Shear-induced structure and dynamics of hydrophobically modified hydroxy ethyl cellulose (hmHEC) in the presence of SDS

Tirtaatmadija, Viyada,Cooper-white, Justin J.,Gason, Samuel J. The Korean Society of Rheology 2002 Korea-Australia rheology journal Vol.14 No.4

The interaction between hydrophobically modified hydroxyethyl cellulose (hmHEC), containing approximately 1 wt% side-alkyl chains of $C_{16}$, and an anionic sodium dodecyl sulphate (SDS) surfactant was investigated. For a semi-dilute solution of 0.5 wt% hmHEC, the previously observed behaviour of a maximum in solution viscosity at intermediate SDS concentrations, followed by a drop at higher SDS concentrations, until above the cmc of surfactant when the solution resembles that of the unsubstituted polymer, was confirmed. Additionally, a two-phase region containing a hydrogel phase and a water-like supernatant was found at low SDS concentrations up to 0.2 wt%, a concentration which is akin to the critical association concentration, cac, of SDS in the presence of hmHEC. Above this concentration, SDS molecules bind strongly to form mixed micellar aggregates with the polymer alkyl side-chains, thus strengthening the network junctions, resulting in the observed increase in viscosity and elastic modulus of the solution. The shear behaviour of this polymer-surfactant complex during steady and step stress experiments was examined In great detail. Between SDS concentrations of 0.2 and 0.25 wt%, the shear viscosity of the hmHEC-polymer complex network undergoes shear-induced thickening, followed by a two-stage shear-induced fracture or break-up of the network. The thickening is thought to be due to structural rearrangement, causing the network of flexible polymers to expand, enabling some polymer hydrophobic groups to be converted from intra- to inter-chain associations. At higher applied stress, a partial local break-up of the network occurs, while at even higher stress, above the critical or network yield stress, a complete fracture of the network into small microgel-like units, Is believed to occur. This second network rupture is progressive with time of shear and no steady state in viscosity was observed even after 300 s. The structure which was reformed after the cessation of shear is found to be significantly different from the original state.

Shear Behavior of Overconsolidated Nakdong River Sandy Silt

Khin Swe Tint,Young Su Kim,In-Shik Seo,Dae-Man Kim KOREAN SOCIETY OF CIVIL ENGINEERS 2007 KSCE JOURNAL OF CIVIL ENGINEERING Vol.11 No.5

<P>In this research, overconsolidated drained, undrained and unconsolidated undrained of Nakdong river sandy silt in triaxial compression tests were performed on specimens of silt with 26% sand content. In CIU and CID tests, the specimens were consolidated isotropically from 100 to 400 ㎪ and unloaded to 200 ㎪ for OCR = 2, unloaded to 100 ㎪ for OCR = 4 and unloaded to 50 ㎪ for OCR = 8 before shear condition. In UU tests, the samples were carried out under effective confining pressure 100 to 400 ㎪ during shear. In CIU-OC tests, the flowing characteristics were observed: the deviator stress decreased with higher OCRs and showed strain-softening behavior after failure. Pore water pressure decreased to negative; that the samples were higher dilative volume change tendency under unloading due to increasing OCRs. CID-OC tests indicated that the deviator stresses increased and presented strain-softening tendency after failure. Became negative due to dilatancy with higher OCRs under small strains. In VU tests, peak deviator stresses were different and displayed strain-softening tendency under higher effective confining pressure after peak value. The pore water pressures increased with small strains before failure and depended on saturation condition at failure. The undrained shear strength and the internal friction angle in UU test cannot be determined accurately due to dilative effect and low-cohesion of sandy silt. By using the concepts of critical state, the stress paths showed similar and all failure points followed to a unique slope line which forms a critical state line (CSL) in stress path diagram.</P>

Characterization at the individual cell level and in whole blood samples of shear stress preventing red blood cells aggregation

