Artykuły w czasopismach na temat „Nonconforming FEM”

Abstract In this paper, we propose two low-order nonconforming finite element methods (FEMs) for the three-dimensional Stokes flow that generalize the nonconforming FEM of Kouhia & Stenberg (1995, A linear nonconforming finite element method for nearly incompressible elasticity and Stokes flow. Comput. Methods Appl. Mech. Eng, 124, 195–212). The finite element spaces proposed in this paper consist of two globally continuous components (one piecewise affine and one enriched component) and one component that is continuous at the midpoints of interior faces. We prove that the discrete Korn inequality and a discrete inf–sup condition hold uniformly in the mesh size and also for a nonempty Neumann boundary. Based on these two results, we show the well-posedness of the discrete problem. Two counterexamples prove that there is no direct generalization of the Kouhia–Stenberg FEM to three space dimensions: the finite element space with one nonconforming and two conforming piecewise affine components does not satisfy a discrete inf–sup condition with piecewise constant pressure approximations, while finite element functions with two nonconforming and one conforming component do not satisfy a discrete Korn inequality.

AbstractIn recent years, the question on the convergence and optimality in the context of adaptive finite element methods has been the subject of intensive studies. However, for nonstandard FEMs such as mixed or nonconforming ones, the lack of Galerkin's orthogonality requires new mathematical arguments. The presented adap- tive algorithm for the Crouzeix-Raviart finite element method and the Poisson model problem is of quasi-optimal complexity. Furthermore it is natural in the sense that collective marking rather than a separate marking is applied or the estimated error and the volume term.

As it is very difficult to construct conforming plate elements and the solutions achieved with conforming elements yield inferior accuracy to those achieved with nonconforming elements on many occasions, nonconforming elements, especially Adini’s element (ACM element), are often recommended for practical usage. However, the convergence, good numerical accuracy, and high computing efficiency of ACM element with irregular physical boundaries cannot be achieved using either the finite element method (FEM) or the numerical manifold method (NMM). The mixed-order NMM with background cells for integration was developed to analyze the bending of nonconforming thin plates with irregular physical boundaries. Regular meshes were selected to improve the convergence performance; background cells were used to improve the integration accuracy without increasing the degrees of freedom, retaining the efficiency as well; the mixed-order local displacement function was taken to improve the interpolation accuracy. With the penalized formulation fitted to the NMM for Kirchhoff’s thin plate bending, a new scheme was proposed to deal with irregular domain boundaries. Based on the present computational framework, comparisons with other studies were performed by taking several typical examples. The results indicated that the solutions achieved with the proposed NMM rapidly converged to the analytical solutions and their accuracy was vastly superior to that achieved with the FEM and the traditional NMM.

Abstract. This survey compares different strategies for guaranteed error control for the lowest-order nonconforming Crouzeix–Raviart finite element method for the Stokes equations. The upper error bound involves the minimal distance of the computed piecewise gradient $\operatorname{D}_{\textup {NC}}u_{\textup {CR}}$ to the gradients of Sobolev functions with exact boundary conditions. Several improved suggestions for the cheap computation of such test functions compete in five benchmark examples. This paper provides numerical evidence that guaranteed error control of the nonconforming FEM is indeed possible for the Stokes equations with overall efficiency indices between 1 to 4 in the asymptotic range.

AbstractIn finite element approximation of the Oseen problem, one needs to handle two major difficulties, namely, the lack of stability due to convection dominance and the incompatibility between the approximating finite element spaces for the velocity and the pressure. These difficulties are addressed in this article by using an edge patch-wise local projection (EPLP) stabilization technique. The article analyses the EPLP stabilized nonconforming finite element methods for the Oseen problem. For approximating the velocity, the lowest-order Crouzeix–Raviart (CR) nonconforming finite element space is considered; whereas for approximating the pressure, two discrete spaces are considered, namely, the piecewise constant polynomial space and the lowest-order CR finite element space. The proposed discrete weak formulation is a combination of the standard Galerkin method, EPLP stabilization and weakly imposed boundary condition by using Nitsche’s technique. The resulting bilinear form satisfies an inf-sup condition with respect to EPLP norm, which leads to the well-posedness of the discrete problem. A priori error analysis assures the optimal order of convergence in both the cases, that is, order one in the case of piecewise constant approximation and \frac{3}{2} in the case of CR-finite element approximation for pressure. The numerical experiments illustrate the theoretical findings.

In the paper, the smoothed finite element method (S-FEM) based on linear triangular elements is used to solve 2D solid contact problems for functionally graded materials. Both conforming and nonconforming contacts algorithms are developed using modified Coulomb friction contact models including tangential strength and normal adhesion. Based on the smoothed Galerkin weak form, the system stiffness matrices are created using the formulation procedures of node-based S-FEM (NS-FEM) and edge-based S-FEM (ES-FEM), and the contact interface equations are discretized by contact point-pairs. Then these discretized system equations are converted into a form of linear complementarity problems (LCPs), which can be further solved efficiently using the Lemke method. The singular value decomposition method is used to deal with the singularity of the stiffness matrices in the procedure constructing the standard LCP, which can greatly improve the stability and accuracy of the numerical results. Numerical examples are presented to investigate the effects of the various parameters of functionally graded materials and comparisons have been made with reference solutions and the standard FEM. The numerical results demonstrate that the strain energy solutions of ES-FEM have higher convergence rate and accuracy compared with that of NS-FEM and FEM for functionally graded materials through the present contact analysis approach.

