP

The heat transfer characteristics of the collector tube is one of the cores of a linear Fresnel reflector-solar thermal power generation system (LFR-CSP). In this paper, the heat transfer model of reflective linear Fresnel single-tube compound parabolic collector (CPC) is established. In light of the normal operating conditions during the day, it is found that the direct normal irradiation (DNI) and loop length exert significant effects on the heat collection and thermal loss performance of the linear Fresnel reflector. With the increase of DNI and unit length, the outlet temperature and heat collection capacity of the collector loop increase significantly. Because of the increase of DNI, the increase of collector heat is higher than that of thermal loss. However, the thermal loss per unit length increases correspondingly with the increase in loop length, and the heat collection efficiency decreases. Ambient temperature and wind velocity are not the main factors affecting the heat collection and thermal loss performance of the linear Fresnel reflector under the prerequisite of a good vacuum degree of the collector tube.

Creation and research of the SAW transducer with a single-phase grid and a piezoelectric zinc oxide film

A method for obtaining a new type of surface acoustic wave (SAW) transducer operating at double frequency with a single-phase closed-loop lattice and a piezoelectric zinc oxide film is developed and experimentally investigated. A method for calculating such a transducer has been developed, its equivalent circuit has been compiled, taking into account propagation losses, losses in the metal film and the inductance of the connecting wires. When the frequency is doubled, the SAW attenuation per unit length increases.

Multi-objective optimization of laminar flow characteristics in helical coiled tubes based on NSGA-II

To meet the requirement of energy conservation and optimize the design of helical coils in laminar flow, the pitch, the coil radius and the average inlet velocity were selected as design parameters to obtain the tendency of the heat transfer and flow resistance characteristics of the helical coils. Heat transfer coefficient and pressure drop per unit length of helical coils were taken as the optimization objective functions. A multi-objective optimization model was established, three candidate points A, B and C were obtained based on Non-dominated Sorted Genetic Algorithm-II (NSGA-II). The results showed that heat transfer coefficient and pressure drop per unit length increase with the pitch and inlet velocity whilst them decrease with coil radius, among which the influence of inlet velocity is the most obvious and the pitch is the least. It was found that the coil radius of most points in Pareto front was relatively concentrated. The comprehensive performance of candidate points A, B, C had been improved significantly by 16.3%, 28.3% and 19.6% respectively.

Numerical investigation of an internal solitary wave interaction with horizontal cylinders

An internal solitary wave (ISW) interaction with different type horizontal cylinders are investigated. The forces induced by ISW on horizontal cylinders are presented. Distributions of the maximum dynamic pressures and flow fields around cylinders are described. Good agreements between numerical results and experimental data of forces on the isolated cylinder are achieved. For the extended cylinder, the vertical forces per unit length increase with the increase in the extended length. The horizontal forces on the extended cylinder change from increasing to decreasing after the centre-to-centre distance exceeding 3.5 times the diameter of the isolated cylinder. The peak and valley values of maximum dynamic pressures impose on the lower side of the leading edge and upper side of the trailing edge of the extended cylinder, respectively. The horizontal forces on each of the two tandem cylinders with different centre-to-centre distances are smaller than those on the isolated cylinder, indicating that the two cylinders play a role to protect each other. The comparison of forces between the two cylinders indicates that larger horizontal forces and smaller vertical forces are imposed on the rear cylinder. The maximum dynamic pressures around the rear cylinder are smaller than those around the front cylinder.

Flow and heat transfer characteristics of alkali metal liquid in a pipe with inscribed regular polygon porous media

Flow and heat transfer characteristics of alkali metal liquid in a pipe with inscribed regular polygon porous media are numerically investigated under local thermodynamic equilibrium condition. The effects of filling ways including inscribed regular polygon filling way and segmented inscribed square filling way under different Darcy number (10-6≤Da≤10) are analyzed. The results show that, the velocity near the wall is violently changed by inserting partially filled porous media due to the high resistance of porous media. For inscribed regular polygon filling way, the PEC value of inscribed square is the maximum, which makes it optimal for heat transfer enhancement. For segmented inscribed square filling way, the average Nusselt number increases as the filled ratio increases while decreases as the unit length increases. Owning to the dominant role of the entrance effect, the smaller the unit length is, the larger the PEC is. The PEC of 5:5 segmented filling way is found superior to other filling ways, possibly because the heat transfer enhancement and flow resistance control reach an excellent balance for that case.

Soil Penetration by Earthworms and Plant Roots--Mechanical Energetics of Bioturbation of Compacted Soils.