Lee, K.,Kinnunen, M.,Danilina, A.V.,Ustinov, V.D.,Shin, S.,Meglinski, I.,Priezzhev, A.V. Pergamon Press ; Elsevier Science Ltd 2016 Journal of biomechanics Vol.49 No.7

The aggregation of red blood cells (RBC) is an intrinsic feature of blood that has a strong impact on its microcirculation. For a number of years it has been attracting a great attention in basic research and clinical studies. Here, we study a relationship between the RBC aggregation parameters measured at the individual cell level and in a whole blood sample. The home made optical tweezers were used to measure the aggregating and disaggregating forces for a pair of interacting RBCs, at the individual cell level, in order to evaluate the corresponding shear stresses. The RheoScan aggregometer was used for the measurements of critical shear stress (CSS) in whole blood samples. The correlation between CSS and the shear stress required to stop an RBC pair from aggregating was found. The shear stress required to disaggregate a pair of RBCs using the double channel optical tweezers appeared to be about 10 times higher than CSS. The correlation between shear stresses required to prevent RBCs from aggregation at the individual cell level and in whole blood samples was estimated and assessed quantitatively. The experimental approach developed has a high potential for advancing hemorheological studies.

Characteristics of Shear Behavior of Remolded Nak-dong River Sandy Silt

김영수,틴킨스웨,김대만 한국지반공학회 2007 한국지반공학회논문집 Vol.23 No.3

The results from normally consolidated isotropic drained and undrained triaxial compression tests (NCIU and NCID) on sand with high silt content were presented in this paper. The experiments were performed on specimens of Nak-dong River sand with 63% silt content under effective confined pressures, 100 kPa to 400 kPa. From test results, Sandy silt became initially compressive but eventually appeared to provide dilatancy response throughout the entire stress-strain curve. The behavior of sandy silt was more difficult to characterize than that of clay and sand due to lower plastic characteristic. Especially, the samples exhibited dilatancy development during shear after failure. The shear behavior and shear strength parameters of sandy silt can be determined as stress-strain behaviors are described by the Mohr-Coulomb failure criterion. The shear behaviors were observed increasing dilatancy volume change tendency with strain-softening tendency after failure. In this paper, the behavior of dilatancy depends on not only sand content but also fine content with low-cohesion during shear in the samples of sandy silt.

호안용 매트리스내 채움재의 한계_허용 전단응력에 관한 연구

배상수,이승윤,지홍기 한국수자원학회 2008 한국수자원학회논문집 Vol.41 No.2

본 논문은 호안용 매트리스내 채움재의 한계_허용 전단응력을 제시하였다. 먼저, 매트리스가 설치된 수로에서 유수력이 작용할 때 각 지점에 대한 유효전단응력을 산정하였다. 다음으로, 입자들의 한계운동을 결정하는데 주로 사용되는 Shields 계수와 전단응력을 이용한 채움재의 평균입경을 산정하였다. 마지막으로, 산정된 각 인자들을 근거로 철망내 개별 암석의 안정조건을 만족시키는 한계_허용 전단응력의 범위를 결정하였다. 또한 매트리스와 사석의 비교를 통해 매트 Critical and allowable shear stress acting on the mattress revetment, is presented in this study. First of all, shear stress at each spot is computed when the hydraulic power act on the waterway. Secondly, median diameter of the filling rocks is computed

제형 및 사인형 주름 강판의 초기 불완전 형상을 고려한 전단 좌굴 특성 비교

서건호,손수덕,이승재,Seo, Geonho,Shon, Sudeok,Lee, Seungjae 한국공간구조학회 2021 한국공간구조학회지 Vol.21 No.4

