Analysis of the tilted flat punch in couple-stress elasticity

In the present paper we explore the response of a half-plane indented by a tilted flat punch with sharp corners in the context of couple-stress elasticity theory. Contact conditions arise in a number of modern engineering applications ranging from structural and geotechnical engineering to micro and nanotechnology. As the contact scales reduce progressively the effects of the microstructure upon the macroscopic material response cannot be ignored. The generalized continuum theory of couple-stress elasticity introduces characteristic material lengths in order to describe the pertinent scale effects that emerge from the underlying material microstructure. The problem under investigation is interesting for three reasons: Firstly, the indentor's geometry is simple so that benchmark results may be extracted. Secondly, important deterioration of the macroscopic results may emerge in the case that a tilting moment is applied on the indentor inadvertently or in the case that the flat punch itself is not self-aligning so that asymmetrical contact pressure distributions arise on the contact faces. Thirdly, the voluntary application of a tilting moment on the flat punch during an experiment gives rise to potential capabilities of the flat punch for the determination of the material microstructural characteristic lengths. The solution methodology is based on singular integral equations which have resulted from a treatment of the mixed boundary value problem via integral transforms and generalized functions. The results show significant departure from the predictions of classical elasticity revealing that valuable information may be deducted from the indentation of a tilted punch of a microstructured solid

ANALYSIS OF PUMPING TEST DATA WITH VARIABLE DISCHARGE IN CONFINED AQUIFERS

Οι αναλυτικές λύσεις σταθερής παροχής άντλησης χρησιμοποιούνται ευρέως για τον προσδιορισμό των υδραυλικών χαρακτηριστικών των υδροφορέων. Ωστόσο, η αντλούμενη παροχή σε φρεάτια που δεν διαθέτουν αυτορρυθμιζόμενο σύστημα ελέγχου, γενικώς μειώνεται με το χρόνο μέχρι την σταθεροποίησή της. Η αγνόηση αυτής της κατάστασης στις δοκιμαστικές αντλήσεις έχει ως συνέπεια την λανθασμένη εκτίμηση των υδρογεωλογικών παραμέτρων. Στην εργασία αυτή παρουσιάζεται μια προσεγγιστική αναλυτική λύση για τον υπολογισμό της πτώσης πιεζομετρικού φορτίου σε κλειστό υδροφορέα λόγω άντλησης με βαθμιαία μεταβαλλόμενη παροχή. Εφαρμογή της λύσης σε πραγματικά δεδομένα δοκιμαστικών αντλήσεων έδωσε πολύ ικανοποιητικά αποτελέσματα.Analytical solutions for constant-rate well pumping tests are widely used to evaluate the aquifer characteristics. However, the discharge of an uncontrolled pumping well generally decreases with time until stabilization. Ignoring this situation in pumping tests, leads to incorrect assessment of the hydrogeological parameters. This paper presents an approximate analytical solution for evaluating drawdown in confined aquifers due to gradually varied discharge. Application of the proposed solution to actual aquifer tests showed very satisfactory results

Wind Load Transfer Mechanisms on a Low Wood Building Using Full-scale Data

The wind-induced response of low-rise wood buildings has been evaluated by monitoring a specially instrumented test building exposed to real wind action. The field facilities included a state-of-the-art data acquisition system which collected wind, pressure and force data. In addition to the field monitoring, a 1:200 scaled model of the test building was tested in the wind tunnel and the envelope wind pressures were estimated for various terrain exposures. The wind-induced pressures obtained from both the full-scale and wind tunnel experiments were incorporated in the finite element model of the test building and its response was numerically derived. Vast amounts of experimental data were generated during the long-term monitoring of the test building. These data were used to successfully verify the simulation approaches in terms of both wind-induced pressures and structural forces. Some limited discrepancies were observed in the peak pressure coefficients for locations close to the roof ridge and corners. The field acquired force data revealed that the majority of the wind uplift force is supported by the two side walls. Moreover, it was experimentally verified that the wind-induced load was attenuated as it was transferred through the buildings' structural system. This attenuation was estimated to be at least 17%, as far as the total foundation uplift force is concerned, and reached the 28% for certain approaching wind directions

Wind-induced Pressures on Patio Covers

A wind tunnel study has been carried out to assess wind loads on patio covers attached to low-rise buildings. A 1:100 geometric scale building and patio cover model was constructed and tested for open exposure conditions. The patio cover model was instrumented with pressure taps on both top and bottom surfaces, allowing the simultaneous measurement of wind pressure/suction on each side of the patio cover. The effect of building/patio height was considered by testing three different model configurations. Local surface and net wind pressure and force coefficients are presented for each model configuration. Correlation analysis was carried out to demonstrate how wind flow on the top and bottom of the patio cover affects the total wind load. The findings are also compared to the limited design guidelines derived by current building codes. Finally, recommendations for design wind load standards and codes of practice are made