We quantify mechanical processes common to soil penetration by earthworms and growing plant roots, including the energetic requirements for soil plastic displacement. The basic mechanical model considers cavity expansion into a plastic wet soil involving wedging by root tips or earthworms via cone-like penetration followed by cavity expansion due to pressurized earthworm hydroskeleton or root radial growth. The mechanical stresses and resulting soil strains determine the mechanical energy required for bioturbation under different soil hydro-mechanical conditions for a realistic range of root/earthworm geometries. Modeling results suggest that higher soil water content and reduced clay content reduce the strain energy required for soil penetration. The critical earthworm or root pressure increases with increased diameter of root or earthworm, however, results are insensitive to the cone apex (shape of the tip). The invested mechanical energy per unit length increase with increasing earthworm and plant root diameters, whereas mechanical energy per unit of displaced soil volume decreases with larger diameters. The study provides a quantitative framework for estimating energy requirements for soil penetration work done by earthworms and plant roots, and delineates intrinsic and external mechanical limits for bioturbation processes. Estimated energy requirements for earthworm biopore networks are linked to consumption of soil organic matter and suggest that earthworm populations are likely to consume a significant fraction of ecosystem net primary production to sustain their subterranean activities.

Effect of geometrical parameters on flow and heat transfer performances in multi-stream spiral-wound heat exchangers

The influences of the changes in geometrical factors, including the space bar thickness, the tube pitch in the first layer, the tube external diameter, the number of layers and the centre core diameter on flow and heat transfer performances in multi-stream spiral-wound heat exchangers are numerical investigated. The shell-side and tube-side Nusselt number and pressure drop per unit length increase with the increase of number of layers, centre core diameter, and tube external diameter, but decrease with the increase of space bar thickness and tube pitch in the first layer. Quantitatively estimation of the affecting performances of these five geometrical parameters is implemented by using the Taguchi method, and the result shows that the contribution rate of them are more than 5%. Thus, the multivariate correlations with the main geometrical parameters considered are developed for shell-side Nusselt number and friction coefficient.

Viscous Dissipation of Polymer Melt in Micro Channels and Macro Channels

Viscous dissipation is the key factor impacting flowing characteristics of polymer melt. In order to study the difference between micro scale and macro scale, experimental studies of viscous dissipation at various shear rate were investigated with several polymers, including PMMA and HDPE, at different temperature when melts flow through 1000μm,500μm,350μm diameter channels of identical aspects ratio in the paper. The results indicate that the temperature rises caused by viscous dissipation increase with increasing shear rate and the temperature rise for some shear rate decreases with increasing melts temperature. The temperature rises decrease significantly with the reduction of the characteristic size of micro channel at the same shear rate. However, the average temperature rises per unit length increase when the character size of channel decreases. This indicates the shear friction gradually increases with the decrease of channel characteristic size. Therefore polymer melt viscous dissipation effects of micro scale dimensions are different from that of macro-scale dimensions.

Instability of Flexible Strip Hanging Over Edge of Flat Frictional Surface

The conditions for an overhanging flexible strip to slide off a flat surface are investigated. This problem may be applicable to pieces of paper, fabric, leather, and other flexible materials, including plastic and metallic strips used herein for experimental comparisons. The critical overhang length depends on (a) the length, weight per unit length, and bending stiffness of the strip, (b) the coefficients of friction (CoFs) between the strip and both the surface and its edge, and (c) the inclination of the surface. The strip is modeled as an inextensible elastica. A shooting method is applied to solve the nonlinear equations that are based on equilibrium, geometry, and Coulomb friction. Three types of equilibrium shape are obtained. In the most common type, one end of the strip overhangs the edge and the other end contains a segment that is in contact with the surface. In another type, contact only occurs at the nonoverhanging end and at the edge. The third type involves the strip balancing on the edge of the surface. The ratio of the critical overhang length to the total strip length is plotted as a function of the surface CoF, edge CoF, and weight parameter for a horizontal surface. In most cases, this ratio increases as the CoFs and the strip’s bending stiffness increase, and decreases as the strip’s weight per unit length increases. The rotation of the strip at the edge tends to increase as the strip’s weight per unit length, the strip’s length, and the surface CoF increase, and to decrease as the strip’s bending stiffness increases. Inclined surfaces are also considered, and the critical overhang length decreases as the surface slopes more downward toward the edge. The theoretical results are compared with experimental data, and the agreement is good.