AbstractIn this paper, a nonconforming mixed finite element method (FEM) is presented to approximate time-dependent Maxwell's equations in a three-dimensional bounded domain with absorbing boundary conditions (ABC). By employing traditional variational formula, instead of adding penalty terms, we show that the discrete scheme is robust. Meanwhile, with the help of the element's typical properties and derivative transfer skills, the convergence analysis and error estimates for semidiscrete and backward Euler fully-discrete schemes are given, respectively. Numerical tests show the validity of the proposed method.

In this paper, based on the L2-1σ scheme and nonconforming EQ1rot finite element method (FEM), a numerical approximation is presented for a class of two-dimensional time-fractional diffusion equations involving variable coefficients. A novel and detailed analysis of the equations with an initial singularity is described on anisotropic meshes. The fully discrete scheme is shown to be unconditionally stable, and optimal second-order accuracy for convergence and superconvergence can be achieved in both time and space directions. Finally, the obtained numerical results are compared with the theoretical analysis, which verifies the accuracy of the proposed method.

<abstract><p>A nonconforming finite element method (FEM) is proposed and analyzed for the clamped thin elastic Kirchhoff plate unilaterally constrained by an elastic obstacle. The discrete scheme is constructed by using the strongly discontinuous Bergan's energy-orthogonal plate element, which has simple degrees of freedom and about 25 percent fewer global dimension than that of the famous triangular Morley element. A novel error analysis is presented to overcome the difficulties caused by the strong discontinuity and derive the optimal estimate. Numerical experiments are carried out to verify the theoretical analysis.</p></abstract>

AbstractA nonconforming rectangular finite element method is proposed to solve a fluid structure interaction problem characterized by the Darcy-Stokes-Brinkman Equation with discontinuous coefficients across the interface of different structures. A uniformly stable mixed finite element together with Nitsche-type matching conditions that automatically adapt to the coupling of different sub-problem combinations are utilized in the discrete algorithm. Compared with other finite element methods in the literature, the new method has some distinguished advantages and features. The Boland-Nicolaides trick is used in proving the inf-sup condition for the multidomain discrete problem. Optimal error estimates are derived for the coupled problem by analyzing the approximation errors and the consistency errors. Numerical examples are also provided to confirm the theoretical results.

Purpose The purpose of this paper is to examine a solution strategy for coupled nonlinear magnetic-thermal problems and apply it to the heating process of a thin moving steel sheet. Performing efficient numerical simulations of induction heating processes becomes ever more important because of faster production development cycles, where the quasi steady-state solution of the problem plays a pivotal role. Design/methodology/approach To avoid time-consuming transient simulations, the eddy current problem is transformed into frequency domain and a harmonic balancing scheme is used to take into account the nonlinear BH-curve. The thermal problem is solved in steady-state domain, which is carried out by including a convective term to model the stationary heat transport due to the sheet velocity. Findings The presented solution strategy is compared to a classical nonlinear transient reference solution of the eddy current problem and shows good convergence, even for a small number of considered harmonics. Originality/value Numerical simulations of induction heating processes are necessary to fully understand certain phenomena, e.g. local overheating of areas in thin structures. With the presented approach it is possible to perform large 3D simulations without excessive computational resources by exploiting certain properties of the multiharmonic solution of the eddy current problem. Together with the use of nonconforming interfaces, the overall computational complexity of the problem can be decreased significantly.

Abstract This article on nonconforming schemes for m harmonic problems simultaneously treats the Crouzeix–Raviart ( m = 1 {m=1} ) and the Morley finite elements ( m = 2 {m=2} ) for the original and for modified right-hand side F in the dual space V * := H - m ⁢ ( Ω ) {V^{*}:=H^{-m}(\Omega)} to the energy space V := H 0 m ⁢ ( Ω ) {V:=H^{m}_{0}(\Omega)} . The smoother J : V nc → V {J:V_{\mathrm{nc}}\to V} in this paper is a companion operator, that is a linear and bounded right-inverse to the nonconforming interpolation operator I nc : V → V nc {I_{\mathrm{nc}}:V\to V_{\mathrm{nc}}} , and modifies the discrete right-hand side F h := F ∘ J ∈ V nc * {F_{h}:=F\circ J\in V_{\mathrm{nc}}^{*}} . The best-approximation property of the modified scheme from Veeser et al. (2018) is recovered and complemented with an analysis of the convergence rates in weaker Sobolev norms. Examples with oscillating data show that the original method may fail to enjoy the best-approximation property but can also be better than the modified scheme. The a posteriori analysis of this paper concerns data oscillations of various types in a class of right-hand sides F ∈ V * {F\in V^{*}} . The reliable error estimates involve explicit constants and can be recommended for explicit error control of the piecewise energy norm. The efficiency follows solely up to data oscillations and examples illustrate this can be problematic.

