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The migration and wake structure of a single bubble in a viscous medium near a vertical wall have been experimentally investigated using a two-camera orthogonal shadowing method combined with a particle image velocimetry system. The effects of bubble size, liquid properties, and migration modes on the motion of a near-wall bubble and its wake structure are discussed. It is shown that, unlike migration in pure water, collisions between bubbles and walls are rare in viscous liquids. As viscosity increases, the mobility of the bubble near the wall changes from 3D to 2D and finally exhibits 1D motion with only one degree of freedom. While 1D motion is dominated by viscous forces, 2D migration is influenced by both wall effects and viscous forces, while 3D migration is primarily affected by bubble size. After analyzing the wakes produced by different factors, it was found that the wakes generated by mobile bubbles in three dimensions exhibit similar shedding patterns to Karman vortex streets, while two-dimensional wakes show stronger continuity. The average topological flow field structure of the bubble wake is obtained through periodic phase averaging, and the effect of different factors on the evolution of near-wall bubble wakes is analyzed. • Phase-averaged analysis of the wake behind a near-wall bubble. • The impact of size and viscosity on the migration of a near-wall bubbles. • Shedding of near-wall bubble wakes. [ABSTRACT FROM AUTHOR]

Due to the deficiency in using the cross-bonded grounding mode, a large circulating current is usually induced in the metal sheaths and armors, reducing the permissible current rating of submarine cables. To address this issue, this paper proposes a novel grounding mode to suppress these circulating currents and enhance the permissible current rating within the voltage limits of metal sheaths and armors. To achieve the best performance of the novel grounding mode, the optimal grounding impedances are given. Theoretical analyses indicate that for general submarine cables, the novel grounding mode can suppress the circulating currents within the voltage limits compared with the two-ends grounding mode, and can reduce the short-circuit terminal voltage of metal sheaths and armors compared with the non-interlinked version of the proposed mode. The numerical results further validate the better comprehensive performances of the novel grounding mode in reducing the power loss and short-circuit overvoltage. [ABSTRACT FROM AUTHOR]

An umbilical cable is a compactly integrated cable consisting of electrical power cables, communication (electric signal) cables, and chemical transposition tubes. An umbilical cable is widely used in developing oil and gas resources of deep and ultra-deep water. With the increment of the length and the functional integration of umbilical cables, the crosstalk becomes a crucial issue in the cable design, and needs to be evaluated carefully before the fabrication and installation. Moreover, the twisted structure of communication cable cores has incurred extra difficulties to the crosstalk calculation. Nevertheless, it is not an easy task to model the complex twisted structure in existing models and methods of the crosstalk computation. In this regard, this paper proposes a numerical methodology for the crosstalk calculation considering the multi-conductor twisted structure of the cable cores. In the methodology, the four-wire twisted structure is modelled as a cascade of uniform multiconductor transmission line (MTL) sections, each wire section covering a length of 1/4 pitch, with abrupt interchanges of wire positions at the ends. The chain-parameter equation is introduced to describe the voltage and current transfer relationship in each MTL section. To obtain the numerical solutions of the twisted cable system, the port constraint equations and the permutation matrices are also required and developed. The per-unit-length parameters of the umbilical cable system are computed by numerical methods. The feasibility to engineering applications and accuracy of the proposed methodology is validated by experimental results, and the crosstalk characteristics of communication cables in a typical umbilical cable under different operating conditions are investigated. [ABSTRACT FROM AUTHOR]

The improved properties of ethylene-vinyl acetate (EVA)-modified cement-based materials have not been fully clarified, especially crack resistance and pore structure. The purpose of this research was to investigate the influence of EVA copolymer on the mechanical performances and microstructural properties of cement paste. Strengths, autogenous and drying shrinkage, and water absorption expansion were investigated to evaluate the mechanical properties and volume stability. The ring restrained shrinkage and chloride permeability tests revealed the crack resistance and enhancement of impermeability. The microstructures of EVA-modified cement-based materials were characterized by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) techniques. The experimental results indicated that mixing EVA into cement-based materials increased the flexural strength, reduced the crack propagation and chloride ion penetration, and reduced the negative capillary pressure by improving the water retention. The addition of EVA resulted the remarkable reduction of harmful pores. The optimal mass fraction of EVA powder was approximately 4%. [ABSTRACT FROM AUTHOR]

