Holes and knots are common defects that occur in wood that affect its value for both structural and high-end aesthetic applications. When these defects are internal to wood they are rarely evident ...from visual inspection. It is therefore important to develop techniques to detect and analyse these defects both in standing trees prior to harvesting them and in processed timber and/or completed wooden structures. This paper presents an effective method to detect and analyse hole defects in wood. The method uses the recorded output wave signal from an ultrasonic device tested on rectangular wood samples. The ultrasonic wave signal is decomposed into its constructive modes using Empirical Mode Decomposition (EMD). This process decomposes a non-stationary non-linear wave signal into its semi-orthogonal bases known as intrinsic mode functions (IMFs). A matrix of all IMFs (except the residual IMF) is then assembled and its covariance matrix derived. The research demonstrates through several experimental studies that the maximum eigenvalue of the proposed covariance matrix is more sensitive to hole defects in wood than traditionally used measures such as time-of-flight. The results provide evidence that the proposed damage sensitive feature (DSF) can successfully detect hole defects in hardwood samples but further work is recommended on its application to other materials. It is anticipated that this method will have wide applicability in the forestry and timber industries for aiding in product value determination.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Plantation-grown Eucalyptus nitens (E. nitens) has been grown predominantly for the pulp and paper industry. In this study, the suitability of E. nitens as a structural material is examined using ...static tensile tests in a universal testing machine. The anisotropic tensile behaviour of 240 Eucalyptus nitens small clear wood samples with a diversity of grain angles was examined in both dry and wet conditions. The samples had a highly anisotropic tensile characterisation in the context of both a low moisture content (MC = 12%) and a high moisture content (MC > its fibre saturation point, FSP). The results showed that, in a high moisture content condition, the wood showed a lower failure strength and more ductility at all grain angles than in a low moisture content condition. The underlying failure mechanism of Eucalyptusnitens timber in tension was determined in detail from the perspective of the microstructure of wood cellulose polymer composites. The mean tensile failure strengths perpendicular and parallel to the fibre direction were, respectively, 5.6 and 91.6 MPa for the low MC and 3.8 and 62.1 MPa for the high MC condition. This research provides a basis for using E. nitens as a potential structural tensile member. The moisture modification factors of Eucalyptus timber at a mean level are higher than those of the traditional construction material, Pinus radiata, implying that E. nitens is promising as a material to be used for tensile members in water saturated conditions.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Slamming loads and pressures on high-speed catamarans with a centre bow (CB) differ from those on conventional catamarans with flat deck structures. The latter are well covered by class rules, which ...provide empirical formulae to calculate the design slamming pressure. An experimental study was therefore performed to quantify slamming pressures in the archways between bow and main hulls and the CB slamming force on a 112 m wave piercing catamaran. The CB length was systematically varied on a 2.5 m hydroelastic segmented catamaran model, which was tested in regular head sea waves at a speed of 2.89 m/s, full-scale equivalent of 38 knots. Slamming pressures were measured by 18 pressure transducers fitted into the CB, while data obtained from CB accelerometers and load cells enabled identification of the slamming force. The results indicate that slamming loads increase significantly with increasing CB length while the maximum peak slamming pressures varies to a lesser extent. It was also found that wave encounter frequency has a strong effect on the location of maximum pressure along the CB, considerably more so than any influence of CB configuration. The distribution of the peak pressures within the CB archway shows that the inboard peak pressures are larger than those at the top of the arch and the outboard locations.
•Slamming loads increase significantly with the increase of the centre bow length.•Maximum peak slamming pressures varies slightly with the increase of centre bow length.•Wave encounter frequency has a strong effect on the location of maximum pressure along the centre bow.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The mechanical properties of fibre-managed Eucalyptus nitens (E. nitens) cross-laminated timber (CLT) have previously been extensively studied, proving the material to be structurally safe and ...reliable. However, the vibration performance of CLT manufactured from this relative new construction species is not yet fully understood, especially under different support conditions. In this study, three types of support conditions, including roller–roller, bearer–bearer and clamp–bearer support conditions, were examined under vibration impulse-response testing performed using a simple but effective and repeatable excitation method consisting of a basketball dropped from a known height and an accelerometer. Six three-ply E. nitens CLT panels considered to have different moduli of elasticity in different layers and one strength-class C24 spruce CLT as a controlled reference were included in this study. The results suggest that the fundamental frequency values can effectively reflect the inherent characteristics of CLT panels (bending stiffness and density); however, no obvious relationship was observed between damping ratios and these inherent properties. The values of frequency constant λ1 were determined to analyse the effect of different support conditions on the values of fundamental frequency. The average values of λ1 for the roller–roller (9.6) and bearer–bearer (10.1) supports align with the theoretical values (9.87) for simply support (S-S) conditions. However, when clamping loads were applied at one edge of the bearer support, the average values of λ1 increased up to 10.8 but remained far below the theoretical values for clamped–pinned (C-S) support (15.4).