Pulse propagation in a fiber Bragg grating written in a slow saturable fiber amplifier

We have developed a model to study nonlinear pulse propagation in a fiber Bragg grating written in an erbium-doped fiber amplifier. The saturation effect in such amplifiers depends on the accumulated energy along the pulse rather than on the pulse instantaneous power. We have shown that the gain saturation effect cannot be neglected when Bragg solitons are amplified by erbium-doped fiber amplifiers. The slow saturation of the amplifier limits the output pulse power, and it tends to split the amplified pulse into several pulses. We have shown that when the propagation velocity of the amplified pulses decreases, the amplifier gain per unit length increases.

Structural Memory in the Contractile Ring Makes the Duration of Cytokinesis Independent of Cell Size

Cytokinesis is accomplished by constriction of a cortical contractile ring. We show that during the early embryonic divisions in C. elegans, ring constriction occurs in two phases--an initial phase at a constant rate followed by a second phase during which the constriction rate decreases in proportion to ring perimeter. Cytokinesis completes in the same amount of time, despite the reduction in cell size during successive divisions, due to a strict proportionality between initial ring size and the constant constriction rate. During closure, the myosin motor in the ring decreases in proportion to perimeter without turning over. We propose a "contractile unit" model to explain how the ring retains a structural memory of its initial size as it disassembles. The scalability of constriction may facilitate coordination of mitotic events and cytokinesis when cell size, and hence the distance traversed by the ring, varies during embryogenesis and in other contexts.

Heat and mass transfer characteristics of a helical absorber using LiBr and LiBr + LiI + LiNO 3 + LiCl solutions

An experimental study has been performed to investigate the heat and mass transfer performance in a falling film absorber of a small-sized absorption chiller/heater. The components of the chiller/heater were concentrically arranged in a cylindrical form with a low temperature generator, an absorber and an evaporator from the center. The arrangement of such a helical-type heat exchanger makes the system more compact compared to a conventional one. As a working fluid, LiBr + LiI + LiNO 3 + LiCl solution is used to get improved heat transfer effect. The heat and mass transfer coefficients of the helical absorber provide similar values compared with the data obtained for horizontal absorbers at similar solution flow rates. The heat and mass transfer coefficients of LiBr + LiI + LiNO 3 + LiCl solution increase as the solution flow rate per unit length increases. However, if the solution flow rate is larger than 0.03 kg/m s, the heat and mass transfer increase is minimal. Thus, 0.03 kg/m s is recommended as an optimal solution flow rate. The heat and mass flux performance of LiBr + LiI + LiNO 3 + LiCl solution shows the tendency of 2–5% increase compared with that of LiBr solution.

Model of a thermal energy storage device integrated into a solar assisted heat pump system for space heating

Details about modelling a sensible heat thermal energy storage (TES) device integrated into a space heating system are given. The two main operating modes are described. Solar air heaters provide thermal energy for driving a vapor compression heat pump. The TES unit ensures a more efficient usage of the collected solar energy. The TES operation is modeled by using two non-linear coupled partial differential equations for the temperature of the storage medium and heat transfer fluid, respectively. Preliminary results show that smaller TES units provide a higher heat flux to the heat pump vaporiser. This makes the small TES unit discharge more rapidly during time periods with higher thermal loads. The larger TES units provide heat during longer time periods, even if the heat flux they supply is generally smaller. The maximum heat flux is extracted from the TES unit during the morning. Both the heat pump COP and exergy efficiency decrease when the TES unit length increases. Also, the monthly thermal energy stored by the TES unit and the monthly energy necessary to drive the heat pump compressor are increased by increasing the TES unit length.

Remanent magnetisation in multifilamentary Bi-2223 tapes with filament bridging

One of the methods used for the separation of hysteresis and coupling losses in multifilamentary Bi-2223 tapes is based on the assumptions that hysteresis losses per unit length are independent of the sample length while coupling losses per unit length increase proportionally to the square of the sample length. We measured the remanent magnetic field of several multifilamentary Bi-2223 tape samples with different length using the Hall probe scanning technique. For most of the tapes, the remanent magnetic field, which is proportional to magnetisation, depended on the sample length. Only for a small number of tapes the sample length did not affect the remanent magnetisation. The observed behavior is attributed to the existence of filament bridging.