To isolate the primary variables influencing acetabular cup and interface stresses, we performed an evaluation of cup loading and cup support variables, using a Statistical Design of Experiments (SDOE) approach. We developed three-dimensional finite element (FEM) models of the pelvis and adjacent bone. Cup support variables included fixation mechanism (cemented or noncemented), amount of bone support, and presence of metal backing. Cup loading variables included head size and cup thickness, cup/head friction, and conformity between the cup and head. Interaction between and among variables was determined using SDOE techniques. Of the variables tested, conformity, head size, and backing emerged as significant influences on stresses. Since initially nonconforming surfaces would be expected to wear into conforming surfaces, conformity is not expected to be a clinically significant variable. This indicates that head size should be tightly toleranced during manufacturing, and that small changes in head size can have a disproportionate influence on the stress environment. In addition, attention should be paid to the use of nonmetal backed cups, in limiting cup/bone interface stresses. No combination of secondary variables could compensate for, or override the effect of, the primary variables. Based on the results using the SDOE approach, adaptive FEM models simulating the wear process may be able to limit their parameters to head size and cup backing.

Nearly incompressible problems in three dimensions are the important problems in practical engineering computation. The volume-locking phenomenon will appear when the commonly used finite elements such as linear elements are applied to the solution of these problems. There are many efficient approaches to overcome this locking phenomenon, one of which is the higher-order conforming finite element method. However, we often use the lower-order nonconforming elements as Wilson elements by considering the computational complexity for three-dimensional (3D) problems considered. In general, the convergence of Wilson elements will heavily rely on the quality of the meshes. It will greatly deteriorate or no longer converge when the mesh distortion is very large. In this paper, the refined element method based on Wilson element is first applied to solve nearly incompressible elasticity problems, and the influence of mesh quality on the refined element is tested numerically. Its validity is verified by some numerical examples. By using the internal condensation method, the refined element discrete system of equations is deduced into the one which is spectrally equivalent to an 8-node hexahedral element discrete system of equations. And then, a type of efficient algebraic multigrid (AMG) preconditioner is presented by combining both the coarsening techniques based on the distance matrix and the effective smoothing operators. The resulting preconditioned conjugate gradient (PCG) method is efficient for 3D nearly incompressible problems. The numerical results verify the efficiency and robustness of the proposed method.

Introduction: Health professionals are unable to predict whether gender nonconforming distress or manifestations will continue after puberty. They also hold varied ideologies about gender. Information about these indicators lacks integration to benefit decision-making about how to intervene in childhood gender dysphoria. Aims: The aim of this review was to synthesize the literature on early indicators that anticipate the continuity of childhood gender dysphoria following puberty. A secondary aim, because of the ideological debates that underpin clinical decisions in transgender health care, was to critically interpret that literature. Methods: A critical interpretive synthesis was selected to integrate and offer a critical appraisal of literature (n=20). Results: A synthesizing argument was developed from four constructs: the intensity of gender dysphoric feelings, the child’s assertion of their gender identity, the stability of gender identity, and gender is a composite of multiple selves. Conclusions: The framing of experts’ arguments fed into presumed stability of gender identity. No single homogenous indicator can be postulated, but a compartmentalizing process is needed to understand the experiential world of a child’s gender nonconformity so that one concept (dysphoria about gender identity) can be teased apart from other investments of gender, body, and sexuality. Our constructs of the intensity of feelings and gender as a composite of multiple selves were found to challenge DSM-5 criteria. Understanding that multiple transitions may occur can help a child locate a gendered positioning in which they are comfortable. This could enable health practitioners offer affirmative care while remaining cautious about using medical treatments that cannot be reversed. The search for indicators itself, however, can be considered a historical moment, given the developments in the field in the 2 years after this review was conducted.

In this article we unravel family religion as a crucial strand of evangelical piety in the late seventeenth century. We show how this programme was promoted in print and manuscript by a group of evangelical clergy from both sides of the conformist divide. Using the printed and manuscript memoirs of John Rastrick, a Lincolnshire clergyman, we explore the construction of clerical sociability through the printed text. In particular, we demonstrate that its heart was the communal reading of scripture and religious literature, confirming the household as the key locus for piety in this period. Whereas historians have traditionally been eager to categorize both clergy and laity in this period as either Anglican or nonconformist, we demonstrate that such a divide was often blurred in practice, in particular as represented through family religion. By focusing on issues such as sociability, the formation of identities, and reading practices, we also reconnect the second half of the century with its early Stuart past, suggesting that its influences and refractions fed into a continuity of evangelical identity, stretching from late sixteenth-century puritanism through the Civil War and Restoration to the onset of Evangelicalism in the eighteenth century. Though they were complex, these continuities help to show that a coherent style of evangelical piety was expressed across the ecclesiastical divide throughout the long seventeenth century.