In this study, the preliminary serviceability performance of cross-laminated timber (CLT) panels constructed from fibre-managed Eucalyptus nitens (E. nitens) was investigated via bending and ...vibration tests. Linear four-point bending tests were performed to determine the stiffness and deflection of all CLT panels under serviceability loads. The dynamic response of CLT panels was tested using a basketball and an accelerometer. The fundamental natural frequencies of all tested panels were above the minimum frequency limit (8 Hz) when extrapolated to spans of up to 4.4 m. The configurations of E. nitens CLT panels were based on different modulus of elasticity (MOE) values for each board. Using higher MOE timber boards as the top and bottom layers can significantly increase the serviceability performance of both bending and vibration tests. The same experiments were carried out on two CLT panels made of strength class C24 Spruce-Pine-Fir to compare the serviceability performance of E. nitens CLT. The results demonstrated that E. nitens is a reliable resource for CLT manufacturing, and exhibits better serviceability performance compared to Spruce CLT. This provides more sustainable options for a species traditionally destined for pulp.
T-foil and stern tabs were installed on a wave-piercing catamaran (Incat Tasmania Hull 061) to improve ship motions and passenger comfort. More than 40 total effective hours of sea trials were ...conducted by the US Navy in 2004, encountering sea states 4–5 in the Atlantic Ocean near the United Kingdom. In this paper the influence of a ride-control system (RCS) on the heave and pitch response amplitude operator (RAO) of the full-scale high-speed catamaran was investigated using the sea trial data. The reduction in motion sickness incidence (MSI) was estimated in order to examine the effectiveness of the RCS in improving passenger comfort. With the existing control algorithm, the vertical accelerations were found to be best controlled by the active T-foil working together with the active stern tabs, while the pitch RAO was mainly mitigated by deploying only the stern tabs. About a 23% reduction was observed in the peak heave RAO with deployment of an active T-foil. The MSI can be reduced by up to 23% with respect to the cases with stern tabs only, depending on the encountered wave conditions, based on ISO recommendation for MSI calculation of a 2-h seaway passage.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Ride control systems are essential for comfort and operability of high-speed ships, but it remains an open question what is the optimum ride control method. To investigate the motions of a 112-m ...high-speed catamaran fitted with a ride control system, a 2.5-m model was tested in a towing tank. The model active control system comprised two transom stern tabs and a central T-Foil beneath the bow. Six ideal motion control feedback algorithms were used to activate the model scale ride control system and surfaces in a closed-loop control system: heave control, local motion control, and pitch control, each in a linear and nonlinear version. The responses were compared with the responses with inactive control surfaces and with no control surfaces fitted. The model was tested in head seas at different wave heights and frequencies and the heave and pitch response amplitude operators (RAOs), response phase operators, and acceleration response were measured. It was found that the passive ride control system reduced the peak heave and pitch motions only slightly. The heave and pitch motions were more strongly reduced by their respective control feedback. This was most evident with nonlinear pitch control, which reduced the maximum pitch RAO by around 50% and the vertical acceleration near the bow by about 40% in 60-mm waves (2.69 m at full scale). These reductions were influenced favorably by phase shifts in the model scale system, which effectively contributed both stiffness and damping in the control action.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Twin hull high-speed catamarans encounter a wide range of sea wave loads. This paper studies the full-scale prediction of global loads on a high-speed catamaran using linear regression analysis based ...on finite element results. Load cases based on Det Norske Veritas rules are applied to a finite element model to derive load–strain transformation. Strain responses are evaluated at 16 different locations on the catamaran finite element model corresponding to the strain gauges positioned on the HSV-2 Swift 98m Incat catamaran during sea trials. A transformation matrix is generated using the concept of ordinary least squares, to convert from strain responses to the equivalent DNV global load cases. This is applied to determine global loads during several sea trial runs in different heading angles and speeds of 10, 20 and 35 knots. These loads then are compared to show each global load severity at specific speed or heading angle.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
High-speed craft frequently experience large wave impact loads due to their large motions and accelerations. One solution to reduce the severity of motion and impact loadings is the installation of ...ride control systems. Part 1 of this study investigates the influence of control algorithms on the motions of a 112-m highspeed catamaran using a 2.5-m model fitted with a ride control system. The present study extends this to investigate the influence of control algorithms on the loads and internal forces acting on a hydroelastic segmented catamaran model. As in Part 1, the model active control system consisted of a center bow T-Foil and two stern tabs. Six motion control feedback algorithms were used to activate the model-scale ride control system and surfaces in a closed loop system: local motion, heave, and pitch control, each in a linear and nonlinear application. The loads were further determined with a passive ride control system and without control surfaces fitted for direct comparison. The model was segmented into seven parts, connected by flexible links that replicate the first two natural frequencies and mode shapes of the 112-m INCAT vessel, enabling isolation and measurement of a center bow force and bending moments at two cross sections along the demi-hulls. The model was tested in regular head seas at different wave heights and frequencies. From these tests, it was found that the pitch control mode was most effective and in 60-mm model-scale waves it significantly reduced the peak slam force by 90% and the average slaminduced bending moment by 75% when compared with a bare hull without ride controls fitted. This clearly demonstrates the effectiveness of a ride control system in reducing wave impact loads acting on high-speed catamaran vessels.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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