This paper conducted a comparative analysis of the shear buckling characteristics of trapezoidal and sinusoidal corrugated steel plates considering of their initial imperfection. Initial imperfection refers to the state where the shape of the corrugated plate is initially not perfect. As such, an initially imperfect shape was assumed using the eigen buckling mode. To calculate the buckling stress of corrugated steel plates, the linear buckling analysis used a boundary condition which was applied to the plate buckling analysis. For the comparison of trapezoidal and sinusoidal corrugation, the shape parameters were assumed using the case where the length and slope of each corrugation were the same, and the initial imperfection was considered to be from 0.1% to 5% based on the length of the steel plate. Here, for the buckling analysis, ANSYS, a commercial FEA program, was used. From the results of buckling analysis, the effect of overall initial imperfection showed that the larger the initial imperfection, the lower the buckling stress. However, in the very thin model, interaction or local buckling was dominant in the perfect shape, and in this case, the buckling stress did not decrease. Besides, the sinusoidal model showed higher buckling stress than the trapezoidal one, and the two corrugation shapes decreased in a similar way.

Assessing the Erosional Properties of Muddy Sediments: Asan Bay Case Study

Ngoran Senan Kiniben,안종환,황규남 (사)한국연안방재학회 2023 한국연안방재학회지 Vol.10 No.4

The study's outcomes reveal that both the critical shear stress needed to initiate erosion and the sediment erosion rate are influenced by various parameters, including the bulk density of sediment and bed shear stress. This comprehensive analysis underscores the vital role that these parameters play in determining sediment erosion characteristics. The presented research contributes to the understanding of erosional behaviors of muddy sediments and their implications. The findings emphasize the importance of comprehending such properties, especially in designing effective erosion control structures and managing water bodies prone to erosion.

금강 하구역 점착성 퇴적물 침식특성의 지엽적ㆍ계절적 변화 해석

임상호(Yim Shang Ho),류홍렬(Ryu Hong-Ryul),황규남(Hwang Kyu-Nam) 대한토목학회 2008 대한토목학회논문집 B Vol.28 No.1B

본 연구의 목적은 금강하구의 표층에 분포하는 점착성 퇴적물의 침식매개변수를 정량적으로 산정하는 것이다. 또한 본 연구는 침식매개변수들의 금강하구역 내에서의 지엽적ㆍ계절적 변화에 대한 조사와 타 지역 분석 결과와의 비교/분석을 통한 공간적 변화에 대한 조사를 포함한다. 점착성 퇴적물의 침식특성은 기본적으로 퇴적물 자체의 물리ㆍ화학적 특성에 의해 크게 영향을 받으므로, 본 연구는 또한 퇴적물의 이러한 기본특성이 침식특성에 미치는 영향에 대한 정성적 분석을 포함한다. 침식실험은 전북대 환형수조를 이용하여 균일저면 조건하에서 수행되었으며, 저면밀도와 바닥전단웅력을 변화시키면서 총 16회의 실험이 수행되었다. 실험결과에 따르면, 금강하구역 점착성 퇴적물은 저면밀도 1.14~1.38 g/㎤ 범위에서 침식한계전단 응력(τ<SUB>ce,s</SUB>)은 0.19~0.41 N/㎡, 침식률 계수(ε<SUB>M,s</SUB>)는 54.26~7.70 ㎎/㎠ㆍhr 범위의 값을 갖는 것으로 나타났다. 또한 산정된 침식 매개변수들은 타 지역 점착성 퇴적물과 비교시 정량적으로 그 값이 크게 다른 것으로 나타났으나, 금강하구역 내에서의 지엽적/계절적 변화는 미미한 것으로 나타났다. The purpose of this study is to quantify the erosion parameters of cohesive sediments in Keum Estuary. This study also involves the examinations on the local/seasonal variation of them in Keum Estuary and on their spatial variation comparing with those of other sites. As erosional properties of cohesive sediments are in general influenced largely by the physico-chemical properties of cohesive sediments themselves, this study also involves the qualitative analyses on the impact by the physicochemical properties. Erosion tests have been performed under the uniform bed condition using the Chonbuk annular flume and total 16 tests have been carried out with various bed densities and bottom shear stresses. Experimental results show that the critical shear stress for erosion varies in the range of 0.19~0.41 N/㎡ and the coefficient of erosion rate varies in the range of 54.26~7.70 ㎎/㎠ㆍhr, over the corresponding bulk-density range of 1.14~1.38 g/㎠. While erosion parameters estimated for Keum estuary sediments are found to be remarkably different in quantity compared with those for cohesive sediments from other sites, their local/seasonal variabilities within Keum Estuary are found to be insignificant.

