Fast iterative solvers for geomechanics in a commercial FE code

There is a pressing need to improve the feasibility of three-dimensional finite element (FE) methods applied to many problems in civil engineering. This is particularly the case for static analyses in geotechnical engineering: ideally, models would be 3D, follow the actual geometry, use non-linear material formulations and allow simulation of construction sequences, and all of this with a reasonable degree of accuracy. One major obstacle to improvements in this regard is the difficulty in solving of the set of (linearised) algebraic equations which arises from a typical discretisation approach. Very large systems become cumbersome for direct techniques to solve economically. This paper describes the incorporation of iterative (rather than direct) solution techniques, developed through University research, into commercial FE software for geotechnics

Three-dimensional FE-EFGM adaptive coupling with application to nonlinear adaptive analysis

Three-dimensional problems with both material and geometrical nonlinearities are of practical importance in many engineering applications, e.g. geomechanics, metal forming and biomechanics. Traditionally, these problems are simulated using an adaptive finite element method (FEM). However, the FEM faces many challenges in modeling these problems, such as mesh distortion and selection of a robust refinement algorithm. Adaptive meshless methods are a more recent technique for modeling these problems and can overcome the inherent mesh based drawbacks of the FEM but are computationally expensive. To take advantage of the good features of both methods, in the method proposed in this paper, initially the whole of the problem domain is modeled using the FEM. During an analysis those elements which violate a predefined error measure are automatically converted to a meshless zone. This zone can be further refined by adding nodes, overcoming computationally expensive FE remeshing. Therefore an appropriate coupling between the FE and the meshless zone is vital for the proposed formulation. One of the most widely used meshless methods, the element-free Galerkin method (EFGM), is used in this research. Maximum entropy shape functions are used instead of the conventional moving least squares based formulations'. These shape functions posses a weak Kronecker delta property at the boundaries of the problem domain, which allows the essential boundary conditions to be imposed directly and also helps to avoid the use of a transition region in the coupling between the FE and the EFG regions. Total Lagrangian formulation is preferred over the updated Lagrangian formulation for modeling finite deformation due to its computational efficiency. The well-established error estimation procedure of Zienkiewicz-Zhu is used in the FE region to determine the elements requiring conversion to the EFGM. The Chung and Belytschko error estimator is used in the EFG region for further adaptive refinement. Numerical examples are presented to demonstrate the performance of the current approach in thre

Tensile strengths of flocculated compacted unsaturated soils

Flocculating agents can be introduced to soils through a number of natural or anthropogenic processes. This paper investigates the effect of flocculant addition (aqueous calcium chloride (CaCl2)) on the tensile strengths of two soils of differing flocculation susceptibility. Tensile strengths were found using the Brazilian (direct splitting) test for a range of suction values. A decrease in tensile strength was found for a soil with high clay content, which was consistent with previous findings in the literature. However, the strength of the soil with lower clay content unexpectedly increased. Results were interpreted using the extended Mohr–Coulomb (EMC) yield criterion fitted to data above the residual suction value. Changes in EMC parameters were used to infer changes in material behaviour on calcium chloride addition. Results have important implications for the design of geotechnical structures, for example engineered cover systems, exposed to flocculating conditions. </jats:p

Synthetic spectra of H Balmer and HeI absorption lines. II: Evolutionary synthesis models for starburst and post-starburst galaxies

We present evolutionary stellar population synthesis models to predict the spectrum of a single-metallicity stellar population, with a spectral sampling of 0.3 A in five spectral regions between 3700 and 5000 A. The models, which are optimized for galaxies with active star formation, synthesize the profiles of the hydrogen Balmer series (Hb, Hg, Hd, H8, H9, H10, H11, H12 and H13) and the neutral helium absorption lines (HeI 4922, HeI 4471, HeI 4388, HeI 4144, HeI 4121, HeI 4026, HeI 4009 and HeI 3819) for a burst with an age ranging from 1 to 1000 Myr, and different assumptions about the stellar initial mass function. Continuous star formation models lasting for 1 Gyr are also presented. The input stellar library includes NLTE absorption profiles for stars hotter than 25000 K and LTE profiles for lower temperatures. The temperature and gravity coverage is 4000 K <Teff< 50000 K and 0.0< log g$< 5.0, respectively. The models can be used to date starburst and post-starburst galaxies until 1 Gyr. They have been tested on data for clusters in the LMC, the super-star cluster B in the starburst galaxy NGC 1569, the nucleus of the dwarf elliptical NGC 205 and a luminous "E+A" galaxy. The full data set is available for retrieval at http://www.iaa.es/ae/e2.html and at http://www.stsci.edu/science/starburst/, or on request from the authors at [email protected]: To be published in ApJS. 48 pages and 20 figure

Photometric Properties of Kiso Ultraviolet-Excess Galaxies in the Lynx-Ursa Major Region