At one point in “The Soul of Man Under Socialism,” an essay that deals directly neither with the soul nor with socialism, Oscar Wilde quotes obliquely from Ralph Waldo Emerson:[People] go through their lives in a sort of coarse comfort, like petted animals, without ever realising that they are probably thinking other people's thoughts, living by other people's standards, wearing practically what one may call other people's second-hand clothes, and never being themselves for a single moment. “He who would be free,” says a fine thinker, “must not conform.” And authority, by bribing people to conform, produces a very gross kind of over-fed barbarism among us. (267)That Wilde was attracted to Emersonian nonconformity is not surprising, and the similarities between the two writers are striking. But my reason for citing Wilde, the ur-homosexual and model of iconoclasm, is that I want to show that Emerson is as innovative a thinker as Wilde, and that indeed on the subject of individualism and personal relationships he is far more so. In fact, Wilde can be seen as taking certain ideas of his teacher Walter Pater and giving them an Emersonian and American cast, expressing more openly Pater's cloistered Oxford radicalism. The “Socialism” essay in particular develops strong connections among aestheticism, individualism, and sociopolitical dissent, revealing a strong desire for alternatives to late-19th-century British society. And of course in the case of Pater as well as Wilde, the need for individualism and the quest for new forms of social connection have obvious links to both writers' alternative sexual orientation. What makes Emerson more radical, more, if you will, “queer,” is precisely that he is not arguing for any sexual orientation, but is attempting — many years before the Oxford aesthetes — to create a free space for alternative forms of gender and new forms of personal relationships to develop. Emerson values dis-orientation more than any orientation.

Abstract The Morley finite element method (FEM) is attractive for semilinear problems with the biharmonic operator as a leading term in the stream function vorticity formulation of two-dimensional Navier–Stokes problem and in the von Kármán equations. This paper establishes a best-approximation a priori error analysis and an a posteriori error analysis of discrete solutions close to an arbitrary regular solution on the continuous level to semilinear problems with a trilinear nonlinearity. The analysis avoids any smallness assumptions on the data, and so has to provide discrete stability by a perturbation analysis before the Newton–Kantorovich theorem can provide the existence of discrete solutions. An abstract framework for the stability analysis in terms of discrete operators from the medius analysis leads to new results on the nonconforming Crouzeix–Raviart FEM for second-order linear nonselfadjoint and indefinite elliptic problems with $L^\infty $ coefficients. The paper identifies six parameters and sufficient conditions for the local a priori and a posteriori error control of conforming and nonconforming discretizations of a class of semilinear elliptic problems first in an abstract framework and then in the two semilinear applications. This leads to new best-approximation error estimates and to a posteriori error estimates in terms of explicit residual-based error control for the conforming and Morley FEM.

AbstractConsider the distributed optimal control problem governed by the von Kármán equations defined on a polygonal domain of {\mathbb{R}^{2}} that describe the deflection of very thin plates with box constraints on the control variable. This article discusses a numerical approximation of the problem that employs the Morley nonconforming finite element method (FEM) to discretize the state and adjoint variables. The control is discretized using piecewise constants. A priori error estimates are derived for the state, adjoint and control variables under minimal regularity assumptions on the exact solution. Error estimates in lower-order norms for the state and adjoint variables are derived. The lower-order estimates for the adjoint variable and a post-processing of control leads to an improved error estimate for the control variable. Numerical results confirm the theoretical results obtained.

AbstractVarious applications in computational fluid dynamics and solid mechanics motivate the development of reliable and efficient adaptive algorithms for nonstandard finite element methods (FEMs). Standard adaptive finite element algorithms consist of the iterative loop of the basic steps Solve, Estimate, Mark and Refine. For separate marking strategies, this standard scheme may be universalised. The (total) error estimator is split into a volume term and an error estimator term.Since the volume term is independent of the discrete solution, an appropriate data approximation may be realised by a high degree of local mesh refinement. This observation results in a natural adaptive algorithm based on separate marking. Its quasi-optimal convergence is proven in this first part for the Poisson model problem and nonconforming Crouzeix-Raviart FEM. The numerical experiments confirm the optimal convergence rates and reveal its flexibility. The second part is devoted to the quasi-optimality of S-AFEM-AA and the pure displacement problem in linear elasticity and the Stokes equations.

AbstractVarious applications in computational fluid dynamics and solid mechanics motivate the development of reliable and efficient adaptive algorithms for nonstandard finite element methods (FEMs). Standard adaptive finite element algorithms consist of the iterative loop of the basic steps Solve, Estimate, Mark, and Refine. For separate marking strategies, this standard scheme may be universalised. The (total) error estimator is split into a volume term and an error estimator term.Since the volume term is independent of the discrete solution, an appropriate data approximation may be realised by a high degree of local mesh refinement. This observation results in a natural adaptive algorithm based on separate marking. Its quasi-optimal convergence is proven in this second part for the pure displacement problem in linear elasticity and the Stokes equations and nonconforming Crouzeix-Raviart FEM. The proofs follow the same general methodology as for the Poisson model problem in the first part of this series. The numerical experiments confirm the optimal convergence rates and reveal its flexibility.