Effects of vegetation and fecal pellets on the erodibility of cohesive sediments: Ganghwa tidal flat, west coast of Korea

Ha, Ho Kyung,Ha, Hun Jun,Seo, Jun Young,Choi, Sun Min Elsevier 2018 Environmental pollution Vol.241 No.-

<P><B>Abstract</B></P> <P>Although the Korean tidal flats in the Yellow Sea have been highlighted as a typical macrotidal system, so far, there have been no measurements of the sediment erodibility and critical shear stress for erosion (<I>τ</I> <SUB> <I>ce</I> </SUB>). Using the Gust erosion microcosm system, a series of field experiments has been conducted in the Ganghwa tidal flat to investigate quantitatively the effects of biogenic materials on the erodibility of intertidal cohesive sediments. Four representative sediment cores with different surficial conditions were analyzed to estimate the <I>τ</I> <SUB> <I>ce</I> </SUB> and eroded mass. Results show that <I>τ</I> <SUB> <I>ce</I> </SUB> of the “free” sediment bed not covered by any biogenic material on the Ganghwa tidal flat was in the range of 0.1–0.2 Pa, whereas the sediment bed partially covered by vegetation (<I>Phragmites communis</I>) or fecal pellets had enhanced <I>τ</I> <SUB> <I>ce</I> </SUB> up to 0.45–0.6 Pa. The physical presence of vegetation or fecal pellets contributed to protection of the sediment bed by blocking the turbulent energy. An inverse relationship between the organic matter included in the eroded mass and the applied shear stress was observed. This suggests that the organic matter enriched in a near-bed fluff layer is highly erodible, and the organic matter within the underlying sediment layer becomes depleted and less erodible with depth. Our study underlines the role of biogenic material in stabilizing the benthic sediment bed in the intertidal zone.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Field experiments were conducted to investigate the effects of biogenic materials on the erodibility of cohesive sediments. </LI> <LI> A critical shear stress for erosion of the “free” sediment bed on the Ganghwa tidal flat was 0.1–0.2 Pa. </LI> <LI> Sediment bed partially covered by vegetation or fecal pellets had the critical shear stress for erosion up to 0.45–0.6 Pa. </LI> <LI> An inverse relationship between the organic matter included in the eroded mass and the applied shear stress was observed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effects of silt contents on the static and dynamic properties of sand-silt mixtures

Hsiao, Darn H.,Phan, Vu T.A. Techno-Press 2014 Geomechanics & engineering Vol.7 No.3

This paper presents a detailed study focused on investigating the effects of silt content on the static and dynamic properties of sand-silt mixtures. Specimens with a low-plastic silt content of 0, 15, 30 and 50% by weight were tested in static triaxial, cyclic triaxial, and resonant columns in addition to consolidation tests to determine such parameters as compression index, internal friction angle, cohesion, cyclic stress ratio, maximum shear modulus, normalized shear modulus and damping ratio. The test procedures were performed on specimens of three cases: constant void ratio index, e = 0.582; same peak deviator stress of 290 kPa; and constant relative density, $D_r$ = 30%. The test results obtained for both the constant-void-ratio-index and constant-relative-density specimens showed that as silt content increased, the internal friction angle, cyclic stress ratio and maximum shear modulus decreased, but cohesion increased. In testing of the same deviator stress specimens, both cohesion and internal friction angle were insignificantly altered with the increase in silt content. In addition, as silt content increased, the maximum shear modulus increased. The cyclic stress ratio first decreased as silt content increased to reach the threshold silt content and increased thereafter with further increases in silt content. Furthermore, the damping ratio was investigated based on different silt contents in three types of specimens.