A study on the performance of L-band EDFAs under different pumping configurations

In this letter, we investigate and compare theoretically the performance of an optimized L-band erbium doped fiber amplifier when an L-band erbium doped fiber (EDF) or an optimized C-band EDF, is used separately as an ASE (amplified spontaneous emission) pump source. We show that the gain per unit length increases with increase in cut-off wavelength independent of the numerical aperture (NA) of the EDF; the pump efficiency peaks in the region of cut-off wavelength between 1075 and 1125 nm, the exact value of which depends upon the level of inversion of the EDF. It is also observed that the pump efficiency as well as the gain per unit length increase with increase in level of inversion for a given cut-off wavelength. The pump efficiency as well as the ASE power per unit length are better for the case when a complete L-band optimized amplifier is used than when an optimized C-band amplifier is used as a pump source to amplify an L-band signal propagating in a cascaded L-band optimized amplifier. Also the gain achieved is much higher if the signal is fed into the entire amplifier with the pump, rather than at an intermediate point.

Is Diffusion or Forced Flow the Main Mechanism of Radon Infiltration into Underground Openings? A Theoretical Study

Abstract The diffusion length in porous materials is usually determined from core samples and not for an underground opening as a whole. Underground structures usually have widely differing porosity and crack systems through which equally widely differing diffusive and convective flows deliver gases into underground openings. This paper discusses whether diffusion, rather than forced flow, can be the major cause of radon infiltration into underground openings. To calculate the diffusion through cracks across a slab, an approach developed by Landman was used in which a single rectangular crack of porosity (cr gives a diffusion flow. The two-dimensional calculation is repeated for a case where there are two cracks per unit length, three cracks, four cracks, etc. while keeping the crack porosity (cr constant. The corresponding forced flow for identical cracks is also calculated for a typical pressure difference across the slab. When the diffusion and forced flow are plotted as a function of the number of cracks per unit length, a crossover occurs where the diffusion flow starts to dominate. In another case where the forced flow is kept constant, an even more dramatic increase in the diffusion flow is observed as the number of cracks per unit length increases.

Small angle x-ray scattering of chromatin. Radius and mass per unit length depend on linker length

Analyses of low angle x-ray scattering from chromatin, isolated by identical procedures but from different species, indicate that fiber diameter and number of nucleosomes per unit length increase with the amount of nucleosome linker DNA. Experiments were conducted at physiological ionic strength to obtain parameters reflecting the structure most likely present in living cells. Guinier analyses were performed on scattering from solutions of soluble chromatin from Necturus maculosus erythrocytes (linker length 48 bp), chicken erythrocytes (linker length 64 bp), and Thyone briareus sperm (linker length 87 bp). The results were extrapolated to infinite dilution to eliminate interparticle contributions to the scattering. Cross-sectional radii of gyration were found to be 10.9 +/- 0.5, 12.1 +/- 0.4, and 15.9 +/- 0.5 nm for Necturus, chicken, and Thyone chromatin, respectively, which are consistent with fiber diameters of 30.8, 34.2, and 45.0 nm. Mass per unit lengths were found to be 6.9 +/- 0.5, 8.3 +/- 0.6, and 11.8 +/- 1.4 nucleosomes per 10 nm for Necturus, chicken, and Thyone chromatin, respectively. The geometrical consequences of the experimental mass per unit lengths and radii of gyration are consistent with a conserved interaction among nucleosomes. Cross-linking agents were found to have little effect on fiber external geometry, but significant effect on internal structure. The absolute values of fiber diameter and mass per unit length, and their dependencies upon linker length agree with the predictions of the double-helical crossed-linker model. A compilation of all published x-ray scattering data from the last decade indicates that the relationship between chromatin structure and linker length is consistent with data obtained by other investigators.

Constancy of a 200 � fiber in human chromatin and chromosomes

The diameter of 200 A for modal chromatin fibers in unstimulated and stimulated peripheral human lymphocytes remains constant within a range of 5% throughout the cell cycle (including metaphase). Fiber dry mass varies slightly more, but its average of 6×10−16 g/μ. remains constant also. — The use of colchicine induces metaphase fibers to shorten and results in a fiber mass per unit length increase of up to twofold. This change does not appear to be related to any change in total chromosomal mass. Fiber shortening, consequently and, with it, shortening of the chromosome are considered to be essentially conformational events.

Variation in the Properties of Cotton Fibers with Length

Variation in the properties of fibers constituting a sample of cotton is one of their most remarkable characteristics. This variation has been studied, in the present paper, on 12 cottons, the fibers having first been sorted into groups based on quartile lengths. It is found that, in gerieral, fiber strength, uniformity of strength, maturity, and reversals per unit length increase with increase in length group, while elongation per unit load decreases. The variation in fineness shows that the extreme length groups are finer than the middle ones. The significance of these findings for elucidating many problems of practical interest is indicated briefly.