• The dynamic mechanical properties and fracture energy of the NSCB samples is presented. • All fracture modes of concrete exhibit the mode Ⅰ failure in NSCB tests. • The dynamic fracture energy shows a significant dependence on loading rate, increasing with the loading rate. • The repaired specimens consume more energy than the notched specimens and have a lower kinetic energy of flying fragments. Concrete constructions commonly contain cracks or defects during forming and service, repair operations are necessary in many situations. However, limited investigations conducted on the dynamic fracture toughness (DFT) of repaired concrete structures. This paper investigates the cracking behavior of concrete structures through notched dynamic semi-circular bend (NSCB) tests performed using a split Hopkinson pressure bar (SHPB) apparatus with two measurement techniques, namely digital image correlation (DIC) and crack propagation gauge (CPG), to capture the flying half angular velocity and crack propagation speed of NSCB concrete specimens under various loads. The results demonstrate a linear increase in both DFT and crack propagation speed of concrete with the loading rate. Additionally, a threshold value exists beyond which the crack speed stabilizes, and the DFT is not evidently influenced by the notch depths. The cracks propagate along the aggregates and remain mostly intact under a relatively low loading rate. With an increased loading rate, the damage pattern of some otherwise deflected aggregates changes resulting in crack penetration and significantly reducing the fracture surface roughness. Repaired specimens exhibit greater energy dissipation at the same loading rate, thereby producing flying fragments with lower kinetic energy, which can prevent secondary damage to internal personnel and structures. [ABSTRACT FROM AUTHOR]

In this paper, we design a linear time-invariant two-input-two-output controller for the permanent magnet synchronous motor (PMSM). First, the nonlinear system of a PMSM is approximated using a linear system with structured uncertainties according to the geometric structures of PMSM. We then design a linear controller for the approximated linear system using a standard $\mu$-synthesis robust control method. The main contribution of this paper is that we recognize that the nonlinear PMSM can be reduced to a linear system to apply the mature modern control theory, without referring to classical PID control, thus largely reducing the design effort. The newly designed robust controller is not only easy to calculate, it is also easy to implement and requires less sensors. By virtue of modern robust control theory, it responds fast to exogenous inputs, and robust against parameter uncertainties as well. The applicability of the designed robust controller is both numerically simulated and experimentally verified on a TMS320 F28335 based control board, with performance further compared with the widely used field-oriented controller. [ABSTRACT FROM PUBLISHER]

In this work we study the estimation problem of the vertical wheel force in a vehicle system subject to non-stationary and unknown excitation, which is a common and critical problem in vehicle durability design. The vehicle system can be approximated by a linear time invariant system under each working condition. However, the working conditions are unknown during the estimation process. A primary–auxiliary model scheduling procedure based on time-domain transmissibilities is proposed and performed to identify the unknown working conditions and estimate the unknown vertical wheel force: In addition to constructing a primary transmissibility family from the pseudo-inputs to the output during the offline stage, an auxiliary transmissibility family is constructed by further decomposing the pseudo-input vector into two parts. The auxiliary family enables identifying the unknown working condition under which the system is currently running, and then an appropriate transmissibility from the primary transmissibility family for estimating the unknown output can be selected during the online estimation stage. Moreover, Finite Impulse Response (FIR) models, ridge regression, and Bayes classifiers are applied to realize the model scheduling procedure. A numerical example and a real-world application to the estimation of the vertical wheel force in a full vehicle system are, respectively, conducted to demonstrate the effectiveness of the proposed method. The results show that the estimates are in good agreement with reference measurements. • A model scheduling framework for the purpose of signal estimation is proposed. • The method is applicable to the systems with switching linear dynamics. • An experimental validation on a full vehicle system is performed to estimate the vertical wheel force. • Good accordance between measurements and estimates is achieved under multiple working conditions. [ABSTRACT FROM AUTHOR]