Abstract Mesh generation for traditional finite element analysis has proven to be very difficult to fully automate especially using hexahedral elements for complex 3D geometry. Several modifications to the finite element method (FEM), such as the meshless methods, have been proposed for avoiding mesh generation. An alternative approach has recently gained popularity where the geometry, created as a solid model in cad software, is embedded or immersed in a nonconforming background mesh for analysis. In this approach, referred to here as the immersed boundary approach, a background mesh that is independent of the geometry is used for piecewise interpolation or approximation of the solution. Therefore, a uniform mesh with regular-shaped or undistorted elements can be used, and such a mesh is easy to generate automatically. When the geometry is immersed in the background mesh, the boundary elements are often only partly inside the geometry and the nodes of the mesh may not be on the boundaries. Many new methods have been developed to integrate over partial elements and to apply boundary and interface conditions when the boundaries of the geometries do not conform to the background mesh. These methods are reviewed in this article with particular emphasis on the implicit boundary method and step boundary method for applying boundary conditions. In addition, B-spline elements and several applications of the immersed boundary approach are surveyed including composite microstructures and structural elements for plates and shells.

Computer-assisted colon cancer detection on the histopathological images has become a tedious task due to its shape characteristics and other biological properties. The images acquired through the histopathological microscope may vary in magnifications for better visibility. This may change the morphological properties and hence an automated magnification independent colon cancer detection system is essential. The manual diagnosis of colon biopsy images is subjective, sluggish, laborious leading to nonconformity between histopathologists due to visual evaluation at various microscopic magnifications. Automatic detection of colon across image magnifications is challenging due to many aspects like tailored segmentation and varying features. This demands techniques that take advantage of the textural, color, and geometric properties of colon tissue. This work exhibits a segmentation approach based on the morphological features derived from the segmented region. Gabor Wavelet, Harris Corner, and DWT-LBP coefficients are extracted as it should not be dependent on the spatial domain with respect to the magnification. These features are fed to the Genetically Optimized Neural Network classifier to classify them as normal and malignant ones. Here, the genetic algorithm is used to learn the best hyper-parameters for a neural network.