We have performed a systematic study of several regions in the sky where the number of galaxies exhibiting star formation (SF) activity is greater than average. We used Kiso ultraviolet-excess galaxies (KUGs) as our SF-enhanced sample. By statistically comparing the KUG and non-KUG distributions, we discovered four KUG-rich regions with a size of $\sim 10^\circ \times 10^\circ$. One of these regions corresponds spatially to a filament of length $\sim 60 h^{-1}$ Mpc in the Lynx-Ursa Major region ($\alpha \sim 9^{\rm h} - 10^{\rm h}, \delta \sim 42^\circ - 48^\circ$). We call this ``the Lynx-Ursa Major (LUM) filament''. We obtained $V(RI)_{\rm C}$ surface photometry of 11 of the KUGs in the LUM filament and used these to investigate the integrated colors, distribution of SF regions, morphologies, and local environments. We found that these KUGs consist of distorted spiral galaxies and compact galaxies with blue colors. Their star formation occurs in the entire disk, and is not confined to just the central regions. The colors of the SF regions imply that active star formation in the spiral galaxies occurred $10^{7 - 8}$ yr ago, while that of the compact objects occurred $10^{6-7}$ yr ago. Though the photometric characteristics of these KUGs are similar to those of interacting galaxies or mergers, most of these KUGs do not show direct evidence of merger processes.Comment: 39 pages LaTeX, using aasms4.sty, 20 figures, ApJS accepted. The Title of the previous one was truncated by the author's mistake, and is corrected. Main body of the paper is unchange

Characterisation of anchor penetration behaviour for Cable burial risk assessment

Offshore wind (OSW) power cable failure currently accounts for 75% of the cost of all insurance claims associated with OSW projects and faults typically take 100+ days to rectify. The most effective method for protecting the cables from anchor damage is to bury them in the seabed, but current guidance on how deep they should be buried is ambiguous. There are a number of variables that influence the penetration depth of anchors, such as the anchor size (considered as the weight in kg), fluke length, fluke angle and the soil type and properties. The fluke length and angle vary depending on anchor size, the type of anchor and the manufacturer. Current industrial guidance suggests that an anchor's penetration behaviour can be predicted based upon its fluke length and vessel displacement and the soil type but this does not consider the physical properties of the soil. In this paper the penetration behaviour of a Class F (AC-14) anchor has been investigated in sand soil beds of varying relative densities. The results indicate that the penetration depth of the anchor is density dependent and that the anchor penetrates deeper than may be anticipated in very loose sands

Depth of lowering and layered soils; a case study from across the North Sea

The Carbon Trust (2015) 'Cable Burial Risk Assessment (CBRA) Methodology' document is widely used in the offshore subsea cable industry to define the cable burial Depth of Lowering (DoL). To-date published work on anchor penetration depths has focused on single homogeneous soil units, offering limited information on the response of different soil layering combinations, and associated contrasting geotechnical properties between soil units. By interrogating >11,000 shallow cores from the entire UK North Sea area, we demonstrate that 'layered' soil combinations (e.g., 'sand over clay') are statistically common across the North Sea study area. The results also highlight the importance of updating current CBRA approaches to include 'layered' soils, and associated changes in geotechnical properties (e.g., strength and density) between single and layered soil units. In addition, we collated geotechnical data for input into physical and numerical modelling undertaken by the University of Dundee and Durham University respectively (see Sharif et al., 2023; Bird et al., 2023 a, b), to assess the implications for the current CBRA Methodology. Ultimately the goal is to create a new CPT-based tool for better constraining the DoL, as part of the EPSRC research grant 'Offshore Cable Burial: How deep is deep enough?'

A 180 Kpc Tidal Tail in the Luminous Infrared Merger Arp 299

We present VLA HI observations and UH88 deep optical B- and R-band observations of the IR luminous merger Arp 299 (= NGC 3690 + IC 694). These data reveal a gas-rich, optically faint tidal tail with a length of over 180 kpc. The size of this tidal feature necessitates an old interaction age for the merger (~750 Myr since first periapse), which is currently experiencing a very young star burst (~20 Myr). The observations reveal a most remarkable structure within the tidal tail: it appears to be composed of two parallel filaments separated by ~20 kpc. One of the filaments is gas rich with little if any starlight, while the other is gas poor. We believe that this bifurcation results from a warped disk in one of the progenitors. The quantities and kinematics of the tidal HI suggest that Arp 299 results from the collision of a retrograde Sab-Sb galaxy (IC 694) and a prograde Sbc-Sc galaxy (NGC 3690) that occurred 750 Myr ago and which will merge into a single object in ~60 Myr. We suggest that the present IR luminous phase in this system is due in part to the retrograde spin of IC 694. Finally, we discuss the apparent lack of tidal dwarf galaxies within the tail.Comment: LaTex, 14 pages, 11 figures, 4 tables, uses emulateapj.sty. Accepted to AJ for July 1999. For version with full-resolution images see http://www.cv.nrao.edu/~jhibbard/a299/HIpaper/a299HI.htm