In this paper, we study several physically feasible quantum secret sharing (QSS) schemes using continuous variable graph state (CVGS). Their implementation protocols are given, and the estimation error formulae are derived. Then, we present a variety of results on the theory of QSS with CVGS. Any $$(k,n)$$ threshold protocol of the three specific schemes satisfying $$\frac{n}{2}

• The contact explosion size effect of reinforced concrete slab is revealed with experiments. • The impact echo device was used to test concrete damage under direct contact explosion. • Suggest choosing a scale ratio of more than 1/4 to reduce size effect under contact explosion. The static size effect of concrete is well known; however, investigations on the size effect of reinforced concrete slabs under direct contact explosion remain scarce. It is of great importance to understand the size effect so that the scale model test results can be applied to real damage of full-scale structures subjected to explosion. This paper presents an experimental investigation consisting of eleven direct contact explosion tests carried out to investigate the size effect phenomenon in reinforced concrete slabs. The results indicate that the explosion size effect is clearly observed; that is, the specimens of smaller sizes had less bottom spalling damage even if the upper crater size was approximately the same proportion. Furthermore, the damaged area tended to decrease as the steel ratio increased. Non-destructive testing can detect the damage location and depth of reinforced concrete slabs after explosion by imaging. Finally, finite element model based on LS-DYNA is developed and validated by experimental results for the numerical investigation of the reinforced concrete slab under direct contact explosion. [ABSTRACT FROM AUTHOR]

• Designed prefabricated prestressed channel slab could resist low-altitude nuclear blast without plastic damage. • The plane charge blast test with long positive duration (more than 2 s) was successfully implemented. • Positive duration was related to the quality of the overlying soil and the air shock wave overpressure design value. • Theoretical calculation and ABAQUS simulation results were verified by experimental data. The study of the mechanical properties of prestressed concrete channel slabs under different plane charge air blasts for applications in civil defense engineering is significant. For this reason, similar simulation tests were conducted on the anti-explosive performance of three 1:3 scale prestressed concrete channel slabs under 9 times plane charge air blast. The positive duration was more than 260 ms to simulate the uniform distribution load of a strong blast air shock wave on the prestressed concrete channel slab. The results showed that the designed prestressed concrete channel slab had good displacement ductility without brittle destruction, which significantly reduced the damage of the blasting impact on the structure. The channel slab could resist an air shock load of 0.467 MPa without damage. On the other hand, the positive duration was not only related to the quality of the overlying soil but also related to the air shock wave overpressure design value. The channel plate is regarded as a rigid-plastic component to calculate its plastic dynamic response under explosive load. In addition, the reliability of the theoretical calculation results and ABAQUS software simulation were verified by experimental data, which provided a feasible analytical method for calculation and simulation research in civil air defense engineering. [ABSTRACT FROM AUTHOR]

The polylactic acid-glycolic acid copolymer (PLGA) has been proven to be applicable in medicine, but there is limited research on its application and safety in the agricultural field. In this paper, thifluzamide PLGA microspheres were prepared via phacoemulsification and solvent volatilization, using the PLGA copolymer as the carrier and thifluzamide as the active component. It was found that the microspheres had good slow-release performance and fungicidal activity against Rhizoctonia solani. A comparative study was conducted to show the effect of thifluzamide PLGA microspheres on cucumber seedlings. Physiological and biochemical indexes of cucumber seedlings, including dry weight, root length, chlorophyll, protein, flavonoids, and total phenol content, indicated that the negative effect of thifluzamide on plant growth could be mitigated when it was wrapped in PLGA microspheres. This work explores the feasibility of PLGA as carriers in fungicide applications. [ABSTRACT FROM AUTHOR]