Ubiquitous in airports, border checkpoints, and other securitised spaces throughout the world, full-body imaging scanners claim to read bodies in order to identify if they pose security threats. Millimetre-wave body imaging machines—the most common type of body scanner—display to the operating security agent a screen with a generic body outline. If an anomaly is found or if an individual does not align with the machine’s understanding of an “average” body, a small box is highlighted and placed around the “problem” area, prompting further inspection in the form of pat-downs or questioning. In this complex security regime governed by such biometric, body-based technologies, it could be argued that nonalignment with bodily normativity as well as an attendant failure to reveal oneself—to become “transparent” (Hall 295)—marks a body as dangerous. As these algorithmic technologies become more pervasive, so too does the imperative to critically examine their purported neutrality and operative logic of revelation and readability.Biometric technologies are marketed as excavators of truth, with their optic potency claiming to demask masquerading bodies. Failure and bias are, however, an inescapable aspect of such technologies that work with narrow parameters of human morphology. Indeed, surveillance technologies have been taken to task for their inherent racial and gender biases (Browne; Pugliese). Facial recognition has, for example, been critiqued for its inability to read darker skin tones (Buolamwini and Gebru), while body scanners have been shown to target transgender bodies (Keyes; Magnet and Rodgers; Quinan). Critical security studies scholar Shoshana Magnet argues that error is endemic to the technological functioning of biometrics, particularly since they operate according to the faulty notion that bodies are “stable” and unchanging repositories of information that can be reified into code (Magnet 2).Although body scanners are presented as being able to reliably expose concealed weapons, they are riddled with incompetencies that misidentify and over-select certain demographics as suspect. Full-body scanners have, for example, caused considerable difficulties for transgender travellers, breast cancer patients, and people who use prosthetics, such as artificial limbs, colonoscopy bags, binders, or prosthetic genitalia (Clarkson; Quinan; Spalding). While it is not in the scope of this article to detail the workings of body imaging technologies and their inconsistencies, a growing body of scholarship has substantiated the claim that these machines unfairly impact those identifying as transgender and non-binary (see, e.g., Beauchamp; Currah and Mulqueen; Magnet and Rogers; Sjoberg). Moreover, they are constructed according to a logic of binary gender: before each person enters the scanner, transportation security officers must make a quick assessment of their gender/sex by pressing either a blue (corresponding to “male”) or pink (corresponding to “female”) button. In this sense, biometric, computerised security systems control and monitor the boundaries between male and female.The ability to “reveal” oneself is henceforth predicated on having a body free of “abnormalities” and fitting neatly into one of the two sex categorisations that the machine demands. Transgender and gender-nonconforming individuals, particularly those who do not have a binary gender presentation or whose presentation does not correspond to the sex marker in their documentation, also face difficulties if the machine flags anomalies (Quinan and Bresser). Drawing on a Foucauldian analysis of power as productive, Toby Beauchamp similarly illustrates how surveillance technologies not only identify but also create and reshape the figure of the dangerous subject in relation to normative configurations of gender, race, and able-bodiedness. By mobilizing narratives of concealment and disguise, heightened security measures frame gender nonconformity as dangerous (Beauchamp, Going Stealth). Although national and supranational authorities market biometric scanning technologies as scientifically neutral and exact methods of identification and verification and as an infallible solution to security risks, such tools of surveillance are clearly shaped by preconceptions and prejudgements about race, gender, and bodily normativity. Not only are they encoded with “prototypical whiteness” (Browne) but they are also built on “grossly stereotypical” configurations of gender (Clarkson).Amongst this increasingly securitised landscape, creative forms of artistic resistance can offer up a means of subverting discriminatory policing and surveillance practices by posing alternate visualisations that reveal and challenge their supposed objectivity. In his 2018 audio-video artwork installation entitled SANCTUM, UK-based American artist Zach Blas delves into how biometric technologies, like those described above, both reveal and (re)shape ontology by utilising the affectual resonance of sexual submission. Evoking the contradictory notions of oppression and pleasure, Blas describes SANCTUM as “a mystical environment that perverts sex dungeons with the apparatuses and procedures of airport body scans, biometric analysis, and predictive policing” (see full description at https://zachblas.info/works/sanctum/).Depicting generic mannequins that stand in for the digitalised rendering of the human forms that pass through body scanners, the installation transports the scanners out of the airport and into a queer environment that collapses sex, security, and weaponry; an environment that is “at once a prison-house of algorithmic capture, a sex dungeon with no genitals, a weapons factory, and a temple to security.” This artistic reframing gestures towards full-body scanning technology’s germination in the military, prisons, and other disciplinary systems, highlighting how its development and use has originated from punitive—rather than protective—contexts.In what follows, we adopt a methodological approach that applies visual analysis and close reading to scrutinise a selection of scenes from SANCTUM that underscore the sadomasochistic power inherent in surveillance technologies. Analysing visual and aural elements of the artistic intervention allows us to complicate the relationship between transparency and recognition and to problematise the dynamic of mandatory complicity and revelation that body scanners warrant. In contrast to a discourse of visibility that characterises algorithmically driven surveillance technology, Blas suggests opacity as a resistance strategy to biometrics' standardisation of identity. Taking an approach informed by critical security studies and queer theory, we also argue that SANCTUM highlights the violence inherent to the practice of reducing the body to a flat, inert surface that purports to align with some sort of “core” identity, a notion that contradicts feminist and queer approaches to identity and corporeality as fluid and changing. In close reading this artistic installation alongside emerging scholarship on the discriminatory effects of biometric technology, this article aims to highlight the potential of art to queer the supposed objectivity and neutrality of biometric surveillance and to critically challenge normative logics of revelation and readability.Corporeal Fetishism and Body HorrorThroughout both his artistic practice and scholarly work, Blas has been critical of the above narrative of biometrics as objective extractors of information. Rather than looking to dominant forms of representation as