Local and Overall Wind Pressure and Force Coefficients for Solar Panels

This paper reports on an experimental study carried out to better understand the wind pressure distribution on stand-alone panel surfaces and panels attached to flat building roofs. A complex model capable to incorporate solar panels at different locations and various inclinations was constructed at a 1:200 geometric scale. Three model panels equipped with pressure taps on both surfaces (36 in total) for point and area-averaged pressure measurements were used. Pressure and force coefficients were computed for every pressure tap and for all the panels. Different configurations were tested under similar conditions in order to examine the effect of various parameters on the experimental results. A minimal gap occurred between the solar panels and the roof of the model. The study found that the net values of pressure coefficients corresponding to different configurations are affected by the panel inclination for the critical 135° wind direction, for which panels on the back location undergo higher suctions in comparison to those in the front. The effect of building height on the solar collector total load is minimal, whereas corner panels are subjected to higher net loads for critical azimuths. Simplified net pressure coefficients for the design of solar panels are provided

Wind Loading on Attached Canopies: Codification Study

A wind tunnel study was performed to examine wind loads on canopies attached to the walls of low-rise buildings. A model of a building with an attached canopy of geometric scale of 1∶100 1∶100 was constructed and tested in a simulated open terrain exposure. The attached canopy model was equipped with pressure taps at both upper and lower surfaces to allow for simultaneous monitoring of wind pressures and evaluation of the overall load. A total of 63 different building/attached canopy configurations were tested for 28 wind directions. Pressure and correlation coefficients were generated to provide a better understanding of how the wind-loading patterns at upper and lower surfaces of the attached canopy contribute to the net loading effect. Current design guidelines and building code and standard provisions are assessed and compared with the experimental results of the present study. The influence of the geometry of each configuration on the experimental net pressure coefficients was assessed and recommendations for design wind load standards and codes of practice are made

Cladding Pressures and Primary Structural System Forces of a Wood Building Exposed to Strong Winds.

Several studies have been carried out on the evaluation of wind-induced pressures on building envelopes. However, there is very limited research on wind-induced forces on the main structural elements of a building including its foundation. Thus, a full-scale monitoring research project was initiated to examine the wind-induced structural forces for a low-rise wood building. The field facilities include two weather stations and a test house equipped with load and pressure sensors. The house is resting on top of twenty-seven 3-axis load cells and is structurally isolated, i.e., the only points of contact between the foundation wall and the superstructure are the load cells. Simultaneously to the load monitoring, 40 pressure taps are recording the envelope pressures both on the roof and the wall surfaces. In addition to the field monitoring, a scaled model of the house was tested in a boundary layer wind tunnel using three different upstream terrain configurations that provided varying levels of turbulence characteristics suitable for comparisons with full-scale values. The analysis of the wind speed and direction field data confirmed the non-uniform variation of the basic terrain properties over the wind direction and this was also verified in the comparison of the field with the wind tunnel results. These comparisons were made in the form of both envelope pressures and total uplift forces at the foundation level and provided useful insight regarding the wind load path inside the structural elements of the building. Experimental findings were also compared to the Canadian Code and American Standard wind provisions and indicated an underestimation of the total uplift force when using the code and standard provisions in some cases

Synchronous Primary Adenocarcinoma and Ancient Schwannoma in the Colon: An Unusual Case Report

Gastrointestinal schwannomas are uncommon stromal tumors of the intestinal tract and colon schwannomas are extremely rare. We report a rare case of ascending colon schwannoma with associated synchronous adenocarcinoma of the sigmoid colon. A 68-year-old man presented with a 20-day history of bleeding per rectum. Colonoscopy revealed a mass of 4.2 cm in diameter with endoluminal protrusion in the sigmoid colon and a second submucosal tumor in the ascending colon. Surgical intervention was suggested and ileo-hemicolectomy was done. Microscopically, the submucosal tumor of 4 cm in diameter showed features of schwannoma with degenerative change (ancient schwannoma). Lesional cells were positive for S100p and negative for actin, desmin, CD34, CD117, and pankeratin. The mass showed features of an invasive moderately differentiated adenocarcinoma. Colon schwannoma is a rare submucosal tumor, and the incidental occurrence with adenocarcinoma has not been well described in the literature

Transternal repair of a giant Morgagni hernia causing cardiac tamponade in a patient with coexisting severe aortic valve stenosis

<p>Abstract</p> <p>Background</p> <p>Foramen of Morgagni hernias have traditionally been repaired by laparotomy, lapascopy or even thoracoscopy. However, the trans-sternal approach should be used when these rare hernias coexist with other cardiac surgical diseases.</p> <p>Case presentation</p> <p>We present the case of a 74 year-old symptomatic male with severe aortic <b>valve </b>stenosis and global respiratory failure due to a giant Morgagni hernia causing additionally cardiac tamponade. The patient underwent simultaneous repair of the hernia defect and aortic valve replacement under cardiopulmonary bypass. The hernia was repaired through the sternotomy approach, without opening of its content and during cardiopulmonary reperfusion.</p> <p>Conclusions</p> <p>Morgagni hernia can rarely accompany cardiac surgical pathologies. The trans-sternal approach for its management is as effective as other popular reconstructive procedures, <b>unless viscera strangulation and necrosis are suspected</b>. If severe compressive effects to the heart dominate the patient's clinical presentation correction during the cardiopulmonary reperfusion period is mandatory.</p