a means for recognition and social change, Blas’s work asks that we strive for creative techniques that precisely queer biometric and legal systems in order to make oneself unaccounted for. For him, “transparency, visibility, and representation to the state should be used tactically, they are never the end goal for a transformative politics but are, ultimately, a trap” (Blas and Gaboury 158). While we would simultaneously argue that invisibility is itself a privilege that is unevenly distributed, his creative work attempts to refuse a politics of visibility and to embrace an “informatic opacity” that is attuned to differences in bodies and identities (Blas).In particular, Blas’s artistic interventions titled Facial Weaponization Suite (2011-14) and Face Cages (2013-16) protest against biometric recognition and the inequalities that these technologies propagate by making masks and wearable metal objects that cannot be detected as human faces. This artistic-activist project contests biometric facial recognition and their attendant inequalities by, as detailed on the artist’s website,making ‘collective masks’ in workshops that are modelled from the aggregated facial data of participants, resulting in amorphous masks that cannot be detected as human faces by biometric facial recognition technologies. The masks are used for public interventions and performances.One mask explores blackness and the racist implications that undergird biometric technologies’ inability to detect dark skin. Meanwhile another mask, which he calls the “Fag Face Mask”, points to the heteronormative underpinnings of facial recognition. Created from the aggregated facial data of queer men, this amorphous pink mask implicitly references—and contests—scientific studies that have attempted to link the identification of sexual orientation through rapid facial recognition techniques.Building on this body of creative work that has advocated for opacity as a tool of social and political transformation, SANCTUM resists the revelatory impulses of biometric technology by turning to the use and abuse of full-body imaging. The installation opens with a shot of a large, dark industrial space. At the far end of a red, spotlighted corridor, a black mask flickers on a screen. A shimmering, oscillating sound reverberates—the opening bars of a techno track—that breaks down in rhythm while the mask evaporates into a cloud of smoke. The camera swivels, and a white figure—the generic mannequin of the body scanner screen—is pummelled by invisible forces as if in a wind tunnel. These ghostly silhouettes appear and reappear in different positions, with some being whipped and others stretched and penetrated by a steel anal hook. Rather than conjuring a traditional horror trope of the body’s terrifying, bloody interior, SANCTUM evokes a new kind of feared and fetishized trope that is endemic to the current era of surveillance capitalism: the abstracted body, standardised and datafied, created through the supposedly objective and efficient gaze of AI-driven machinery.Resting on the floor in front of the ominous animated mask are neon fragments arranged in an occultist formation—hands or half a face. By breaking the body down into component parts— “from retina to fingerprints”—biometric technologies “purport to make individual bodies endlessly replicable, segmentable and transmissible in the transnational spaces of global capital” (Magnet 8). The notion that bodies can be seamlessly turned into blueprints extracted from biological and cultural contexts has been described by Donna Haraway as “corporeal fetishism” (Haraway, Modest). In the context of SANCTUM, Blas illustrates the dangers of mistaking a model for a “concrete entity” (Haraway, “Situated” 147). Indeed, the digital cartography of the generic mannequin becomes no longer a mode of representation but instead a technoscientific truth.Several scenes in SANCTUM also illustrate a process whereby substances are extracted from the mannequins and used as tools to enact violence. In one such instance, a silver webbing is generated over a kneeling figure. Upon closer inspection, this geometric structure, which is reminiscent of Blas’s earlier Face Cages project, is a replication of the triangulated patterns produced by facial recognition software in its mapping of distance between eyes, nose, and mouth. In the next scene, this “map” breaks apart into singular shapes that float and transform into a metallic whip, before eventually reconstituting themselves as a penetrative douche hose that causes the mannequin to spasm and vomit a pixelated liquid. Its secretions levitate and become the webbing, and then the sequence begins anew.In another scene, a mannequin is held upside-down and force-fed a bubbling liquid that is being pumped through tubes from its arms, legs, and stomach. These depictions visualise Magnet’s argument that biometric renderings of bodies are understood not to be “tropic” or “historically specific” but are instead presented as “plumbing individual depths in order to extract core identity” (5). In this sense, this visual representation calls to mind biometrics’ reification of body and identity, obfuscating what Haraway would describe as the “situatedness of knowledge”. Blas’s work, however, forces a critique of these very systems, as the materials extracted from the bodies of the mannequins in SANCTUM allude to how biometric cartographies drawn from travellers are utilised to justify detainment. These security technologies employ what Magnet has referred to as “surveillant scopophilia,” that is, new ways and forms of looking at the human body “disassembled into component parts while simultaneously working to assuage individual anxieties about safety and security through the promise of surveillance” (17). The transparent body—the body that can submit and reveal itself—is ironically represented by the distinctly genderless translucent mannequins. Although the generic mannequins are seemingly blank slates, the installation simultaneously forces a conversation about the ways in which biometrics draw upon and perpetuate assumptions about gender, race, and sexuality.Biometric SubjugationOn her 2016 critically acclaimed album HOPELESSNESS, openly transgender singer, composer, and visual artist Anohni performs a deviant subjectivity that highlights the above dynamics that mark the contemporary surveillance discourse. To an imagined “daddy” technocrat, she sings:Watch me… I know you love me'Cause you're always watching me'Case I'm involved in evil'Case I'm involved in terrorism'Case I'm involved in child molestersEvoking a queer sexual frisson, Anohni describes how, as a trans woman, she is hyper-visible to state institutions. She narrates a voyeuristic relation where trans bodies are policed as threats to public safety rather than protected from systemic discrimination. Through the seemingly benevolent “daddy” character and the play on ‘cause (i.e., because) and ‘case (i.e., in case), she highlights how gender-nonconforming individuals are predictively surveilled and assumed to already be guilty. Reflecting on daddy-boy sexual paradigms, Jack Halberstam reads the “sideways” relations of queer practices as an enactment of “rupture as substitution” to create a new project that “holds on to vestiges of the old but distorts” (226). Upending power and control, queer art has the capacity to both reveal and undermine hegemonic structures while simultaneously allowing for the distortion of the old to create something new.Employing the sublimatory relations of bondage, discipline, sadism, and masochism (BDSM), Blas’s queer installation similarly creates a sideways representation that re-orientates the logic of the biometric scanners, thereby unveiling the always already sexualised relations of scrutiny and interrogation as well as the submissive complicity they demand. Replacing the airport environment with a dark and foreboding mise-en-scène allows Blas to focus on capture rather than mobility, highlighting the ways in which border checkpoints (including those instantiated by the airport) encourage free travel for some while foreclosing movement for others. Building on Sara Ahmed’s “phenomenology of being stopped”, Magnet considers what happens when we turn our gaze to those “who fail to pass the checkpoint” (107). In SANCTUM, the same actions are played out again and again on spectral beings who are trapped in various states: they shudder in cages, are chained to the floor, or are projected against the parameters of mounted screens. One ghostly figure, for instance, lies pinned down by metallic grappling hooks, arms raised above the head in a recognisable stance of surrender, conjuring up the now-familiar image of a traveller standing in the cylindrical scanner machine, waiting to be screened. In portraying this extended moment of immobility, Blas lays bare the deep contradictions in the rhetoric of “freedom of movement” that underlies such spaces.On a global level, media reporting, scientific studies, and policy documents proclaim that biometrics are essential to ensuring personal safety and national security. Within the public imagination, these technologies become seductive because of their marked ability to identify terrorist attackers—to reveal threatening bodies—thereby appealing to the anxious citizen’s fear of the disguised suicide bomber. Yet for marginalised identities prefigured as criminal or deceptive—including transgender and black and brown bodies—the inability to perform such acts of revelation via submission to screening can result in humiliation and further discrimination, public shaming, and even tortuous inquiry – acts that are played out in SANCTUM.Masked GenitalsFeminist surveillance studies scholar Rachel Hall has referred to the impetus for revelation in the post-9/11 era as a desire for a universal “aesthetics of transparency” in which the world and the body is turned inside-out so that there are no longer “secrets or interiors … in which terrorists or terrorist threats might find refuge” (127). Hall takes up the case study of Umar Farouk Abdulmutallab (infamously known as “the Underwear Bomber”) who attempted to detonate plastic explosives hidden in his underwear while onboard a flight from Amsterdam to Detroit on 25 December 2009. Hall argues that this event signified a coalescence of fears surrounding bodies of colour, genitalia, and terrorism. News reports following the incident stated that Abdulmutallab tucked his penis to make room for the explosive, thereby “queer[ing] the aspiring terrorist by indirectly referencing his willingness … to make room for a substitute phallus” (Hall 289). Overtly manifested in the Underwear Bomber incident is also a desire to voyeuristically expose a hidden, threatening interiority, which is inherently implicated with anxieties surrounding gender deviance. Beauchamp elaborates on how gender deviance and transgression have coalesced with terrorism, which was exemplified in the wake of the 9/11 attacks when the United States Department of Homeland Security issued a memo that male terrorists “may dress as females in order to discourage scrutiny” (“Artful” 359). Although this advisory did not explicitly reference transgender populations, it linked “deviant” gender presentation—to which we could also add Abdulmutallab’s tucking of his penis—with threats to national security (Beauchamp, Going Stealth). This also calls to mind a broader discussion of the ways in which genitalia feature in the screening process. Prior to the introduction of millimetre-wave body scanning technology, the most common form of scanner used was the backscatter imaging machine, which displayed “naked” body images of each passenger to the security agent. Due to privacy concerns, these machines were replaced by the scanners currently in place which use a generic outline of a passenger (exemplified in SANCTUM) to detect possible threats.It is here worth returning to Blas’s installation, as it also implicitly critiques the security protocols that attempt to reveal genitalia as both threatening and as evidence of an inner truth about a body. At one moment in the installation a bayonet-like object pierces the blank crotch of the mannequin, shattering it into holographic fragments. The apparent genderlessness of the mannequins is contrasted with these graphic sexual acts. The penetrating metallic instrument that breaks into the loin of the mannequin, combined with the camera shot that slowly zooms in on this action, draws attention to a surveillant fascination with genitalia and revelation. As Nicholas L. Clarkson documents in his analysis of airport security protocols governing prostheses, including limbs and packies (silicone penis prostheses), genitals are a central component of the screening process. While it is stipulated that physical searches should not require travellers to remove items of clothing, such as underwear, or to expose their genitals to staff for inspection, prosthetics are routinely screened and examined. This practice can create tensions for trans or disabled passengers with prosthetics in so-called “sensitive” areas, particularly as guidelines for security measures are often implemented by airport staff who are not properly trained in transgender-sensitive protocols.ConclusionAccording to media technologies scholar Jeremy Packer, “rather than being treated as one to be protected from an exterior force and one’s self, the citizen is now treated as an always potential threat, a becoming bomb” (382). Although this technological policing impacts all who are subjected to security regimes (which is to say, everyone), this amalgamation of body and bomb has exacerbated the ways in which bodies socially coded as threatening or deceptive are targeted by security and surveillance regimes. Nonetheless, others have argued that the use of invasive forms of surveillance can be justified by the state as an exchange: that citizens should willingly give up their right to privacy in exchange for safety (Monahan 1). Rather than subscribing to this paradigm, Blas’ SANCTUM critiques the violence of mandatory complicity in this “trade-off” narrative. Because their operationalisation rests on normative notions of embodiment that are governed by preconceptions around gender, race, sexuality and ability, surveillance systems demand that bodies become transparent. This disproportionally affects those whose bodies do not match norms, with trans and queer bodies often becoming unreadable (Kafer and Grinberg). The shadowy realm of SANCTUM illustrates this tension between biometric revelation and resistance, but also suggests that opacity may be a tool of transformation in the face of such discriminatory violations that are built into surveillance.ReferencesAhmed, Sara. “A Phenomenology of Whiteness.” Feminist Theory 8.2 (2007): 149–68.Beauchamp, Toby. “Artful Concealment and Strategic Visibility: Transgender Bodies and U.S. State Surveillance after 9/11.” Surveillance & Society 6.4 (2009): 356–66.———. Going Stealth: Transgender Politics and U.S. Surveillance Practices. 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